Tool sharpening RPMs debate....

[Rick Cicciarelli]

Is there really THAT much of a difference between whether you are using a grinder running at around 1750 RPMs vs 3000 RPMs or is it just a matter off using a lighter touch for less time? Seems like there are differing opinions on whether or not one is really better than the other, or if it even matters. It seems like the actual wheel being used is the more important part? And with that, what would be the best grit for your fine turning tools and chisels?

[Belton Garvin]

I think the 2 biggest concerns are:

1. The heat created by the faster RPMs changing the hardness properties of your tools.

2. The amount of metal taken off at faster speeds.

One can work just as well as the other if you have the patience and take your time. Just my .02

Bear

[Steve Sawyer]

There is only one issue to consider in powered sharpening, and that is heat. Too much of it will remove the temper from the blade making it useless for woodworking unless you put it through a heat-treating process.

If you can control the heat, than you can use any grinding wheel of any type, but it's obviously easier to do that with a) slow rotation speed b) lubrication with a cooling agent (e.g. water) c) friable grinding stones such as aluminum oxide and d) using very light pressure between the tool and the stone.

I use a 6" (3600 RPM??) bench grinder with one of those blue Norton grinding stones dressed into a shallow arc shape, and use a technique described in a recent issue of Fine Woodworking IIRC. It really just uses the "crown" of that slightly curved surface and a light touch, placing fingers directly behind the edge (so you can feel any heat) with a dunk into some water after every 2nd or 3rd pass.

In comparison, you can use a Tormek or similar wet grinder at slow speed without having to worry about over heating. I would also say that most consider a grinder as simply a way of establishing the bevel (either flat or hollow ground), not as a way of actually putting an edge on the tool. You will still need to hone or strop to remove the scratches/serrations added by a powered grinding stone of any grit.

I also use a WS3000 after the grinding to put the final edge on the tool.

The bottom line is that if you use the right technique, you can get away with just about any grinder at any speed, but you run a greater chance of damaging an edge while you're learning that technique if you go with a dry standard wheel at high speed.

[Rick Cicciarelli]

How do you use a wet stone on a gouge?

[Ken Garlock]

Hi Rick.

I have a Baldor 6" 1800 RPM grinder that works very well using Norton 3X wheels.

Steve has hit it on the head, heat is your enemy regardless of speed. The only secret to using a 3600 RPM grinder is to keep it well dressed. Using the wheel will cause the grinding surface to glaze over. When glazed, the wheel does not cut cleanly and becomes a slick friction surface that heats the tool and can cause permanent damage.

Whether you use 1800 or 3600, get yourself a diamond dressing tool, and use it.

Diamond dressing tools are your tools friend.

[David Christopher]

http://www.traditionalwoodworker.com/images/Tormek-Gouge-Jig-sm.jpg (http://www.traditionalwoodworker.com/product_info.php/cPath/691/products_id/4238)http://www.traditionalwoodworker.com/images/Tormek-Profiled-Wheels-sm.jpgthis is how they do it

[Bob Hallowell]

Rick you don't need to worry about removing the temper from the tool, as almost all tools are made from hss. I use a 3450 grinder and have never had a problem, as I have state before I don't see the big deal on speed. The wolverine jig directions call for a 3450rpm grinder but it doesn't matter. I think most buy the slow speed delta from woodcraft caue it's cheap and comes with white wheels.

Bob

[Jeff Nicol]

Grinders and sanders and hand honing all have there place in sharpening tools. I just replaced my 15yr old 3300rpm 6" grinder to a slower 1750 8" grinder. I would have kept the old one but it was on it's last leg and owed me nothing. I will go through it and use it in my pole shed out in the country when the need arises. So to get on with what I think. The higher speed grinder is not as forgiving if you are doing anything freehand. If you stop in one place put to much pressure you can take a lot of metal off fast and create heat quickly. The new grinder has white wheels on it and cuts much slower so I have greater control over what I am doing. I am happy with the change also because the 8" wheels are wider. I use a wolverine jig to sharpen my swept back grind bowl gouges but everything else so far I do freehand with no problems. The honing debate will continue to rear it's head in every post about sharpening, do it if you want or don't do it. It is a waste of time during roughing as the amount of sand, dirt, grit etc will dull the edge anyway and you will need to go to the grinder and touch up anyway. I will hone on some final cuts on certain woods or highly figured wood but that is all. If you have a little to much perfectionist in you or are an old time flat worker, honing seems to go hand in hand with them. As that being said my carving chisels and hand planes are honed to as sharp an edge I can get.

So use what you have and try things you don't, but not likeing one over the other is your choice and yours alone. I like Root beer and I hate Coke Cola, but I will drink the Coke if there is nothing else!

