building a frame for a Twin Cam A...

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

Post by Prof » Fri May 22, 2020 10:44 pm

Left side of battery box needs a floor. It will be supported by a welded in back. Swing arm is raised to its highest position so we can be sure the belt will clear. Always allow for the fact that the belt or chain describes a slight arc when it is under power.

Here the back has been bent out of some 2.6mm plate and two nuts are set up ready to be welded in place to hold the base of the battery box...
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Tack welded in place...
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Front support will be welded to front of battery box. It is folded in the vice to be the correct angle for; 1. the rearward slope that just clears the primary case, but then angles up for belt clearance, 2. the angle of the front section. This requires a fair bit of measuring. Because the box needs to be easily removed without scratching paint work I play safe and make provision to bolt it...
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Because nuts underneath can be seen if a person squats, nuts are rounded off in the lathe. blue arrow shows a rounded nut. Green arrow is the 'backstop'...
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Nuts welded in. Bronze weld can be nicely flowed so little or no touch up is needed...
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chopper checked for level. As previously mentioned, best way to level bike is off rear wheel...
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Wooden wedge used to set the front bracket level for welding...
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Welded in place. Now to measure up for the floor. Measurements allow for some extra metal around edges which will be trimmed once floor is fitted...
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Floor cut and folded...
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Spirit level and square used to mark the outer edge, which will be kept to two bends for simplicity and in case it is to be chromed...
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Marked out and drilled...
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Front next... For larger patterns I use aluminium caravan siding. It is easy to cut but retains bends better than cardboard. Pattern on right was first. Left one is the final verson...
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Long slot has to carry both coil leads plus wiring loom which stock is very bulky. The two lots of plastic tube will be cut off and the wires taped. Space taken up will be half...
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Pattern in place and a chance to have a look at this cool mild classic chopper...
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Front panel will be bolted at the bottom and top. Red arrow is front panel. Purple arrow points to an 1/4 UNF threaded bung 20mm long. Bolt will r run through a 45mm tube so it can be easily accessed. Tube will be welded to side of backbone...
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Front panel cut and folded on edges to match angle of sides...
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Two bung sets are made, but panel ends up so secure with just one top attachment that the other one is not used. Piece of 3mm flattened angle will be welded to bottom of panel to locate it on the front of the floor...
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Set in place...
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Bund and tube clamped ready for tack welding. I try to minimise the number of different sized bolts and screws... in this case all 1/4 UNF, battery box all 5/16 UNF etc...
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Bung welded in place. Two nuts welded on each angled edge to secure the sides yet to be made. Bottom angle has been welded in place...
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Fits beautifully, nice and tight once bolted up. White arrow points to bottom piece of angle. Panel is easily removed without fouling frame...
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Sides next but not tonight!
Chopit'nrideit... Prof

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

Post by Prof » Sun May 24, 2020 10:18 pm

Doing the final post on electrics box right now...

Now for the sides. I will suggest that Garry have these chromed. So extra care is needed to keep them with out ripples that would show up once they are shiny. Once again the two sides are made from 2mm sheet steel.

