3D Pocket Clearing - manual Stepover for Ball endmills

[Anonymous]

So I have this 3D surface I want to machine out of MDF. My plan was to first use a 3D Pocket operation for Roughing and then a Scallop toolpath for the finish - both with an 8mm ball endmill.

When I'm configuring the 3D Pocket operation I'm prompted to set the stepover manually, that's logical to me because Fusion doesn't know what grade of finish you want wo achieve with this operation. I just want it to remove material as fast as possible and don't care about stepover cusps. So I'm manually setting the max stepover to 8mm and the min stepover to 6mm and tick the box for allowing stepover cusps.

The problem is, regardless of what I fill in for the max and min stepover values, I always get the same result. The calculated stepover is something between ~2mm and ~6mm. This is unnecessarily wasting my time and the machine and endmill could handle higher stepovers.

Has somebody experienced the same problem or knows a fix for it?

[Anonymous]

What value do you have in the "Stock to leave" parameter? If that is the default 0.020", then the amount in the cusp would be larger than 0.020" on any surface that wasn't nearly flat.

If you are using an 8mm ball mill, then 6mm stepover is still very aggressive and will leave a very irregular surface for the finish pass. The goal is to get as uniform a surface as possible for the finish pass so the cutter bends by a uniform amount. Any change is the amount of force on the cutter will show up on the surface of the finish cut. In your case it may not matter, but in other materials this will result in an orange peel look to the part.

Also, many people don't realize just how rough MDF is on cutting tools. The binding glue in the fibers is very strong and dulls cutters very quickly. 

[Anonymous]

Stock to leave is 1mm. And yes, you're right with your explanations and I'm aware of the abrasive nature of MDF. But the problem is that obviously i can't manually control the stepover for ball cutters. For said 8mm endmill it won't go higher as perhaps 5mm. Even if the minimal stepover is set to something above 5mm.

[kb9ydn]

It appears that the step over settings are limited to the radius of the tool or less.  So for your 8mm diameter too the maximum step over is 4mm.  I'm not sure if this is an arbitrary limit or if there is a specific reason for it.

C|

[XanderLuciano]

Well I really wouldn't recommend doing this, but technically it will work.. you can tell the CAM you are using a 16mm diameter tool, set the stepover to 8mm, then set the radial stock to leave to -7.95mm (it won't let you set it greater than or equal to the tool radius), and the axial stock to leave to 0. This should give you the toolpath you desire. Just note the calculated cusp heights will be incorrect since it's a larger tool, but the toolpath will be like what you are after.

Xander