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Standard or Slow Speed Bench Grinder?

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paulc

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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
 

Cheshirechappie

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I'm not sure that there's any substantive difference between high-speed and slow-speed bench grinders, except that the high-speed ones take metal off quicker. Some people find high-speed grinders rather intimidating, but relax a bit more using a slower-speed version, which probably results in a slightly better finished grind.

Tips when using a high-speed grinder - one is to dress the periphery of the wheel to a very slight crown, and keep the job moving sideways. Don't let it dwell at one spot, or it is very likely to overheat. A coarser wheel (about 40 grit) is probably a better bet than a fine one for general woodwork tool grinding, used with fairly light pressure - just enough to allow the wheel to cut. Also, dress the wheel as soon as it becomes glazed or clogged - both will increase the chances of overheating. It's also worth replacing the 'general purpose' wheels that some budget bench grinders are supplied with - the white Aluminium Oxide or pink Norton wheels sold by the woodwork specialist suppliers will run cooler (but being more friable, will make more dust - you never get something for nothing!).

By the way - do use eye protection while using high-speed grinders. They do fling dust and metal particles about, and getting one in the eye is not pleasant.
 

Fergal

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I know some will be horrified by what I'm about to say, but I find a belt sander does a good job of restoring the bevel on a chipped chisel or plane blade. You get a nice, flat bevel rather than a hollow grind like you'd get on a wheel and it's quick!

You can then hone it on a wet stone or whatever method you prefer. For somebody like me who does not enjoy spending hours sharpening, this is the most expedient way of keeping my blades sharp.
 

shed9

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Slow and high speed grinders will both get the job done but the slow speed is probably the better option if you can. The slow speed variant will be smoother and more controllable in the grinding process. It will also be more suitable for CBN wheels if you go that route.
In terms of wheel width, the wider the wheel the easier it will be to true up an edge although a jig may negate that to some extent. Just as important as speed and width, you need to account for motor wattage, wheel type and diameter. Obvious I know but the larger the diameter of the wheel, the less pronounced the hollow will be (don't be put off by the hollow itself, this is not a bad thing).

Personally if I was starting from your position and your budget allows for it, I would get a slow speed grinder and fit at least one 200mm CBN wheel. This will be safer (CBN won't shatter), more controllable, heat won't be an issue and you will be closer to where you want to be when you take the tool edge to stones.
 

deema

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I’ve tried al sorts of combinations, of slow / fast coupled with white grey and ruby wheels. My own experiences suggest to me that a slow grinder is just that, slow at getting the work done . A properly dressed wheel and not applying pressure coupled with dipping the item in water every now and again means that all wheel types and grinders do the job well. I believe it’s more about dressing the wheel, and technique rather than marketing hype of the latest cool grinding system.

A dirt cheap belt sander and a few home made jigs is the simplest and cheapest solution for just about any grinding. This is what a Sorby ProEdge is effectively.
 

--Tom--

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I thought CBN preferred higher speeds (in the 6,500 to 12,000 sfpm range) which would need a high speed grinder to get close to (8” @ 2850 rpm is 6000sfpm)

Biggest difference you’ll make in my view is to make or buy a better tool rest
 

Rorschach

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I went slow speed because I wanted to fit an add on belt grinder and 1400rpm was a better speed for that. It also had the advantage of being a little more controllable on the stone side.

High speed grinders are great for hogging off material, and I have a couple of 6", but a slower speed, especially for an 8" grinder is much nicer and safer for fine work like tool grinding.
 

ED65

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paulc":317ylxus said:
Besides lessening the chance of overheating, are there any other advantages to slow speed grinders?
I'm with deema on this one on the question of speed.

I have a variable speed grinder and have used it near the bottom end of its range for most of the time I've had it and while you gain a great sense of control and it helps build confidence if you're new to grinding oh my goodness is it slow. I've turned the grinder up now that I have more experience using it and expect I'll keep it at this speed (backed off a smidge from max which is how I like to run all variable-speed tools) for almost everything.

While I also agree that a belt sander + jigs is a great way to go, if you can stretch to CBN then it's well worth it because it makes grinding pretty much foolproof – it's essentially impossible to blue an edge – and you're getting a hollow grind which some people find invaluable (Derek Cohen is a big fan). You might find this recent YouTube vid from Gosforth Handyman useful, which I think was posted somewhere on UKW previously: Changing Bench Grinder Wheels - CBN Wheel on my Record Power RSBG6

paulc":317ylxus said:
Are the any tasks that standard / high speed grinders can do, that slow speed grinders cannot?
Just to check, do you mean slower standard bench grinders here and not something akin to the Tormek?

paulc":317ylxus said:
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?
Since you have diamond plates already might I suggest getting a cheapie ultra-coarse grit (150# or lower) from AliExpress. Should be less than a fiver. They are nearly unbelievably fast, so much so that I still sometimes dress abused edges completely by hand to save the hassle of unpacking my grinder which I don't have a permanent station for. I restored three old cast steel firmers this way recently one after the other, taking more than 1mm of steel from the edge of one, and it didn't take an absurdly long time as it would on a standard "coarse" plate (which invariably are more medium than truly coarse).

Based on that I'm actually confirmed in my opinion that the typical woodworker actually doesn't have to have a grinder at all. For me repair/refurbishment of old chisels and plane irons is the sole reason to need a grinder.
 

paulc

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Thanks for all of the advice and information. I was looking at the slow speed grinders in Dictum, but you've all given me food for thought.

Cheers
 

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