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I just bought a new bowl chuck with dovetail jaws. I tried using it in the expansion mode, turning an angled recess into the bottom of the bowl. I believe i had enough depth and the right angle on the dovetail, but the bowl would wobble out when i tried to turn the inside (i tried three separate times). Any suggestions on what i might be doing wrong? What should i be more precise about?
I have found that the recess method of mounting a bowl blank only works well with dry wood. If you have a green bowl blank, I believe that a tenon works best and the serrated type of jaws seems to hold better. If you are cutting a mortise to mount your blank make sure the bowl diameter is not very large compared to your jaw size. The mortise shoudl be slightly larger than your jaws when they are fully closed, the dovetail needs to be only a few degrees and the depth of the mortise must be less than the depth of your jaws. The bottom of the mortise must be flat so that the jaws set against the bottom of the mortise. If you cut the mortise too deep and the bowl does not set on top of the jaws your bowl will wobble. I only use a mortise in very dry wood of small depth and not too large of a diameter. For example for my 2 inch jaws a 6 inch bowl would be just about max. I install the larger 4 inch jaws for going over about 6 or 8 inches. Hope this helps and if you have a woodturning club in your area, I am sure you can find some excellent help there.
Whenever you use a chuck, it is critical that two surfaces make good contact with the piece. The faces that contract or expand to grip the wood; and the faces of the jaws that face the tailstock. You should try to have full surface contact with those outside faces of the jaws to provide a bearing surface for the piece. Without that contact, it is very difficult to support a piece. Make sure that your tenon, or recess, is not so deep that it bottoms on the inside of the chuck before it bottoms on the outside face of the jaws.
Also, remember that your tenon, or recess, should be very close to the closed size of the jaws for full diameter contact.
Hope this helps.
Tim, Here is a little bit more to add. When you cut the tenon it should fit the profile of the jaws as close as you can get. I have a tool made that it cut to fit the profile of the dovetail jaws and it is foolproof. It the depth is a little shallow that creates some trouble but the at the bottom of the dovetail cut make sure it is completly flat and the jaws make good contact with the wood. So what I do is take the bowl off the lathe and mount the chuck to the bowl while bowl is on the bench. This way you can see if there are any chips or obstructions stopping you from getting complete contact with the wood and jaws. Also don't make the dovetail cut to big around, meaning if the jaws are completly expanded they will grip less than if they are open about 1/8" -1/4" between the jaws. The closer the jaws are to a complete circle the better the grip as the pressure will be equal around the jaws. Hope this helps.
Jeff
Kurt and Jeff gave you some good advice. Measure your jaws closed. Then make your opening or tenon maybe a 1/8" to 1/4" larger. Also inside your recess or on a tenon make sure the the jaws are flush with the wood. If you don't you will get wobble. If you make a tenon to big and your jaws are fully expanded you are only gripping on 8 points or just the corners of the jaws.