Here cut to basic size and rolled to follow the line of the seat rail. I have not done it exactly but bent it between two pieces of angle in the vice. Curve is over about 20mm. This will look better than a sharp bent as the rest of the chopper consists of flowing curves. The rolled area is kept to 20mm to reduce any imperfections you might get if trying to roll over a larger area...
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Final trim all around and marks made for front mounting holes...
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Rear will have one top 1/4 UNF threaded mount. Here the piece of 6mm plate has been cut and marked...
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This is transfered to the side...
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Drilled. No matter how much care is taken, it is difficult to get highly accurate holes in thin plate. So I don't drill the mounting bracket until side is drilled. I also drill a larger hole that the bolt to be used; for 1/4" usually 7 or 7.5mm. This allows for slight innacuracies and for final clearance fitting. The side covers need to not touch the paint work...
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Rear mount drilled, threaded and welded in place. I would normally have the side plates in under the seat rails a little more but to fit the battery with out the terminal bolts touching the side plate, I have had to keep it out further...
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Left side now...
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Rolled curve can be easily seen here. The base has been curved to match after side cover bent not before...
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Rear upper mount set up same as the right side...
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Key switch will mount on the front curve and in far enough to easily be snagged, but still in easy reach...
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Arrow shows the centre mark for the switch. This is made large enough so we can make sure the drill bit is staying on centre as we drill. The switch has two flats to prevent it moving when the key is turned. Requires two measurements; inner...
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... and outer...
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We drill the smaller diameter hole (15mm) and then use a die grinder or file to open (19mm) it out in the red marked areas. Final shape of hole is shown on right...
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Initial hole drilled...
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Ground to final shape and switch mounted...
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Coil and cut out switch box have been mounted. Fuse box is next. I try to mount all components so that they are easily accessed (especially important for fuses), easily removed and connections easily accessed for cleaning and tightening. I mark and cut out the stock fuse mount...
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Parallel lines can be marked with a verniers, but do it too often and point will get rounded. Ok here as I am marking the paint...
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Mount welded in place and fuse box installed. Green dotted lines mark where to gussets that will double as front seat mounts will be welded in. Fuse box needs to be back a little and lower so they won't get damaged by the tabs on the seat...
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Harley for some reason seem to like circuit breakers. I normally replace their main circuit breaker with an inline fuse, but will keep this one for simplicity... I make a mount our of some 2mm steel and weld it into place. When the painting is complete, it breaker box will be pop rivitted in place...
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Electrics box now done. There are still a couple of minor components to mount and some holes to make for wiring entry and exit, but I will leave that until rest of chopper welded up. Then I will run the wiring and finish box and cut some of the wiring to lengths so the box isn't filled with a tangled snarl of wiring. I have tried to keep components to the side, it can be used to store spare globes, fuses and other bits and pieces.

Lionel got enthusiastic and took a couple of pics of Da Prof at work. This shot shows the low slung digger look of this chopper. I am really thrilled at how it is turning out and hope Garry will be too...
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Rear guard mounting next followed by sissy bar, tailight and tank mounting. Coming soon...
Chopit'nrideit... Prof

El Skitzo
Posts: 805
Joined: Wed Sep 30, 2009 6:40 pm
Location: Perth, WA

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

Post by El Skitzo » Thu May 28, 2020 9:15 am

That's a lot of work, well done!

Not easy hiding everything on a modern bike that's for sure
'65 Triumph Chopper (project)
'64 Triumph Chopper (project)

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

Post by Prof » Thu May 28, 2020 10:43 pm

We need to build the seat first and then we can set up the guard and sissy bar mount...

Measure at widest point. Seat width is same as centre (highest point) of each seat rail...
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Guestimate the seat back height allowing for a slight backward lean of the passenger seat. This slope is to reduce the passenger's tendency to slide forwards when braking...
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I build all my seat bases out of 3mm aluminium; it is light but still and also easily formed. Here marked out as a rectangle (total width and length) with a centre line...
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Now shaped...
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Front curve is marked with a dividers (compass). To find the centre, we draw an arc (A) from the front where the curve will meet the centre point...
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Another arc (B) swung from where the curve will meat the seat side...
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So now we can swing an arc (C) that will the be front curve. Do the same for the other side and we have an even curve ready to cut...
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I use an angle grinder to cut aluminium. Wax is applied to both sides of the blade and it cuts through ally like butter. I used to use a jigsaw, but angle grinder is easier. Curves can also be cut by doing a series of shallow cuts...
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Once cut out time to bend. Gauge is set to angle of seat back...
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Seat bent up in my folder. Other places I have shown how to bend using angle iron in a vice with a G clamp on the other end...
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Some consolidated foam roughly cut so size. I only ever use consolidated foam though it is hard to access. It retains its life for years and years and years and (oops sorry) but it is good...
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I use an electric knife of very sharp serated fishing knife to cut the foam...
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Gary and his mate come down to try out the seat. He wants some changes. Needs a little more padding under his behind, plus some extra length in the front to cover the frame...
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An extra 30mm removed from passenger seat...
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Cutting off the front to extend it...
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Cardboard pattern; needs a little extra length...
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Nose cut out and joined in. The front curve was small enough to use an existing circle... in this case a 1mm angle grinder blade! A strip of 3mm ally is used and pop riveted very thoroughly. Needs to be strong to resist stress of stretched vinyl and also repeated sliding in and out when the seat is removed...
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Underneath is smooth. Ally counterbored so rivet heads are flush...
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Setting up the rear mounting/sissy bar brackets is next...
Chopit'nrideit... Prof

