20. Moulding #1...

A blow by blow photographic account of chopping from stock to chop... This projcet has been given its own forum due to the large number of photos it contains making uploading slow for those of you still on "dial up".
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Prof
Founder, Choppers Australia
Posts: 5800
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
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20. Moulding #1...

Post by Prof » Sun Feb 04, 2007 11:19 pm

Frame Moulding...

Why mould... Couple of reasons, all equally valid.
1. A moulded frame and tank looks great and can make the whole bike visually flow,
2. A moulded frame is easy to clean,
3. Moulding covers iregularities of welding and covers evidence of removed brackets,
3. Moulding provides more effective painting surfaces,
4. You can change the character of your chopper with moulding eg add scallops, ridges change from round to square etc

Aim...
When you mould, your aim is two fold...
1. to cover nicks and gaps
2. To make joints seamless

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1. Nicks & Gaps... On Figure 1, 'B' is a filled in nick, 'A; is a filled in gap created by two joined pieces of metal and also by a bulky weld. You don't want to weaken the weld by grinding it smooth so you must mould over it.

2. Making joints seamless... Figure 2 shows two pieces of converging metal. The aim as shown by the dotted line is to change direction from the one to the other with moulding so that you can't see where the change between one direction and the other really begins.

Figure 3. shows an actual example on Michael's bike... the pressed gusset behind the steering head. The welding along the edge of the two pieces of sheet metal making up the gusset leave a really uneven edge. Where they join the top and down tubes, there is an abrupt change in direction. Moulding to the dotted line ('A') corrects these visually ugly joins...

On this bike moulding is kept simple, just to clean up irregularities and provide better painting surfaces and especially for easy cleaning.

Step one: sheet metal...
The thicker your moulding, the more likely it is to crack, so where it is possible to fill indents more than 3/8" use sheet metal. Also be aware that your frame tubing flexes so don't mould too thickly where tube meets gussets...

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This is the rear of the frame under the swing arm pivot. I use metal from computer cases (my sons built computers for years, so I have plenty). It is cut closely to size, bent where necessary and tack welded (5mm intervals) to frame.

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This same area after moulding. Dished area above the three holes is for a nut that is welded to the rear footpeg bracket that bolts through these holes...

Tools...

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Wood rasp gets down the high spots and achieves basic shapes. Take care not to hit the metal too hard or you will have lots of scratches to fix later. In more confined areas such as around gussets on frame tubes etc, I use a coarse round file about 3/4 inch in diameter and sometimes resort to a skinnier1/4' round file. You can get really accurate with these especially if you twist it as you scrape...

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40 and 80 grit paper gives you final contours. The black shpaes are sanding blocks made from thin conveyer belt rubber or old mudflaps... about 3/8" thick. Stiff yet flexible. One of them has a curved edge to allow you to get into tight spots. The point on it is also for tight little corners...

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Breaking the sand paper grain... Sanding paper has a stiff glue holding grains onto paper. If you try to bend it, it wil crack with a sharp edge... no good foe sanding into corners. Solution is to break the grain. Do this by pulling paper at 45 degrees tightly over a sharp edge first one way and then at 90 degreees to that. Paper will now curve easily and evenly. By the way, my knee is where my other hand would normally be when doing this, but I had to take the photo as well!

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I mix putty on a 'bat' with a handle 4" long and a blade 8" by 5". One edge of the bat's blade (see previous pic) is sharp to clean putty of my knife and for breaking grain on sand paper. I use an old kitchen knife for mixing and applying putty. A scraper comes with tin and works fine. I like the knife because on complex things like bike frames you can get putty into corners easier.

Putty to hardener mix is pea of hardener to golf ball of putty. I usually only mix half those amounts. Mix til hardener colouring is consistant through out the mix. Insufficient hardener and putty will not set. Too much and you can't get in on before it 'goes off'. In hot weather putty goes off much quicker than in normal temps.

Rear guard...

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Here is the rear guard ready to mould. Moulding has to be done to fair in taillight. about 10 original bolt holes have been welded up and need filling as well at some other uneven spots...

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A view from the underside showing threaded metal plates to take bolts that fix guard to frame. Fresh welded piece of bar is a reinforcement I'd forgotten. It reinforces the area from rear guard mounts to rear light and has a threaded hole (right side with bolt in it) to hold bolt that will fix a quickly removable pannier frame in place.

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This pic shows welds where guard was pulled in to keep to wheel shape as well as the holes that had to be welded in... pain of a job.

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This is second layer of body putty. Keep layers resonably thin to ensure a good job. Make sure each layer is 'worked' onto the previous layer. This ensures that it 'sticks' and doesn't peel off at eges when sanding.

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To fair in taillight, I put holder in place and covered edges with tape so putty wouldn't stick. Then I puttied up to it. As putty gets thin when filing it back, tape shows through the tansluscent putty. This allows you to file right up to the tape without damaging the taillight holder underneath. Note the rasp scratches in the steel that I mentioned earlier.

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Final layer of putty to finish few low bits.

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Stage one finished... Putty filed down to correct contours. Taillight holder fits nicely. Sanded with 80 grit. When rest of bike is done, we will then blow out any surface air holes with the compressor, fix these and any scratches with finishing putty and final sanding with 180...
Last edited by Prof on Mon Feb 26, 2007 12:45 am, edited 6 times in total.
Chopit'nrideit... Prof

Prof
Founder, Choppers Australia
Posts: 5800
Joined: Sat Oct 22, 2005 3:54 pm
Location: Willunga, South Australia
Contact:

xxx

Post by Prof » Sat Feb 24, 2007 12:29 am

This reply is the only way of keeping Moulding post in its proper place! Stupid computers!!!!
Chopit'nrideit... Prof

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