ID grinding hard chrome.

[EmanuelGoldstein]

.. as the wheel goes through the interruptions it deflects. If it deflects down it suddenly has a greater bite, where if it's a touch above center that's not as likely.

But it's a band-daid and band-aids almost always bite you in the ass. If the wheel is not grinding reliably, so you resort to some tricks to keep it from digging in, then it also will never repeat. Then getting the size you want is just a matter of luck. That's not a great approach.

Pulled out the calculator, actually your wheel speed is only a few thou below "generally accepted priciples", that's nothing to worry about. Lesson : don't do math in your head But I keep thinking Borazon would be better, it is much sharper than oxide wheels. Haven't done enough chrome to make a definitive statement on that but I'd give it a try. Or diamond. Or Cubitron II. Something less likely to skate across the top.

 

[Terry Keeley]

Don Bailey mentions cutting on the corner of the wheel at 14:00, anyone doing that?

 

[eKretz]

He doesn't mean turning the wheel so that the wheel is cutting on the corner, he's just describing how a normal grinding wheel cuts on a rigid grinder. With the wheel dressed square to the part being ground, the wheel corner does most of the work (along with whatever portion of the wheel that you are advancing with each revolution of the workpiece, which is why I mentioned that you need to slow that stroke down). He's describing how the portion of the wheel behind that stays nice and sharp and picks up anything that the initial part of the wheel misses as it dulls and/or wears.

 

[eKretz]

I also want to add: you need to remember that if you are cutting your wheel's "contact patch" down by dressing the wheel to a narrower effective width you need to slow that stroke down even further. And I'd sure like to see you stick an indicator on that spindle out near the grinding wheel and give a little push/pull by hand in a video so we can get an idea of how rigid that setup is.

 

[Terry Keeley]

I also want to add: you need to remember that if you are cutting your wheel's "contact patch" down by dressing the wheel to a narrower effective width you need to slow that stroke down even further. And I'd sure like to see you stick an indicator on that spindle out near the grinding wheel and give a little push/pull by hand in a video so we can get an idea of how rigid that setup is.

I stuck a good tenths indicator on the spindle arbor and low and behold I had nearly a thou of radial play, when I push/pull on the spindle nose with the same moderate force there's virtually nothing. I had to make up some special tools to get it apart.

The bearings don't seem to be anything special, think it's worth the money to go with ceramic hybrids? There's no lube, just what's in them from the factory (air motor has oil mist), it runs at 30K.

Fronts are R168ZZ (1/4x3/8x1/8), rears are 686ZZ (6x13x5).

 

[eKretz]

I stuck a good tenths indicator on the spindle arbor and low and behold I had nearly a thou of radial play, when I push/pull on the spindle nose with the same moderate force there's virtually nothing. I had to make up some special tools to get it apart.

The bearings don't seem to be anything special, think it's worth the money to go with ceramic hybrids? There's no lube, just what's in them from the factory (air motor has oil mist), it runs at 30K.

Fronts are R168ZZ (1/4x3/8x1/8), rears are 686ZZ (6x13x5).

I would make that decision based on how much more they cost vs. how much use you'll get out of them. If you use the grinder all the time then it might make sense. If you use it once in a blue moon, maybe not, and just have some spare bearings on hand. Are those just plain spherical ball bearings then? I almost expected to see little angular contact bearings with the fancy grinder spindle. Guess they probably don't make them that small. Do those spacers on the bearings set preload then? Might be you could've just took a shave off of one of those; do you have a surface grinder? May have to do it on a diamond plate by hand or make a little lapping fixture they are so small.

 

[Terry Keeley]

I would make that decision based on how much more they cost vs. how much use you'll get out of them. If you use the grinder all the time then it might make sense. If you use it once in a blue moon, maybe not, and just have some spare bearings on hand. Are those just plain spherical ball bearings then? I almost expected to see little angular contact bearings with the fancy grinder spindle. Guess they probably don't make them that small. Do those spacers on the bearings set preload then? Might be you could've just took a shave off of one of those; do you have a surface grinder? May have to do it on a diamond plate by hand or make a little lapping fixture they are so small.

They're nothing fancy, just plain stainless C3 bearings. The small inch 168's are hard to find in a name brand, I saw listings for NMB's but they'll havta be ordered and could take weeks. I did find them local, even with ceramic balls for the 168 at a decent price but they're China for sure.

R168ZZ

R686ZZ

Think I'll give them a shot but keep looking for something better.

Yup, the shims must set the preload but I wouldn't want to mess with them, I've used it enough where it probably needs new bearings anyway. Surprising they aren't lubed in some way.

 

[Turbowerks]

Terry, I have used these guys in the past to supply odd turbocharger ball bearings imported for sure but have had success with them. The have supplied some of them in grw german made bearings not listed on their site, also boca bearing is another importer of small bearings used in rc jets and dental hand pieces. Good luck.

When I find it I don’t need it
When I need it I can’t find it!

 

[Big B]

They're nothing fancy, just plain stainless C3 bearings. The small inch 168's are hard to find in a name brand, I saw listings for NMB's but they'll havta be ordered and could take weeks. I did find them local, even with ceramic balls for the 168 at a decent price but they're China for sure.

R168ZZ

R686ZZ

Think I'll give them a shot but keep looking for something better.

Yup, the shims must set the preload but I wouldn't want to mess with them, I've used it enough where it probably needs new bearings anyway. Surprising they aren't lubed in some way.

Have you checked your diamond yet to see if the point is sharp?

 

[Terry Keeley]

Terry, I have used these guys in the past to supply odd turbocharger ball bearings imported for sure but have had success with them. The have supplied some of them in grw german made bearings not listed on their site, also boca bearing is another importer of small bearings used in rc jets and dental hand pieces. Good luck.

