Thread Milling 1/4-18npt

[Tenextoolco]

Hi All,

I'm threadmilling my first 1/4-18npt and would like some help on the programming.The theadmill is a Morse carbide threadmill. I will be drilling the hole with a 7/16 diameter hsco drill and chamfer the hole with the proper size chamfer. The material is 303 ss. I would like to threadmill the hole without using a taper reamer. Any help on the program and the feed and speeds would be great.
Thanks,

Jim

[Konrad]

Have never done it...wouldn't you think 1/4 is a little small?..I always just drill and tap, 303 is not that bad.

Konrad

[keebler303]

Its 1/4 NPT, so its more like 1/2" in diameter. I have never done it so the feeds and speeds I have no idea.

For the code, you need to rapid down into the hole, then do a helix which gets bigger as it goes up, following the taper. The helix should have a pitch of 1/18". Not sure exactly what your threadmill looks like but something like that should work.

Also consider the fact that you may be able to get a tapered drill bit and get the tapered hole in one operation.

Matt

[kz1670]

I just finished a job that is exactly what you are doing (may have done by now). I used a tapered cutter to go around the hole and set up the angle.
Then used an NPT thread mill. Went down .250", threaded down to .550" in a normal thread milling manner at 700 RPM. I know some guys who didnt bother with putting in the taper first in aluminum. I was doing 30 holes in stainless. Better safe than sorry.

[extanker59]

Did this kind of job a few years ago. Don't think I tapered the hole first, even with 303 ss. We had an NPT indexable threadmill from Kennametal. I seem to recall going to depth first and helixing up. I'm pretty sure they recommended that. Not bad at all.

I think? Seem to recall? Pretty sure? LOL. Older than I was and it was a few years ago.

[Fred the thread]

Don't forget that when thread milling a taper thread, that the arc radius increases as you helically interpolate your way out of the hole, so just 'helixing up' won't leave the cutter at the correct place after 1 orbit, but will leave a 'snail-cam' shape.
It is like climbing a spiral staircase inside a cone, every step up, the wall moves further away from the centre!

If you need more help with the part-programming side, get back to me.
Fred the thread