Aluminum gearbox plates: Inner contours breaking bit

Hello Everybody,

As some of you may know, I am part of a student robotics team called Team 3161. We take part in a global competition called FRC. This year, we designed our own gearboxes and we are cutting the main plates on our Onefinity WW.

I tried using a contour-cut to cut out some lightening pockets in our plate, but the offcut snapped off, jamming the cutter between the part and itself, snapping the endmill. See pic below.

I tried leaving an onion skin, but for the inner contours, it is way too time-consuming and somewhat impossible to de-burr them.

The finish looks pretty horrible in that pic, but I have since dialled in the feeds and speeds + finishing passes for contouring/pocketing, and now we get a much nicer finish.

I could try pocketing all those holes and then run a finishing contour cut, but it would take almost 2 hours to do so using a 1/4" endmill and a legacy pocket-toolpath (non-adaptive). The CAM software I’m using is called HSM and doesn’t have the ability to do tabs :slightly_frowning_face:.

What do you suggest I try? I have to cut 4 of these plates.

Thanks for your help!

If you want to share your model I can do the cam in Fusion with tabs and send it back to you.


Hello Nick,

I’m currently playing around in Fusion, but that would be great to have as a backup if I can’t figure that out.

On another note, I’m looking for more of a permanent solution, as these parts are not the only ones we will be cutting throughout the season. Due to the nature of the season, we try to keep the turn-around time for CAD > PART as short as possible. I don’t want to use F360 (we use SolidWorks) but I might have to :sob:.

Again, thanks for your help. I sent you a STEP file via DMs and I will let you know if we end up using your toolpath!

If your CAM software allows you to control where the cut starts and stops it is possible to do it without tabs. Think about having the offcut piece attached as long and as solidly as possible until the last moment. Then control where that last moment is. In other words don’t let your last pass be too thin. So when the cutter breaks thru the bottom as it cuts around the contour the uncut portion of the contour is thick enough to keep the offcut from moving. Have your start and stop of that last pass be in the middle of a straight section. When the offcut finally breaks loose there will not be a corner of it that can get sucked into the cutter.

This strategy will depend very heavily on the shape and size of the offcut part. If it is small enough to rotate in the pocket once it comes loose then all bets are off. Once you let one corner of that offcut come in contact with the cutter breakage is sure to follow.

Finishing needs to a separate program. Once the roughing breaks that off cut free it should lift ant stop so you can get that off cut out of there.a


You could try doing them as pockets instead of contours. Yes it slower but it’s faster than breaking your bit and starting over.

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Also, I used to coach the Carmel High school team in CA for the First Robotics Competition. Good luck!

Thanks Woody, what team number is that?

It’s 2035. Not to be confused with Carmel ID.

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