quality of spindle bearings

[hms50]

I was following a thread about spindle run out and someone mentioned the possibility of cheap bearings having been used to save money/keep the price down on some import mills. Does anyone know what grade Bridgeport used? What is the price ratio between "general" purpose bearings and somthing like a grade 7? As you can tell, I've never done any spindle building or repair.

Thanks
hms50

[Rotate]

Quality machines should use ABEC 7 or ABEC 9 bearings. However, you can't just take a poorly made machine and replace the bearing with a higher grade and expect it work like a high quality machine. Big part of achieving high precision is mounting the bearings in a properly machined housing with the proper clearance. Too tight and you distort the outer ring and all the accuracy of ABEC 9 is out the window, too loose and you get gulling which will also distor the ring. The same goes for the spindle.

Albert

[John Stevenson]

Right lads asbestos suit time because I know I'm going to get some flack over this.
In my opinion for a home shop use it doesn't matter about the class of bearings in a mill spindle provided they are in good condition, a good make and adjusted correctly.

Now before everybody starts getting there pens out and telling me about ABEC7's and 9's etc let me explain how I came by this thought.

I have a Bridgeport mill, a genuine one not a clone although mine was built by Adcock and Shipley under license in the UK. I use this for general repair work. A while ago I noticed that the quality of the cut was suffering on the edge of slots etc. Then I noticed that it had end play in the spindle.
I stripped the spindle down and found the bearings were worn. I know the price of new precision spindle bearings and had a ring around to price some up. If the worst came to the worst I was prepared to replace these with standard bearings. As it happens I found two precision bearings on the shelf as old stock. But my reasoning was twofold as follows:-

[1] When the machine was new these bearings were also new. As these wore at some point before I noticed any problems with the machine, the precision bearings must have reached the quality of standard bearings but I didn't know. So at what point do you replace bearings?

[2] Secondly the bridgport design is quite long in the tooth. When it was designed ABEC7 bearings were as good as could be made. But with modern manufacturing technology bearings have improved and even the bearing techs agree with this. I asked one what was more accurate, a 1950 ABEC7 or a modern standard bearing. I was told the modern bearing would be better.
So in effect fitting modern ABEC7's or 9's is far in front of what the machine was designed to do and in all probability is no improvement.

As most of the home shop machines have come from industry and probably had a hard neglected life fitting a set of standard bearings will be a vast improvement over the worn bearingsthat are in, regardless of class.
What does matter is the fitting of these the get the optimum out of the setup.
I think Albert covers this quite well in his post above.

Does anyone else see this reasoning?

John S.

[JCHannum]

John;

I agree with you. I think too much time is spent by some HSM's needlessly worrying about the last 0.00001" of accuracy in his equipment. I, for one am not this good, my equpment is better than me, and I am not trying to produce a zillion pieces to ISO 9001 or whatever standards.

If it works, does not chatter, destroy tooling or the operator it is most likely of an acceptable quality for our work.

[Thrud]

I agree with all of the above comments. The great expense and care required to install class 7 or better bearings is all for naught if the rest of the machine is not up to it. If you don't need higher precision the high costs of tools to do that type of work can buy a lot of good tooling and accessories. Some common sense has to be applied in all machinery and tooling purchases. Worry about high precision when you actually require it.

Considering the quality of work done by our grandfathers with equipment worse than even the cheap imports I am astonished at what they were capable of with much less. We are so spoiled...

Dave

[This message has been edited by Thrud (edited 04-04-2002).]

[JCHannum]

Our grandfathers used their hands and heads.

[hms50]

Thanks for the info, I agree most hsm's don't need more precision in there mills. What I need is more time to practice and enjoy my projects. I was just curious about price differances and what effects spindle performance.

John, I agree with your logic about new "standard bearings" being as good or better than old grade 7. But is it true that bearings wear out gradualy? My rather limited experiance has been with ball bearings in motors, idlers on mowing machines and belt drive jackshafts. These seem to often fail from leaky seals and the resulting lack of lubrication, or brinelling (spell?),of the balls in the bearing assem. do to side loading and impact. Both of these problems lead to a rapid distruction of the bearing. What does cause bearing failure in spindles?

Thanks hms50

[jwoitasek]

Hi Guy's

Ok I'm going to shoot from the hip.

From what I have seen doing maintenance for the last 30 years is

#1 lubrication failure.
lack of lubricant or Wrong lubricant.
there are lubricants that WILL NOT mix with others and can gel and harden causing the bearing to fail quicker.
It does not matter the bearing is trash.

