Centering square stock in a 4 jaw chuck
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    Default Centering square stock in a 4 jaw chuck

    I am making some manifolds in 2" square 6061 T6. They have each end tapped 3/4 NPT with a partition between them with a small hole to limit gas flow. One end has four 1/4 NC mounting holes. They do not need to be super accurate, no tolerance given, but I want to keep them reasonably true. The stock is running about .016" oversized, not an issue. I have a 4 jaw independent chuck and have been trying to center the parts, then always loosen the same jaws to change parts. The other jaws seem to shift even though I don't touch them. Does anyone have a trick to quickly center them?

    Bill

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    I've used a center in the tailstock to eyeball to a centered hole in stock to get close relatively speaking if it's not critical.

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    Quote Originally Posted by 9100 View Post
    I am making some manifolds in 2" square 6061 T6. They have each end tapped 3/4 NPT with a partition between them with a small hole to limit gas flow. One end has four 1/4 NC mounting holes. They do not need to be super accurate, no tolerance given, but I want to keep them reasonably true. The stock is running about .016" oversized, not an issue. I have a 4 jaw independent chuck and have been trying to center the parts, then always loosen the same jaws to change parts. The other jaws seem to shift even though I don't touch them. Does anyone have a trick to quickly center them?

    Bill
    Surely. Ignorant vise.

    On the drillpress. Drill bushing in fixture, yah have more than a few.

    Or even a mill. Dials or DRO will do.

    It ain't lathe WORK.

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    Joe Pieczynski posted a clever way to indicate square stock in a 4 jaw.

    Go to 2:47 in video.


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    Quote Originally Posted by thermite View Post
    Surely. Ignorant vise.

    On the drillpress. Drill bushing in fixture, yah have more than a few.

    Or even a mill. Dials or DRO will do.

    It ain't lathe WORK.
    FUCKING thermite...


    Nothing to add to OP or his question....

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    Quote Originally Posted by Mike1974 View Post
    FUCKING thermite...


    Nothing to add to OP or his question....
    Well, no, not so much. Old age thing. But I got me some grand memories of it!


    Be as hard-headed "nothing exists but the Holy LATHE" as you care to be.
    Not coming outta MY time-budget.

    I rather suspect Bill P. DOES HAVE a drillpress? And/or a mill?

    Lotta extra work to use a lathe when all as is needed is to drill and tap some functional, gas-tight, but not otherwise position-critical holes.

    In rectangular stock as ain't even needing to be turnt into "round", yet?

    Why?

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    For quick indication square or rectangles I lay a 12" scale across the part diagonally with the end of the scale resting against the way or saddle then put the indicator tip on the scale so you don't have to pull it back for each flat. Indicates just like round bar. There used to be a vid on YouTube showing the method but I cant find it now.

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    Quote Originally Posted by g-coder05 View Post
    For quick indication square or rectangles I lay a 12" scale across the part diagonally with the end of the scale resting against the way or saddle then put the indicator tip on the scale so you don't have to pull it back for each flat. Indicates just like round bar. There used to be a vid on YouTube showing the method but I cant find it now.
    Any polygon, same deal. Just "rock" to pick-up each corner. Providing.. the corner ain't damaged nor assymetrically chamfered.

    Most shapes - hex was common - need some machinist-fu at the jaws as well.

    But when the 4-J of a "company" lathe may as well have been welded to the spindle 30 years earlier? No other option anywhere under-roof but a faceplate, even so? Be happy your 4-J HAS Tee-slots, too!

    Yer on their clock. Yah run what yah got.

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    Something like this is what I was referring to. Just let the scale/ruler flap across the stock when rotated and save a lot of time.

    capture.jpg

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    OK - purists close your eyes or go for coffee.

    I have done many 00's if not 000's of such parts by - making a sleeve / bush the ID = to the across corners dim of the stock (it works on rectangular too) - with a bout a 3/8'' wall, and then slitting

    Slide stock in to bush and clamp in 3 jaw - making sure the split is <> equidistance between 2 jaws and <> centre of the face of the material.

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    I've seen the same thing, where the jaws seem to move when you remove the part and chuck up another one. I like the idea of a round bushing for a high volume production run. I've made small ones to fit in a collet, including one on a 10 degree angle, as the part had a round feature on a ten degree angle from the square stock. Of course, a milling machine would work, too....

    My quick set-up for a 4 jaw is to eyeball the part, then bring a tool in from the side to just touch one flat. Zero it, then back off and rotate the spindle 180 degrees. Touch again, and note the difference. Move the tool half the distance, then adjust the part in the chuck to just touch the tool. Do the same thing on the other two flats, and you'll be close enough to tweak it with an indicator if desired.

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    Quote Originally Posted by Limy Sami View Post
    OK - purists close your eyes or go for coffee.

