Good High Speed Spindle

[Bob La Londe]

I have found quite a lot online regarding spindle design, bearing stacking, preload etc. 

[Bob La Londe]

I'd probably go with a pair of 7202 bearings (15x35x11mm)  mounted back to back for maximum speed (26000 rpm) and rigidity. To get  to 30000 rpm would mean going for something like 7200 bearings (10x30x9mm) which is getting quite small for you to make whilst maintaining strength in the parts.

I think much past any of this and you're getting into quite a specialised area of machine tools where everything has to be beyond being good 

20000+rpm is pretty good in my book.


Martin.

I looked up 7202 bearing and most list RPMs in the 18-21K range.  So what bearing is in those Chinese motors that turn 24000RPM and have an ER16 Collet chuck on them?  If the goal (mine is) to get top speeds and take the load off the motor bearings to save motors they might be a good choice.  Once I have a working spindle design I can always make more of them, so I can swap them out to replace bearings at my liesure. 

Nothing "wrong" with 20K.  I did a lot of this kind of work with a 10K spindle.  It was just slow.  Now that I have done it at 30K I am kinda spoiled, and yes I have had a few people tell me I may be more of an "expert" at the narrow field of high speed aluminum machining than many real machinists. 

[blowlamp]

Take a look here http://www.skf.com/skf/productcatalogue/jsp/viewers/productTableViewer.jsp?presentationType=3&lang=en&tableName=1_3_1

Martin.

[Bob La Londe]

Now that is interesting.  I had not seen that chart before.  I have done a quick search on the SKF 7202, and those I have seen to seam to be an open not shielded design.  When I just punched in 7202 bearing on Google all the ones that came up listed a lower RPM rating.  I don't think any were SKF though. 

[Bob La Londe]

Martin,  Thank you.  I'm not sure I am going to go the way you went, but I do really appreciate the help and the knowledge and insight your method gave. 

[blowlamp]

Good luck to you, whichever way you do it.


Martin.

[Bob La Londe]

I am actually thinking of a modification of your idea to build a speed multiplier using the stock mill spindle as the motive force.  After a conversation with somebody else making some of the same types of parts I am I discovered with a more rigid machine they are turning much slower speeds than I expected. 

[blowlamp]

Bob.
Do you mean something like this?

http://www.hemingwaykits.com/acatalog/Speed_Increaser.html



Martin.

[Bob La Londe]

That uses a planetary gear, and if I recall it has a single bearing on the drive.  Its a neat idea, but probably a little under built.  I want something I can abuse for 5-10,000 hours before a tear down. 

Naw.  I was thinking 3 pairs of spindle quality bearings on 3 shafts with 2 3:1 cog belt pulleys to get about 6:1 speed increase with an er collet chuck in the last set.  The main and intermediate don't have to be able to spin as fast as the final set so they can be more robust.  Only reason I have not started already is I would like the final drive to be concentric with the main drive, and I have not figured out a simple elegant way to accomplish that yet.  Hmmm.... I think I might have just figured it out. 

I would probably just buy a speeder on ebay, but they all have CAT shanks.  I need a robust straight shank or a KWIK 200 (or RS200) shank. 

[blowlamp]

That uses a planetary gear, and if I recall it has a single bearing on the drive.  Its a neat idea, but probably a little under built.  I want something I can abuse for 5-10,000 hours before a tear down.  

Naw.  I was thinking 3 pairs of spindle quality bearings on 3 shafts with 2 3:1 cog belt pulleys to get about 6:1 speed increase with an er collet chuck in the last set.  The main and intermediate don't have to be able to spin as fast as the final set so they can be more robust.  Only reason I have not started already is I would like the final drive to be concentric with the main drive, and I have not figured out a simple elegant way to accomplish that yet.  Hmmm.... I think I might have just figured it out.  

I would probably just buy a speeder on ebay, but they all have CAT shanks.  I need a robust straight shank or a KWIK 200 (or RS200) shank.  

Been there and done that, Bob.

You might have your calcs wrong though, because 3x3=9 times speed increase, if you're doing it the way I think you are.

I'm pretty sure you'll come across many problems doing it that way, because I know I did. As soon as you start gearing things up, you run into problems with frictional losses being multiplied. By using belts, more energy losses are incurred due to their continual flexing.

I mean, you're at a six times (torque) disadvantage purely due to the gearing effect, add in the belt and other frictional losses such as grease lubrication etc and that might bump the disadvantage to ten times - maybe more, who knows? And definitely no lip type oil seals!

The first bearing-set after the main spindle also has to be without play, run concentrically so the whole assembly doesn't wobble, as well as be able to resist the cutting forces - all with minimal friction.

It's how I came to the design I showed earlier - simple and free running.


Martin.

[Bob La Londe]

Of course.  Doh!  I did screw up the calc.  Duh!  I have a 5 HP (3.7 kw ?) spindle on the machine in question.  I would just buy a decent speeder if I could find one to fit, but this has a Kwik 200 (same as RS200) spindle taper.  The only speeder I have found that I "might" be able to use and afford is a used straight shank.  That leaves me wondering about the bearing quality and condition both.  

I would like to have a speeder that is concentric with the main spindle to use the power of the spindle for big cutters and the speed of the speed multiplier for small cutters on the same work piece without having to rezero every time I change it.  

[Bob La Londe]

A commercial example.  I would sure like to hear if anybody is using this in continuous duty. 
http://www.tormach.com/product_pcnc_acc_speeder.html

[blowlamp]

The Tormach speeder looks like it only gears up by a factor of three, which might not be enough for your application.

http://www.youtube.com/watch?v=UOxlRIw0Z1U

Martin.

[Bob La Londe]

Yeah.  I know.  I wasn't planning on buying it.  Just showing it as an example of a belt driven speeder "commercially" available.  They did pick the ER16 collet holder which is a nice size for modest and small cutters.  Also, ER16 collets are readily available from lots of sources.  It has not been around long enough to be able to ask people how it has held up to continuous service though. 

[blowlamp]

I don't know how the costs (or the idea itself) would stack up for you, but could this be a way forward?

Take one (or two) of Tormach's spare hi-speed cartridges here http://www.tormach.com/store/index.php?app=ecom&ns=prodshow&ref=31342 and make an adapter so it would either fit straight into your spindle taper or a collet in your spindle. 

With a cutout in this adapter to allow access to the Polyflex belt pulley, you could rig up some motor arrangement similar to mine, or maybe mount it directly to the side of the milling machine head with a few brackets.

The advantage would be that all the hard design and machining work is done for you and it'd be possible to swap the spindle in a few minutes and overhaul the other at your leasure.

Martin.