Slow speed grinder

[Rob Miller]

I've discovered my old Delta single speed 6" grinder just runs to fast to sharpen my chisels without overheating them. I don't have $600+ to spring for a high quality grinder but I am seeing some two-speed grinders that are fairly inexpensive. They claim to run at around 1725 RPM and content that's slow enough to keep the heat down. What are your experiences with grinders? Is 1725 slow enough or am I still going to have overheating issues? I don't want to spring for a grinder just to find out it's not going to be any good for sharpening.

Thanks!
Rob

[Doug W Swanson]

I have a slow speed grinder from Woodcraft and it works fine. I'm currently using the stone wheels that came with it but am waiting for a CBN to arrive soon. I paid around $100 for it on sale and it works great for my needs....

[Reed Gray]

The Rikon grinder is the one that Woodcraft is selling now. Looks to be a fairly good grinder. 8 inch wheels, and slow speed. It has a 1/2 hp motor, and I do like more heavy duty, but it works.

Your 6 inch grinder, at high speed runs about the same feet per minute as the 8 inch grinders (pretty sure as some one else did the math on that one). Your tools may be over heating because of too much pressure (very light touch is all that is needed for sharpening), and/or the wheels may need to be dressed/cleaned.

robo hippy

[Paul Gilbert]

The formula for the circumference of a circle is Pi*D (diameter in ft.). The surface speed would therefore be Pi*D*RPM = ft/min

For a 6" wheel at 3450 rpm this is = 5419 ft/min.
For a 8" wheel at 1750 rpm this is = 3664 ft/min

[Rob Miller]

The formula for the circumference of a circle is Pi*D (diameter in ft.). The surface speed would therefore be Pi*D*RPM = ft/min

For a 6" wheel at 3450 rpm this is = 5419 ft/min.
For a 8" wheel at 1750 rpm this is = 3664 ft/min

Still sounds pretty fast given the Tormec turns at 120 rpm.

[Brian Ashton]

Still sounds pretty fast given the Tormec turns at 120 rpm.

You've missed a key point or more accurately 400 + key points.

[Brian Ashton]

I've discovered my old Delta single speed 6" grinder just runs to fast to sharpen my chisels without overheating them. I don't have $600+ to spring for a high quality grinder but I am seeing some two-speed grinders that are fairly inexpensive. They claim to run at around 1725 RPM and content that's slow enough to keep the heat down. What are your experiences with grinders? Is 1725 slow enough or am I still going to have overheating issues? I don't want to spring for a grinder just to find out it's not going to be any good for sharpening.

Thanks!
Rob

Obviously you have a lathe, do you have an outboard spindle and a tool rest system that can utilise it. If so get yourself a mandrel that will hold a grinding wheel. You'll have a very economical slow speed grinder.

[Christopher Collins]

get a speed controller and plug the grinder into it.
http://www.amazon.com/MLCS-9400-Standard-Router-Control/dp/B001JHQ3G8/ref=sr_1_3?ie=UTF8&qid=1397263074&sr=8-3&keywords=speed+controller

[Brian Ashton]

get a speed controller and plug the grinder into it.
http://www.amazon.com/MLCS-9400-Standard-Router-Control/dp/B001JHQ3G8/ref=sr_1_3?ie=UTF8&qid=1397263074&sr=8-3&keywords=speed+controller

Do they work on induction (brushless) motors. I didn't think there was a way of turning a single phase induction motor into a variable speed motor.

[Rob Miller]

get a speed controller and plug the grinder into it.
http://www.amazon.com/MLCS-9400-Standard-Router-Control/dp/B001JHQ3G8/ref=sr_1_3?ie=UTF8&qid=1397263074&sr=8-3&keywords=speed+controller

No, it won't work with an induction motor.

[Rob Miller]

You've missed a key point or more accurately 400 + key points.

And that is?

[Reed Gray]

Thanks for the Math Paul. It has been a while. I thought the fpm was closer. Now, if you want a variable speed grinder, there is this one. It costs more than my Baldor grinder...

http://www.cuttermasters.com/portfolio/tradesman-dc/

robo hippy

[Steve Paxman]

http://www.amazon.com/gp/product/B00E8I3XRW

i just got this one and set it up with the wolverine jig. Works great once you dress the wheels, and seems sturdy and solid to me.

[Rob Miller]

http://www.amazon.com/gp/product/B00E8I3XRW

i just got this one and set it up with the wolverine jig. Works great once you dress the wheels, and seems sturdy and solid to me.

I was looking at that one. So, the original question was -- is the 1725 rpm slow enough to prevent overheating? Does yours work well without overheating the metal?