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

Post by Prof » Tue Jun 02, 2020 10:23 pm

Seat Mounting...

Rear seat mount is also the rear guard support and ties the two rear frame tubes together, so needs to be reasonably substantial. Step one is to ensure it is square. This is done by measuring from a common point which in this case is a centre marked on the backbone ready to drill as the tank rear mount...
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A piece of 30 x 30 x 3 angle is cut and fitted to the angle of the tubes. Flat piece of steel bar you can see is used so we can keep the top of the angle level with the top of the tubes. Not noticeable here is that because the seat back has a rearward lean, I have hammered out the angle on the anvil to increase the angle from 90 degrees to about 100 degrees (forgot a pic,sorry)...
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Before welding in place, holes need to be drilled for the two guard mounting bolts. A set square us used against the tyre after it has been aligned. This allows us to work out the tyre centre on the angle. It is also a check that tubing is evenly spaced of the centre of the wheel, which (because we are just sooo clever!) it is...
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Holes drilled so they are in about 40mm from the edge of the guard to allow for its curve. Flat bar again used as we tack weld to ensure it is level with tops of tubing...
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Now for the seat back. Garry has already designated sissy bar height, so for good looks we make the seat back 200 or so below the top of the sissy bar. An angle grinder blade is just the right diameter to trace around for the top...
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Cut out and checked for square on the seat base. Top of seat back is narrower than the bottom but still wide enough to give comfortable support to the passenger's back. It is clamped and attached to the seat base with pop rivets as we did with the front...
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More foam is cut to rough shape and set up to complete padding on seat. It is cut on a band saw, An extra bit needs to be added to the rider's seat to make up for the extension we previously added...
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to mark a narrow strip of foam accurately you often have to keep one side straight by pressing it against a straight edge in this case a couple pieces of 12mm flat bar...
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That's it for tonight. Will add more soon...
Chopit'nrideit... Prof

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

Post by Prof » Sat Jun 06, 2020 10:27 pm

Sissy Bar...

Garry and I played around with a few designs for a simple sissy bar. He liked a plain round top, but I suggested it be narrowed so the whole thing didn't look so wide. He was happy with this and we drew it up on a piece of particle board. I have made a number of formers over the years and this one is the right size...
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Former is mounted in the vice and a piece of ally welding rod used to mark the centre and then locate where the bend will start. Piece of angle at top of pic is welded to the former and retains the round bar as it is bent.
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16mm (5/8") round bar is used for sissy bar and wedged into place at the correct location. Peter Fonda's Easy Rider 1/2" bar would not have lasted far into a real journey across the USA!...
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Bar now heated and slowly bent...
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There is a trick to this. Bending must be slow and the heat progress with the bend. If you go too fast the round bar will pop out at the arrow and you will have a lopsided bend. It will end up slightly lopsided anyway and you will have to reheat and straighten it at this point...just takes some patience and you get better with experience...
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Now onto my jig. Pegs are removable and here are used in the outer holes to accomodate the wider loop at the top. Inner holes are for a narrower sissy bar. Bar is first bent around outeside peg and then the inside peg is installed and the bar bent back inwards...
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Both sides now bent around the pegs to the correct distance apart at the bottom of the sissy bar. Here being checked off a centre line...
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Done...
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Now to mount the sissy bar. This piece of flat bar has been marked for the two mounting brackets and ready to be drilled (3/8") and cut out...
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Bar height measured and one leg of bar marked...
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Distance measured from the top centre of the sissy bar and the second side measured to match...
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I missed a couple of pics here, but the process can be found on other posts. Once one bracket is tacked, a plumbob is used on the levelled chopper to ensure the sissy bar is perfectly upright in case the seat back is slightly off centre. In this case it is fine and second side is tacked. The two matching mounts to be welded to the frame tubes can be seen ready to be attached (white arrow)...
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Mounts are bolted to sissy bar brackets and tacked in place and everything re checked for square...
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Seat back is held in place with a cross piece on the sissy bar. Because we have kept brackets on the bike, sissy bar shape etc rounded, I mark up a rounded cross piece...
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This is cut out and drilled and then linished. I have modified my lininsher to allow the belt to sag over a longer distance to make smoothing off curves like this easier...
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A hole is drilled in the seat back and a thread inserted...
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I have brought the cross piece down a bit more than initially planned...
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Mount tacked into place the seat back bolted in place. I will leave the cross piece tacked until seat comes back from upholsterer because he wants to put some thin carpet under it and this will likely mean slightly raising the cross piece...
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Next job will be front seat mounts and rear guard. Stay tuned...
Chopit'nrideit... Prof

