Grinding speeds

[mkemmet]

I am looking at purchasing the four-piece sharpening system and variable-speed bench grinder from PSI. I see the system (grinder and jig) is getting a 4.5 star rating on a 5 point grading scale. As a retired engineer I'd like to learn more about grinding wheel speeds before I purchase any system. Is there such a thing as a sharpening speed grinding wheel chart? Using my current system, a fixed-speed grinder, I have blued (overheated) the tips of my tools a few times too many times. I am very interested in specifics on grinding speeds. Thanks!

 

[sbwertz]

I bought the CBN wheels. First, they work with a high speed grinder or a low speed grinder, so If you already have a high speed grinder, you don't have to buy another. Second, they grind cool. The tools don't get very hot when sharpening. They don't ever have to be replaced. They don't get smaller with use. They don't have to be dressed. They will sharpen carbide tools and the new high carbide steel tools that are coming on the market. Warning...don't grind mild steel on them.

 

[JimB]

There isn't a chart. Most people have a slow speed grinder. They run at 1725rpm. However, some use a regular grinder that runs at 3450 rpm.

You don't mention what kind of tools you are sharpening or how you are sharpening them. If they are HSS then a little bluing isn't going to hurt them. However, if this is happening when you are sharpening (not shaping) then you are pressing much to hard for much to long. Sharpening only requires the weight of the tool. You should not be pressing. It should also only take a few seconds to get a fresh edge on your tools.

 

[Dick Mahany]

I haven't seen a comprehensive speed chart.

I have a Delta 8" variable speed grinder and it is just OK. I use a friable Aluminum Oxide at high speed on one side for roughing M2 or PM steels to shape custom profiles or for quick stock removal. On the other side I use a CBN wheel and typically prefer slow speed for sharpening.

I've read so many different opinions regarding high vs low speeds that it made my head hurt, so I purchased the Delta VS grinder. I really don't care for the speed regulation surges on that grinder, but it is what it is.

If I replace it, it will definitely be with a Rikon slow speed grinder as it has so many excellent reviews for the price point. (Baldor isn't in the budget )

 

[Woodchipper]

What JimB said. I have a Rikon low speed grinder and bought the complete Wolverine set-up. Could have saved a bit by buying the whole system at once. FWIW, Woodcraft sometimes has the grinder alone for $99.95.

 

[bsshog40]

I went from a regular full speed grinder to a variable. Was able to sharpen at about 1750 rpms. Didn't help my sharpening skills very much but I did save on metal being ground off. Lol I eventually bought me a Robert Sorby system. Love it!

 

[leehljp]

While slow grinders are often listed in the 1350 rpm range, there is another much slower speed that uses water wheels. Water wheels are generally exceptional for excellent sharpening without heat, but glacier slow for bringing new tools to SHAPE.

CBN wheels for HSS are excellent and the speed is almost irrelevant as too heating. The following link discusses some aspects of speed without heat:

http://www.penturners.org/forum/f30/cbn-wheels-grinder-155103/

As to your understanding of speed = heat, CBN wheels on HSS does not follow suit. it can get hot, but just the tip if you over do it, i.e apply too much pressure. With CBN wheels pressure is not needed.

 

[Curly]

Dressing a wheel often keeps them sharp, producing less heat. Blueing draws out the temper of carbon steels. High Speed Steels (HSS) were originally designed for machining metals and they hold their sharpness even when approaching red hot. Blueing HSS doesn't make any difference to the tool just don't quench it in cold water as it causes micro fractures. That makes them dull faster.

What kind of wheels do you have on your grinder? If you pull off the wheel there should be a number and letter code on the blotters that will tell you the material it is made of, what it is bonded with and the friability. https://www.aaabrasives.com/blog/post/how-to-read-grinding-wheel-spec/ The right type of wheel makes a big difference in sharpening. You won't likely find much on speeds unless it is for surface grinders so they can get maximum material removal rates. There is a maximum speed on the wheels for safety and generally the slower the speed the quicker it will go out of round requiring dressing to correct. The wheel behaves harder when fast. You're an engineer so hunting down that sort of info is right up your alley.

 

[Wildman]

Never good idea to blue your turning tool regardless of tool steel! Use light pressure at the grinding wheel regardless of bench grinders max RPM's no load speed. In industrail sharpening they use water and sometimes water & oil while grinding to cool the steel.

More familar with Wolverine system but any sharpening system should help with a light touch and getting repeatability every time you sharpen your tools. There are a lot of systems out today to chose from!

Packard Woodworks: The Woodturner's Source: Sharpening Supplies

Been using 3450 RPM grinder, with 6" wheels, and 1/3 HP for more than twenty years. Have sharpen tools on 8" wheel and preder that size but not going to fix what's not broken untill my old grinder quits, Don't care about no load RPM's.

GRINDING WHEEL and ABRASIVES BASICS

 

[sbwertz]

Off topic, but if you are using the wolverine system and don't have the skew attachment, it is available here at about half the price. It is fifteen dollars now, it was only ten when I bought it a year ago. It is 38 dollars from Wolverine.

https://smile.amazon.com/gp/product/B01K7JT9UK/ref=ppx_od_dt_b_detailpages00?ie=UTF8&psc=1

 

[wolf creek knives]

While slow grinders are often listed in the 1350 rpm range, there is another much slower speed that uses water wheels. Water wheels are generally exceptional for excellent sharpening without heat, but glacier slow for bringing new tools to SHAPE.

CBN wheels for HSS are excellent and the speed is almost irrelevant as too heating. The following link discusses some aspects of speed without heat:

http://www.penturners.org/forum/f30/cbn-wheels-grinder-155103/

As to your understanding of speed = heat, CBN wheels on HSS does not follow suit. it can get hot, but just the tip if you over do it, i.e apply too much pressure. With CBN wheels pressure is not needed.

I use a water wheel grinder that works great. Got it from Grizzly quite a few years ago. I don't use it a lot as once I have the tool to the profile I want I use a hand held sharpening stone to keep the edges sharp. I sharpen with the stone between every piece I turn unless it gets dull mid-way through a piece, then I sharpen the tool mid-way. I don't worry about heat, wearing out my tools or the speed of the grinder. It can get kind of messy when using the water wheel but I just use an old towel under the grinder and everything stays dry...except for the towel.