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Threadmilling problem


So not a Guru
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We have some 321 stainless parts that require 4 each 4-40 holes tapped 0.560" deep, they are thru holes. We purchased a couple of Harvey 2 flute single-point threadmills they have a 5/8" reach, .080" cutter dia 0.04" neck. The recommended speeds & feeds are 3 equal passes at 9550RPM 0.60IPM. We drilled them with 2.3mm holes.

We had to rerun the toolpath 13X, increasing the radial offset 0.0012" every time, before the thread gage would fit. That came to a total comp of 0.013"! It took over 4 hours to get the hole threaded.

When we ran the next hole, with the 0.013" of comp active, no surprise, it broke the tool. Harvey's tech representative doesn't appear to understand that the 0.0012" passes were necessary due to their recommendations perhaps being incorrect. He says we need to run with their recommendations...that we just told him we attempted.

Okay, I'm done ranting on.

Does anyone have any recommendations for us to be able to make this work?

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The neck on that tool will be tiny...I am actually surprised with that much deflection that it's not breaking

I would find a multi-tooth threadmill instead...also make sure your major thread dia is programmed properly, 4-40 thread date says 0.1189 / 0.1120 I would make sure I programmed at .122

4 to 5 passes including spring "should be" sufficient 

 

 

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You tried tapping it? I would try to roll form it and see if that works. If you chose to roll form it then make sure you ream to within .0005" of the size they call out and go .0005 bigger verses smaller. Use a good cutting oil not coolant if you attempt to roll form or tap it. Moly-Lube might work, but still a huge fan of tapping oil in SS.

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1 minute ago, crazy^millman said:

You tried tapping it? I would try to roll form it and see if that works. If you chose to roll form it then make sure you ream to within .0005" of the size they call out and go .0005 bigger verses smaller. Use a good cutting oil not coolant if you attempt to roll form or tap it. Moly-Lube might work, but still a huge fan of tapping oil in SS.

The spec doesn't allow for form tapping.😡

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It is a class 3 or class 2 thread. A class 2 thread allows for a bigger Min diameter. Try making the min diameter within .0002" of the max and try a standard tap. If your machine can peck tap then peck tap it using .01 to .02 pecks. I would start at 1000 rpms and go from there. Don't use a floating holder in peck tapping. All the best, but I would get away from Threadmill that deep. Maybe threadmill 1X and then chase by hand with a tap I have done that before with good success. Just have to have a good feel and steady hand on such a small tap. I have hand tapped 2-56 in Ti using this method and would only break a tap about every 40-50 holes, but that was 20 years ago. I don't have that feel anymore like I use to.

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40 minutes ago, crazy^millman said:

Moly-Lube

I have had good results with a mixture of Moly Dee and Copper Ease even with cut taps...

The tools tend to go off pretty quick so you would have to be pretty conservative changing tools.

I think I would agree with Ron on this one.

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6 minutes ago, crazy^millman said:

It is a class 3 or class 2 thread. A class 2 thread allows for a bigger Min diameter. Try making the min diameter within .0002" of the max and try a standard tap. If your machine can peck tap then peck tap it using .01 to .02 pecks. I would start at 1000 rpms and go from there. Don't use a floating holder in peck tapping. All the best, but I would get away from Threadmill that deep. Maybe threadmill 1X and then chase by hand with a tap I have done that before with good success. Just have to have a good feel and steady hand on such a small tap. I have hand tapped 2-56 in Ti using this method and would only break a tap about every 40-50 holes, but that was 20 years ago. I don't have that feel anymore like I use to.

It's actually a UNJC thread, so that requires a larger size hole. I had already decided to run the threadmill, then chase the holes with a tap. I can't see this working any other way at this point.

Dude, nobody asked me, or I would have no bid this as soon as I saw the depth & material. I'm just the guy who's supposed to make it work. 😉

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5 hours ago, So not a Guru said:

We have some 321 stainless parts that require 4 each 4-40 holes tapped 0.560" deep, they are thru holes. We purchased a couple of Harvey 2 flute single-point threadmills they have a 5/8" reach, .080" cutter dia 0.04" neck. The recommended speeds & feeds are 3 equal passes at 9550RPM 0.60IPM. We drilled them with 2.3mm holes.

We had to rerun the toolpath 13X, increasing the radial offset 0.0012" every time, before the thread gage would fit. That came to a total comp of 0.013"! It took over 4 hours to get the hole threaded.

When we ran the next hole, with the 0.013" of comp active, no surprise, it broke the tool. Harvey's tech representative doesn't appear to understand that the 0.0012" passes were necessary due to their recommendations perhaps being incorrect. He says we need to run with their recommendations...that we just told him we attempted.

Okay, I'm done ranting on.

Does anyone have any recommendations for us to be able to make this work?

We’ve had great luck with these in Ti. Buy 2, jig grind the neck on one, run the standard as deep as it will go...finish with the modified one.  Hope that’s of some use, good luck. 

Scientific Cutting Tools40 to 64 TPI, Internal/External Single Profile Thread Mill

#4" Noml Diam, 0.08" Cut Diam, 3/16" Shank Diam, 3 Flute, 0.045" Neck Diam, 0.3" Neck Length, 2" OAL, Bright Finish

 

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Carmex mini style. they have 3 threads on them all day every day. I never use taps anymore. They make a series specifically for hard materials. I still program it as a single style so that I get the complete helix.... They even have 3 in 1 threadmills no hole required although I would not recommend it for your application. The key is multipass on holes like this.. Hard maerial like that I would give it 3 passes with the last one being almost a spring pass.  Also Harvey makes good tools but their techs are useless IMHO....

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1 hour ago, zachlancy said:

I would try reducing spindle speed & feed until you get the harmonics out of the cut. I used to thread mill a lot of 6-32's in 316ss and the mfg speeds were unusable. I'd always bring the SFM way down until it was a nice sounding cut. Probably will require 3-4 stepovers.

Yes, I cut the feed in half and got a lot closer to a usable thread. Still having to chase it with a tap afterward, but it's working.

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58 minutes ago, So not a Guru said:

Yes, I cut the feed in half and got a lot closer to a usable thread. Still having to chase it with a tap afterward, but it's working.

If you cut the feed more, maybe you wouldn't have to chase it at all?

It sounds like a classic case of tool deflection.

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