Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: lokey on March 26, 2009, 09:32:06 PM
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Hi, I am running Mach3 with a Zenbot. I am having trouble with the X axis. During a cut the X axis shifts to the positive. The start location shows a shift to the positive of about 1/8 of an inch after the cut is complete. This problem is causing mis-alignment on all the chains being cut. Is there a solution to this problem? Thanks in advance for any any help received.
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Does the X DRO have the shift in it?
Which direction are you cutting?
Hood
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Hi, The DRO does not show the shift. Cuts are in the counter clock wise direction.
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Could be a few things the most likely is you are losing steps, try reducing the accel and vel in motor tuning a bit.
Hood
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Hi, I reduced the acceleration and the velocity . Now the circles are oval and mis-aligned.
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can you give an example of what you are actually doing as your description in the first post is not very clear to me I am afraid.
Hood
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Hi I tighten the belts and set x and y motor tuning equal to each other. It helped a lot.
Listed are measurement results:
G1 X 0.3
DRO 0.2990
dial indicator measurement = 0.294
G1 X 0.0
DRO 0.0
dial indicator measurement = 0.004
If there is any thing else I can do to zero in the Zenbot please let me know.
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Sounds like you may have your steps per unit set slightly wrong,
is it steppers?
What stepping do your drives have, ie full, half, 10 micro steping?
Any reduction between motors and screws?
Pitch of screws?
Hood
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Hi, the stepper motors are set to 1/8 th. I am using a Zenbot with kevilar drive belts.
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Do the drivebelts connect to a balscrew or are they fixed directly to an axis?
If the former what is the pitch of the ballscrew and is there any reduction between motor pulley and ballscrew pulley?
If the latter what is the pitch of the belt and how many teeth are on the motors pulley?
Hood
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Hi, the formula that came with the machine is .695 x 200 x 8 = 1112 steps per inch. I found a video for calibration but I am not sure I under stand it. It measures the distance of a known part and compares it to the DRO readout and then adjusts the steps per inch setting accordingly. I will have to watch the video a few more times. If you have any ideas please let me know.
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200 is the steps per rev of the stepper motor, the 8 is the microstepping and the .695 must be the distance traveled in one rev of the motor so assuming that is correct then the Steps per should be as stated 1112.
If it had ballscrews then the calculation would definitely be the way to set the steps per but as its a timing belt there may be some slight errors in the pitch which is not working in your favour so if you have an accurate means of measuring you could use the "Set Steps per Unit" utility on the settings page but that will only ever be as accurate as your measurements.
Hood
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Hi, I found the axis calibration tool on the setting page of Mach 3. After calibration I was able to use G code to move the axis a set distance and the dial indicator show the correct distance was moved. The DRO showed the movement to be short by .0003 and when I returned it zero the dial indicator returned to zero, but the DRO would be 0.0009. When I run a cut with a lot of x changes the error adds up and creates a real noticeably affect making the part useless because it is a rotor and it is out of round. If you know of a way to correct this problem please let me know. Thank you for all your efforts. Best Regards
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Your problem will be the low resolution of your system, 1112 steps per inch equates to a resolution of 0.00089928...... which just so happens is what your DRO is showing ;)
In reality your resolution wont even be that good because microsteps are not uniform or exact, if you want better resolution you unfortunately need a better machine.
Having said that it should not increase in error as Mach keeps a track of it, it is likely to be that your steps per unit are not quite right if you are getting an increase.
Hood
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You also say "out of round" that could be causeg by backlash if the out of round is at the cardinal points.
Hood