Milling 3030 T-Slot Extruded Aluminum

I’m upgrading my Prusa i3 MK2 printer with a 3030 aluminum frame. I need to drill and counterbore eight 8mm holes so that I can bolt the frame together. Any ideas on how to set up ESTLcam mill out the counter bore and then drill the 8mm hole?

Are you going to be doing the counter bore with the same bit?

You can have a helical hole for the counter bore. Define the depth, then make a drill or helical bore for the drill. You can have it just start at the top, which will cut away imaginary material when it’s going through the bore, or you can change it’s start depth. Be aware that the total depth is the depth plus the start depth. So if you have a 1mm counter bore, and you’re cutting 3mm deep, the drill operation would start at 1 and be a depth of 2, not 3mm.

EstlCAM should cut them in the right order by default, but if that’s ever wrong, you can define the order for each operation manually, by setting the counter bores to 10 and the drills to 20 or something.

I’m hoping to use a 1/8" or 1/4" single flute end mill to do the counter bore and hole.

Pocket or helical drill.

OK, good. Then I think my answer is right. Ryan is right that a pocket would also work. You’ll need the counter bore in the design.

Another thought I just had is where to set the xy zero point. Should it be in the center of the design or the distance from center of design to end of workpiece + raduis of tool? For example, two of the holes need to be 100m from the end of the workpiece.

Hmmm. Yeah, setting up that cut is going to be the tough part, for sure…

You could put a 1/2" chunk of ply in the CNC, then cut out an ‘L’ shape, with an overcut in the corner, then put the 3030 in that corner. That would make it square to the CNC, and have the right offsets. You’d just make sure the ‘L’ cut has the origin in the corner, and the 3030 cut has it’s origin in the corner, and then you just make sure you don’t turn the motors off between setups.

If I were doing it, I’d just set up a single cut. Draw a circle the diameter you want the counter bore to be. Put a second circle centered in this circle that’s 8mm in diameter. Put your zero point centered in this circle. Select helical drill for the outer circle, set it however deep you want your counter bore to be. Make a second helical drill for the center circle and make it pop out the other side, give it half a millimeter or so. Now you just mark your extrusion with where you want your holes and center your bit on those holes, rezero and hit go. You could even do what Jeff mentioned, but just put a single piece of straight plywood on the outside of your L. That way you have a reference so all your holes are aligned. If it’s off along the length a little it shouldn’t be too bad, but side to side is where you want it straight.

I think the main difficulty here is to make sure the holes will be 100% parallel to your extrusion.
For this, I suggest you to use the probe functions of Estlcam, there is a nice feature which allows you to check for alignment and automatically compensate via software. Just use a long alignment probing distance, to make this as accurate as possible.
This way, you can make sure that everything is aligned very easily.

Also, I don’t suggest you to make deep holes, just mark the spots by drilling one or two millimeters with a tiny bit, then use a drill press. There is a good chance to screw up if you try to drill through the whole thing with the MPCNC.

I think I’ll test your suggestions on some spare 2x4s and then go from there. Thanks much.