I'm looking for an inexpensive 8" low-speed bench grinder for touching up lathe tools. I already have a standard speed grinder I'd use for large removal and reshaping tools. The HF Bauer variable speed grinder goes down to 2000 rpm while fixed speed low-speed grinders are spec'd at 1750rpm. I intend to put CBN wheels on it but is 2K slow enough for CBN wheels? Note that I do not do a lot of turning so I won't be putting a lot of hours on a sharpening system so I don't want to spend big $$ for a high-end grinder. TIA!
Hello Dan.
Like many things in woodturning, a lot may depend on what you want to or end up turning. Hard, dry wood? Bowls from green wood? Many people are happy sharpening on coarser wheels than I prefer but I think we mostly turn different things. I often turn smaller, detailed things from dry wood, fine-grained, often quite hard species.
My preference is the 1750rpm is for CBN. Most turners I know use them. In fact, I would often like a slower speed. I use one wheel on a very low speed Tormek - my favorite for some tools.
That said, as Dwayne mentioned, 2000 rpm should be fine. A higher speed might be a problem with increased heat for hardened non-HSS tools, but it's almost impossible to overheat a HSS tool
BTW, after using various grits of CBN I settled on 60 and 600 for my lathe tool bench grinder - I use the 60 when shaping custom tools and the 600 to sharpen skews, parting tool, bowl gouges, etc., and the custom tools. I put a finer grit CBN wheel on the Tormek for my spindle gouges.
If shopping for CBN wheels at some point, there are various widths and styles. I prefer the wider wheels (1.5"), square edges instead of radiused, and with 1" of grit down the flat sides of the wheel. This lets me grind and sharpen various custom tools. I think the radiused edged CBN wheels have only limited use to most turners, plus they take away from the useful width of the wheel. (The extra width is especially nice when grinding skews.) Be aware of the arbor size when buying CBN - all my 8" grinders use 5/8" diameter. And while the wheel guards are important for standard grinding wheels you can (or may even have to) take them off for CBN.
Also, it's advisable to get a set of spherical washers for each wheel - they can compensate for irregularities in the mounting which can keep the wheels from running true.
Many people, including me, use the Oneway Wolverine jig for lathe tools, combined with the Oneway Varigrind for gouges. I like the Wolverine Mini platform instead of the standard large for most tools.
I like to mount the grinder and the Wolverine bases to a square of 3/4" plywood so the grinder and platform can be moved on my sharpening bench if needed. I've also carried them to events to show sharpening techniques.
I did use conventional grinding wheels for a long time - used fairly fine grit compared to most, the blue Norton 3X. I did find the Oneway grinding wheel balancers mounted on the wheels helped me get a better edge on the tools. But going to CBN was a big improvement.
A 1/2 hp grinder is enough for aluminum CBN wheels. Some of the heavier steel CBN wheels were a bit slow to start with 1/2hp but I don't think that will hurt the grinder motor.
JKJ