[Mcgyver]

I want a very light duty spindle, circuit board milling, maybe engraving etc. I'm thinking of making it to hold foredom collets (I have them). Preference is to avoid the cost of abec7's and if possible run with regular class _____ angular contact bearings. I'm thinking that for these light, less-than-precision applications the cheapo bearings will work, but if wrong it would be easy to convert to the class 7's. I'll run at a speed in keeping with the bearings limitations.

I've attached a cross section of what i'm thinking of making.

one question concerns lubrication, if this spindle was used upright, what stops the top bearing from running dry and the bottom be overloaded with oil? another question concerns the fits. I know you usually light interference fit the rotating part, but what about the other? sliding, loctite, loose? I'm also a little unsure of the correct use of seals

In general though I'd like to improve my spindle and bearing knowledge, so don’t be shy, blast away - what would you change or do differently?

[ViperTX]

Well you should be using bearings that are packed with grease and not oiled bearings...which would require splash or pressure lubrication.

[JRoque]

Hello. From your requirements above, you might want to look into a small trim router as a possible solution - if that's an option. I've seen some of these go for $39 and spin up to 28K RPM which is pretty good for PCB, etc.

IMHO, having dual bearings on the lower side for your intended application might be an overkill. When you use dual bearings like that they should be a matched pair. That's to reduce binding and the heat generated by mismatched bearings where one "runs-out" in one direction and the other in the opposite. Dual bearings are great for heavy thrust applications, as I understand it. For PCB and carving, having one lower and one upper bearing might just do. Depending on your tooling requirements, some of those skate bearings on eBay can work for you. They aren't that expensive and some are, in fact, ABEC7.

I had a great time making my own spindle which is coming up to a year in service cutting everything from plastics to steel. If you have a lathe and patience you can certainly do it and have lots of fun while at it. The knowledge you'll pick up is also great. I had more than a few folks on this forum help me out with my project and that made all the difference. Some are still around waiting for the magic words to jump in. Think Beetlejuice except the three words are: spindle, spindle, spindle! They'll be here helping you out in a flash.

JR

[WayneHill]

...
one question concerns lubrication, if this spindle was used upright, what stops the top bearing from running dry and the bottom be overloaded with oil? another question concerns the fits. I know you usually light interference fit the rotating part, but what about the other? sliding, loctite, loose? I'm also a little unsure of the correct use of seals

In general though I'd like to improve my spindle and bearing knowledge, so don’t be shy, blast away - what would you change or do differently?

Sealed bearings.

[NC Cams]

Spend the money and buy a set of 7202CTYDULPA7's for the bottom, bolt them in, grind tool mount surface after assy and be done with it - factory grease should be adequate. if no grease, use a light fill of Kluber high speed spindle grease.

A/C's are pricey to begin with and high speeds are gonna necessitate good running accuracy. Don't go cheap where it counts.

A 6202VVCE or C3E will work at the top.

Want to go cheap - use some 6202VVC3E's and shim them to create a DB configuration for the bottom. Shim to obtain about 2% of the radial capacity of the bearing.

How much shim to get that??? Load the bearing with the amount of preload, measure the ring offset and make your shim accordingly. DO that for both bearings and add the shim thickness. YOu have no idea how hard this is to do an what a PITA it is to do.

Even when you do this, runout can/may/will suck because C3E grade bearings have a lot of runout potential that ABEC 7's don't.

Too much trouble to do this??? See first paragraph.

Oh, and some skate bearings are ABEC 7's and some are noise and or Q/C reject ABEC 1's - darn near ANYTHING works in a skateboard. How lucky do you feel????

[Mcgyver]

guys great info, thanks. I'd like at least take a shot at it with C3E grade because the its 1/6 the price - If it fails I can change over.

JR, I went with A/C together mainly because of thermal expansion – if I went the A/C, one at each end, I’d either have a thermal expansion issue OR would have to preload with a spring (not sure that’s a good idea with helical cutters) ?

Shim to obtain about 2% of the radial capacity of the bearing.

How much shim to get that??? Load the bearing with the amount of preload, measure the ring offset and make your shim accordingly. DO that for both bearings and add the shim thickness.

