Toolpath leaving extra material unintentionally

[thespaltydog]

I'm trying to cut out an opening in a table top for a piece of glass. I ran this on my machine and the dimensions are actually .125" short total in both directions. I've gone through my model setup and both tool paths to make sure I didn't have any "stock to leave" selected. I can't seem to figure out where this is coming from. I tried running the job again thinking maybe the bit deflected the first time around but it didn't cut any additional material off the second time around. 

What I'm looking for:

18" x 22" through hole (2D Contour tool path)

20" x 24" x 1/4" recess (2D Adaptive tool path)

What I'm getting:

17 7/8" x 21 7/8" through hole

19 7/8" x 23 7/8" x 1/4" recess

I've gone through my design and checked all my dimensions. Everything seems to show I should get the right openings according to my file but for some reason it's slightly off when executed.

Hoping a second set of eyes might spot something I'm missing.

Thanks!

Logan

[Joshua.Aigen]

Hi @thespaltydog, because the amount it is off is exactly the radius of the 1/4" endmill it leads me to think that maybe you are doubling your tool compensation. In Fusion I see that it is selected and the post processor will compensate, now if your machine is also doing this compensation then that is another 1/8". 

[thespaltydog]

Interesting, I've never messed with this parameter before and this is the first time I've experienced this issue. So if I updated the value to off then that might fix it? I'm not really familiar with this parameter.

[seth.madore]

@thespaltydog what is your machine and post processor? When you setup the tool, do you do anything more than establish the tool length? (such as defining tool diameter)

Neither of your toolpaths (in your supplied file) invoke cutter compensation, so I'm a bit doubtful of the influence that switching to another mode would have.

At the risk of sounding like a....well, I'll just ask; are you certain that the tool is the proper diameter? You have it defined as .25" diameter. Have you verified that to be true?

[thespaltydog]

@seth.madore I'm using an OpenBuilds Lead1515 machine along with their GRBL BlackBox controller. I import the tool settings into fusion from the manufacturer and use that when selecting my tool. On the machine, I have an XYZ probe that I use to set my position on the machine. When using this probe I do specify the tool diameter which in this case was .25".

I thought the same thing, so I checked the tool and it did measure to be .25" in diameter. It's just confusing because this is only the second job I've done with this cutter. The first job was cutting out different parts from a different file but those came out just fine. 

[seth.madore]

Which post processor do you use in Fusion? Could you share that and your posted .nc code?

[thespaltydog]

@seth.madore Is this what you're looking for? My "Post" is set to OpenBuilds CNC : GRBL/Blackbox / OpenbuildsFusion360PostGrbl . I ended up making my dimensions 1/8" larger in fusion and when I ran the job on my machine everything came out to my desired dimensions. (Still 1/8" shorter than my fusion values) I'm planning on doing some tests with a new file from scratch to see if that fixes anything but haven't had a chance to yet.

Is there a way to attach my gcode file for the post? I tried but it mentions that it's not an accepted file format. Is there a different way to share? My file is around 6500 lines long so I want to check before pasting all that in a forum post. haha