DIY spindle design

[Lee Roberts]

Really nice job mate, have you got any pics or movies of it working ?

[Jeremy]

Thanks, Lee. I'll try and see if I can take some video of it running after I've fixed the lower bearing problem, as long as I can work out how to get the camera to shoot video! (I know it can do it, but will have to sort out how to get Quicktime changed to avi or mpg, I think!).

Jeremy

[Jeremy]

No videos yet, but I do have an update. During bench testing I found that the motor electronic speed controller was getting pretty warm at mid-range speeds. It was fine when flat out, but would get too hot to touch after 20 to 30 seconds at mid-range. I tried fitting a heatsink to it, but there was clearly something not quite right.

After enquiring on an electric vehicle forum (my interest in CNC is to build EV parts) a couple of the more experienced RC model motor guys suggested I needed to derate the controller to a greater degree if it was to deliver higher power at mid-speed. This makes sense, as a model aircraft propeller absorbs power in proportion to the cube of it's rpm, so the controller wouldn't be optimised for running at high currents at part throttle.

I thought I'd been conservative in buying a 40 amp controller when the most my power supply can put out is 30 amps, but it seems that I was wrong. I've switched to a spare 120 amp controller I have for another project and the performance has been transformed. Not only does the controller not get warm, but the speed control is very smooth indeed and the motor starts from a standstill very well. The other plus point is that the motor no-load current has reduced by about 50%, which goes to show how inefficient the original controller was.

Although the motor whines a bit at max speed (around 16,000 rpm) it's not excessively loud. I've been testing it in my study and have so far not elicited any complaints from SWMBO, which would not be the case if I fired up a router in here!

I've still got a bit of fettling to do, including reducing the drag on the bottom bearing, but all told I'm exceptionally pleased with the outcome so far. It looks like it will meet my design goals of being compact, relatively quiet, affordable and fairly accurate.

Jeremy

[Jeremy]

Hi Kip,

Thanks for the kind words, I just need to crack on with the rest of it now!

The cut out in the housing is to allow the Lovejoy coupling to be connected and also to allow the top collar, that retains the spindle in the housing, to be secured. These both have screws that are inserted from the side to lock them in place, with those for the spindle collar being threaded into the spindle itself.

You can buy some brushless motors from UK model shops, but they are much more expensive than direct from Hobby City in China. My experience with using some of these motors is that the really cheap ones are under-rated and not very efficient, but the mid-range ones are surprisingly good, often not much less efficient or less well made than the really expensive ones.

The key is knowing what to buy. The motors are rated in terms of maximum power (in watts) and also Kv, which is the rpm per volt. This latter figure is important, as it allows the use of a motor that will run at the right sort of speed for the application. In general, it seems that using a high Kv motor and then gearing it down with a reduction belt drive is probably a better way to go, as it reduces the low speed torque requirement from the motor. One of the regular contributors on the Ev forum I frequent has converted his Taig Mill to run on an RC brushless motor (his name is Matt Schumaker and he has a web site here: http://www.recumbents.com/WISIL/shumaker/default.htm with some details of his mill conversion, towards the bottom of the page). Matt gave me some advice on motors and controllers recently, quote:

"Jeremy,

I am running a small outrunner on my CNC too. I have over 100 hours on it so far without any issues. I am running a Castle Creations Phoenix35 ESC on it from a 24 volt, 20 amp power supply.

The issue I think you are having is more a matter of the controller than the motor. Also, I am running a belt drive rather than direct drive. For aluminum cutting, I run it 3 to 1 reduction. For carbon fiber cutting I am running 1 to 1.3 overdrive. This gives me 13,000 RPM at the spindle. My Taig spindle uses huge bearings (maybe 1 and 1/2 inch OD). Yet, my ESC runs fine even driving those huge bearings at such a high speed.

You may be having problems partly because of the low motor RPM as well.

A Castle Creations 35 or 45 amp ESC is relatively innexpensive. I would go that route.

Matt"

A look around the Hobby City site will soon give you an idea as to what's available. The controller that didn't work well for me was one of their very cheap 40A SuperSimple series ( see here: http://www.hobbycity.com/hobbycity/s...Simple_40A_ESC ). Maybe I shouldn't be surprised that it didn't work well, as it cost less than $12.....

The controller I have that works well is a complete over kill, as it's rated at 120 amps continuous, 130 amps peak. It's also less than ideal as it is a relatively high voltage unit (30 volts max) and so doesn't have a built in 5 volt regulator to drive the servo tester needed as a speed control. I will probably go for a higher rated SuperSimple controller for the spindle, I think. The 70 amp version looks as if it might well be better, but again it has no BEC (battery eliminator circuit) so would need a separate 5 volt regulator. This won't be a problem if I put the speed controller in the main box, though, as I already have a 5 volt supply available there.

If you want to do some price comparisons, then probably one of the cheaper UK model shop sites is this one: http://www.budget-rc.co.uk .

Jeremy

[Jeremy]

Another update. I took the spindle apart this afternoon and was a bit surprised at what I found. The lower bearing inner bore was stuck fairly tightly to the shaft, and when I got it free there was brown staining on both the shaft and the bearing inner face. It cleaned off OK, but it's clear that the bearing was running much hotter internally than I thought - I think the staining was burnt oil.

Luckily I had a spare bearing, so I managed to bore a naffigravit off the inside of the bearing housing and reassemble the spindle. This has completely transformed it, as it now spins much more freely than it did before. It also runs more quietly and will reach a much higher off-load maximum rpm (it sounds like a jet when flat out!).

So far building this has taught me a few useful lessons:

1) Don't buy really cheap Chinese speed controllers unless you derate them a great deal.

2) Ball bearing fits are far more critical than I would have thought and make a significant difference to the way the spindle runs.

3) The 550 watt rated motor has more than enough power, even when derated by running it at 12V and 30 amps.

4) My machining skills are gradually getting good enough for precision work, even when using my extensively tweaked and modified Chinese mini-lathe.

Jeremy

[ChrisG]

Hi Jeremy,

I've just set up an X1 mill with DIYCNC gear. I'm now looking at building a 1mtr x 0.75mtr router. It's been sometime since you made your brushless spindle, I wonder how it's performing? I wondered about using a watercooled esc if heat was a problem.

Very useful thread.
Chris

[blackburn mark]

ER11 C8 100mm straight shaft ebay... 8mm shaft (good for mounting straight through a sutable brushless motor)
C10 10mm shafts are like rocking horse s**t
C12 12mm shafts are more common

[Scott]

anyone have videos of these diy spindles cutting aluminum ??

[blackburn mark]

anyone have videos of these diy spindles cutting aluminum ??

[HankMcSpank]

Hey Mark.....a very slick video - well done! I'm assuming that due to the amount of Bokeh you've played, that you used a DSLR?

Which editing package did you use?