When I find it I don’t need it
When I need it I can’t find it!

Thanks, the links I put are the Kanuckistan partner of VXB, I also looked at Boca. The metric 686 seems common enough in "name" brand (GRW are excellent, so are WIB) but the small inch R168 doesn't seem to be carried much any more. Dunno if it would make a difference anyway, the NMB's are made in Singapore.

 

[eKretz]

Have you checked your diamond yet to see if the point is sharp?

He did explicitly mention trying a brand spanking new single point Norton dressing diamond or I would have been asking that as well.

Terry, you mentioned at some point that the grinder can only mount 1/8" shank pre-mounted grinding pins or some sort of thing you made yourself that can mount a grinding wheel with 1/4" ID - what does that look like? It's not still on an 1/8" shank is it? That could be another part of your problem. If you're limited to that little bitty shank size you'll probably need to keep your wheel diameter down pretty small so you don't overpower that shank.

 

[CarbideBob]

Since you have posted a couple links I have to ask.
Picking up the phone and asking Diagrind for help not so good?
Bob

 

[Terry Keeley]

He did explicitly mention trying a brand spanking new single point Norton dressing diamond or I would have been asking that as well.

Terry, you mentioned at some point that the grinder can only mount 1/8" shank pre-mounted grinding pins or some sort of thing you made yourself that can mount a grinding wheel with 1/4" ID - what does that look like? It's not still on an 1/8" shank is it? That could be another part of your problem. If you're limited to that little bitty shank size you'll probably need to keep your wheel diameter down pretty small so you don't overpower that shank.

The arbors have a 5mm end (2nd from left), I made a couple of tight fitting flanges to adapt it to 1/4". The fitting for mounted points can only take 1/8" shank points.

Included are all the wheels I've tried.

Since you have posted a couple links I have to ask.
Picking up the phone and asking Diagrind for help not so good?
Bob

They were great, see post #27.

 

[EmanuelGoldstein]

Totally anecdotal here but when dressing little aluminum oxide wheels, I'd brush off the loose rocks after a dress with my fingers. Got a little hot and made the tips smooth enough for nylons-fondling (look ma ! no runs !) but didn't do any real damage.

If you tried that with borazon, the end of the finger came back all bloody.

 

[eKretz]

You might try a "cracker jack" style dresser (with the spinning pointed wheels) too. A wheel dressed with one of those is about the sharpest and most free-cutting way to dress a vitrified wheel I know of. (You would have a gash on the 'ole finger trying the touch on that wheel EG! I've done that touch on the diamond dressed wheels to knock the loose bits out too, they're very smooth, not nearly as sharp - more or less polishing up the calluses).

If that doesn't work, and a very coarse and open (electroplated would probably be good) CBN wheel doesn't work, I'm about out of ideas other than changing to a stouter spindle. I think one of those ideas ought to do the trick though.

 

[Mechanola]

The grinding body must not be too hard. Its softness lies in the strength of the bond. The harder the part is the more the stone should sand out just at the rate of not firing up as you experience.

 

[eKretz]

The grinding body must not be too hard. Its softness lies in the strength of the bond. The harder the part is the more the stone should sand out just at the rate of not firing up as you experience.

He is in the right ballpark range already at J/K. His problem is I believe more related to lack of stiffness in the setup - the large diameter wheel on an 1/8" shank is definitely not doing any favors. The bearings will help a little, but I think this is gonna end up at: gotta get that wheel super sharp. Not enough rigidity there for much of anything else.

 

[EmanuelGoldstein]

You might try a "cracker jack" style dresser (with the spinning pointed wheels) too. A wheel dressed with one of those is about the sharpest and most free-cutting way to dress a vitrified wheel I know of.

Would have been interesting to mess with but all the grinders I've used had single-point diamonds. Especially on an id grinder where you adjust the diamond to be at the same place as the finished hole diameter. They have a threaded mount so you rotate the contraption to move the diamond in and out when you set up the job.

Luckily I'm old or I'd probably try to make some halfass thingamajig to try out your dresser. But I'm guessing much of our captain's problem will go away when he gets tighter bearings in there. You can't very well take off a tenth if your spindle deflects a thousandth.

 

[eKretz]

He can try raising the spindle but I really don't think that will do anything. He's not hogging, just trying to fuzz out a smidge. There literally should be almost zero tool pressure in that direction. And he'll need to use shims to do it as far as I can see... PITA.

At this point, after replacing those bearings I'd narrow that wheel down as much as possible and slow the stroke speed down as much as possible, maybe even switching over to the lathe's feed instead to get better quantitative control over it. Adjust up from there and see if it helps. I think it will.

The carbide shank idea is probably a good one. Maybe use an 1/8" carbide shank and epoxy on a steel 1/4" adapter so you can still use the replaceable wheels easier.

Then if you have one try the cracker jack dresser. If not, rip that diamond dresser through there quick with a little heavier depth/cut to try to knock the abrasive particles out rather than cut them. That generally works decently. Light dressing with a diamond tends to close up the wheel more and works better for finishing. If you want the sharpest wheel you can get the best approach in my experience is to try to knock or tear the individual abrasive particles out. You might need to come back at the end and just dust on a finish with a little finer dress.

 

[eKretz]

If his machine takes 5mm arbors, he'll want to use all of that with a carbide shank. If he wants the wheel removable, then an adapter as you suggest could have a 5mm bore hole into a ~10mm rod that's then turned down to mount the 1/4" bore wheels, with the adapter bonded to the carbide rod.

Going from .197 OD to .125 OD in carbide would likely cost you all the stiffness gains from using carbide in the first place.

Yes you're right. I missed that latest post 5mm tidbit, thought he only had the ability to take 1/8" shank tooling.