tool grinding

Lots of old wive's [or old machinist's] tales about this. Some of these are even true in a production environment, which won't apply to low volume, lack of time pressure hobby or home shop machining.

General rule is that you don't want any combination of tool and material which will "react." For example, iron is known to dissolve carbon when it is hot/molten. Thus you want to avoid green [silicone carbide] or diamond wheels on steel. This holds true for cutting tools as well. Diamond tools don't work too well/long machining steel. Ceramic [aluminium oxide] tools don't seem to last too well on aluminum.

Having said that, with the light use a typical grinder gets in the home machine shop you most likely won't see much difference.

Biggest single tip is to keep your wheels "dressed" so they will cut rather than rub. If you use aluminium oxide [white] wheels the silicone carbide blocks, typically 1" X 1" X 6" will do a fine job. If you use the green rocks, I suggest buying a inexpensive diamond dresser [< 10$] and fabricating a holder out of a square or rectangular piece of steel. Normally the diamond dressers are round and tend to get away from you. Remember to rotate the diamond in the holder block to avoid grinding flats on it and it will last you a lifetime.

Take a look at my website in the craft machining section to see the tool grinding fixtures we made as a class project. see:

these and a machinists protractor, even the first term students were able to grind a "line-out" acme thread tool. It won't make that much difference if the HSS gets hot (see how hot it gets when you are cutting), but try to keep any carbide tools cool and never dunk hot carbide in water as this will cause microcracking and it will quickly fail in use although it may look fine.

One trick is to use a 5 or 6 inch diameter abrasive loaded nylon brush in a drill press at medium speed. These are commonly available in hardware stores and have blue bristles with a 1/4 inch shank. Use on the your new ground tool to give the effect of hand honing in removing the wire edge. Also works well on resharpened drill bits.

If you have not done so I suggest you buy the South Bend and Sheldon lathe book reprints from Lindsay. These give a good explication of the terms and have lots of pictures. see

Just don't get discourages when the right hand tool your were grinding turns out to be left handed. It has happened to everyone.

Uncle George

Diamond wheels should never be used for grinding steel or iron unless the surface speed is reduced such that you can't generate any red heat. Diamonds are quite rapidly dissolved by the metal otherwise. The result is dull diamonds, which create more heat, which dissolve all the faster. There are no exceptions to that rule, regardless of application. Home shop makes no difference, for the diamond has no idea of knowing that is should be forgiving.

Green wheels are silicon carbide, and, like diamond wheels, are readily absorbed by steel at high temperatures. The net result is a rapid dulling of the wheel, necessitating frequent dressing. Because the wheel is absorbed by steel, it is dulled almost instantly and glazes over, refusing to cut. Silicon carbide wheels (not green ones) should be used for all non-ferrous applications, and for cast iron. Aluminum oxide wheels should be used for steel.

Green silicon wheels are bonded such that they break down rapidly to keep exposing fresh grain, an offset for grinding carbide. It is much harder than even heat treated steel, so the grains dull quickly. When you grind softer materials, the result is rapid shedding of the grain, so wheel life is seriously reduced. While that is an inconvenience, the real threat is in breathing the dust. Silicon carbide can be the source of silicosis.

Dressing grinding wheels for off-hand grinding should not be accomplished with a diamond. Such a dressed wheel will always cut excessively hot, and require considerably more pressure to achieve an equal amount of work as compared to a wheel that is dressed by either a star type dresser (I don't like them), or a dressing stick. Using a diamond to true the wheel is a great idea, but the surface should then be slightly roughed to break the fine surface created by the diamond. The difference is readily noticeable when you use such wheels. Star dressers provide the best of all surfaces for off-hand grinding, but they can be difficult to use, especially when the stars have considerable wear on the pivots, and they often are quite wasteful of your wheels. Dressing sticks provide a surface almost as good, and are much easier to apply. Make certain your choice is not a solid boron carbide type dressing stick. The one that serves your needs best is a sintered silicon carbide stick, relatively coarse. They are available in 1" square sticks, usually 6" long.

Harold

I have the same Baldor clone, and the same wheels. I have no idea what those wheels are, but they're far harder than any other "Green wheel" I've ever used. Even with a diamond dressing, they don't open up and cut, not even HSS. Grinding the steel on a brazed carbide tool with a good wheel would normally leave grooves in the green wheel, with these, the metal only takes a nice polish, which isn't what I was after.

They do nicely for my wood lathe chisels, but seem to generate more heat than work.

Diamond wheels cutting HSS will plug very rapidly, most often burning the cutting edge rather than sharpening. For just "touching" the cutting edge, to get a really sharp tool, they work ok, but any more than just a polish and they plug.

My choice, were I to buy only one diamond wheel, medium. The fine wheels can give a beautiful edge, but can also take forever if you have to take any amount off. The coarse wheel leaves scratches behind that are enough to start a crack.

Rich.

Note that the Drill Doctor successfully uses a diamond wheel to sharpen HSS, as do chain saw sharpeners.

Personally I use an aluminum oxide wheel for coarse grinding to shape and a silicon carbide one for final finishing and have had no problem. Last night I resharpened an HSS lathe cutoff bit on the SiC wheel to an edge that peeled smooth, shiny steel foil off a Grade 5 bolt without a hint of chatter.

jw

Another "trick" is to put a fine green wheen on one side and a fine white wheel on the other side. Use a belt sander with the zarconium oxide belt [blue abrasive] to rough out your HSS tools and the fine rocks to polish. Most likely you will only be touching up any carbide so the fine wheel will be adequate for that.

Most any of the inexpensive 4X36 belt sanders are adequate. Even better if it comes with a disk. Get 600 or 1200 grit disks from the automotive paint section and polish your tools to a high gloss.

Uncle George

Most diamond wheels should NOT be used on regular (high speed) grinders to grind steels. They are fine for carbide. The same is true for the 'green' Si-Carbide wheels. Grinding steels will soon wreck either type wheel. Note: ... there are LOW speed diamond wheel grinders that can be used on steels (Glendo, etc.) ... these are a whole different animal than the so called 'carbide' grinder you purchased.

For common tool steels you should get a 'white' aluminum oxide wheel. These are available with the steel backs as required for this type grinder. MSC has them, as do others.

One thing to watch out for. I bought two of the HF grinders, one for my home shop, one for university where I work. They are generally satisfactory, BUT ...

One cast-iron wheel guard on one grinder was bored a bit off center. No problem with the 'green' wheels provided. I ordered two 'white' wheels from MSC, and these were about 1/8" larger in diameter. That was perhaps

1/16" too big to fit in the off-center wheel guard.

I solved the problem by unbolting the bad wheel guard and setting it up on the rotary table on my mill, then milled out the inside of the guard to approximate concentricity with the mounting hole. Only a small amount needed to be removed from one side of the guard ... ample thickness remained. I used a ball-end mill to avoid any sharp stress-riser internal corners. Now it works fine. This was a minor job for anyone with a mill. I suppose it could have been done freehand with a die grinder and some care.

Considering that the HF grinder is about half the cost of the other such imported grinders, it seems a good value, even WITH the added work on one of four wheel guards. It's a just typical HF (and imported in general) quality control problem.

Dan Mitchell ============

Thanks to all that replied. I guess I'll get a white wheel for tool steel and a med. diamond for carbide. Thanks all for the information. Dick