Standard or slow speed bench grinder?

[Paul Carson]

Hello,

I’m on the brink of buying my first bench grinder and wondered if you could help me with the following questions:

• Besides lessening the chance of overheating, are there any other advantages to slow speed grinders?

• Are the any tasks that standard / high speed grinders can do, that slow speed grinders cannot?

• How much of an advantage are wide wheels – 40mm vs 25mm?

• I will continue to sharpen on diamond stones / strop but intend to use the grinder for fast stock removal when creating new bevels / getting past pitting on old blades – any other tips or advice?

All information and advice appreciated.

Many thanks,

Paul

[Jim Becker]

My personal preference is for the slow speed version both for "heat" considerations (although CBN wheels can now help with that) as well as to be "more forgiving" on the bite since I don't use my grinder often and therefore, don't have the "touch" that folks who grind frequently do. I'm soon to invest in the CBN wheels that I mentioned, however. There were not available, to the best of my knowledge, when I last bought new wheels as that was quite a few years ago.

[Mel Fulks]

Most of the grinding wheels that come with new grinders are low quality. That translates to a lot of heat and not much
metal moving. I find the white wheels cut well, but there are a lot of options. I've been grinding stuff frequently for a
long time and prefer the 1725 speed . But some super talented guys prefer the faster grinders; as they have the skill to
go from water to stone quickly and accurately .

[Tom M King]

Since you need to ask, get the slow speed one. I have a CBN wheel on a high speed grinder. I can use it without burning an edge corner, but my helpers can't.

[Derek Cohen]

Heat is an issue for most steel types. Heat is not an issue if you are grinding HSS (M2) for use on the lathe. For everything else, there is the capacity to affect the hardness of the steel.

"Slow speed" usually refers to water-cooled grinders, such as the Tormek. They assure one that the steel remains cool. However they are slow, and CBN wheels are taking away some of the insurance against over-heating the edge.

CBN wheels are for plane blades and bench chisels (but not the laminated Japanese chisels). I use 80 grit (for removing a lot of steel) and 180 grit (for most uses, such as hollow grinding fir sharpening). For lathe chisels you would want to go up as high as possible (350).

My bench grinder is a "half speed", which runs fast enough to burn steel with a CBN wheel if you are not careful. This is better than a "full speed" machine, the alternative, which is what I would use if just grnding lathe chisels as it will work faster, and damn the heat for HSS.

Regards from Perth

Derek

[Jim Becker]

Derek, you bring up an interesting thing relative to "slow speed grinder" mentioning Tormek, etc. I agree that these large wheel types are absolutely slow speed grinders. In many of the conversations about grinders, however, "slow speed" is often referring to the 17xx rpm units as an alternative to the 36xx rpm types. What you call "half speed" grinders. I guess we need to be more specific at this point.

[Chris Fournier]

This is a very heated topic I have 3450 RPM grinders with 46/60 grit wheels, the wheel recipes I can't cite from memory but they have a friabilty that reduces burning issues. I have over a few decades developed a decent touch with these grinders and need no others. I can grind quickly and efficiently and then move to honing. There is no doubt that I am in the minority here. Practice is required. To my way of thinking this is the fastest, most efficient, and cheapest method to move to sharp. But you have to be a student and diligent with your technique and process. I sharpen woodworking, metalworking, and culinary tools on my grinders.

Most folks will want to go with 1750 RPM grinders but burning and sub-standard results are still possible. The Tormek won't burn a tool but sub-standard results are still possible!

[Phil Mueller]

I have a slow speed grinder with 1.5” CBN wheels and the Oneway Wolverine Tool Rests. Like Jim, I don’t use it often enough to have the touch. Because of that, I like the wider wheel as I can sharpen any chisel up to 1.5” without having to move the chisel from side to side. I don’t use a guide, so essentially free hand. The wider wheel makes it easier for me to get things square.

Plane irons are another issue, and I’m getting a bit better sliding them back and forth, but it is still a good amount of time spent checking for square, correcting, check again, tweak...etc.

[Derek Cohen]

Derek, you bring up an interesting thing relative to "slow speed grinder" mentioning Tormek, etc. I agree that these large wheel types are absolutely slow speed grinders. In many of the conversations about grinders, however, "slow speed" is often referring to the 17xx rpm units as an alternative to the 36xx rpm types. What you call "half speed" grinders. I guess we need to be more specific at this point.

