CBN - too much runout on my bench grinder? Better grinders?

I have a Metabo DS 200 grinder - older model with a 17mm shaft. I have always been very happy with this grinder - runs smooth and very little vibration with a dressed wheel (Norton 3X wheels).

I just bought a Vicmarc CBN wheel however and was very disappointed with the amount of visible wobble I can see in the wheel, and vibration is worse than with my dressed Norton wheels.

I don't have a gauge indicator to measure runout properly, but using my vernier on the side of the wheel at the outer edge, it looks like I have approx 0.4mm of wobble and the equivalent across the face of the wheel. Because my grinder has an odd shaft size - 17mm, I had to get the 16mm bushing with my wheel and have the centre of the bushing bored out to 17mm. My first thought was that the bore of the bushing was not made perfectly parallel to the outer surface, and that might be the case, but taking it off and turning the grinder shaft with my engineers square sitting up against it I can see some visible runout on the shaft itself. So its looking like my grinder may not be up to the task of turning this CBN wheel for effective sharpening...

How much run out do people think is acceptable to get good sharpening results?

Have people measured the runout on their grinders? What brand/model do you have and what tolerance did you measure?

I plan to buy a dial indicator so I can accurately measure the shaft runout as well as the mounted bushing runout to figure out if I have an issue with the bushing or not, and how bad the runout is at the actual shaft. If the grinder proves no good then I will probably turn it into a buffing station and then be in the market for a new grinder to turn the CBN wheel. What grinders have people had success with?

Oddy, I run an old A&A grinder with no descernable runout.

Is the grinder secured to the bench?

Some data from my two 40+ year old old GMF 1HP 3P grinders.

The shafts have <0.005 mm of run out i.e. I can barely see the needle on the indicator move.
These are very nice grinders and I have them running on a VFD so, variable speed, and if they vibrate on one frequency it usually just takes a shift of a few Hz either side to minimise the vibration.

Because of the vibe minimisation feature of a VFD I haven't tried to tune up any wheels I have placed on these drives.
I just bolted the wheels on and I don't consider them to be that special but the are good enough for what I do.

My CBN wheel has a side to side run out of 0.23 mm and an out of round of 0.13 mm.
There's no grit on the side of this wheel so the side to side run out is not that relevant.
I know the supplied 5/8" bush for this wheel is slightly too large as it slides in and out easier than it should.
When I get round to it I will turn up another bush.

On the same shaft as the CBN wheel is a flat 6" diamond lapping wheel and that has a max run out 0.10 mm at the outer edge and 0.03 mm on the inner edge.
This wheel is quite thin and is backed by a 75 mm support plate/bush which has a fir fit I made so I consider this pretty good. I use this wheel for TC and TIG tips.

On the other spindle of this grinder is a linisher/multi tool (belt grinder) on it.
Although it is a reasonably well made product there is not so much need for this to be precise although any gross runout would add to general grinder vibration
The machined drive surface of the cast Al drive pulley is about the only place I can measure run out and it has a side to side run out of 0.10 mm and an out of round of 0.15mm.

On the GMF second grinder I have green wheel which hardly ever gets used and a 125 mm thin kerf cutting wheel.
The green wheel has 0.5mm of out of round run out but it really needs dressing.

I also have an well used and abused single phase Abbott & Ashby which has a shaft run out of <0.01mm.
This has a wire and a scotchbrite wheel on it so no need for precision with these.
If you are looking at getting another grinder I would recommend these and although they are not cheap they are well made.

From my experience your wheel is within spec most of these wheels are not "tool room" standard and are sold for woodworkers, this why they are so inexpensive

Thanks for the feedback all, and Pat for measuring my runout this morning with dial indicator.
Well it looks like the the bushing is good and the runout is originating from the grinder shaft. The effect the shaft runout has at the edge of the wheel means quite a noticeable wobble visible with the naked eye. This is not what I was expecting from my setup, and checking out Pat's grinder, he has no visible wobble / runout in his wheels at all.
I have had a go at sharpening a skew with it and it seems to have still done a reasonable job, but I can feel vibration through the tool and I am sure this chatter means only part of the wheel is in use. Not sure if this will give me the best possible edge either.

Might have to keep my eye out for garage sales and an old, quality grinder. Can anyone recommend any new grinders for quality and using with CBN wheels?

Quote:

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Originally Posted by Oddy

Thanks for the feedback all, and Pat for measuring my runout this morning with dial indicator.
Well it looks like the the bushing is good and the runout is originating from the grinder shaft. The effect the shaft runout has at the edge of the wheel means quite a noticeable wobble visible with the naked eye. This is not what I was expecting from my setup, and checking out Pat's grinder, he has no visible wobble / runout in his wheels at all.
I have had a go at sharpening a skew with it and it seems to have still done a reasonable job, but I can feel vibration through the tool and I am sure this chatter means only part of the wheel is in use. Not sure if this will give me the best possible edge either.

