Machining internal acme threads?

[LazyMan]

I would like to machine an internal ACME 1/2-10 5 start thread in acetal. Anyone know if I can do this on the a Tormach? I have not had any luck finding a tap.

[jeffrey001]

If you have a rotary table, it could be possible, I think, I did not see your setup.

You would index the rotary table by 72 degrees for each pass

How big is the hole.


Jeff

[n1k86]

You'll probably have to either tap it or single point it on a lathe. If it were the same pitch but a much wider diameter it would be possible but the lead angle that the cutter will have to follow (cut tangent to) is too steep. For steep lead angle threads, the cutter needs to follow the lead angle, (tilting your rotary table would accomplish this) and the deeper you cut the closer the shank comes to the I.D. You would need a very skinny tool shank (almost certainly a custom tool), and be very limited in depth if you tried to threadmill this.


I would buy some threaded rod from the source below and then file/grind some cutting edges into it to make a tap.

1/2 X .200 Right Hand Hi-Lead Lead Screws & Nuts for Power Transmission - Roton Products, Inc.


Another source for nuts of this size is dumpsterCNC - anti-backlash solutions for home and industrial linear motion . He might be willing to thread some parts for you for an extra fee.

[Don Clement]

Although not ACME I made my own double start 5/16-11 tap for tapping Turcite A http://i72.photobucket.com/albums/i1...leStartTap.jpg

Don

[LazyMan]

I was originally planning on using those dumpsercnc nuts but, I wanted to experiment with a spring loaded dual nut design and I may need to make a small batch of these. I know dumpster cnc threads his ABL nuts on a DIY slant bed lathe. Looks like I am going to need a tap.

Although not ACME I made my own double start 5/16-11 tap for tapping Turcite A http://i72.photobucket.com/albums/i1...leStartTap.jpg

That looks very nice. How did you go about making it? Is it heat treated?

[Don Clement]

Don wrote:"Although not ACME I made my own double start 5/16-11 tap for tapping Turcite http://i72.photobucket.com/albums/i1...leStartTap.jpg "

That looks very nice. How did you go about making it? Is it heat treated?

Made it on my manual 12x36 lathe using a Vardex 3ER20UN insert. I selected double start 11tpi with my 8tpi lead screw lathe because then I could close the half-nut on odd/even numbers of the threading dial for the separate thread starts. Here is a picture of my threading setup: http://i72.photobucket.com/albums/i1...Threading3.jpg Note the follow rest for the 5/16" diameter rod.

I suppose an ACME thread form could have been made on a similar double start thread by using a fine pitch insert such as a Vardex 3ER16ACME on threading a double start 8tpi ACME leadscrew.

No I didn’t heat treat the tap since it was used to make soft Turcite-X & Turcite-A antibacklash nuts such as the ones shown here: http://i72.photobucket.com/albums/i1...f/TurciteX.jpg Since the tap was machined from O-1 drill rod it could have been heat treated.

Don