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

Post by Prof » Sun Jun 07, 2020 11:05 pm

Mounting rear guard...

I give Garry the usual selection of guards and he decides on a short flat guard with narrow valences. This CB750 rear guard gives the look he wants...
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A new flat guard with a rear lip comes out of stock and we begin work. This little tool is used to give a right angled mark on a curve; easy for any chopper jock to knock up in his workshop...
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Set square gives a straight line across the guard and Garry attacks the guard with gusto...
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Meanwhile Lionel is setting up the exhaust system so I can make brackets for it...
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Double check on wheel alignment with a long straight edge and piece of 30x30 square tube...
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Lionel at the other end...
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Rear wheel is 50mm fatter than the front, so the front of the straight edge is spaced out with a piece of 25mm tube. One rear wheel adjuster moves the axle until the front and rear of the straight edge touches front and rear of both tyres...
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Centre of tyre is marked on the rear cross piece and lines up with the centre....
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The radius of the guard is much greater than the tyre radius. It needs to be wedged so it can be pulled in to more closely match the wheel. Use that little tool again to keep cuts square...
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If guard is not cut accurately, it will end up with a twist, so a set square is used to mark the cuts on the other side...
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Cuts tack welded...
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Guard is checked for correct radius. It has pulled in a bit, so each weld gets a thump with a small sledge sot open up the cut. That does the trick...
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Relief cut out for rear belt. Wheel is actually pulled up to its highest position and guard marked and an extra 30mm added to the cut to allow for belt expansion at speed. If the chain guard came this far forwards we would have to allow for that as well. It doesn't so all is ok...
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Front mount is made from some 25mm angle. It is drilled before cutting to the shape of the seat rail cross piece. Then welded in...
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Guard is marked and drilled to match the mounting holes and then nutcerts are installed. Lionell did this while I was sorting out the exhaust brackets and I forgot to get some pics. Sorry. Mount you see on the rear exhaust is temporary. Because the engine is rubber mounted, front and rear exhaust mounts have to attach to engine and gear box. We'll show you them soon...
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Seat front mounts next...
Chopit'nrideit... Prof

El Skitzo
Posts: 805
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 Jun 08, 2020 9:34 am

Wow starting to look very complete
'65 Triumph Chopper (project)
'64 Triumph Chopper (project)

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

Post by Prof » Mon Jun 08, 2020 2:47 pm

Four processes left on the seat; 1.fab up two sides, 2.built front mounts, 3. finish padding, 4. upholstery.

The last will by Tony, a local motorcycle only upholsterer who has been in the business since Noah was a lad.

Seat needs to be strengthened by building in side pieces under the passenger seat. They will obviously also cover an unsightly gap...
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Lionel makes up the cardboard pattern...
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The sides made from 3mm aluminium with full length tabs which are folded in so the sides can be attached with...
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... pop rivets. A slight gap shows...
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Gentle tapping out along the bottom with a hammer closes it up. Just enough space is left for upholstery to fit against the rear seat rails...
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Front mounts...

