Finally cut some aluminum. Used 4mm smw3d bit, 550 mm/min, .4mm doc, 15K rpm.
@Brandon_Byrne Congrats man! It gets easier from here 
I’m just glad I was able to pass that hurdle. Still not satisfied with the results, I’ll continue to tweak things as I go. I added some miters to make the table sturdier, and had the 6061 sitting up on a 3/4 MDF. I actually broke the 4mm bit on this cut; the very tip broke off but I let it continue and it actually seemed to do better with the tip broken off. Before it broke off I think I visually saw the spindle struggle/slow down a few times but once the tip broke it stopped struggling. If I had to guess, too much doc? I’ll try the same settings tomorrow with a new bit and maybe .2 or .3 doc.
Still playing around with the optimal way to cut aluminum for my setup. I am looking at that open source feeds and speeds chart and have a question, mainly targeted at @Eclsnowman . I see that entry you have for 1140 mm/min, .3mm doc, 24000 rpm cut of aluminum; Plugging it into GWizard, it looks like it has a good deflection number and good chipload, however surface speed is 990 sfm. From what I read the ideal for aluminum is 250 sfm. My main issue now is that I get good cuts and chiploads but only with really high sfm (ie, 990 sfm) and my workpiece and bit get extremely hot. How do you deal with workpiece heat? It seems like if I let it go the entire cut it will just get too hot and melt the aluminum chips to the bit.
If I run that fast I melt chips into the kerf. Perhaps that is done with coolant? I run dry.
I have found heat is definitely an issue, higher feed rates help reduce he’s it building up in any specific area, but still the chips come off almost hot enough to burn me. I have experimented with squirts of wd40 which works reasonably well, but the fumes are a little unpleasant. I found alcohol works pretty well but is also a bit of a flash fire risk. I do also run compressed air sometimes which I think helps with cooling just enough.
It seems like higher feedrate and higher RPM works a lot better, save for the heat issue. ie, if I was cutting at 24000 rpm and 1140 mm/min, if I halfed both I should have the same chipload and surface speed… but the spindle seems to really struggle with any RPM under 15000. I’ve been watching videos too to see how other routers look while cutting aluminum and I found this video:
What kind of parameters is this guy running that makes it look like his aluminum vanishes making perfect chips with 0 struggle at all? I want to do that.
My machine is nowhere near stiff enough to run jerk settings that high.
Ahh so many different parameters and things that go into CNC routing. I don’t even know how jerk applies to cutting, except that it’s the derivative of acceleration.
That guys machine is honestly probably a lot more stiff than the R7, so that will help a lot. Its also a question of bit usage, he’s got a 6mm bit there, you can go way more aggressive with that thickness. The bit is also from what I can tell that looks like at least a 2 flute high spiral bit. I have one of those and it really throws the metal away at a high angle. Plus he’s using air so thats blasting away the chips all the time and helping with cooling, that is till he switches to actually using coolant which honestly is the right thing to do for a quality aluminum finish anyway.
But yes, there are SO many variables to play with with CNC and what works for one job may not work for another. It really is a skill that has to be learnt, and re-learnt for every machine you use since they’re all different.
If you want a seat of the pants feel for jerk settings multiply yours by 1000 and run a job in the air. I run my settings that fast when I am using a laser.
PS If you jerk a router like I jerk my laser it will break bits.
I’ve started looking into my spindle settings because at times it seems like the spindle stutters/chokes. My running current with no load is 2A, and the running voltage is 50V. Is this correct?
Are you measuring the current at the spindle or at the wall?
So there are two sides. I am sure you are measuring 50v at the spindle output. Are you measuring current in those same wires or on the wires that go to the wall plug? I can borrow a clamp and measure mine but I want to make sure we are comparing apples to apples.
I wasn’t physically measuring anything, just going off the VFD sensor readings. I don’t know much about VFD / spindle electronics, but it looks like the voltage is proportional to spindle frequency; higher voltage when spindle is spinning faster. My current as read on the VFD (push/hold monitor, use right arrow to scroll to current) consistently reads between 2 - 2.3A depending on if the spindle is free spinning or under load. The max current on the spindle says 10A, but the VFD is reporting only using 2 - 2.3A, so I don’t know if this is some weird 2A per phase or 2A RMS or what. Measuring motor gets screw when you involve motors.
Thank you for that information. I will dig into what I can measure. I was hoping that the voltage and current were constant and only the frequency was changing.
I will have to check when I get home, but is there a variance in these 800W spindles? The one on smw3d says 5A max but I am 99% sure mine says 10A max. If that’s the case, the VFDs on smw3d are preconfigured for the 800W spindles, so my upper current limit might be way lower than what my spindle is spec’d for. Here is the SMW3D spindle picture showing 5A, I will check mine when I get home. This could explain why my spindle seems to stutter at lower speeds, it is hitting a torque limit half as much as it should.
800w at 120 volts is 6.6 amps. We really should get to the bottom of that.