Warning about "radiused" CBN wheels

[Derek Cohen]

Recall that early reports of the CBN wheel I received was excellent. Look how straight this grind was and how fine the micro bevel could be made ..

http://www.inthewoodshop.com/WoodworkTechniques/UltimateGrindingSharpeningSetUp_html_71b2c2d0.jpg

Article: http://www.inthewoodshop.com/WoodworkTechniques/UltimateGrindingSharpeningSetUp.html

After several weeks I have noted that the wheels are no longer grinding a straight edge when using the Tormek BGM-100 toolrest. It is now wavy …

http://www.inthewoodshop.com/WoodworkTechniques/UltimateGrindingSharpeningSetUp_html_m3d283217.jpg
The wheel looks fine with a Starrett straight edge across the face ...


http://www.inthewoodshop.com/WoodworkTechniques/UltimateGrindingSharpeningSetUp_html_m416dcfee.jpg

On examination, using light, I have noted that the face of the wheels is not flat but concave (curves inward) ..

This is the 80 grit I purchased on eBay, but the 180 grit from D-way is similar.

http://www.inthewoodshop.com/WoodworkTechniques/UltimateGrindingSharpeningSetUp_html_m386e1815.jpg


The wheels continue to cut as strongly and cleanly.

I have checked and re-checked the tool rest, removed it, replaced it … the result is always the same: a curvy or radiused edge. One can get past this if freehanding on a simple tool rest, but not when the blade is guided by the BGM-100. I tested the toolrest and blades on the Tormek, and the result was a perfectly straight grind. Clearly the concave on the CBN wheel is the problem.

It may just be that I am using wheels with radiused edges and the CBN wheels with straight faces are not affected. I am looking into this at this time.


Regards from Perth

Derek

[Tom M King]

I bought my radiused edge 180 D-way wheel in the Fall of 2013. I'm running it on a full speed grinder. It's still flat, and I've had no such issues. It still spins on a perfect circle in perfect balance. I'm sure I've used it much more than the average hobbyist woodworker would use one. Since it's that much older than yours, there's probably a good chance that it's out of a different manufactured batch. Also, it probably should be noted that all chisels and irons that I've sharpened on it are O1 or whatever "Sheffield Steel" is (which seems a little harder on the grinder by feel).

Sorry you've had this trouble.

[Don Bunce]

I bought a Dway 180 grit wheel Aug '13. I just checked it, and it is slightly concave, also.

I use a Robo Rest, and mainly use it for sharpening turning tools, so it hasn't been a problem, but you'd think for the price these wheels are, they should be straight....


You might want to post this on the turners forum, as many turners are using these wheels, to see if others have the same problem.

[ken hatch]

Derek,

I'm just setting up a CBN wheel with a straight face. Just checked it with a straight edge and it has even light all the way across.

I'll be watching this thread,

ken

[Reinis Kanders]

I did a cursory check and mine seems to be ok. I got it from Wodturning Wonders or something like that. I do think I will get a flat wheel at some point, mine has a radiused corners and so only 3/4" is effectively flat. I am not sure of what use those radiused corners will be for me, he was out of stock for regular ones when I purchased them. Mine are also made from some sort of aluminum.

[Derek Cohen]

Please read my follow up here: http://www.sawmillcreek.org/showthread.php?228376-Follow-up-on-CBN-wheels-for-flat-woodworkers&p=2386144#post2386144

Regards from Perth

Derek