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Blacksmithing and metalworking questions answered.

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Grinding, Buffing and Wire (briefly):

One thing you can't have enough of is motorized wheels. Grinders, buffers and otherwise.

Wire brush or wheel:

I have always tried to have a motor (1/3HP 1800RPM) set up with a wire brush. 6" diameter with .0104 stainless wire does the best job for me. (Note: Previously I had the wrong heavier wire listed) The small wire size is gentle enough that is doesn't mar most work. You can really lean on it when cleaning rust off tool steel. The 6" diameter keeps the FPM down where the wheel does not cut. This is useful for cleaning files and removing rust from tools without hurting the finish.

(setup at left has buffing wheel)

Always use stainless wheels on stainless. Bits of a carbon steel wire wheel will embed in stainless and show up as rust later!


Locksmiths use a nifty little plastic strand (non-metalic wire) wheel. These little wheels are easy on the fingers and are sold as "safety" wheels. Generally they are only good for light deburing of non-ferrous work. The things they DO work on they are very handy for!

Buffing Wheels:

Before setting up a buffing wheel check the FPM (feet per minute) that is most efficient for the type of work you are going to be doing. Machinery's Handbook says 7500 FPM but quotes a manufacturer that says 4000 to 6000 FPM. To get into tight places I have a small 4" wheel setup on a buffer thats belted up to turn 5400 RPM (6785 FPM). My regular 8" wheels turn about 3600 RPM. This means they start at 7500 FPM and as they wear they are still in an efficient buffing range.

When you get into buffing be sure to get several grades of buffing compound.

  • Rouge (red) is used put a fine polish on soft materials (gold, silver, aluminium). It will put the last bit of "color" into brass.
  • Tripoli (red brown) is used for general purpose buffing and for "roughing" prior to using Rouge.
  • Emery (black) is used to cut hard materials such as tool steel or to put a final edge on a knife. Emery comes in many different grades or sizes of grit but my source only carries one or a "common" grade.
  • White is used for stainless steel. Stainless is very abrasion resistant and Tripoli just gets hot, emery leaves scratches.
Note that there are other buffing compounds. Aluminium oxide is sold in 80 (very coarse) to 400 grit and is sometimes coded with colors such as green and blue to indicate type. Emery is also available in various colors and there are special compounds for plastics. However, I have used tripoli and rouge on clear acrylic and polycarbonate. The critical factor when buffing plastic is to not melt it.

Grinding Wheels:

The harder the material, the softer the wheel! Seems backward but thats how it works. The softness however is speaking of the friability of the wheel. Hard materials dull the abrasive and load the surface. The softness lets this dull loaded material to wear off.

On a bench or pedestal grinder, never grind a piece of work that is heavier than the wheel. Heavy work can bounce and on the return shatter the wheel. Keeping the "shatter guards" properly adjusted can help prevent a shatered wheel from seriously injuring the operator. The shatter guards are those little rectangular pieces that are perpendicular to the OD of the wheel. If the wheel breaks, the pieces slam into the guards and stop the rotational movement. If properly mounted with its paper washers and steel support flanges there should be no loose flying pieces if the wheel breaks. Always use a reinforced resinoid wheel (the type used on hand grinders) or a belt sander for work heavier than the wheels of your bench grinder.

Flap Wheels are another wonderful tool to have on a little bench mounted motor. They can not blow up like a "vitreous" wheel on a grinder, therefore they are handy for deburing heavy work, radiusing and blending. They cut almost any material equally well. I use Norton Resinall Metallites.

Dressing Vitreous (Hard) Wheels:

For precision grinding such as sharpening drill bits, lathe cutters and fine quality chisles use a diamond. Single point industrial diamonds are mounted in a pointed steel holder (diamond at the point). These are surprisingly low cost and produce that "like new" smooth face on your grinding wheels. If you have a bench grinder in your shop for sharpening tools and don't have a diamond dresser you are not getting the most out of your grinder.

Diamond Wheels:

For sharpening carbide cutters a diamond wheel is the only way to get good results. Diamond wheels are made of steel and have the diamond dust impregnated into a hard rubber or bronze matrix. To dress these wheels, remove them from the grinder and machine in a lathe at low speed. Dressing is only required when the surface becomes loaded or rough. Diamond wheels are normally one of two wheels on a "tool grinder". The other is a soft "green" wheel used for high speed cutter bits and some grades of carbide. Both require water for best results.

What speed are the large belt driven pedestal grinders designed to run?

The old heavy cast base, floor mount, dual stone models. Anyone here have any recommendations?
Bernard Tappel - Saturday, 01/07/06

Grinder Speeds:

Big grinders come in many sizes from 8" up to 30" (200 - 750 mm). The speed is a function of wheel diameter. Generaly the limitation is the safe operating speed of the wheel which is usually about 1.5 times the working speed. This is limited by the strength of the materials which the stones are made. Speeds available are determined by the AC power frequency (60Hz) and directly coupled motors.

Without polling a bunch of manufacturers or researching wheels my GUESS is:

  6" (150mm) - 3600 to 4200 RPM
  8" (200mm) - 2400 to 3600* RPM
10" (245mm) - 1500 - 1800* to 2400 RPM
12" (305mm) - 1200 - 1800** RPM
14" (356mm) - 1200 - 1800** RPM
16" (405mm) - 1000 - 1500 PRM
18" (460mm) - 900 - 1200 RPM
24" (610mm) - 600 - 900*** RPM

* Black & Decker specs
** Cincinatti specs
*** Standard brand c. 1942

Well. . I DID poll some catalog data after creating this chart. I was right on or a little conservative in spots.

The above assumes properly rated good wheels (ring tested) mounted correctly with paper washers and flanges then speed tested and trued before use. See our iForge demo on grinder safety for shatter guard adjustment. Always consult the wheel manufacturer for ratings and mounting.

You must remember that these big old grinders were designed to be VERY aggressive fast grinders. The larger ones were used to clean up iron castings that were as large a a man could convieniently lift all day. The more conservative speeds are more frindly and controllable. Slow speed grinders were often made for wire brushing as well.

Those designed without motors for flat belt operation had no ratings that I could find. They assumed a skilled mechanic or plant engineer would install the machine based on the wheel size rating and use.
- guru - Sunday, 01/08/06
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