Grit

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: GlennW, Harold_V

Post Reply
Glenn Brooks
Posts: 2930
Joined: Mon Nov 10, 2014 1:39 pm
Location: Woodinville, Washington

Grit

Post by Glenn Brooks »

So, looking for a short primer on grit sizes for abrasive wheels. And why are wheel grits nothing like belt grits?

More specifically, why grit in sanding disks and belts are rated differently that grit in aluminium oxide wheels for say, my 8” pedestal grinder?

For example, I recently purchased a replacement 8” x1”, 24 grit, AO wheel for my baldor pedestal grinder. The grit in the wheel is microscopic compared to a 60 grit sanding disk. And, this new 24 grit wheel is almost useless for removing material. It acts similar to 180 grit emery cloth - all it does is polish mild steel. Whereas my old worn down wheel could Hogg out real quantities of material. Yet Both wheel textures seem almost identical in feel. (Alas the data sheet on my old wheel is worn down so much,so I have no idea what grit size it was rated at new. )

And what grit size should I try to find, to replace this dainty new wheel?

Thanks,
Glenn
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Grit

Post by Harold_V »

Plain and simple. It most likely is NOT 24 grit, regardless of what it may say in the markings (what does the wheel display in that regard?).

Do you have a basic understanding of types of abrasives, their hardness, and how to select a wheel? If not, do some research. It's not hard to understand and making the wrong decision can be quite frustrating. The proper wheel for a given job is very desirable.

One wheel will not serve all needs. You must have hard and soft wheels. If you grind anything that is not considered ferrous, you should have at least one silicon carbide wheel. They do NOT serve for grinding steels. They do serve for grinding cast iron. Much more needs to be known to make an informed decision.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Glenn Brooks
Posts: 2930
Joined: Mon Nov 10, 2014 1:39 pm
Location: Woodinville, Washington

Re: Grit

Post by Glenn Brooks »

Harold_V wrote: Sat Sep 18, 2021 2:01 am Plain and simple. It most likely is NOT 24 grit, regardless of what it may say in the markings (what does the wheel display in that regard?).
H
Harold, yes, that was my thought also. But The wheel is definitely marked as 24 grit, for metals. But it does not hogg material anywhere close to what it should.

However, there is clearly different grit in vitreous wheels versus sanding disks or belts. Still curious what the standards are for the two different grit styles... there must be two different definitions for belts versus wheels...

Glenn
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
User avatar
Harold_V
Posts: 20231
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Grit

Post by Harold_V »

Glenn Brooks wrote: Sat Sep 18, 2021 1:23 pm The wheel is definitely marked as 24 grit, for metals.
It would be interesting to read exactly what it says. The line marked on wheels normally provides a complete description of the wheel's characteristics, and that includes abrasive size, abrasive type, bond type, how hard it is, as well as how densely it is made. A dense, hard wheel will display horrible cutting characteristics when applied to the wrong materials (metal types). I might note that it is highly unusual for a grinding wheel to be marked as suitable for metals, although that may be common for parting wheels or wheels intended for use in welding. While the reason may not be obvious, one does NOT use the same abrasive type for steel as one would for other metals, so marking a wheel as proper for metal is clearly not a good idea unless the metal type is specified. To be clear, applying a silicon carbide wheel to steel would yield horrible performance, a wheel that glazes and dulls almost instantly, and removes virtually no metal in the process.

As for grit size, that should be standard for wheels as well as belts. The difference is wheels are formed and cured by various means and may be of such a nature that the process creates the illusion of a solid, while belts have the abrasives adhered by a different process, so the individual grains are more apparent, especially in the coarser grain sizes.

That said, I am unaware of more than one grading system for abrasive grit sizes. If there is such a difference, I'd certainly like to be better informed.

It might help tremendously if you provided more information. The type of wheel you're using, as well as the type of material you're attempting to grind. As an example, if you're using an angle grinder with an aluminum oxide wheel and attempting to grind a grade of stainless, I would expect your wheel to perform very poorly.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Conrad_R_Hoffman
Posts: 440
Joined: Wed May 24, 2006 8:40 am
Location: Canandaigua, NY
Contact:

Re: Grit

Post by Conrad_R_Hoffman »

Most everybody uses the FEPA European Mesh System. This page is useful- https://www.fine-tools.com/G10019.html But, as above, there are lots of other variables. Then you have the seeded wheels that work well in production, but need a stouter grinder than the typical Harig or Boyar-Schultz many of us have.
Conrad

1947 Logan 211 Lathe, Grizzly G1006 mill/drill, Clausing DP,
Boyar-Schultz 612H surface grinder, Sunnen hone, import
bandsaw, lots of measurement stuff, cutters, clutter & stuff.


"May the root sum of the squares of the Forces be with you."
Post Reply