Truing CBN Wheels?

[GadgetBuilder]

I have nearly completed a Brooks grinder and purchased an AbTec CBN
taper cup wheel, as seen here:


I set the metal section of the wheel to run true within about a half
thou, then measured the outside of the CBN composite rim as +/- 5 thou
runout. This runout causes some vibration and a sort of whirring noise
from the motor/spindle area. I tried touching the outside of the CBN
with a diamond point - this polished the diamond nicely but did little
for the wheel

So, I looked around on the net and found that diamond points are not
recommended for truing CBN wheels, see:

http://www.ndlab.com/Information_Resin.htm

They recommend coolant and a metal bonded diamond nib -- which
apparently differs from a cluster diamond. Or alternatively, a
carbide wheel in a brake fixture.

I have neither of the recommended tools so was wondering what others
have done to true CBN composite wheels in the home shop. Are diamond
nibs available? Are plans available for a brake fixture for wheel
truing? (Norton has a brake fixture but it costs much more than my grinder... ( http://www.drillspot.com/products/34..._Truing_Device ) Or is there a different way of truing CBN wheels?

I also found a reference to truing with a mild steel block, but haven't found more info on how to do this? See: http://www.diamondedge.co.nz/shop/Su...nd+Truing.html

Also, I didn't expect to be using coolant with this grinder; any
thoughts on how to handle this aspect of truing CBN?

Not being able to true the CBN wheel has been a show stopper; any help or ideas would be appreciated.

John

[BobWarfield]

Wow, that's quite a nice looking project. More pictures please!

Cheers,

BW

[lazlo]

He's got a complete build-log on his web page Bob -- very impressive:

http://www.gadgetbuilder.com/

http://www.gadgetbuilder.com/Brooks%20Grinder.html

[Norman Atkinson]

Truing CBN

Sorry to interfere with what is an excellent piece of work and one which I have long recommended especially with high postal charges and higher prices of UK castings.
However, Lazlo and I corresponded about another similar design called the Stent. I said that it could be made by fabrication.
A few days ago, I saw a local advert for a Stent and came back with it.
It was also fabricated.

So I have a Quorn, a Kennet, a Stent and Clarkson plus a part set of part machined Stent castings under the bench.( Overkill?)

I suspect that my 'diamond wheel' on the Clarkson looks identical to your CBN one. I, too, have been fiddling on and note that despite my 'wobbles' that I am getting a near mirror finish on HSS.

Splendid piece of kit there!

Norm

[Betterhalf]

CBN wheel made correctly should not need dressing. Coolant be sure to use one (if you must) that has no oils. Oils gum up CBN Very quickly and stop cutting action.

To Clean up can use a Silicone Carbide soft dressing stick is the best. Or if touched lightly with small Aluminum Oxide stick. Can also soak wheel in soft water then blow out with compressed air to clean.

[macona]

CBN wheels are dressed with aluminum oxide stones. Diamond used Silicon Carbide and then AlO to open up the grit.

[Evan]

If you need to actually true a CBN wheel by removing the abrasive until it is true running then the only reasonable method is to run it against a coarse grit diamond stone or wheel of the electroplated type. I just trued one of mine the other day this way against an unused profile edge of a 10" diamond wheel I have. It removes the CBN grit promptly. Once the wheel is trued then it must be deglazed to reopen the grit. This is done with a silicon carbide dressing stick or a piece of silicone carbide wheel. When correctly trued and dressed the grit will have a matte unglazed appearance.

However, as Betterhalf has said, a properly made CBN wheel will not need truing from new, only if it is worn unevenly. A new CBN wheel should be true to better than .001".

[thistle]

I bought a couple of Betterhalfs CBN wheels , and for giggles stuck them on the spindle with out indicating anything in ,or dressing - they work fine out of the box, as she says .

[GadgetBuilder]

Thanks for all the responses. The wheel I purchased from AbTec via eBay is shown here: http://www.abtec4abrasives.com/d11v9...01347-70-p.asp

The CBN face of the wheel runs true, as it should. I found that the metal section of the wheel had runout of about +/- 2 thou with respect to the mounting hole. I initially made the wheel adapter fit the wheel hole precisely so I adjusted the adapter to allow offsetting the wheel on the adapter (by tapping lightly with a piece of wood then tightening), allowing me to true the metal section of the wheel.

