Messages

11

General Mach Discussion / Re: Incorrect Z-Axis zero/home position

« on: June 21, 2017, 09:27:31 AM »

Well, I was hoping for an easy fix, but after redoing the Z-axis calibration it is still doing the exact same thing.  The calibration is now spot on for 4 and 5 inches (the longest travel I could measure safely).  I made sure to have backlash removed, and repeated the calibration tests several times to ensure it was correct. 

I have tried a few other tests; changing the safe-Z setting from machine coordinate zero (roughly 200+ mm travel for the tests) to just 10mm and 100mm.  The lesser the travel, the lesser the discrepancy.  But there IS still a discrepancy, incrementally worse each time I repeat the process.  The amount that it is off is determined by the distance traveled - the further the travel, the further it's off. 

So for example: if the Z-Axis moves up 100mm it's off by about .2mm.  If the Z-Axis only moves up by 50mm, it's off by about .02  With the 100mm travel test, for each of these runs it returns to yet another increment of .2mm off.  So after the second run of 100mm, it's off by .about .4.  Third time is off by .6 etc.  It's not 100% consistent - but often times is very close.

I also tried slowing the velocity and acceleration way down, thinking that maybe the motor or coupler was skipping/slipping - but this did not seem to help.  I have assumed that it would not be motor missed steps or the coupler slipping, because I don't think it would be so consistently off each move.   So it appears that regardless of how fast or slow it tries to get there, it always travels in the negative direction by slightly too short an amount.  And then incrementally does this each time I repeat the process.

I'm at wits end here on what to test....

Thanks for your patience.

Scott

12

General Mach Discussion / Re: Incorrect Z-Axis zero/home position

« on: June 20, 2017, 07:24:55 PM »

Ha!  Seems like I have some recovering to do from CNC ADD

I did originally do the X & Y axis with the longest controlled measurement I could get. The Z was done early on as well - and the short check today was just to make sure it wasn't terribly off. But it looks like I need to get back on that Z-axis with a longer measurement to rule that out. Let's hope it's something that simple.

13

General Mach Discussion / Re: Incorrect Z-Axis zero/home position

« on: June 20, 2017, 06:05:41 PM »

Thanks so much Rich.

When I thought more about it after posting, I thought the same thing - why do I always think of these things right after I walk out the door??? .

I did test calibration this morning and made some very slight adjustments - but only using travel of 1.5" which may be leaving some errors in the longer throw I have on the Z-Axis.

I will do a more thorough calibration tomorrow when I get back to the shop. It does seem like the most logical cause.

Appreciate the reply. I'll post back any results I get.

14

General Mach Discussion / Incorrect Z-Axis zero/home position

« on: June 20, 2017, 01:40:33 PM »

Hey folks,

First post here on the forum.  New to Mach3 and had no luck with a search - although I've had great results researching here in the past.  Hoping someone might point me in a direction for checking the issue I'm having.

I am running a DIY built machine with THK linear rails/trucks, ballscrews and Nema 23 motors.  I have measured backlash to be in the vicinity of about .02mm (no compensation applied in Mach3).  The machine is set up with homing switches on the X,Y & Z axis.  When I first start the machine, I home it using the "ref all" button, with all axis traveling to the home switches and backing off correctly.  I then jog to a position and set/zero the work coordinate G53 position (Z-axis done with a touch plate).   

The problem I have is when I jog away from the WCS zero, then hit "Go to Zero" button the Z-axis returns to a location slightly lower than it should (Go to Zero move always includes the Z-axis traveling up to the machine zero first, then back down to the WCS zero).  I narrowed down the issue by doing this repeatedly - each time hitting the "Go to Zero" button - triggering the Z-axis to travel to the machine zero and then back to the WCS zero.  Eventually I noticed that each time it returned to the WCS zero, it was a little lower than the last time.

I tested the issue by measuring the discrepancy of distance traveled at both the bottom (by locating to WCS zero) and top (by locating to machine zero) of the Z-axis with a dial indicator.  I made sure to remove any backlash before beginning to travel up to the machine zero.  It appears to be incrementally off by about .07mm each pass.  By repeatedly locating to the work zero and then MDI G28 Z0, back and forth, the axis is clearly not reaching the same machine zero location at the top, always stopping shy of the previous location that the machine zeroed to during the Homing operation.  So it seems that traveling between the WCS zero and the machine zero is pretty consistently the same distance, but always offset by a bit.  This puts the cutter too low - and even lower each time the machine raises up and back down to the WCS zero.  Hope this makes sense. 

If you need clarification, please let me know.  Any thoughts on what to test next?  Is this a software or hardware issue?

Thanks in advance for any help, tips and/or tricks,

Scott

15

Mach4 General Discussion / Re: New people welcome !! Come in here and introduce your self!

« on: February 11, 2017, 08:59:30 PM »

Hey folks. First post here. Been soaking up as much as I can on the forum - in preparation for my first experience with Mach3. I'm in the process of putting together a small(ish) gantry style CNC, based around aluminum extrusion and tooling plate. Looking forward to learning the software - and hoping to be able to get some more great info here.

My previous experience has been with a small CNC router built using open source hardware and software. Fun and rewarding, and a great way to learn the ropes, but very frustrating at times. This next machine will have a larger cutting area, be more rigid, and I'm banking on much more solid in the software department. I currently use Solidworks for CAD with the HSMxpress CAM plugin.

Thanks for all the great info you all provide.

Scott