NC, trying to follow you - so I'd need to physically apply a load to the bearing and measure with shim stock the cap between inner and outer race? Is this because the distance you are measuring in bearings (in this class) is not consistent? ie the amount of shim required will change from bearing to bearing?

From the comments, you guys are saying if you squash two non- matched A/C's together there is no preload? i.e. only abec7's or better have this feature? for example skf has universal matchable A/C as opposed to matched pairs.

that being the case, then i need to grind two washer-shaped disks, one corresponding to the inner race and one to the outer, with the difference in thickness being the preload amount?

YOu have no idea how hard this is to do an what a PITA it is to do.

I don't doubt you know what you’re talking about, any ideas on the set up needed to create this load and measure it? I sort know what you mean in theory but trying to picture it

I don't want to rely on luck, I'd buy a quality brand, just don't know that i'm ready to spend $300 for the matched set, well you may convince me, but I'd still like to take a shot at it and appreciate the knowledge share in the interim.

[NC Cams]

The bearings I mentioned in my prior post are already ground for light (ergo the L) preload. The DU denotes "universal mount" as in the bearings are preground for spec'd preload at DB, DF or DT mount. Bolt in and fly.

Re: preload shims for C3E regulars

1. Determine 2% preload force.
2. Apply said force to inner ring while supporting outer ring of 1 bearing.
3. Measure ring offset in BOTH directions for EACh bearing - they WON"T be equal as raceways are NOT perfectly centered in regular ball bearings.
4. Determine TOTAL shim required to insert between ring (you have to offset EACh bearing ring so load each with 2%) with appropiate placement 'tween innner or outer race for DB or DF config as needed.

Setup??? real accurate surface plates, real accurate dial indicators that read in 0.001mm (not inches), real accurate weights. Check out bearing charts for rough "L" preloads.

NOTE: even a 15 deg contact angle in an A/C bearing is more rigid and accurately ground than a C3E bearing. They grind the A/C's assuming/knowing that A/C will occur - C3E"s are ground for 100% RADIAL load assumption and axial load is a consequential occurance of misalignment/happenstance. This is why any situation where axial load MUST be applied to a conventional bearing has the "contact factory for assistance" caveat.

Example: a 150 preload on a pair of shimmed up 6204's are a handfull to turn on a ball screw and still has axial play potential under load. A 500 lb preload on a 20TAC47 "204" size ball screw bearing turns with a fraction of the force and has NO axial clearance.

The gap in the foto you attached is the "offset" you're trying to duplicate via shims. In the foto, the load that closes the gap when you TIGHTEN the bearings' inner rings together solid is what you're trying to generate.

You'd get the same effect by putting a shim between the outer rings and then clamping the inner rings together.

YOu can spend $300 and bolt the thing togther or spend goodness knows how many hours trying to make/figure out shims. We're not talking thousanths of preload shims, were talking microns (0.001mm) as being critical as you're talking NEGATIVE clearance of SOLID OBJECTS.

This is bearings, not nuclear weapons nor rocket science we're talking about, so microns DO matter.

Besides, the raceways of a 6200 series bearing aren't precise enough to hold/measure a consistent preload AND the inner ring raceway runout is MULTIPLES of that of an ABEC 7 - check it out and you'll see. Ditto that for raceway axial runout - not the case with A/C's of ABEC 7 grade.

So, when/if you get the preload, you still have mucho micron runout potential. Does it matter? the smaller the tool and higher the speed the more critical that runout issues become. You be the judge...

Roughly speaking inner ring runout doubles as you go from ABEC 7 to ABEC 5 and doubles again when you go from ABEC 5 to ABED 1 or 3. THis runout makes it tough to match 2 620x's so as the axis are ultimately coaxial. You may luck out out but I wouldn't count on it.

As much as it may hurt to spend the $$$'s, you are getting what you pay for.... I did my share of shiming and "getting by" - life has gotten too short of late to mess with that sort of thing anymore....

[Mcgyver]

NC, thanks for taking the time to go into detail - you make a compelling case on going abec 7. most of the time i'm a do-right-guy in the shop and as you say I have to accept the performance gap - but am still wavering, i can always 'upgrade', then again...

