Grinding spindle bearings

I'm busy making a small grinding spindle for what is suppsosed to become a cutter grinder. I plan to use a 180mm dia cup wheel. I went for a 6006 bearing in front and a 6005 at the back. Aprox 3" apart. Are these bearings sufficient for service in a cutter grinder or should I choose something else ? I plan to push them from time to time to 10K rpm for cutting HSS with diamond disks.

Angelar contact bearings are a better choise
Perhaps a construction with a spring load
More difficult to make but a better result I think

You're right Peter but this is only for fun - it won't see any hard work.

For hobby use 6005 and 6006 bearings would be fine. Only problem with them is when you buy sealed bearings they tend to be packed with too much grease, and they run REALLY hot. Get shielded bearings, not sealed bearings, so you don't have the increased heat from the seal. I f you get double shielded bearings, pop off the inner shields, leave them off, and remove some of the excess grease. At 2000 rpm these bearings run fine, but at 10,000 rpm the grease makes them run hot.

I build my grinders with two pairs of bellville washers to preload the bearings. If you want to use the same design, and you can't find any bellville washers, I can slip four in the mail for you. I don't think they cost much, I buy them in bags of 500. I have them in both your bearing sizes. If you use standard 6000 series bearings and not preload them, you're gonna find the endplay in the bearings is not really acceptable. Amazing how much the inner race can move inside the outer race. With the bellville washers this play is taken out.

Thanks Brian! I've initialy tried a tapered roller in front but picked up a vibration at some 2500rpm I couldn't get rid off. The bearings I'm using now are the cheapest crap money can buy - just to get a feel for the thing. Once all the contraption is "wired" together I'll add front and back covers and run 'em in oil.

Brian, are you talking about using Belleville washers for deep groove radials or angular contact bearings?

I make several different type of spindles- one has the spacer sleeve and the spindle ground as an assembly, which means they are exactly the same length. This spindle goes into a head that turns a maximum of 5500 rpm. No bellville washers in this unit. The bearings are basically back to back, except for the approximate five inch spacer. I've built this spindle with both deep groove and angular contact bearings. The grinders get bellville washers, whether I use deep groove or angular contact bearings. If you were using deep groove bearings and you didn't spring load one of the races, you would never be able to use it as a grinder. Those bearings can have a ton of freeplay. You'd never know where your grinding wheel was at. If you can grap your spindle and move it in and out, you're gonna have problems grinding with a face wheel.

When I first bought VersaMil, the prior owners had switched to using deep groove bearings from angular contacts. I understand trying to keep costs down- installing $6.00 each bearings verses almost $200.00 spindle bearing pairs. The VersaMil grinders certainly aren't a high end grinder, although with the correct bearings, they are pretty darn nice. I switched back to angular contact bearings, for the grinders, and I selectively use deep grooves in the high speed heads. I reject the bearings with an excessive amount of end play. I've bought at least a 1000 bearings, so I know when one feels good, verses the feel of a crap bearing. Cheaper to buy name brand (SKF) bearings, and throw some away, than to specify a more precision bearing, and pay 20 times the money.

BTW, MSC has a number of sizes of bearing preload Bellevilles. Fairly inexpensive as well.

They work quite well. It is amazing the difference, even with a relatively cheap bearing.

Bearings have what is known as "clearance", the cheaper the more.... It may be both radial and axial, although one-sided angular contact bearings have really only one loaded direction. A deep groove has both radial and axial What Brian called "freeplay". That ends up allowing chatter in a machine tool spindle.

With angular contact ball bearings, preload does wonders for stiffening up the spindle against chatter and all sorts of deflection. it takes up the "freeplay" and runs the balls under some initial load so that there is a restoring force to bring the spindle back to center.

A spring preload is not as solid as a "nut" preload, but it is a whole lot more forgiving, and I would agree it ought to be fine for a grinder.

Solid "nut" preload can actually reduce loaded deflection by taking up some of the elasticity.

The downside is potentially reduced life even if run unloaded aside from preload. Generally there are curves showing life vs load, with various amounts of preload.

Brian,

You mentioned that you were thread grinding in a previous thread. Are you running a VersaMil with a grinding head and some kind of creep feed on a lathe? Or do you have a dedicated thread grinder?

Just wondering if you could do thread grinding with a VersaMil...

