[js530]

I'm trying to use 1" UHMW round with a 27/64 hole and a homemade tap made from a piece of acme screw, but the nut is just too tight. I can barly spin the screw by hand. I've tried heating the nut hot enough to melt the plastic, but that doesn't work. Using silicone doesn't work also. Any ideas?

[trubleshtr]

can you post a pic of the homemade tap? a picture is worth a thousand words.
I tend to tapper the tap and then grid 2-4 parrallel grooves up the tap, trying to make the edges sharpe. shape the end to handle a wrench, and pound tapping fluid to the screw as turning it.

[js530]

I have the nut tapped, it's just the nut is very difficult to rotate, even when dripping with silicone.

As far as the homemade tap goes, it's 1/2 10 tpi acme with a 3/4" taper at the end. A picture would be fairly difficult, for now I'll try sharpening the edges and tapping it again.

[ger21]

With the tap I made, I tapered about 1-1/2", and put 4 grooves in it. The more times I run it through, the looser it gets. This is with Delrin. I also noticed that the heat from just holding it in my hand for a few minutes will cause it to expand and get looser. If you'rs is really tight, the tap is probably not removing enough material.

[lurch]

Have you tried freezing the nut and then retapping????

[js530]

Have you tried freezing the nut and then retapping????

Not yet...I will tomorrow.

[jeffs555]

I would tend to think the edges of the grooves you put in the tap are not sharp enough. If the cutting edges are rounded, it will compress the plastic instead of cutting it, and make it a tight fit. I cut three grooves in my homemade tap with a cutoff wheel in a grinder, and they feel very sharp to the touch. The delrin nuts I tapped spin easily on my 1/2" acme rods, with no lubrication.

[Konrad]

Freezing is a good idea...if it doesn't work, you could cut the nut, [saw cut] then squeeze together a bit before tapping, if the wall if heavy enough, you could perhaps leave it, or welded, or put a collar around, where you could adjusted it with a set screw as it wears.
Konrad

[jcc3inc]

If your "tap" is sharp enough, you still don't have any clearance since the plastic likely has some give, and the resultant tapped hole is a bit undersized. You can either split the finished nut as was mentioned before, or maybe you could saw cut your "tap" in two directions at 90 degrees to each other, then expand the "tap" by some means so that the tap is now oversized, then redo the hole.

Jack C.