Soft Jaws Question

7HC

7HC

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Ok, it's a 'stupid if you don't ask' kind of question, but what are lathe chuck soft jaws?
Same as the regular jaws but made from a softer metal like brass or aluminum, or is it term describing a different style of jaw?
Or maybe like vise soft jaws, something that slips over the regular jaws?

M
 
On 3/6 jaw chucks with 2 piece jaws, you can get "replacement" jaws that bolt on in place of the "top" jaw, but made of softer, machinable material, like aluminum or mild steel. The intent is to allow a good bit of contact for a certain diameter, perhaps on a finished part or let's say one end that's finished. It can thus be bored (or turned) to a near zero runout and close fit. It's commonplace to do this for finishing the second end of a part. The part can be chucked easily and work continued without the hassle of a 4 jaw, without the jaw marks from hard jaws.

Many can be purchased, ready to bolt on, or made from scratch. I've taken old, worn out hard top jaws and welded stock to them and then machined to the desired size, in place.

You'll see this strategy more in production shops than in the hobby shop, but having a set is very handy.
 
Thanks, I'm learning a lot on this site.

I don't think I'm going to have to worry about soft jaws until I step up to a bigger lathe with two piece jaws.

M
 
I find soft jaws super useful in my Kurt style milling vises. I can drill or mill the jaws for special holding jobs or accuracy.

There's an outfit called "Monster Jaws" that sells a great variety of them for mill or lathe on eBay and on their Web site. They sell 'em for 6" Kurt vise for as low as nine bucks a pair - nicely CNC machined
 
I URGE you to not make chuck jaws out of BRASS,nor would I of aluminum. Brass is a slippery metal. When I was inexperienced,I made a brass bushing to hold an end mill. In spite of tightening the end mill as tight as I could with the draw bar,the spiral end mills would quickly suck right out of the bushing. I learned to only make holding things from STEEL (mild steel is fine). As for aluminum,I'd think that the soft metal would soon compress,and allow the jaws to tilt back a bit and not give full support to the work held in them.

I may be disputed in the aluminum jaw part,but personally,I'd avoid them if you expect them to last,or not fling a heavy part at you. If you machine soft steel jaws to "caress"your part,they will not mar the work. If the work is so soft you are still concerned,put clay free paper between the jaws and the work. Brown paper bag is clay free,less slippery than shiny paper that has clay in it to make it shiny.
 
anybody willing to post some pictures of the different one that are home made ?
 
I've never seen brass soft jaws for lathe chucks. I tend to agree with George with the mechanical properties that make brass good for bearing material are just the properties not desirable in a grip-required application.

I would respectfully disagree with him on aluminum, however. What I have observed is that when the machining of the jaws leaves definite feedlines, there is a pretty good grip (right the opposite of brass, incidentally). Also, due to the lighter weight, less clamping force is lost to centrifugal force. With hydraulic or pneumatic power chucks, this is a real problem, as there is no "feel" to begin with for the operator to gauge how tight the chuck is holding the part. I have seen parts flung out of those chucks by someone dialing down the clamping pressure in order to keep from crushing or distorting a delicate part. It can be a touchy balance.

He is spot on with the lack of durability and strength of aluminum jaws, however. Most commonly, aluminum soft jaws are used on short runs. In the case of heavy cutting during roughing operations, aluminum jaws can be distorted and lose their grip, and toss parts. So they have their strengths and weaknesses.
 
Since I haven't actually used aluminum jaws,I bow to Tony's experience. The properties of the metal didn't make it seem like a great choice,so,except for the gripping part,I got it right.
 
Unlike most manual chucks, most power chucks do not have a single keyed location for the top jaw. There are various pitches of finer serrations that position the top jaw on the master jaw. That cab be a pain. Still, you can buy ready made soft jaws to fit just about any of them.

Here's a soft jaw system that I can highly recommend:

http://www.j-loc.com/J-LOC-C-STYLE-INFO.HTM

Inserts are changeable within seconds, and maintain 0.0005 repeatability, as long as they are marked to fit back into each jaw where they were originally machined. They're not cheap, but you can machine your own inserts if you like, out of whatever material you like.


George, the biggest weakness I can think of for the aluminum soft jaws it wreck tolerance. But then, who wouldn't remachine any soft jaw after a wreck? They're actually pretty good. I use a cheat system for small parts on one of my lathes. I simply took some 1.75" OD bar 1" long and drilled/c'bored on center to allow the jaw bolt to hold it on the inner hole on the master jaw. I can usually just close the chuck all the way up against the aluminum. Then, after machining to fit the part, either set them aside for next time, or if I didn't have to machine too deeply, just rotate them about the single bolt hole and start again. I do a few thin parts (think flat washers) and for second side operations, it works very well. I can hold 0.0005 length and parallelism without a problem. Works kind of like an emergency collet, with greater range. All I've got at the moment is some really used up ones, or I'd furnish a pic. Well, maybe that would be good to illustrate. Ill see if I can get a pic after I finish the job in that lathe, where I'm not presently using them. I'll stick them on.....ahh, I do have a job coming up where I'll need them, so I'll do it then. Next day or so.
 
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