Faceplace turning, then expanding chuck

Multiple choice:

a) the recess was not formed properly. The cuts must be clean, the bottom of the recess must be flat or slightly concave, and the sides should be slightly dovetailed.

b) when mounting the piece, press in at its center, not the sides to ensure it fits flat against the face of the jaws.

c) you are expecting too much accuracy. In my experience works never runs perfectly true, there is always a very slight amount of runout, though not usually enough to cause a problem.

d) the chuck bit into the recess denting it, caused by either overtightening, the sides of the recess not properly formed, or the diameter of the recess does not match the optimal diameter of the jaws (when then form a perfect circle). This will be more of a problem in softer woods.

e) the chuck itself is not running true. Tighten the jaws up and check for runout on the flat face and the sides of the jaws. Any inaccuracies here will be magnified when you mount a piece of work with a larger diameter or depth.

In short, if you want accuracy, you want to form a recess that maximises the contact area between the sides of the jaws and the wood, so that the gripping pressure is applied to the wood over a large surface area. What you don't want is a lot of pressure in just a few spots.

Hi Bruce,

You may be doing nothing wrong. Wood being compressible and 'warpible' often needs to be cleaned up whenever it's moved from a holding method, even off & back on the same chuck. You might have cut the dovetail too deep and it's not seating squarely on the chuck or the chuck's adapter might not be registering squarely to the spindle. You might want to try cutting around the edge and over the top for a short distance before removing from the faceplate. If you have a swivelling head lathe, is it lined up?

Not to worry, offset edge trivits are considered in some quarters to be art. :)

Turn to Safety, Arch Fortiter

how about a wild guess by someone with less than a week of chuck experience? *lol*

Make sure that you're not cutting your recess/tenon too deep... you want to make sure that the tenon isn't deep enough to "bottom out" on the chuck face, which will prevent it from running true..

yes, I did RTFM... and now I'm really confused..

Sounds to me like you simply don't have the recess sitting squarely on the face of the jaws.

I like to

1) lay the workpiece face down on a flat surface 2) set the chuck loosely on top, wiggling to make sure you have good contact with the face of the recess 3) gravity holds the chuck jaws against the face of the recess 4) tighten slightly Be careful not to over tighten. If you hear wood splintering, you are probably too tight. Do not back off, but don't tighten so much next time. 5) remount the chuck to the headstock spindle

In my experience, it is only by blind luck that I get the second side to run true to the first one but the above method seems to tilt the odds in my favor and lessens the runout that does occur. I plan on only working each face one time because the wood will behave differently each time I remount it.

(Tell my wife I need 3-4 more chucks, okay?)

Bill

Good advice from others, in this order.

1) Don't cut the recess deeper than the dovetail. You will see that the dovetail portion does _not_ go all the way down the jaws on the 50mm, and you don't even need to bottom to that point to hold a piece firmly. 2) Keep it clean when you reverse. A curl, or if you have sanded, a bit of packed dust can affect your seating. Mark one mod zero lungs or mechanical air to clean. Oh yes, no tearout - counts as dirt, but it's attached. 3) Set the piece over the jaws, tighten a bit, jiggle and make sure it seats. I use my tailstock as a third arm. 4) Spin and look at the _back_ of the piece. You're going to true the face anyway. On a bowl, look for side to side. Don't be satisfied with close. If you've done one through three, it _must_ rotate as true as your chuck. 5) Don't be afraid to backtrack as far as you need to troubleshoot.

Arch says

You have inspired me again, Arch!

nothing jumping out at you is a GOOD thing on a lathe, Bruce.. *g*