Wrong hole size

When using the 2D adaptive strategy in Fusion 360 (with a 1/8" carbide endmill) the hole cut (in 3/4" MDF) is small. The CAD diameter is 7.6mm but the cut is 6.6mm.

Information:
Machine was made and not purchased, Running RAMPS 1.4 with the most recent dual endstop firmware (from Ryan’s github)
I am using the post processor for fusion found here: https://www.v1engineering.com/forum/topic/fusion-360/page/6/#post-22917

Are you using a finishing pass?

Are you using a finishing pass?

I have turned the “stock to leave” option off and take a very small width of cut. I do not use a finishing pass though.

Try it with a 0.5mm finishing pass, a little slower than your normal cut.

I changed my 1/8" endmill from having a diameter of 3.125 mm to having a diameter of 2.125 mm and now my holes are the right size… What setting in fusion could be responsible for this?

Have you measured the actual diameter of your endmill, either directly or indirectly by plunging it and measuring the resulting hole? I’ve never had a problem with fusion giving me a different hole size than I have in the model.

I have measured the cuts from jogging a moving tool, the cut is closer to 3.17 than 3.125. The huge problem is that the end dimensions are off by 1 mm. This isn’t an issue with the firmware or deflection, there is clearly something that I am doing wrong in fusion but I don’t have enough experience with fusion to figure it out.

I would say do a quick test in estlcam to see if the results are the same or better. Fusion is extremely hard to troubleshoot because of all those settings. Try in estlcam, we can easily figure out there what settings you need and what size hole you get. This will give results you can get then have something to compare to in fusion, but I do not use fusion for this reason. I do not need 5 tabs of settings, I just need a part.

If you only want to use fusion you will need to provide screenshots of all your settings tabs, tool tab, and post processor settings.

Reviewing the options in fusion, nothing catches my eye that would seem to cause that. Have you checked the tool configuration in the fusion tool library?

I 2nd Ryan’s recommendation though to make a test cut in estlcam though, that would rule out machine/firmware issues.

Does fusion use the diameter or the radius for its CAM?

Looks like the full diameter.

UPDATE: I had a friend who also has a MPCNC send me some Gcode and the hole his gcode produced was the correct size. This means that the error is definitely the way I have my cut configured in fusion since he also used fusion to generate his gcode.

I will update this post when I find what setting in fusion was messing up the hole size.

Had a thought on this over the weekend. What is the depth of cutting surface on your bit? Are you cutting through with one pass in 3/4" material? If the length of cut on the bit is less than the the depth of the material it is only going to be able to cut the helix portion. When it tries to enlarge the circle, the shank part of the bit above the teeth will just ride on the material keeping it from cutting.

The length of the flutes is not long enough to cut the hole at depth so I run the cut in 2 passes. However even when I run a cut to a depth less than the length of the flutes the hole in 1 mm undersized.

I messed around with fusion to try to figure out what parameter is causing the hole to be undersized but I have not found the correlation yet, will keep you updated.

Don’t know if it will help or not, but here are the settings I used this weekend for a 1/8" endmill cutting a series of 9mm holes for threaded inserts for my spoil board. 9mm holes in CAM made 9mm holes in the board. I use a different post processor though, it is here on the forums somewhere, called MPCNC_Mill_Laser. It should be here.

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