Defective chuck?

[Gordon Thompson]

Wondering if i could possibly have a defective chuck. Its a Nova midi chuck, and I cannot get it to hold a piece of wood. it's been sent rolling across the garage floor so many times now, i've lost count.....

The piece is 5 and 3/4 in diameter - and 2 3/4 tall. it's purpleheart, so it's pretty heavy for its size. the tenon is 7/8 in diameter and 5/8 deep.

I've been trying with the 25mm jaw set - these jaws are straight so the tenon is not dovetailed.

I've even tried without the jaws, and just grabbing it with the jawless chuck.

Should I reasonably expect this to hold? I am thinking of trying to return it, but don't want to argue with woodcraft.....

Thanks for any insight!

oh- the lathe is a jet midi - 1014i. i'm trying to turn at 500 rpm.

[Brodie Brickey]

Gordon,

On a 5+ inch diameter block, I would have a 1.5-2 inch tenon generally.

If the chuck won't close and hold, then take it back. WoodCraft will take a product back for the first year. You might if they're close, stop by and have them test it. Bring the piece of wood with you. You might be using it wrong in some way I can't visualize and usually WoodCraft has at least one experienced turner around.

Chucks have their greatest holding power when they're almost closed. If your jaws are completely open, then that could also be an issue.

[Jason Clark2]

I agree, I'd be using my 50mm jaws and a tenon about 2" diameter and 1/4 - 3/8" deep for a piece that's 5 3/4" diameter. It's also important that the flat top of the jaws have a square shoulder to mate against and that the tenon doesn't bottom out on the jaws before the top of the jaws mate with the shoulder.

Jason

[Gordon Thompson]

i did initailly plan to use the 50mm jaws that came with it......but make a mistake and made the tenon too small for those jaws :mad: then picked up the 25mm set.....

on the 25mm set, the jaws are not completly closed, nor completly open...somewhat in the middle...tenon is not bottoming out...

[Brodie Brickey]

Gordon,

Swing back to WoodCraft if you can. Have them look at it. With the torque that you'll have on that large a piece, I would not be surprised to have it ripped out.

Alternately, chuck it up, bring the tailstock up in support. Cut a larger tennon just above your existing one, and try again. Use a parting tool to get a clean shoulder, then cut off the old tennon if its in the way of the jaws. You can also put a tennon on the other side if you have the room. Then turn a new tennon to replace the old one. If you're makeing a box, consider the two tennon option.

[Gordon Seto]

You are using the wrong jaw. Try using 1/3 the diameter as guide line. Your piece is 6.5+ times the tenon.
Did you match the dots on the jaws to the number on the jaw slides?
Woodcraft now has 90 days satisfaction guarantee instead of 1 year.

[Chris Struttman]

Do your jaws use one or two screws per section? The ones that use only one screw do not work very well in compression mode. You might want to cut a recess and try it in expansion mode.

[Mike Peace]

I have those jaws. Your work is too big for the 25mm jaws. Yeah, I know - who wants to read the fine print? However, you should go back and carefully read the guidance that came with the jaws. Even thoughtthe Tecknatools documentation is sometimes a little weak on clarity, I found rereading allowed some of the mystery to be revealed.

[Ryan Baker]

Not only is the piece way too big for the 25mm jaws (and that tenon size), the 25mm jaws are a poor choice in that application because of only one mounting screw and the smooth jaws. They are mostly made for expansion mounting, or compression work with very small pieces. Something like the 35mm spigot jaws would be much more appropriate, but your tenon is already too small for that.

[Jeff Nicol]

Gordon, The tenon is to long and it is to small of a diameter for that size of blank. It might hold if you bring the tailstock up to do all the turning you can before you take the tailstock away. Purple heart is heavy and dense so the 25mm jaws might not grip it. It is hard to help when it is not in front of me. I could come up with a solution then! You could turn another piece of wood and make a hole in it that would fit over the tenon you have and start over. This way you save the wood and get a stonger and bigger tenon. I have done it on occasion when not paying attention to what size I have turned the tenon. Hope that works.

Jeff

[Gordon Seto]

One other important factor is the chuck has best holding power when you make the tenon or recess as close to the full circle of diameter of the closed jaws. Of course you have to allow for shrinkage.
http://www.teknatool.com/products/Chuck_Accessories/Jaw_Sets/downloads/Min-Max%20Ranges%20Jaw%20Table%20(inch)Sep06.pdf (http://www.teknatool.com/products/Chuck_Accessories/Jaw_Sets/downloads/Min-Max%20Ranges%20Jaw%20Table%20%28inch%29Sep06.pdf)
The 25 mm jaw has 0.394" inside diameter. When you open the jaw all the way, only the two corners of each jaw dug into the tenon. There is too little contact area; the wood would crumble. When your tenon is slightly bigger than the full circle of the jaws, you will have the contact area of 4 arcs.
For the same reason, if the recess is too big, only the apex of each jaw would make contact.http://i118.photobucket.com/albums/o83/gbseto/6ebdab33.jpg

[Harvey Schneider]

All of the above is true! I just want to add that I had problems with very hard wood not being gripped by the midi chuck. The only solution was very light cuts. With the SN2 I haven't had the same problems.
What should help is to have the tenon diameter just slightly larger than the minimum diameter of the chuck's grip range. That way there is maximum contact between chuck jaw and tenon.