building a frame for a Twin Cam A...

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Prof
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building a frame for a Twin Cam A...

Post by Prof » Tue May 14, 2019 9:35 am

Garry dropped in his twin cam recently purchased from NSW (writeoff). NSW does not alow repairable writeoffs, so although this only has bent forks and and broken indicators, it has to have a new non Harley frame. Ridiculous, but due to bike laws being tied in with car rules and done to reduce rebirthing...
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I have learnt a bit about modern HD's so far in this exercise. Garry 's FXR is a twin cam A motor which is rubber mounted. Twin Cam B's were introduced with twin balance shafts a couple of years later and were solid mounted in response to buyer feedback. Plenty of custom frames exist for the B motors, but we have so far found only the Rolling Thunder frame below that does a rubber mount twin cam frame...
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If the motor was a solid mount B, we could use a soft tail design, but that is ruled out because the rear of the motor has to be attached to a flexible rear swing arm.

I spent some time talking to a Harley shop and chasing info on the net and all advise against solid mounting the A motor; apparently frame cracking issues.

We have another alternative and that is building a new frame in house. I'm just waiting on my engineer to get back to me on a question about this approach, and we can get on with the project.

Garry wants the bike to be fairly standard but with a springer. We'll use a Meatballs springer and add some rake to retain stock trail, plus add another inch or so for better highway handling... Garry lives out in the sticks.

More soon as I know something...
Chopit'nrideit... Prof

Prof
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Re: Twin Cam needs new frame

Post by Prof » Sat Feb 22, 2020 10:28 pm

Finally have a fast computer and access to all my picture files. I've been able to begin catching up on work as a result of a variety of family and other set backs, so at last we can show you Garry's build.

Quite a few hours went into researching frames. We found two possibilities claiming to suit the rubber mounted Twin Cam A, but some things just did not seem right, so I decided our safest bet was a new in house TCS frame.

Because the bike is a statutory write-off it has to be engineered as a current independent build known as an ICV (Individually Constructed Vehicle.

Step one... engineer comes here and we discuss construction of the frame, shape and tube size and type, gussetting etc. Then materials are ordered and I build the frame.

Step two... Engineer comes again to check that is what we decided, weld quality etc and takes a bunch of photos. He then sends in application for VIN.

Step three... frame is completed, moulded and painted and entire chopper is assembled. It has to comply with ADR's and current regs (as with any new bike entering Australia) therefore indicators, e marked lens, mirror size, handlebar height, width, lighting, labelling on switches etc etc etc!

Step four... Engineer does final inspection including brake and noise tests. Takes heaps more photos and does a big writeup for the road traffic blokes (oh sorry! and sheilas).

Step five... They say "Oo how cool!" and arrange an inspection time, which of course we will pass and they then hand us a form that allows the owner trot into the nearest Service SA centre to register the machine.

Step one was completed last year and I am now building the frame. To keep things as easy as possible, we will run original (stock) brakes, wiring loom and exhausts.

At this stage Garry wanted the bike close to stock but with a springer. A benefit of the time lapse between him bringing the bike in and starting on the frame has meant he has decided to be a little less traditional and wants a King'Queen seat, medium height sissy bar, bobbed rear guard, custom tail light and head light and forward controls. With some advice from this ol chopper jock, he agrees to a bit of extra rake and some stretch in the frame. Result is at this stage nice looking machine that appears to be moving fast just standing still. I think he'll love the result. It will definitely be much nicer to ride than the stock machine.

So with out further ado, let's get into it...

My new worker, Lionell, is taksed with dismantling the bike. We will be using the motor/gearbox, swingarm, both brakes, rear shocks and the front wheel (with new rim and stainless spokes) hand controls plus the other parts mentioned...
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Now for rake and trail and adherance to the Ridikulous Rool. Working this out will give us the height of the steering head, the first thing we need to begin setting up for our new frame. I have calculated that with a moderate increase in rake a 2" over Meatballs springer will be about right and got that sent over from Bendigo. Four over would have been nice, but Garry has not ridden choppers before and began wanting something near stock so the 2" over is a bit of a compromise.

