Grinder Wheel Question

[Orlando Gonzalez]

My 6" CM grinder just died and I am in the market for a new one. I'm looking at the 8" slow-speed grinder from WC for fast steel removal. My question is whether there is a big difference in the hollow grind in going from an 8" wheel to a 10" wheel since I just got the Grizzly 10" wet-grinder to set the final bevel before going to stones/sandpaper. Or should I get a 10" grinder.

Thanks
OG

[Paul Atkins]

Draw a 8" circle and a 10" circle and compare them with your blades.

[Johnny Kleso]

I have a 10" HF bench grinder I got on sale for $77 but think they are now over $100 like $120 if I remember correctly..

I would get the 8" slow grinder from WC last week they where $79 but I think sale ended...

There is a difference between the 8 and 10 and it is easily seen but if your just roughing the blade for the 10" wet its not an issue just rough grind it a few degrees steeper that the 10" wet setting...

[Robert Rozaieski]

Why two grinders? I'd use the 10" wet grinder you have to do the initial bevel and then go to the stones. FWIW all I use is a cheap 6" high speed grinder before I go to the stones.

[Danny Burns]

My 6" CM grinder just died and I am in the market for a new one. I'm looking at the 8" slow-speed grinder from WC for fast steel removal. My question is whether there is a big difference in the hollow grind in going from an 8" wheel to a 10" wheel since I just got the Grizzly 10" wet-grinder to set the final bevel before going to stones/sandpaper. Or should I get a 10" grinder.

Thanks
OG

A 10" grinder will have a 1.25 times faster grind than an 8" if the RPM 's are the same.
The surface feet per minute, sfpm, on a 10" slow RPM grinder is very close to the same 6" high RPM grinder.

6" @ 1725 RPM - 2709 sfpm
6" @ 3450 RPM - 5419 sfpm
8" @ 1725 RPM - 3612 sfpm
8" @ 3450 RPM - 7225 sfpm
10" @ 1725 RPM - 4516 sfpm


Going from an 8" grinder to a 10" water wheel is going from a sharp curve to a less sharp curve, and so the 10" wheel will just sharpen the bevel edge, and the bevel heel. Not a problem. It would be a problem going the other direction.

The question of how much of a hollow grind you get has to do with how big the bevel is. The bigger the bevel, the more hollow the grind.

Let's say a chisel has a 1/2" bevel.
6" wheel gives 0.00521" hollow.
8" wheel gives 0.00391" hollow.
10" wheel gives 0.00313" hollow.


3/16" plane blade.
6" wheel gives 0.00073" hollow
8" wheel gives 0.00055" hollow.
10" wheel gives 0.00044" hollow.

For reference a human hair is around 0.0016" thick.

If you go with a 10" grinder, and a 10" water wheel, you will be using up more of you abrasive on the water wheel, since you will be getting close to 100% contact.
Since the only part that works is the very bevel edge most of the time, then using an 8" wheel on your grinder will save you water wheel abrasive.

[Orlando Gonzalez]

Johnny & Danny - Thanks for the info and advice. I'll be getting the 8" WC grinder.

Robert - trying to rough grind a blade with the Griz at 90rpm is like watching molasses run uphill, which I tried after the 6" died. :eek: The 8" will just set the rough bevel before going to the Griz to tune it up.

Paul - Thanks, will do. It will give me a better understanding of the geometry of grinding.

Happy Holidays

Orlando