sharp taps for plastic

I've been playing with tapping plastics like HDPE and so forth and not
surpisingly discovered that sharp taps and drill bits and not taking small
cuts seems to help.
So the question is how does one source "sharp" taps in the 6-32 to 3/8"
sizes? Is there a certain brand or type that cuts plastic out of the box
better? Internet wisdom seems to show that looser taps like H5 are better
as well as they make up for the plastic shrinking back into shape.
Any other tips?
Reply to
Cydrome Leader
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Stone (or sand/Dremel) the flute grooves to sharpen them.
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I'm glad I bought mine before they became so valuable.
Reply to
Jim Wilkins
I have a 70-year-old box of slips, which I use when I can, but I still find a need for pieces of wet/dry wrapped around a nail or dowel. I haven't sharpened a tap for decades but that's how I used to sharpen them.
That's the same thing I do for many steps in building fishing rods. I usually cut a narrow strip and wrap it around in a spiral, using glue to hold it in place. It's handier than digging out slips that have different radii on opposite edges.
Reply to
Most mass-produced taps are for steel, and the tooth geometry isn't good for plastics. You can hand-stone a tap for brass (by establishing a circa-90-degree edge, and that's about right for plastic, too. This is a good use for an old carbon steel tap that hasn't got a good edge, because you're making a new edge anyhow.
The 'sharp' steel-cutting edge is more acute than you want, because steel doesn't stretch when being cut; plastic does (elastic snap-back is the unfortunate result).
Reply to
But then most don't know how to tap or cut threads with a die. I have seen so many just crank away. Then complain.
With plastic you do it under water. Edge pressure melts plastic. With water and working slow the tap / thread is cut without problem. Lube and cooling.
Reply to
Martin Eastburn

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