This contraption allows us to work all this out because we can move the steering head up and down and adjust the rake...
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First the 550 Rool. I set up the springer up on a 19" wheel and set the RR at 500mm. This is the horizontal distance between the centre of the steering head and the bottom centre of the forks (the axle on telescopics). Because this is a springer and I haven't tried to get one past regio arguing that on a springer it should be the centre of the bottom of the back legs not the actual axle, we will play safe and use the axle as our measuring point...
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What rake do we end up with? 37.5 degrees. 9.5 degrees over stock. That's quite manageable.
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Now check for trail. Stock trail on this model HD is 4.1" I want to go to between 5" and 6". Any more and a less than died in the wool chopper jock would not like the heavier low speed feeling. Comes out to just over 5"...
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Play around a bit more increasing rake and checking figures. Decide on the 500 RR, 37.5 degree rake and just over 5" trail.Gives us a steering head height of 900mm, about an inch lower that stock. I like this because we can achieve a cool rakish frame with the steering head dropped a bit... will have a slight digger look...
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Rake is now dialled into the frame jig...
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Stock ground clearance is 6.5" and I will keep to that. Set up a bunch of wooden blocks on which to initially rest the motor...
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Now have to do a myriad (and I do mean a myriad of measurements) so I can build the front and rear mounts for the motor on the jig. Finding places to secure the motor/gearbox that would not interfere with the frame mounts can be a bit of a challenge and was here, as eventually I had to modify both. Just a few pics of the dozens of measurements made). Rear of garbox...
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Front engine mounting needed spacers...
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Numerous checks on original frame eg front engine mount is off centre...
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Turning up some spacers...
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First mount being set up...
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More checks for squareness...
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Engine is hoisted up with block and tackle and st on the blocks. Here, rear mount has been made and attached...
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Front mount done. Swing arm now attached to rear of gearbox...
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Jig is checked for level. Engine is double checked for level and centred at the front with a plumbob and the rear to the centre of the tyre...
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Distance of stock steering head from a known points (bottom engine mount) is measured...
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Four inches of stretch is added and steering head height and rake checked.

Why the 4" of stretch? 1. The extra rake throws the handle bars back towards the rider so the steering head needs to move forwards. Garry lives a few hundred miles out of the city with mostly straight roads. The extra wheel base will make for a more stable bike on the highway.

It will make it a little slower in really tight corners like small roundabouts and T junctions, but most riding will be on the highway so let's make sure it is a good highway bike. He'll be laughing when out with his mates, as it will be so much more relaxing to ride...
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Next machine up a steering head. Although the modern HD's have bearing cups integral with the steering head, I prefer those used on earlier frames that have removable bearing cups. It allows us if needed to use 3 degree raked cups to increase of decrease rake if different forks get used down the track. I use a heavy walled pipe for steering head...
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Steering head and bearing cups installed...
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Now back the the rear end. Swing arm has 3.5" travel so we need to know highest and lowest points of swing arm, tyre, and drive belt. One inch flat bar and 1/4" round is used to make up some guides so we don't stick a frame member in the wrong place!...
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Curved flat bar yo see here is the highest point of the tyre (plus 3/4" clearance) to allow for when it hits one of our many SA road bumps. I am planning a traditional style frame, but with rails behind the seat that follow the highest point of the wheel. Let's see how the standard shocker will fit. The stock mounting point is well forwards of the axle which creates a problem for the top mount. It would be way above the curved rail. So we cut off the bottom mounts and move them back a couple of inches. Shocker now fits. For strength, because we are dropping the seat rail lower than stock, we will slope the shocker a little extra. This will harden the ride slightly but be hardly noticeable...
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OK. So that's the basic set up. Now to build the frame around what we have set up. Heaps more measuring to clear everything, but still keep a rakish look. That will be for our next post shortly...
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
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Re: building a frame for a Twin Cam A...

Post by Prof » Mon Feb 24, 2020 12:08 pm

Now ready to build the frame. Just one pic missed off last post. To locate top shocker mount we cut and drill a piece of 20 square tube with full length and collapsed length of rear shocker...
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Tubing...
Discussions with the engineer resulted in main tubing to be 32mm DOM x 3mm wall. Backbone 50 x 50 x 4 square tube. Square backbone is to keep it simialar to the original frame. Wall thickness is greater. Rest is up to my discretion.

Tubing suitable for motorcycle frames is 1. ERW which is the normal tube you would buy at ans steel supply place. It can be identified by an inner weld seam running the length of the tube. 2. DOM which is ERW that has been resized over a mandrel to remove the weld seam and create a uniform wall thickness. DOM is also more rigid than ERW because the steel has been slightly compressed squeezing it between the mandrel and the outer former.

I use 25mm x 3mm ERW for frames on up to 90's choppers, but go to the larger DOM on the big inch motors as they develop more power and expecially more torque (twisting of the frame). Steam pipe which is similar to DOM but softer for easy bending is not suitable as frame tubing. Ordinary pipe in smaller diameters very definitely a no no expecially 'water pipe'.

Pipe (not water pipe) is suitable for backbones if at least 2" diameter and 4-5mm wall thickness.

Note that tube size is quoted as Outer Diameter and wall thickness whereas pipe is quoted as Inner Diameter and wall thickness.

Because we are now gong to be cutting and welding tubing is is time for a check on alignments. My laser guide is put into the steering head. You can align steering head fairly accurately if you machine up a piece of tube to exactly fit in the steering head with a centralised pointer at the other end. A quarter of a mil out in the steering head will be magnified 8 or so times by the time the error is transmitted to ground level = 4mm; .5mm = 8mm!

