Space between ball bearings?

[Jaepheth]

Ok, so I'm building a tail vise for my workbench.
Instead of purchasing factory made thrust bearings or bronze washers, I cheaped out and bought a bag of 6mm diameter SS ball bearings.

These will be sandwiched between two SS washers, and held in place by copper and steel sleeves:

Marine grease will be added during final assembly.

Is there a rule of thumb for how much of a gap needs to be around each individual ball to prevent binding? Is this amount different for the space between bearings and space between the ring of bearings and each wall?

Error correction: The maximum orbit would have a gap of 4.24 mm (radius) between the bearings and the inner ring and 0 clearance between bearings and the outer ring (if you used all 16.6 bearings).

A middle orbit would have 14.39 bearings. (Formula (using radians) for finding # of bearings: X = pi/(arcsin(r2/r1)) where X = # bearings, r2 = bearing radius, r1 = orbit radius)

I'm thinking I need to use something close to the minimum orbit so that the bearings remain centered around the axis. Or else I'll need an additional inner spacer ring to keep the bearings centered.

 

[Howard]

I wish you had labeled it as threaded rod and not an axle.

That aside, I have honestly never considered building my own bearing, whether thrust or radial.

 

[Jaepheth]

I wish you had labeled it as threaded rod and not an axle.

Sorry. I didn't think it mattered much. Basically the copper sheath is there to prevent the threads from interfering with the ball bearings.

It also occurs to me I could arrange the ball bearings in a manner like this:

I haven't worked out the math for that sort of configuration, but the same general problem is the same, how much space to allow between bearings.

 

[phucheneh]

...ball bearing assemblies are not expensive.

https://www.google.com/url?sa=t&rct...N-1tfAWKaPlXNAQzw&sig2=yksJdGhpQudlYgnt-6m8-Q

Also, the actual balls are hardened steel. Stainless washers are not. The balls are going to tear up the washers.

 

[herm0016]

i would scrap this idea and get a proper roller bearing. ball bearings for thrust are really no good at all.

The balls are going to be much harder than the washers, this will really not work well at all. for thrust you would need an angular contact ball bearing for a proper setup. a needle roller thrust bearing will me much easier and cheaper and actually work for your applacation.


bottom of the page:

http://www.mcmaster.com/#standard-rolling-element-thrust-bearings/=lunkkt

 

[phucheneh]

What? That's the opposite of a good way to use a needle bearing.

With them laid out flat like that, you're giving each end of the rollers a different distance to travel.

 

[herm0016]

What? That's the opposite of a good way to use a needle bearing.

With them laid out flat like that, you're giving each end of the rollers a different distance to travel.

yes... but... surface area.

this is exactly the correct app. for a roller bearing, the surface area of the rollers is much greater than that of the balls. this is why an angular contact ball bearing is much better than what the OP is proposing. what the op is proposing is going to dimple the washers the first time he uses it, and will become worthless after a small amount of use. a simple oil impregnated bronze washer will have longer and better performance.

do you propose that the op's solution is going to work at all?

 

[phucheneh]

do you propose that the op's solution is going to work at all?

No, sir, I do not.

But I think a premade ball bearing assembly would work fine, unless he's tightening his vice with Thor's hammer.

It's not just the tip of the balls taking the load (heh...tip...balls...load). If surround by a proper race, there's plenty of support.

 

[Jaepheth]

Also, the actual balls are hardened steel. Stainless washers are not. The balls are going to tear up the washers.

Will this hold true even if the peak speed is ~80rpm and max axial load is will be...oh... I'd guess 100psi?

 

[Howard]

Will this hold true even if the peak speed is ~80rpm and max axial load is will be...oh... I'd guess 100psi?

How did you calculate that?

 

[phucheneh]

What axial load? I thought this bearing was just going to be for movement under compressive forces?

 

[Jaepheth]

it's a hand crank, so I can't really see myself moving it more than 1.5 rotations per second
and it's primary function will be clamping wood, and I don't think I'd exceed the clamping pressure of one of those little quick grip clamps (~97psi)

 

[Jaepheth]

What axial load? I thought this bearing was just going to be for movement under compressive forces?

sorry, wrong term.

