Messages

41

General Mach Discussion / Re: After using the “Steps Per Unit” in “Axis Calibration” my CNC wont run properly

« on: September 02, 2008, 08:22:09 PM »

Acceleration is a function of the motors, the machine, the drivers, etc., etc., and will be different for every axis, and every machine. X will generally be quite different from Y, because it's fighting a higher mass and hence inertia. Start low, and work your way up, checking at each step that it will reliably rapid to the correct position. If you go too far, you'll find you lose position randomly. There's really little to be gained by going to max acceleration except for bragging rights, so I wouldn't push it.
You may also be hitting mid-band resonance. Are you using Geckos? If so, you should adjust the resonance compensation. It will be different for the two axes.

Regards,
Ray L.

How will I know when I'm hitting mid-band resonance?  I am not using Geckos but would a damper work, I have been reading about this on the CNCZone

I would post a photo but an new and don't know how.
Background:  200 in/oz steppers, Probotix isolated BOB and drivers 24V PS.
My homemade CNC is a fixed gantry, with a 24" X 24" work area, using 1/2" 10 TPI, 1 start acme screws, the X axis is running on 1" dia fully supported lin brgs, It is moving the Z axis and a wood router.  My Y axis is running on gas pipe with roller bearings on the top and side of the pipe, the pipe is supported under the X axis travel area.  I am a wood hobbyist and this was the most rigid machine I could make and have the lightest loads on the steppers.   I have linear bearings and ball screws for all axis for my next machine and it will be a movable gantry with each side screw driven.  That is if I ever get the bugs out of this one and enough confidence to start cutting parts.

42

General Mach Discussion / Re: After using the “Steps Per Unit” in “Axis Calibration” my CNC wont run properly

« on: September 02, 2008, 06:22:30 PM »

The buzzing is undoubtedly the stepper stalling because you're trying to step too fast. You doubled the steps/unit, but didn't change the max speed, so the step rate during jog was doubled, and the motors can't handle it. First, reduce the max speed on the motor tuning dialog to a low number, like 10IPM. Then check the jog operation. I think you'll find it works fine, just slow. While you're there, check the move distance is correct. Once both of those are OK, then play with max speed and acceleration, and set them low enough that the motors don't stall.
But, sounds to me like you're really in half-step mode, not full step. Either that, or you have a 2:1 mechanical reduction you've left out of the calculation. For 10-pitch screws, full-step 200PPR motors, steps/unit *will* be 2000 in inch mode.

Regards,
Ray L.

Thanks Ray,

I slowed all the axis IPM from 40 (I had ran at 40 for days without any stalling) to 10.  And they all moved normal but naturally slowly.
I am in full step.  And steps set to 2000 per in.   I input 2" and it moved 2"

I have a fixed gantry machine.

With the steppers turned off the amount of force required to turn both the X and Y acme threads by hand is about the same.  However on the Y axis it will now JOG at 100 IPM no problem, but the X axis stalls at over 40 IPM.  If I run the X axis at 30 and jog it is impossible to stall it by pushing on the axis as it moves, but set it to 40 and I can push on it an dstall it easily.

That is strange all I did was slow the axis down to 10 ran all the axis, now i can run the Y at 100+ without any hesitation?

What should the acelleration and G force be?  Or is this a factor?

43

General Mach Discussion / After using the “Steps Per Unit” in “Axis Calibration” my CNC wont run properly

« on: September 02, 2008, 04:53:55 PM »

Using Mach3

Am in the process of fine tuning my CNC and have hit a snag while setting my “Steps Per Unit” in “Axis Calibration”.

I have been air cutting and using a pen to draw the various Gcode files, everything was repeating and running smoothly except that everything was half size. Sounds like I need to adjust the Steps Per Unit.  My drivers are set to "Full Step"  And in "Motor Tuning" the Steps per Unit was showing 2000. I am using a 10 TPI Acme so this sounds correct.  ? ? ?

I went into the Settings Tab and selected “Steps Per Unit” in “Axis Calibration” then the X axis, deleted the 0 and input 2”. Ran that and measured and it was 1”, input that figure and saved it. Did the same I think for the Z axis.

Went back to the Motor Tuning the Steps per Unit was still showing 2000. Hmmmm Thought this should be a different number now after what I did above.

Tried a X and Y axis manual jog and the stepper makes about one revolution and stops, and buzzes if I hold the jog button. It does this in both directions. It does this every time I press X jog.

Tried Z axis manual jog and it moves a few stepper rev. but only about 1 turn in the down direction every time I hit jog.

In the Diag screen each axis moves toward home slowly as long as i hold the button.

As I said everything was OK before I tried the “Steps Per Unit” in “Axis Calibration” utility.

Any Ideas on how to fix this?

Thanks

44

General Mach Discussion / Re: Always in the Slow Jog Mode

« on: March 25, 2008, 07:29:04 PM »

Took your advice and changed the Motor Outputs to “A” and the input signals to A also.
See screen shots below.

Moved the jumper from Z on the BOB to the A position and the other end to the Z driver.
X and Y are working normally.  Z will not move + or -.

Checked the Dir voltage and both + and - were 0.

Connected the jumper from A on the BOB to the Y driver. 
The Y stepper will move + and -.
Could not measure voltage cables in way.

Connected the jumper from the Y on the BOB to the Z driver. 
The Z stepper will not move.

Looks like the Z driver card is not operating.
Replaced jumpers back to Y-Y   and A-Z

Took the Y cable connection to stepper and put it on Z stepper.  Z stepper will go + and – when going through the Y drive card.
Nothing is wrong with the Z stepper.

Could it still be Mach3?
I'll send PM with phone no.

45

General Mach Discussion / Re: Always in the Slow Jog Mode

« on: March 25, 2008, 02:11:37 PM »

Chip
I have to run an errand will be back later
Thanks
Hager

46

General Mach Discussion / Re: Always in the Slow Jog Mode

« on: March 25, 2008, 02:10:40 PM »

Here are the electrical test results, looks like my BOB might be damaged.

47

General Mach Discussion / Re: Always in the Slow Jog Mode

« on: March 25, 2008, 02:08:07 PM »

Mr.Chips

Are the step/dir Low actives set the same as your X axis in Ports & pins ?

Maybe this board is wear-ed, Try changing the dir Low actives for Y, Z to opposite state

Lost your Phone # give me a call.

Thanks, Chip

Here is a shot of the ports and pins and they are currently set.

48

General Mach Discussion / Re: Always in the Slow Jog Mode

« on: March 25, 2008, 05:14:05 AM »

Checking voltages on BOB   
X+ = 5.1  X- = 0     Moves on both directions
Y+ = 0    Y- = 0      Only moves in one direction
Z+ = 5.1    Z- =5.1  Only moves in one direction

BOB output voltages are not correct on Y and Z axis.

49

General Mach Discussion / Re: Always in the Slow Jog Mode

« on: March 25, 2008, 04:54:49 AM »

Ha Ha from the photos I posted I can see the Dir and Gnd connections of the X Y and Z.  Bot don't tee any markings on the Driver boards.
I'll go out and check the BOB anyway.

50

General Mach Discussion / Re: Always in the Slow Jog Mode

« on: March 25, 2008, 04:52:26 AM »

I unplugged the parallel cable and tested X Y and Z dir. on the cable  
X+ = 5.1  X- = 0   
Y+ = 0    Y- =5.1 
Z+ = 0    Z- =5.1

So the signal is good coming out of the parallel port and cable.

I’m not able to identify the Dir pins on either the BOB or driver cards.