That said I figure that alignment up to 3mm error would not be noticed on a chopper, but do my best to keep it within 1mm. Frame flex in hard cornering will most likely cause more misalignment than that remembering also that tyres flex as well... and frames do need a certain amount of flex to reduce stress points breaking. That said keep alignment of steering head within 3mm...
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Laser pointer mark...
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Steering head is also checked for centre...
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... and rake rechecked...
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A metre rule is used to mock up backbone and this allows me to then use my 'angleometer' to establish angle of cut in backbone...
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Angle cut and bottom and top curved to match steering head. Still needs a bit more shaping. Very, very important to have all tubing joins a very exact fit to prevent pulling and twisting out of alignment when welded. As a weld cools it contracts and will pull tubing to one side quite dramatically...
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Backbone needs to be curved over the rear cylinder for clearance and so we can have the correct steering head height and the lowest possible seat height. A series of very precise cuts are made. Lines of cutting are drawn with a square. If the cuts are out of square you can end up with a bend and twist to the right or left...
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Backbone set up on our chopper. The motor has to be able to be removed from the frame so the bottom of the 32mm bottom frame tubing will be level with the bottom of the motor. That means I need to allow 40mm clearance above the motor, the main clearance being the rear cylinder. Wooden blocks in the photo are the spacers needed to accomplish this...
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Next is the rear vertical that carries the rear rubber mount at the bottom rear of the gearbox. Here I use 75 x 30 x 4 rectangular tube...
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We need reinforcement so the bolts don't crush the tubing. I cut up two pieces of solid bar to fit...
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One piece has to be grooved to clear the welding seam...
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A couple of holes are drilled to plug weld the bar in place...
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Holes for the rubber mount are now marked and drilled...
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Bolted in place. Now to work out a backwards sweep to keep it close the the guard and allow as much seating space as possible...
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Angle is established and a pattern cut out. Location of bend is marked with square. Pattern is used to work out how much metal has to be removed...
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This is then marked out of tube...
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Very carefully cut and bent...
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Perfect...
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Battery needs to fit in under 25mm frame rail. Lines up nicely with end of backbone...
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Squared up ready for welding...
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As previously mentioned, welds pull as they cool and shrink. A piece of tube is tacked across the cuts to be welded to keep the correct angle...
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Cuts chamfered...
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Tacks across bottom edge then tube turned over...
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... and second set of tacks done. They are then left to cool before removing the tacked on tube...
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Steering head tacked. Because weld pulls on cooling (have you got that message yet!!?) I do a quick tack at top left then around the other side and bottom right, then bottom left and top right. Same for the rear...
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Lower tubes next... and that requires lots of measuring. Our next post.
Chopit'nrideit... Prof

Prof
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Re: building a frame for a Twin Cam A...

Post by Prof » Tue Feb 25, 2020 11:37 pm

Lower frame tubes right side...

The lower frame tubes start at the steering head sweep under the motor on both sides turn up behind the clutch/gearbox and when they get close to the shocker top mount curve around to line up with the top of the rear guard.

Each side needs to be identical. The bottom of the lower tubes will be level with the bottom of the motor. they also need to keep as close to the crankcase/primary cover for greatest strength and good looks. The right side needs to clear the stock exhaust which will be mounted to pass inspection.

The front right down tube could easily get in the way of the exhaust as it exits the front head. Both down tubes need to be in a good position so we don't end up with an ugly front rubber mount set up. We also need to think of how forward controls will be mounted off the down tubes.

To the rear, the left side has to clear the primary cover, the belt drive when under full shocker compression and end up in front of the shocker top mount, then swing in towards the guard so we don't end up with an ugly fat rear end.

The right side has to clear the exhaust, allow the swing arm bolt to be retracted and also end up in front of the shocker top mount.

Measure, measure, test, test. We will need to use tight curves to accomplish all this. I have two different radius formers on my bender so the smaller radius one will need to be used.

Now we want some supports for the tubes as they pass under the chopper. I use a couple of scissor jacks, square tube of angle iron and level them with wedges...
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Lay a piece of tube so I can mark where bends and cuts will be...
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To make bending simpler, I will fabricate each side in two pieces, joined in a spot where they will later be joined across the bottom by the sidestand set up. Turn up a pair of slugs and will drill holes in frames for plug welding. Length slugs should extend into each tube is 1.5 x ID of tube...
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Now for the angle of the down tube sections keeping in mind clearances with exhaust and positioning for front engine mount...
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Bends are marked from where they start and an arrow shows the part of the tube that will be in the bend...
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First one bent and tested for fit. Spot on first time. Bender former is marked so it can be brought to same position for second bend; this needs to be done because the tube springs back when the bender is released...
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Tubes laid side by side to ensure they are exact same bend. Arrow shows we need a little more on the second tube...
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This can be tweaked in the vice with a long piece of pipe...
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Angle correct and second tube cut to exact same length from bend. Set squares or a high long block of wood will keep the two tubes in proper alignment for measuring...
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Plan for rear section of tubes. Measure twice and bend once! This is checked that it works for both sides. Again direction and start of bend is marked clearly...
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My long 'angleometer' is used to get the correct angle...
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Both rear sections bent and joined temporarily to front sections with slugs. You'll notice that the front tubes start bending a little later than normal.
This is so the rubber mount bracket doesn't poke out forwards too far...
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Next post we will curve the rear tubes using heat. When doing this work I've just desribed you can't be too patient and careful...
Chopit'nrideit... Prof

Prof
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Re: building a frame for a Twin Cam A...

