Messages

1

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

« on: February 21, 2011, 06:31:22 AM »

I spent six hours yesterday making test cuts, measuring things and making adjustments.  What finally fixed the problem was setting the steps per inch back to nominal (calculated) and turning on 1/8 microstepping.  For some strange reason it now cuts within about .002.  I tried with with single step and the same settings and I was off by .011 to .019.  When I went to 1/8 microstepping it came right back to where it should be.  This completely baffles me as to why but at this point, I could care less, it works.

Keith

2

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

« on: February 19, 2011, 06:01:48 PM »

I think you misunderstood what I meant about inside and outside.  If I cut a pocket that is supposed to be 2" x 2" the material removed is actaully 1.990 x 1.990.  If I write another program and make a profile that is 2" x 2" the material left is 1.990 x 1.990.  If my cutter was too big or my runout was large then the pocket should be bigger than 2" and the profile less than 2".  If my tool was undersize then the pocket should be less than 2" and the profile larger than 2".  Since they are both small it just doesn't make any sense to me. 

I tried playing around with backlash.  I put a dial indicator on each axis.  Jogged it .100 in one direction and then .100 back to zero.  It goes right back exactly to zero.  If I had backlash it would have undershot the zero and not made it all the way back.

One of the other posts mentioned maybe inaccurate leadscrews.  The ones I bought were the 1/2 -10 single start from Enco.  They aren't the best but aren't hardware store threaded rod either.  How would I go about checking them for accuracy?

Keith

3

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

« on: February 19, 2011, 04:03:38 PM »

Looking at the driver mfg website it looks like I may have the step active wrong.  It should be active high and I think it may be active low.  I will also try cutting in the other direction tonight to see what happens. 

The material is just 1/2" mdf and I am using a 1/4" upcut spiral bit.  I already have a finishing path programed.  It takes .020 on the last pass.  With the soft material I doubt that it is tool flex that is causing the issue.  I don't really expect to get .001 accuracy with the machine but it is really throwing me why both inside and outside cuts are coming up small.  Things like runout, tool diameter, flexing, etc should all make the inside and outside cut sizes opposite of each other.  If one is big the other should be small.  Seeing how they are both small I was thinking that maybe it is the software or controller that is causing the issue.  It could be the active high/low problem but I would think that I would only be off by one or two steps with each move.

Keith

4

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

« on: February 19, 2011, 10:53:41 AM »

I can go up to 1/8th microstepping on my controllers but have kept it at single step just for simplicity for now.  I will try upping it and see if it helps.  I am pretty sure I have the step and direction active settings correct.  When I jog the machine it goes in the correct direction.  What would setting the step active high vs low do?  Will it still work in either one or would the motor not turn if I had it wrong?  The pulse width is set to 5.  It doesn't seem to be missing steps since the dimensional error is repeatable.

Keith

5

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

6

General Mach Discussion / Re: Hesitation between Lines of G-code

« on: February 16, 2011, 05:41:15 PM »

Here it is.  I tried a few other settings quickly.  The amount of pause is directly proportional to the accel rate.  If I up the accel rate you can still hear the quick hesitation but it is alot harder to actaully feel.

Keith

7

General Mach Discussion / Re: Hesitation between Lines of G-code

« on: February 16, 2011, 04:51:17 PM »

What is an xml?  Do you mean the g-code?

Keith

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General Mach Discussion / Re: Hesitation between Lines of G-code

« on: February 16, 2011, 03:56:44 PM »

No.  As far as I know, backlash is turned off.  I checked backlash with a dial indicator and it was under .001 so I didn't bother to turn it on in Mach3.  Even if it was turned on, it shouldn't make a difference with two straight lines in a row.  If I write a program that such as:

G01 X0 Y5 Z1
G01 X0 Y10 Z1

I wll get a slight pause when it goes from the 1st line to the 2nd one. 

Keith

9

General Mach Discussion / Re: Uneven cut on letters

« on: February 16, 2011, 02:32:36 PM »

Your friends v-cave sofware is an illegal copy.  There are some copies floating around on the net of the vectric software and they all have this problem.  They all work fine except for the z-axis which is set to constantly either ascend or descend from the intial dept set.  Vectric was smart and leaves out certain parts of the code for their software until you actually purchase it from them.  The correct post processor code is one of those pieces left out.

Keith

10

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