Bearing recs please

I'm building an engraving spindle using a high speed bldc motor made for a model airplane. Today I'll be testing the first iteration at about 14,400 rpm. This is the highest speed my motors will go. If the test goes OK I'll be buying higher speed motors and will need bearings. My plan is to use ER8 collets in an ER8 holder that has a

10mm OD. So the ER8 holder will be the spindle. Which means the bearings will have a 10mm ID and a max OD of 30mm in order to fit into the spindle housing which will fit into a 1.5 ID tool holder. I think what I want is a couple deep groove bearings. The axial and radial loads will be small but the RPM so high that the dynamic load may be high. I will try using the load calculator at the SKF website but would also appreciate advice from folks here who do this kind of thing and can steer me in the right direction. Even though the SKF website has all sorts of great info I have been unable to find an SKF ball bearing catalog online. I need this in order to plug the right SKF part number into the bearing calculator. Thanks, Eric
Reply to
etpm
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I am a retired electronic engineer so my advice is worth what you pay for i t.

But looking in the Grainger catalog , a 6200 bearing has a 10 mm bore, a 30 mm OD and a 9 mm width. I would see if a industry standard bearing is rat ed for the speed of your motor that you are planning to buy. You can get h igh speed bearings with ceramic balls, but I think ordinary bearings may be good enough.

Dan

Reply to
dcaster

I think you can't be looking very hard on the SKF site as I've always been able to find the technical information for bearings quite easily. From Dan's suggestion of a 6200 here is the shielded version information

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Reply to
David Billington

Greetings David, I spent over an hour last night looking for specific bearings on the SKF website. I must be blind or stupid because you found it right off. I was looking for a bearing catalog. I see I should have been looking at the product tables. Thanks, Eric

Reply to
etpm

SKF seem to have reorganised the site somewhat from when I last looked maybe a year ago but typed 6200 into the search box and got the data. As you probably now know rooting around in the products menu get you to deep groove ball bearings and a little more gets a list such as this

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. I rarely need to use their site as I have a printed copy of their bearing catalogue from years back and the information changes little, the basics being the same. I would be interested to see how your project progresses.

Reply to
David Billington

First you ought to decide how stiff you'd like your spindle to be. Simplest and cheapest will be a pair of deep groove bearings with a spring preload. If you want stiffness more like a milling or grinding spindle you'll need to go to a precision angular contact pair in order to get the preload right.

Springs will make setting the preload relatively easy with regular deep groove bearings, but with a sacrifice of stiffness. Springs = springy.

And the preload is critical at these speeds.

This would be a suitable angular contact pair. Light preload, 15 degree contact angle.

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If you use deep groove bearings, I'd suggest SKF's electric motor quality bearings. They're claimed to be a couple grades higher than their ABEC1 rating in a few areas, including runout. I think "JEM" in the SKF number is what you're looking for.

You'll also need to decide whether to use a pair of bearings at the spindle nose plus a single floating bearing at the tail, or two bearings separated by spacers. Easy to do with spring preload, requires substantial care otherwise.

Lubrication will also be critical. Kluber Isoflex NBU15 grease is probably OK, but Kluber may be able to recommend something else. I've found them helpful on the phone on a couple occasions.

Barden, NSK, and Fafnir seem to have better info that SKF on precision and high speed bearings.

By the way, if you're using "dynamic load" as it's presented in the bearing manuals, I think you're misinterpreting what it means. The dynamic load rating is used to predict the time to failure of a bearing by fatigue of the balls or races. The static load rating is the load that will cause a permanent deformation of a specific magnitude in the balls and races.

Reply to
Ned Simmons

A cheap accurate off the shelf ER16 spindle that will happily turn 10K all day long is the one used on the Taig mill. It starts to get warm at about

12K, and that's about its limit with the stock bearings. That being said. The limitation is not the bearings. It's the seals. The rubber seals on the lower bearings create friction which is the primary cause of heat buildup on light duty jobs like engraving. Swap that out for one with a metal shield and the rating of the same bearings is 15-16K.