Two 3mm gussets are welded into the front of the seat rails. Two seat tabs will catch under these...
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Tabs cut and bent a little so they easily slide under the gussets. One has been bent (arrow) and the other is still in the bender. You can do this in a vice easily; you just have to make sure bends are at right angles...
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Tabs placed on a flat surface and angle of bends checked. Right hand one (red arrow) is bent slightly more, so goes back in the bender for a slight tweek...
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Tabs will mount under the front of the seat and be secured with 1/4" bolts through the seat base into threaded plates. Here getting marked for drilling...
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Securing plates (6mm steel bar) threaded. Top pot contains lubricant, bottom pot kerosene to clean tap from under neath before it is removed...
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Fame tubes (seat rails) are marked with texta to show location of rear of gussets (red arrow) and edges of backbone (white arrow). These are translated to seat base so tabs can be correctly located...
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Holes drilled in the seat base are 10mm diameter to allow fine adjustment...
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Tabs bolted lightly and seat slid into place. Tabs need to be moved forwards slightly. Bolts now tightened...
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Seat base drilled for two locking bolts. These will hold the threaded inner plate in place so tabs can be removed for upholstery without losing the threaded plate inside. Threaded plate is threaded and holes in seat base slightly counter bored so the button heads don't protrude quite so much...
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Done. Setting seat mounts up like this means that the tabs can be removed while upholstering. Then what ever thickness upholstery is put under the seat, the tab clearance to frame will not change...
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Padding can now be glued in place. I use Selley's Quick Grip. It is runnier than their Gel Grip but I think sticks better. A 40mm strip of glue on both base and foam is sufficient...
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All the bits glued in place. I have more detailed explanations of seat padding in other posts...
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Trimmed with sharp knife...
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Shaped with angle grinder (more on this elsewhere also)...
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Finally covered with 3/8" foam that has one side closed. It covers any minor bumps in the consolidated foam and leaves a nice finish for final vinyl covering...
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Black foam stretches really well. I start by stretching and gluing at extreme points (arrows)and then doing the rest by degrees so I get no ripples. Not glued to padding but just 3mm edge of seat base...
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All gluing done...
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Trimmed with angle grinder...
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Finished and ready for...
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Tony who will now work his magic. Seat will look pretty classy and match the colour of the frame and tins...
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Getting close to finished now; tank needs to be mounted, dent knocked and some fillers put in to close gaps, Tail and headlight need mounting, Forwards have to be built and pipes and side stand mounted. This pic shows mounted tank and tail light but we will still show how we do it. Coming soon...
Chopit'nrideit... Prof

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

Post by Prof » Thu Jun 18, 2020 9:30 pm

Taillight now; Garry peruses my display of tailights (the biggest range in SA) and picks out a few possibilities. Because the chopper has to go through the engineering and regio process, lights and reflectors have to be E Marked, even though there is no difference in quality... in fact the difference is impossible to tell in most cases...
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Oval light appeals to Garry, which is good because I have an E marked version. We cut a combined tail light/number plate holder from 3mm aluminium. Remember to always use wax on your angle grinder blade when cutting aluminium. If Garry had wanted a light that did not have an E marked version we would have had to make second mount so lights c ould be swapped later. Oops! Who said that!..
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Centre of guard marked. Current SA regs do not allow. side mounted taillights. They must be centrally mounted and within in (I think) 15 degrees of vertical). Minimum height from ground is 350mm and max is 900mm.
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Tailight/number plate combo will be mounted on the sissy bar as Garry is not into camping so is unlikely to need the space on the rear of the backrest. Two tabs are cut out of 5mm steel bar and 4 holes marked and centre punched. The centre is found by measuring equal distances from each edge, so we can finish the corner with a tidy rounded edge...
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Rounded ends marked using a divider.and will now be tapped for 1/4 UNF...
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Taillight needs to be level. A longish piece of 50mm bar is clamped as a guide to the back of the sissy bar and checked for level (red dots). Parallelogram is easily made and very useful in any chopper jock's workshop...
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Four holes are drilled in the aluminium mounting and tapped for 3/16UNF button heads to hold the number plate...
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It is to be mounted 20mm above the guard. This is both for looks and to prevent damage to the rear guard paintwork. Here height of guide being measured...
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Checking for centre...
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Mounting tabs tacked to sissy bar and aluminium mount marked...
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It is not easy to be absolutely exact with drilling, so holes are drilled a bit larger. However, for some reason despite all efforts including holding my mouth right, holes still had to be modified with a die grinder...
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Mounted and looks pretty cool. Ally is countersunk so once the countersunk bolts are installed the tail light will sit nice and flat...
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We'll show you our real cool rear indicator set up next...
Chopit'nrideit... Prof

