Grinder for CBN wheels

VAST disappointment with current offerings so far. Two grinders in and the CBN wheels STILL don't spin true.

Can anyone suggest a fabulous grinder to support CBN wheels?

I've two Abbot and Ashbys 8" and they are decent grinders but no matter what I do they will not balance the wheels smoothly.

The wheels are Woodcut Trugrinds from Carrols with 5/8 holes.

I've also tried the Self Aligning spherical washers from Woodturning wonders (https://woodturnerswonders.com/colle...al-washer-sets), which get me closer, but its still not accurate.

What's your definition of accurate?

What's your best "side" and "front" runout?

Can you get a smooth action with other wheels?

As far as grinders go, Brobo (Waldown) are supposed to be the bees knees but make sure you are sitting down when you check prices.

My CBN wheel on my 3P GMF (+VFD) does not run true but the VFD does enable me to find a lower vibe spot than at 50Hz.

Ill try to measure those, but is it so hard to expect close to zero?

These are prescission wheels (apparently). Is it impossible to get an equally precise grinder?

What do others do?

Is is clear the wheels are not spinning true, for when grinding the tool "tings" on the surface, plus I can physically see the imbalance.

Yes, I've tried rotating them 1/4 a turn to reduce imbalance, back-and-forth, rotating them a little bit, flipping them over, etc, etc... plus used the above washer systems to remove nut-induced movement.

Mine run on a cheap Carbatec 8" and as it winds up and slows down it "thrums" for a second or two but when it's rev'ed up it smoothes right out. Does the job. Phil.

I believe that Woodturners Wonders sell washers that centre the wheels. My own wheels run very true - they take 8 1/2 minutes to come to a stop from switch off! My grinder is a half-speed Carbatec 1 hp that I have had about 8 or 9 years. they are no longer sold.

Regards from Perth

Derek

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Originally Posted by derekcohen

I believe that Woodturners Wonders sell washers that centre the wheels. My own wheels run very true - they take 8 1/2 minutes to come to a stop from switch off! My grinder is a half-speed Carbatec 1 hp that I have had about 8 or 9 years. they are no longer sold.

Regards from Perth

Derek

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Somewhere in the archives there is a thread discussing this and the washers Derek is referring to and they work because I bought a set. In that thread someone posted a link to a supplier in Oz that can supply the same item. This is a link to images of what we are talking about...

https://www.google.com.au/search?q=s...w=1423&bih=724

WP, have you run the grinder without any wheels on it? Does it run vibration free? That may tell you something.

Have you run the grinder with one wheel mounted at a time? That may tell you if it is only one wheel causing the problem or both. If a wheel is good one one end and a problem on the other it may point to a problem shaft at that end.

It would be surprising that you ended up with two problem wheels, in which case you are right to be looking at the grinder as the source of your problem.

If you are getting tool bounce it sounds like a runout issue. Do you think your issue is runout or balance. I had a balance issue with one wheel (a diamond, not CBN) and overcame that by adding counterweights. It's a tedious and time consuming process, but it did solve my problem. But, as you say, CBN wheels should come balanced.

After thorough testing, if one wheel is good and the other a problem, you know which wheel to send back for a replacement. Carrolls has a good reputation. Give Jim a ring to discuss.

Sent from my ZTE T84 using Tapatalk

Yes, I have the Woodturners Wonders washers. They took a fair bit out, but didn't fix the problem.

I tried both sides on both grinders.

I might get the Vicmarc grinder. Ill need to change the wheels as they are 5/8 and the Vicmarc uses 16mm arbors. :(

Not so bad, perhaps. The wheels are in excellent condition (might sell them), so I might buy the 350/1000 kits of wheels from WTW.....

Gotta admit, this is twisting my undies.

(BTW, thanks everyone for your ideas and suggestions).

Edit: I will try to use a kit on BOTH sides of the wheel.... I bought four kits :)

Hi woodPixel, here is a thread I started some time back on the exact same topic:
CBN - too much runout on my bench grinder? Better grinders?

I'd recommend not to rush out and buy a Vicmarc grinder - I checked out one of these and found it to be worse than my existing Metabo. Another person on above thread also commented on bad experience with the Vicmarc grinder.
If you are experiencing a visible wobble when you spin the wheel slowly by hand, first easy test to try is loosen off the nut and try again. If this improves the visible wobble then the nut is inducing at least some of the runout and spherical washers might help to correct.
Next I would get hold of a dial indicator and measure the shaft runout to see if that is really the issue or not.
If I were buying another grinder I would want to check the shafts of the actual one I am buying with a dial indicator before handing over my cash (or test it with my CBN wheel).

Evan, lubricate the washer seats to allow them to self align when tightening the nut. it is not solely the nut that is the problem but a combination of the nut being badly machined and badly formed threads on the shaft that do not have good tolerances to the nut. You will find that if you the the nut is screwed onto the shaft you can move the nut with your hand and if the machining of both the nut and the shaft was good that would not be possible or at worse only minimal. Prior to using the washers I threw all the plastic bushings away and made new metal ones and I still had the problem until I used the self aligning washers. Even then I could induce a small amount of run out when tightening the nut until I lubricated the washer seat. I also lapped the nut face on a diamond stone to clean it up which might be an issue and to cap it off this was all on the VICMARK grinder, it is no better than any other.

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Originally Posted by woodPixel

Edit: I will try to use a kit on BOTH sides of the wheel.... I bought four kits :)

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Don't do that as the wheel has to be aligned to at least one square edge, the ground flat washer. If you use two kits you will guarantee that the wheel will wobble.

Yeah, two kits was terrible. It flapped around like a politician.

I have a Baldor 6" grinder with CBN wheels on it. I haven't measured the runout, but I know that I can't feel any while they're spinning, and they cut smooth as butter.

As has been kind of touched on, what's your definition of true? How is this effecting your ability to grind?

FWIW I am truly impressed with my Baldor. I was reluctant to come off the cash for a grinder, thinking that it wouldn't be worth it for "just a spinning motor", but I was dead wrong. It's an improvement in every way and my grinding experience is vastly improved.

How are you bushing/shimming the wheels? It took me a while to figure it out, but the product you want is called a "precision arbor shim". Basically a really accurate washer. The washers that come with the grinder are crap, even on a high end one. They're made for stone wheels which can be trued with a diamond dressing stick, not for a precision cbn wheel.

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Originally Posted by woodPixel

Edit: I will try to use a kit on BOTH sides of the wheel.... I bought four kits :)

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As noted above not a good idea as you found out.:oo: You have got the correct size arbour bushes? There is not much difference between the two sizes but there is a difference. I'll do you a favour, pack it all up and send it to me and you won't have the problem any longer, I'll even pay the freight or come down and get it from you, I can't be fairer than that.