8" grinding wheels turning at 1750 RPM?

No, too slow. It's quite common for a 7" wheel to be able to be run @

3,600 RPM, and some 8" wheels are so marked as well. Power-wise, 1/2 horse is fine for sharpening toolbits, but would be a slight compromise for heavier grinding. You could get by with it by taking it easy, though. If you really want to use it, you'd have to run larger wheels, say 12".

Wheels should be run at their recommended speeds so they behave as they're intended. Slowing wheels down makes them behave as if they're softer than they are- which means that speeding them up makes them behave as if they're harder than they are. I'm sure you understand that the abrasive doesn't change--it's the way the bonding agent behaves.

Almost all grinding wheels will be marked with a recommended maximum speed. Try to run as closely to that speed as you can without going over. Exploding wheels are very unforgiving, generally leading to death. If you don't know about ringing a wheel before putting it to use, get the concept down pat, for it can be the difference between life and death for you. Simply place the wheel on something that won't dampen vibration (screwdriver blade, for example), and tap it *lightly* with a slightly hard object, like a screwdriver handle. The wheel should ring like a bell. If it makes a dull thunk kind of sound, it's most likely cracked, and cracked wheels explode when spooled up. The best thing to do with the wheel like that is break it so it can't be used by some unsuspecting fool.

Be certain to match the abrasive of the wheel to the work you're doing. If you're grinding steel, use aluminum oxide. Other materials, including cast iron, silicon carbide is a better choice. There's lots to know about grinding, so you'll do well to ask questions along the way, which I've noticed is your style, anyway. That way you can pick up on important things as they become a problem for you. There's a few of us with grinding experience that will keep watch over you.

Harold

Aha, thank you.

Never thought of that, it's a good idea...

Thank you Harold. I don't know if I will end up buying 12" wheel or a

3450 RPM motor. I am curious if there are 3450 RPM 3 phase motors with a 5/8" shaft. I will definitely ask more questions, as exploding wheels are indeed extremely dangerous! i

Don't put a whole lot of eggs in this basket. My 10" is powered a little on the lite side at 5 hp. I forget the speed but is belt driven faster than the motor. What do you want to do, sharpen your golf tees? However, a 6" wheel on a belt driven arbor with 1/2 hp is a workhorse.

That's an interesting approach. The wheel running slower than advised will cut much cooler, due in part to it behaving much softer and sloughing off easier. It's hard on wheel life, but that shouldn't be a problem for touch-up. If one was roughing HSS blanks, that would be a serious mistake, though. The blank starts acting like a dressing stick.

Harold

Thanks... I will check things out. I am very confused about how I can make a higher HP grinder (say 2 HP). Basically, I cannot find shaft adapters. I do not want to make one myself for safety reasons, I would rather buy one from a company that has been making them for years and knows all the gotchas.

i

Thanks, I will check into it...

i

If you want a working powerful grinder, buy or make a belt-driven arbor, forget the adaptors or go to

(one of my customers)

Thanks Tom. I will call them tomorrow to see what they have to say. On their website, they list arbors for 5/8" shaft, same as available from Harbor freight.

i

Ok First off don't let the guys safety ranting scare you away. I've watched you enough to know that you learn from what ever advise you get and making the arbor is not beyond your capability or tooling (you do still have the lathe right) just your knowledge. Well that's easily correctable right here. I feel this is a perfect learning project for someone to make on a lathe. It covers all the basic operations you need to know for proper lathe operations.

Second I still go with the belt recommendation from earlier but if you insist on a straight arbor then let's go through the steps of making one.

First things first. Since you're wanting to mount such a big wheel on this arbor start with at least a piece of 1 1/4" stock 1 3/8" or even 1 1/2" would be better. I like to see a minimum of 1/4" wall on a socket like this with more being better but be sure to at least have

3/16" wall.

You need to drill and BORE the socket that slips over the shaft of the motor. Just drilling will not give you the size and straightness you need for this hole. Look at this step as a good piece to learn this process. If you want you can use pieces of scrap pipe to practice boring to size. You will need to know how to do this if you're going to many projects on a lathe so it's time to learn it. If you have any questions there's more than enough people on this forum willing to answer them. In fact the real problem is that the variety of answers can be overwhelming to a beginner.

