I have a small issue with my y-axis and would assume the same with my z-axis as they are both on pulleys
the issue I have is calibration
this only came to light when I tried to cut my dragon out on Sunday night when I tried to cut a distance on my y-axis off 300 mm as that was the size of my model and when I measured it it was 286 mm. at first I thought it was the model software and the scale factor, so I set my spindle to cut at 286 mm and to my surprise my spindle came up short.
well today I have set it to cut/drill three hole in a triangle of 100 mm and it's cut it out at around 95 mm
how do I recalibrate my CNC Machine Mach3 is the software I'm using
goto the menu :CONFIG then :MOTOR TUNING under that.
In the left lower corner of the dialogue box is "steps per".
Your error is not consistent, so there is more to this, it looks like you need to move 5% more which needs 5% more "steps per" in the triangle example the error is closer to 10% presuming it is an equilateral triangle.
The same dialog enables you to set the acceleration, if that is wound up too high then it will cause you problems, so till you have steps per correct I suggest you wind the acceleration right down.
You need to remove backlash from the equation by moving in a direction before stopping and then continuing motion for the purpose of measurement. So dont just move from Y0 to Y100, first move to Y-10, then Y0 then Y100 and measure the Y0 Y100 progress.
Note the settings before you hack them ;-) Someone cleverer than I might be able to tell you exactly what to change it to but suck it and see has always worked for me.
hope that helps you.
James ring me and I'll walk you thru sorting this it's not a problem just probably slightly over tuned or miss calculated steps.. . .Easy fix.!!
It's a 2:1 ratio with 500mm pitch screw, so 10mm effective pitch and (I think) 1600step/rev. That means in mach3 it should say 160step/mm, or at least that's what I would have entered for you (or 80 if it's actually on 800step/rev). I can't see why it would have changed unless you accidently changed it when I suggested lowering the acceleration, but even so if the error is inconsistent something more interesting is happening.
Looks like it was a right angled/isosceles triangle as 95*300/100=285mm. If you're just using a ruler that easily accounts for the 1mm difference. I'm surprised as I checked it with digital calliper over 300mm and it was spot on.
I told Luke how to work these values out, see if he remembers
Feel free to call me too if Jazz or Luke haven't already sorted it.
I would like to thank Jazz for helping me calibrate my CNC by using Mach3 to work out the correct steps per mm
all calibrated now cheers Jazz
and I've cut my collet holder out now
I made collet holder by merely drilling a line of holes in a spare piece of wood with the right size (quite big) drill. Works perfectly well...the next one will be incorporated into the gantry and store them in a circular array. Prizes for guessing why!
What was wrong with the values in the end? Strange that they would change for no apparent reason.
The general idea is to incorporate two tool racks hidden *inside* the gantry, one either side with 8 tools on each and have it so the Z-axis retracts inside the gantry, tool holder slides under spindle and rotates to the right tool ... tool is changed then the Z-axis drops down to carry on as normal. The only issue with this plan is it will add overhang to the Z-axis, reducing rigidity, and loose a bit of travel. I've got 400mm of travel to play with, so that's not a big deal. Using 760mm profile rails. I've had the profile rails for a long time but not been able to decide or afford to mount them properly.
Last edited by Jonathan; 26-01-2012 at 10:18 PM.
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