Restoring ball way accuracy with larger balls

Long story short, I have a T&C grinder with ball ways somewhat worn, with track in the ball way which is probably 2-3 thou deep.

short of (expensive) regrinding, I read that restoring accuracy is possible using larger balls - so I am thinking of using 7/8 balls instead of 3/4 which are currently there.

But, there are couple of issues I see:

First, the ways use two V-s on one side, and V with flat way on the other side. Larger ball will help on V ways, but on the flat that ball will stay exactly in the same worn path.

Second, larger ball will not raise both sides identically. I made some calculations, and using 0.125" ball size increase will add additional 0.026" per V assuming it is 90 degree angle. so on the side with two V-s will be 0.026" higher than the other.

what is the best way to compensate for both issues? the only thing came into my mind is epoxying 0.025" full hard shim stock on the top surface of the flat way.. don't know if it will hold though, or may press the shim back to the worn groove.
are there any better methods?

Thinking of it, grinding 0.004" from the flat way (to remove the worn groove), and then using 0.03" shim stock under it sounds most promising, but unfortunately I don't have access to a surface grinder to regrind the flat way.

I would leave it alone or regrind, the larger balls sounds like a train wreck...Phil

Green Rabbit said:

...
Second, larger ball will not raise both sides identically. I made some calculations, and using 0.125" ball size increase will add additional 0.026" per V assuming it is 90 degree angle. so on the side with two V-s will be 0.026" higher than the other.
.

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Kudos for at least finding this but Ouch.
Consider staying with the original sized balls and lapping the ways with a long rod and paste, The round surface may be better than the new.
Also wonder if that .002 deep track was not put there as new. Is it wear or intentional?
Bob

CarbideBob said:

Consider staying with the original sized balls and lapping the ways with a long rod and paste, The round surface may be better than the new.
Also wonder if that .002 deep track was not put there as new. Is it wear or intentional?
Bob

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I really like the idea with rod and lapping. 3/4" precision ground rods are inexpensive, dykem will show if there are low spots that need more lapping around them. And a piece of clean/fresh rod can be used to measure consistency of the track depth along the way.
Is this a common practice or something you've just came up with?

on V-s, the rod would be self-centering, but I'll need to find a way to keep rod centered on the flat way. But, a simple 3d printed jug should do it

The track is wear from what I can tell, as its depth is not consistent - more in the middle, less on the sides.

Do it and be sure to tell us all about it and how successful it was. A lot of pictures. It should be interesting and I also have the same opinion as Phil.

One caveat about lapping: the rod that you will be using as a lap should be softer than the ways, otherwise you will end up lapping the rod instead.

Paolo

.... I have a T&C grinder with ball ways somewhat worn, with track in the ball way which is probably 2-3 thou deep.....short of (expensive) regrinding, I read that restoring accuracy is possible....

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What accuracy problems have you identified and how?

One caveat about lapping: the rod that you will be using as a lap should be softer than the ways, otherwise you will end up lapping the rod instead.

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also ideally the lap will be a true charged lap (or series of charged laps) not a rod messing around in loose free abrasive.
Perhaps brass or soft bronze, even aluminum? lap(s), Thomson or other ball rod for the test gage? Manifestly the "track" arc/dia can/should be larger than the ball dia.

smt

stephen thomas said:

What accuracy problems have you identified and how?

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I put a magnetic chuck on one the right side of the table and resurfaced it. Then, raised the grinding wheel and put a dial indicator tip just under the wheel and moved the chuck around - it reads zeros across the entire surface. After that, I moved the indicator tip to the right (3-4 inch of the wheel location) and repeated - the indicator shows variance a bit under 0.002"

I understand that if I put the chuck to the center of the table, it would have a better flatness, but that also means I will have to remove, reinstall and perhaps resurface it every single time I need to do some other op. keeping it on a side would allow me to rarely move the chuck around.

stephen thomas said:

also ideally the lap will be a true charged lap (or series of charged laps) not a rod messing around in loose free abrasive.
Perhaps brass or soft bronze, even aluminum? lap(s), Thomson or other ball rod for the test gage? Manifestly the "track" arc/dia can/should be larger than the ball dia.
smt

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Softer material should not be a problem, I could cut a rod pieces on a lathe, and put some groves in it for abrasive. A shallow thread cut or just a pattern of groves. Larger diameter makes sense to me, to ensure smaller balls will actually "fall" into those groves. Any idea by how much larger?

Also, what is the benefit of using a ball screw vs a regular precision ground rod as a gauge? I don't have one laying around, don't know if it worth buying just as a gauge

Given the 2 sets of results for the tests you described, the test procedure sounds anomalous.
In any event, it has not necessarily isolated the ways as the "error" source unless there are other parts to the procedure not described.

If the chuck honestly grinds flat & parallel as described but perhaps proven by means independent of the table and ways of the subject machine, then why not just mount it over there and leave it as desired? Work will also be ground parallel to the chuck surface.

Also, what is the benefit of using a ball screw....

