Baffled..On a Stupid Puzzle

[Phil3]

This is such an embarassing question and puzzle I very nearly did not even post it. If I can't solve this, I may need future help tying my shoes.

I recently acquired a Jet 8" bench grinder and the stamped metal flanges were not flat, so decided to start making new ones. But, at the same time, decided to true up the old ones, for machining practice, since I am new and need experience. After truing, the wheel still wobbles. The original Jet wheel and a white oxide aluminum one I bought both wobble. ??? I checked runout on the grinder motor shaft (5/8") flange and it is close to .001". More than I expected, but that would translate out to around .010" at the periphery and the wobble looks much worse than that. Sometimes when I mount the wheel, it runs with minor wobble, other times much more. Tests I have done:

1) Mount wheel, and most of the time, very visible lateral runout. Remount wheel and may be less.
2) Install inner flange, a spacer (short piece of PVC pipe) and nut and flange appears to run true. Radial runout is terrible, but no matter.
3) Install both flanges facing one another and against one another, with spacer (so nut can engage shaft threads) and flanges run pretty true (lateral runout).

Truing process:

1) Clamped flange in 4 jaw chuck and machined flat small raised boss that shaft flange or shaft nut bears against. Made sure chuck face was clean. No low or high spots left.
2) Made up a shaft with shoulder on end that mimics shaft in grinder. Drilled and tapped hole in end. Fitted grinder flange over shaft against shoulder. Flange sits just proud of end of shaft. Installed cap screw with washer to clamp flange to shaft. This was tight enough for me to face the large face of the flange. No high or low spots left.
3) Reversed flange again and repeated Step #1. No high or low spots left.

The grinding wheel appears flat, but the Norton has terrible radial runout. The grinder vibrates noticeably with either wheel.

I sure hope the new flanges I am making work well, but given that the old ones are giving me fits even after machining, I am less than confident.

Please help what must be something obvious I am overlooking or doing wrong.

- Phil

[STRR]

Phil,

I think the answer is in your statement that the wheels sometime run near true and sometimes not depending on mounting. It would appear to me that the wheels are not true them selves. On the other hand, if it was JUST the wheels, they would be out of or in true ALL the time. SO, there must be some kind of run out when the wheels are mounted but not when you measure just the shafts themselves.

Here goes my best guess: You have some bearing slop and some shaft flex when the wheels are mounted and none or much less when they are not mounted. If the wheels are out of balance and/or true, they work together on the bearing slop and the shaft flex to make things vibrate and look really bad.

You might try mounting each wheel on a true center axle and seeing just how true they actually are. You might also buy a rotary lawn mower blade balance cone thingy and put your wheels on it, one at a time. This will tell you if the wheels are in balance or not. The wheels may be out of balance causing all the problems and/or the holes may not be perpendicular to the faces.

Hope this gives you some ideas,
Terry Miller

[JimGlass]

This is just a thought. The wheel ID and the grinder shaft should be a very close fit. Close enough there should be almost no clearance between the two. That fit determines concentricity of the wheel. Sometimes bushings are needed for wheels with different OD's from the shaft. Excess clearance between the wheel and shaft would explain what you are seeing.

Did you check the mounting shaft and the mounting flange for concentricity and squareness?
Jim

[BillTodd]

The wheel ID and the grinder shaft should be a very close fit.

Warning: not to tight. You don't want to crack the wheel as the shaft expands!

If the shafts on the grinder are at fault, you may have better luck truing the flanges on the grinder. You could rig up a tool post type grinder to just finish the flanges while spinning on the grinder shaft.

Bill

[Harold_V]

The wheel ID and the grinder shaft should be a very close fit.

Warning: not to tight. You don't want to crack the wheel as the shaft expands!

It's worse than that, and the circumstances described in this thread are an excellent example.

If the sides of a wheel are not dead parallel, or if the bore of the wheel is not perfectly perpendicular to the sides, tightening the flanges can result in a fractured wheel, leading to serious injury or death. A tight fit of the wheel assures that will happen.