Prof
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Posts: 5972
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Re: building a frame for a Twin Cam A...

Post by Prof » Sun Jun 21, 2020 6:03 pm

Rear Indicators...

Haven't seen this done before, though I'm sure it has been. Makes for a very tidy set up and also a clean finish to the frame rails. Instead of the standard mounting procedure, we are pulling the electrics out of the indicators and mounting them in the end of each seat rail.

Because this is an ICV that will have to run the full gamut of big Brother's checks we have to abide by certain rules; 1. Lens have to be E marked though they are identical to non E marked lens, 2. Position and visibility...

For rear indicators, the clearance between the inner edges of the two illuminating surfaces shall be at least 180 mm on the condition that the prescriptions of paragraph 2.11. are applied even when the registration plate is mounted;
6.3.3.2. in height: not less than 350 mm nor more than 1,200 mm above the ground;
6.3.3.3. in length: the forward distance between the centre reference of the rear indicators and the transverse plane which constitutes the rearmost limit of the vehicle’s over-all length shall not exceed 300 mm.
6.3.4. Geometric visibility
Horizontal angles: 20 degrees inwards, 80 degrees outwards
Vertical angles; 15 degrees above and below the horizontal.
The vertical angle below the horizontal may be reduced to 5 degrees , however, if the height of the lamps is less than 750 mm.


Inner distance between lens is 220mm so that is fine. Height is no problem. Distance from rear of tyre is well under 300mm, Lights are horizontal. Main issue is inner angle of visibility which is 20 degrees and by building mounts an extra 20mm rearwards that requirement is covered.

So now to step one; dismantle indicator. It will be fitted into end of 32mm DOM frame tubing...
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Now turn up the mounting...
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Machined and a indent milled to take the globe holder retaining tab which has been considerable shortened. The slightly smaller rim matches the lens diameter...
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A small flat milled on the outer edge for the lens retaining screw...
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Globe holder tab drilled. When drilling something as thin and narrow as this it is a good idea to clamp it (vice or pliers) so the tab doesn't get twisted out of shape if the drill bit catches...
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Globe holder held in place by a 8-32 UNC screw...
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Finished mountings ready to be welded into the ends of the frame...
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Wiring will exit the tubes just forwards of the rear seat mount. Here you can see the chamfer bit used to remove sharp edges around the holes. A ball end is used on a die grinder to remove inside burrs...
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Taillight and indicator wiring will run along outside of guard under seat out of sight. Piece of computer paper folded to mark equal spaces for attaching wiring clips...
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Position on the sides marked using the pen and fingers like a marking gauge...
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Curtain rod will do fine for the clips; marked 10mm wide ready to cut...
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Cutting process. When cutting parts you need with an angle grinder, develop the habit of cutting to within half a mil of the end so they don't drop to floor, but can be easily twisted off...
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Clips welded in place...
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With the oxy already being used to weld, I turn up the heat and heat around the two guard threads and with a bolt, angle them up a bit so keep the mounting bolts square in the frame cross member...
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Back to the indicator mounts and weld them into the frame to create a seamless extension...
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A couple of views of one of the installed indicators...
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If you want to mount your indicators in your rear tubes and don't have a lathe, you can simply glue the globe holder in with Roof and Gutter Silicone. Lens can be held in place with a screw through the tube. You will have to solder an earth wire to the globe holder and run it to earth.
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5972
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
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Re: building a frame for a Twin Cam A...

