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Topics - RWElphinstone

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General Mach Discussion / Pocket widths different on x and y axis
« on: August 01, 2017, 02:07:48 PM »
Hi all,

I have a strange one for you. Personally, I'm at my wits end. Let me preface this by saying I have a home built Greenbull Clone (it's similar to the Greenbull by BuildYourCNC.com) and it cuts 4' x 8' sheets of MDF on a regular basis. It runs on roller chain on both the x and y-axis, and with a screw on the z-axis.

Here's an image that hopefully helps to illustrate my problem:

In this image, the square outside dimensions are 15" x 15". Each of the pockets inside have a width of 0.66", to allow me to fit 15mm MDF snugly. Now, here's where I have an issue. When I cut the one on the right (horizontally aligned in the image), it cuts fine. The gantry travels along the x-axis for the length, and the width of the pocket is enough to support the snug insertion of the MDF. When I cut the one on the left, however (vertically aligned in the image), the width of the pocket is different. It is so that the MDF will not fit into the pocket, and the edge of the wood actually 'bumps' into the edge of the pocket. I physically have to sand the piece to be inserted, or else, risk damaging the pocket or the wood.

Now, here's where I am having trouble understanding what may be happening. I thought, "oh, well, the x-axis may not be properly configured, and that's why all of my pockets seem to be tighter", and that's when I modified the motor stepping settings. I cut and recut the same piece using different settings, until such time as the tight pockets were the same width of the proper ones. Here's the problem. When I finally measured everything out, the 15" x 15" square was now 15 1/8" on the x-axis side. Not good.

So, my question to the experts here is, what could this be? Could this be backlash, due to the longer chain drive on the x-axis? If so, can backlash affect internal (pocket) cuts and external cuts differently? The chain drive on both has very little play in it, so I think I've firmed it up as much as it can be, so if I assign settings in the Mach3 backlash settings, may this also affect the dimensions of other cuts, outside of the pockets?

I hope I've explained this properly. As I mentioned, I'm at my wits end. I really don't want to go into every design I've created, and manually modify the pockets on the x-axis to be 'wider' than the y-axis cuts. (Especially considering I regularly rotate parts on a sheet, to fit other cuts, and this would cause significant issue.)

I really, really hope someone has seen this before, or has some advice on how I may rectify this issue. I appreciate any input!

Thank you!


Hey all,

I've implemented a macro for my auto-tool zero script, based upon information I found on this wonderful site, however, I would like to improve on the code somewhat if possible. (And, of course, not being a programmer, I do not know how to do so!) My current code will lower the z-axis slowly, until it registers the touch plate I built, and then will take the thickness of the plate into effect, zero the z-axis and return to 1" above the stock. This is the code I am presently using for my z-axis zeroing:

Code: [Select]
Code "(Now attempting to Zero the Z-Axis.)"

PlateThickness = 0.11811 'Z-plate thickness DRO

If GetOemLed (825)=0 Then 'Check to see if the probe is already grounded or faulty
DoOEMButton (1010) 'zero the Z axis so the probe move will start from here
Code "G4 P5" 'this delay gives me time to get from computer to hold probe in place
Code "G31Z-40 F500" 'probing move, can set the feed rate here as well as how far to move
While IsMoving() 'wait while it happens
ZProbePos = GetVar(2002) 'get the exact point the probe was hit
Code "G0 Z" &ZProbePos 'go back to that point, always a very small amount of overrun
While IsMoving ()
Call SetDro (2, PlateThickness) 'set the Z axis DRO to whatever is set as plate thickness
Code "G4 P0.25" 'Pause for Dro to update.
Code "G0 Z1" 'put the Z retract height you want here
Code "(Z axis is now zeroed)" 'puts this message in the status bar
Code "(Z-Plate is grounded, check connection and try again)"'this goes in the status bar if applicable
Exit Sub
End If   

What I would like to do is similar, with the x-axis and y-axis limit switches. I would like to manually bring the x-axis and y-axis within 6" of the zero values (no code required here - I'll move the machine myself) and then have it slowly approach the x-axis, and then once it touches it, it should move 1/4" in the positive, and set the x-axis zero for the machine to this value. Then, I would like it to have it do the same for the y-axis. (Have it slowly approach the y-axis, and then once it touches it, it should move 1/4" in the positive, and set the y-axis zero for the machine to this value.)

I have had a number of issues in the past whereby my machine has gotten caught up on stock, and then losing it's location values because of it. (The machine would get jammed up, and the software would still think it was moving.) As such, I've then had to reposition the router and manually reset the x-axis and y-axis. I figure if I can implement this code properly, it will improve everything significantly. First, I won't have to perform the manual process any longer, and second, I should be able to perform cuts on the same sheet once the system is re-aligned properly. (On occasion, I've had to recut into the same parts, but after the manual process, it can be out by 1/8" or more, which as you can imagine, is not good enough for anything. So, toss that part away.)

My other questions are these:

  • Can the limit switches do this, if they are already assigned in Mach3 as "limit switches"?
  • If the machine gets jammed up, and accidentally click a limit switch, will it run this code or just stop?
  • If they don't run the code when the limit switch is hit, is there an opportunity to have the machine run (perhaps different) code that will automatically try to re-align to zero on the x-axis and y-axis, and restart the cut at the point at which it failed?

I would like to say that I appreciate all of the help I've received over the years here. While I haven't posted too much, I've read and learned a lot here. I would really, really appreciate any help you guys are prepared to give.



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