Wheels are not expected to be perfectly concentric with the bore when they are installed. If they are, it's a gift. That's what dressing is about. A mandrel with a locating boss (or adapter bushings) should always have clearance, to avoid problems that can be associated with the manufacturing of grinding wheels. If one desires to be able to remove and replace grinding wheels, keeping concentricity, replaceable hubs should be incorporated, such as are used on cutter grinders and some surface grinders.

Harold

[Mr Ron]

Have you tried dressing the wheel?

[roundnose]

Even on my grinding machines that use Sopko type removable hubs, and toolroom wheels, there is always run-out.
I have a Jet 8" bench grinder, other then putting new bearings in it, its been pretty good.
The smaller hub size, stamped flanges, and probably less precision made wheels, there is more run-out on bench grinders.
Not saying this is the right thing to do, but this is what I do.
Along with dressing the face of the wheel, I dress both sides of the wheel back an inch or so.
I do this gently with a Norbide dressing stick, rather then tryng that with a wheel crusher.
Makes for smoother running, and better grinding.
Good idea to stand to the side for a minute. when starting any grinder.

[Harold_V]

Even on my grinding machines that use Sopko type removable hubs, and toolroom wheels, there is always run-out.

Correct, because they, too, have adequate clearance on the wheel to prevent breaking the wheel when it is installed. Wheels, when first mounted, should be dressed, irrespective of the type of grinder in question. Wheels mount on hubs virtually the same way they mount on other grinders. It's the precision tapered hub that permits removal and replacement of the wheel (via hub removal, not wheel removal), eliminating dressing with each installation. That's quite important when using diamond or CBN wheels.
(I realize you know this, roundnose---I'm speaking to those that may not be familiar with T&C grinders.)

Harold

[Phil3]

Well, I am completely stymied. A grinding wheel on this grinder, even with machined flat flanges , looks like a potatoe chip spinning around. It wobbles, badly, just as badly as it did before I machined the flanges. I did more testing, without the grinding wheel.

Axial runout on the grinder shaft flange is about .001". Radial is even less. I slipped onto the grinder shaft, both flanges, facing one another, but with no grinding wheel. I then slid on the plastic bushing that came with the Norton grinding wheel, and then finally the nut, which was gently tightened. This test was done just to make sure the flanges are running true. They did on the lathe after maching, but not on the grinder. Axial runout is readily apparent and excessive. I can not measure it as I would need to indicate off the back side of the flange, which is rough and which I did not machine flat. But, you can watch it wobble. The degree of wobble varies depending on where the pair of flanges are placed on the shaft and where the flanges are in rotational relation to one another. This would all seem to indicate the mating surfaces of the shaft flange and/or flanges are not flat and running true. But they are!

The shaft axial runout is .001". The flange runout when mounted on the lathe is less than .001", no surprise since the lathe just machined the surface flat. But, put it all together on the grinder shaft, and it is very wobbly. ??? It is like 2 + 2 = 5. At least to my novice mind.

I can think of only one possible thing. The inner surface of the grinder shaft nut is not flat. This means that the shaft flange and the inner surface of the nut (effectively the flange surface on the other side of the grinding wheel) are not parallel. When tightened, the pair of flanges sits flat against the large nut, but not flat against the smaller shaft flange or shoulder. I can check this and machine the nut flat. If that does not work, I really am at a total loss.

Please note all these tests are done without the grinder under power. Spinning by hand makes the problems VERY evident.

- Phil

[Harold_V]

It may be that the cut that creates the shoulder on which the inner flange bears is not at a right angle, or it may have been a cut terminated without dwell, so there's not a square shoulder, but a helix on which the flange bears. I suggest you remove the armature from the motor, then make a setup that permits a truing cut on the shoulder. I would also not discount the idea that the thread was generated by means that permitted a loss of perpendicularity.

Is it safe to assume you bored the flanges and faced the face in the same setup, so the bore is at a right angle to the flange? If so, and you did NOT machine the second side with soft jaws, you may be well served to place the flanges on the table of your mill, then take a skim cut off the face, where the nut and shoulder of the shaft bear. That will ensure that the two faces are parallel. Also, ensure that the innner flange is not resting on a radius, allowing the flange to lean. If you do not have much experience, you may be creating problems that may not be obvious to you when making your setup.

