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02-17-2013, 05:21 PM #1
Having a problem with a Tension/compression tap holder.
We have a bar job that we have been running for years that require tapping M10x1.5 (OSG 3 flt spiral taps) in 12L14 1." deep in a 1.3" deep 9mm hole with a .060" chamfer. Have been using the same Mari T/C ER 25 tap holder for the last 2-3 years and now my son says he having trouble with it its either tapping to .5" deep or going to the bottom of the hole and breaking the tap.
I'm out of the country and trying to help him trouble shoot the problem via email so he can get the parts done. He's still learning but generally has no problems setting up and running repeat jobs.
Here is what I know so far; he says the holder looks fine but there is a small amount of movement or dead spot ( between T an C ) of about .050" which I don't think should be a problem. Called Mari Tech support and they recommended removing the front spring and ball bearings to convert it to a tension only holder.
Any other advise or suggestions I can pass on?
02-17-2013, 06:01 PM #2
My ER20 maritool holder like this seems to have less spring tension on the hole entry then my old Universal Engineering brand holder. On hard to start taps the tap will press in the hole and compress the spring until it engages and cuts. It could be that sometimes it engages without any compression and then another time it would run to the bottom of the spring travel before engaging. The best solution would be to watch it engage and maybe try a different holder or springs. I think that different springs can be purchased from mari. The time I had the most trouble was with a roll form tap that took a lot of force to start. Sometimes it would take off and engage and others I would feel like it was going to smash the tap before taking off. I think that there is no problem with stiffer springs altogether. It isn't like you are running an 0-80 tap.
02-17-2013, 06:25 PM #3
He hasn't torn the holder down yet but I'm betting it has a broken spring inside and may explain the dead spot. Told him to use the ER32 holder and get-r-done.
I had no idea that Mari's holders could be converted to a hard start configuration.
02-17-2013, 06:31 PM #4
I hate compression in a tap holder!
Certainly this is your issue. Whether it is a broken spring, or chipped tap, drill chips setting on the edge of the hole, or ??? either way - it is a tap starting repeatability issue.
Some holders you can crank a screw down in the shank end to limit the comp travel.
Others you may need to actually make a solid plug to take the place of the spring.
Compression is only required for RE-tapping a hole - so that the tap can align with the pre-existing thread.
If the return spring pulls it back to a hard start - you will git repeatable depths.
Make sure not to overfeed now.
I just went through this on one machine last week...
..could not get the threads to tighten up no-matter how I offset the holder (in X or Y on a lathe) and finally slowed the feedrate down a little more, and it tightened right up. I was programmed .8"/min less than nominal, but was still pushing the pitch on an older control.
Not had that trouble on newer machines.
Keep in mind that by slowing the feedrate to less than nominal will require less Z depth - unless you are dwelling to allow the self feed to run out to release point.
Think Snow Eh!
02-17-2013, 06:44 PM #5
I have Mari Tools tension/compression holder also. The reason your tapping to deep or bottoming the tap is the holder is stuck in extension. I've found that when tightening the taps you put dents in the ball hole and after a while the thing gets sticky from interference with the raised dent on the outer body and inner body. Only fix is to take it apart and stone the dents. I really need to make a spanner type wrench to hook into the ball race and hopefully it will help alleviate the problem.
02-17-2013, 06:51 PM #6
If you are only tapping 1/2" deep or bottoming out in a 1.3" deep hole, running the same program, its not a problem with the holder...
Its most likely spindle speed, Tach, encoder, stupid little magnet and hall effect sensor.
Stupid questions to ask, because you are on the phone, and can't see what's happening.
Is the kid screwing around with the over ride knobs?
Is it a straight shank holder in a collet? And he keeps programming it deeper and sometimes it holds, bottoms out and breaks and sometimes it slips, and taps shallow?
I guess if the TC holder is gummed up and not pulling back to neutral, and sticking out too far you could tap too deep. In that case take it apart and clean it. I've taken them
apart, its super simple.
Its something stupid. It almost always is, it just depends on how much money you throw at it before you figure it out.
Edit: I'm not inferring that your kid is an idiot, just that dealing with stuff over the phone is tough.