crucible rex mmm questions

I purchased these at an old shop sale and can't find any idea what composition they are and have never seen unground hss does anyone have any idea? nothing come up on search. Im going sharpen one up and see how it cuts

Try "books" section on google, plenty of results. I don't have time to look at all of them now but :" Rex MMM describes the characteristics of their molybdenum- tungsten-cobalt high speed steel."

Google books search is very powerful tool.

I was going to say "look harder because Crucible is still in business" but it looks like Rex MMM has been discontinued for quite some time. It's a tungsten-molybdenum-cobalt HSS, with nominal alloy composition:
(source: The selection and hardening of tool steels, first edition, Lawrence H. Seabright, McGraw-Hill Book Company, 1950) Credit to jhruska who brought this book to our attention three months ago in this thread.

I'd guess Rex MMM was a war-years substitute for Rex AAA, which has substantially more tungsten and less molybdenum. After the war, the standard M35 grade would be a pretty close match for the proprietary Rex MMM.

thank you, the knowledge on this site is amazing.
I had never tried searching google books, before will try that

Unground HSS blanks are (or were) not that uncommon. I have quite a few pieces, though not this make.
Nice detective work, sfriedberg.

idacal said:

thank you, the knowledge on this site is amazing.
I had never tried searching google books, before will try that

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It's especially handy for old books that are not copyrighted anymore and you can download them freely from Hathi foundation/trust or some other digital library.

Nice find - if you like HSS lathe tools you will love that Rex MMM .maybe not when grinding it to shape though, it's kinda on the hard side

I might be able to finally identify the stack of Rex MM I have.

Edit: looks like it goes from Rex M2 to Rex MMM.

Box of 3/4 MM here - untouched and has been around a long time

johnoder said:

Box of 3/4 MM here - untouched and has been around a long time

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I just emailed Crucible: they have never heard of it.....I sent a photo of some for proof.

billzweig said:

Unground HSS blanks are (or were) not that uncommon. I have quite a few pieces, though not this make.
Nice detective work, sfriedberg.

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While unground blanks are not as popular as they were years ago they are still available from almost any tool supply or industrial supply house. Over the years I've bought several boxes of them in different sizes and compositions. The last purchase was half a dozen boxes about 5 years ago from a surplus equipment dealer. I'm glad I bought them when I did.

Most boxes contain either 50 or 75 blanks. The larger sizes were $.50 per blank, while the smaller ones were $.25 per blank. There is still an ample supply left, but most have been made into different form tools. They don't get used on a daily basis, but it sure is nice to just go to the drawer and pick out the one I need rather then have to spend an hour making it.

When shopping for HSS tooling make sure you inquire at several different vendors. There seems to be a wide variation in prices. I recently needed a couple larger size blanks. I went online to 3 different suppliers. Their prices varied from $3.80 per blank to over $12.00 for the exact same brand and composition.

In my shop I use HSS tooling about 3-1 over carbide. It's not that I dislike carbide, I just prefer HSS because it's the less expensive and can easily be resharpened.

SAG 180 said:

I might be able to finally identify the stack of Rex MM I have.

Edit: looks like it goes from Rex M2 to Rex MMM.

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Woldman's Engineering Alloys - Google Books

Pretty close to AISI M2

Journal of the Aeronautical Sciences - Google Books :

"REX MM (5.50% W, 4.00% Mo, 4% Cr, 1.50% V. .80% Q, is the general-purpose substitute for REX AA and is .."

billzweig said:

Unground HSS blanks are (or were) not that uncommon. I have quite a few pieces, though not this make.
Nice detective work, sfriedberg.

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I don't think I have EVER seen a Crucible A, AA, or AAA that WAS ground. Soo.. if the "M" series was - as reasonable - one of the MANY wartime substitutes of abundant, (stateside mines, even), Molybdenum for scarcer Tungsten, then yes - same market, same "finish" fits well.

As to the comment about "loving it?" Not here. Moly WAS a "substitute".

T1's always seemed to last longer at knocking the edges off corncob weldup better than Moly-anything, T8's (Rex 95) otherwise held a sharper edge, longer.

YMMV

It looks like the Rex MMM has an extra 5-5.5.5% cobalt over the Rex MM composition and the Rex MM is not quite M2 steel.

Monarchist said:

I don't think I have EVER seen a Crucible A, AA, or AAA that WAS ground. Soo.. if the "M" series was - as reasonable - one of the MANY wartime substitutes of abundant, (stateside mines, even), Molybdenum for scarcer Tungsten, then yes - same market, same "finish" fits well.

As to the comment about "loving it?" Not here. Moly WAS a "substitute".
T1's always seemed to last longer at knocking the edges off corncob weldup better than Moly-anything, T8's (Rex 95) otherwise held a sharper edge, longer.
YMMV

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T-15 is even harder to grind.