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Not what i suggested.
But my terminology was unclear.
"Roundrail shafting such as Thomson brand or other precision round linear ways for ball bushings"

Re: size, it's not my project. i was commenting on lapping process, and keeping the gage and the lapping tool separate. If i were to take that approach, I'd probably start with the lap on size, and assume it would make the track somewhat larger due to process. The real point is that the track radius not be smaller than the ball radius. However, given that the balls currently run on a flat? (infinite radius) & a V? (2 sides of infinite radii) There is clearly room for windage so long as everything stays parallel. If not, the balls will climb the sides of one of the surfaces as they diverge. Which could suggest keeping the flat way, flat.

There's other geometry to inspect & take into account, whatever you do.
For instance, suppose the table surface (not the ways) is a current problem (or future problem of any work)?


smt

stephen thomas said:

Given the 2 sets of results for the tests you described, the test procedure sounds anomalous.

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I think the test maybe not the most representative, but valid. Consider consequences of a ball track wear when resurfacing the chuck: as the chuck moves right to left, it will climb and dive following the track, and the grinding wheel will print the same curved profile into the chuck top surface. When indicated from under the wheel, the indicator won't show as the ways/chuck curves will cancel each other out.

But when indicated left or right under the wheel, the variance will start to show - because the curved track on the ways will reveal itself before (or after) chuck curve compensates it. Same will happen if I move the chuck right or left on the table - but then, problems on the table itself may show even more - that's why Id rather have it fixed.

stephen thomas said:

In any event, it has not necessarily isolated the ways as the "error" source unless there are other parts to the procedure not described.

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Well, the chuck was not moved between resurfacing and indicating. So even if table is not flat or parallel to the X axis(I am sure it has problems, despite that I shimmed it where I could), it would only show as deeper/shallower grind into the chuck surface when grinding it.
I indicated the surface during X axis movement only, not touching Y at the same time. From what I can see, the only problem that can produce such result is when the table does not move as a straight line along the X axis, which is pointing at X ways vertical curvature.

Of course, if the reason of that curvature is for example a twisted cabinet base, then lapping wont fix anything. So far I don't have good ideas how to reliably isolate it, but if the gauge shows that way's thickness differ, it seem to worth fixing (it is very unlikely that cabinet base twist, if present, compensates it)

stephen thomas said:

"Roundrail shafting such as Thomson brand or other precision round linear ways for ball bushings"

smt

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That one makes total sense, thank you!

Here's my confusion:

I put a magnetic chuck on one the right side of the table and resurfaced it.

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Then, raised the grinding wheel and put a dial indicator tip just under the wheel and moved the chuck around - it reads zeros across the entire surface.

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I was impressed - took it to mean that you unstrapped the chuck, and ran it around on the table under the indicator. It seemed surprising that you found no error. However, my procedure-related reservation was that that did not eliminate the existing table flat/parallel condition.

For most T & C work, the wheel approaches the work at 90 deg to the table surface. Given your concerns are you planning to use it as a surface grinder? The older workhorses I'm familiar with (Cincy #2, Norton) have Y (Wheelhead height) actuators that are rather coarse for surface grinding.

It would strike me that whatever process you take to eliminating error, the error ought to be identified and quantified by reliable independent means first. Perhaps shim a 12 x 18 surface plate on it and tram that to start? Or independent straight edges in both table way axes?

smt

stephen thomas said:

For most T & C work, the wheel approaches the work at 90 deg to the table surface. Given your concerns are you planning to use it as a surface grinder? The older workhorses I'm familiar with (Cincy #2, Norton) have Y (Wheelhead height) actuators that are rather coarse for surface grinding.

It would strike me that whatever process you take to eliminating error, the error ought to be identified and quantified by reliable independent means first. Perhaps shim a 12 x 18 surface plate on it and tram that to start? Or independent straight edges in both table way axes?

smt

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Well, I don't have room for both surface and T&C grinders, so decided to versatility of t&c is more important to me. Sharpening/resizing reamers or end mills, grinding OD/ID tapers etc. And it does not do such a bad job on surface grinding finish, too, granted I take my time and install appropriate wheel, well balanced, fresh dressed it etc.
And you are right it does not have fine feed for vertical adjustments. So typically, if I need to get within couple of tens, I would put an indicator on a part and zero it before turning the handwheel, and then go by the indicator readings. it is slow, but considering I don't do it often, it works for me.

And you are right, using a straight edge or surface plate is a better idea, at least before messing with the ways. It can also better show me how much I am exactly off a straight line, and if the readings are getting confirm a pattern of ways wear (concave center, raised edges). Later, once the ways are removed, similar pattern from the gauge readings could tell the problem can be fixed for by lapping.

Thanks for helping me to sort this out!

Before you do anything, you NEED to at very least get yourself a machine level, preferably a surface plate too.

From what I can gather from your posts, it sounds like you are able to see a little bit of table sag at the end of the machines travel. There is a chance the sag is being exaggerated because the machine is out of level. It could also be caused by twist. Level it first, get the twist out, and then check it.

