Grinding drill bits

I had the opportunity to hand-sharpen a half-inch twist drill bit yesterday, when my too-fast drill press busted the tip of a cobalt 0.5" bit while I was trying to drill a piece of 304 stainless steel sheet

0.060" thick.

I took Harold Vordos' suggestion if a while ago and sharpened an old HSS bit freehand. It worked, and wasn't near as hard to do as it sounds.

I'm now trying to sharpen the split-point cobalt drill. It won't be split-pint anymore, but that's OK.

At least one grindstone on the 6" Ryobi doesn't run true, wobbling from side to side, making the world vibrate. What would be good replacement, by make and model? Or, does one simply shim the wheel with cardboard?

Joe Gwinn

Reply to
Joseph Gwinn
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Dress the wheel to a sharp edge square to it's side and you can split the point also and thin the web. As for a wheel try something no harder than K, the zirc doped aluminum oxide ones cut cool. What is wrong with your grinder is most likely the stamped wheel flanges, try lapping them on some silicon carbide paper on a flat surface.

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Welcome brother!

Reply to
Tom Gardner

What bamboo said. You can split the point, too, but study one well before you try, so you understand what you're trying to accomplish. It's important for the split point to be dead on center and have the proper angles, so it takes a little skill. You can do it!

Never shim a wheel. You risk cracking by the uneven clamping pressure you'd achieve by the shims. It's good to remember that you should never run a wheel without the blotter while we're talking about the subject. The blotter's purpose is to spread clamping forces such that minor wheel irregularities don't cause cracking when the flanges are tightened. Don't over tighten. It's not necessary.

As bamboo suggested, check the flanges that they run true. If they do, using a long handled diamond, dress the sides of the wheel until it runs true. It's not uncommon for wheels to not be parallel, which will make the world vibrate, as you suggested. You should be pleasantly surprised that your grinder runs quite smoothly when you're finished. You can follow up with a dressing stick if the sides display some light grooving after you've applied the diamond. You should be able to steady the diamond on the wheel guard adequately to achieve acceptable results.


Reply to
Harold and Susan Vordos

If it's the original stone, pitch them.

I got some Norton stones from MSC and you wouldn't believe the difference. Smoother running, faster cutting and less grit being thrown off the wheel. I got a medium and a coarse stone for my 10" HF grinder.

Just my 2 cents. I also replaced the "gun" in my sandblasting cabinet that I got from HF with one from an American mfg. Night and day difference as well.

If we only had managment that had balls to go against the import stuff and quit raping the American consumer. Lots of stuff could be made here at a modest profit. It wouldn't be the cheapest but quality could then prevail. Just look at the Japanese cars and trucks built in the USA./Rant OFF

Bart D. Hull Tempe, Arizona


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Joseph Gw> I had the opportunity to hand-sharpen a half-inch twist drill bit

Reply to
Bart D. Hull

After some practice. I understand the split-point geometry well enough, but first I need some practice hand-grinding, so I'll do plain points at first.

The wheels do have blotters, the labels.

Following another poster's suggestion, I hand flattened the mating surfaces by wet sanding on a granite surface plate, and broke the sharp corners with a hand file. Stones still wobbled, but one possible cause eliminated. The irregularities should also be much reduced, if the two surfaces of the flanges are parallel.

The stones are 1" wide and 8" (not 6") in diameter, on a 5/8" arbor, are gray, and claims to be made by Ryobi.

Define "over-tighten", please. The spindle nuts are now looser than they were in the as-received machine, but still I'd like to know the limit to be avoided.

The flanges are pressed metal, and the shoulder on the shaft isn't very large, so I'm wondering if the shoulder is setting on the uneven area where the 5/8 hole was punched out. The flanges fit tightly upon the

5/8 shaft.

Using a dial indicator, I measured the wobble on one flange: 0.008" at

1.25" radius. This would translate to (4/1.25)(0.008)= 0.0256" at the outer edge of the stone. This is approximately what I see by eye. (Don't want to grind the dial indicator probe tip, so didn't indicate against the stone.)

Originally, the wobble was much worse than above, but was reduced by rotating the stone on the shaft and looking for minimum wobble, so something isn't square to the shaft.

I'm wondering if the problem is the flanges. Is there a source for machined (versus pressed) steel flanges? I haven't found such things in MSC and like catalogs.