I think i used c3e in ignorace - thought you were refering to a lower class of A/C bearings, but still A/C (vs say deep grove). I've been trying to clarify c3e without much luck

is it sufficient to request abec7 or do they need to be matched pairs (or is that redundant) for pricing, I want to make sure I’m asking about the right thing. I've a surface grinder and can hold tenths if I hold my breath, but 100ths? haha, not likely and as you point out that doesn't correct the radial run out. I’m guessing these lower class bearings would be better suited in a light spindle with the bearings at separate ends of the spindle and preloading via springs – then any variance between the to isn’t going to bind as it would in back to back

any comments on the general arrangement of bearings & seals?

JR, any plans or sketchs kicking around on your design?

thanks again for all guidance - much appreciated

[miljnor]

Let me first say that everything NC cams is saying about the bearings sounds right! (as in I am not disputing anything he is saying)

Now! Who is making the spindle housing? and do you have clean room facilities and microscope inspection equipement? You guys are talking microns, do you know the size of an average dust partical (not to mention the nasty metalized type dust in a shop environment)

If not, anything above abec 5 (japanese not the cheepise) is probably not going to do you much good.

I have built about 5 spindles for various purposes in my time (definitely not an expert) The current incarnation is using good quality abec 3 tapered bearings in my cheap chinese mill spindle, runout is less than .0002" not bad for throwing it together. Now keep in mind at the speeds I am going to go (roughly 7k rpm) I will probably blow this thing to he!L and gone. But, its just a test to see how much I can get out of how little. Every one of the spindles I made with varying precision/care have turned out less the .0005" runout.

That being said if its a light duty mill you will probably have more deflection than anything else so this problem is mute.

just my 2 cents.

[NC Cams]

C2 = less than "normal" clearance
CM = lower half of "normal" clearance tolerance spread
C = normal clearance (not usually part of brg number)
C3 = more than "normal" clearance
C4 = more than C3
C5 = more than C4

the actual value for "normal" varies from size to size

"E" simply denotes "electric motor noise test".

In my original post, I spec'd out the EXACT p/n's that you could use (preload, ABEC, size per your drawing, everything). Specifically, ABEC 7's at the bottom and an acceptable bearing for the top (an abec 3 on top would be better but not mandatory).

.0005 runout on say a full size mill is not much but .0005 runout on a spindle that is trying to drill a 0.025" diameter hole in a PCB is something totally different. Microns DO count at some point in time and, with respect to bearings, quite often.

Yes, spindle construction tolerances also count quite a bit but I just figured that dealing with proper bearing selection was sufficient for this thread.....

[Mcgyver]

NC, was more asking about abec7 & matched sets as a general understanding question - I know you spec'd out the bearing to this design, and its appreciated. My objective is two fold, one getting a spindle built and also learning along the way - I'm sure i'm not the only one who appreciates the professional insight into the somewhat confusing (to me anyway) world of bearings.

I have, well, few delusions about my working ability . microns? don't allow them in my shop. tenth's and concentricity? yeah, on a good day. but you're not turning to microns to do a proper job on a housing are you? isn't a tenth or two accuracy on a light interference fit adequate? in other words at the bearing level I can see microns counting, at the spindle and housing level, working more accurate than a tenth (or two) exceeds my ability and equipment.

what advice would have for fit on the shaft and housing? what design do you follow? can you share it?

thanks again for the help guys

[pstockley]

I am also in the process of designing a spindle and I would highly recommend you go to NSK, Barden and Torrington and print out their design sections for super precision bearings. 90% of your questions will be answered. Hopefully I will have my conceptual 3D model finished soon and I will post it for critique. It all looks deceptively simple until you get into the details such as tolerances for fits, thermal expansion, shielding etc etc etc.

Warning the files below are pretty big:

http://www.bardenbearings.com/literatr.htm

http://www.timken.com/products/bearings/catalogs/

http://www.jp.nsk.com/app01/en/catal...gi?ec=bearings

[Mcgyver]

thanks for links, the brings it together nicely. have been reading alot on bearing sites- maybe i'm a combo of fast reader slow learner? i'll keep reading

[miljnor]

Wow those sights have alot of litterature. Do you have any recomendations for starting reading?