Post by Prof » Fri Mar 13, 2020 10:46 pm

Sorry for the delay. I've been trying against the odds to get this thread up to the current situation, and at last finally can get some done tonight...

My favourite treatment on the rear of swing arm chopper frames is a curve that matches the top of the guard. This requires bending a wide curve in the tube. Years ago, I bought a tube roller to do this job, but it is too inaccurate and wastes a lot of tube, so frame has to be curved using heat...
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Tube is progressively pulled around a former. Trick to an even curve is slowly progressing the heat as pressure is placed on the tube. An extension (arrow) is usually needed especially in the case of 32mm DOM...
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First curved frame set up. Not shown here are a couple of photos I lost that show the wheel raised to its maximum height plus safety gap of 5/8" (16mm). Tube needs a bit of a recurve to get it just right and final shape shown here...
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Backbone is now completely welded up at curve...
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Tack welded to steering head. The four tacks are done in a set sequence to minimise twisting. Bottom left, top right, bottom right top left as quick as possible... then laser used to check alignment once welds have cooled. Backbone is attached so that there is about 10mm clearance to top of steering head to allow for weld to be kept a little way away from the bearing mount. This is because welding will tend to distort the tube if it is done too near to the edge. I also prefer where possible to weld the steering head to back bone before I weld the rear of the backbone. Less chance of steering head coming out of alignment that way, but not always possible...
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Backbone now tacked at rear...
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Second rear rail is now curved and checked against first one. Again a couple of goes are needed to get them matching exactly. Levelled then...
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...end checked for vertical. If vertical it means the two are the exact same length...
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Arrow shows some heat being applied again to a spot to even up end of curves...
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A final couple of cold tweeks are done using a long piece of pipe in the vice...
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NOW LOTS OF MEASURING! Rear rails have to clear a whole lot of parts. Must clear swing arm as it moves up and down (bottom red arrow). Must clear drive belt as it moves up and down (top red arrow). Needs to clear motor sump and primary drive inner case. With these parameters established a wooden guide block is clamped to keep it at the right location (green arrow). Of course...
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... the right side has to also clear everything... including the exhausts (green arrow). Also has to allow a socket to get to the swing arm shaft...
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Both frame bottom rails need to be the same distance from the rear upright. You need to be patient at this point. It is important to get everything lining up and clearing everything. If you don't take much care at this point frame will be out of alignment which can cause all kinds of nightmares later on. I've had frames come into the workshop with seat rails different lengths, out of level (leaving the seat on an angle) and even the shocker mounts in one case a full inch out and different heights!..
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An angle is tacked to the rear post to ensure the rear frame rails are even. Bike is checked for level and tacked angle levelled...
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Measurements to each side are taken from a central point in this case the steering head...
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Frame angle has to match on each side. Again, a whole pile of measuring and finally another guide block clamped in place...
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With all this done, we can now fabricate lower and upper rectangular sections that join the two rails to the rear post. That will be the subject of the next post. Thanks for your patience.
Chopit'nrideit... Prof

Youngblood
Posts: 384
Joined: Wed Oct 24, 2007 1:48 pm
Location: North-Eastern suburbs- Adelaide

Re: building a frame for a Twin Cam A...

Post by Youngblood » Sat Apr 04, 2020 11:50 pm

Love this post Prof, keep posting, thanks.

8) 8) 8)
Youngblood

Prof
Founder, Choppers Australia
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Re: building a frame for a Twin Cam A...

Post by Prof » Tue Apr 07, 2020 9:18 am

Glad you are enjoying it. Frame almost done, just need time to get posts up.
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5962
Joined: Sat Oct 22, 2005 3:54 pm
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Re: building a frame for a Twin Cam A...

Post by Prof » Wed Apr 29, 2020 10:54 pm

I cheated and had left overs for tea tonight, so I could have some time to get up some more pics of Garry 's machine.

We are a long way past this post, but I will continue to take it step by step in the hope that it will help some chopper jocks do a good job of their own choppers. My posts are designed to show you what I've found to be my best approach to the many aspects of frame building, explaining the whys and wherefores and hopefully helping you to avoid the many pit falls. Although I have equipment most home builders won't possess, I try to let you know how you can do it as without big equipment expenditure.

