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cuts are off a bit
« on: January 28, 2008, 04:55:41 AM »
I cut out some router clamps out of MDF using mach, the outside dimensions were about 1/16" too big, and the inside circle cutout was about 1/16" too small in diameter. I checked the g-code and it looked dead on (the farthest points away from each other were exactly what I designed). I've been through the steps per axis over and over and they are correct. I can't tell if it is a mechanical problem or software. Is there a way to compensate for this in mach?

I cut a few other things as well, and they all are off about the same.

Thanks!

Offline Hood

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Re: cuts are off a bit
« Reply #1 on: January 28, 2008, 06:02:02 AM »
Have you allowed for the cutter radius in your code? If yes do you possibly have offsets set up for the tool you are using?
Hood
Re: cuts are off a bit
« Reply #2 on: January 28, 2008, 02:58:07 PM »
I did allow for the cutter radius in the code, but in Mach, I'm not sure how to set up the offsets, nothing is different from the normal setup of the program. I went through the manual, may have missed something, but I'm confused. I'm using a 1/4" straight end mill to cut through MDF.

Offline Hood

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Re: cuts are off a bit
« Reply #3 on: January 28, 2008, 06:09:37 PM »
Try putting a G40 in the start of your code and see if that helps.
If that doesnt help can you attach your code and xml. You will need to rename your xml to be able to attach it here on the forum.
Hood
Re: cuts are off a bit
« Reply #4 on: January 29, 2008, 09:59:43 PM »
OK, tried putting G40 in the start of my code saved on the controller computer, didn't change anything. The router also jerks while cutting circles or arcs, which makes me think it could be a mechanical issue, but I tried generating a circle from one of the wizards in mach, and it seemed to run much smoother, but it also had a bigger radius as the mach wizard just sat there when I tried to make the diameter 3.5 like in this gcode.. So I'm back to wondering if it is the computer or some software issue.

The machine jerks like this whether or not it is actually cutting. I ran it while 'cutting air' and it didn't change the jerking action.

I have attached the GCode I am using, I don't know what you mean by xml. ?

I would really like to get this thing running perfectly (to my standards anyway), I have a lot of time and money wrapped up in this project. I appreciate the help!

Offline Hood

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Re: cuts are off a bit
« Reply #5 on: January 30, 2008, 05:29:58 AM »
The xml is in your Mach3 folder, if you are using a standard mill profile it will be named Mach3Mill.xml if you are using your own custom profile it will be whatever you called it.xml

 I will have a look at your code later  today when I am finished milling but from a quick look it doesnt seem great code generation as the circle is made up of lots of short straight lines rather than arcs. What did you use to generate the code?
Hood

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Re: cuts are off a bit
« Reply #6 on: January 30, 2008, 08:19:17 AM »
OK had a look at your code and if you are using a 1/4inch cutter the inside circle will come out at 3.25 inch Dia . The outside sizes will be X= 6inch Y=5.875inch.

Is this the size it is meant to be?

Hood
Re: cuts are off a bit
« Reply #7 on: January 30, 2008, 02:23:58 PM »
OK,

So, in the code, the farthest points away from each other repsective to the circle are 3.25". I thought this was the center of the bit? So If I'm using a 1/4" bit, shouldn't it be cutting 1/8" extra off all sides? Where am I wrong?

The circle comes out to 3 7/16" when its cut. The outside dimensions come out to a little over 6" on the X, almost exactly 6" on the Y. Please excuse my tape measure. I'm new to CNC and have a digital caliper on the way.

The other issue is the jerking. I have been reading other issues with cutting circles. I have found that some software exports dxf files as a bunch of little lines instead of true circles. I'm using AutoCAD to design these things, any thoughts on that? Does the G Code look any different for true circles? I'm also curious if changing the CV settings in Mach will help out at all?

Thanks!
Re: cuts are off a bit
« Reply #8 on: January 30, 2008, 02:29:30 PM »
Whoops, I missed that you already answered that it is made up of a lot of lines.

A friend of mine had his buddy at work generate it with ArtCAM. I put most of my funds into the machine and havn't really decided on a CAM option yet. I wouldn't mind using LazyCAM but it is a bit difficult to understand.

Is this a CAM issue, or could I be saving it wrong as a dxf? I need to save it as an R12 DXF or nothing will open it, not even lazycam.
Re: cuts are off a bit
« Reply #9 on: January 31, 2008, 03:30:44 AM »
OK, so I watched a lazycam video and it no longer looks COMPLETELY foreign to me anymore. I generated the gcode as attached here, does it look better to solve my jerking motions?

It uses G2, which is apparently this 'clockwise interpolation' to cut the arcs, which I'm trying to understand what that actually means from the limited definitions I can find on the net. The G code is a little wacked out, but I think it will work a bit better, I'll test it out tomorrow.