[pstockley]

Just read the ones marked as super precision or machine tool bearings.

[NC Cams]

Thanks PSTOCKLEY for the links. Saves a lot of boring (to some) bearing speak on my part. I'll start reposting them as future inquires warrant.

Keep this in mind: When you preload a bearing, you are ultimately loading ALL the balls. Thus, any misalignment DOES start to apply an uneven "pivot" load so to speak. Thus some balls get loaded heavier than others (much higher stress), more importantly, however, ball skidding can occur as the balls go into and out of the load zone.

Yes it isn't rocket science BUT you can get within a mile and be quite effective wiht a rocket strike - miss clearance or improperly fit a bearing too tight and microns do matter.

1" = 25.4mm

1 micron = 0.001mm

Some simple math will show you how a micron relates to a tenth....

At 10K or whatever, it doesn't take long to skid the hell out of a ball and for it to start to fail - ala locked up tire analogy of flat spotting. Things get ugly soon after.

Bearings are elegantly simple in their precise complexity....

[NC Cams]

Even more elemenatary and just as important are the sections on bearing fits to housings/shafts. This info goes a long way, especially in rectifying "bad habits" that have procreated themselves into "acceptability".

When you start doing spindles, things get much tighter tolerance wise as "machine tool" spindles are supposed to more precise than the parts you're gonna make with them....

Be prepared to be shocked at the values (and be prepared to work in metrics, the bearing world is pretty much all metric based).

Granted, you may not need the accuracy of a machine tool spindle but as you take the slop out of bearings, they become MUCH more intolerant of "off" conditions.

[Mcgyver]

in addition to all the technical and design criteria that go into a spindle design, there is also an important consideration that isn't much being talked about - what are the resources at hand to the builder?

I don't think I did a good job of communicating...for example your response suggests you took my tenth vs. micron comment as not understanding the difference or not knowing how to convert between the two. No offense taken, but my point was I'm capable, with the equipment i have, of working to a certain level of accuracy and I know where that is. I don’t have the ability to turn to a micron nor do I have I clean room for assembly, so designs that require these for success clearly are academic – the limitations must be balanced by the design and expected performance.

NC, you seem very negative on a diy spindle. I buy into the logic that making a 20x rpm >.0001 tir milling spindle with a 5hp motor has special challenges, is probably not practical in the home shop and is worth the 1000’s one would cost. On the other hand there have been 1000’s of homemade spindles made over the years, both for grinding and milling.

That I cannot obtain the performance of a $3000 spindle is not exclusive to the notion of building a useful spindle? I’m moderately experienced, have decent manual equipment and can turn to a tenth when I work at – I’m having a hard time believing it’s so stacked against me that it isn’t worth trying. What is about the shaft/housing that is going to be beyond my abilities, and if so, what’s a better design strategy given those constraints?

Links to bearing sites are fine, I’ve read a lot in the past and have no objection to self help. On the other hand, this is information not knowledge. Knowledge is taking that information and applying context and experience – that’s why it’s so great to get access to the people here who know what they’re doing.

Thanks for the help

[pstockley]

I not sure NC is say it can't be done, just don't expect to slap in a set of standard bearings and expect to be able to spin a spindle to 10,000rpm and have it a) last any length of time and b) be accurate. Most of the home made spindles I have seen are either very small and not very precise (the fast ones) or don't go much above 3000rpm.

However, that doesn't mean it can't be done. You need to use the right parts and be able to machine to the required tolerances. Of the top of my head, you are looking for around 0.0000944" MAXIMUM interference fit between the spindle and bearing for say a 20 to 50mm super precision bearing. For the same bearing, the spindle can be a maximum of 0.00015" undersize, so you have around 0.00024" to play with. Obviously different bearing types have different tolerances but what I quoted was a ballpark figure. I don't think you are going to get these tolerances by turning alone, grinding is going to be required.

[pstockley]

Just to add, given the allowances above and the different tolerances of the bearings themselves from ABEC 1 to ABEC 7, I think it is unlikely that you can build a spindle with low grade bearings and then fit something like a set of ABEC 7's later. You will probably have to make or modify (if you are lucky) the spindle and housing again.