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View Full Version : re-posted, for ingcntry, how to cut ACME threads



billyboy
11-04-2006, 09:03 PM
think you should have made a new post for this question, you may get a better responce from the guy's.

bill

lngcntry
Junior Member Join Date: Nov 2006
Posts: 1

How do you turn Acme thhreads on a lathe?

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How do you set up a lathe to turn acme threads?Do you set the cross-slide to 14 1/2 degrees?Also when starting on the second start how do you turn the workpiece exactly 180 degrees? I have tried but have not been able to get the grooves to come out evenly spaced.

Jim Hubbell
11-04-2006, 09:49 PM
A few years back I needed to cut some acme thds. to fit the lead screw on my lathe. The split-nut was about worn out. I ground a tool bit to fit the into the lead screw and set it up on a boring bar. Set it up exactly 90deg. to the axis of the unthreaded halfnut.

The top feed was set about 1/2deg. steeper than the side of the thread.

It sounds like you wish to cut multiple pitch threads. If so, finish the first then mark your gear train. Pull the gears apart and turn the spindle 1/2 turn and remesh the gears. Cut the second to match the first thread.

If the above is not clear, ask again and I or someone will try to make it more plain.

Herm Williams
11-04-2006, 10:16 PM
I have found some lathes that have square threads on the lead screw, and one (a cinc 17 x 57 hydroshift that is not symmetrical). It is something to consider when you grind the thread cutting tool. Anyway let us know how it works out, I am still learning.
my two cents worth
re

Mcgyver
11-04-2006, 10:20 PM
your question is very broad, cutting acme threads is for the most part just like any other thread as far as set up and technique. the work is often long so use a travelling steady. like a V thread, the tool has to be accurately ground, however unlike a V thread, the tool has to be not just the right angles, but the right width across the end - different for each pitch. grind the tool with the aid of an acme thread gauge is the easiest way to go imo. thread angle is 29 not 60 so set the compound over 14 and a bit. when I've done it, I've used free cutting steel as it is a very wide cut.

dp
11-04-2006, 10:39 PM
The right shaped tools and the proper clearances for helix angle can't hurt. This isn't an ACME thread, but the challenges are the same - and he did an internal as well as external version. I love this guy's work. I wish he'd have posted a picture of his cutting tool:

http://homepage3.nifty.com/amigos/screw_jack/screw_jack-e.htm

The details are probably covered in one of the Audel books and certainly in the Machinery's Handbook. If I were doing it I'd definitely go through the process with aluminum first. It's cheap and forgiving.

vmil3
11-05-2006, 12:33 AM
Hi Bill,
We need to know your lathe make and model ?, pitch of thread (is it odd or even number of tpi?) and how many starts?, (sounds like a double start). Are you threading a shaft or a nut?

When we had this job, we ground the roughing bit with a narrower tip (flat) than what was required, this thinning of the tool bit removes much of the chatter, also we ground a 5 deg top rake on the tool bit as most of our acme threads were cut on 316 stainless steel. The compound is set 90 deg to the cross slide not at 14-1/2 deg. The threads were cut down to depth, then widened using the compound slide,checking with the mateing nut or shop gage. At work we bought top notch carbides for threading the tought 316 SS.

If your thread pitch is odd number of teeth, and you are cutting a double start thread, we would cut both threads at the same time watching the thread dial, engage numbered line first follow by engaging on non numbered line, then reapeting.
Here is a pic of a 1-1/2 dia 2-1/2 pitch double start thread being cut on a 10 foot long piece of 316 SS.

http://img.photobucket.com/albums/v727/vmil3/Acmethread.jpg

recoilless
11-06-2006, 02:08 PM
Billyboy: I got the same advice that vmil gave about cutting w/ compound set parallel to work ( bit at 90 deg). I've found it helps with larger pitches because the amount of material being removed on flank and root is greater than that on a 60 degree(flank only). Also, never tried slipping gear for double start, I've used the T-dial.

lngcntry
11-09-2006, 09:07 PM
Thanks for all the help. I was able to cut the threads on a 3/4 shaft yesterday and today I made a nut for it out of brass. I was very pleased with it.Thanks again!

GRH
11-09-2006, 09:40 PM
Do not be surprised if in time the nut will not turn on the thread, a lot depends on the material of the screw,any colled rolled steel is BAD as it is full of stresses, I prefer G & P stressproof , first I roughout a V thread then using a tool similar to a parting/cutoff I remove more material so I have a weird looking square thread, about a week later I use a undersize Acme tool and make it into a acme thread again undersize as the shaft has stretched due to the amount of metal removed, kinda like it unwinds, again about 2-3 weeks later after it has stabilized I finish to final size and have NEVER had a problem using this technique.

Regards Graeme (A retired engineer from Cincinnati Milacron)