Homemade ACME tap.

[martyxxx]

I needed to make some delrin acme nuts so I decided to fabricate my own tap from piece of threaded rod because commercialy available ones cost a bit to much for me. I made a little research on the subject by google and find several web pages and made a tap which didn't work very well. So I went to google again and this time I looked at commercialy made ones. On the following pictures is result of my second atempt on acme tap and this time it was success . Tap has cylindrical nose, about 8mm long instead of sharp one and it really helps to cut thread straight. As seen on one of the pictures grooves should be milled past centre to get sharp angle on the cutting edge. It can go even more past centre as I discovered lately because amount of removed material during cutting acme thread is quite big and I need to do several passes. Any comments are welcome.

Martin

[Geof]

That is a very nice job.

I have two small hints:

If you are doing many nuts try to get white Delrin. We make thousands of parts out of Delrin and have found that black Delrin is much more abrasive than white Delrin. High Speed Steel tools wear very quickly with black Delrin.

Try freezing the Delrin to get slightly more clearance on the thread. Cutting the thread using the tap made from the threaded rod means the thread is exactly the same size as the rod, or even smaller is the tap is not sharp and the Delrin deforms. Freezing the Delrin shrinks it and then after the thread is cut when it warms up and expands there is more clearance.

[Guldberg]

You can make the tap longer to reduce the force needed to tap. Ive made a similar tap for a 16mmx4mm thread, it was almost 150mm long, but i could use a cordless drill to run it back and forth. As you said, it removes quite a bit of material, so a lot of passes is needed

[martyxxx]

You are right, longer tap means lower force but it will take a much longer time for me to make it (the tap I mean). This one took me about 2+ hours to do. I just started to learn how to operate lathe and mill and this is my first job in steel. I plan to make only several nuts, so it's OK. The tap itself is very sharp (I dressed the cutting edge by really fine abrasive stick) and it cuts to plastic very well. Freezing delrin before tapping is a good idea, maybe it will not be needed in this case since nut rotate on the threaded rod stiffly but it seems that motor can handle it.

[Ch_Irawan]

I use a Ball Mill (not End Mill) to cut the cutting edge of my home made acme tap, the shape will be very similar to the commercial one.

-ichan

[Rance]

More info. for you Martin:

www.cnczone.com/forums/showthread.php?t=28265
www.cnczone.com/forums/showthread.php?p=62299 (post #88'ish)

[grahamshere]

Hey guys, I was wondering if a tap for a hi lead screw can be made the same way? for something like a 8 tpi 4 start . I'm not sure how much a tap for that would cost but I'm sure it,ll be expensive so I'd rather make my own. Graham

[martyxxx]

It could be done but I think since it's 4 start it should be four times longer (tappered part of it) than single start one.

[grahamshere]

Thanks Marty for the help. so how should single start tap be? Also how did you mill the tap. can it be done with a bench grinder? Graham