Guest editor Mark Palma restores a CBN wheel which has seen better days
CBN wheels are a popular upgrade for a grinder. In Woodturning 380 I gave an overview of this upgrade and some reasons why you may want to add them to your shop kit. Over time CBN wheels get used and possibly abused, so let’s look at what we can do to possibly revive a CBN wheel.
The wheel as found
The wheel in this article was found in my father-in-law’s shop after his passing. Dean was an old- school woodworker and woodturner and I very much doubt he ever read the instructions that came with any tool. I found this wheel in the back of a drawer and decided to bring it home and see if its forlorn state could be reversed. Cubic boron nitride (CBN) is a very hard material that sharpens with near the properties of diamonds.
However, CBN cannot be used on carbon steel tools or non-ferrous metals (aluminium and brass for example). For decades turners used carbon steel turning tools. Sears must have sold a million sets all by themselves. Turners also seem to have a hard time getting rid of old tools, even if they don’t use them. In Dean’s shop I found a rack of carbon steel tools, many with new edges on them. My suspicion is that he may have accidentally used a CBN wheel on these tools. The wheel seemed to have hunks of metal stuck to it and was rusty.
Materials gathered, ready to begin
I researched what I could on this situation, but other than a few YouTube videos that all took one approach, there wasn’t much information available. I started researching ways to remove rust and metal fragments and found myself in the automotive parts stores. After looking at products and reflecting on what worked for me in my own car restoration endeavours, I decided to use a multi-step approach.
The manufacturer of the wheel clearly warned never to use the wheel on carbon steel or it would do irreversible damage. I went to its website and actually read the instructions that come with the wheel. Use on carbon steel was not covered by the lifetime warranty. I would heed that warning. I proceeded with the thinking that (1) I couldn’t make it worse, and (2) maybe I could make it usable again.
Soaking the wheel
I thought I would start where others suggested with a heavy spray of penetrating oil. I soaked the wheel in a pie pan with penetrating oil over a two-day period, rotating the area in the oil bath every few hours. I took a brass brush, gently scrubbed the side that I soaked and then wiped it down with a shop towel. I repeated this step several times. Over a period of time the amount of metal debris I saw in the penetrating oil was increasing, so I was accomplishing something.
Penetrating oil is mainly kerosene, so treat it with care as it is highly flammable. It also smells, so use in a well-ventilated area. The same goes for any rags you use for wiping down the wheel – they can spontaneously combust so follow safe practices with disposal of these rags. The next step was to spray down the wheel with brake cleaner. This stuff needs to be sprayed outside and wear protective gloves when using it. It blasted off more debris and I again wiped down the wheel as I sprayed it, disposing of these rags with care as well. I had not seen this step suggested anywhere, but it seemed to loosen more build-up in the wheel. It made sense as it is designed to remove brake dust from automotive wheel assemblies.
Abrasive cleaner
Next, I temporarily mounted the wheel on my grinder and tried three different approaches to cleaning the wheel. In the drawer next to the wheel when I found it was an abrasive stick labelled CBN Cleaner. So, I tried it. It seemed to just gum up the wheel and not much more, so I stopped that approach. Diamond wheel manufactures recommend a white eraser that looks like an old- fashioned ‘pen’ eraser. I tried one of those and it seemed to help. The material between the grit in the wheel was less than before. Lastly, I took a small stainless steel brush (don’t use a wire brush as they are carbon steel, which caused the problem in the first place), touched the brush to the wheel (wear eye protection) and it seemed to dig out more junk. Then I took the eraser to it again and called it quits.
Conclusion
Well, we made the wheel usable again and I think it would give good service for several more years. It still has some evidence of rust, but the chunks of metal that were stuck to the wheel are now gone. It cuts well when tested on a few tools – all high-speed steel or other similar approved materials. I would say we returned it to 80-85% service through these steps. I don’t know what led to it ending up in a drawer, but it must have stopped working or I think it would have stayed on my father-in-law’s grinder.
The project was a success. For a wheel that is just dirty this process would have probably got it back to 90-95%. Give it a try if your wheel is not cutting as it should, and if you haven’t already done so, throw away those old carbon steel tools.