So we are now ready to do the seat rails and rear upper cross member then head up to the steering head.

Some measuring done to work out how wide seat rails should be at the front. The seat rails slope considerably, so we have to be careful Garry's thighs won't foul the front of the seat... ie the seat will have to be a bit narrower at the front than on a chopper with flatter seat rails. One rail bent and then the second checked for accuracy using three set squares...
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Rails are now set in position and a curve ground in them to match the rear uprights to which they will be attached... and the closer the fit the stronger the weld...
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Front cut is a bit more of a challenge. The spirit level has been used to keep the rails parallel to the top of the back bone, so the correct angle cut can be made. Mitre gauge is used to achieve main angle of cut...
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Cut angle is double checked with the seat rail on a flat surface and using a small square against the end (forgot a pic sorry) Second rail now carefully measured against first one. You can't be too careful with your measuring...
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Backbone marked with a square. This is important to get both seat rails attached at exactly the same distance from the steering head. Even two mil out will look awful!...
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Tacked and double checked with spirit level. Note battery whose height regulated position of seat rails. It will go on the right side, but flat top of primary allows it to be used easily for spacing... just enough to clear the bottom of the seat rails...
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Before welding at the rear we have to ensure both sides are the same distance from centre. Distance is determined by clearance of frame to drive belt on full compression of shockers. A jack needed to get the spacing. Rail is jacked out more than needed so when it springs back it will be in the right place. Just jacking it to the distance is not good enough because it will want to pull in when the jack is removed so bringing unwanted tension into the frame members...
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Cardboard pattern made. Sometimes you will end up making two or three before you get everything fitting without any gaps which will cause weld to pull and put tension into the frame...
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Left side upper spacer made and welded in...
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Ah! Starting to look good!..
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Jack used again to get correct spacing on right side...
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Seat rails and upper spacers welded in...
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You will remember that each side cradle has been made in two pieces. The join has been placed where a cross member will go under the motor/gearbox join. On the stock bike this also carries the side stand, and we will follow suit, so a pile of measurements are made. It will be too complex to build while the motor is in the frame, so we will leave it until rest of frame is built and we can remove the motor for access...
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So, up to the steering head. Front sections of cradle can be rotated in and out so we can easily fit them to the front. I prefer it this way because it is not easy to get multiple bends identical and it means you can set up the front and rear separately. Front down tubes will mount to the backbone in traditional HD fashion. This allows the steering head to be boxed in rather than having bulky gusseting back under the backbone. I also allows the steering head to sit further forwards which give the chopper a bit more of a racy look...
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Angle cut and tested...
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Tube will be able to fit within the wide backbone with just a bit shaved off...
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Centre marked and then a set square (forgot the pic) used to ascertain that angle of the cut that will join the two tubes to one another...
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Left side cut...
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With both tubes cut and in place, a square is used to make sure they are both level...
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Distance from centre is checked. Right side it the guide here because it has to clear the exhaust coming out of the head. Exhaust is set to clear and also I make sure a socket can easily access the two header nuts...
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Exhaust can just be seen under the leather protection prior to welding...
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The choppers final shape is starting to show...
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Front tubes need are reinforced with a triangular gusset... much neater (and stronger) than some frames with just a tubular cross piece...
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Gusset template is folded down the centre to improve accuracy...
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Curve is formed the same way...
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Gusset can do with some relief so a series of holes will be drilled starting with smaller at the top grading to larger...
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Distances between holes a graded as well and the centres established, centre drilled. Cross hatched circle in centre is the possible location of a reinforcing tube to the backbone, but I am hoping to get away with a couple of small gussets in its place... something I will run by the engineer once steering head area is complete...
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Smallest and largest holes are drilled...
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and the ruler used to work out the exact sizes of the middle ones...
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Welded in place. A small 8mm gusset has been welded in above. The steering head area will be boxed in, but this just adds a bit of extra strength because in so doing, we have increased the contact area (weld length) between the steering head and the down tubes. Weld length is one of the important considerations when joining frame members and the steering head are is one of the most important, probably being the most stressed when riding and the last piece you want to have came adrift or even just flex too much. I have seen plenty of broken stock frames so it is imperative that as a one off builder, with out a test frame to work to death to see what breaks, that we over engineer our frame...
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A final pic so far...
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Bed time and another day on this chopper tomorrow. It is almost done and almost ready to disassemble and final weld. But I do aim to get more posts up more quickly now that some other matters are out of the way... Stay tuned...
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5962
Joined: Sat Oct 22, 2005 3:54 pm
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Re: building a frame for a Twin Cam A...

Post by Prof » Thu Apr 30, 2020 11:23 pm

Boxing in the Steering Head...

The steering head and about 12 inches along the backbone are both high stress areas and need to be treated accordingly. Our backbone is more than substantial but will have a tube connecting it to the down tube gusset or a pair of small gussets to the steering head just to be extra safe.

