H E L P - - - Steps Per Unit

[tjskcnc]

This is driving me nuts!!!!!!

I've run this countless times using the process detailed in the Mach3 documentation and I seem to be unable to come up with the right numbers.

Table X-axis is belt driven:
All measurements are XL (pitch at 0.2 - 5 teeth per inch.)
Pulley on motor shaft has 15 teeth.
Pulley on axis has 30 teeth (drives 2 belts, one on each side of the gantry.)
Pulley on belt has 15 teeth.
Gecko G540 @ 10 microsteps

Pulley on motor drives pulley on axis which drives pulley on belt.

What are the proper formulas to configure "Steps Per Unit"?

Even better, what is the actual number I need to put in the "Steps Per" box.

let me know if you need more info.

Thanks.

[jalessi]

Tjskcnc,

There is a easier way to do this accurately.


Step 1: In order to get close I suggest turning the motor one "1" revolution and measuring the axis travel with a dial indicator.

Once you have that data we can calculate the steps per and use the Mach3 Axis Calibration Utility to automatically set it spot on.

I would be happy to walk you through the process.

Jeff...

[jalessi]

Tjskcnc,

Hoss made this video tutorial , it will give you a good idea on how the Axis Calibration Utility works.

http://www.youtube.com/profile?user=...30/XkO5tc-jSxw

Jeff...

[rowbare]

Hoss made this video that outlines the calibration that Jeff mentionned:

http://www.cnczone.com/forums/showpo...&postcount=702

As for calculations: Motor makes one turn, shaft makes 1/2 turn which means the belt advances 7.5 teeth or 1.5 inches per turn which works out to 2/3 turns per inch. It took you 2000 microsteps (200steps * 10) to turn that motor one revolution thus 2000 * 2/3 = 1333.33... pulses per inch. For starters, set the acceleration really low to 1 or 2. This should get you moving, then you can do the calibration to fine-tune it.

Depending on how heavy your gantry is and what you are cutting, you will probably find that you are under geared. At a conservative 600 rpm motor speed you would be getting 900 ipm rapids but very little cutting torque. That is why I suggested you set the acceleration values so low. If you set them too high you will stall as soon as you try to rapid.

hope this helps!
bob

[tjskcnc]

Thanks for the quick response.
There is no drive screw.
There is a 15 tooth pulley on the motor shaft. This drives a 30 tooth pulley on a 1/2" steel shaft.
Both ends of the shaft have a 15 tooth pulley driving belts connected to each side of the gantry.
All Xl sizes (.2 pitch).
A 15 tooth pulley driving a 30 tooth pulley driving 2 @ 15 tooth pulleys (one on each side of the axis.)
I will try to purchase a dial indicator this Friday.

The design is based on the Solsylva 2'x4' R&P table, but using belts instead of R&P. Also, table cutting area is 4'x8'.

[tjskcnc]

Should I be changing the gearing on my pulleys?
Meaning, should I add/subtract/change pulleys and or teeth per pulley?
I plan on using this table for sign work using V-Carve Pro, Solidworks, and mastercam X3.
Rapids in excess of 500" per minute are fun to watch, but my goal is cutting at an average of 100 " per minute.

Time to call it a night, but please continue to respond. I'm here to learn.

[ger21]

I think you have two turns of the motor per 1 turn of the drive pulleys. If so, the travel would be pi times the pitch dia. of the 15 tooth pulley divided by 2. Divide the travel by 2000 and that should be your steps/unit.

You really should be aiming for 200-300ipm cutting speed, especially with a 4x8 machine. I always cut at 125-150ipm (machine max), and would cut faster if I could. 100ipm is not very fast for cutting wood.

[tjskcnc]

ger21 and all others - thanks for your help.

Running the formulas (prior to your responses) in the Mach3 installation pdf, I came up with 1666.666.... for steps per unit. I used the auto set feature in Mach3 ( which was suggested in a response) using just a measuring tape and came up with 1330.75xxxx... which shows my calculations were way off.

I tried the suggestion of 1333.333.... and the number appears to be accurate.

I will be rebuilding the gantry next week, so I will not be able to make any actual cuts to check accuracy until then. I will respond at that time to let you know how it all turned out.