I am “engraving” a half inch line with trochoidal oscillation to find out what speeds my MPCNC can handle. Estlcam has an option for for trochoidal oscillation that defaulted to 0.002" for me. I was playing around with the other settings, and was just leaving that at default at first. I ended up disabling and noticing that I could increase the step length and feed without getting chatter then. I know settings will vary with each build, but I was curious if anyone else ran into issues when using the Z oscillation, and if anyone had thoughts about if it would be better to run smaller steps and slower speeds so it can be used, or to disable it and run the larger steps and faster feed. I also thought I was having an issue with chatter at the initial plunge into the work, but I think it’s actually just the aluminum tearing out.
And just because I like to add pictures, here is my test block. The large square and the one hole in it are from some previous experiments, before I realized I was getting aluminum chips all over my control board. I was holding off on doing aluminum until I get an enclosed case finish, but then found some aluminum sheets in my garage that I decided I wanted to use for the case panels. I ended up rigging up a temporary shield using a housing that covered something on an industrial paper cutting machine I scrapped last fall so I could take the motors and encoders off of it.
When I pulled the block off the table to inspect in closer, it looks like the swirls for the initial plunge are just wider than the cut. I have a couple that I ramped in at 25 degrees, and the ramp is wider than the actual cut as well.
I am trying out trichordal cutting for doing the part cut outs as well, not just for pocketing. I did a couple squares that were supposed to be 1/2", but both ended up about 0.03" over. On the bright side, both were consistently 0.03" over, so I don’t think it’s due just to deflection from the router. I need to do some testing to figure out if I changed something that threw off the mm per steps, or maybe if it is just deflection.
I did one with a finishing pass, and one without. Both had the same error. I butted my endmill up against an edge, the moved it away from it 6cm, and measured the distance with calipers, and it was pretty much spot on (within margin of error I could get my my calipers). I am thinking it may be deflection in the endmill when trying to do a 1/8" deep cut all at once, but when I choked up the endmill further into the collet, I don’t think I tightened it enough, and broke my end mill. Of course I just cleaned in there, which means I can’t find where I put my end mills now.
I thought to check the width of the “engraving” cuts I did when first testing trochoidal cutting, and they are actually narrower than they should be by about the same amounts that the 1/2" squares are over. So the trochoidal cutting isn’t doing the diameter it should, but that wouldn’t explain why the finishing pass was off too. I think I may need to slow things down past the point of just not getting noticeable chatter. My Z-axis is pretty high still since I don’t have a dedicated 3D printer yet. I should hook a pen back up and do trochoidal cutting and measure the outer diameter of the swirls to see what it is.