As previously explained, combined weld length is one of the critical components of structural strength and we have added a small gusset into the inner top of the area to be boxed. Six mm steel plate will now tie the bottom of the steering head to the down tubes with
and 3mm side gussets.

Here cardboard pattern made...
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Pattern for bottom plate which will be curved. You often see custom builds with curved tubing. A curved piece is less rigid than a straight piece of tube. The same goes for curved sheet metal gussets. Our bottom plate is thick enough to not succumb, and when tied to the side plates will not be an issue anyway, but thought this issue worth mentioning to future chopper builders...
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Matching the curves...
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Bottom plate being shaped into the steering head...
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Curving it on the anvil with a heavy hammer. Need to keep both sides even. A parallel jaw pliers very useful for holding steel you are belting...
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Checking against pattern...
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Bottom plate is welded into the steering head from the top so I can get a decent weld in with minimal distortion of the steering head. Too much distortion and the bearing will not fit in...
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A piece of round bar welded into the top rear for a bit extra strength...
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Side plates welded in. Welds can look messy because we have to do very short runs from side to side to reduce movement of the steering head due to heat. Laser is used to keep a check on alignment...Any low spots filled...
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Rear set post attachment...

Setting up this cross bar is complex. It is a major structural piece; the forces on the steering head are transferred to this piece. It has to resist frame twist when cornering and it has to clear the bottom drive belt which follows a shallow arc at speed and more so under acceleration.

Matching it up to the cradle tubes requires a steep forward angle. The cradle could not come further back with out looking boxy and also this run always wants to be as short as possible as it is carrying the rear shockers. Also welding across the tube needs to be reduced as much as possible.

You will notice on many stock steel tubed bikes that welds on gussets and cross members run parallel to the cradle tubes not across them. A weld around the circumference of a tube creates a weak area. This is why old school springers can often snap at the bottom of the lower triple tree where the back leg has been welded around its circumference. Also why they experimented with clamped back legs...

Took a considerable amount of time to develop a cardboard pattern to cover these requirements...
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Cross piece will be made from 50 x 25 x 3mm rectangular tube. Full pattern. Rectangle in middle shows the two initial cuts on the straight tube. Two sloped lines are the second cuts on the centre piece...
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Tube marked. Both sets of cuts need to be the same length so no gaps appear when folding the tube to its final shape...
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Cuts and chamfered at 45 degrees so piece can be ground smooth. Here final welded...
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Welded to seat post...
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And cradle tubes...
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Next job is shocker mounts. Tomorrow night perhaps...
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5962
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Re: building a frame for a Twin Cam A...

Post by Prof » Sat May 02, 2020 6:27 pm

Shocker mounts...

To set up rear end, one shocker is dismantled and compressed. Wheel is blocked up to previously measured amount of travel. This is calculated most accurately by comparing the length of a fully extended shocker against a fully compressed one. It can be done by measuring an extended shocker's amount of inner shaft showing, but not quite as easy to get it right. In both cases allowance of a 50 percent crush of the buffer rubber needs to taken into account.

Photo below shows that my original pattern for the curved tubes was a bit out. Top of frame tubes should line up with top of rear mudguard. Obviously way too low. Tyre needs some extra clearance (20mm) when on full compression. This allows for variations in tyre diameter depending on tyre brand, expansion of tyre at speed on a hot day, gravel and mud and just a bit of a safety margin as well. I use an old O ring chain on top of a thick leather strap of my grandfathers horse harness!...
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Chopper's level is rechecked and then tube heated and bent upwards to correct height...
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Second tube treated similarly and both measured for equidistnce form the centre line...
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Now we can set up the shocker mounts, so firstly, here is the finished job...
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Let's look briefly at how we did it...

Measurements were done when we were constructing the curve of the rear frame section and also the angle the tubing came up from under the motor. To give the rear tubes some rear angle, it was necessary to move the bottom shocker mounts on the swing arm to the rear a couple of inches. This is now rechecked. Bottom mounts are tacked to the swing arm and a top mount machined.

Top mount now machined. Groove is to fit into the curved tube; plus we also want to gain as much space as we can to reduce the rearward position of the bottom mounts...
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Top mounts are aligned with a piece of 1/2 inch threaded bar and clamped. Measurements are made to the rear shocker mounts and double checked vertically against the swing arm to make sure everything is square...
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Mounts are also measured from the steering head. All takes time, but I've seen some badly missaligned top mounts over the years!...
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I machined the original top mount bolts, but the hex section (red arrow) sits the shocker out too far (green arrow) so...
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I buy some 1/2" by 3/8" shoulder bolts the correct length. Unfortunately most imperial shoulder bolts (actually called shoulder screws) are not a standard stock item and I have to buy a box of 100!.. and the blighters ain't cheap even though the local Konnect bloke gives them to me at their cost. These will be welded in place to allow one handed loosening and tightening of the nut...
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Bottom shocker mounts need slight adjustment rearwards and are also brought out to the edge of the swing arm. A pair of 1/2" bolts have their hex heads machined off and are welded into the bottom mounts which are now secured with some extra weld...
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Next to be done are the front and top engine mounts and the chopper can land on its own two feet for the first time...
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5962
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Re: building a frame for a Twin Cam A...

