Rigid tapping skips holes randomly

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rk9268vc
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Rigid tapping skips holes randomly

Post by rk9268vc »

first try at rigid tapping

it skipped two holes and i dont know why. looks like it started and then immediately stopped the cycle
no errors showing in the mdi/ code readout thing

here is a video of it doing it
report and gcode attached


spindle motor is a 2.1hp 1600w servo, tapping at 640rpm
tap holder is a tension/compression holder from tormach
tap is 1/4-20 into aluminum
1001 tap test 14 20 op1.nc
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suntravel
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Re: Rigid tapping skips holes randomly

Post by suntravel »

From Mill Manual:

Note: If rigid tapping is enabled, a Q may be used to set the thread lead
or pitch. However, because Q is not modal in the case of Rigid Tapping, you must specify Q on every line
at which Rigid Tapping is to occur.


; Using Tool 22 Rigid Tap 4-40
G84 X1.862 Y1.627 Q0.025 Z-0.19 R0.1 ; tap rst hole
G84 X2.862 Y1.627 Q0.025 Z-0.19 R0.1 ; tap second hole, must use Q
G84 X4.262 Y1.627 Q0.025 Z-0.19 R0.1 ; tap third hole, must use Q
G80 ; cancel canned cycle

Your G-code is not right for rigid tapping, but you have set P#36 for rigid tapping

Uwe
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Re: Rigid tapping skips holes randomly

Post by cnckeith »

and the easy way to create proper rigid tap g code is to use Centroid's Intercon conversational programming. even if you want to use a cad cam system you can at least use Intercon to create "good" g code and compare it to the g code the cad cam system is outputting.
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suntravel
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Re: Rigid tapping skips holes randomly

Post by suntravel »

Also get rid of the encoder problems, this is the key element for rigid tapping ;-)

Uwe
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Re: Rigid tapping skips holes randomly

Post by Dave_C »

Even after you get the G-code corrected you may still see an issue, I know I did at first until I got all the settings for Rigid Taping set right.

In my case I was skipping holes just like you are showing, and I could not figure out why. The problem turned out to be that the minimum tapping speed was too high. I set the minimum down to 360 from 640 and it worked fine from then on.

Drive accel and decell all comes into play when doing rigid taping as does clearance above the part, dwell time and all related parameters.

For example: If are coming up out of a hole the spindle has to reverse and then acell to the set taping speed. If it does not hit that speed as it starts to move in, it will make a short approach toward the hole and then retract due to spindle speed. Or if your encoder sends it and incorrect speed it might withdraw and go on to the next hole.

Try setting you minimum taping speed down and do an air run without changing the G-code and see if it still skips holes.

I did a video after the fix here:


Dave C.
Grizzly G0678 Mill ,CNC conversion with Acorn. G4004G Lathe, Mach 3 conversion to Acorn.
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Re: Rigid tapping skips holes randomly

Post by cnckeith »

nice, glad you got things working, thanks for posting the video.

i run in air first..then tap in wax..if you have any issues at all the wax thread will be ruined. Its a great test...then go metal...
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Re: Rigid tapping skips holes randomly

Post by Dave_C »

cnckeith wrote: Fri Jul 01, 2022 5:26 pm nice, glad you got things working, thanks for posting the video.

i run in air first..then tap in wax..if you have any issues at all the wax thread will be ruined. Its a great test...then go metal...
My video above is not by the OP, I'm just sharing that I had a similar issue and sharing how I solved my issue. I'm not sure if his issue is the same but wanted to share just in case it helped.

Dave C.
Grizzly G0678 Mill ,CNC conversion with Acorn. G4004G Lathe, Mach 3 conversion to Acorn.
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Re: Rigid tapping skips holes randomly

Post by rk9268vc »

update:

here is a video doing a bunch of holes in a 8x10" x 1/2" cast plate


got it to stop skipping holes by reducing the minimum rpm to 300 as Dave suggested. thanks

still rolls over the top thread of the hole though. This is caused by the encoder problems, acorn thinks the spindle is spinning ~120 rpm faster than it actually is. I had to set the tapping hole depth .375 inches deeper than it actually is for the tap to go all the way through the .500 deep plate

still havent done whatever uwe said with the custom code and still dont know what Q does.
I use fusion for cam and dont want to learn intercon or manually edit code. If someone has a post processor for fusion that adds whatever that Q does, i would appreciate it (assuming that i need it)
just tap 375 deep.nc
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rk9268vc
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Re: Rigid tapping skips holes randomly

Post by rk9268vc »

i am experimenting with altering the tpi in fusion to fix the speed missmatch

basically, as seen in the video, with stock settings the spindle isnt turning as much as acorn thinks it is, so the tap holder is in compression
When the tap is extracted, it spins on the top of the thread 4 ish times as the spring relaxes, rounding over the top thread

to fix this i have been trying altering tpi in fusion. Basically for a 5/16-18 tap, i tell fusion it is 24tpi. This causes the mill to turn more times putting the holder in tension. Now when the tap is removed it springs back up instead of spinning on top of the thread.
Now i just need to find a balance so it doesnt pull the last thread off when it goes up. some more experimenting needed
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Re: Rigid tapping skips holes randomly

Post by cnckeith »

I would calibrate the spindle and then create the same program using intercon, you can create the intercon file in about 2 minutes even without ever using it before. super easy.
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
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