Announcement

Collapse
No announcement yet.

Oh Fu.uudge! Dropped my 4jaw chuck

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Carld
    replied
    lynnl, from the way you describe it a good weld shop could safely weld it and you would never have an issue with it. As you describe it the crack is not in a loaded or sensitive area.

    Leave a comment:


  • ckelloug
    replied
    Of course the bad thing about cracks is that they propagate. . . It's not good in this case but in some cases crack points are drilled to increase the crack tip radius beyond which they want to propagate at the loads encountered. On other types of parts, an insane surface finish is specified so that there are no imperfections in the surface to cause stress concentration. Vibration and other intangibles can also cause cracks to grow.

    The crack will be stressed by tightening the chuck. It will also be stressed by cutting forces since these put a torque on the chuck. The forces that we understand might not make the crack grow but the forces we don't anticipate could be a day ruining experience. Just remember what it's like when you get a chuck key thrown at you and imagine how it would feel if the entire chuck (or half of it) got thrown at you.

    In fact, by my calculation, that chuck spinning at 500 rpm's is storing 150J or about the energy of a .22LR Rifle round** While it may take a good shot to kill you with a .22 rifle, Murphy has been known to be a good shot on our worst days.See the energy content of rifle bullets at http://en.wikipedia.org/wiki/Muzzle_energy.

    Do you really want to wonder where this energy will go if the crack liberates it suddenly?

    **
    E=I*w^2
    I=m*r^2/2
    w=500rpm*(1min/60seconds)*(2Pi Radians)/revolution
    Assume chuck mass=22 kg (50 lbs)
    Radius as given at .1m (8 inch diameter)

    Leave a comment:


  • lynnl
    replied
    Originally posted by ahidley
    Wont the crack get stressed when you tighten the jaws?

    No, where this crack is located I don't think it has any bearing on the structural integrity at all. ...or certainly not much anyway.

    Leave a comment:


  • ahidley
    replied
    Wont the crack get stressed when you tighten the jaws?

    New chinese 8 inch 4jaw, independant is $79 from shars.com
    D1-4 mounting $155
    Who cares about the runout because its independant anyways.

    self centering 4 jaw $129

    Leave a comment:


  • lynnl
    replied
    Originally posted by tattoomike68
    A cracked chuck says" I will hit you in the face with 20+ pounds at 60 MPH"

    send it to the foundry gods or use it on a rotary table where its doing low RPMs.

    you can weld it up and use it for low rpm work, I tend to machine faster when using a 4 jaw but that chuck is no longer safe.

    By my calculations, with an 8" chuck revolving at 500rpm (my lathe's max), that chunk is moving at about 11.89 mph. (8 X 3.14 X 500 X 60 = in/hr; divided by 12 = ft/hr; divided by 5280 = mph) I'd guess its weight at no more than about 4 oz.

    While the chunk is in place there is no significant out-of-balance issue.

    I certainly agree, it's not as safe as it used to be. But I don't think it's any great catastrophe waiting to happen either. Tho it does bear watching and exercising caution.

    Leave a comment:


  • BadDog
    replied
    On my new lathe, the chucks are almost too big to manage by hand. The 10" 3 jaw is a hassle for me to mount by hand, and nobody I know is going to mount that 15" Rohm 4 jaw by hand. Evan's stick might be sufficient once you get it on the bed, but my large spindle bore would mean you need a 2.25" stick to get the chuck near centered (with jaws snug). So I made a cradle for the 10" from 2x4 scrap. Cut and nailed (no contact) it together with glue, then sealed it with paraffin wax. Now the 10" is easy to mount and remove, just plop it in the cradle and slide onto the spindle. I'll need a crane of some sort (or some robust helper) just to get the 15" onto the bed, so no cradle for it yet...

    Leave a comment:


  • thistle
    replied
    I would not use the chuck on the lathe any more.

    HSM or MW magazines have had a few gadgets in the past
    to help with chuck mounting.

    One good one is to bandsaw a block of wood- shaped so that bottom slides on the lathe bed, the top is cut to the shape of the chuck when it is aspindle height.
    you plop the chuck on and slide it up to the spindle nose.

