Double tapping and thread tolerance

Our shop does a lot of thread tapping in delrin round stock, including double lead and quad lead Acme threads. The conversation we have been having is concerning tapping twice and the Haas machines ability to repeat tap and hold the pitch tolerance of the thread. When tapped twice the threads are looser than when having tapped just tapped once. I say it is the nature of the delrin material and the Haas can rigid tap repeatedly. The engineers think it is from the double taping not repeating ...I don't have an answer or a way to verify it if I did.....So my question is, what is the repeatability of the Haas rigid tapping.... Thanks Andy

By "double tapping", are you talking about your multiple start threads? Or are you talking about re tapping an existing hole? If the former, I have no idea why one lead would effect another lead. If the latter, then you are taking a spring pass and the expectation would be the thread would be larger than before, as with any spring pass with any other tool.

I don't know specifically about lathes, but in our mill, we rigid tap down to 0-80 in 304, 6061, plastics, etc. at 6,000 RPM (it doesn't actually reach that), and we've done many, many thousands of holes. We've never had an issue from the machine being inaccurate.

Thanks Matt, I am talking about tapping an existing hole twice. We have tapped many thousands of holes as well in the mills and it has never been an issue, although we rarely tap the same hole twice. We were having issues with thread fit on a job and tapping twice seemed to help. It was suggested that we shouldn't be doing that because inaccuracies in the machine (ie;does it start in the exact same place) could change the pitch diameter. We are going to be doing this job in a lathe in the near future.

That's interesting. I run multi-cycle tappig with certain UN taps, but those are all single-lead threads and have the unified 60º thread shape. I've always heard that weird things happen with multi-lead taps but I don't have experience rigid tapping those in particular. I would think that the tapping cycle would be accurate enough, but perhaps the material is getting snagged when the tap re-enters, causing it to snag some extra material to make it a little more sloppy. It doesn't sound like there would be an easy fix for that, though, outside of using a custom-made undersize tap of something...

I have no problem at all in re-tapping a holes here either.

Check one thing though: go to "Parameters," "Common SW 1 (Parameters 57)" page and you will see that the 5th line down is "Rigid Tap" and of course that is and should be a 1, but go down to line 7 and make sure it is also set to 1. That line is telling the control to "Repeat Rigid Tap" and this means it will synchronize the spindle every time it taps. Without that being at "1", the machine will not sync, but just start from wherever the spindle is. Just saves half a second or so when off, so just leave it on and set at one.

Mike

If you are referring to 57: 7 Exact stop mode chg, It is set to 1
Thanks Andy

No, not exact stop, "Rept Rig Tap" If it is not where I said it was in your software version, then find it in your parameters. It must be set to 1 also, or you can't re-tap a hole.

Mike

Quote:

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Originally Posted by obiwon

If you are referring to 57: 7 Exact stop mode chg, It is set to 1
Thanks Andy

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You are in "Setting Graphics" not parameters. Go to Parameters and check the page I have given you a pic of.

Mike

You still alive?

I was on the right page and there is no line for REPEAT RIGID TAP. I checked all our machines and only one of them had that, the 2001 MiniMill. Must on older machines? Our newest is a 2015 VF2.

Sorry I could not help.

Mike

Thanks Mike, we did find it ..setting 133 on the newer machines. The older Minimill has it in paramerters were you said it was.

Did it help on the threads?