Dimensions 90% of programmed dimensions

[belfi]

Hi there,

Help please! I am new around here and completely new to CNC Plasma. My partner previously just used a handheld plasma. We have a Fangling 2300AX controller and use FastCam. What we are currently struggling with is the cut dimensions are not matching the programmed dimensions of a file. It is cutting about 90% of the specified dimensions. However, if we use a pre-programmed shape on the controller, it cuts that exactly to the correct size.

Attached is the G-code from fastcam and G-code and the controller G-code file. I note the G code from the inbuilt shape on the controller looks quite different to the one from FastCam. The Fastcam file does cut but the dimensions are only coming out at 180mm x 180mm.

Any ideas to resolve this would be greatly appreciated. It seems odd to me that the inbuilt file is the right dimensions, but any other files are not. So seems like this is maybe a file issue rather than a calibration issue.

Thanks
Fiona

G-Code 100mm square Controller.jpg

G-Code 200mm square FastCam.jpg

[adbuch]

I expect that either you need to scale your files to a size that matches your required output cut size, or adjust your "turns ratio" in your control software so that when you command it to move an inch, it actually moves an inch. This is often measured using a dial indicator for an accurate measurement of the travel in the x and y directions. The photos below show using a dial indicator to measure the actual travel vs. the commanded travel. This is for a Centroid Acorn cnc12 system, but the same principles apply to other tables as well.

David

20191123_234024_resized.jpg

turns ratio.jpg

[weldguy]

I hear what your saying David however the OP mentioned that if he uses pre-programmed parts from the controller they cut to the correct size.

Given that the parts are 20mm under size (10mm on each side) I think it may just be the kerf width that is causing the under size parts.

It is possible that the pre-programmed parts account for the width of the kerf.

Do you know if you are entering the kerf width anywhere in the FastCam software?

[acourtjester]

There are some checks that can be executed to insure the correct size. Using other software to verify the correct size or use a pen plotter to mark on paper to save metal before cutting. I use Inkscape to check the object size (outside dimensions) to upsize of downsize as needed.
Moving between software packages can effect many things in a file. Many member use different packages to check or to make changes or change file types while planning a project.

test size.JPG

[adbuch]

I hear what your saying David however the OP mentioned that if he uses pre-programmed parts from the controller they cut to the correct size.

Given that the parts are 20mm under size (10mm on each side) I think it may just be the kerf width that is causing the under size parts.

It is possible that the pre-programmed parts account for the width of the kerf.

Do you know if you are entering the kerf width anywhere in the FastCam software?

Weldguy - I would assume that the preprogrammed part and the other parts are all using the same kerf width setting, unless the OP has changed that setting in the meantime. Also 20mm is about 3/4", so he would have had to put in a kerf width setting of around 3/8" (0.375") - which makes no sense to me. My typical kerf width settings are usually less than 0.050".

David

[weldguy]

Weldguy - I would assume that the preprogrammed part and the other parts are all using the same kerf width setting, unless the OP has changed that setting in the meantime. Also 20mm is about 3/4", so he would have had to put in a kerf width setting of around 3/8" (0.375") - which makes no sense to me. My typical kerf width settings are usually less than 0.050".

David

Good point David. I had 2mm on my mind despite reading and typing 20mm in my reply. Damn metric system messes with my mind every time

[belfi]

Thanks so much for your help everyone. It turned out to be a combination of both the kerf settings and also the turns ratio in the controller software. We now have this sorted to the right size. Many thanks

[weldguy]

Great to hear and thanks for posting back with your results.