Don't write it off just because its on a hobby mill either. Its rated for

1/4 HP. Now I know folks who run real VMCs are shaking their head, but with the tiny little cutters used for engraving you rarely see significantly measurable horsepower requirements. Heck, a 1/4 HP is enough to do actual light milling. I think complete replacement spindles for the Taig sell for about $110-120. While it may not be off the shelf ready for YOUR application, it might be worth tearing one apart to see if you can learn anything for making yours. If you need real speed and all you are doing is engraving almost any of those cheap 3 phase Chinese spindles on ebay will do ok for that.
Reply to
Bob La Londe

Greetings Ned, The reason I'm looking at dynamic load is because of the lifetime. I was surprised to see lifetimes of about 40 hours, and even less, for some bearings. I would really like to only put in one set of bearings. I'm not sure how stiff the thing needs to be. It will be used with standard engraving tools and maybe with endmills up to about .187 max diameter. But most likely just for engraving. Thanks, Eric.

Reply to
etpm

Greetings Bob,

10,000 is way too slow. The motors I'm looking at will provide enough hp, more than 1/4, at the speeds I want and in the space I want. Do you have any experience with the cheap Chinese spindles? How small are they? Will they, for example, fit into a 1.5 dia tool holder? My spindle will, if it works the way I think it will. Can you provide some links please with any units you have direct experience with or that someone you know has direct experience with? The replies I have recieved so far are why I posted the message in the first place. I'm pretty confident that I will be able to do actual precise metal cutting with a home made 40,000 rpm spindle, which is what this group is all about. Thanks, Eric
Reply to
etpm

Actually I gave you guidelines up to about 16K. Not 10K. Your own stated test speed was 14.4K. I gave you a cheap alternative that has a proven track record and hundreds if not thousands of users. Something you could tear apart and copy into your own footprint.

You might be able to provide a hundred or a thousand horsepower, but the small cutters used for engraving won't stand up to even very small fractional horsepower forces. Go to Zero Divides website and plug some cutters into his FS Wizard speed feed calculator and see what it say the HP requirements are. For cutters engraving size most calculations for horsepower come up so small it just says zero.

I do not recall you posting speeds you want in the post I replied to. I do recall you saying you were going to test at 14.4K.

Do

Yes.

How small are

A typical 24K RPM 1 horsepower is 65 MM. Some of the more powerful ones are

80mm, and some are upto 100mm.

Not unless you make one heck of a mount and have a lot of z clearance. I could do it. However, most folks use them as a companion spindle on one side since they are a full motor and spindle in one. I have one that turns

35K RPM.

My

I can but I feel your reply to my honest attempt to help you is a bit adversarial so I choose not to take the effort.

Over about 15K balance becomes critical. Collets, closer nuts, even the tools can be an issue. I have run a lot of tools at 28000 to 34000 RPM, and they work. You may need to find somebody who can dynamically balance your home made spindle and all your closer nuts after you are finished. I agree

10K is pretty slow by today's standards for engraving, but once you get about 15-16K trivial forces become important.

You are welcome.

Reply to
Bob La Londe

Porter-Cable makes a belt drive offset base for this model router - 1:1 ratio , but you could gear it up or down .

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And they're relatively inexpensive .

Reply to
Terry Coombs

Greetings Bob, I see from reading the post you replied to that 40,000 RPM is not mentioned. Oops. About my reply sounding adverserial I did not mean it to sound adverserial. But after reading it I can see how it may have sounded that way. Sorry about that. It was certainly not my intention to insult or in any other way offend you. I'm not being flip. Too often folks here insult others when someone has asked or replied to a question. It may sound stupid to someone but the person asking the question didn't think it was stupid. My goal with the spindle is to get something I can hold in the CAT 40 tool holder without a lot of hang out. I do not want a spindle added to the side of the main spindle. I did consider this at first and drew up a clamp arrangement but didn't like it. I also made in the past a spindle that mounts in an NMTB 40 holder and uses a belt drive to a motor mounted off to the side. And though it works OK I have really never liked it much. Cheers, Eric

Reply to
etpm

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