Toolpath misses some pockets and/or does unwanted passes over face of material

[maxxxw]

Hi,

I'm pretty new to Fusion 360 and trying to create a tool path in CAM but unable to get what I want. I think I am missing one of the tolerance settings or something similar. I think the issue could be that I have 12mm pockets and a 12mm tool. If I switch to a 10mm tool then all pockets are cleared but with 12mm some are left.

The issues are in two operations...

Ramp clearing (pic 1): Some pockets are missing from the tool path. I can't work out why. I've measured the model and they are all the same width (12mm).

3D pocket clearing (pic 3): Same issue as with ramping but also I don't want to do passes over the top of the material. The material is already flat and I don't to waste time on this. How can I stop this? It's the blue tool path lines.

Thanks!

[LibertyMachine · Accepted solution]

Welcome to the forums!

To answer your questions, in no specific order:

Changing the tool diameter to 11.999 mm completely clears everything. There are other ways of getting it to work with the same sized tool, but it involves different selections and fiddling. Easiest thing is to tweak the size just a bit (it doesn't take much).

Of course, you might notice that it's now doing a return pass that is basically cutting nothing. And that's true, it is. Again, the way to get around it would be with different selection methods, such as a simple 2D Contour and selecting only one side of the slot, using Multiple depth passes and it would probably be a better solution for this exact part.

For the Pocket operation, setting the Top Height to "Model Top" eliminates the pass it does on the top surface.

Ramping is a 3D finishing operation, typically used for a part with more....features. Think of a car or a cone. Ramp is a great tool in those aspects. For a relatively 2D part such as this, it's not applied properly. 

Honestly, if you're going to be roughing out the part with a tool that is already "to size", there is going to be nothing left for you to come back and take a finish pass. If you want to take a finish pass on all the surfaces, I strongly encourage using a smaller tool.

[maxxxw]

Thanks very much for the reply.

Changing the tool diameter to 11.999 mm completely clears everything. There are other ways of getting it to work with the same sized tool, but it involves different selections and fiddling. Easiest thing is to tweak the size just a bit (it doesn't take much).

Yes, that worked. OK then that means that my model is not 100% accurate, that's annoying. I checked with the ruler but this time selected "All decimals" for precision and sure enough it was 12.0000000000000053mm. That's really annoying because I did everything snapped to the grid or by typing the angles or distances. Is this normal? Is there an obvious beginners mistake I made in my model to end up like this?

For the Pocket operation, setting the Top Height to "Model Top" eliminates the pass it does on the top surface.

Yes, perfect, thanks! 

Ramping is a 3D finishing operation, typically used for a part with more....features. Think of a car or a cone. Ramp is a great tool in those aspects. For a relatively 2D part such as this, it's not applied properly.

Great, thanks for the tip.

[LibertyMachine]

This is completely normal. There are always rounding errors at some level in CAD systems. In this case, it's such a negligible value, you learn to just roll with it

[maxxxw]

Is another setting like "don't do an extra pass if it's only for 0.003mm" Instead of editing all the tools to be smaller?

[LibertyMachine]

No, not really. Your best bet would be to go to 2D Contour and select a  single line. I seem to recall someone at one point someone had found a way to do it in one shot, but I don't think it was a pocket routine....

[daniel_lyall]

@LibertyMachine traces can do it in one shot buts it dangerous if you don't know fusion's cam to well, the cutter and sketch has to be dead nuts.

[maxxxw]

Just a follow up for anyone else who finds this thread, I was able to get it to work with the 12mm tool by just setting the tolerance to 0.1 mm (it was on 0.01). Then all pockets were done.

I tried the 2D pocket but couldn't work out how to get it to step down at 2-3mm at a time? It seems to want to mill the whole depth of the pocket.

Anyway, thanks again for the replies.