Use 7" grinding wheel on 6" bench grinder?

[Forty Niner]

I'm thinking about mounting a 7" face type 5 /recessed grinding wheel on a spare 6" bench grinder. 6" face type recessed grinding wheels are scarce.
The wheel is certified for the speed (3580). I can machine a proper mounting adapter to hold it on the grinder shaft.
The wheel will be used to sharpen drill bits on the face, after my newly acquired but old drill sharpening fixture is mounted to it.
I can fabricate a larger diameter wheel guard.

I'm thinking this will work, but would like to have comments. Anybody tried this?

 

[cathead]

Give at least a little thought to speeds and centrifugal force when you deviate from the norms.

 

[Jimsehr]

Think about using an old frying pan or pot for a wheel guard.

 

[RJSakowski]

As long as you don't exceed the rated speed of the wheel, you should be fine. You will experience a slight reduction in available torque due to the increased diameter but that shouldn't impact you for your intended purpose.

 

[bill stupak]

Don't know if this matters, but the SFM of a larger wheel will be higher given the same speed and maybe burn up bits easier.

 

[RJSakowski]

Don't know if this matters, but the SFM of a larger wheel will be higher given the same speed and maybe burn up bits easier.

I can't imagine that you would get the tip of a HSS drill hot enough to pull the temper. Hardness in M2 HSS starts to draw at a red heat. That's why it's called high speed steel.

The difference in surface speed of a 7" wheel vs. a 6" is only 17%.

 

[Forty Niner]

Don't know if this matters, but the SFM of a larger wheel will be higher given the same speed and maybe burn up bits easier.

True about the SFM on the outer diameter, but where I will be doing the grinding will be more like 5 or 6 inches diameter. Because I will be grinding on the face, not the OD.

 

[T Bredehoft]

I will be grinding on the face, not the OD.

Very good point. A half-inch in from the edge will be the same surface feet as a 6" edge wheel.

 

[Jake M]

I'm thinking about mounting a 7" face type 5 /recessed grinding wheel on a spare 6" bench grinder. 6" face type recessed grinding wheels are scarce.
The wheel is certified for the speed (3580). I can machine a proper mounting adapter to hold it on the grinder shaft.
The wheel will be used to sharpen drill bits on the face, after my newly acquired but old drill sharpening fixture is mounted to it.
I can fabricate a larger diameter wheel guard.

I'm thinking this will work, but would like to have comments. Anybody tried this?

If the RPMs are good, the RPMs are good. The wheel doesn't care about the original diameter of the original guards, it only sees RPMs. Most 8 inch grinders have the same RPM rating. Sure, outside surface speed increases some, but loads of us sharpen HSS on 3600 RPM 8 inch grinders withoutr taking surface speeds too far. You'd be reducing RPMs over that benchmark.

Always respect the wheel when you're making adapters, they're heavy, brittle, and are more than happy to ruin your day. It's not aerospace stuff, but make it good and it'll be good. Make it good enough, and "maybe" it'll be good enough. Ugly is fine, but make it fit at least like a factory piece. That's not a rediculouosly high bar, and better is nicer.

All in all, you're not changing much as far as the grinder it's self is concerned, and the wheel is going to be use "on label"... Bench grinders deserve a lot more respect and attention than they (usually) recieve, but in this case, I don't believe you're challenging part of the setup in any way that's going to need any attention outside of the usual.
The only concern I can come up with is if (if....) the wheel comes out heavier, or it's weight distributed towards the outside more, if the grinder has trouble coming up to speed, you might have to loose the "other" wheel to lighten it back up. On the other hand... It might be zero to minimal impact. I'd keep an eye on it when you first start it up, but I sure wouldn't sweat overit preemptively.