Topic: DIY back-cut tranny questions.

[fang]

Howdy y'all.
I posted this in the performance forum, but thought that some of you who don't frequent over there might be able to help.

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 several 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/tooling/etc.  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, and if it goes well.....

Peace and grease,
Fang.


EDIT:  I added some pics over on page 2 of this thread.  LINK

[phil71]

My main advice is have someone do it. My second piece of advice is, if you're gonna attempt it, have a second clean set around.. the one you will eventually send to these guys> http://www.aperaceparts.com/transmissions.html when you wreck them !

[fang]

Phil, thanks for playing, but that was 100% the most useless post you will make all day.

Not even a little helpful. 

[phil71]

i thought it would save you time.

[BuffaloBill]

fang,

I'm all for doing things myself that some others might thing impractical.  I have no experience with the mod you're considering, but have often found machining advice here:
http://www.practicalmachinist.com/

Bill

[lostinthe202]

Fang,

I think what Phil was, not so tactfully, trying to say is that doing mods on transmission internals often requires close tolerance work that in turn requires careful setups and machining practices and tooling that are often not achievable/available in a home shop.

I'm not saying that you shouldn't attempt it, you'll never know if you don't try, but you'll need to do A LOT of research first.  You might consider looking into your local community college for machining courses, or for a good auto program that includes transmission rebuilding as they would likely have both good input and resources for you to take advantage of.

Good luck!

[cougar]

Hey Fang ; I've worked in a few machine shops in my time. Have operated most all the manual pieces of equiptment that you'll find in one. Since you've gone and gotten a piece of equiptment like that I'll assume (Uh Oh) that you've worked with 'em. If so you know that you're gonna need some special fixtures and tooling. But check out the "Net" and you will be able to find the info you'll need. Don't know exactly what you've got but since you've got spares to play with, H*ll go for it everybodies got to do something for the "first time" !!  Good luck and keep us posted.    ...cougar...

[fang]

Thanks Cougar.
Basically, I have a big drill press that can double as a vertical mill....  Sort of.  With it fully extended and spinning around 150rpm, I measured less than 0.001" runout at the bit. So at least it is nice and tight.

Back cutting trannys is not rocket science.  You simply cut the male and female parts, angling their matching faces a couple degrees so there is a more positive grab.  I will plan on cutting them to two degrees.

The rest is just jigging it up correctly and finding the right tooling.
I already have the jigging, but I am not sure about the best tooling for the male tranny dogs -- it will require some sort of of a small hole cutting bit which cuts on the ID.  I am sure the tool is out there.  I simply am not familiar with it....

I honestly am kind of surprised at all the worry about me doing it right!  I am not going to rattle off my credentials, but I simply am not worried about it.  Plus I have MANY transmissions just sitting around from blown motors, etc.  There is no reason not to figure it out and give it a whirl. 

If anyone is familiar with the best tool for the job.  Please feel free to chime in.

Peace and grease.
-Fang

[Xnavylfr]

The machining is not the hardest part, it is getting everything clamped and jigged down TIGHT so NOTHING moves on you while you are milling. If a part is slighly off and you start a cut , the slightly becomes the GRAND CANYON... STOP, BACK UP 2 STEPS, THROW PART AWAY, START OVER.
I've done things on AIRCRAFT with just hand tools just because people said it COULDN'T be done...

SLOW IS BETTER!!!!!

Xnavylfr(CHUCK)

[fang]

I spent some time trying to chase down the hole-cutting milling bit today.... no luck at the several local places.   

I did get some hardware to better attach my milling vice.  Who knows.... that might even end up straight and strong by the end of the day.

[754]

 Are they flat surface or round dogs, if they are round, you may need a rotary table. Good luck with it.

[scottly]

I spent some time trying to chase down the hole-cutting milling bit today.... no luck at the several local places.   

Sounds like you are looking for a "core drill". Once again, not the way I would attack this....

[754]

As far as I know they need to be ground, if you are maybe thinking of a hollow end mill, I doubt it would work well on a drill press, lack of rigidity. If it's hard you need carbide, and lack of rigidity will probably chip it..

[Pecantree]

Fang:
Because I didn't know better I did this with the transmission on my 750.
Used a 3/8 single mill burr and a 3 degree tilt on my drill table.
Also about two weeks, a tube of Prussian blue, some files and a dremal.


Getting all 3 dogs to engage equally in any hole was the most tedious.
After working a dog or receiving hole, would remount the gears on the shaft, mark one side with the blue,
then engage once. Then file or grind. Did this over and over and over.
The transmission feels rock solid except for #2. Next time I pull the engine I'll work on that some more.
I'm real curious how the wear patterns are on the dogs.
Overall I'm pretty happy with how it turned out.
But I won't do it again. Too much time.

Good Luck
Steve

[70CB750]

I would be afraid that machine you picked up is not stiff enough for this kind of work.  If it was me, i would work on other projects to get the feel what this machine - got any maker/number whatnot btw? - is capable of doing.

[fang]

Like my genitals, as far as drill presses go, they do not get much larger nor more stiff.  Its amazing I can even walk.  This is a large, production drill press.  Fully extended there is only about 0.001" of run out (measured at the bit). 

