Using expansion chuck

[Faust M. Ruggiero]

When you folks make a recess in a turning to accommodate your chuck in "expansion" mode, how deep do you go? I tried it for the first time and expect I could have made the recess less deep. I cut in 3" wide and 3/8" deep for a 10" shallow bowl I was experimenting with. My chuck is a Oneway Talon and does not require a dovetail.
fmr

[David E Keller]

I don't use the expansion mode very often for bowls, but I'd say I usually go somewhere between 1/4 and 3/8".

[John Keeton]

Faust, for me it depends somewhat on the wood and form. If I am doing a shallow form that will leave plenty of wood around the recess - probably somewhere between 1/8" and 3/16". Otherwise, closer to 1/4", but probably not quite that much.

I think Leo uses a very shallow recess. Perhaps he will comment.

[Reed Gray]

The important thing isn't how deep you go, but how close your are to the proper diameter. If your chuck jaws closed measure 2 inches across, you want your recess to be 2 1/8 inch wide. If you expand those jaws into a 3 inch diameter recess, you don't have a very good grip. I turn bowls up to 18 inch diameter with a recess of about 3/16 inch deep. Just coincidentally, your recess depth is the same as your tenon depth.

Dove tailed jaws do give a better grip than straight jaws. There is a reason why it is used so often in flat work to really hold things together. A dove tailed scraper makes it easy to cut.

robo hippy

[Neil Strong]

With Reed's caveat on matching jaw/recess diameters and given sufficient meat in foot ring:


3/16" for most pieces.
Can go down to 1/8" on smaller pieces, even 3/16" with some hardwoods
Up to 1/4" on 20"+ pieces.... as much a matter of appearance as necessity

Precise matching of the angle on the dovetail recess to the jaw dovetail is also important. You may need to make up different dovetail scrapers for your different jaw sets.
.

[Leo Van Der Loo]

When you folks make a recess in a turning to accommodate your chuck in "expansion" mode, how deep do you go? I tried it for the first time and expect I could have made the recess less deep. I cut in 3" wide and 3/8" deep for a 10" shallow bowl I was experimenting with. My chuck is a Oneway Talon and does not require a dovetail.
fmr

Faust I use the recess about 90% of the time, especially in bowls.

Since you have the Oneway with the regular jaws you can see the small ridges that grab the wood and a very precise size of the recess is not needed like with dovetail jaws to get a good hold.

163631

The depth of the recess doesn't have to very deep at all, basically the ridges have to be in the recess, that's about 1/8", but the wood around the recess has to be sound to do that, and strong enough to hold the pressure of the jaws, and that depends on how tight you try to crank the jaws :eek:.

That is the other thing to be aware off, how sound is the wood, like in this picture the softer spalted wood on the middle bowl has a deeper recess than the two other ones that have better wood, and in the other picture it shows that I used CA to stabilize and strengthen the wood around the recess.

163632 163633

The way I tighten my chuck most every time is holding the piece with one hand and tighten the chuck with my other, then spinning by hand the lathe to see how well the piece is running true, before tightening the chuck any more, if running true I will tighten with one hand only and go to the other side of the chuck and do it again, the softer wood will let the ridges from the chuck go into the wood so I will keep going around till the chuck is snug and not easily tightened any more.

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So basically you can suit yourself as to how deep you want to go, just don't forget the recess when hollowing, DAMHIKT :p

Also the more wood you have the greater the chance of splitting, one of the reasons I don't like using a tenon, beside the tenon breaking right off the bowl at times.

If you get a bad catch the wood might come out of the chuck, but you can remount it usually, though I don't recall the last time this happened to me :)

[Faust M. Ruggiero]

Thanks for taking the time to help. Leo, the fact that you post pix is such a great help. My first recess looked like a canyon compared to yours. Tomorrow evening I will make another piece with a 1/8" deep recess. I'll keep it under 10" in diameter. I do try to cut my tenon the "sweet" size for the jaw set I am using. My first effort was just a flat piece meant to experiment with the recess method. I liked it because it seemed like it would make cleaning up the bottom easier. Leo's pictures make me really excited to try again.
Right now I have only black locust blanks to work with. They are hard but I am sure they are solid and able to take the pressure of the expanding jaws.
Thanks again, I'll report on my efforts.
fmr

[Antonio Martinez]

Check this out:

http://www.youtube.com/watch?v=Yqhr-GwXLgo&feature=youtube_gdata

[Dave Ogren]

Faust,

I use recesses 100% of the time and have had tremendous great sucess. I use VicMarc 120 chucks. Their closed dia. is 2 5/8" so I make the recess about 2 3/4" to accomodate the warping and shrinking during drying. I make the recess depth 3/16" to 1/4" deep. This has worked perfectly for everything up to 20++" dia. finished bowls. Good luck.

Dave

[Reed Gray]

Captain Eddy's video is very well done. One of the best explanations I have seen on how to make a recess.

I also use the Vicmark chucks. I drill a 2 5/8 inch recess on the top surface of the bowl blank and expand into that instead of using a face plate or screw chuck. Much faster, and just as secure.

robo hippy

[Faust M. Ruggiero]

Hey Gents,
Thanks for the additional info. