Grinding wheel question

A24P4B A - Aluminum Oxide

Try

Cheers,

Bruce (bruceinbangkokatgmaildotcom)

The designation of those wheels indicates they are aluminum oxide, 24 grit, P hardness, 4 structure (indicating the abrasive bits are close together) and that the wheels are resinoid bonded. You could expect them to be slow to shed abrasive as they dull, and to hold up well, although they may not grind real well because they are so hard and dense. Depends on your application, really. If you grind mild steel regularly (weld shop, for example), they may work quite well on a large pedestal grinder. Sorry, can't provide any more info, I've never used a wheel that coarse, nor that hard.

Harold

I ain't no expert, but it seems to me that there's quite a bit of difference between the P and the L hardness. As previously mentioned, the harder they are, the less they shed grains and present new, sharp grains to the workpiece. I'll bet the guy either has an overstock of something that didn't sell well or he bought them and doesn't want to use them. I use L or M on my surface grinder. I listen for loading down of the spindle motor and for the sparks to turn a little redder to tell me it's time to dress (I'm grinding anvils mostly, and hogging for all its worth). If you could buy one and try it, that'd be best. I'd think that for general use on a pedestal grinder that you'd want a softer wheel so you didn't have to dress as often.

I have never used a wheel that coarse either, but I have used 24 and 36 grit disks on my angle grinders from time to time.

Pete Stanaitis

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Bob wrote:

Thank you guys. I ended up buying them. I am optimistic that they will work out. The coarse grit will be good for sharpenening mower blades (mine and neighbors), which is a frequent activity this time of the year.

Bob

Luck!

I expect they'll be too hard for that job, but I could be wrong. Mower blades are heat treated to some degree, so a softer wheel would be desirable, not only for faster and easier cutting, but to prevent annealing the blade.

One thing that will make them behave softer is to run them under recommended speed. That's the nature of grinding wheels.

Harold

You might want to try sharpening those blades with an angle grinder if you have one. I clamp my mower blades down to a table outside with the beveled side up and have at it. Much, much nicer being able to see exactly what you are doing that way.

The plastic nose cone off from the larger fireworks rockets works good for balancing blades too. Pound maybe a three inch nail into a block of wood nice and straight. Nip the head off and dress to a dull point, place cone over nail, place blade on cone. My home brew job works better than the similar model I bought for blades, which is none too sensitive.

How about fluid colling the grind vs. dry and high heat.

What do you suggest for lawn mower blades ?

I'd have to make a jig - but that is just some of the fun.

Mart>> Thank you guys. I ended up buying them. I am optimistic that they

I would expect they are nothing more than medium carbon steel, so over heating can result in annealing. Keeping the material below 375 degrees F is a good idea. You'll find that the edge heats quickly due to the lack of mass, a condition that is exacerbated with a hard and dense wheel. Coolant can be quite useful, but even with a light spray you can over-heat the edge. Watch for discoloration. It's a sign of a loaded or dull wheel, or one that is too hard for the material. If you see anything beyond a straw color develop, I'd be concerned were it my project.

Harold

Doesn't make any difference. Almost all steel alloys are heat treated by the carbon cycle, so they behave very much the same. Precipitation hardening alloys are a different matter, but I can't imagine they'd use one of them for a lawn mower blade. There would be no benefits that couldn't be reaped from carbon steel, which is the least expensive material to use. By the way, if the blade(s) truly are too hard to drill, that's all the more reason to use a soft wheel. Hard material and hard wheels are a terrible combination, sure to grind slow and very hot.

I'm curios what kind of lawn mower you're talking about. I have a JD rider lawn mower---with double blades. They are easily sharpened with a file, assuming that's your choice.

Blades that are so hard that they won't file (or drill) are subject to shattering when they hit hard objects. They may appear hard to drill, but I dare say you can drill them with a cobalt drill. You just have to know how to use it. Hand drilling is likely beyond possibility.

Harold

Harold, I mow with a Toro 325 Groundsmaster. It has 3 - 25 in blades. They are about 3/8 in thick and hold up remarkably well. I can get by with only one or maybe two sharpenings per season.

The wheels arrived and look good. I'll put one on next time I need a new one and see how it does.

Bob

It will be interesting to hear of your results. Thanks for keeping us in mind.

Harold