If you do this and still have issues, then put the next size set of roller balls in and regrind the table (assuming its also usable as a surface grinder based on your other posts), having a slight slant on the bottom (way) side isn't going to mean diddly. If you don't want to have grind s 0.026" off the table, then go with a combo of 13/16" and 21mm balls, that will get you to within 0.005" off the bat.

If that doesn't work due to wear in the flat side of the way, you could try and switch the flat side from balls to rollers. This should work IF the V runs true to the flat its ground into.

If that doesn't work then I would say it's time to be reground. I have my doubts about trying to lap it. If the slide ways are of decent length the 3/4" lap bar you use is just going to conform to the wear in the ways, you might even make things worse.

stephen thomas said:

Perhaps shim a 12 x 18 surface plate on it and tram that to start?

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I wanted to advocate that method -- it is how I measured the accuracy of my surface grinder. Note however that I did not have a way to tram it precisely enough. So after I had spent some time trying (without success) to tram the plate, I instead placed it on three points (small cardboard pieces!) , measured the top, and then removed the X and Y linear tilts in software, using the linear regression function in an Excel spreadsheet. A description is here: https://www.practicalmachinist.com/...or-under-chuck-324747/index3.html#post2896025

Hi All:
I thing TheBigLebowski has nailed it in post #13:

Popping bigger balls in the vee side brings the contact points out of the worn track as the OP originally commented.
They can be 20 mm or 21 mm diameter and you can easily determine what size rollers will match properly in CAD and then verify you've got it right by turning a pair of temporary pins and putting the whole works together and blueing the flat ways.
As soon as you get a good contact patch when the test rollers run through the blueing, you know what size permanent rollers to buy.

If you can't find a source for the right sized rollers, buying a bunch of gauge pins and cutting them up to function as rollers allows you to preserve the original flat way without having to touch it, other than stoning the burs away, and you can pick your pins in whatever size you need to, just from McMaster Carr or any other place that sells gauge pins.

You will have to make a cage for the rollers, a piece of phenolic plate will work just fine.
So will a piece of brass.

It's the most attractive way by far that I can see, short of doing the rebuild properly by regrinding the ways.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
www.vancouverwireedm.com

They can be 20 mm or 21 mm diameter and you can easily determine what size rollers will match properly in CAD and then verify you've got it right by turning a pair of temporary pins and putting the whole works together and blueing the flat ways.

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Missing a detail or i don't understand your suggestion completely? (regarding rollers)

the ways use two V-s on one side, and V with flat way on the other side.

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I still feel the OP needs to map the existing geometry before doing anything. Might be the wear as presumed, might be castings that "settled". Other issues include dealing with the rack height. Is it known what machine this is?

smt

Hi Stephen:
I interpreted that quote to mean that the x axis slide has a female vee on the table and a female vee on the saddle on one side; and a female vee on the saddle and a flat track on the table on the other side.

To go with rollers on the second side would require them to be long enough to straddle the second vee on the saddle. and yes, it's a big, cringeworthy bodge.
However, the vee tracks on my Kent grinder are pretty small and it has 16 mm balls I believe, so the length of roller needed to straddle it is not a great idea, but not that bad either.
Yeah running the rollers on the edges of the vee is pretty hokey, and if those edges are not parallel with the track it's not gonna work, and it's gonna wear faster than it otherwise would, but it might get the OP up and running without having to do much to the grinder, and it is completely reversible if it ends up being unsatisfactory...just take the new balls and rollers back out and reinstall the originals.


So I took a liberty in my interpretation, and maybe I'm wrong with it.
However, the principle still holds...if the double vee track is filled with identical diameter balls and the flat track is filled with the proper sized rollers, to make the table sit evenly on every rolling element at the same time, then all the balls and rollers will contribute to the load carrying of the table so long as the table isn't warped, the saddle casting isn't warped, and the rolling elements are running on an unworn part of the tracks.

To your last point; the OP is not hoping to rebuild the machine properly...he's hoping for a quick and dirty that will make it better than it is now.
If this was going to be a proper rebuild then yes, the first step is mapping what he's actually got, and then working out a good plan to tackle it methodically.

But if he can't justify the cash to regrind the ball tracks, it's going to be a bodge however he does it, and that may well be plenty good enough for what he wants to do with the machine.
If he throws in new balls and rollers and makes it 75% better, he might end up happier than a pig in shit; and that's enough of a win for me.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

Hi again All:
Another thing he could do if he has a big enough mill:
Take the flat ball ways out of the machine, widen the pocket they sit in, and elongate the bolt holes that hold in the track.
He can then shift the track sideways, shim it in place, and end up with the balls riding on an unworn part of the track.
Now he puts bigger balls in the vee track, finds the right size mating balls to get him close with the flat track and re-scrapes the top of the table to get it parallel to the spindle again.

It needs a biggish mill but it's reasonably simple to do.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining