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Getting 2 different size cuts on each side of machine
« on: December 23, 2015, 12:33:54 PM »
Im using mach 3 on industrial cnc machine 4x8 table.
I have this re occuring constant problem where the right side of machine cuts correct and left side of machine cuts 1/32 over.
I have thought since the begining it was the machine and not the mach software but i have exhausted all possibilities with the machine.
I am curious , is it possible there is some setting in mach3 that would cause this to happen?

For more info i have done the following to my industrial cnc machine.
The tech supports there have been helpful even offering to pick up machine.
1) changed x driver
2) changed x cable
3) checked connections to motor.
4) installed " smooth stepper " device (supposed to make machine run better.)
5) changed parallel cables
6) changed circuit board to where printer cable gets attached.
7) calibrated mach 3 many times to see if changes were made. Using "axis calibrator"
8) realigned top racks for pinion to ride in
9) when that didnt fix it i requested entirely new racks and mounted them myself but problem still there.
10) changed computer 3 times even getting manufacturer suggested one.

I have done all these and more trying to resolve this issue. Company was willing to pick up machine but they said what i was thinking " we changed every part on the machine "

Any insight would be greatly appreciated whether its on machine or in mach 3 ....there were some other minor adjustments made in mach such as motor tuning.
This problem has occured since day one of machine (although not noticed ) and as of today its a year with same problem.

Joseph marrone inspiredcabinetry .

Much much appreciated

Offline BR549

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Re: Getting 2 different size cuts on each side of machine
« Reply #1 on: December 23, 2015, 03:25:55 PM »
Does the problem reoccur front to back ? DOes it repeat the same effect every time in the exact same spot ?

Are you talking about errors on a feature size lets say a circle and a circle cut on the left side is different  than the one on the right side ? IS the circle perfectly round or out of round ?

Did you use the exact same Gcode sequence on each test and just move the work offset over from left to right.

IF the front left different from the back left ?

Is X different than Y ??

Did you check for pinion runout ? Did you check for gear clearance in the rack or IF the rack runs exactly parallel with the gear all teh way across the Y

I can go on but I think you get the idea ??
« Last Edit: December 23, 2015, 03:33:04 PM by BR549 »
Re: Getting 2 different size cuts on each side of machine
« Reply #2 on: December 23, 2015, 06:14:43 PM »
No it does not occur front to back (my y axis) only left to right (my x axis)

I should also mention , because i know they are set different per machine, my x axis (where the problem is ) is driven by 1 motor along 48". The y axis is driven by 2 motors but theres no problem on that axis .

Yes it is always the correct size on the left side of the table (my x 0-24" ) and always incorrect on right side of table (my x 24-48)  however i can recalibrate the x axis so it cuts correct on right side but then left side would come out bigger.

Yes ive used the same gcode. Problem has occured for over a year .  Im mostly running cabinets parts on my machine so its sometimes more critical then others. Same gcode one gets generated by " cabinet vision" other gets generated by aspire vcarve pro.

Oh ....i see..... Draw one box and cut it then offset 24" ....i will have to give that one a try although i imagine the same result will occur but i will try that one .

No its the same result the full 96" off the machine same result no matter where i cut along the y axis.

Next question a little tough to answer . Not sure what " pinion run out " means but i did disconnect the x motor and push the x axis manually.  There were minute discrepentcies in play between the rack and pinion system ....i painfully adjusted that so the tension was equal along the whole run ...... I literally had to use a sheet of paper to get it just right . I honestly feel and felt that it cant possibly be this critical but did it anyway.  Adter all that the problem was still identical.im not sure about the " parallel " question either unless i answered that above . But i did also shim the thompson rail out again about the thickness of 2 sheets of paper in 2 spots......i was convinced at the time this would solve it but it didnt.   That box still cuts exactly 1/32" different then other side.

It just kind of bugs me that the problem is so consisttant and exact ly wrong.  Its not like the right side varies in how much its iff by . Especially when i made some of the changes above ,.....you would think that making some of those adjustments its kind of impossible NOT to get a different result.   Which is y i turned to the mach forums.  Hoping there is some setting for 1/2 the table (which i know how it sounds just writing it but i had to give it a shot)

Let me know what you think and im already thankful for your response

Re: Getting 2 different size cuts on each side of machine
« Reply #3 on: December 23, 2015, 06:22:56 PM »
Oh regarding the circles.  Earlier in the year the techs at machine place told me to leave 1/16" play in gear that rides the rack .....i guess thats called the pinion? But anyway with that slop in there i was having problems with my circles a.k.a hinge boreouts. But after i snugged that back up so there was no play the hinges boreouts  came out perfect again.

