View Full Version : polishing stone designations?

07-29-2014, 11:37 AM
not long ago I picked up a set of "Toolroom Polishing Stones" from Enco.. last minute buy
with a few promo codes, so price was right.

Its the 20pc, I think 4 grits each in 5 types.

Anyway, their designations read "EDM, SU, MFP, OT, and MMH". I have each of those
in 120 grit and up (to 400 maybe).

Anyone shed some light on what those mean?



Old Hat
07-29-2014, 12:40 PM
Same as in grinding wheels, accept even more important to use the correct stone.

The part you are benching will be of some hardness depending on design.
The stones are made to "parish" in varying degrees.
The material removed in each stroke will have different charactoristics depending on
hardness and to an extent on the alloy.

Assuming propper technique, the rate of "brakedown" of each stone allows for
dulling of the grit, where~upon it begins to clog. That grit which is failing now brakes away,
exposing fresh grit. The wrong selection, &/or wrong downforce and attack angle
loads the stone with metal and tares the surface of your work.

Further some stones work wet, some dry, some wet or dry.
Kerosene or mineral spirits is your fluid. NOW thay say it was a bad bad thing
that we worked endlessly bare handed in kerosene. I've switched to the lightest
vegetable oils I can find if I have to stone more than say 20 minutes.


It should be noted that wet~stoning done correctly will necessitate a separate oil~cup. . .
for each grit. as you refine your work moving to finer and finer gritts,
keep each stone in it's own oil~cup. Otherwise by dipping in a common cup
you can pick up coarser grit on your finer stone. And that's a naughty Boy!

07-29-2014, 01:14 PM
EDM: Stones are designed to remove the tough hard scale left by Electro-Discharge Machining.

MFP Mould Maker Plus - Slightly harder than MF, the MFP cuts well with slower breakdown. These stones produce fast stock removal and are widely used on hardened steel surfaces, as well as to rough finish non-ferrous materials. It is a good choice for contours and radii, and generates a silky mat surface on hardened steels. Can be used on non-ferrous materials.

MMH Mould Maker Hard - Harder than MF and MFP .

OT Oil Treated -Able to be used on hard or soft mould and die steels, OT stones are made from white premium grade Aluminum Oxide, in a medium/hard bond, which is soaked in oil during the manufacturing process. This enables the stones to be used, if required, without lubrication. OT stones maintain good shape during use, and are excellent for processing either machined or fine EDM surfaces.

SU Soft-Ultra - Stones have been specially developed for use on soft and non-ferrous metals, with excellent results obtained on aluminum in particular. Manufactured with an extra soft bond, the US stone shapes readily to contours. Fast cutting without loading.

Old Hat
07-29-2014, 01:24 PM
Like with grinding wheels;
When in dout work from soft to hard bond.
Start out with little more than the weight of your hand for down force.