3 Jaw chuck on Rotary Table

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Harold_V
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Post by Harold_V »

BadDog wrote:Soft jaw capability is the only thing that makes me consider mounting a 3 jaw on the rotab. I've wished for it a couple of times. But then I'm so cheap it actually HURTS to have to cut a soft jaw for a single job, though I do it.
It's not really necessary. If you use a spider to locate the jaws for machining, you can set jaws that are similar in profile to your needs and remove only a few thou for the new setup. You need not even clean up the old surface completely---just cut enough so you achieve a decent mounting surface that won't indent the parts when chucked. By reversing soft jaws, you can have two profiles per set and get by with only three sets or so. I did that when in business and had no problems at all.

Again, key to success is an adjustable spider, so you don't have to remove unnecessary material from the jaws.

Hard aluminum (6061-T6, or even better, 7075-T6) serves quite well for soft jaws, but if you'd like to use them for the rest of your life, make them from mild steel. When you've used them to the point of being useless, simply weld on a new piece of material and start all over again.

For the record, I have made soft jaw setups for one-offs as long as I remember. It is one of the finest methods of holding parts.

Harold
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BadDog
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Post by BadDog »

I could surely do with a better "spider" system. But I really don't waste all that much as it is. It's more a psychological thing I guess, but I'm fighting to overcome it. :D

And have been making my soft jaws from mild steel, mainly because I had some conveniently sized when I needed to make them. I also make them a bit over-sized (and caught flack for it due to safety concerns) to provide more support/range and longer life. I was even given some "mystery" steel that turned out to be some sort of tool steel. Had to cut with carbide and a file wouldn't even debur it. Made a pretty decent set of "hard jaws". :oops: Haven't figured out quite what to do with those as they are too hard to easily manage the heavily interrupted cut and would more likely damage parts as well... :? I've got some aluminum jaws that came to me with a junk chuck, but they are "well used", so I've been "saving them" for a rainy day. Last time I used them was to hold an Albrecht chuck shell for disassembly.

Still so much to learn (and unlearn)...
Russ
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Harold_V
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Post by Harold_V »

BadDog wrote:I could surely do with a better "spider" system. But I really don't waste all that much as it is. It's more a psychological thing I guess, but I'm fighting to overcome it. :D
No big deal, really. Many years ago I posted on soft jaws. I commented on the spider I use, even posted a picture. If you're interested I could provide a link.

You've been quick to pick up tips that I, along with others, have posted. If you're interested in the spider, it's just a fairly large nut that is drilled and tapped 5/16-18 near one edge (that's important), which accommodates various lengths of socket head cap screws. You could just as easily use a short length of hex stock, maybe 1½" or so, with a center hole. If you think you could use one, insure that the three holes are evenly spaced and centered on the nut, which helps minimize side loading of the jaws. That can be the source of runout if the slides on your chuck are loose.

With an adjustable spider, you can set size such that as little as ten thou will clean up jaws.
The real benefit is you avoid looking for a piece of material that's "just right" in diameter for the particular setup you're trying to make. It's really handy when you have to re-mount a set of jaws to run the same part, or diameter, again. Mine never go back in the same position in spite of being keyed and marked for position. A few thou and they're true again.

Harold
Leroyt
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Post by Leroyt »

Harold, I would like to hear more about soft jaws and the spider, would you post the link.
Thanks,
Leroy............
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Bill_Cook
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Post by Bill_Cook »

Thanks BadDog, my 4 jaw that came with my lathe has the integral mount so that is why I had not seen this feature. I can see how that would help, provided the bolt holes are large enough to provide adequate attachment via T-nuts in the slots. The ones on the e-bay chuck look a bit small for that use. Is that all that secures the chuck to a back plate? They seem a bit puny for a chunk of iron like that chuck plus what it is holding when doing turning on a lathe.
For work within it's capacity I regularly use a six inch plain back 4 jaw on the mill table. It's held down by two of its 1/4 or 5/16 mounting holes, and it holds fine. If it becomes a problem, the holes can be enlarged or new ones drilled to match the table slot distances. There are no working parts between the independent jaws.

As for deformation, the ~two inch thick webbed iron chuck body is beefier than the edges of the 11/16" T slots in the table, and 5/8" T slot bolts haven't caused any problems there.

Milling - jaws up - a scroll will accumulate chips affecting concentricity and longevity. Coolant can even wash small chips into the area behind the scroll. The jaw screws on an independent jaw chuck are much easier to clean than an enclosed scroll.

Centering the 4 jaw on a rotary table can be accomplished by milling most of the raised area between the register and OD away, leaving tongues to key into the T slots. Three would do. Four would require more care to machine accurately. If the T slots in the table are "as cast", they should be cleaned up where the tongues will be. If they don't cross the center accurately enough, this can be dealt with in the positioning of the tongues, or the T slots can be accurized. New mounting holes can be drilled through the tongues if desired...

An independent jaw chuck by nature doesn't need to be centered any more accurately than by sight.

A plain back chuck doesn't need a back plate to be used. The extra height will decrease the capacity of the mill, and make the setup less rigid. If you don't believe it, try some heavy milling in a vice with and without a swivel base.


BC
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BadDog
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Post by BadDog »

Thanks Harold. That sounds familiar and I think I've seen the old post some time back. Just haven't taken time (what, 30 minutes tops? <sigh>) to make one. And you've got it dead right. Never thought to make a "spider" when nothing was in process. Then "oh, I need soft jaws for this", followed by, "Aw crap, that piece is a little big. No, that one is too small. Oh well, this is close enough..." :D I try to keep lists of things I need to do when not actively doing something on my major projects. But then I loose the list... :oops: But the spider is going on the current list, maybe I'll get around to it after the lathe is up and running, but before the list is lost...
Russ
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Harold_V
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Post by Harold_V »

Leroyt wrote:Harold, I would like to hear more about soft jaws and the spider, would you post the link.
Thanks,
Leroy............
Sure thing, Leroy!

http://www.chaski.org/homemachinist/vie ... php?t=4266


Harold
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