Brushless spindle for CNC router

[CaptainObvious]

Well, mostly printed anyway...

The spindle that came with my CNC router is not very good, at least not for working with hard materials, and since the mountings on the machine only accept a 52mm diameter spindle it seemed that either I modified the router to take other sizes of spindles or made my own custom spindle, so...

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It works very well, at least on the bench; runs smooth, and has very little runout but the front bearings get hot after a few minutes or running it. I was expecting some heat, hence the aluminium front cover to help dissipate it, but this is more than I anticipated; I may had preloaded too much the two angular contact bearings at the front.
The motor is a 700Kv, 1500W brushless motor used for model aircraft, plenty of power there. There's a flexible shaft coupling in the red housing to match the 6mm motor shaft with the 8mm chuck shaft; as mentioned before there's two angular contact bearings at the front (or bottom if you will) and one more on the motor side.

If I have time today I'll disassemble the front bearings, reduce the preload and try again to see if that makes an improvement; if not I'm already milling an all aluminium bearing housing that should help dissipate the heat much better.

[Mjolinor]

Is it an outrunner, it doesn't look like it.

I use an outrunner and it has been running fine for about 4 years.

Which bearing gets hot? Front being top or bottom? I used a 10mm shank so correspondingly 10mm bearings and it works fine for hours.

[CaptainObvious]

Is it an outrunner, it doesn't look like it.

I use an outrunner and it has been running fine for about 4 years.

Which bearing gets hot? Front being top or bottom? I used a 10mm shank so correspondingly 10mm bearings and it works fine for hours.

Yes, it's an outrunner motor, the bearings that get hot are the bottom ones, closer to the chuck. Maybe the other bearing on the motor side gets hot too, but without disassembling the spindle I couldn't tell.
As I said, I'm going to open the front and reduce the preloading and see how that works; besides that I may try different bearings, I'm using ABEC-5 608Z at the moment.

[Mjolinor]

I just use normal 10mm cheapies off ebay, been running a while now.

I did expect them to seize up long before now but I use it mainly for PCBs and wood so it doesn't get much loading. The biggest cutter I have is 3mm but usually it is 0.1 mm that I use.

I just bought a new 8mm spindle and when I find a motor with an 8mm shaft I will rebuild it butt it's fine for now. I only built it initially to see if it would work but it worked that well I never did owt else with it.

[CaptainObvious]

I just use normal 10mm cheapies off ebay, been running a while now.

I did expect them to seize up long before now but I use it mainly for PCBs and wood so it doesn't get much loading. The biggest cutter I have is 3mm but usually it is 0.1 mm that I use.

I just bought a new 8mm spindle and when I find a motor with an 8mm shaft I will rebuild it butt it's fine for now. I only built it initially to see if it would work but it worked that well I never did owt else with it.

For the motor I'm thinking of ordering one of these later on, it has an 8mm shaft so it should make for an easier and more compact installation.

[Mjolinor]

That is what I had in mind but I am tight and won't pay that much. I'll wait till one lands in my lap free.

[CaptainObvious]

Good luck with that

I opened up the spindle and found that a washer between the bottom bearings was rubbing against the bearing shield, that may had been the source of the heat. I'll fix that, put it back together and test again.

[CaptainObvious]

I printed a new version of the spindle, this one using a CNC machined front bearing holder, but I'm thinking of designing a 3D printed one too.
The bearings I've used so far are the 608Z type, which are not suitable for this type of application, so I've ordered some angular contact 708 bearings instead, those shouldn't heat up as the ones I'm using now so they would be more suitable for a fully printed spindle.
The new one can mounted lower on the spindle holder, because it doesn't have the square shape to join the motor holder; the old one was about 1cm too high and short endmills and drill bits couldn't reach all the way down.
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Eventually I'm planning to do a full metal spindle (I've made the design, need to mill it), but I want to test the printed one to see if it works any better than the original router spindle, also to keep it as a back up in case the brushed spindle conks out.

[Mjolinor]

Why don't you dismantle the motor and put the chuck shaft into the motor directly so that the bearings on the chuck shaft have the motor between them. That will allow you to make it much shorter. The motor would be in the middle of your black bit and the red bit would be another machined bearing mount.

I have bought an 8 mm chuck and will get an 8 mm shafted motor so that I can do this when I get round to it.

[CaptainObvious]

Why don't you dismantle the motor and put the chuck shaft into the motor directly so that the bearings on the chuck shaft have the motor between them. That will allow you to make it much shorter. The motor would be in the middle of your black bit and the red bit would be another machined bearing mount.

I have bought an 8 mm chuck and will get an 8 mm shafted motor so that I can do this when I get round to it.

The motor has a 6mm shaft and the chuck shaft is 8mm, so that won't fit, that's why I'm using a flexible coupler in between them. One advantage of that is that I could easily replace the motor for another one, for example I want to use the router to cut foam cores for wings, cutting the foam doesn't require a lot of power so I can use a smaller and quieter motor instead.
The other issue is that the motor is 52mm in diameter, so it has to be placed above the spindle holder anyway.