Offline bfgstew

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Re: Getting 2 different size cuts on each side of machine
« Reply #4 on: December 23, 2015, 06:57:41 PM »
If you cut a 2" square on the X zero side then cut a series of 2" squares across the table to the X+ side of the table, how would the squares measure up? Also check were the 2" cut outs come to, are they out relative to the Gcode. Is the problem cummulative or in one position. Cummulative would point to wear in drive or incorrect step set up. One position would point to broken tooth/gear/chain link................?
Good luck

Offline BR549

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Re: Getting 2 different size cuts on each side of machine
« Reply #5 on: December 23, 2015, 08:11:21 PM »
OK Mach3 software has NO idea if you are on the left or right side of the table IF you use the same Gcode. So that tells me you have a mechanical problem on the gantry drive mechanism not being the exact same on both sides. Is the gear rack full length across the gantry or 2 piece. If 2 piece where is the split ?  . The amount of gear clearance WILL change the pinion pitch circle diameter of teh gear and rack so it could change the exact motion from the left to the right side if there is MORE clearance on one side compared to the other.

Check in the formula section of config and Make SURE there are no values in the formula lines.

« Last Edit: December 23, 2015, 08:13:31 PM by BR549 »

Offline Tweakie.CNC

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Re: Getting 2 different size cuts on each side of machine
« Reply #6 on: December 24, 2015, 07:13:58 AM »
Just thinking out loud...

If the X axis rack is in two parts is the pitch of each part 'exactly' the same ??
Alternately if the rack is in one part then is the pitch 'exactly' the same along the whole of its length ??

Not sure how you would check it (without removing the rack) but there must be a way.

Re: Getting 2 different size cuts on each side of machine
« Reply #7 on: December 24, 2015, 01:39:10 PM »
Man i am soooo happy i posted .
You guys are giving me great info and im glad we are all on the page with the thought processes here.
Ive asked colleagues around me but they are not familiar so this has been a great help!

@tweakie .
Yes x axis is in 2 parts . My racks are not pitched they are straight up and down although ive been told the pitched ones are better because more teeth grab instead of just one . Its something i might have to look into .
I did ask for entirely new racks from manufacturer to replace the existing ones to rule out that. Although not that u r mentioning pitch i will have to go back and triple check they are sitting flat .

yeah i kind of figured it had nothing to do with mach i was just running out of options. Plus there are soooooo many micro adjustments inside mach that i thought there might be a small possibility .
Yes the split in the racks is directly down the center. Its approx 2 26" racks with a seam in the center. I changed both those racks to brand new from the manufacturer and attached them both atop the gantry. I kept motor disconnected and manually pushed spindle back and farth readjusting until it was smooth and even the whole way.
Is the " pinion " the gear with all the teeth that interlock the rack? Cause that has not been changed and these responses are leading to that being an issue. Although maybe not. Ill adress that in next response .
Also what is or where is " formula section in config" u know what .....illl have to reread when im in the shop.

@  bfgstew
Funny u say that . I did think along the same lines and ran a test cutting 4" squares instead of 2" and i did notice very very slight dimension changes from Square to square (less then 1/64 or around) note : this test was pre smooth stepper. But when measuring 7 squares together they would measure the correct dimension on one side of the machine and that same 1/32 off on the other side. The pinion(gear) that runs along the rack may have a damaged or worn tooth.  I have visually checked it but since since the variation is so slight maybe its not visible with the eye and i need a better way to check that.

My high school math escapes me . The diameter of the pinion gear is approx 6" what would be the outside perimeter?. Or is that the cicumfrance ? Is that pie.r2? The reason why i ask is if there is one ormore damaged tooth on that wheel wouldnt the error in dimension still occur on both sides of the table ?  Unless its somehow happening 1 x on 1s and 2x's on the other.

After all the changes and part replacements ive done above this is one small piece ive never replaced.

This seems like the next logical part to replace and see if it remedies it.
Thanks to all!
Ill check back in in a 2 or so weeks if this remedied the problem.


Offline BR549

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Re: Getting 2 different size cuts on each side of machine
« Reply #8 on: December 24, 2015, 04:49:21 PM »
IF it were a pinion gear problem then you would see the error everywhere . The rack on the right hand side is pointing as the Problem  As teh left hand side cuts correctly.  I would seriously look at gear clearance all the way across that rack. IF you can then switch racks from side to side and see IF the problem follows the switch.  I think IF you look closely at the tooth clearance on that rack then the problem may show itself.

What you are looking for is the gear pitch diameter that is what sets up the motion. It is the point where the gear tooth is making constant contact with the rack tooth. 

Offline RICH

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Re: Getting 2 different size cuts on each side of machine
« Reply #9 on: December 25, 2015, 10:09:49 AM »
Just something easy to do using the calibrate feature:.

1. Calibrate movement  of one of the racks. Set the steps per unit based on that.
2. Now move the gantry to the other rack. Calibrate that rack for the same travel .
   The steps per unit and distance should be the same as in 1.
3. Now move midway in rack / step 1. and use calibrate across the spit between the two racks.

Move in one direct and take out the backlash.

Now reverse the direction  of movement opposite of what you did above and do the same.

Make note of the each step. You will find any difference between one rack and the other, across the joint line,
and opposite direction. Key here is to be able to measure the travel distance accurately.