All the force will be trying to squeeze the washers together

 

[Jaepheth]

Oh... fuck me.

I swear the cheapest 5/8 bronze washers I could find last time I looked were ~ $50 for a pack of 25.

Now these show up.

I guess nevermind about the whole thread.

 

[disappoint]

Darn I thought all this time you were asking for help on a mechanical engineering homework problem.

 

[Gillbot]

No, sir, I do not.

But I think a premade ball bearing assembly would work fine, unless he's tightening his vice with Thor's hammer.

It's not just the tip of the balls taking the load (heh...tip...balls...load). If surround by a proper race, there's plenty of support.

Home made bearings will not support the forces of a vice, even if Thor's hammer wasn't tightening it. The races and roller elements are made of specific materials and go through proprietary surface treatments to reduce deformation under load.

Get a proper bearing.

Will it work? Maybe, but one can't tell for how long. Would you want to have something under force when it let go and possibly flies apart into your face/eye?

 

[phucheneh]

Home made bearings will not support the forces of a vice, even if Thor's hammer wasn't tightening it. The races and roller elements are made of specific materials and go through proprietary surface treatments to reduce deformation under load.

Get a proper bearing.

Will it work? Maybe, but one can't tell for how long. Would you want to have something under force when it let go and possibly flies apart into your face/eye?

...so, 'quoted for emphasis'? Or did you just want to pick a random post to 'correct,' without actually realizing that you weren't correcting anyone?

 

[BrokenVisage]

Sorry. I didn't think it mattered much.

Oh, it matters. Like not adding beans to chili.

 

[Red Squirrel]

I'm no expert but wouldn't you want to use all of the same type of metal for the entire assembly? That way you prevent varying thermal expansions as well as corrosion, though corrosion is probably not an issue here due to the lube.

 

[phucheneh]

I'm no expert but wouldn't you want to use all of the same type of metal for the entire assembly? That way you prevent varying thermal expansions as well as corrosion, though corrosion is probably not an issue here due to the lube.

AFAIK bearing races are not as hard as the balls themselves. For all intents and purposes, ball bearings just can't be worn...they'll break before they change diameter. But races can wear.

The race is still damned hard, though.

 

[Jaepheth]

I'm no expert but wouldn't you want to use all of the same type of metal for the entire assembly? That way you prevent varying thermal expansions as well as corrosion, though corrosion is probably not an issue here due to the lube.

Just using the easiest to find stuff lying around. 1/2 copper pipe coupler from home depot has a 5/8 inner diameter off the shelf. I happen to already have the shim stock on hand. I had extra washers too. So I thought i'd try to get away with spending $1 on some bearings to finish the project.

 

[JJ650]

...ball bearing assemblies are not expensive.

https://www.google.com/url?sa=t&rct...N-1tfAWKaPlXNAQzw&sig2=yksJdGhpQudlYgnt-6m8-Q

Also, the actual balls are hardened steel. Stainless washers are not. The balls are going to tear up the washers.

Being in business with a forger that supplies seamless, rolled rings to bearing manufacturers...a single "one off" bearing will be relatively expensive...especially Timken. They likes the money.

 

[herm0016]

Being in business with a forger that supplies seamless, rolled rings to bearing manufacturers...a single "one off" bearing will be relatively expensive...especially Timken. They likes the money.

op does not need a custom timken.

Chinese from mcmaster will work great.

 

[Meghan54]

Being in business with a forger that supplies seamless, rolled rings to bearing manufacturers...a single "one off" bearing will be relatively expensive...especially Timken. They likes the money.

How about stupidly expensive? This is from my wife who worked for almost 2 decades as a production manager for Torrington Bearings, which was once part of Timken---when Timken wanted some of Torrington's tech.

Of course, all Timken did for Torrington was to chase off the small but profitable accounts and try to concentrate solely on mega-accounts, only to drive the company damned near into insolvency.

 

[Bubbaleone]

If you're building this style woodworking tail vise...

...sintered bronze thrust washers with a dab of molybdenum grease are all you need.