    I have done many 00's if not 000's of such parts by - making a sleeve / bush the ID = to the across corners dim of the stock (it works on rectangular too) - with a bout a 3/8'' wall, and then slitting

    Slide stock in to bush and clamp in 3 jaw - making sure the split is <> equidistance between 2 jaws and <> centre of the face of the material.
    Well.. taking note yah didn't NEED to broach to fit, just left ID cylindrical and gripped the corners?

    I'd call that right clever, actually.

    Especially if yah used shiney-wood and just let it form its own micro-vee-blocks as it went along. Match to the old ones, or rotate to clean metal. No foul, either way?

    Should work on a six-jaw just as well - probably better.

    Or even a four. Indicate off the smoother OD of the bushing instead of the polygonal stock?

    For "purists" who HAVE a cawfee.. and would prefer to reach their end of days without need of investing in a scroll-operated 3-Jaw. Not THAT "pure" anyway - given the 2-Jaw and 6-Jaw are "scroll operated".



    Even so.. WITHOUT sech of a bushing already to-hand, drill press mought have spit out the first drilled and tapped finished part by the time a lathe is completing the second hole. Quite aside from time-eating set up, the part shown is easier to manage all-around in a vise - and then the DP makes and taps holes faster, each go than a lathe.

    That's all it does, but it is what it does best.. or it would not need to exist.

    CNC mill can beat it.

    Manual mill has some precision advantages over a DP, but is otherwise overall slower at basic round holes, generally has less daylight and such, fussier workholding as well.

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    TriHonu and G-coder have just the sort of solutions I was looking for. In fact, the rubberband holding four strips could be extended to finding the center on a mill by putting the indicator on the spindle. Limy has a good idea but 3/4 NPT tapping, even in aluminum, takes a fair amount of torque and slipping might be a problem.

    As to methodology, the only drill press I have is permanently set up with a Commander tapper. In a shop doing prototype and experimental work, a drill press is mostly useless. On a machine where you may be replacing or adding assemblies, you finish off every surface square and straight so it can be a reference plane if needed and drill all holes on even centers. That way, if a hole spacing appears to be about .800", you know it is exactly .800" and square with the base.

    Re making the actual part, I have a Boston Digital CNC mill that does not have a spindle encoder and so is not suitable for rigid tapping, a Promax J head BP clone with the same tiny back gears as the originals, not rated for tapping this large. Besides, the switch is the standard one that needs to be switched on and off. If you are a little slow switching off, you ruin a part. The lathe is a Sheldon R15 with a 15 hp DC motor with variable supply, robust back gears, and jog buttons. Besides, it has a graduated collar on the tailstock quill just like the cross slide and compound so I can bore to accurate depths, by far the best choice.

    Bill

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    Quote Originally Posted by 9100 View Post
    only drill press I have is permanently set up with a Commander tapper.
    ...

    Boston Digital CNC mill that does not have a spindle encoder and so is not suitable for rigid tapping, a Promax J head BP clone with the same tiny back gears as the originals, not rated for tapping this large.
    ..
    The lathe is a Sheldon R15 with a 15 hp DC motor with variable supply, robust back gears, and jog buttons. Besides, it has a graduated collar on the tailstock quill just like the cross slide and compound so I can bore to accurate depths, by far the best choice.

    Bill
    Yah run what yah got.

    Fast and easy 1/2 HP Walker-Turner one side of the shop, clumsier 7 hoss Alzmettal AB5/S the other side, and a mill between? I'd not need a lathe for the part you are making. Ran taps over an inch into mild steel, 5 HP fossil of an ATW radial, so the AB5/S will surely drive 'em, too. Part of why I have it, my only vertical mill spindle weak as it is. Horizontal has the balls, but Oy! No clutch! The nuisance for tapping! Faster by hand, mere 3/4" pipe-and related fittings tribe.

    Interesting sharing exercise on aligning stock - regardless of how it got a start.

    Thanks for that!

    "Young" Bill


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    Try swapping the jaws around it can make a difference maybe its just my worn 4jaw-Loosen the same 2 jaws each time.Quick way initialy measure across flats and put a round bar in-easier to dial in.But whatever way you do it think your always going to get a slight movement especially if the square stock is not precision so a couple thou or not perfectly parallel and it will show up on your DTI

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    A couple big orings around the jaws to hold them in? No tolerance, .020 or more runout acceptable? Layout with center square, punch, align with tailstock center? Stack all of them in mill vise? Many ways to run it. I would do them in the lathe.

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    As much as it galls me to agree with Thermite, he is right. A knee mill or CNC mill is the place to do the job. I have run lots of this kind of work and did it both ways. Learned the hard way.

    JH

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    I have run this job before and know how to do it. It is an ongoing periodical order from people who use this part in a system they build. The only issue is that centering is a bother. The tabs held on by a rubber band is the answer I needed.

    Bill

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    It turns out to be even simpler. If I use the MT adapter for a stop, the parts are about 3/8" behind the jaws. The jaws have a concave radius but it is large enough that an indicator reads a low spot in the center of the jaw. Centering the part is hardly more work than centering a round piece. I don't have to worry whether the stock is right on dimension, just get all four readings the same.

    Bill


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