Calculating Steps with Xylotex Board

[cxixer]

OK, I have gotten this far with my cnc setup. Mach3 is installed and works with my xylotex board. I am trying to setup the steps per inch, and am confused with everything I read. I've been through this forum, the mach forum, and the xylotex forum and searched and can't find a simple answer to this.

I'm using the Xylotex 4 axis kit with a XS-3525/8S-4 board set up in 1/8 stepping mode which means 1600 steps/rev.

The Z axis is currently 1/2"-13 allthread (until I get a 1/2"-10 acme tap).

The X axis uses rack and pinion with racks from: http://www.stdsteel.com/gr_stock.htm (part number 200012)
These have a 16 pitch, and I'm using gears with 24 teeth.

The Y axis uses the same rack and pinion setup, one on each side with it's own motor, rack, and gear.

So my question is ... I'm looking in Mach3 at Config>Motor Tuning under "Steps per" , and don't know how to figure out what to put in there for my setup.

Here's what I have so far:

Z axis -
Mach 3 steps per unit = steps/rev * motor revs/unit

motor revs/inch= 13
steps/rev = 200*8 = 1600

steps per unit = 13*1600 = 20800

um.... am I close? That's all I can figure out from reading mach3's setup manual. And I have less of a clue when it comes to the x and y axis.

Also - since I am slaving the A axis to the Y axis, one motor will have to turn opposite of the other, right? How do I set that up?

[ger21]

Yes, 20,800 is right.

If your rack and pinion is direct drive, then your pinion should move 1.5 x pi per revolution, or 4.71238898 inches per rev. (1.5 is the pitch diameter of the pinion, circumference is 2 x pi x radius, or pi x diameter). You have 1600 steps per revolution, so 1600 divided by 4.71238898 = 339.5305452627100 steps per unit. I think that's right.

To reverse the axis, check the rev box in the home/ limits screen.

[cxixer]

Thanks! I appreciate it. I'll try those numbers and see how it looks.

[vpcnc]

I was hoping to see the final reply if all worked out on this one.

[cxixer]

Hey, the calculations are dead on. Great help! After getting sick of doing the calculations by hand, I wrote a calculator, you can download it at cutfiles .com in the software section! It works with R&P and lead screws.

[Richster]

Sorry to hijack this thread... I set my machine up for metric operation this weekend using M8 threaded rod which has the normal stated 1.25mm thread pitch. I can confirm that the steps per unit, for a Xylotex drive, calculates as 1600/1.25 = 1280 steps/mm. I haven't completed the Y-axis yet, but would expect this to be much the same.

That's fine - BUT my machine will gain about 2mm over 800mm travel. Is this likely to be due to manufacturing tolerances on the threaded rod, and is this quite normal?

The error works out at 0.25%, which is about 0.0025mm per thread.

I could always compensate for this by reducing the steps per mm slightly, in my case, 1596 steps/unit.

Cheers - Richster