building a frame for a Twin Cam A...

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Prof
Founder, Choppers Australia
Posts: 5954
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 » 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
Founder, Choppers Australia
Posts: 5954
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 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: 794
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
Founder, Choppers Australia
Posts: 5954
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 » 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

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