The main things I'm concerned about on this part is to make the hole at least 2 times the diameter deep with 3 times being a better figure.

Be sure the stock is running true when you do the boring and if it isn't then take a light cut across the outside of the socket area till it is running true. This is so that you can be sure you're running true with the socket when you turn it around for the other operations.

Make the socket size to maybe 0.002" oversize of the shaft. Size is better but you can get by with a slight bit of oversize before the shaft doesn't run true enough to use without vibration.

Put 4 setscrews in the socket when you get to that part of the operation. Two inline with the keyway and two more 90deg around from the first two. Put one about 1/2" from the end of the bore and another about 1/2" from the outside end of the socket. Repeat with the other two.

The next lathe operation is the turning of the shaft for the grinding wheel. You need to turn this to size or a little under. Again here size is better but 0.002" or even 0.003" under isn't going to kill you. You'll have to true the wheel after getting it mounted anyway. You need to be sure and leave at least 1/4" and I'd prefer more like 1/2" - 3/4" of the adapter full size between the bottom of the bore and the socket and the square shoulder you'll leave at the end of turning the shaft down. If you get to close to the socket then there won't be enough metal to be strong enough for safety. Be sure that the shoulder you leave is faced square and straight since this will be what makes the wheel run true. I'd recommend you make this 1" dia since that's the standard size for most grinding wheels without the use of bushings. It needs to be long enough for the width grinding wheel you intend to use plus two washers, and a nut. Add at least 1/2" to this figure for future expansion.

Now we get to the slightly tricky part. You need to thread the arbor for the nut. The best way to do this is to cut the threads on the lathe. Again this is something you can and should practice. It will turn into a valuable skill later on. Don't thread all the way to the shoulder. Figure out the thinnest grinding wheel you'll likely use and add the thickness of one washer to figure out what length should be left unthreaded. I'd make them right hand for easier access to nuts. Just be sure to mount the motor so that the arbor is sticking out the right hand side as you're looking at it to make sure the nut won't unscrew when you use it.

Now you need to make the washers. These are important as was brought up before. They need to be sized to the size grinding wheel you intend to use. Probably around 3"-4" dia in this case. I'd start with at least 3/8" thickness. You need to face one side flat. Then you can mount them one at a time in the arbor itself with a piece of pipe that's been faced square on both ends between the nut and the washer. You can then face the other side straight as far as you can before hitting the pipe. If you want you can also under cut the inner portion leaving about a 1/4"-3/8" wide portion to contact the wheel at this time. Once that's done to both you'll need to chuck the washers backup to face off the tit in the middle that was left because of the pipe. Doing it this way will make sure that the washers run true to the arbor.

If you want you can taper the outside of the washers while they're on the arbor. At the very least you should round the corner that's away from the wheel.

This should get you started anyway. I'm sure there will be many people chiming in with good advise and or horror stories. Don't let the horror stories scare you away. They're good advise as well about what not to do.

Wayne Cook Shamrock, TX

Thanks Wayne, your post makes sense 100%. I saved it and will print it out if I ever get to this point. Meanwhile, I will also explore belt drive as a possibility. Here, I can buy appropriate pipe or threaded rod and be quite safe and happy. All I will need is pillow block bearings and shaft and pulleys. That could be a better long term solution, although possibly more expensive and time consuming.

i

It would be more expensive but more useful in the long run. Threaded rod is ok but not the best. Just be sure and double nut the left hand wheel if you use threaded rod. I built one that way a long time ago before I ever had a lathe. Again 1" is a good size though 3/4" would cost less and be good enough.

Actually I think it's the wheel guards that are going to be more of a problem for you without welding capability.

Wayne Cook Shamrock, TX

Skip the Harbor Freight wheels. They are crap.

I bought a Norton 60 grit wheel for one side of my 2HP Harbor Freight grinder and a 10" buffing wheel for the other side.

Night and day difference in quality of grind and how much material was being taken off. Needed a lot less pressure to do the same amount of grinding.

I have two HF wheels I'll sell you. I keep them on a shelf in case I somehow destroy the Norton and need an immediate spare.

Bart D. Hull snipped-for-privacy@inficad.com Tempe, Arizona

Check

my Subaru Engine Conversion Check Tango II I'm building.

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