Monday, October 29, 2012

Raleigh Chain Case: Adapting A Screw To Fit

Adapting Parts: Raleigh brake pad screw converted to chain case screw.

Sometimes you run into a part that you just cannot locate. This happened to be the case with the Raleigh Dawn rod brake roadster's front chaincase mounting screw. A 26 inch Raleigh full chaincase needs to be able to mount to the frame both at the back (via a two piece clamp) and at the front- via a screw that binds the chain case to the frame. In this case I had the rear clamp but not the front screw. I wanted to test fist the chain case. 

Raleigh screws use a proprietary 26 TPI type thread system. A normal 24 TPI screw will not work. Metric 1mm pitch screws sort of work, but won't full tighten. I tried an M6 bolt, but it wouldn't bite down enough. That meant it was time to improvise.

I went through my parts and found an old set of Raleigh sports brake frames. These are the metal frames that hold the rubber caliper brake pads. The thing was looking for was the screw. Being Raleigh parts, the pitch would be correct, I just needed to make sure the size was correct.

Sure enough, the size was the same, so I opened up the frame and extracted the screw. The screw's head was a football shaped flat thing without any bit slot. I could sort of get an adjustable wrench to turn the item, but then I figured I would adapt the part by cutting in a slot for a screwdriver.

I took a Dremel cutting wheel like the one shown below and on medium speed cut a slot into the screw head.

The slot is certainly not as perfect as a precision manufactured one, but it would allow some power in turning the screw in. I plan on using blue Loctite or perhaps a lock washer to secure it ones I am ready for final mounting. This will keep it from vibrating out, but still allow me to take it out if need be.

Below is the test fitted chain case. It needs to be cleaned and painted to match, but I can at least be fairly sure it will mount and fit correctly. The screw I adapted will go a long way to making sure it will stay tight and fit properly. 

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