trying to make ACME tap, no luck.

[phantomcow2]

I am trying to tap delrin nuts for a 5/8-8 2 start ACMe leadscrew that i've got sitting around, with limit success.
I cut off an end of the screw, turned a taper, and tried to go at it. It is very difficult to turn, and does not seem to be forming any threads at all. Can somebody guide me in the right direction?

[HuFlungDung]

Did you cut some lengthwise gashes in it (called flutes) to create cutting edges? When you have done that, then it would be a good idea to sand some clearance on the outside of the taper.

Likely an upright stationary belt or disk sander would work well for this, so you can see what you are doing. Once you have created the flutes, then you can define the cutting edge of a right hand tap to be the edge that leads the cut as you wind the tap into the hole. From the front edge to the back edge, that is where you grind some clearance on the taper outside diameter. Working carefully on the sander, you can sand clearance starting at the back edge of the tooth and rotating the part slowly and carefully, stopping just short of the taper profile that you turned on the lathe. You want the original taper profile to be untouched, and clearance ground all the way back from that.

Try to do this evenly to all the flutes of the tap. I'd suggest 3 or 4 flutes in your tap unless you have a machine setup, or a pilot on the end of the tap to guide the tap straight into the hole.

If you have a standard plug style thread tap of any sort to study, you can see how the clearance is ground on a factory edge, and try to copy it.

[phantomcow2]

It sounds like there is a lot more to making this tap than i was expecting...
But it seems to be that many people tap their own ACME nuts from delrin, so i think it sounds possible.
I will mill four 1/8" flutes in the soon to be tap tommorow.

I've got plenty of plug taps i can study, but none are ACME. What is it that makes acme taps so expensive?

[mikie]

probaly the fact that there a4re not many produced, plus making square thread is a pain, unless it is groung. I just retrofitted my x-axis with a 3/4" acme and i made a tap from spare thread. I tapered the end and machined relief grooves like hiflung mentioned.

I have yet to test it out, but i suspect it will work fine. Well, it looks like a tap to me, so i figure it will work.

/Mikie

[phantomcow2]

The thing that i odnt get is how it cuts.
With a 60 degree you can clearly see how it cuts. But with this ACME it is very smooth

[trubleshtr]

Like hung mentioned. You need to cut grooves across the threads in your tap to create a cutting edge, and a place for the chips to go as it cuts into the delrin. Also try some tap fluid as you go, and work the threads back and forth, don't try to cut the whole length of the hole in one forward motion, back up every 1/2 turn or so and clear the chip being created.

[phantomcow2]

Alright so the edges of the flutes are actually doing the cutting? ANd these grooves allow chips to go in.
I use "Safe Tap" fluid whenever i tap metals, did not think it was necessary for plastic. But i guess it wont hurt anything.
Will a few passes with a 1/8" end mill be sufficient for grooves?

[2muchstuff]

From past experiences don't use oil when tapping plastic. The oil will allow the tap to push the plastic out of the way slightly leaving a slightly smaller tapped hole causing a tight fit. Plastic is self lubricating enough.

[phantomcow2]

A milled 4 flutes, making passes with a 3/16 end mill. Turned a taper, and what a difference this makes! I cut the delrin MUCH easier, and the nut is the smoothest non ballnut i have felt, it really glides on that thing.

[2muchstuff]

Glad to hear that it worked out for you.