Z Axis Plunging too Deep into part < part zero, tool offsets, turns ratio >

[milling]

Tom, I don't think im losing steps- not sure why its doing what its doing. Typically the feedrate for the centerdril was 5in/min

i believe the rapid feed is set at 50 i believe

[swissi]

Tom, I don't think im losing steps- not sure why its doing what its doing. Typically the feedrate for the centerdril was 5in/min

i believe the rapid feed is set at 50 i believe

As Marty said, something does not look right with your revs/inch and counts/rev setup.

You can easily check if the 4000 steps/rev of your drivers are correct by doing the following:

• Set the Revs/Inch for all axes to 1

• Make a marker on all 3 motor couplers with a piece of tape or a Sharpie

• Open the MDI and enter the following command: G91 X1 F5

• The motor coupler should make exactly a full 360 degree turn and stop at the same position it started. If this is not the case, then the 4000 counts/rev settings of your driver are incorrect

• Do above steps for the Y and Z axes as well

This will give you confirmation that the 4000 counts/rev are correct as I have the suspicions that something is not right with your settings.

-swissi

[cncsnw]

If the problem comes and goes without your having changed the part program, or the tool offsets, or the part zero location, then it is probably not related to your part programming or job setup procedures. And no, you don't have to use a new and different WCS for every job you run.

If the problem comes and goes without program or setup changes, then it is an intermittent electrical or mechanical failure. The reason people are questioning your screw pitch settings is because if you have a machine with unreliable motor commands -- where the stepper drives think they are receiving more or fewer steps than the control sent out -- then when you try to calibrate revs/inch, you will get inconsistent results that do not match up with the lead of your ballscrews.

It is easy to measure the lead of the ballscrews directly. Just lay a ruler along it and count the inches or millimeters in 10 or 12 threads; or count the threads in four or five inches, or 100 or 120 mm. If you do not know for certain whether your screws are metric or imperial, it is helpful to have both types of ruler available.

You should do as swissi recommends, to verify your counts/rev settings. Watch closely, to see that it makes only one turn. If counts/rev were actually 2000, then with your setting of 4000 it would still end up back on the one-turn mark, but it would take two turns to get there.

In the failure example from this morning, after you took the pictures with the cutter 0.9" above the part, and the DRO reading 1.2", did you cancel the job and press Tool Check to return to home? When you did, did it return to the exact Z height it had homed to? Or did it come up short by 0.3" or more?

[milling]

Thanks all for the advice. Ill try to do all of the checks and get back.

cncsnw: i did cancel the job and pressed tool check and yes it went back to the microswitch as normal and did not fall short.

[milling]

So I found out that I did not have a dip switch set correctly on the Y axis driver- it was set at 5000. After setting to 4000 I recalibrated the Y axis and got something that more resembles the X axis as it should seeing that the pitch is the same- so thanks for that.

I re-ran a program for the fun of it but still got something where the Z axis was off by about .300" or so. Thought the Y axis may have been related to the issue but it does not appear to be.

I did check to make sure that the Z axis driver was set at 4000 - and it was. So that part is ok. I am still confused on this becasue when I command the z axis to move an inch it does, two inch, three inch and so on. I can try to get rid of the parameter 3 and put it back the way it was and set up the tools with a z-ref and try that. I saw cncKeith recommend the parameter 3 be changed to 2 on one of his videos and it does make sense on a bed mill. Ill try it and see what happens- or if you think its a waste of time let me know. I think I set up the tools like 5 times and nothing seems to fix whats happening.

Thanks

[martyscncgarage]

So I found out that I did not have a dip switch set correctly on the Y axis driver- it was set at 5000. After setting to 4000 I recalibrated the Y axis and got something that more resembles the X axis as it should seeing that the pitch is the same- so thanks for that.

I re-ran a program for the fun of it but still got something where the Z axis was off by about .300" or so. Thought the Y axis may have been related to the issue but it does not appear to be.

I did check to make sure that the Z axis driver was set at 4000 - and it was. So that part is ok. I am still confused on this becasue when I command the z axis to move an inch it does, two inch, three inch and so on. I can try to get rid of the parameter 3 and put it back the way it was and set up the tools with a z-ref and try that. I saw cncKeith recommend the parameter 3 be changed to 2 on one of his videos and it does make sense on a bed mill. Ill try it and see what happens- or if you think its a waste of time let me know. I think I set up the tools like 5 times and nothing seems to fix whats happening.

Thanks

Take the time to finish setting up your machine....THEN worry about parts....
Cart before the horse thing.

Marty

[milling]

Marty, i set all the axis and am pretty confident with them. I changed parameter 3 back to 0 and used a reference tool. However, something is still wrong I think with the way z-ref is choosing the number. Im pretty sure it should insert the machine # and not the WCS #. Any ideas on this? If I recall when the z ref was the actual machine #- the part machined correctly?

Pictures attached

[milling]

photos

[milling]

Please let me know if Im doing this right. tHOUGHT I was

I use a 123 block on the x table surface- touch my ref tool to the 123 block and hit F1 and set the z-ref. I then carry on with the other tools doing the same thing- touching off to the 123 block on the x table surface and then hit F2 to manual measure.

Still not sure why ots using the WCS- this does not make sense. The WCS is for the actual part that is being machined isin't it? I would think tool heights should be from a ref surface- let me know

Thanks

[milling]

when im ready to machine a part, I bring whatever tool is in the spindle (as long as its in the library) to the work surface (surface of the material to be machined) I then go onto part setup- leave x as 0 and hit F10, I do the same for y, for z I also leave that at 0 and enter the tool being used to touch off the top of the material and hit F10