Jim, just so.

A 10" Tormek runs at 120 rpm. That is "slow".

A full (or high) speed bench grinder can vary a little, depending on whether 50 or 60 Hz. Somewhere around 3500 rpm.

A half-speed bench grinder surprisingly runs half the speed of a full speed grinder, and it is not that slow at 1750 rpm.

Recently, Tormek have introduced a diamond wheel to their range. I imagine that this is to counter the CBN wheels coming onto the market. Diamond is fine as long as run at this slow speed (120 rpm). If faster, say 1750 rpm, the heat will cause the carbon in the diamond to migrate to the steel, and the diamonds will wear out.

CBN is almost as hard as diamond and will not be affected by heat in the way diamonds are. Diamond, however, is the medium of choice if grinding carbide.

The article on my sharpening system (again - but relevant if you are looking at CBN): http://www.inthewoodshop.com/Woodwor...ningSetUp.html

Regards from Perth

Derek

[Randall J Cox]

I've had a slow speed 1750rpm grinder for many years. Suits me just fine, have a regular grinding wheel on one side and a white wide on the other side most of the time. Latey I have been taking off the white and installed my wire wheel and also my buffing wheel (back and forth) as I'm rebuilding an old Delta 10" 1940s bandsaw. I find the 1750 to be very suitable for all tasks. I'd buy the same grinder all over again. Randy

[Rod Sheridan]

Most of my power sharpening and grinding is done on a 1" belt sander.

There's a wide range of grits, all the way into micron ratings as well as leather belts for stropping.

http://www.leevalley.com/en/Wood/pag...4884&cat=43072

I also have an 8" 1725RPM grinder with after market wheels, I don't use it as often as the belt grinder above.

Regards, Rod.

[Tom M King]

I bought my Metabo full speed grinder before Rikon came out with their low speed grinders, but a lot of people seem to like their Rikon's. I ordered several different brands, and sent them back before I found the Metabo that was smooth enough to satisfy me. If Metabo had made a low speed grinder, I would have bought one.

https://www.rikontools.com/category/bench-grinders I see they now have a variable speed one, but I have not heard from anyone that owns one.

[Julian Behrisch Elce]

I think that if a given amount of metal needs to be removed the heat generated will be the same no matter how you remove the metal. If you’re nervous, generating that heat more slowly might make you happier. I use an 8" high speed grinder with the Norton 3x wheels. I shape the coarse wheel slightly convex like Joel Moscovitz recommended. It’s a wonderful system that grinds very quickly. Yes, I can easily overheat tools, but I can just as easily avoid it. Many seem to have the idea that you only have to wave metal near a regular grinder for it to droop in your hand like a noodle. Just set up, grind gently, and check your progress every few seconds. Keep a finger carefully on the tool near the wheel and that’ll tell you when to pause and cool a bit. It’s really quite easy.

[Tom M King]

The efficiency of the cutting matters too though. Just as a glazed wheel will generate more heat, in the other direction, a CBN wheel is so efficient at cutting metal that it puts little heat into the metal being cut. It does put some in though. It's Way faster than any friable wheel, and puts less heat in the tool at the same time.

If I only had my own experience with my full speed grinder, and CBN wheel, that is what I would recommend. But since I have helpers that I want to do grinding, so I don't have to do all of it, I need a little more help with slower grinder speed, and recommend the lower speed for anyone buying their first one.

[James Pallas]

Mostly opinion here. I've been grinding steel a long time. I prefer high speed grinders. I think slow speed grinders were made for safety years ago. When you are running a 10" x2" wheel at 3600 the wheel has to be good, which was not the case years ago. You just work faster on high speed grinders. I don't find it much different to work with width of wheels. Some people like to shape the wheel a little convex. If you prefer that than wheel width doesn't mean much. I shape my wheels flat. I bought a CBN wheel and like it for some things. I keep a regular 36 grit wheel on one side and use that as much or more than the CBN wheel. If I could have both speeds and felt I needed a slower speed for large wheels I guess I would do that. With high speed just stay away from feather edging until you get a feel for it. I can't remember how long it has been since I burned any steel but it has been a very long time including pin points on awls and such. I've never owned one of the Tormek type grinders but have used one a bit. My opinion of those is "TOO SLOW". I don't know of anything that is an advantage for either other than speed and experience.
Jim