DIY spindle design

[Jeremy]

I've started this new thread here, rather than continue on the collet discussion thread.

Prompted by the discussion on collet types in the other thread, I purchased an ER16 collet chuck, with a straight 20mm shank 100mm long, from Arc Euro, together with a couple of collets. My intention is to build a relatively high speed spindle for my CNC router project.

First off, full marks to Arc Euro - less than 24 hours from order to delivery.

I've just ordered a suitable motor, but have reduced my maximum speed requirement a bit to make bearing choice more affordable. The motor and speed controller I've opted for is rated at 550 watts, but my power will be limited to about 360 watts by the 12V, 30A power supply I already have.

The motor is a three phase brushless one, with a Kv of 1400, giving me a maximum rpm of about 16,800 at 12V. Total cost for the motor and speed controller, including postage, was just under £33.

I've also just ordered some deep groove bearings, that are rated at 20,000rpm, so should be OK in this application (I hope).

I'm hoping to be able to build a fairly high speed spindle, suitable for light duty routing with small diameter tools and a high degree of accuracy. The ER16 chuck is pretty good as far as I can tell. I can't see a difference on a DTI between the run out on the shaft OD (due to the innacuracy of my 3 jaw lathe chuck that I stuck it in to test) and the run out of a 1/4" bit of tool steel in the collet. My guess is that it's better than about 1/2 thou TIR, which should be OK for fine work like PCB milling.

Next job is turning up a bit of 2 1/2" diameter alloy bar to make the housing, then milling a mounting flat on it to allow it to fit to the Z axis plate. The motor will be directly coupled to the top of the spindle. I'm hoping that the combination of direct drive and a three phase brushless motor should make for a quiet spindle.

I'll post pictures as soon as I get something machined up.

Jeremy

[Jeremy]

I'm hoping it'll be fun, although until I read the collet thread I hadn't thought of doing this - I was just going to buy a small router or die grinder to use, so this is yet more work!

Robin wrote (in the other thread I was clogging up with this stuff)

Hi Jeremy

What is a suitable coupling for 500 revs/second?

Balance probably isn't a prime consideration, but no bending parts obviously.

I'd probably go for a rod though one shaft engaging a pair of driving dogs on the other, then spend half an hour adjusting it 'till it ran quiet

best

Robin

Good question. I've been looking at the small Huco and Lovejoy couplings and think I might be able to adapt one of the ones that uses an elastomer spider. Hopefully this will reduce any noise and allow for a small degree of misalignment. Now that I'm being less ambitious with my speed expectations (due to the difficulty in getting affordable bearings) the problem sould be simpler.

I may revert to driving the spindle with a small belt drive, as although this would be more bulky, it might well end up simpler to build.

Jeremy

[Jeremy]

Thanks for the link to that eBay seller. I've already ordered bearings, but the Lovejoy couplings they stock look to be a good deal, so I've ordered some. The 050 size should be OK for my steppers and the 035 size look like they'll work OK for the spindle couplings, as they are rated to 31,000 rpm.

The next challenge is to work out an easy way to connect the chuck shaft to the coupling.

Jeremy

[Jeremy]

That's a good price for the chuck, cheaper than the one I purchased from Arc Euro, even allowing for the shipping charges.

I think I've worked out a way to couple the chuck shaft to the motor, using a small Lovejoy coupling. The only problem I can foresee is vibration if I can't get everything perfectly aligned.

BTW, the motor I have ordered is this one: http://tinyurl.com/5dcho4, which was $30.16.

The speed controller is this one: http://tinyurl.com/5l8ols, which was $11.30.

I've used these RC electric motors in other projects and found them to be quite amazing, they will deliver lots of power with an excellent overall efficiency. Best of all, they are cheap and have no brushes etc to wear out.

Having seen those collet prices on that CTC eBay shop, I'm now tempted to do what I originally planned and replace my clunky old Clarkson with an ER25 set-up.

Jeremy

[Jeremy]

Well, I now have all the bits to build the spindle, so shall; have to crack on and see if I can get it to work.

The motor and controller arrived from China pretty quickly, as did the bearings and lovejoy couplings bought via Bearing Boys and ebay. The motor and controller are tiny, it's quite amazing to think that the motor is rated at 550 watts. This is a real advantage though, as it means that the complete spindle assembly will be a cylinder with an overall diameter of about 1.5". I'm toying with the idea of fitting the Z axis in between the Y axis rails, primarily so that I can (hopefully) gain some added stiffness by minimising offset loads from the cutter. The narrow diameter of this spindle is ideal for this, although it will mean offsetting the Y axis leadscrew to one side (although I can't see this being an issue).

