Author Topic: DIY back-cut tranny questions.  (Read 988 times)

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Offline fang

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DIY back-cut tranny questions.
« on: December 07, 2012, 12:19:36 pm »
Howdy y'all.
I just picked up a very big, happy drill press with a nice variable angle milling table attached to it.  (I think it weighs around 400lbs?) Everything seems tight and correct, and I am very excited about this piece of equipment.  It needs a bit of fine tuning, but it is more or less ready for some work.

I have several projects in mind, but I fell asleep last night with visions of back-cut transmissions dancing in my head...  I have a ton of spare (some junk) CB transmissions sitting around, and I want to figure out how to back-cut them.

So I am interested in what tooling will be required.  Our trannies have round dogs, so I am assuming  that the males will need some sort of hole cutting bit, but as I have never done this before, I am not too sure where to look for the bits.  I think the female part should be reasonably easy. 

Any and all advice and input is greatly appreciated.  Heck.  I'll even post pictures of my learning curve.

Peace and grease,

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Offline scottly

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Re: DIY back-cut tranny questions.
« Reply #1 on: December 07, 2012, 08:29:30 pm »
Fang, when I back-cut the dogs on my trans, I did it manually with grinding stones in a Dremel. Grind a bit, then test the fit, and grind a bit more. A drill press is NOT the ideal machine for this job in any case, rotary table or not..
PS, only the thrust side of the dogs need to be back-cut.
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Offline Greggo

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Re: DIY back-cut tranny questions.
« Reply #2 on: December 07, 2012, 09:15:17 pm »

Offline Greg H

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Re: DIY back-cut tranny questions.
« Reply #3 on: December 08, 2012, 12:48:52 am »
Very interesting this 8)  , Subscribed  :)

Offline turboguzzi

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Re: DIY back-cut tranny questions.
« Reply #4 on: December 08, 2012, 02:23:48 am »
i did it with a drill press too using the adjustable tilting base to get the right angle.

what helpd me most was making some jigs to get more precision/constancy . for straight faced dogs , turning on a late a stub to hold the gears in position + a little 6mm allen bolt next to it to serve as a stop for the dogs. this way you can (more or less...) get the same cut taken for say, the X numbers of engaging dogs. every thing was mounted on a piece of sliding 6mm plate so i was taking a few light  "slices" then moving to next dog.
for rounded dogs its more tricky, i've attached to the base a sort of 3mm thick half moon so that i could rotate the whole gear around its axis,

a bit hard to explain, regretfully i dont have pictures of that set up,
considering how primitive it all was, the improvement in shifting was pretty amazing and that self undercut gearbox never had any more the dreaded 500/4 shift fork wear problem.
« Last Edit: December 08, 2012, 02:25:25 am by turboguzzi »