Robert

You guys might not believe this but at a small job shop I worked at, we had a Brown & Sharp #5 surface grinder that puked its plain spindle bearing but found the $6,000 replacement cost way more than what the WW II era grinder was worth. So our 70 year old-time machinist-guru lathe guy got the solution - bore out the spindle to accept truck wheel bearings (tapered roller bearings) at about $40 each, and install those. It worked. The first couple of months you could see a slight wave pattern to the finish, nothing worth measuring, and that went away as the bearings wore. An $80-plus-labor fix.

Never take those old timers for granted.

Steve

bore out the spindle to accept truck wheel bearings (tapered roller bearings)

Click to expand...

Sooo, what was the surface finish like?

Truck bearings have a lot higher runout specs than the ABEC-7 bearings used in surface grinders.

Lazlo, A VersaMil can THREADMILL, but I don't think it would be an effective thread grinder. I suppose in a pinch, you could dress a wheel to the correct angle, and thread grind on a lathe, but what for. I don't think the results would be worth the effort. You're right about the creep feed, that's just what you have to do, but you can traverse the work faster than milling. I suppose you could grind in back gear, at around 15 to 20 rpm, but with the smaller wheel, I doubt you could get the surface feet up fast enough. As long as you can pivot the grinder head for the helix of the thread though, I bet it would work. Frankly, I've never thought about trying it. Thread grinding needs copious amounts of OIL applied to the work. The mess you would create on a lathe, no matter what the results were, wouldn't be worth the extensive clean up. Seems like no matter how careful I am, operating my fully shielded thread grinder, by the time I'm done with some parts, I reek of oil. It's in my hair, on my face- it's everywhere! I see these machines without covers, and collectors, and know the operators when they go home for the day, have got to be met by a disgruntled wife.

I have real thread grinders, that use 19 inch diameter wheels,so I'm spoiled. It's really nice to have the real deal. Back in the bad years of 2001 and 2002, while a lot of shops were getting rid of their machines, I was buying them. After the first few batches of $8000.00 ground leadscrews came in my door, the thought of making them myself was really appealing- especially since thread grinders could be purchased for a tenth of what I paid for one run of screws. Over a period of four years, I purchased 7 thread grinders, a couple are junk, three are nice, and one is almost the ultimate thread grinder. The method to my madness, is set up each grinder for particular threads- and leave it. One of my thread grinders incredibly enough, is set up for tap grinding.

You'll want to use some type of preload using these bearings. Even cheap electric motors use a wave spring to load the bearings to prevent the balls from skidding in the races. RPM above 5000 will need oil lubrication as the grease will break down, run out and toast the bearings. If you use spring preloads mount the front bearing rigid and make sure the spring pulls the spindle towards the back (you don't want to unload the preload when face wheel grinding). McMaster-Carr has pages of bearing preload and belleville springs with preloads from 5 to 10,000 lbs. If you use nut preloading you check the preload by running the spindle and seeing if it gets hot. Run the spindle at about 3000 for 10 to 15 min and put your hand on the spindle. It should be warm but not hot. If you can hold your hand on it for 30 seconds you're fine. If its too hot lossen the preload and try again. My Leblond tool and cutter grinder came from the factory with tapered roller bearings and works just fine (solid nut preload, oil lube). Tapered rollers just like regular bearings can be bought in different tolerance classes and can be just as good as ABEC-7s. The "000" class used in my Agathon workheads have the same runout specs as a ABEC-7 but they cost $4000 each and delivery is 4 to 6 months. Tapered are normally used when there will be high axial loads (for example Blanchards use tapered rollers in the spindles). They are used in wheel bearings to take the sideways load when cornering.

Thanks guys ! Great advice - much apreciated. I'll tell you what got me started in this : I saw on the NET some British "project" for a small tool and cutter grinder. I didn't like the pretentiousnes of the articles and decided to make my own. I'm a shaper nut and need some decent setup to make cutters. I'd also like to sharpen reamers. I'll drop pics as I go along and I'll irritate everybody with stupid questions.

High grade taper bearings should work well in a grinder with the right preload. You could even use a spring to set the preload so it would stay constant at any temp.

Using a belleville washer with a ball bearing is a good idea as long as the pressure is not excessive. I would only adjust it to a very low tension so as to only remove the end play in the spindle. Any more may short life the bearings.

Carl, the manual for my MAHO says 5um clearance. No spring or washer. I tried to use a tapered roller bearing in front and kept vibrating even at zero clearance. But I can try again I suppose...