So I want to make some skis… it seems much easier to make the moulds and cores with a CNC router, so I decided to have a crack at the MPCNC as a kind of practice and to use for some other projects - pretty sure now I’ll end up with a Lowrider as well for the actual task…
Apart from some difficulty flashing the Rambo board with the dual limit switch firmware, the build was super simple! I used some aluminium extrusion for the base frame that I, ahem, aquired from the scrap pile at work (as i’m the guy who decides what we write off…as well as being the guy who orders it - theres a conflict of interest in there somewhere). The RH in the garage changes pretty rapidly and everything goes wonky if its only made of wood.
The rails are 1.5mm x 25.4mm SS. Regretted this immediately as soon as I tried to drill them. Forgotten how hard SS is… its also a bit unnecessary on this machine i think.
Bought a 0.8kw chinese spindle doodah from ebay and immediately took it apart to see what everyone was complaining about. Seems ok to me for the money. Smooth as silk once i’d figured out the VFD settings for the 400hz spindle (the VFD comes setup for 50hz) - even the ER 11 collet nut has been balanced (!?). Some people seem to have an issue with runout on these spindles, pretty sure thats not going to be a limiting factor in the accuracy of this machine. Need to run it pretty fast as its air cooled though.
Messed around with Estlcam for the first time today, some MDF and a 4mm ball end mill. Seems to work. Cut some test shapes (all within about 0.2mm), letters, and checked the repeatability of the limit switches by doing the oval three times between homes (the central line is about 0.75mm wide and fairly consistent around its length). Got some work to tweak step overs for each mill size, and feed rates, but pretty happy!
I’m using a touch plate for z homing. (crocodile clip and a sliver of that old tape measure with the paint sanded off…)
Some tidying up to do - the power cable for spindle, gnarly case lid, somewhere to sit the laptop…
The message would have been clearer with a smaller mill…
Sexy in the black and silver color scheme! Would recommend you slide the Z lower up to the bottom of the flexible coupler to support it with the bearing. This will also reduce backlash of the leadscrew.
Good call Mike, I stretched the coupler a little when tightening up the grub screws, to ensure the leadscrew is tight against the stepper shaft, but can’t hurt to also move the bearing support up a bit too. Pretty sure my base isn’t any more accurate than 0.5 - 1mm at the very best over the whole area, so a bit of backlash won’t make an appreciable difference in my use-case.
Every little helps though.
In truth, the spindle has such a long shaft that the Z axis is a bit low - I need to re-drill the holes for the tool mount in the tubes and raise it slightly to get some more Z travel at some point.
Actually, I guess it really isn’t backlash, per se, but the weight of the spindle and/or pull of the bit cutting can cause the coupler to stretch. If you capture it between the shaft of the motor (by butting the leadscrew and shaft together like you did when pre-stretching the coupler) and the lower z mount, then it has no where to go. Should you decide to surface the spoilboard, you will find you can keep some pretty good tolerances in the z axis.
I’m in the same boat with the makita router. Debating on whether to try to raise the tool or lower the center portion of the bed. I feel like raising the tool still won’t be the best choice as the z rails will still extend significantly into the work area at times. Decisions, decisions…
Hello Pete! Im on the way to buy a 0.8 kW spindle like you. In this 2 years, is it happen something wrong or is it a nice spindle?
And… What inverter do you use? 1.5 kW ? Thanks
Hi Alfio, yep the spindle is still ok, and the inverter is the 1.5kw model, which also seems to be ok. Programming it was pretty straightforward once I’d figured out how it’s supposed to work in terms of frequency and phases etc (I’m not really that familiar with the mechanics of motors etc)
I ran into loads of problems with resonance though, so I made the MPCNC into a plasma cutter instead. For this it works fine, and is a joy to use (once I’d figured out how to stop the interference from the plasma cutter nailing the electronics mid-cut…)
Using it as a router, with the spindle running at certain rpms and feed rates I’d get resonance and the cut would be ragged and holes would end up the wrong size etc. Its probably cos the machine is pretty big (too big for anything with lateral resistance to the cut, except for vinyl cutting). I’d recommend looking at other designs if you need a larger format router. Like maybe the lowrider, or the oxcnc stuff that might be my next project…
Thanks a lot for update. I love hear that the mpcnc is still running … I can’t imagine how beautiful it is now with plasma cutter mount!
Your problem with resonance it’s 90% the long conduits problem. Mine cnc has got standard dimensions. 300mmx 300mm (And is still big !!) , I’ll hope with 0.8 kW cut aluminium better than 500W DC spindle.
Cut some test shapes (all within about 0.2mm), letters, and checked the repeatability of the limit switches by doing the oval three times between homes (the central line is about 0.75mm wide and fairly consistent around its length). Got some work to tweak step overs for each mill size, and feed rates, but pretty happy!
