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kenrinc
02-25-2005, 06:31 PM
I'm experimenting with cutting a 3/8-10 ACME LH leadscrew. I can't find any documentation on how to grind the toolbit. "How to run a lathe" gives next to nothing on the bit itself, only a top view showing how to grind it to fit the ACME screw gauge. Anywone have a picture or diagram. One book I saw showed a "skewed" rectangle when looking at the tool from the front.

Any thoughts on material? I've got a lot of 12L14 laying around. This is a home shop not a business. Screw will be used for a cross slide vice.

Ken-

trains4
02-25-2005, 08:29 PM
You can buy carbide inserts that have 3 tips ground for a particular pitch of Acme thread. You can make a holder for the insert without too much trouble. Notice that you need to calculate the helix angle of the thread and tilt the insert so it matches that, otherwise you'll have trouble with relief angles.

charlie coghill
02-25-2005, 08:45 PM
Ken, have you checked Machinery's hand book? There is some information there, just don't know it it will answer your question.
Charlie

Evan
02-25-2005, 08:53 PM
Have a look here about 2/3 down the page.

http://www.americanmachinetools.com/how_to_use_a_lathe.htm

Bruce Griffing
02-25-2005, 10:40 PM
I looked at Evan's reference. Pretty good, but the formula for the tip width is wrong. It implies a wider and wider tip with increasing number of threads per inch. This must be a reciprocal relationship, so the factor P should be in the denominator. If it were me, I'd look it up in Handbook.

JRouche
02-25-2005, 11:45 PM
Hello, 10 tpi acme has a root width of .03187". JRouche

Sorry, forgot to give reference and formula.

Width of the tool point:
.3707 divided by the number of threads per inch then subtract .0052" for clearance.

The reference is actually three books:

1). Screwcutting in the lathe . Workshop prctices series #3. Martin Cleeve

2). The Amateur's lathe. L.H. Sparey

3). Advanced machine work. Robert H. Smith

Now, where the heck is my Machinery's hand book? it must (better be) be down stairs.

[This message has been edited by JRouche (edited 02-25-2005).]

happy02
02-26-2005, 02:07 AM
You need a 29* thread tool gauge. The depth of thread is half the pitch +.10. Grind your tool to fit this tip width and to 29* and you can cut 10 thds. acme.

[This message has been edited by happy02 (edited 02-26-2005).]

Charlie Rose
02-26-2005, 03:43 AM
Tap drill hole for this thread is 3/8- pitch or .275" your tool must be smaller than that to clear coming out . You'll have better luck with a tap.

JRouche
02-26-2005, 01:17 PM
Almost sounds like the thread for my south bend steady rest fingers? Is that what you are doing.

I was gonna make a spare set. I got the brass and was gonna make the tap but got busy. Way too many projects on the burner, most are going up in flames. JRouche

Jim Bass
02-26-2005, 11:06 PM
Ken,
When you cut your ACME thread turn your compound so that it is parallel to the leadscrew you are cutting. After you cut the thread to the proper depth and your nut still will not spin on, then crank your compound .001" towards the headstock and make another pass on the leadscrew (sometimes two or three). The reason for this is when you grind the tool bit to cut the ACME thread it has to be ground at a perfect 29deg. Hard to do when you hand grind a tool.

Yours, Jim