Problem using a chuck (Resolved)

[woodfarmer]

Hi all
I am a little puzzled with the chuck I am using. It has dovetail shaped jaws and I am cutting a mortice with the inside tapered to suit the dove tail. But the work piece rattles. The jaws are tight but still the workpiece can be made to move a little in as much as it is not held firmly in the direction of being against the face of the chuck I have tried it both ways, with the mortice shallow enough to keep the work slightly proud of the chuck face and with it deeper with the work held against the face as it is secured. The movement is barely perceptible but I can hear it sometimes, depending on the type of cut I am taking. I have to say I am used to cutting mortices for various faceplates and never had any problems.

What do I need to do to have it secure and immobile in the jaws?

 

[SVB]

Hi there,

Tricky to be too prescriptive without seeing the situation but I would make the following points:

From your description I think you are expanding the jaws into a recess? No matter, what is of paramount importance is the quality of the shoulder you turn that will be held against the vertical face of the jaws. This is where the load is transmitted, the mortice (recess is a term more often used) or spigot is secondary to this in many ways. Having said that, do try to match the profile of the jaws you are using (Axminster C jaws being the unusual profile when gripping a tenon) and ensure neither the tenon nor recess allows the work piece to bottom out as this will then prevent the vertical shoulder you have carefully turned (see previous) from doing the intended job against the end face of the jaw.

Only other thing I can think of is thar the jaws are too small for item or you are working with too great an overhang.

If both chucking and size / overhang fine then lathe headstock bearings start to come into question but let's not go there until other factors ruled out as are probably more likely.

PS just thought, if soft timber and has significant sap wood still present in gripping area, that can deform greater than the more dense heart wood and cause issues.

If none of above, I'm sure others will have thoughts but a photo or two of arrangement would help.

Simon

 

[Robbo3]

As Simon says, or put another way,

Whether you use a recess or a male spigot, in both cases the work must rest on the front face of the jaws ie there must be a gap between the work & the chuck face. It is this that prevents sideways movement more than the pressure exerted by the jaws.

Chas has in the past provided a line drawing to emphasize this point ... but I can't find it to give you the link.

 

[SVB]

ie there must be a gap between the work & the chuck face.

I think Robbo needs a 'not' in this sentence?!? :wink:

Simon

 

[cedarwood]

ie there must be a gap between the work & the chuck face.

I think Robbo needs a 'not' in this sentence?!? :wink:

Simon

No he doesn't he is perfectly correct, there must be NO gap between the jaw face and the work piece, but there MUST be a gap between the work piece spigot and the chuck face.

 

[Spindle]

Hi

A quick illustration to demonstrate where clearance is / is not required when chucking:

In addition to this:

Are the jaw adaptors and jaws fitted to their correct respective locations? do they all meet together when the chuck is fully closed?

Is the work actually loose or is it something rattling inside the chuck - on some chucks the chuck key sockets rattle.

Are you turning a fair way out from the chuck, ( eg goblets), if so tailstock support should be used whenever possible.

Regards Mick

 

[CHJ]

One thing to check is that you are making your socket or spigot the correct size to match the true circle formed by the jaws.

By the very nature of how the jaws are manufactured they will have a 3-4mm gap between the segments when forming a true circle, if you attempt to grip a socket or spigot too far removed from this ideal then you will only be gripping on the 'high' points and things can become unstable as the small contact area wood compresses under working loads.

Make yourself some simple marking gauges to avoid having to keep measuring the sizes.
The odd mm here or there is not super critical with most woods but the closer you are the better.

 

[monkeybiter]

I prefer to make the angle of the recess or spigot slightly closer to the parallel [to the axis of rotation] than the jaw dovetail angle. This allows the tips of the jaws to compress the wood and form a perfect mating surface.... in an ideal world.

When you've chucked a piece nice and tight [as tight as you can if it's a spigot, or as tight as the wood can support if it's a recess] is the movement you detect relative to the chuck or is there movement of the chuck/piece relative to the lathe bed [or fixed tool rest] ?

 

[woodfarmer]

Thanks to all your help. Today I solved it. The chuck was working loose on the spindle. It needs to be wound on the threads with a tiny bit of a whack. This puts the back of the chuck against the spindle securely. I have been just winding the spindle with my left hand onto the faceplates and chuck, faceplates ok, chuck not. So If I leave the spindle lock in and wind it up it is then firm with no play.

It is good that I can have the workpiece off the front of the chuck as having it flat makes the recess so deep I was beginning to think I would be better off with face plates and screws.