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Replacement balls for surface grinder roller ways?


Feb 17, 2017
I need to replace the balls for my surface grinder. They are a common size, 5/8. What kind of precision is good enough? The best I have been able to find is +- .0001" but maybe I'm not looking in the right place or maybe I'm overthinking it and that is good enough?
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looks like Walmart amd Amazon have G-25 balls
I would call a local machine repair shop and ask where to find balls
And get a price on G-10 and G-5balls.
I really don't know what quality balls are used in a new highy quality grinder.

Good to know that new balls wont be much help if ball ways are worn.
Some times taking out a couple end of travel balls can be a Hack way to improve long travel error. but a spacer may be needed to keep balls from going to the end of ball ways.
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I can get get get G25 balls cheaply at mcmaster. I'm tempted to buy twice as much as I need and measure them, picking out the closest matching ones.

The ways and ball cages are fine. The grinder was stored with the table off and balls separate but the balls were not stored well and they rusted so now they need to be replaced.
If that is your plan then you might get a gram scale and sort them by weight.

At amazon gram scales are about 10 bucks, (to .00 gram)
That way you might better sell the left overs as sorted by weight.
We were told that dry was best / so they did not collect stuck on abrasive grits.
I would check them for de mag / see if any will pick up a small tab of .001 shim stock.
looks like they may be about 16.41G
save some egg cartons for balls ansd set themom your scale in a plastic bottlr cap

*If you do this please report your weight variance findings.
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Ball grades control more than absolute diameter tolerance, they also control sphericity and size variation within a batch. I’d go with grade 5 balls (or gr 3) in 440C stainless or 52100 steel. Try Tsubaki Nakashima, you may need to email or get on the phone but they will sell in qty 50-500.
Hi Buck,
If that is your plan then you might get a gram scale and sort them by weight.

that won't work, that kind of scale does not have nearly enough resolution.

A 5/8" steel ball (15.875mm diameter) will weigh about 16 grams. A G25 ball should be accurate to about 25 millionths of an inch which is a bit over half a micron, or 0.0005mm. If you change the diameter by TWICE that amount, one micron, you change the mass by 0.003 grams. No scale that Amazon sells can reliably resolve the difference between 16.000 grams and 16.003 grams. [For a few hundred to a few thousand dollars you can buy laboratory scales that have a resolution of 0.001 grams, but if you look at the technical specs, you will see that the linearity/repeatability is more like 0.005 grams. And, even if you had a perfect scale, I'm skeptical that the density of steel is constant to better than one part in 10,000.)

I agree with you that wear in the ball ways seems like much more of an issue. If the ways were perfect then using stock G25 balls will produce less than one micron error in the vertical direction and probably much less since those errors will tend to average out.

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Thanks Bruce,
I was wondering how much change could be detected.

Trying to measure one has to consider size and out of round and most of us don’t have such equipment or talent. I can measure down to a few millionths, but one would have to measure each ball multiple times for out of round.
I guess one has to go with the ball manufacture’s grading and pay for the grade of one's choosing.
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A reputable source will provide balls that are matched and that meet the specs, so I don't think they need to be checked, just handled with care. And it does not cost a lot. I recently bought a bag of 100 G10 hardened bearing-steel balls, a bit more than 4mm in size. I think the entire bag was 6 bucks plus shipping.

Here are forty matched 5/8" hardened steel balls, G20 (20 millionths of an inch precision) for less than 10 bucks:
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Were you happy with what you received? I can't say G10 bearings advertised as 'slingshot ammo' is confidence inspiring.
I thought the same thing! I haven't finished the replacement ball cages, so I haven't finished the project and used them yet to really know for sure. Everything I was able to find about the company seemed solid and for the price I figured it was hard to go wrong...not really much risk if they turned out to be junk. I called the company to ask a question, but can't recall what it was about...they were helpful and friendly. I may have been asking about local pickup since they're so close to me. It might be worth a call to ask what sort of specs they meet.
A hack method if one is not going to regrind the racks.

Most ball rack wear is pretty even except for at the ends.
It may be logical to limit the travel to exclude the use of the last of long travel where the V runs out perhaps adding a hard wood spacer.
At the big shop we sent out the ball racks after Cincinnati said we would be Ok doing that to .035 stock removal. Most had less than .010 deep wear.
Getting the racks back we shimmed them to original height.
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An older long travel design was the table riding on a chain, much like a motorcycle chain that would dip into an oil bath at each end, The oil dip was lubrication and cleaning. With this the in-line control was a straight parallel that was held straight with a set of bearings, one side fixed and the other spring loaded, This made a v way not needed..
So here is an update. I ended up ordering 5/8 52100 balls from Mcmaster since I was ordering some things anyway and they were cheap enough. They came with a certificate and are from the same lot. I checked a few from the order at random and their size variation is less than the ability of the tools I have at hand can measure - they all measure .6250. Good enough for the grinder they are getting installed in IMO.
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