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Trouble Tapping 3/4-12 ACME 5C x 4.0" THRU Heat Treated 4130

HYPER-TECH

HYPER-TECH

Plastic
Joined
Oct 13, 2020
Tapping 3/4-12 ACME 5C x 4.0" thru Heat Treated 4130
Success Stories : GO

I wish it were that easy, we have been struggling with tapping this thread for over a week with no joy. Spent over $600 on a custom carbide tap that starts fine and ends oversize. The gauge provided by our customer gets tight half way thru and the "NO GO" goes on the opposite side. Using Molly-D to cut with. Just can't figure out why it's getting tight then opening up. Tap appears to be in good shape. Does anyone have a suggestion?
 
HYPER-TECH said:
You think perhaps holes should have been tapped prior to heat treating?
Click to expand...

No, I think if stress is being relieved when you cut the threads they could move. A roughing tap would bulk most of the material and allow it to "relax" then the finishing tap would "true" them up.

That is if it's cause the material is moving.

I've never ran into the problem you are experiencing, just trying to point out some things that may have not been though about.
 
HYPER-TECH said:
Tapping 3/4-12 ACME 5C x 4.0" thru Heat Treated 4130
Success Stories : GO

I wish it were that easy, we have been struggling with tapping this thread for over a week with no joy. Spent over $600 on a custom carbide tap that starts fine and ends oversize. The gauge provided by our customer gets tight half way thru and the "NO GO" goes on the opposite side. Using Molly-D to cut with. Just can't figure out why it's getting tight then opening up. Tap appears to be in good shape. Does anyone have a suggestion?
Click to expand...

My guess ase you didnt say turnign or milling but same pretty much eitherway.
your minor Dia isnt straight(drilled hole), which is causeing your tap to walk hence being tight in middle and loose on back end. I am assuming your tap is running true?
 
Delw said:
My guess ase you didnt say turnign or milling but same pretty much eitherway.
your minor Dia isnt straight(drilled hole), which is causeing your tap to walk hence being tight in middle and loose on back end. I am assuming your tap is running true?
Click to expand...

threads were single pointed in using a threading bar on lathe
 
HYPER-TECH said:
threads were single pointed in using a threading bar on lathe
Click to expand...

Never had one good then tight in middle then big in back. however if your part is then wall you maybe clamping to hard on the OD which will cause the back to be big when you release it.

whats you dia of the part?

you did say tapping, but yet single pointing so I am going to assume you dont have alot of lathe experiance , and you mention 5c in there as well so now I am going to assume its a 5c collet your holding with.

if so whats the collet size and od size of the part. where you holding the part in the collet? front back center?
if the part is holding on the back you could have some run out, hence why its size in the front no go in the middle and big in the back.
your have a
another thing is chip packing, that will throw your threading tool off.


try to be specific in the post as its lathe work its pretty simple and most here have been there done that so to speak.
do you have taper in your program? Post the program up while your at it.
 
You mention tap 3 or 4 times, even go so far as to say the tap looks fine, then its single point in a lathe?

You don't say how hard this thing is but as long as the threads didn't change size any I'd definitely put the threads in before you harden it.

So what you've got a 1/2" or 5/8" bar hanging out 4 1/4" Threading 3/4" ACME?

Brent
 
How hard is the part? tapping or single point threading? Carbide tap? Why? Roughing the thread prior to HT might be a good idea, but that bore is going to shrink with heat treating, but its better than roughing it after its hardened.
 
yardbird said:
You mention tap 3 or 4 times, even go so far as to say the tap looks fine, then its single point in a lathe?

You don't say how hard this thing is but as long as the threads didn't change size any I'd definitely put the threads in before you harden it.

So what you've got a 1/2" or 5/8" bar hanging out 4 1/4" Threading 3/4" ACME?

Brent
Click to expand...

What could possibly go wrong here? :popcorn:
 
HYPER-TECH said:
Tapping 3/4-12 ACME 5C x 4.0" thru Heat Treated 4130
Success Stories : GO

I wish it were that easy, we have been struggling with tapping this thread for over a week with no joy. Spent over $600 on a custom carbide tap that starts fine and ends oversize. The gauge provided by our customer gets tight half way thru and the "NO GO" goes on the opposite side. Using Molly-D to cut with. Just can't figure out why it's getting tight then opening up. Tap appears to be in good shape. Does anyone have a suggestion?
Click to expand...

Something is moving.

and im with the rest of you, is it a tap, or is it a boring bar type with an internal thread insert
 
Thanks for the input...

I'm pretty sure we've got it figured out.
Thanks again for the assistance.
 

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