What are "soft jaws" and how and why are they used?

HMF

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Newbie question: What exactly are "soft jaws" and why would you use "soft jaws" in a lathe chuck as opposed to normal hardened jaws?

Thanks,

Nelson
 
I use soft jaws quite a bit. Soft jaws are simply jaws machined to fit a chuck in place of the hardened and ground factory jaws, typically on a 3 jaw, that are bored (or turned) to fit closely on a machined surface cut on a previous operation. They can incorporate a shoulder to "stop" against to gain close repeatability for length/depth operations. They can be shop made, or bought.

I respect all the effort shown by guys doing their level best to achieve low TIR on their chucks, but for production work in particular, a set of soft jaws is the more economical approach (IMO). Plus they leave very little marking of the finished surfaces. They are of no use on rough stock.
 
I'm really big on soft jaws, you bet.

Here's the classic, in the milling machine vise, holding knurled pieces for drilling and tapping. I machined the recess to fit the part exactly, so there's no damage no matter how hard I squeeze:

axaknobs13.jpg


I made up sets of "disposable" soft jaws to fit various vises, so I can slip them in for more causal use without having to take off the hard jaws:

disposablesoftjaws04.jpg

When I got my new 6" Wilton banch vise, the first thing I did was remove the hardened toothy steel jaws, and replace them with cold-rolled steel soft jaws, so the vise would take the scars more than my work. I V-grooved one jaw horizontally, and the other vertically, to hold round items, and while I was at it, I made them bigger, too:

wiltonjaws02.jpg

I made up a few sets of aluminum pieces with magnets, so I can stick 'em on any vise jaw for soft gripping:

minisoftjaws01.jpg
 
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