Over the last few days I have ordered some tooling, and am excited about posting some pics once I have a chance to test it out.  Some of it is coming from China, so it is likely not to arrive until the end of the year.

I have decided to buy several different small Carbide-Tipped Hole Saws in the 13mm to 15mm size.   I have encountered several issues when trying to research this stuff, but hopefully at least one of these will work.  I really don't like buying several varieties of crap in the dark, hoping one of them will be a treasure.

1.  A CB's round Transmission Dogs are 10mm -- so ideally I would find a hole cutter with an ID of 10.5mm to 11mm.
2.  Hole saws list their Outside Diameter, not the Inside Diameter of their cutting surface.
3.  None of sellers list the wall thickness of their cutting surface, and so far no one has replied to any of my emailed questions.
4.  There are very few options for hole cutting on sizes below 3/4" -- most people would just use a large drill bit.
5.  The quality of the small hole bits seems to vary dramatically
6.  Most of the Carbide Hole cutters are tooled with their cutting surface on the OD edge, not the ID edge -- It is likely I will have to re-tool the bits I receive to sharpen the ID cutting edge.  This will be slightly delicate work....
7.  So far all of my shopping has been from pictures and descriptions; I have been to several places, but have not found anything appropriate locally.


Peace and grease.
-Steve

[lrutt]

seems like an indexing table would be a must. and you'd have to do both the mail and female portions. Setup would be a very touchy thing. You'd have to run it in very small increments to not overload the machine as it appears to not be a dedicated milling machine. As for cutting the holes, a custom end mill might be what you need, but then you have to machine at an angle to match the dogs you've cut. And how much of an angle do they cut? just a few degrees?

[iron_worker]

Can somewhat put a sketch up of what is actually trying to be accomplished? I'm having a hard time visualizing it.

IW

[Vreihenmotor6]

find a small diameter one of these with the proper angle and go for it?

[chickenman_26]

Can somewhat put a sketch up of what is actually trying to be accomplished? I'm having a hard time visualizing it.

IW

From APE transmission's webpage...

What exactly is undercutting?

The transmission gears lock together with a series of "dogs' or "dogs and slots" The photo below shows several of the dogs engaged together so that both gears turn together. Under hard use, the gears can began to separate until the dogs become disengaged, this causes the transmission to jump out of gear.

 Now notice in the above photo the dogs that are in the circle. They both have angles cut on them where they meet. This causes them to lock together. They cannot separate without first backing up to unload the angles. This is an undercut. On APE transmissions, all of the dogs get these precise angle cuts.

Road race "up and down" cuts have angles machined on both sides of the dog so it works the same way under acceleration load and deceleration load.
 

[754]

Are they always straight cut?, i think some are round,,.. Straight be easy on my B@S grinder..

[fang]

I need to cut round ones. 

-Fang

[754]

Pin and hole..correct.. Use stones, spin with die grinder if needed..

[lostinthe202]

I would be afraid that machine you picked up is not stiff enough for this kind of work.  If it was me, i would work on other projects to get the feel what this machine - got any maker/number whatnot btw? - is capable of doing.

Like my genitals, as far as drill presses go, they do not get much larger nor more stiff.  Its amazing I can even walk.  This is a large, production drill press.  Fully extended there is only about 0.001" of run out (measured at the bit).   

For the sake of polite conversation we'll kick your genitalia aside (however difficult that may prove) and say that runout has nothing to do with how rigid your drill press is.

Every machine tool with a spinning work axis has runout.  How much depends on the quality of the machine tool.  There are milling machines capable of holding 5 decimal places (yes, .00001") but they also need to be in a temperature controlled room with very specific conditions required of the tooling, cut process, speeds, feeds and material handling to achieve that accuracy.  The runout on such machines is so small as to be impossible to measure with the instruments that anyone reading this is likely to possess, but it's rigidity is going to be next to nothing.

Rigidity is a function not only of how well the machine was built, but also what it is intended to do.  A drill press, even one that is made for a production environment, is going to be robust in the force and rigidity it can supply in a downward direction because that is what it was built to do, drill holes.  Milling rigidity requires different design characteristics.  The spindle bearings in a quality milling machine look much different than in a drill press.  They are designed to accommodate forces moving perpendicular to the spinning axis as opposed to the drill press where the forces are along the spinning axis.

I'm not saying that your industrial drill press isn't up to the job, the amount of material you're talking about removing is pretty minor and any drill press worth it's weight in non-rusted 4-4 pipes will have at least a #3 morse taper which will give you the option of getting a solid holder for whatever size cutters you've bought so that you won't be tempted to hold your milling cutters in a drill chuck which will guarantee the loss of any rigidity your drill press can supply.

I'd love to see what drill you've got, I love old machinery and I love seeing it put to use!

[fang]

Thanks Lost.
I agree with you and appreciate your thoughts. 

I the tooling I purchased will take several weeks to arrive from overseas, but I am excited to see what I can do and post some pics of the process.

Peace and grease,
-Fang