I'm going to try and machine up a small spigot to fit into the end of the chuck shaft (it's internally threaded 10mm) to couple to the lovejoy connector, as I need to get the shaft size down to something similar to that of the motor (the motor shaft is 4mm). Luckily there is a small counterbore in the chuck shaft, just above the start of the threaded section, that seems to be very concentric to the shaft OD (I can't measure any run-out with a DTI). I'm hoping that I can use this to align my shaft adapter, although if it's a thou or two out it won't really matter, as the coupling will cope with up to about 15 thou of misalignment.

It looks like this evening will be spent boring lumps of alloy bar and machining up the shaft adapter. I'll post pictures as soon as it's done.

Jeremy

[Jeremy]

I've made a start on the spindle today. Spent a couple of hours turning a bit of 1.5" 6082-T6 bar into swarf...............

All told it's turned out OK. I turned a bit of bar up to fit as an end cap to hold the 550 watt motor (yes, I know it doesn't look like a 550 watt motor, but it's very efficient at around 85 to 90%). I turned up a small adapter to fit into the M10 threaded hole in the end of the collet chuck to fit to the lovejoy coupling. I am reasonably happy with the way it turned out, the runout at the coupling is around 3 thou, well within the 15 thou coupling limit.

The big bar has been bored out to take a pair of bearings, one at the end and another just below the cutout (the cutout is to allow the coupling to be assembled).

I just need to make a spacer to fit to the nose bearing and space the chuck out about 10mm from the bearing (to allow spanner access) and make up a clamp ring to fit at the top of the collet chuck 20mm shaft and allow the bearing pre-load to be set.

The thing with the wires poking out is the 40 amp speed controller. It's a bit of an overkill, as my power supply is only rated to 30 amps, but it should do the job. The current plan is to fit it into a small die cast alloy box next to the spindle and build a servo tester to drive it. This will give me a manual speed control, which I may seek to change to auto at a later date.

Hopefully I should end up with something much more robust and accurate than a Dremel, with a fair bit more power. The motor may need a fan fitted to the top for extra cooling, I'll see how it goes.



Jeremy

[Lee Roberts]

Looking very nice Jeremy, how much would you say it has cost you so far to make this ? Would you be looking to make some more?

[Jeremy]

Total cost to date is about £60, not including the 12V 30A power supply that I already had. Similar power supplies cost about £25 to £30 via ebay.

This is strictly a one-off for my router build. I'm after something that will spin at a reasonably high speed so that I can use small diameter tools, but don't really needs lots of power, as it'll only be cutting light stuff. Mind you, I suspect that the few hundred watts that this little unit will deliver should make it pretty powerful for it's size. If anyone want more power, the place I purchased this little 550 watt motor also sells some nice 2800 watt model motors for around £30 each. I have a few for another project, the snag being that they draw around 80 amps each, so need fairly hefty power supplies.

I also wanted a fair degree of accuracy, without the fairly horrid run-out that Dremel-like tools have, as I'd like to try using it for milling PCB's as well. So far I think I'm on-track to have a fairly solid little spindle with relatively good accuracy, probably better than a thou TIR.

Jeremy

[philbur]

Small cutters really need much better than a thou TIR. Better than a tenth would be much more suitable. Otherwise the necessary low chip load per tooth will leave you cutting on one flute only. A decent level of precision in the bearings is called for, together with good adjustment for preload. No-name deep grove bearings of unknown class may not get you there. The other killer will be the concentricity of the spindle taper with the bearings seats.

Get these two points right and you are on a winner. Get them wrong an it's going to be a so-so spindle.

Just some thoughts
PHil

PS: I haven't read the whole thread so if I missed something sorry.

So far I think I'm on-track to have a fairly solid little spindle with relatively good accuracy, probably better than a thou TIR.

Jeremy

[Jeremy]

All good points, Phil, if this were for a precision machine cutting a hard material like steel.

It's going on to a table top router type machine though, intended to cut moulds for composite parts, from mainly EPS foam and MDF. The idea was to make something with a power similar to a small trim router or the larger Dremel type machines, but smaller in diameter, with more robust bearings, a better level of spindle accuracy and, most importantly, a much lower noise level.

If the whole machine turns out to be sufficiently accurate, I may use it for milling/drilling PCBs, although I suspect that the spindle speed will be too low for that task, so I may need to build another, faster, one.

If I get a spindle that is compact, quiet and comparable in accuracy and overall cost to a trim router then it will certainly meet my requirements.

Jeremy