help with threading 2.5" 4tpi

[treg]

I have a kennametal top notch tip that does to "4"tpi. but that sure is a big thread. i've done these before with a canned cycle. i input a value of A60 in the text and that helps alot. i do 5 tpi frequently with good results. 4 on the other hand really dont like it. anyone know the best way to cut alternating flank. ecentually roughing/surfacing the thread. ive tried in mastercam and dont seem to want to do it. anyone else done these threeads? should i look to a new tool from another supplier?? help!!
thanks

[Geof]

You could try the tedious way; we do 4tpi stub acme on 1/2" diameter leaded steel which presents a similar challenge, you cannot plunge straight in or even angle in because the cut is so wide.

I wrote a program that use a tool that is for a much smaller thread profile and has four threading cycles each in its own subroutine. The machine cycles through the subroutines and gradually works down to the final profile.

You maybe able to do something similar:

Down to have the thread depth, or a bit less on the thread centerline.

Offset Z plus the correct amount and go down so you have cut one side of the profile to the final point.

Offset Z minus and do the same.

Go back to the centerline and finish the profile down to the root diameter.

With a bit of luck the blend between the cuts on the flanks of the thread will be unnoticeable.

[Delw]

Geof's way works pretty good, on big threads like that you can also use a square toplock to rough with as well and off set the "Z" accordingly.
you can draw it up on a cad program to figure out how much you need to offset it,

one other way on your finaly pass's is to slow the rpm up to a crawl this will give a good finish on most metals and less chatter I have done threads as low as 50 rpm.
Remember there is alot of force on the part cutting a big thread like that due to the thread form, so rigidity is a MUST.
your top notch /top lock will work fine.

[treg]

thanks so much guys!
i think we are going to rough it out at a fast pace then slow her down for the end. sounds right. little bit of the old with the new !!!! thanks again
trevor

[protrxrptr17]

I have cut 2" 4.5 tpi before with the same tool. I used g76 with A60 and it went pretty well.