View Full Version : Lathe chuck question

04-05-2006, 07:41 PM
Alright- i've mentioned this in some one else's thread but i thought i'd go ahead and post it as a new thread. I have a smithy midas machine. I know - i wish i had the room and money, i.e. transportation and other money along with the upfront cost of the machine, to buy a full size lathe and do away with the milling machine for right now, but since that wasn't an option this has worked out well for me - and it provides me a great oppurtunitry to learn some stuff. Anyway, here's the trouble: my chuck no longer scrolls properly. i checked the the runout on the backing plate and it was pretty darn good - well within the tolerances listed in the machines specs (.001 where tolerances said .005). The work piece, when chucked up, turns way off center. Looking at it when its all the way closed, jaw number three doesnt meet the others at the same time, basically the other two hit each other and stop but the number three jaw is about 1/16 away from the others. Now, what are your general thoughts about this? Is it likely a problem with the chuck or the jaws? I took them apart and reassembled and did not notice any major knicks or dammage to either the back of the jaws or the scrolling part of the chuck.

04-05-2006, 07:52 PM
No doubt you either placed them in the wrong slots, or scrolled them wrong. Take them all out. Each jaw (somewhere) will be marked, either 1,2 or 3. The chuck has the same markings on it somewhere, just look. When you find these, look in the #1 slot on the chuck and start scrolling. When you see the tooth just start to spline in, back off a bit and insert #1 jaw. Same for the next two jaws. Can't go wrong

04-05-2006, 08:00 PM
Well- i'll try it again but i did that twice, both times carefull to put them in the right order...it was turning off center before i removed the jaws but i'm an eternal optimist. If thats all thats wrong i would be very happy! I'll try it again when i get a bit of time. Thanks for the reply

i guess i should've added that i made an oversight by turning my friend loose on the lathe. I gave him a thirty minute talk explaining most of the basics, which is pretty much all i know :) , and then figured he'd be ok just turning some off of a round shaft. He made to deep a cut and popped a big old piece of iron way crooked in the chuck. I'm not trying to blame this on him, i recognize it was really my fault for not being there to supervise - i was across the garage working on another component of our project.

04-05-2006, 08:27 PM
That only means one thing. If the scroll and jaw threads are ok, then the jaw is bent. Insert the outside jaws and see if they are the same. If not, bent jaw. Happy turning.

charlie coghill
04-05-2006, 08:55 PM
Take the chuck apart and look at the scroll. Look for any chips or for the scroll thread not being concentric with the rest of the thread.

John Foster
04-05-2006, 10:00 PM
Ken has it right Put the reverse jaws in and chuck several different size pieces. If they all runs true then you have a bad chuck jaw in the first set. In all probability it will be out also which means you have a streched scroll or the chuck body has been streched. Not much you can do for either problem except to replace the chuck. I'm betting on the scroll which is why I said to try several pieces. You want to hit the strechespot, if there is one. Takng it apart would probably show up a streched scroll, too. John