Can you post a couple pictures of your grinder? Please make them large enough to be useful (at least 800 pixels in width)----the board software will size it to a thumbnail. A close-up of the mounting surface for the wheel would be desirable, as well as one showing the entire grinder, for perspective.

An adapter can be made that will eliminate all of the problems you're experiencing. You may wish to pursue that project, but lets see what's going on before making that decision.

Harold

[Phil3]

It may be that the cut that creates the shoulder on which the inner flange bears is not at a right angle, or it may have been a cut terminated without dwell, so there's not a square shoulder, but a helix on which the flange bears. I suggest you remove the armature from the motor, then make a setup that permits a truing cut on the shoulder. I would also not discount the idea that the thread was generated by means that permitted a loss of perpendicularity.

Yes, it is possible there is shaft shoulder is not square on the inside 90 degree shoulder angle. I looked at it with a magnifying glass, but could not really tell.
Disassembling a brand new grinder to square up the shoulder is not something I really want to do, so will consider that only after I can really tell what is happening there. Perhaps some bluing will help me see any contact problems.

Is it safe to assume you bored the flanges and faced the face in the same setup, so the bore is at a right angle to the flange? If so, and you did NOT machine the second side with soft jaws, you may be well served to place the flanges on the table of your mill, then take a skim cut off the face, where the nut and shoulder of the shaft bear. That will ensure that the two faces are parallel.

No, soft jaws not used. Process was.
1) Flange first in chuck with large diameter against face of chuck. Faced small side of flange.
2) Then, securely put machined flange on a shaft with shoulder (mimic of grinder shaft) and faced the large diameter side.
3) Then put flange back in lathe chuck and repeated step 1.

Also, ensure that the innner flange is not resting on a radius, allowing the flange to lean. If you do not have much experience, you may be creating problems that may not be obvious to you when making your setup.

Good point. My inexperience shows. Will make sure the bore is square and clean. It isn't now, since I never touched it.

Can you post a couple pictures of your grinder? Please make them large enough to be useful (at least 800 pixels in width)----the board software will size it to a thumbnail. A close-up of the mounting surface for the wheel would be desirable, as well as one showing the entire grinder, for perspective.

Sure, will do when I get home.

An adapter can be made that will eliminate all of the problems you're experiencing. You may wish to pursue that project, but lets see what's going on before making that decision.

I am making new flanges, but wanted to fix these flanges for the experience. They are giving me more experience and challenges than I expected!

Thank you for your patience and help. It is most welcome. Thank you.

- Phil

[Harold_V]

Yes, it is possible there is shaft shoulder is not square on the inside 90 degree shoulder angle. I looked at it with a magnifying glass, but could not really tell.

I'd like you to inspect the shoulder, looking for an inside corner radius. I assume it has one, although they may have provided an undercut instead. In any case, don't trust your vision, even magnified. Place the tip of a DTI against the shoulder, then rotate the shaft. It's important to determine if the shoulder is not a helix, or some deviation from a straight cut. That's what concerns me, even though it's a long shot. If the grinder was made in China, you can expect all kinds of deviations from acceptable work. Do note, I'm not critical of Chinese equipment---but I've had my own experiences and understand that they don't always have experienced workers, so they're prone to making mistakes.

Disassembling a brand new grinder to square up the shoulder is not something I really want to do, so will consider that only after I can really tell what is happening there.

I can understand your reluctance to dismantle the motor, especially if that's new territory for you, but they're generally pretty straight forward and can be dismantled rather quickly. The clean up cut would take but seconds, although, if you don't find a center hole in the armature (not likely to), you may have to use a steady rest. All depends on how you grip the shaft. If you have soft jaw capabilities, or if you have collet capabilities, that should provide more than a substantial setup. That's assuming you can place the shoulder such that it is only slightly extended beyond the collet. If it is held such that the shaft on the opposite side is gripped, there's no way you should try to take the cut without support.

Perhaps some bluing will help me see any contact problems.

Possible, but I expect not. That's especially true if too much blue is used. You'd be far better served to trust a DTI, assuming there's a surface on which you can run the (tiny) tip. If there isn't, you may have discovered the problem (see my comments, above).

Harold