Post by Prof » Mon Jul 06, 2020 10:58 pm

Mounting the fuel tank...

We are using the stock tank because Garry will be travelling longish distances (He lives 200 miles from civilisation!) and because it is actually quite a good proportioned tank. We are making some changes though; front will be raised about 3", cowl that covers filler and fuel gauge areas will have its front and rear extensions cut off. This will require an extra mounting point installed in tank. Tank will be moulded to cover joins that were hidden by the cowl extensions.

Anyway, to do all this requires new front and rear mounts. Usually when I raise a tank I am able to increase fuel storage by dropping the tunnel. However, Garry reckons it holds enough now and the extra cost would not be justified.

Old mounts are cut off and we begin setting up the rear mount, made of 3mm thick flat bar...
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Needs to be folded. Here establishing the angle of the fold...
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Folding can be done with a hammer in the vice in my cool old folder...
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The tank's tunnel is wider than our backbone, so the mount is cut to clear backbone and fill in the gaps on each side...
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Block of wood supports the bracket which would otherwise slip in the vice...
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Before any heat gets near a fuel tank, it is essential to ensure there are no fumes left inside. Even if a tank has been empty for a while, fumes can be released from between any metal joins inside. A tank blowing up in your face can be fatal so unless you are highly insured and have a death wish, best be safe rather than sorry.
1. wash out tank with detergent and water. If is has fuel residue inside (or light rust), chuck some gravel in with the water and shake vigorously. Make sure you can get the gravel out though!
2.You can fill the tank with water prior to welding so all the inner space is taken up by water and there is no space for expanding fumes or you can blow it out with compressed air s you see here and then...
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3. I prefer to prepare the tank further by filling in with carbon monoxide... and the shovel is a great producer of the stuff...
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4. Now one final precautionary act. Put the tank behind a solid surface (steel door in my case), light the oxy torch and poke it near the hole. If you've don the job properly nothing will happen. If you haven't and there are still fuel residues or vapours you will enjoy various degrees of noise and flame!!!!
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Back mount welded in . If there are gaps to be filled and or the metal is very thin, I use bronze rod. Modern tanks are VERY thin so take care...
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Wooden block sets the tank at the right height...
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Mount/filler is again made from 3mm steel plate. Part of the original mounting bracket is still attached to the tunnel and we will weld to this...
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Hole drilled in mount and filler section curved to match tank curve...
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As mount is tacked in place a ruler is run across high points (white arrows) at front of tank. This prevents any part of it protruding or sitting too far in and requiring excess bog...
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I am going to weld a second but smaller piece of 3mm flat bar over the mounting bracket and part way up the filler section. Tab is cleaned off and a thin layer of bronze laid on it. Then using plenty of heat we will weld in the extra piece. If we produce enough heat the two pieces making up the tab will weld together all the way through. You can see the finished tab in a later pic...
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The hole is redrilled after welding as some of the bronze protrudes into the hole...
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Tank now put in place and rear mounting point marked. Then checked for centre...
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A smallish hole is drilled first and then the correct size drilled. As we drill we check for centre as drill bits like to wander. Drill can be angled to correct any error. Here final check...
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Meantime the threaded bungs are machined. Threads are 3/8" UNF . Red arrow shows the initial 10mm drilled to 3/8". Rest is drilled to suit the UNF tap. This ensures the mounting bolt can never be cross threaded...
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Steel around hole in backbone is brought to red heat a couple of times and tapped in with a ball pene hammer. This allows me to have a thin lip on the threaded bung that will not protrude above the top of the backbone...
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Bung tapped in...
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Ruler used to check that it does not protrude...
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A long bolt is screwed into the bung so we can use a set square to keep the bung square as it is welded...
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In both planes...
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Job done. Once again , bronze easiest way to do this...
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Tank will be rubber mounted on 3mm rubber. These HD's do not vibrate like the older shovels and panheads, so the rubber can be thin. When bike is finally assembled, I will machine up a cupped stainless washer to contain a rubber washer for the top...
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Now for the front...
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Same procedure for the front hole. Here you can see hole being checked before it is fully drilled so drill can be angled if it is off centre...
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Heated and tapped in...
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Bung welded in the same as for the rear bung...
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Once again, gaps need filling each side. Bunring off paint...
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Left side needs relief for the wiring loom. Wiring look has plastic covers stripped off. Two lots of wiring each with their own plastic cover makes for a massive ugly mess. Combining the wires in one loom which will have one thin cover (I manage so remove 3 doubled up wires) will make this a bit more of a righteous chop, despite regs requiring total idiot proofing switch condominiums on the handle bars!!!!
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Fillers welded in on both sides and some final detailed filling done with bronze to match the curved edges of the square backbone...
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Well there it is. A strongly and neatly mounted tank. Next dent knocking and tidying up and mounting the cowl on top of the tank...
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5972
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 Jul 08, 2020 9:28 pm

