length to chuck on lathe part
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    Default length to chuck on lathe part

    I need to run some parts that are bigger and heavier than the usual size in our shop and need some advice. Parts will be made from 9" by 10.5" long 6061 aluminum. Parts will be grooved in the middle to 5" leaving the ends a bigger diameter and will be bored to about 3.0". While doing any turning i will probably use a tailstock for support. But for facing, drilling and boring im worried about part coming out of chuck. These will be run on hitachi seiki cnc lathe with a 10" chuck. What kind of jaw length do i need to feel safe? Should i buy long aluminum jaws i can bore out to at least 2" or maybe 3" deep for chucking? My hardened jaws only have about 1/2" gripping length on them. Our normal work size is like 5" x 5" long parts. We do bigger diameter stuff sometimes like 9" but always under 5" long. Any advice would be appreciated. Thanks.

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    Quote Originally Posted by Getsideways View Post
    I need to run some parts that are bigger and heavier than the usual size in our shop and need some advice. Parts will be made from 9" by 10.5" long 6061 aluminum. Parts will be grooved in the middle to 5" leaving the ends a bigger diameter and will be bored to about 3.0". While doing any turning i will probably use a tailstock for support. But for facing, drilling and boring im worried about part coming out of chuck. These will be run on hitachi seiki cnc lathe with a 10" chuck. What kind of jaw length do i need to feel safe? Should i buy long aluminum jaws i can bore out to at least 2" or maybe 3" deep for chucking? My hardened jaws only have about 1/2" gripping length on them. Our normal work size is like 5" x 5" long parts. We do bigger diameter stuff sometimes like 9" but always under 5" long. Any advice would be appreciated. Thanks.
    CNC brings limitations as well as advantages, so this might not be useful, but..

    An "all manual lathe" guy might "batch process" as follows:

    First op: Put a clearance bore 10.5" through on a(ny) decent drillpress,

    Second op: IF, and ONLY IF, your Drillpress can't deliver with a decent reamer, Lay the now "tube" on a raised & shimmed vee-block PAIR atop the lathe carriage (presuming no hor-bore), and ream or line bore it to finished ID.

    Drillpress OR lathe, the work don't motate. Boring bar or bespoke "D" reamer does. "D" reamers are cheap and cheerful. Accurate, too.

    Third op: Using that finished bore, mount it on an internal (tapered sleeve) expanding mandrel 'tween centers, so as to face both ends and turn the OD & reduced center in one final setup, and with "rather good" concentricity to the bore. "Automagically" good, even. Not a lot of set-up time to it if your mandrels are decent goods.

    Or you MAKE a good 'un.

    Nuisance work, three-stepping it, but near-zero risk of it getting away and ruining a part.

    Or ruining your whole day.

    Steady rests exist, too. For all-manual lathes, anyway. You might not have one?
    Mandrels can he had faster and cheaper than steady OR tall jaws, work better, can be DIY'ed faster and cheaper if need be, too.

    CNC is at its best with custom workholding engineered to the specific work at hand ....and even "live" tooling.

    Odds and sods that do not fit your on-hand workholding and tooling can be a Royal Pain in the Computerized Numerical Control arse.

    You knew that already, yah?

    Trying to EXTEND sub-optimal workholding with nought but taller jaws?
    Fraught with risk. You knew that also.

    It CAN work.

    Mandrels will work. Least-risk.

    Not new.

    2CW

    And of COURSE I have the mandrels.

    Breakheart Tool single-enders as well.

    Preparation is 90% of any job.

    Preparation to do each job CHEAPLY, too!
    Last edited by thermite; 06-07-2021 at 01:47 PM.

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    Might consider machining a circular dovetail on the end of the part, and bore a set of soft jaws to match. If necessary, buy the stock with enough extra length to do this if you have to sacrifice the end of the bar for the sake of chucking it. I'd cut the angled surface on the stock by means of the manual lathe, but you can probably do it with great care on the cnc as well.

    Some guys might use carbide grippers (with the diamond knurl pattern) mounted in a set of soft jaws. With a power chuck, you can set those in pretty good into the stock.


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