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PostPosted: Mon Aug 04, 2008 4:34 pm 
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What is the best way to attach a 3 jaw self centering lathe type chuck on an 8 inch Rotary Table.

I am thinking of mounting a 6 inch chuck. The table has 4 T-slots that do not go all the way to center. I do not as yet have the chuck, so suggestions as to what type, brand, size, back plate, etc will be appreciated. Also will modifications to a typical chuck be required to accomplish the attachment.

Comments for technique of centering up the chuck on the rotary table would also be appreciated. What I had in mind was to make up a mandrel that would fit the #3 Morse Taper center hole int the rotary table and extend through the chuck, so that I could close the chuck on the mandrel to align it before clamping the chuck to the table

Of course if there is a better or more convenient option than putting a lathe chuck on the table, I am open to suggestions.


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PostPosted: Mon Aug 04, 2008 5:16 pm 
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If you use a three jaw on your rotab, it needs to be an adjust tru type so you can set your work up concentric to the rotation every time. Just like on a lathe, the three jaw is just ballpark center.

The other option is a four jaw. That's what I'd do unless you plan on production or very repetitive work, where the adjust tru would remain centered for multiple chuckings on the same diameter.

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PostPosted: Mon Aug 04, 2008 5:24 pm 
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Another advantage to the 4 jaw is that it has 4 mounting holes like the table, and won't likely need a back plate. It pays to keep setups close.

BC


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PostPosted: Mon Aug 04, 2008 6:43 pm 
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MikeC wrote:
The other option is a four jaw. That's what I'd do unless you plan on production or very repetitive work, where the adjust tru would remain centered for multiple chuckings on the same diameter.

This is my option. I have 4 jaws for (not always on) my 6" Hartford Indexer and my 12" Troyke. Easily mounted when needed, holds (mostly) arbitrarily shaped parts, and easily "dialed in" for whatever feature needs to be concentric.

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PostPosted: Mon Aug 04, 2008 7:46 pm 
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Bill_Cook wrote:
Another advantage to the 4 jaw is that it has 4 mounting holes like the table, and won't likely need a back plate. It pays to keep setups close. BC
Please elaborate ? I am unaware of any holes in a chuck that would be useful for mounting it to a rotary table or why there is anything inherent that would result in a 4 jaw having exactly 4 holes Is this perhaps a particular characteristic of the brand or model of chuck you have?


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PostPosted: Mon Aug 04, 2008 8:00 pm 
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Most all 4 jaws (those that do not have integral mounts) have 4 holes for attaching a back plate. These holes are generally located between 1/3 and 1/2 of the chuck radius from center, and between each of the 4 jaws. A quick search on ebay turns up this example which shows it quite clearly.

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PostPosted: Mon Aug 04, 2008 8:05 pm 
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Oh, and this is not characteristic of any brand, but rather a characteristic of "universal" chucks intended for use with a back plate matching the intended spindle. I have 2x8" Pratt Burnerds, 1x8" HD Cushman, 1x6" Pratt Burnered, and 1x10" Buck; all with the same 4 bolt pattern in the face...

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PostPosted: Mon Aug 04, 2008 8:18 pm 
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BadDog wrote:
Most all 4 jaws (those that do not have integral mounts) have 4 holes for attaching a back plate.
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.


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PostPosted: Mon Aug 04, 2008 9:43 pm 
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The bolts on on 10" Buck chuck are 7/16 SHCS (if I recall correctly). The main locating feature is the register, so the bolts are more than adequate.

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PostPosted: Mon Aug 04, 2008 10:38 pm 
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Here is a link that I found helpful.

Fitting a chuck to a rotary table, - one answer
<http://bbs.homeshopmachinist.net/showthread.php?t=20653>

Dave


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PostPosted: Mon Aug 04, 2008 11:29 pm 
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dgoddard wrote:
What is the best way to attach a 3 jaw self centering lathe type chuck on an 8 inch Rotary Table.

Best way?

Hard to say.

Here's a good way.

Use a piece of aluminum plate that has been faced parallel by turning both faces at least two times. That way you relieve the internal stresses and end up with what is a reasonably flat and parallel. I'd suggest plate no thinner than 3/4", to allow for the SHCS's that will be required to mount the plate to the rotab without having any projections.

Turn the OD (same diameter as the rotab) and a register that fits the inside of your chuck, and if you have what I prefer in a rotab, a straight bore instead of a Mores taper, bore a hole on center that will accommodate a locating spud so you can drop the plate on your rotab and have it very close to center. Drill and counterbore the back side of the adapter plate for the socket head mounting screws that will be used to mount the plate to the chuck, then on the opposite face, drill and counterbore four holes (don't forget to allow clearance for the chuck body) that will allow the plate to be bolted to the rotab using the T slots, again, with SHCS's. Done.

Make sure the locating spud is easily removed so you can insert long shafts when necessary, or if you must dial the chuck to center when holding specific sizes. By choosing this method, you can avoid an adjust tru chuck and still achieve the same results. The chuck becomes even more useable if you have soft jaw capabilities.

Harold


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PostPosted: Mon Aug 04, 2008 11:42 pm 
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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. Once I get the new lathe tooling in order, I really need to break down and make a dozen or more sets so I'll quit feeling like I need to save every ounce of metal I can (to avoid "using them up" and needing to make more).

Anyway, for a 3 jaw, I don't use it often enough for "speed" or "per part simple convenience" to matter. In fact, no more than I use it, considering the up-front cost, I would probably never make up the time it took to mount the thing. My 4 jaws were all dirt cheap and easily mounted with 4 bolts and t-nuts. And with the 4 jaw I can just set it on, get it somewhere in the vicinity of close, bolt it down, then dial the relevant feature using the jaws. Not much longer to do that fooling with a 3 jaw AFTER it's been mounted/adapted, but without the up-front cost in money or time.

Now, if I could just find an inexpensive flat back 4 jaw with 2-piece jaws THAT would be just the ticket for me! :D

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