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Choosing a bench grinder

Stuart_Burns's picture

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Can anyone help with choosing a bench grinder? I need a grinder for basic chisel and plane sharpening. From what I have read so far the recommended speed and style appears to be a 6" or 8" 1450 RPM. Yet when I go looking to buy one they are almost all 3400 RPM? One of my local tools shops said they could source a 6" bench grinder at 1450 RPM from General. Is this an okay brand and does the speed really matter?

Danford_C._Jennings's picture

(post #90874, reply #1 of 9)

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Stuart,

While I don't use my bench grinder for sharpening chisels and plane irons, if you choose to go that route, bigger and slower is better, which also means more expensive. Some prefer a hollow grind on their cutting tools, but heat can destroy the temper of the tool. 3500 RPM is much too fast. Garrett-Wade has a line of moderately priced slow speed vertical grinders. Go to: http://www.garrettwade.com

Dano

JimGG_'s picture

(post #90874, reply #2 of 9)

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Stuart: Speed does matter. Speed kills. Increased speed=increased friction=increased heat, which draws out the hardness of the steel at the cutting edge. When the edge is annealed (softened), it will not hold an edge. You have to then grind back to where it is still hard. If you overheat again, you grind off more steel. Chisels don't last long if you overheat the edge, which is why a slower RPM is on your side. Another option is the water-cooled grinder. Tormek is an example. You'll never overheat a cutting tool with a water-cooled grinder. Tormeks aren't cheap. I never used one, so can't give any opinions on them. Decades ago I bought a wet grinder made by Prairie. Later I put a Japanese water stone on it which I bought from Woodcraft (No longer in Woodcraft catalog). The Prairie grinder is still sold at Country Workshops (www.countryworkshops.org/). Prairie is cheaper than Tormec. You can save money by buying it without the motor. I use a 1/4 HP on mine. Look for yardsale motors. You should not assume that you even need a power grinder. If you can avoid hitting nails and dropping chisels on concrete floors, you have very little steel to remove. You can get coarse Japanese water stones in 200 grit or use aluminum oxide paper sheets. (General, if the Canadian Co., is a good brand).

Larry_Williams's picture

(post #90874, reply #3 of 9)

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Wait Stuart!!!!

There more to it all than what's here or, at least, different opinions and experiences. I'd write a long post that disagrees with the others here but I've already done that a number of times. My advise is to get the 3,450 rpm Deluxe version of a 6" Baldor grinder which has cast iron tool rests.

A lot of people buy a cheap grinder then proceed to put fine wheels on it and never maintain those wheels. It's a sure recipe for over heating anything you grind. Use a coarse wheel, which will likely come on any decent grinder you buy and skip all those grinding wheels that were really intended for highly accurate surface grinders. Instead, put a little money into a wheel dresser.

The higher speed actually makes truing and dressing your grinding wheel easier. The coarse wheel will generate far less heat than a fine wheel and, if kept properly dressed, will make grinding quick and painless. Grinding is only a rough shaping operation and it only takes a couple passes on a medium stone to remove the signatures of a coarse wheel.

Walk into any machine shop where tool steel grinding takes place and ask when grinder to use for chisels and plane irons. You'll quickly be introduced to a Baldor or equivalent.

For a lot more information see an article on our web site: http://www.planemaker.com/articles/grinding2.html

Larry Williams

JimGG_'s picture

(post #90874, reply #4 of 9)

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Machine shops use "highspeed steel" and carbide steel to cut metal. Highspeed steel contains alloys which make it possible to run at much higher temperatures than high-carbon steel. Highspeed steel can reach a dull red color (from the heat of friction) and still retain hardness. High-carbon steel, at a dull red color, would have been annealed. Woodworking lathe chisels are available in high-speed steel and high carbon steel. Bench chisels and plane irons typically are not made in high-speed steel. They're made in high carbon steel, which, is quickly annealed by the heat of friction. The tip of the cutting edge is only a few thousands of an inch thick. It can turn blue in a second. A dry grinder is great for HHS woodworking lathe tools. I own a 3450 RPM dry grinder; it was one of the first tools I bought. I've got the coarse white wheels on it to reduce friction. In retrospect, I don't think I need a dry electric grinder. The wet grinders don't ever overheat tools.It's possible to grind without lifting the tool once and you'll get just one polished bevel (My Japanese stone in the Prairie is #1000 grit).

Larry_Williams's picture

(post #90874, reply #5 of 9)

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Jim,

We do a fair amount of metal work in our shop. You can grind the most basic metal-working tool bit's on a bench grinder but it takes special wheels. Most metal-working cutters, though, require highly specialized grinders for sharpening if they can be sharpened at all and still maintain necessary tolerances. Most grinding in a metal shop is actually done on the different metal parts involved in a project. It's rare to find a machine shop involved in machining high speed steel or carbide. Avoiding heat during grinding is critical on machined parts, even those of unhardened tool steel, because of heat distortion and it's effect on tolerances.

A grinding wheel, like all abrasives, is a cutting tool. It comes with a renewable surface that must be maintained for proper function. Picture never changing sanding belts on a stationary belt sander. Soon, when the belt is worn and dull, you'll over heat and burn everything you try to sand. That's exactly what happens with a grinding wheel...even your white ones. While those white wheels were actually developed and intended for specialized operations like surface grinding, they do need to be dressed and maintained. If not, they'll generate too much heat.

Before you condemn high speed grinders, I suggest you learn how to properly use one. It's a simple skill but a skill none the less.

Larry Williams

Jamie_S.'s picture

(post #90874, reply #6 of 9)

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JimGG -- thanks for the link to countryworkshops! What a great site.

BTW, one possible source for a low-speed, small motor, at least if you live in a cold area of the country, is furnace installers. We had our oil furnace replaced last week ($$ouch$$), and had the techs leave the old motor and blower here. I haven't had a chance to look at the specs on the motor yet, but I'd think it will work for **some** kind of woodworking thing, hopefully to power a grinding station. They normally just throw 'em in the metal recycle bin at the landfill.

JimGG_'s picture

(post #90874, reply #7 of 9)

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I have equipped my dry electric grinder with a cooling device which might interest readers. If nothing else, it's nice-to-know information which might be useful later. It's made by a company called Koolmist. A small stainless steel box holds water and is connected to an air compressor. A flex tube with nozzle blasts tiny water droplets at the point of grinding, which keeps the steel from overheating. It uses very little water, so you don't need a drain pipe. You can get them at MSC (www.mscdirect.com). Stock #09413105. If you already own a water-holding tank, cheaper models are available. FWW mag. had an article on this which is now in the book "Fine Woodworking on Planes and Chisels", p. 86. The author says he uses 40 PSI. Each sharpening system has advantages and disadvantages in terms of results and costs. You pays you money, you takes you chances.

Steveayerse's picture

Best bench grinder! (post #90874, reply #8 of 9)

Hello guys, this one is a really old thread, however I can't miss a chance to revive it! Yesterday I wrote a huge post reviewing 5 different bench grinders, so if someone still looking for the best bench grinder, I invite you to read my blog!

Read my blog and learn from my mistakes and success stories about woodworking!

leminhtien's picture

Download over 16,000 (post #90874, reply #9 of 9)

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