calibration

**luke11cnc** · 24-01-2012

Hello all
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

James:exclaim::exclaim::exclaim:

**Jon S** · 24-01-2012

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.

Jon

**JAZZCNC** · 24-01-2012

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.!!

**Jonathan** · 25-01-2012

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.

**luke11cnc** · 26-01-2012

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

James

**JAZZCNC** · 26-01-2012

Originally Posted by luke11cnc

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

James

Pleased could help and glad your sorted and cutting true. And your further down the road than me if you've cut your collet holder.!! One of them I'll do it later when I've spare time job's, but I,ve only had them 3yrs so there's time yet. . :dance:

**Jonathan** · 26-01-2012

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.

**JAZZCNC** · 26-01-2012

Originally Posted by Jonathan

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.

Mine involves a piece of wood but it's even more techni-not than that.!!. . . . 13 nails with heads snipped..

**luke11cnc** · 26-01-2012

Originally Posted by Jonathan

Prizes for guessing why!

what do we win Jonathan (tool changer for free) LOL

I haven't got a clue Jonathan maybe the belts have stretched a bit ?? but it was out about 6%

James

**Jonathan** · 26-01-2012

Originally Posted by luke11cnc

what do we win Jonathan (tool changer for free) LOL

No idea...but chip won it. The ATC mechanism seems solid, just need to solve issues with the bearing arrangement and it'll be ready to go.
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.

Originally Posted by luke11cnc

I haven't got a clue Jonathan maybe the belts have stretched a bit ?? but it was out about 6%

Timing belts don't stretch by 6%! Even if they did it's the number of teeth that determine the ratio. What number is in step/mm for the Y-axis under config-motor tuning?

Originally Posted by JAZZCNC

Mine involves a piece of wood but it's even more techni-not than that.!!. . . . 13 nails with heads snipped..

So you've only got the metric collets.