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Parts smaller than they should be.
« on: July 23, 2015, 04:13:03 PM »
I purchased a cnc plasma table running mach3. I've figured out how to turn drawings into Gcode using Inkscape/sheetcam.
I can cut them on my table and they turn out really nice except that the parts cut are coming out proportionally smaller than the drawing.
For example, a piece that's supposed to be 11" long, ends up being about 8" long.

When I measure the part in sheetcam, it shows that it's the correct size. But the part always ends up proportionally smaller after cutting.

Any idea why this would be?
Thanks Kindly

Offline ger21

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Re: Parts smaller than they should be.
« Reply #1 on: July 23, 2015, 04:23:48 PM »
Your steps/unit is set wrong.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Parts smaller than they should be.
« Reply #2 on: July 23, 2015, 04:40:38 PM »
Wow!! Thanks for the speedy reply ger21! I'll dig around for a tutorial on that and try and figure it out.
Much appreciated!! ;D
Re: Parts smaller than they should be.
« Reply #3 on: July 23, 2015, 06:33:56 PM »
The guys that i bought the table told me to make sure to set the scaling to 'metric' upon processing in Sheetcam.
I'm thinking I may have somehow changed the units to Inches in Mach by accident, so the steps were probably originally set for millimeters
since metric is the standard up here in Canada.

When I go into Mach settings, I see the little light under the Units selection is lit 'green' under Inches.
But when I try to click the button  under 'Units'  to select MM (The one with 'Cntrl U' under it)  to switch it to MM ,it won't change.
Should  i be able to change it there? Is there another place to change it?

Thanks again for the help.
Dan

Offline ger21

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Re: Parts smaller than they should be.
« Reply #4 on: July 23, 2015, 07:59:32 PM »
metric to inches scaling issues will have you off by a factor of 25x.

First. go to Config menu, and select "Select Native Units".
If it's not mm, then change it to mm, and close and restart mach3.

Next, go to the setting page and see if it's in inches or mm's.

If it's in inches, go to the MDO page, and hit the "enter" key on the keyboard, and then type "G21", and hit enter again.

Then close and restart Mach3.

Then jog the machine and see if it's moving the correct amount. If not, your steps/unit are wrong.

Make sure that you're using a metric post from Sheetcam, and that there is no G20 in your g-code.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Parts smaller than they should be.
« Reply #5 on: July 23, 2015, 11:02:20 PM »
Thanks very much!!
One thing, and I'm sure this is going to be a dumb question but....
Is the MDO page found in the menu in Mach?
Not sure what that is.

Thanks again for your help
Very much appreciated
Dan

Offline ger21

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Re: Parts smaller than they should be.
« Reply #6 on: July 23, 2015, 11:03:41 PM »
Sorry, that was supposed to be MDI.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html