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?

"Cydrome Leader" wrote in message
...
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?

Stone (or sand/Dremel) the flute grooves to sharpen them.

https://www.amazon.com/Round-Edge-Sl.../dp/B0006NFEQG
I'm glad I bought mine before they became so valuable.

On Saturday, February 23, 2019 at 8:14:58 PM UTC-5, Jim Wilkins wrote:
"Cydrome Leader" wrote in message
...
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?

Stone (or sand/Dremel) the flute grooves to sharpen them.

https://www.amazon.com/Round-Edge-Sl.../dp/B0006NFEQG
I'm glad I bought mine before they became so valuable.

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.

--
Ed Huntress

On Saturday, February 23, 2019 at 4:08:43 PM UTC-8, Cydrome Leader wrote:
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?

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).

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.

Martin

On 2/24/2019 1:49 AM, whit3rd wrote:
On Saturday, February 23, 2019 at 4:08:43 PM UTC-8, Cydrome Leader wrote:
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?

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).