2D contour model vs reality error

[wouter.piessens]

Hey all,

Newbie here...relative new...having been using Fusion 360 for about 2 months, in combination with a Ooznet Workbee and Makita router.  

This weekend I was trying to make simple joints for a box, and noticed that simulation does not match the actual cnc milled result.  (see drawing below, backup file also attached)

The distance between A & B in model is 18mm, but CNC mills it as approx 16m.  The distance between C&D is also meant to be 18mm, but CNC mills it at 20mm.   I am using a 1/8 inch (3.175mm) 2 flute up cut bit, which I have calibrated in the tool library. It looks like an offset of approx 1 mm for the router axis.

I am at a loss why this happens. Am I overlooking a setting somewhere?

[seth.madore]

First off, the tool that you have defined in your toolpath is a .25" tool, not .125". However, that would make external features quite small, and internal features quite large. Assuming you have mistyped what you're using in your original post, it looks to me like either deflection is occurring, or the scaling on your axis is slightly off

[wouter.piessens]

Thanks for replying.  It wasn't a typo, but looking back at the backup file, I do wonder why I didn't see the 1/4 inch tool earlier. I edited the file in F360 before posting here (for next testrun), and perhaps that is where the change in router bit happened.  Thanks for pointing it out, either way, thanks.

Scaling: It happened in all "pockets", exactly same way, so that rules out scaling along one axis, I am afraid.

Deflection sounds possible though, and presumably hard to fix.   I was running at 2540mm/min along x&y,  with approx 19000 rpm in the router. I guess I will have to reduce some of these speeds, and try again, right?  

I will test again later this week on an evening. My daytime jobs sits in the way of having fun 😞

[wouter.piessens · Accepted solution]

Quick update here...Done another test run with a subsequent calliper measurement, and discovered the error is caused by the machine or milling tool, not by the software in any way.   I guess I have found the limitations of the CNC now, and will have to compensate in Fusion 360 to overcome those limitation.

This case can be closed. Thanks for helping out.

[jhackney1972]

Normally you close your own Forum posts.  When someone gives you an acceptable solution, your select that post and then select the Accept Solution icon at the bottom.  You have to be logged in, as the poster to see this icon.  This does three things, it closes the post, it allows others with a similar issue to find a possible solution and last it acknowledges the Forum post that gave your the solution.

In this case, you gave your own answer so I went ahead and clicked the Accept Solution icon, on your solution post, for you.  By the way, in a lot of cases you will get more than one post that answers your question, you have the ability to Accept Solution to as many posts as you feel gave you help toward a solution.