[Keith Westfall]

I've got a 'fast speed' 8" grinder, white wheels (soft) and no problems. Your tools shouldn't be doing much more than barely resting on the wheel. They don't even hardly get warm....

I'd look at your wheels and tool pressure on the wheel.

[Ron Rutter]

My grinder consists of a mandrel with a 4 grove pulley, mounted stones, an old 1/4hp 1725 rpm motor & a v-belt! Works great.
I suppose one could use a variable speed drill set-up. They are actually a DC motor.
Ron.

[Brian Ashton]

And that is?

OP said he didn't have much money to spend. 400 for a grinder is somewhat expensive isn't it for someone on a limited budget. That being 400 is the base price...

[Brian Ashton]

I was looking at that one. So, the original question was -- is the 1725 rpm slow enough to prevent overheating? Does yours work well without overheating the metal?


No it's not. Even 100rpm will over heat a tool if you work it hard enough. 1750 will allow a fair bit more time (in the case of sharpening chisels up to 10s of seconds more) to work the tool before you reach critical temps.

[Rob Miller]

I've got a 'fast speed' 8" grinder, white wheels (soft) and no problems. Your tools shouldn't be doing much more than barely resting on the wheel. They don't even hardly get warm....

I'd look at your wheels and tool pressure on the wheel.

Okay. I'm sure the issue is my technique then -- probably trying to overwork the fine grit stone (I've only got a fine one). I'll pick up a 60 grit for the other side so I can get the angles right with less pressure. Probably don't need a new grinder at all.

[Rob Miller]

Should I be wetting the wheel before grinding?

[Steve Paxman]

No it's not. Even 100rpm will over heat a tool if you work it hard enough. 1750 will allow a fair bit more time (in the case of sharpening chisels up to 10s of seconds more) to work the tool before you reach critical temps.

I agree with Brian. This is what everyone is talking about when they say "slow speed grinder." For what it's worth, lots of people also use the faster speed grinders without issue as well. You just have to know your tools and adapt your technique to match.

[Reed Gray]

Over heating is generally from pushing too hard, and/or having a loaded or dirty wheel, which is like using worn out loaded up abrasive discs (heat and no cutting). The biggest thing most of us need to learn is that a very gentle cut is all that is needed, and far to often we 'grind' rather than 'sharpen'.

robo hippy

[Rob Miller]

Over heating is generally from pushing too hard, and/or having a loaded or dirty wheel, which is like using worn out loaded up abrasive discs (heat and no cutting). The biggest thing most of us need to learn is that a very gentle cut is all that is needed, and far to often we 'grind' rather than 'sharpen'.

robo hippy

Yeah, my wheel is either 100 or 150 grit and I think I'm pressing too hard to get it to take off more metal than I should be with that grit. I'll get a 60 grit wheel to get the shape right before finishing it up with the fine wheel.

[Dale Gillaspy]

Yes, the 1725 is plenty slow enough. It is pretty much the "industry standard" if there is such a thing. In reality, if you are using HSS or "newer" tools such as powdered metal, the 3250 is plenty slow enough as well. Heat or "blueing" doesn't damage that steel the way it did high carbon. I would start with clean, dressed wheels and a very light touch. I know several professional turners that use a 6" high speed grinder.

[Rob Miller]

Okay, so I put the 60 grit wheel back on and dressed it and it was fine -- that did the trick.

[Brian Ashton]

Okay. I'm sure the issue is my technique then -- probably trying to overwork the fine grit stone (I've only got a fine one). I'll pick up a 60 grit for the other side so I can get the angles right with less pressure. Probably don't need a new grinder at all.

It's even more important that you buy a wheel dresser and diamond shaper for the grinder. These will keep your wheels fresh and flat - no matter what wheel you use. It might be that your fine wheel is warn too much and is therefore generating a lot of heat.

[Rob Miller]

It's even more important that you buy a wheel dresser and diamond shaper for the grinder. These will keep your wheels fresh and flat - no matter what wheel you use. It might be that your fine wheel is warn too much and is therefore generating a lot of heat.

Not in this case -- it's a brand new wheel. I did get a diamond wheel dresser also and dressed both the old and new wheels before use.

[Terry Vaughan]

For many years I used an 8" high speed grinder with the factory fitted gray wheels for carbon steel tools as well as high speed steel ones and was happy with the edges. I never seriously burned the steel and didn't normally use a water quench either.

I'm not recommending this approach, just saying it can work perfectly well. It's necessary to use a light touch with no pressure on the wheel, keep the wheels clean and not grind carbon steel for more than a few seconds before you let it rest for a bit.