Another poster suggested ditching the OEM stones, which are made by Ryobi. Is this likely to solve the problem, or at least help?

Joe Gwinn

Reply to
Joseph Gwinn

I may do this. That wheel does throw lots of grit. But I'm suspicious that the real problem is that the flanges aren't riding square to the shaft. Perhaps I have both problems.

Joe Gwinn

Reply to
Joseph Gwinn

. I understand the split-point geometry well enough,

Certainly not a bad idea. Hand sharpening is a bit of an art and requires considerable practice. No sense rushing things.

The term "stone" is not generally applied to grinding *wheels* in the industry.

Do you have any machining capabilities? I'd suggest to you that making new flanges would be in order. Having read below that your flanges are pressed steel, I can't help but think that they are in large part your problem. The very idea that you moved the wheel about and got it to run better indicates to me that the wheel(s) are also not great. That doesn't mean they aren't serviceable, assuming you can get flanges that run true. You can always dress the sides of a wheel to improve how it runs. Fact is, that's fairly common.

The problem of wheels not being parallel is not uncommon, which I may have mentioned. Norton has a terrific reputation in the abrasive world, and still manages to turn out the occasional wheel that isn't parallel.

The only problem I see is that the abrasive is likely not well suited to grinding HSS. You will be somewhat limited as to the wheels that are available to you, however. The greatest selection tends to come from wheels that have a 1-1/4" arbor. Such wheels are used on cutter grinders and small surface grinders.

Sort of hard to describe. If you hold the wheel by hand, and tighten the nut with a wrench, when the wrench overcomes your ability to hold the wheel from turning, you have it tight enough to serve without problems. I tighten wheels on my grinder by that method and don't have any problems with the wheels coming loose, even when running in reverse. If you do heavy grinding, such as might be done in welding, that may not be tight enough.

That clearly sucks. Flanges should run true, or be free to float, so they

*can't* hold a wheel at an angle. The shoulder on the arbor should be true. In turn, it should hold the flange true. Anything less isn't a good thing.

Good decision. No need to-----the flanges tell you everything you need to know. Until they run true, nothing else matters.

Assuming you end up with wheels that have a similar discrepancy, and you have the good fortune to align them such that the errors cancel one another, yes, it could help, but the best fix is to get the flanges running true. Once you do that, you can readily correct the wheels by dressing, should they need correcting.

If all else fails, and you're "stuck" with the flanges that don't run true, you might try tapping them gently with a soft hammer until you get them to run true. If they are a snug fit on the arbor, as you suggest, that could improve performance. Beyond that, the way I see it, new flanges are in order.

Let us know how it goes.


Reply to
Harold and Susan Vordos

Like whetstone? (Picture old guy sharpening a knife on an old sandstone wet wheel.) Actually, I did wonder what the correct term was these days.

I don't yet have the equipment to make my own flanges. Does anyone know of a supplier? I have to believe that people need flanges. Perhaps available as a repair part?

I'll look into Norton, after the flange problem is solved.

One can get expanders; I've seen them in the catalogs, but none that would bridge 5/8 to 1-1/4, if I recall. Perhaps this would also solve the flange problem. Any suggestions of possible sources?

What kinds of wheel are best for HSS? (I don't plan to use much carbide, at least not at first.)

As luck would have it, that's exactly what I did, once I got the nuts off (they were far tighter).

The left-handed nut wouldn't turn freely by hand on the thread until I fitted it with a little valve-grinding compound and elbow grease.

I thought as much. So, the flanges are problem one.

Later, I did an approximate indication on the stone, carefully lifting the tip before moving the stone. It was a bit fiddly and inaccurate (because indicator assembly isn't bolted to anything), but the wobble is in fact the ~0.025" at 4" radius expected from extrapolation of the flange wobble.

All roads appear to lead to those flanges.

What I can do is to manually hand-grind the flange using wet sandpaper on the surface plate, or hand-scrape the flange, but this is likely to be a slow process, like hand-grinding a telescope mirror.

I have to believe that machined flanges can be bought.

Another thing I may try is to call Ryobi and complain. But I don't know that this will help, as all they are likely to do is give me some more of the same kind of stamped metal flanges in the irrational hope that they will somehow be better.

Joe Gwinn

Reply to
Joseph Gwinn

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