2. Low tunnel and boxing...

Step by step progress on a recent Frisco mounted King Sportster tank exercise...
Post Reply
Prof
Founder, Choppers Australia
Posts: 5797
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

2. Low tunnel and boxing...

Post by Prof » Sat Dec 15, 2007 2:23 pm

Tex's tank is to be basically Frisco mounted... ie with its bottom on the top rail. Tex actually wants the bottom of the tank to sit level with the bottom of the rail rather than on top in true Frisco fashion.

Image
Here again are the original brackets, he wants to retain... so a 'box' has to be made at each end of the tank to accomodate them. Then a low tunnel has to be constructed between the boxes....

Image
First step is marking out and cutting some 2mm thick steel sheet. This is the front box...

A bit about folding sheet metal...
Image
You can easily bend sheet metal in your shed. You do not need a fancy bender. All you need is a vice, two pieces of angle iron and G clamp and a nice big flat hammer...

Image
To make it easier to set up, weld a tab on each end of one of the pieces of angle, so the angle iron always lines up...

Image
When bending sheet metal, tap it gently (too hard or at an angle will bruise the metal) along its full length, BUT only bend it part way each run. This reduces getting things miss shapen. With 2mm metal you would take about four runs to get a 90º

Image
In the case of the front box for the tank, a variation is needed. Unlike the rear box, the front box does not go to top of tank, so an extra narrow fold is needed. To do a bend like this, two pieces of angle are held vertically in vice to hold the partly folde box. This allows the centre piece to be folded without affecting the two sides...

Image
You can see the two pieces of angle iron better in this shot (This is a sample for instruction purposes, not Tex's tank box... but I figured it would be beneficial at this stage...

Image
Next, the rear box is cut out, folded and then shaped to fit the rear curve of the tank. Notice that the inner edges have been bent in slightly to make welding easier.

Image
You can see the bent in edges in thi pic also. The large double cross marking on the inside of the tank is to do with placement of two tell tails that will be mounted in the tank. The dark line to the left is where the box was to originally come, but that did not allow enough room for the tell tales. Box had to be made longer. Sorting this out took a couple of phone calls to Tex to get measurements of the tell tales he was planning to use.

Image
Tank frot squared up for front box. Metal folded out to allow a stronger weld...

Image
The two boxes made and in their places. The old tunnel will be cut up and used for the connecting low tunnel section...

Image
Cut down tunnel fitted and rear box marked for cutting out.

All this may seem complicated, but just take it one step at a time. Don't rush. Even when you are used to doing this sort of thing, mistakes get made and parts have to be redone or the design altered. Mistakes are a necessary part of gaining experience. If you make a mistake, learn from it. The only failures are those who do nothing for fear of making mistakes. Sermon ended!

Image
Cutting out the curve with an angle grinder. Cut a 'V' as you see here. Then cut smaller 'Vs' into what's left on each side (you can see a short cut on the left ready to be 'Vd'. Then round it out using a grinder blade or a large round file...

Image
After triple checking that everything fits, the three pieces comprising the tunnel are tack welded, rechecked and then welded on both sides. This is the front box....

Image
Before weding in tunnel, rear mounting tab is cut from a piece of 2.5mm tube (old shocker from a 504 Peugeot!). Diameter was worked out by ading 8mm to top frame tube diameter. This is to allow for a thin rubber cushion to go between this mounting tab and the frame to reduce viabration on the tank and also to protect paintwork...

Image
When welding sheet metal, you must tack weld over the full distance to prevent distortion and reduce heat concentration...
Image
Then fill in complete lengths with short runs alternating from side to side and end to end. This method does not contribute to leaks where welds join. In a subsequent pressure test, this tank had no leaks along these seams...

Image
Last job is to mark in and drill the hole for the tap. Tap is kept as far to the rear as possible. In Tex's case, it could not go all the way to the rear as the tap would then foul the fromt of his rear rocker cover.

Next... Front mounting brackets
Chopit'nrideit... Prof

Post Reply

Return to “Major Tank Renovations...”