Lathe Accy Grind Polish GBI Superfinisher

Interesting device, don't know anything about them but could see applications where one just wants to take off a few tenths and doesn't want the hassle of mounting the toolpost grinder. Are the wheels geared to run at the same speed or does the bottom wheel run faster than the driving wheel?

regards Mark Rand RTFM

I don't recognize that one, but superfinishing and superpolishing were used for high-end shaft applications a few decades ago. I don't know about now.

Those two terms have specific meanings, BTW, which relates to the way pressure is applied to the work. I haven't tried to look them up but get back to us if you don't find anything. I probably have descriptions in one of my manufacturing process books.

-- Ed Huntress

It seems odd, but the lower grinding wheel turns at about half the speed of the top wheel. The gears are arranged (from top to bottom) 17, 32, 32, 36T. The wheel shafts and the two intermediate gears are all turning on ball bearing assemblies.

If the figures in the charts are correct, and I would expect that experience would be a factor, it's claimed that .0001" removal or less can be attained with the correct wheel grit and spindle and feed speeds. Additionally, more stock can be removed with coarser wheels if needed.

I've never done any precision grinding on a lathe or other machines, and taking just one ten-thousandth off of a diameter seems a bit astonishing to me.

Yep, lots of terms for real professionals/tradesmen, Ed. For my purposes, shiny means purty, but primarily smooth, and maybe straight.

I don't have a clue of how to attain a specific finish, but I could probably sit and stare at one of those sample plates/gages for about an hour.

A machinist friend, not just a hobbiest like myself, has told me about developing superpolishing techniques at Westinghouse decades ago, on big parts for defense contracts. A small technological edge could mean big contracts.

Something that you might find interesting, though, is that the techniques actually can be applied in hobby work. I don't remember much about it but superfinishers "float" the abrasive on the workpiece, so that only the high points are touched. Although they don't produce a better finish than fine grinding, they produce better cylindricity.

Superpolishing was (is?) a little different, although the basic principle is the same: work on the high spots.

The terms have gotten a little corrupted over the years, but it was a big deal back in the '50s, and superfinishing and superpolishing machines were being used, as I said, for high-performance shaft work. That may be what your friend was doing at Westinghouse. Turbine shafts were one of the key applications.

In a way, they're a bit like cylindrical lapping, but they don't follow the workpiece like lapping does. So they maintain whatever straightness and concentricity the machine is capable of, unlike lapping. Lapping will give you great cylindricity but it doesn't do anything to improve whatever straightness and concentricity they start with.

-- Ed Huntress

-------- Super finishing is a relatively old process, developed I believe by Chrysler in the late 20s or early 30s. It was mainly applied to main and rod bearing journals. The intent is to take an already smooth surface and knock off the peaks to get as much bearing surface a possible, so 0.0001 or less was all that was required/desired.

It is now called micro-honing in many cases

still being done for race engines and other very high end applications

Unka' George [George McDuffee]

------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?

Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).

BTW, Ed and others, I didn't mean to imply that this tool was either a superfinisher, or a superpolisher by definition, it's actually just the tradename that GBI called this particular tool.

Thanks, George for the additional info and links.

My intentions are to post any other findings, and report any results to RCM when I get around to using it.

Yeah, I realized that, which is why I took the time to relate some things about superfinishers, so that newbies or people who aren't familiar with less-well-known industrial machining processes wouldn't be confused by it.

I don't know how this particular device does its job, but it doesn't appear to be a superfinisher by the recognized definition of the term.

-- Ed Huntress