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The chatter does means only part of the wheel is in use and may also eventually ruin the wheel. CBN is not meant to have the workpiece constantly touching-not touching the wheel but to have a steady pressure otherwise the CBM material will slowly be knocked off the wheel

I imagine a slow speed grinder would to some extent degate machining tolerances in a CBN wheel?

Dave TTC
Turning Wood Into Art

I've not heard of a CBN user, with either a high-speed or half-speed bench grinder, mentioning out-of round or vibration. The wheels come balanced from the factory (mine certainly were). My own set up (half-speed Carbatec from about 10 years ago - probably the same machine as the Vicmark) has nothing to notice. When I switch off, the wheels take 8 1/2 minutes to spin to a stop. Very smooth.

I would suspect either a rogue wheel (in which case get it replaced) or a spindle out of straight, which you mentioned (in which case get a better machine?).

Two things to try first: see if you can balance the wheel. You sort of did this with your white wheel by truing it. Mark a position on the outside of the spindle and an adjoining line on the wheel. Then turn the wheel incrementally, testing it with each small turn, to see if the vibration reduces.

The second possibility is to get washes that centre the wheels. It may be that the wheel is not fitting well enough, and that is adding to your woes.

Regards from Perth

Derek

I used Bendan Stemp's on a new slow speed grinder by vicmarc or vermec. Something was definitely wrong as it was considerably out. Still got a sharp edge but not a pleasure to use.

I have used others such as retired's and they were a pleasure to use

Dave TTC
Turning Wood Into Art

Dave please edit your post?
Before I miss interpreted it and go to town on you.[emoji849][emoji849]

Apostrophe s

Fixed. Now as in belonging to Bendan Stemp. As the subject matter is CBN wheels I would assume most would get that we are talking about a CBN wheel belonging to Brendan Stemp on a slow speed grinder badged by one of the above whereas the other CBN wheel belonged to retired. I dont think his grinder was slow speed

Dave TTC
Turning Wood Into Art

I have just fitted one of these spherical washer sets and simply put it does what it says and removes all the run out. It was a bit of a hassle getting it and Ken Rizza went out of his way to get it to me and has my thanks. If anyone wants one and to simplify things I would do a group order if the interest was there.

http://woodturnerswonders.com/collec...al-washer-sets

Sounds like a good idea. Keep me informed if you are getting more

Dave TTC
Turning Wood Into Art

Well I checked out one of the Vicmarc grinders today in person and sadly it appears to be of significantly lower build quality than my existing Metabo. I also took my CBN wheel in to try it out for wobble/runout - thanks to Timberbits for graciously letting me try on their demo unit.
Observations were that the quality/design of the bushings supplied with the grinder are unlikely to give you an accurate, true running wheel. Fitting my wheel with these bushing confirmed my suspicion. The amount of "wobble" at the edge of the CBN wheel was comparable to my Metabo - probably about 0.4mm and very obvious when you set a square on the table with the blade almost touching the wheel. Maybe my expectations were too high - but I have seen Pat's setup (an old Australian made A&A) and there is zero wobble that can be seen with the naked eye.
I think the mounting technique may have a lot to do with this. Maybe the shafts on the Vicmarc are dead true, but you are let down by those bushings.
The spherical washers Chris has tried above sound promising for compensating for our poor mounting solutions. I've done a lot of measurements on my Metabo now and have found that with the shaft nut loosened off, the wobble in my wheel is significantly better. The fact that the wobble can be improved by loosening the nut means that the wobble is more than shaft runout related, and makes me think that it may be possible to compensate for the wobble by applying pressure from the nut differently. The answer may be spherical washers, or even a washer that is slightly thicker on one side than the other - this could be rotated to adjust for the best position to compensate for the uneven pressure the shaft nut is applying across the side of the wheel.
It looks like there is only 1 size spherical washer sold at the link provided by Chris above, but a quick google search shows these are fairly common things and available in many sizes that can probably be purchased locally. If I get my Metabo sorted with sphericals or some other method I will post an update. I might shoot an email to Vicmarc also to ask their advice, since it is one of their wheels I am using.
Sorry for the long post - but hopefully the info is helpful to someone.

Quote:

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Originally Posted by Oddy

I've done a lot of measurements on my Metabo now and have found that with the shaft nut loosened off, the wobble in my wheel is significantly better. The fact that the wobble can be improved by loosening the nut means that the wobble is more than shaft runout related, and makes me think that it may be possible to compensate for the wobble by applying pressure from the nut differently.

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Is the nut not the problem? I'm thinking that if the nut was properly square that shouldn't happen.