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1

General Mach Discussion / Need Help - All Dimensions coming out small

« on: February 19, 2011, 09:22:31 AM »

I'm having a problem with my wood router running Mach3.  When I make my cuts everything is coming out smaller than it should be.  If I make a 2"X2" square it actually is coming out 1.994x1.994.  I first thought that maybe my cutting tool size was off so I then tried a 2"x2" pocket.  That came out 1.988 x 1.988.  This is really confusing me.  If my tool was too big then the OD on the profile would be undersize and the ID on the pocket would be oversize.  They are both coming out undersize.  The pockets appear to be 2x as far off as the profiles for finish dimension.  Any ideas on what could be causing this?  I am running probotix drivers and powermax II stepper motors and 1/2-10 acme 1 start screws.  My motor tuning has steps set to 2000 per inch.  The machine doesn't have any measurable backlash that I can find.  I put a dial indicator on each axis and jogged it 1" forward and 1" back and it came right back to zero.  There doesn't appear to be any tool offsets setup in Mach3.  Any ideas what else to check?

Keith

2

General Mach Discussion / Hesitation between Lines of G-code

« on: February 16, 2011, 02:18:06 PM »

I posted this on the yahoo group but figured I would try here as well.
I need some help. I built a JGRO wood router and am playing around with it
using Mach3 Mill. I am having a problem where the stepper motors are having a
slight hesitation between each line of g-code. It does not matter if it is a
circle or a straight line. If I write code for two straight lines connected to
each other I get a slight pause inbetween each line when I run the code. I have
tried it both with CV on and with exact stop on. It didn't make a difference.
I have backlash set to zero so I know it isn't a compensation issue. It is
almost like the computer takes a break from sending the pulses to the parallel
port each time the screen updates to the next line of code. The final dimensons
come out ok so I know it isn't actually loosing steps, it just makes the machine
run very jerky. I don't know if it matters but here are the details of my
setup.

Probotix bi-polar drivers with the non-isolated breakout board
256 oz/in powermax II bi-polar motors
1/2-10 acme threaded rod with dumpster anti-backlash nuts and lovejoy's
motor tuning 2000, 70ipm, accel 4, pulse width 2 - no microstepping
The program was drawn in autocad and cut2d was used as the cam program
Cutting at 35ipm and .200 depth per cut in mdf

Everything seems find with the setup except for the pauses between lines of
code. The machine jogs, rapids, and moves using MDI with no problems.

Any suggestions?


Keith