Then, with the metal section running true I checked the outer surface of the CBN and found it to have +/- 5 thou runout. I assume this runout unbalances the wheel such that it causes vibration, leading to my idea that I'd like to true the outside edge (not the working face, which seems fine).

Given the input in this thread that the wheel should run true if properly made, I wrote to AbTec to ask what the specifications are for runout and am awaiting an answer. I purchased the wheel from AbTec via eBay almost a year ago expecting (in a fit of optimism) to finish the grinder more quickly

I tried truing the outside of the wheel with a carbide stone dipped in water. This seemed to be working initially when it removed some of the composite but once the CBN grit was proud of the surface it seemed to rapidly grind down the carbide stone with no further effect on the wheel.

If I can ever get this wheel to run true I expect it will last a long while based on what it has done to the carbide stone and to my single point diamond. I have used the wheel to grind some HSS and it cuts much better than the alox and carbide wheels I have used previously.

Evan's thought of using a diamond wheel to true the CBN wheel would be good if my shop were better equipped and included a diamond wheel.

I'm still looking for more info on truing a CBN wheel with a mild steel block per this reference: http://www.diamondedge.co.nz/shop/Su...nd+Truing.html


John

[Evan]

Your attempt to true the wheel with carbide was only removing the binder which opens up the grit. That's why it started cutting. However, CBN isn't recommended for carbide grinding because it will eventually glaze the wheel with a very hard to remove finish That's why I had to true mine since I had been using it to grind carbide. I am currently lacking a fine grit diamond wheel to use for carbide.

I am not familiar with using a mild steel block for truing. I'm not sure how it would work. You can use cast iron, particularly chilled cast iron to true the face of CBN cup wheels as it contains excess carbon that forms very hard iron carbides that are able to abrade the CBN.

[oldtiffie]

"True-ing up"

Most tool &cutter and surface grinders have a 1 1/4" (31.75mm) spindle spigot to mount the wheels on. There are other sizes.

Probably the best way to mount the diamond/Borazon(CBN) wheel is the intuitive/traditional way are per previously posted link:

http://www.ndlab.com/Information_Resin.htm

MOUNTING: The following recommendations are given so that the best results may be obtained in using diamond wheels: Care should be taken in mounting a diamond wheel. Flanges; back plates; spindles should be clean, free of burrs, and run true. By using an indicator and tapping lightly on a wood block held against the wheel, indicate the wheel within .0005” of the true rotation. Tighten the flanges securely and recheck with an indicator before using. When mounting a cup type wheel, use shims inserted between the back plate and the wheel to obtain a true running face. The use of permanent mounting should be practiced where convenient.

The whole idea is to get the cutting/grinding face/s as true as you can. I think that no more than a thou (0.001") - or even 2 (0.002") at a pinch will do in most cases.

Dressing is a last resort unless necessary as the wheel will probably be dismounted for another at some time and when you want the diamond.CBN wheel mounted again you will lose too much by needlessly re-dressing it.

And these wheels cost!!. But with a bit of care they last a long time and do some great work.

I have 4 (original plus 3 spares - spares ~$200 each!!) balanced hubs for my surface grinder and I've got over 10 wheels!! so I've go to change sometime. My T&C grinder does not have a balancing hub - so the wheel gets mounted "as is".

"Side throw" is not a problem as witness that very few T&C or surface grinder wheels are not dressed on the side anywhere as near often as on the periphery of the wheel. And they work fine with some relatively minor "side throw".

If your diamond/CBN wheel only touches on one part then so be it. If you have set it up to within a thou (or two) it should be good to go.

The average HSM shop or even small jobbing shop can get by with that and without the too often recurrent and possibly needless buying of new/replacement wheels.

If you have a balanced hub - use it to balance the wheel - if not - don't worry.

If you "free-hand" (ie hand-hold) grind a tool - as on a pedestal grinder (which you can) on that wheel the run-out will be of no significance but it will still do the job.

Give it try.