How to re-harden small vice jaws?

Hi all,
At a recent watchmaker's fair I bought a small vice. Old, in bad shape, but better than anything I've got at the moment. The thing actually cracked in
half somewhere in its lifetime and was welded back together by someone with a very big welding machine. The problem was that the jaws were not parallel properly after that; there was a .7 mm gap on one side.
I've annealed the jaws and filed and sanded them back into shape. They close well now, and are beautifully straight, smooth and polished, just as I wanted.
My question: how can I best re-harden them? The jaws are only 6 cm wide, but I'm only used to working with tiny pieces of steel to make watch components or small tools. Can I just heat to cherry red and quench in oil? And then temper by re-polishing and heating to some colour (blue, for example)?
I only have a torch, no kiln or something like that.
Cheers!
Rob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Assuming the material is medium carbon steel or better, you can heat the jaws until they are no longer magnetic, then quench. You risk cracking them if you quench too quickly, so oil may be the better choice. Once quenched, do as you suggested and draw back the hardness ever so slightly.
When you quench, it's important that you insert the jaws in the quenching medium such that one side does not cool faster than the other, otherwise you'll bow the pieces and you'll not be any better off than you were before. Inserting them straight in, from one end, is likely the best choice.
The best scenario, judging from your description of the repaired broken body, would have been to make the corrections on the body of the vise instead of the jaws, which could then remain parallel and could be easily resurfaced without effort, using a surface grinder. Hand working the jaws may still prove to have been a bad choice.
Even with proper quenching, you may find that the jaws don't remain flat, and will need to be worked once again.
Luck with the project! How about a report after you've finished?
Harold
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hi Harold,
Harold and Susan Vordos wrote:

Thanks, also to the other posters. This is exactly what I did, and then drew the temper to brownish. Seems to have worked quite well..

Yes, possibly.. But I thought it would be hard to file the vice body without introducing some rounding of the flat behind the jaws. The way the jaws slot into the body means I can only file the body in one direction, i.e. sideways, and can't correct any rounding by filing vertically or by draw-filing. (I hope this is a comprehensible description)
Cheers!
Rob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sounds like it turned out quite well, Rob. Congrats!
I understand about your choice in working the jaws instead of the body. There are times when one does what works best. The thing that really matters is that it now serves your purpose.
Harold
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Rob Kramer wrote: ...

Do you really want them hard? Why? Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.