Author Topic: Air pressure spindle (Read 8328 times)

NeoTech · « **on:** August 23, 2013, 03:36:33 AM »

Have anyone attempted making a pressurized air spindle? Like the one in a small die grinder??

awemawson · « **Reply #1 on:** August 23, 2013, 07:38:51 AM »

Yes I have one I made for engraving in my Bridgeport Interact. Trivial construction comprising a spindle with the smallest ER collets mounting a toothed gear with air impinging at a tangent on the teeth and exiting through the spindle bearings to keep them cool and lubricated. (oiled air of course)

I seem to remember clocking it at 40,000 rpm despite the bearings being rated at nothing like that.

I'll follow up with photos when I can dig it out

PekkaNF · « **Reply #2 on:** August 23, 2013, 08:18:50 AM »

Great. Pictures. Please.

Did you made oscillating drive?

Pekka

NeoTech · « **Reply #3 on:** August 23, 2013, 08:34:03 AM »

Ah nice.. a gear or something was my idea as well. I guess you didnt use ac bearings then?! I have these small ac bearing four of them. would just need like a ER11 collet straight shank type of thing..

Pete W. · « **Reply #4 on:** August 23, 2013, 09:45:54 AM »

Quote from: awemawson on August 23, 2013, 07:38:51 AM

....... mounting a toothed gear with air impinging at a tangent on the teeth ..........

Hi there, Andrew,

Was your spindle noisy?

(well, maybe not quite!) In the days before mains electricity was common, some folks used to charge their wireless set L.T. batteries (aka 'lead-acid accumulators') from a dynamo connected to a Pelton wheel driven by mains water from the kitchen tap! The pulsating back pressure coupled acoustically into the water main and the Water Board guys were able to locate such installations at great distances using their sounding sticks.

awemawson · « **Reply #5 on:** August 23, 2013, 11:25:14 AM »

OK some pictures for your delight and delectation!

I cnc milled the shape of the body from the solid, and hobbed the gear in some aluminium alloy that was to hand (I seem to remember it started life as a timing belt pulley)

I bought an ER11 'extension spindle' and modified it for the spindle - don't ask me about the bearings as I cannot remember - it seems I made it in 2005 - they were just something I had to hand probably, but certainly not rated for the speed they are spinning

Just spun it up - yes it screams but not enough to stop the traffic. Took ages to slow down so I could put it back in the cupboard.

sparky961 · « **Reply #6 on:** August 23, 2013, 12:46:44 PM »

Gotta love simplicity. Is the spindle held in place just by a press fit in the bearings, or is there some sort of thrust washer behind it?

awemawson · « **Reply #7 on:** August 23, 2013, 01:18:49 PM »

I seem to remember that the spindle casing was bored out at each end for the bearings to press in with a collar between them. The spindle had a shoulder resting against the lower inner race, and there is a small collar between the upper inner race and the wheel, but that might all be conjecture !

PekkaNF · « **Reply #8 on:** August 23, 2013, 02:36:13 PM »

Quote from: NeoTech on August 23, 2013, 08:34:03 AM

Ah nice.. a gear or something was my idea as well. I guess you didnt use ac bearings then?! I have these small ac bearing four of them. would just need like a ER11 collet straight shank type of thing..

Bought three ER11 straight shank collet chucks...none of them was good fit to a 12 mm ID bearing. And I think the shank tolerances are often more on minus side than 00. But with some luck and locktite I have heard it's done.

Pekka

NeoTech · « **Reply #9 on:** August 23, 2013, 03:31:32 PM »

ah looks lika good setup for a tool post grinder. =)

awemawson · « **Reply #10 on:** August 23, 2013, 05:06:31 PM »

Quote from: NeoTech on August 23, 2013, 03:31:32 PM

ah looks lika good setup for a tool post grinder. =)

Too fast with no control over speed - quite easy to explode even small stones at the speed this runs

sparky961 · « **Reply #11 on:** August 23, 2013, 08:23:52 PM »

Good to know... I was thinking it was a good idea on first reading.

NeoTech · « **Reply #12 on:** August 24, 2013, 02:29:44 AM »

Well if you restrict the airflow, wouldnt the rpm come down? You dont really need it to go 40.000 rpm to work.. =)

awemawson · « **Reply #13 on:** August 24, 2013, 03:26:29 AM »

Your face and chest old chap. I wouldn't personally do it. For the same reason a grinder should never be based on one of the 'universal' ac/dc motors where the upper speed is undefined.

If you've ever seen the damage an exploding grindstone makes you'd want to take ALL precautions to avoid it happening.

PekkaNF · « **Reply #14 on:** August 24, 2013, 04:36:47 AM »

Yup universal motors and some "turbine" type spindles the characteristic curve of motor is very poor for this kind of application. They tend to race when not loaded and stall when loaded

Therefore works perfectly on vacuumcleaners and such where load (fan) can be designed with such a power absorption curve that maces load and motor. To make universal motor to work on die grinder takes a little designing.

High frequency squirrel cage motor motors and air vane motors (die grinders) makes logical choice.

Pekka

Pete. · « **Reply #15 on:** August 24, 2013, 05:09:15 AM »

A 15mm stone at 40k rpm has a tip speed of 31.5m/sec, or 70mph, but the projectile speed radially from a burst stone can be very much higher.

Pete W. · « **Reply #16 on:** August 24, 2013, 08:38:17 AM »

Hi there, all,

I've just 'bumped' my old thread about grinding wheel safety. Would that be a suitable place for further posts on that topic, leaving Neotech's thread to discuss air spindles?

NeoTech · « **Reply #17 on:** August 24, 2013, 11:05:49 AM »

yeah well no one really needs a 40.000rpm air spindle for doing toolpost grinding or as a support grinding spindle for the milling machine. But well i did a small test with a gear a bunch of skateboard bearings and a axle in a plastic housing.. it was easy to surpass 25-26.000 rpm (my rpm measuring device is laser based its not that exact). But it gets scary fast as hell.. I think i will leave the design with a toothed gear for driving the spindle.. the weight of the gear makes it move fast really fast and have a hard time to self-brake.

cidrontmg · « **Reply #18 on:** August 24, 2013, 05:39:29 PM »

I'm just wondering if there's really (actually two) a (ball) bearing in an air spindle? Or there's no ball bearings, instead there's "air" bearings, that cushion the pressurized air, and "floats" inside the rotor, and there's never a contact between the rotor and the housing. And since the bearing friction is some orders of magnitude bigger than a ball bearing, the air bearing can easily self-destruct with centrifugal force.
I have been many many times using with the dental drill. Current drills can operate at up to 800,000 rpm, but usually 400,000 rpm works fine. The torque is not much, but the interesting thing is their absence of vibration.

NeoTech · « **Reply #19 on:** August 25, 2013, 03:27:08 AM »

Most airspindles have 4 ball bearings, 2 in each end of a angular contact type. At least those i have found diagrams for.

But well i guess you could make use of an air bearing in this application, just a hassle to make the bearing surface and the vent and feed holes.. never got it right myself.

News:

Author Topic: Air pressure spindle (Read 8328 times)