Acme Internal Thread 1 ½ - 0.250P-2.000L-ACME-2G-LH (8 START) Help

[pandiyan.innova]

Hi all I am cutting a Multi-start ACME Internal thread with the following spec. [1 ½ - 0.250P-2.000L-ACME-2G-LH (8 START)] using sandvik inserts.
The thread runs for about 3" long. I am getting major problems with cuttings wrapping around the part and inserts breaking. As lead is 2” tool should move 2” per revolution of spindle so we r facing lot of problem. Whether it can be done in CNC machine or conventional lathe is preferred? Please guide what method I should follow and in which way helix angle will affect the insert breakage and how we have to rectify it.
It is being done on a CNC Lathe with spindle power 7.5/11kW and Fanuc Oi Mate-TC controller.
And is there any possibility to rough the profile with DCMT, VCMT, ID grooving (or) HSS boring bar before finishing the thread. Which cycle is preferred G76 or G33 and is there any way of doing a modified in feed. Does any one have any suggestions to this as I have loads more to do and am eating chimes and inserts like there going out of fashion.
I have tried the messing with surface speed but this seems to do nothing. And depths of cut but again nothing seems to be doing anything.
Thank you for your time.

[RICHARD ZASTROW]

paniyan.innova, You may have a problem which you already noted. Check the relief angle below the actual cutting face to be sure there is clearance and no rubbing or interference on that surface. With the 2" lead that could be a problem.

[burbankbrewer]

What material are you cutting? What rpm, depth of cut are you cutting at? Look at the insert to see where it is touching the material. You may need to grind the sides of the insert to get more clearance. If you look at the specs for the insert it will tell you what you can cut with it. I bet it won't include what you are trying to cut.

[Mcgyver]

looking at a pic of a long lead like this makes me think creating an internal thread with 2" lead is as much a broaching op as turning. given that the feed rate is going influence the cutting speed as much as the rpm's, I'd guess this is a slow sfm job, else how could the carriage keep up? if that's the case, grind up a hss tool for the job so you know you have clearance. In other words, if you are busting inserts likely because its such odd shape tool you require to give adequate clearance, and if i'm right and you can't get the sfm to benefit from carbide, grind up a hss tool and see if it solves your problem.

[burbankbrewer]

Originally Posted by Mcgyver looking at a pic of a long lead like this makes me think creating an internal thread with 2" lead is as much a broaching op as turning. given that the feed rate is going influence the cutting speed as much as the rpm's, I'd guess this is a slow sfm job, else how could the carriage keep up? if that's the case, grind up a hss tool for the job so you know you have clearance. In other words, if you are busting inserts likely because its such odd shape tool you require to give adequate clearance, and if i'm right and you can't get the sfm to benefit from carbide, grind up a hss tool and see if it solves your problem.

Or send it to a threadmill............

[Geof]

There was a thread on a similar topic a short while ago and someone pointed out that angled shims are available to put the cutting edge of the tool perpendicular to the travel of the material past it.

Here it is:

Acme Thread 4tpi Help.

You will need to read through the posts.

[ajl6549]

Check with Sandvik to see if the tool your using is appropriate for your app.

[pandiyan.innova]

Hi thank you all of you for your suggestions. Finally we got a HSS tool with high rake angle and profile tilted to the helix of the thread we have done only sample it comes ok but finishing seems very poor please suggest us to improve the finishing.
Once again thanking you all for your time.