Lathe G code program debug help needed

[adrewfis]

I agree with you Marty. Just purchased the short TEMCo limit switches. I had some of the roller type switches but they weren't as short as the ones you recommended.

Ok, so when I pressed cycle start this evening, both motors went to their respective limit switches in the negative direction and settled right in front of them. I checked the Machine coordinates and both were at 0.0000. Next, I jogged both motors as far to the negative side as I could and they read: X = -5.0000 and Z = -15.0000.

I ended up switching all the feedrates to F/M instead of F/R and ran the sample part. It did the facing operation and the profile just fine this time but at the end it crashed through both limit switches at max speed.

[cncsnw]

And when it got to the switches, what were the DRO positions, in Machine Coordinates (Alt-D)?

If you search your CNC program file for "G99", you will see that it is still trying to do the Profile finish pass, plus a couple miscellaneous moves, in feed-per-revolution mode.

[adrewfis]

See attached for DRO position at home. The pic with X = +7.1800 and Z = +4.1476 is when I homed both axis at the beginning. They both said 0.0000 in machine coordinates. The pic with X = +4.4753 and Z = +1.5980 are the DRO positions right before crashing through the limit switches. The pic that shows X = -1.3524 and Z =-2.5496 are the Machine coordinates prior to crashing.

[adrewfis]

So after making several adjustments, I'm still back at square one. I had a near catastrophe trying to turn down some hex stock on Sunday night with the cutter taking off way too much in one pass and program said I was exceeding the travel limits even though it shouldn't have. I ended up tightening the allen screws on the pulleys and ball screw coupler and re-calculating the axis configuration for both motors to the point where the MP4 device will jog both axis the correct distances (6" for Z and 4" for X). HOWEVER, when trying to do the same with the MDI g-code commands, it's nowhere close (like inches off). I'm not sure where the error is occuring but this seems like it might be an error within the actual program. The report is attached. Would appreciate it someone could steer me in the right direction.

[tblough]

Post a copy of the cnc file you are trying to run. My guess is you are exceeding the acceleration capacity of your drives and you are loosing steps. With thousands of Acorn users, I sincerely doubt you've discovered a "Serious Issue with CNC12 V4.5" just getting your machine setup.

[tblough]

...re-calculating the axis configuration for both motors to the point where the MP4 device will jog both axis the correct distances (6" for Z and 4" for X)...

Your revs per inch are all set to 5.000 and your encoder counts per rev are 1600. Can you describe the "re-calculations" you did? The 5.000 implies that your screws are exactly 0.2 pitch and your encoder counts are very low. By any chance are your encoders 1600 LINES per inch? If so your rncoder counts should be 1600 * 4 = 6400.

[martyscncgarage]

EDITED
I am with Tom. It looks like you don't have the control setup correctly for the machine.
You have Clearpath SDSK motors. Usually the standard option is 800cpr, OR the enhance version is 6400. WHICH motors do you have?
What pitch ballscrews do you have?
Direct Driving the screws from the motor?
You do not use the MPG for fine tuning DRO's Use at least a good dial indicator

You must have the proper Steps/Revolution value in Axis Configuration as well as the Overall Turns Ratio first. Then fine tune DRO's
I have attached the COARSE DRO Adjustment and the FINE DRO adjustment out of the Mill Operator's manual to give you an idea. It is a little more difficult to setup a lathe. If you have a good dial indicator, you can get pretty close so long as you set the indicator as close to parallel to the axis.
For example, you can gently put a dial indicator in the chuck and let its tip hit the tool post which should be perfectly perpendicular (square) to the Spindle centerline. You can then put an indicator in the tool post and a right angle plate set square to the Z axis and run the indicator tip into the right angle plate.

This video might help a little explain the setup process of one axis. Did you change out your limit switches to the short throw switches?

[martyscncgarage]

By the way, you can roughly see what your ballscrew pitch is by setting a pair of calipers at 1" and then holding them up to the ballscrew and counting how many Threads Per Inch you have....

[martyscncgarage]

You can also validate if you set the motor steps per revolution correctly by changing the Overall Turns Ratio to 1.
Set a part Zero for the axis being tested first.
From MDI command a 1" move, the motor shaft should turn exactly one revolution. (This is best done with the motor uncoupled from the machine)

Marty

[adrewfis]

I'm curious where you are seeing 5 revolutions per inch? I am on a lathe and only use the first 2 axis (Z & X respectively). See attached screenshots showing the Axis Configuration page where it seems I do have 6400 revs filled in for both of my motors. They the are the ClearPath CPM-SDSK-2321S-ELN stepper motors (enhanced version for both).

The X-axis has 4 threads per inch and Z-axis has 5 TPI. I initially used these numbers with Marty's spreadsheet to calculate the turns ratio several times plus a dial indicator to get within .0000" or .0005" for each axis. I couldn't use a dial indicator this time because the MDI program/settings are so screwed up it knocks the whole dial indicator & base down as it exceeds the travel by multiple inches. That is why I used a tape measure WITH the MP4 and did not soley rely on what the MP4 said. The tape measure approach got it extremely close per the display settings on the MP4. I will do the same approach with the MDI later this evening but will have to set the Z axis close to home so it doesn't exceed the limits I had set. I think that was the reason I went with the MP4 last night as the MDI was knocking over the base and exceeding travel limits.

I don't have the part program with me. However, I seriously doubt 8 inches per minute is too fast for my setup. I believe the near catastrophe with that part program was the set screws on the pulleys were loose. Once I tightened them down hard, I recalibrated everything and I was still left with this issue. FYI, I'm not trying to run a part until I get these settings corrected. Things seem to work in JOG mode just not in program mode or MDI.

Marty, the limit switches you recommended came in last night and I will now have to modify my brackets (make them higher) since the tail is super short and I had accounted for the longer tails originally. I was surprised that this machine homes really good for how sloppy the current limit switches I have installed. Irregardless, I plan to swap them out later this week. Thanks for all your input.