Good luck and if it cuts the way you like that is all that matters

As much "CENTS" as I have!

Jeff

[Rick Cicciarelli]

I guess the reason I was asking is because I was given a grinder that is a ~3000rpm grinder. But it looks like I will still need to buy a different set of wheels for it if I want to use it for sharpening. So I guess I was going back and forth between spending ~$75 on wheels for my current grinder, or just using that for other cleanup work and going out and buying a devoted sharpening grinder from Woodcraft that includes the necessary sharpening wheels....

[Bob Hallowell]

Rick you can buy just one wheel to save money. I leave a regular wheel on one side of my grinder for misc. stuff. I would keep the grinder you have.

[David Walser]

Rick,

As others have mentioned, heat is the enemy when it comes to using a grinder. However, in the case of modern high speed steels (and the even more modern powdered steels) used in virtually all new turning tools, the enemy has been defeated before the battle's begun. To draw the temper from HSS, you need to get the temperature above 1400 degrees (F) (IIRC). That's all but impossible to do with a high-speed grinder. (IIRC, you would need to get the tool a bright red in color. In the case of high carbon tool steel, which was the standard for turning tools until about 15 years ago, getting the steel to turn blue -- a much lower temperature than bright red -- would draw the temper.)

Some have suggested that you should combat heat by quenching the tool water. That's good advice if you're grinding a high carbon steel plane blade. It's not good advice for grinding something made from HSS. Qenching HSS may cause micro-fractures and ruin the edge.

So, why use a slow speed grinder if heat isn't a problem? Because, for most of us, using a slower grinder is easier. It's easier to learn how to create a sharp edge and shape and it's easier to do after we've learned. It also doesn't take that much longer. If you're a production turner, the quicker (very slightly quicker) sharpening and shaping from a high speed grinder might make sense.

[Burt Alcantara]

I started off with a 3600 RPM grinder. As it was my first grinder and I knew nothing about sharpening, I was able to make a lot of metal stumps. In frustration, I bought the "slow speed" grinder and vari-jig. Was much better but still had problems. Took a class with Trent Bosch. He showed me how to sharpen in exactly 1 minute. Since then, and with a lot of reading and practicing I'm able to sharpen my gouges as I want.

Then, recently I bought a Tormek. Mostly to sharpen my kitchen knives. Now, this is a slow grinder - 90 rpm. My knives have never been sharper and I know I'm not doing them correctly. I'll give the gouges a try very soon as I understand they come out sharper and last longer.

As they say, YMMV,
Burt

[Gary Chester]

So I guess I was going back and forth between spending ~$75 on wheels for my current grinder, or just using that for other cleanup work and going out and buying a devoted sharpening grinder from Woodcraft that includes the necessary sharpening wheels....


I bought the dedicated grinder and jig for sharpening and kept my old grinder for the "dirty work".

[charlie knighton]

i agree with Ken that dressing the stone is very important, i have a plastic pan full of water and shavings, only need the water and paper towel, to clean the gouge or chisel before sharpning, that way i do not add to the dressing problem of the stone

this was passed on to me at a demo or on a thread

[Paul Atkins]

My grinders are about 1400 rpm -just due to pulley size- and altho heat might not be as much of a problem with hss, not all of my tools are that. I grind my turning tools, japanese chisels, Hock plane blades, jointer blades and drill bits all on the same grinders, so slower is better for me.

[Dean Thomas]

Temper is an issue with carbon steel tools. According to a couple of metals guys, you'd have to get the sucker RED HOT in order to mess up a HSS tool. These guys are both engineer-level guys that study that stuff. Both say that you'd run out of steel before you got it red.

Speeds are an issue always, but according to one source, it's more a question of control than anything else. You can do more damage quicker at high rev.

Oneway knows something about metal, too. They recommend a specific grit and specific speed to use with their tools. If they were concerned about amateurs or novices screwing things up, don't we know they would have NOT recommended high speeds? And don't you know that the Wolverine would have been designed around a Tormec instead of a dry grinding wheel??

Just did a bit of math. I have a 6" grinder and an 8" grinder. 6" is high speed and the 8" is dual speed. When we talk about turning, remember how concerned we are about SURFACE speed more than RPM? Here's some interesting math, IMO:

A 6" wheel at 3650rpm runs at an amazing 5,733 surface feet per minute (sfm). An 8" wheel at 3650rpm runs at 7,644 sfm. The same 8" wheel at half speed or 1825rpm comes in at 3,822 sfm. Oneway recommends 8" wheels and 3650. Oneway might not be "the" authority, but I do think their opinions are important enough to consider.