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Tool steel in rolling mill?

I have a rod of tool steel that is 3.1mm square. I need a 2.5mm square rod to use as a mandrel for fabricating a setting for a square gemstone. I can file down the rod but that is laborious. Is it OK to put a tool steel rod in a rolling mill? If it’s doable, should I anneal the rod first? Thanks for your advice.


You will need to roll it while the steel is red hot; probably not a good idea to do it in a jewelry sized rolling mill, will damage the rollers

No, forge it to whatever size you need or buy a mandrel.

Thanks guys. I figured as much. Will file the rod down. I do have a square bezel mandrel but even the tip of that is not small enough for what I need.


You could anneal a square needle file (just get it red hot and quench it) and then file it; probably easier than filing a round rod and you’d know it was good steel. Also, the needle file would have a bit of a taper which might be helpful.

Rather than filing, consider an angle grinder. You can take that rod down to its required dimensions in no time. I have gotten good use of the one I got at Harbor Freight over a decade ago. Its about $40.

Using an old square needle file is a great idea. Easy to file off the teeth once annealed. Then I have a square bezel for very small gems. Thanks.

Quenching the steel from red hot will only re-harden it. Tool steel needs to be cooled as slowly as possible after heating to a red heat. It is frequently done by burying it in an insulating material such as perlite. Can also be done in a kiln, slowly dropping the temp from ~1450 - 1650 Deg F. Google “annealing tool steel” for more detailed info.

– alonzo

I think running a piece of tool steel through a rolling mill is a recipe for disappointment. I suspect you won’t get the results you want and you will get to buy a new mil.

I would heat it up to a nice color and hammer it out to the desired size. File it to a finished size and then harden it.

Working with tool steel is a very interesting study. There is a lot of procedure to follow for the finished result. Unless you plan to work with it often it may be less expensive, time and cash wise to buy a new mandrel.

Don Meixner

Just file it or buy a better fitting piece. This steel should never be in anyones rollers