what is the technique for a stripped thread in hardened material?, how to re-tap a pinion shaft threads / Tranny problems Options

[brant]

Ok...
so I had a big transmission failure
this box was built by a friend, at a clinic

I'm guessing the 30mm Bolt (for the speedo drive) was not torqued correctly?
apparently it came loose

the stack slid
and drove the brass angle drive through the back of the tail cone

the little button in the picture is the plug from the magnesium tail cone

but as you can see the bolt threads were heavily damaged
I have a replacement bolt with good threads

but the threads inside the pinion shaft received some damage also
I have the correct tap
but the material of the pinion shaft is so hard, that I can't get the tap to start


What is the technique to thread something hardened?

I'm betting the process involved heat, and softening the metal then rehardening...
which may not be a good idea with a pinion shaft
so I may need to build a different transmission
but if I could tap this thread, I'd be willing to give this box a shot.


any metal experts out there.. or machinist know if this is possible?

thanks in advance
brant

[Superhawk996]

You're probably not going to like the answer.

I'd just start with a fresh shaft.

Options I'm aware of:

1) Carbide drill and carbide taps. Neither are cheap and both are painfully slow cutting. Carbide is also brittle by nature. Carbide is prone to chipping and breakage with tool vibration & chatter. If you break off a carbide you're screwed and only recourse will be to EDM it.

Here's a solid carbide M6x1.0 tap -- $163 each! (IMG:style_emoticons/default/yikes.gif)
https://www.mscdirect.com/browse/tnpla/3144...ASABEgK12fD_BwE

2) EDM the threads in. Yes it can be done. You won't like the costs involved to do it.


https://www.youtube.com/watch?v=x3hEXA_q-dE


Maybe someone else has good ideas but my past history of drilling tapping hardened shafts as DIY has a spotty track record and that is with a vertical mill and a lathe at my disposal.

[brant]

You're probably not going to like the answer.

I'd just start with a fresh shaft.

Options I'm aware of:

1) Carbide drill and carbide taps. Neither are cheap and both are painfully slow cutting. Carbide is also brittle by nature. If you break off a carbide you're screwed and only recourse will be to EDM it.

2) EDM the threads in. Yes it can be done. You won't like the costs involved to do it.

Maybe someone else has good ideas but my past history of drilling tapping hardened shafts as DYI has a spotty track record and that is with a vertical mill and a lathe at my disposal.

I have the fear that you are correct. and I need to build a different transmission... alot more work. I guess the good news is that I have a lot of decent core parts now

[brant]

Ouch... the M12x1.50 carbides... start at 400 up

pretty sure that changing the pinion requires matching the Ring and resetting the pinion depth...

easier to start with a whole new box I guess

[Gint]

Is that on the one that grenaded? Not the one I had right? Let's talk later. I'll call ya.

[brant]

Yes. The one that died
I’m hoping to be in the garage and open yours tonight

Honestly I wish this bolt was not stripped. This box would be save-able other than one bolt

[ChrisFoley]

Sometimes threaded holes aren't as hard as the surrounding metal, depending on the exact material and processing.
It may be worth attempting to run a cobalt tap into the hole before considering the shaft garbage.

[brant]

Sometimes threaded holes aren't as hard as the surrounding metal, depending on the exact material and processing.
It may be worth attempting to run a cobalt tap into the hole before considering the shaft garbage.

I might call a few machine shops around here and see if one of them has the correct cobalt tap...

very little to loose

the price of the tap doesn't look like a good purchase for my 1x use

[Superhawk996]

the price of the tap doesn't look like a good purchase for my 1x use

Chris is referring to a COBALT tap. More expensive and slightly harder than HSS but way less expensive than Carbide.

Wouldn't hurt to try that to see if it will cut at all.

Disregard. I didn't read your response properly.

[ChrisFoley]

MSC has this one for under $28
12x1.5 tap

[sixnotfour]

die grind first 2 thread out it's, fuched

[ChrisFoley]

One more point about working with hard metal, if you can cut it with a file, you can tap it without requiring carbide.

[brant]

Chris, Jeff, EVERYONE....


thank you again for all of the advice
tips
and help


Update
I followed Jeff's idea.
I carefully measured the depth and used a dremel to remove 2 or so threads from the beginning that were mushroomed.

and then.... I WAS ABLE TO GET MY TAP STARTED
success... threads restored. bolt inserted ... blue lock tite used... torque achieved

I'm going to pull the box from the chassis now and finish the rebuild.
I've got the stack back together and ever thing looks visually good
I even replaced 1st syncro while I was there.

once I get the shell out, I'll wash it out better... replace both side shaft seals and the front main while I'm there.... planning on pulling tonight.

Hopefully I'll save this box as all of the sliders and parts are really in decent shape
(reflecting the few thousand miles put on it since Jeff (RIP) built it at a clinic

thanks again EVERONE!


Gint. Hopefully I can return your cores soon
I washed up the one missing the shift console
brant

[Gint]

(IMG:style_emoticons/default/smilie_pokal.gif) That's great!

I'm in no rush. I cleaned up the shop so I could put the truck in there. Which meant that everything got pushed to the sides and I don't have room for them at the moment. Without more cleaning and purging. (IMG:style_emoticons/default/smile.gif) Talk to you about it later.

[Superhawk996]

and then.... I WAS ABLE TO GET MY TAP STARTED
success... threads restored. bolt inserted ... blue lock tite used... torque achieved

I'm glad to be wrong -- Great news that you were able to save the shaft.

And . . . I may have learned a new trick along the way. (IMG:style_emoticons/default/pray.gif)