Centroid Community CNC Support Forum

I was learning how to compute motor revs/inch. The example on page 30 (9.4) of the install guide "ajax_mpu11_allin1_cnc11_mill_install.pdf" shows how to do the calculations.
I am old and make mistakes with math problems, so I decided to write a small calculator to do it for me.
After finishing writing the program I entered the data from the example, into my program.
I could not get the correct answer as stated in example.

" How to compute motor revs/inch:
Commanded distance / Distance moved = multiplier
Multiplier * Current revs/inch = corrected revs/inch
Ex: Commanded Distance = 6.0000” = .99400~ (multiplier)
Distance moved = 6.0036”
.99400 * 5.0000 = 4.97000 New motor revs/inch"

Finally I realized the instructions answer is wrong!?? (I think)
6.0000/6.0036 is not = .99400 It seems to be .9994
Is that a large error? And am I wrong.

The program I wrote is freeware
It does all three axis, just enter the values.
As with any thing you download - check my program with a virus checker
if anyone finds a problem with it please post it here.


Thank You
Ron Derkis
rderkis@hotmail.com

Ron,

Obviously your math is correct. There is a typo in the manual. Thanks for pointing that out.

And yes, slipping a decimal like that would create a very measurable error in the size of your part(s) .

It was a real question I didn't know, how serious it was.
I only pointed out the mistake, to point out that using my calculator will cut down on the likely hood of these mistakes.

Finally I realized the instructions answer is wrong!?? (I think)
6.0000/6.0036 is not = .99400 It seems to be .9994
Is that a large error? And am I wrong.
---------
You're correct, and that's a HUGE error... something a bit more than 0.5%

It's just a typo. I've learned to NEVER trust a printed document for any math described in it. I always run the calculations as the process is described. Then, if I get a discrepancy, it's easy to backtrack through just the step where it showed up.

You can trust the guy who DID the math, but you can't trust the person who transcribed it! <G>

Lloyd