I am currently engraving and cutting aluminum with my MPCNC ( 25mm stainless steel tubing, PLA for all parts except for the spindle holder, 34cm x 30cm work envelope, Makita spindle). The parts are mostly accurate +/- 0,07mm.
But with a 3mm 2 flute HSS endmill it takes ages before the part is finished. When I use a 5mm or 6mm endmill for roughing and the earlier mentioned 3mm endmill for finishing I need two more finishing passes to achieve the same accuracy.
Is it possible to further strengthen the Z-Axis inorder to reduce the needed finishing passes to one? I have already tightened all screws for the bearings and my spindle is mounted so that the collet is level with the bottom of the Z-Axis.
Thank you for helping me to reduce my machining time.
I havenāt experienced milling aluminum yet, but I have spent a lot of time lurking and absorbing information.
Aluminum is possible on the MPCNC, but itās still outside the original design envelope. These machines are designed to be inexpensive hobbyist tools, and not compete with the $$$$ mills you see in some videos. It will never be a fast machine for milling metals. There are inherent āflawsā in the system that can really only be solved by throwing slabs of steel and/or granite along with the accompanying cash at them.
What you currently have looks phenomenal (+/- 0.07mm? Thatās pretty damned tight!) I hate to say it, but if you need moar sped!, then you can either paint it red, or replace it with a $$$$ mill that supports the speeds youāre looking for.
Oh, and maybe switch to a 1-flute carbide endmill. And a speed control for your spindle to slow it down. I think thatās the correct line of thought. Slower spindle speeds, fewer flutes, bigger chips, cooler bitā¦
Iād have to defer to those with more experience for feeds and speeds, not to mention Fusion360 advice (especially on the CAM side of things). I think you could probably get a deeper DOC, but cut back on the WOC a little. Use as much of the cutting surface of your bit as possible, rather than just the tip. But again, I defer to those with more experience.
Why are you needing 2 finishing passes? Is that due to DOC, or step over?
If itās due to DOC, can you reduce the āstock to leaveā from the bigger bits so that you can do a single full depth finishing pass?
I donāt cut aluminum, but when I use a finishing pass, I try to make it full DOC and a very, very small WOC so that the tool can run quite fast around the perimeter.
Increasing rigidity comes mostly from making it shorter, as Kyle said. 2x longer is 4x less rigid. Unless there is something wrong with the machine, there probably arenāt other off the shelf solutions.
My Z Travel is 7cm. Due to my machine vise the part is 2cm higher than the bed. The stick out from the bottom from the Z bearing to the bottom of the steel tube is ca. 4-5cm when machining.
When I use 2 finishing passes the tolerance gets tighter and the surface quality improves. My finishing passes are full depth an remove the 0,1mm stock to leave from the roughing cut.
I was excited to see someone else mention tolerances in that area on aluminum. I always say mine are ā.0x mm tolerancesā and no one ever believes me lol. Your settings look pretty close to mine. I use a 1/8" single flute upcut from Ryanās shop. In fusion Iām usually running 1mm DOC 450mm/s speed for contours/slotting/whatever, and 3.7mm for adaptive cuts. I canāt remember the rest of the settings. I usually leave .1-.5 material for a finish pass. I think .5 is the default, sometimes I remember to change it to .1. For either setting I do one finishing pass and nearly always achieve .0x tolerances on x/y.
Iām running higher rpmās though. I switched to a variable speed makita too but so far Iāve been too lazy to mess with my settings so I just keep it maxed out to match my old dw660 settings.
I used your advice to improve my cutting parameters. It just works and it is fast.
For my adaptive roughing cut I use 2,5mm DOC with 0,6mm WOC, 400mm/min feed and 20.000 rpm.
For my adaptive finishing pass I use the entire depth of the endmill and 0,3mm WOC and 350mm/min feed. The finishing pass removes the 0,1 mm axial and radial stock to leave.
For the test piece a 12mm cylinder with a 8,5 mm square on top and a 6mm polygon on top of that inorder to test x movements, y movements, xy movements and x y interpolation.
I achived Ā± 0.04 mm for the square, +0,06 for the cylinder and + 0,12mm on the angled planes of the polygon and - 0,04 mm for the polygon planes that were an the y-axis.
