DIY CNC router – new 2.2kW water cooled spindle
For Christmas I was lucky enough to be given a new spindle for my DIY cnc machine. Until this point I had been using a combination of a small rotary tool, essentially a knock-off Dremel, and a bosh palm router.
the small rotary tool was good for small bits, however it was not really designed for continuous operation over hours of cnc time, and inevitably it burned out.
knowing full well that the bosh palm router was similarly not really intended for continuous operation I was keen to avoid the same problem. So I looked around and found the wonder that is a 2.2kW water cooled spindle. Then I dropped some heavy hints, and since I have the best wife in the world, she bought me one for Christmas.
It is epic.
the spindle weighs about 5.5kg, It comes with a separate box of electronics (VFD) for managing the 3 phase voltage frequency. essentially you dial up a frequency on the control box, and it sends that to the spindle which maps to a particular rpm.
This is a serious piece of industrial equipment, I needed to buy the appropriate power cabling, and wire it up. I did a lot of research and I have a pretty decent familiarity with doing this sort of thing, I would advise against doing this unless you are very confident. high voltage wiring is not something to take a chance on. I bought a crimping tool especially to make a nice job of the wiring, and be triple sure there were no stray wires making odd connections.
I was initially worried that the z-axis might not be able to lift the additional weight, it is significantly heavier than the bosh router. However it seems to cope just fine.
I also mounted the VFD onto a big metal plate, itself mounted off of a hardwood back piece. this ensures proper air clearance around the box, for cooling etc. the metal plate came from an old tv table I had. At this point that table has been cut up and used into all sorts of different things ;-)The hard wood back came from a hi-fi cabinet my dad made probably 20 years ago. I have a feeling the wood originally came from an x-ray machine room decommissioning (they used to have hard wood tool racks or something), since that is where he wound up with a bunch of such materials during his career as an engineer.
In any case I got everything wired up, and started up the spindle and was delighted by just how quiet this thing is. At full speed (24,000rpm) i can still easily hear myself talk. No more need for ear defenders!
Now this is water cooled, and whilst it will probably be a long time before I really push it hard enough to require the cooling. I set that part up also. I got a huge bucket (intended for wine making) and put in 70:30 mix of de-ionised water and anti-freeze coolant. submerged the pump in it and plumbed everything together. based on my research this much fluid should be able to passively cool around 400watts of heat. That number was an estimate assuming the worst case of a 2.2kW spindle, 80% efficient and thus putting out around 400W of that as heat. If it ever becomes a problem that it is not sufficient I can either add a load more fluid to the reservoir for passive cooling, or I could put a radiator inline. But I’m guessing it will not be an issue.
I have done a couple of test runs, and I’m super happy with how much power this thing has, I actually had an incident with the gcode generated by F-engrave, it was supposed to be metric, but for some reason grbl didn’t like a couple of the commands and wound up ignoring the call to set metric mode. So rather than attempt to plunge 1mm into the surface, it tried to plunge 1 *inch* into the surface. luckily it was doing this along a path and slowly getting to depth so I was able to hit the brakes before it got too far, but by then it was already probably 10mm down and going strong. the spindle didn’t have any trouble at all maintaining 12000 rpm as it plunged on in. But I am not quite ready to stress test it…
The other great thing is that the spindle takes er20 collets which range from 1mm to about 13mm, this means I can use all my router bits, and all my Dremel bits, plus other specialist cnc bits that I bought. It’s a quick change to swap out the collet so no more having to remount different machines to do detail versus heavy work.
However, all this awesome is tempered by one issue which I can no longer ignore. As I have discovered over the course of this project, every time I fix an issue, it reveals another which was previously not significant enough to be noticeable. This time the issue was how poorly my electronics setup handles interference. Previously this had not been terribly evident, however now there is a big 240v variable frequency motor right there, and even with shielding it is obviously putting out some EM. In this case it is getting picked up on the step/dir pins of my easydrivers, and causing the axis motors to twitch (very evident when you start or stop the spindle) and this causes lost steps etc.
So for the moment I am still not able to achieve the accuracy I want, I have on order a bunch of capacitors and the plan is to essentially sprinkle them around the circuit board in an attempt to prevent the EM interference from causing a problem. If that doesn’t work, then I will likely return to the drawing board on the driver electronics, but I’m hoping it won’t come to that. Unfortunately despite having ordered my capacitors last weekend, I’m still waiting for delivery, and Maplin has failed me in that they hold essentially no stock, and 1 cap is not going to do it.