Post by Prof » Sat May 02, 2020 10:05 pm

Engine mounts...

Front engine mount is next. Remembering this is a rubber mounted motor, this front mount needs to be substantial. A measure up of the stock mount provides a guide for this one... as usual, we will go a bit stronger.

I have to make a new frame mount on the jig as the existing one gets in the way of our cross piece. That done mounting spot is pressed into a piece of computer paper...
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That pattern plus some measurements give us the basic mount in 10mm steel. Squares and very careful measuring with verniers and steel rule, plus centre punching and centre drilling the holes is essential for accuracy. If the holes are not pretty much spot on, one bolt will take the bulk of the stress...
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Top angles cut in so now location of bend back to the down tubes can be marked...
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Only way to get an accurate bend in heavy metal like this is to cut part way in with an angle grinder, bend and weld opening caused by the bend. I have a hydraulic press that could also do it, but without a jig this is the quickest way...
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Working out angle. Arrow shows where rear of cross piece will contact the down tube. The front will be 10mm further forwards and be level with the front of the tube. This will look neat and also gives us a nice area to get a deep penetrating weld... saves chamfering...
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Bending in my heavy engineers vice (jaws are offset) with a big old shifter bought at a swap meet for this kind of work...
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The more leverage, the easier to bend and more importantly the more control you have...
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Bent and welded...
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Welded in place. The ends of the cross piece needed grinding to fit the angle and curve of the down tubes and took a while to get perfect with no gaps... needs patience and concentration...
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Top mount is relatively simple and built the same way. A stainless spacer is turned in the lathe to reduce the length of the bracket for better rigidity. Once the engine is out of the frame for final welding two 3mm trianglular gussets will be welded in...
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Ready now to be put on its own two wheels...
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5962
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Re: building a frame for a Twin Cam A...

Post by Prof » Sat May 02, 2020 11:14 pm

On two wheels at last...

Ready to be separated from it umbilical cord and enter into its new world.

A set of handle bars will be needed to manouver the chopper around the workshop. Front end is a 2" over Meatballs springer (from Bendigo, Vic) so we first need to knock up a set of risers. Handlebars are a pair of stainless pullbacks I made last year.

Threads in top of springer rear legs are 3/4 UNF. Risers will be drilled out to take a 1/2" UNF socket head cap screw, so we cut up a 3/4" UNF bolt and then...
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...drill and tap a 1/2" UNF thread inside...
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Top of riser is counter bored with a flattened drill bit for the socket head...
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3/4 adaptors are pulled up tightly against the bottom of the risers and then the assemblies are screwed into the springer legs. Pull backs slide over the risers and are retained with a small socket head cap screw...
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Chopper can now be lowered onto terra firma...
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Chopper is lowered onto the springer, nuts tightened up...
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And wow! Here 'tis on its wheels and ready for action... well soon...
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More coming, Extra frame work, electrics box, sissy bar, king queen seat, forward controls and then some...
Chopit'nrideit... Prof

El Skitzo
Posts: 798
Joined: Wed Sep 30, 2009 6:40 pm
Location: Perth, WA

Re: building a frame for a Twin Cam A...

Post by El Skitzo » Mon May 04, 2020 9:42 am

That's come a long way, well done!
'65 Triumph Chopper (project)
'64 Triumph Chopper (project)

Prof
Founder, Choppers Australia
Posts: 5962
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Re: building a frame for a Twin Cam A...

Post by Prof » Sun May 10, 2020 10:27 pm

A gusset behind the steering head and a structural member under the seat left to do.

I asked the engineer if he wanted me to run a tube from the bottom of the steering head back to the middle of the backbone or if he would accept a pair of triangular gussets. He was happy with the latter. the gussets are cut out of 6mm plate and welded flush with the outside of the backbone and the down tube. Will become an nice area for some pin striping/scrolls etc if Garry is interested...
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Once both gussets were shaped, they were clamped together and finished on the linisher (or what ever method you might use). This way both are identical...
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The strongest structure is for as direct a possible line between the steering head and the swing arm pivot. A straight line is not usually possible, so we get it as close to the ideal as possible. We need 40mm clearance between the top of the starter and frame and the same above the back cylinder, so the engine can be easily removed/installed. Block of wood on top of starter gives the clearance we need...
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Cardboard pattern is transfered to a piece of 50 x 25 x 3 tube. It is important to keep things square and to have tube close fitting; hence the square...
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This is only lightly tack welded in place, because it will need to be removed later for attachment points for the battery and a number of the electrical components. It will be finally welded flush with the right side of the 50 x 50 backbone to give as much space for the electrics on the left side and provide a flush backing fo the battery box which will be on the right side...
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Next up electric box, component mounting and battery box...
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5962
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

Re: building a frame for a Twin Cam A...