#2 Contaimination.
either from lubricant or getting into the bearing and or bearing housing.

#3 abuse.
Doing things that the bearing was not designed for.

Anyway's you guy's may disagree with this call, But as one song say's " Thats my story and I'm sticking to it."
JRW

[Thrud]

Major causes of newly installed bearing failures can be from improper installation 77%, poor lubrication and/or maintenance 14%, overloading, alignment, other causes 8.65%, with .35% due to manufacturing defects. Most bearing companies can give you similar stats for their products. (this are approximate for indusrtial gearboxes and from memory - don't quote me)

JRW observations are the standard causes of properly installed bearings. Any farmer can admit to this...

All hardened bearings eventually start to fracture and flake from physical loading and the balls or rollers develop flat spots which accelerate the wear but if properly maintained the bearing can have a exceptional service life.

As John has stated todays bearings are far better than the days of old and get better every day. Many bearing companies now feature rebuilding of expensive bearings and spindles as a 40-60% savings over the cost of new replacements.

We live in interesting times indeed.

[Bob Quale]

When you say old grade 7 bearings compared to new bearings, Do you mean motor bearings in or general porpose bearing, like those sold in MSC? Also where can I learn to install them corectly? you know, so there is no end play and they last.

I see in HSM where people have made tool post grinders. Would general porpose bearings work with proper intallation?

Bob

[John Stevenson]

Bob,
The spindle bearing under discussion for the Bridgeport are angular contact bearings and not common or garden ball races.
Angular contact bearings are very similat to tapered roller bearings in that the load is taken up one way only.
Two of these back to back with the nessesary shims / spacers can be preloaded to zero backlash.

John S.

[Thrud]

Bob Quale:
re:tool post grinders

One (somewhat) low cost way to go is to adapt a unit such as the Sherline (they can be run up to 10,000 rpm with a pulley kit now) headstock. It is sealed and pretty well maintenance free, can handle small burrs and larger wheels.

If you use the Sherline headstock you may want to consider making a tool grinder utilizing it as well (dual purpose). It could even be used to make a small surface grinder as well. Lots of possibilities.

You can roll your own grinding spindle as well - but doing a good job on a spindle is time consuming.

I use a Foredom 1/4hp flexshaft machine with the super duty collet handpiece (the handpiece is overbuilt and over priced $350) mounted in a machined block to accept the handpiece. I can grind with diamond or carbide burrs as well as wheels rated for 20k rpm use. When I was thinking of a toolpost grinder I checked prices and quickly changed my mind. I had the Foredom, so I use it (occasionaly).

Re: Instructions for proper bearing installation
Any bearing distributor can tell you the proper installation procedure for the bearing you purchase.

For a lathe or mill that are to receive class 7 or higher bearings it would be to your advantage to have the pros do it - if they screw it up you would have legal recourse - not the case if you do it yourself.

[crypto]

My first Bridgeport, an old round ram type, had received much heavy job shop use. Bearings were very noisy. Grade 7 too costly. Bearing supplier suggested I try same bearings as used in electric motors. Bearings perhaps a little noisier than grade 7 but have been running fine for 25 years or so. Seemingly just as accurate as my newer Bridgeport.

[Ragarsed Raglan]

I agree with what John Stevenson said about modern bearings. I was recently looking to replace some grade 6 Timken taper rollers in the headstock of my lathe when I got hit with a cost of around $200 dollars EACH bearing. I rang around thinking the bearing suppliers were onto a fast buck, same answer all over. Seems like years ago Grade 3, 4, 5, 6, & 7 Timkens were selected by hand from the production batches. Thats why they are so expensive ~ you're paying for some guy in an inspection lab sorting through bucketfulls of bearings to find the elusive grade 7! (he's probably on a pension now anyway), I opted for a standard Timken replacement bearing ($45 the pair) with no loss of (detectable) accuracy.

Now the bad news ~ whilst looking for the Timken bearings I was told production was being run down at the European manufacturing centres (they are due to close in 2003) looks like they are going out East - so get the quality stuff whilst you can.

As for Bridgeport accuracy being improved by a spindle bearing job, I have heard the best single improvement to a Bridgeport is to replace the 7/8" pin that the head hangs on with something more substantial.

Ragarse

[Thrud]

The high grade bearing have better finishes, tighter tolerance, and are made from their special crucible steels not the production stuff.

Even if Timken quit making bearings their heat treating and steel making business will keep them busy for a long time to come.