# What are "soft jaws" and what are the benefits of using them?



## HMF (Apr 20, 2011)

Guys,

Sorry for yet another "newbie" question:

I have seen people refer to "soft jaws" for a lathe. My question is, what are "soft jaws", and what are the benefits of using them on a lathe?

Can they be made?

Thanks,


Nelson


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## b.lindsey (Apr 20, 2011)

Generally, soft jaws are used with chucks that have 2 piece jaws, one piece that mates with the scroll of the chuck and separate "front" pieces that hold the work. Soft jaws replace these gripping parts of the jaws. Their purpose can be several fold. First they can be machined "true" since all 3 jaw chucks have some inherent runout. Second they can be machined to hold specific parts that may have a shape not easily held by a regular jaw. Once this is done they can be saved in case that same job must be done again later on, or remachined to fit another job. The main point is that they are of a softer material...mild steel or aluminum...and thus can be machined where hardened jaws can not. And finally, being of a softer and generally less expensive material they are to some degree disposable. Thats my 2 cents worth...lol

Bill


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## Tony Wells (Apr 21, 2011)

Very useful indeed. They are normally 1018 or 1020 steel, or aluminum. I've used these with great success:

http://www.workholding.com/J-LOC-D-STYLE-INFO.HTM

They can be turned or bored to suit the configuration of the part being made. If you're working on rough stock, like hot rolled, then their are no advantages in the first operation, where you chuck the OD. After machining a true surface, then soft jaws come into their own. They are capable of very true chucking with no indicating required. You can't move anything anyway, since they grip as well as they do. On a machined round, with as much surface area as is available, they grip well. You can bore to a fixed depth to shoulder your part against, thus preserving a Z axis reference so you can hold feature locations. You can also use the faces of the jaws the same way. Just push the shoulder from the previous operation against it. OAL is easy to hold very closely.

Another advantage in using the aluminum style is in the non marring of the finished surface. Another is the ability to grip virtually 360 degrees of the part, reducing chuck crush that induces out of round condition on thin walled parts.

I'm sure there are more features, but I can't think on an empty stomach.


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## Instrumentmaker (May 20, 2011)

Hi All,

This is my first post/reply on here, thanks for having me. Happened to see the soft jaw thread.

Oh Man! I rely on soft jaws quite a lot. So handy for holding awkward parts.

Make sure to clamp down on a spacer to put some back pressure on the chuck jaws or in the vise before milling, boring, turning a space for the part. I made that mistake the first time I tried using a closer in the collet chuck. It rattled and sang and danced a little jig. Left me scratching my head. 

I just made a post on my blog about soft jaws on the milling machine vise. Don't forget, they are useful for milling too. Hope it makes sense.

http://theshoplowdown.blogspot.com/2011/05/soft-jaws-on-vise.html

-Lau


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## HMF (Aug 4, 2011)

Here is a good thread on "soft jaws":

http://www.chaski.org/homemachinist/viewtopic.php?f=44&amp;t=4266

Enjoy!


Nelson


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