Post by Prof » Wed May 20, 2020 9:40 pm

Mounting electrics...

With Garry 's approval I am building a traditional chopper style electrics box to house the battery and electrical components. Mounting the battery is a bit of a challenge due to its bulk. Unlike Harley, I will have the two terminals to the out side. Battery will also mount on the left, because there is a little more space. The two other major components (size wise) are the coil (red arrow) and an ugly thing that switches the bike off if it leans over too far (green arrow); electronic mercury switch I guess. The oem mounting plate (white arrow) will get the flick. Fuses, ignition switch, indicator box and a couple of of other bits also have to fit on the left side along with their bulky connectors and a pile of wire.

Because the components are now in different places, wiring though long enough to reach the new positions is in some cases way too long, so they will be cut and re joined when bike is welded ready for moulding and paint.
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Battery box first. It will form part of the electrics box so needs to be substantial and will be built out of 3mm plate.

Here measured and drawn up. Drawing (green arrow, which will probably do your head in because it is not well done) shows shape and allows me to write in the three dimensions (length, breadth and depth). It is known as an isometric and consists of three dimensions; all vertical lines are vertical, and left and right lines are drawn at 30 degrees to horizontal... very useful when planning a part as it gives a good idea of final shape.

Other drawing,(red arrow) is what is called a development. This is the isometric flattened and shows us what shape will have to be cut out of a piece of sheet metal. Scribbles (blue arrow) are two additions; one being the total length and the other the total width of our piece of sheet metal. Figures are taken off the development, which is the other value of drawing it...
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Here drawn out on the 3mm steel plate. Dotted lines show bends. A folds to meet A and B folds to meet B...
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Cut out with angle grinder and first side bent. Second side about to be bent. This is done in my folder, but can easily be done between two pieces of angle held in a vice which I showed earlier on...
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BUT, how to do that third bend? I have a set of two pieces of 10mm plate cut to size for HD batteries. The two pieces of plate sit in the vice and the part to be bent is sandwiched between them. The front piece of 10mm plate has a piece welded to it so that when a hammer is used to finish the bend the whole kit and kaboodle doesn't slide down through the vice...
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Piece to be folded is pulled part way down with hands first and finished off gently with a hammer. Gently other wise steel will be bruised and go out of shape (and look crummy as well)...
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Here are the two pieces of plate. Front one is on bottom with piece of angle welded at the top (far end) and a smaller piece of angle welded to the bottom (green arrow). Holds the rear 10mm plate and the piece to be bent in place...
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Final tapping on a hard surface to get sides to be welded matching...
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Try out the battery. Great! It fits! Could use a strap like this to secure battery. We'll see...
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Steel welded with the Henrob...
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Now for this silly mercury switch thing...
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It will fit at the rear of the electrics box, but will have to protrude through the bottom. Needs to be able to be easily removed, mainly while we are constructing every thing. Has to be perfectly vertical in all dimensions. Here with the backing plate cut off...
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Welded in place...
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As stated in the previous post, we have to remove the angled frame piece which is just lightly tacked in place to do mountings for coil and battery box. The coil position is worked out as is the battery box mounting. All sounds simple doesn't it, but a lot of thought goes into getting things to fit in a tight space, so they are easily accessible, removable and their wiring connections easy to reach and remove.

Battery box will be held by one bolt at the front and two at the back. Front fixed thread is now machined to fit through the angled frame piece...
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All my fixed threads are counter bored 8-10mm so bolt can easily locate and no cross thread; an important issue where the thread may not be easy to see or reach...
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A short piece of 3mm angle cut, drilled and shaped and welded to the battery box. Now held in place and drilling location marked...
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Angle piece of frame now removed for drilling and welding. Note that the fixed thread is stepped. The smaller diameter hole drilled through both sides, then the large one on just one side...
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Coil mounts machined and threaded. They are stepped so the coil actually slips over them (orange line).
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Clamped in place with coil holding them the correct distance apart, tacked with mig...
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And then gas welded along with the battery front threaded mount...
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Components mounted and everything checked for fit...
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Frame piece tacked back in place and battery box now set up to do rear mount...
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A piece of 3 x 25 is drilled and another pair of fixed threads (bungs) made...
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Holes drilled. Drill was able to clear outer frame tubes because this was built into the initial planning...
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Fixed threads welded in place. For added strength, they were made with 2mm thick rims about 5mm wide...
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Flat mount welded to box...
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Final mounting...
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Next we will build the electrics box to go around all of this...
Chopit'nrideit... Prof

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