Last two jobs on tank...

Tank has a nasty deep fold on the right hand side from being hit by the forks in the accident that got this bike written off. Dent is forced out using a bar inside and heat...
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Fortunately, this tank has a fuel gauge hole so we can access the inside of the tank . Flame is kept low to move out small patches of the tank at a time. Steel on these modern tanks are very thin so care has to be taken; and ye caint just pop the hole dent like in the old days!...
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A piece of threaded rod with a nut welded then ground to a gentle curve is used to push our the heated steel...
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the job is not as neat as I would have liked. It's been a while since I've done one. It was a new experience for Crowy using the Henrob and I had him running the flame a bit too large. As a result we ended up some wrinkles. At this point Jason showed up. He's doing the filling and painting and reckoned it was fine as it was as the wrinkles were only a couple of mm deep...
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So, not the best job though adequate and the main thing is that the pressed out section stayed a fraction below the final outline, so it can be moulded without any metal high spots.

Last job on the tank before moulding and painting is to modify the cowl. Original set up has a long tail that was attached to rear mounting bolt so it covered the join in the two tank halves. All of this will be moulded smooth.

Tail is cut off and shaped...
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The width is drawn up on a piece of paper and a arc swung with a compass. This is cut out and traced around to get the smooth curve on the rear of the cowl...
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Centre found and a third mounting hole drilled with a step drill. Wooden block in jaws of vice supports the thin metal...
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A blind threaded bung is machined...
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The metal around the hole is heated and tapped in so the bung will sit flush...
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Bung welded in the second job we have to do means the drain pipe is cut off and welded shut... not really needed...
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Cowl has a large opening to fit the rubber hose that normally exits here. This has to be filled...
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A piece of the original tail is cut to fit the opening. It has to be curved very slightly to match the curve of the cowl. This is done with two pairs of pliers...
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Welded with gas and thin steel rod. A few low spots (red arrows) show once the cowl is run over the linisher...
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Gentle tapping with a fine hammer on the anvil pushes low parts out...
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Finished. Ready for the chrome plater. I will drop it into Jason so he can mould the tank for a close fit. When chopper is assembled a very thin rubber edging will protect the paint from the chromed cowl...
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Jason now has tank and cowl. Frame is moulded and waiting for me to check seat fitting before he paints it. Then he'll be getting onto the tank and front and rear guards. I am currently setting up the front guard and brake which should be ready in a couple of days... just waiting on some steel and some brass spacer washers. A few other jobs still to show you and then we will be finally caught up to the actual build progress.
Chopit'nrideit... Prof

El Skitzo
Posts: 805
Joined: Wed Sep 30, 2009 6:40 pm
Location: Perth, WA

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

Post by El Skitzo » Thu Jul 09, 2020 9:38 am

Nice work!
'65 Triumph Chopper (project)
'64 Triumph Chopper (project)

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