    Evans stick is a good idea.

    Leave a comment:


  • hardtail
    replied
    lynnl if you drill the crack as suggested and weld it up and only you ever use it, I'm sure you could get by with low rpm work, the trouble is for it never to be sold or used by someone else.......it will likely be slightly out of balance anyway for speedy manouvers

    I pulled a shyhook/toolpost crane out of the dumpster a couple weeks ago and it's doubtful I will ever use it as I'm going to fab up a monorail system out of unistrut but it's yours if YOU want it, the shipping would probably be a killer though........frown

    Leave a comment:


  • BobC
    replied
    [QUOTE=Evan]You need to make yourself a chuck stick. Hardwood from an old shovel or whatever works well.
    QUOTE]

    Nice idea. I will do it.
    Thanks,
    Bob

    Leave a comment:


  • Evan
    replied
    Why don't you snug the chuck stick in the jaws before removing the chuck from the spindle so the chuck will be centered on the threads when you put it on? Just leave the stick in the chuck.
    Because I didn't think of it.

    The pattern is for more grip. My hands don't work well (nor does any other part). I get momentary spikes of pain that are entirely unpredictable and cause me to drop things frequently.

    Leave a comment:


  • winchman
    replied
    Evan,

    Why don't you snug the chuck stick in the jaws before removing the chuck from the spindle so the chuck will be centered on the threads when you put it on? Just leave the stick in the chuck.

    What's the pattern on the right end of the stick?

    Roger

    Leave a comment:


  • Evan
    replied
    I agree that it shouldn't be returned to service on the lathe. For the crack you can prevent it from going further by stop drilling it with perhaps a 1/8" hole about a 1/4" beyond the furthest perceptible part of the crack. That provides a radius to spread the forces in the end of the crack so it won't propagate.

    Leave a comment:


  • MickeyD
    replied
    I have never seen any cracks get better but I have seen a lot get worse quickly. I think what you have now is a very valuable positioning jig. This can make welding and brazing easier, assembling things simpler, and tons of other uses. Just be glad that it did not crush your foot or some other body part you might be interested in keeping.

    Leave a comment:


  • Guest's Avatar
    Guest replied
    A cracked chuck says" I will hit you in the face with 20+ pounds at 60 MPH"

    send it to the foundry gods or use it on a rotary table where its doing low RPMs.

    you can weld it up and use it for low rpm work, I tend to machine faster when using a 4 jaw but that chuck is no longer safe.

    Leave a comment:


  • lynnl
    replied
    Originally posted by Carld
    it was just waiting for you to turn your back. You could have watched it for an hour and when you turned around, KABAM.

    Back rim??? does that mean it fell on the threaded hub and the crack is an arc in line with the circumference?
    No it didn't hit on the back plate.

    Basically it landed on the periphery of the chuck body, but the back side of the periphery hit first. i.e. the jaw side was slightly higher.
    Looking at the back side of the chuck, it's solid in the four areas where the pinions are, but sort of hollowed out in the areas between. That is to say the back of the chuck body is webbed, with the pinions in the four webs. So the chuck periphery over those hollowed out areas is only about 3/8" or so thick. It's noticeably lighter than my 8" 3 jaw because of those hollowed portions.
    I think if it had landed on, or closer to one of the pinions it would've sustained no damage.

    After looking closer, the crescent shaped crack does not extend all the way at one of its ends. I've wrapped 4 layers of industrial strength duct tape around the chuck over the cracked area, which should tend to preclude it breaking loose further, or at least briefly contain the shrapnel if it should fly loose.

    From the looks of it, I'd say the odds of it coming loose are probably no more than 5-10%. But I do want to get it fixed.

    Yeah that's what I did (after the fact) Evan.

    I've always thought about making a cradle, with radius to match the chucks, to support the things when changing. Maybe even include a couple of pairs of ball bearings to permit screwing it on while fully supported. I may give that more serious thought now.

    Leave a comment:

Working...
X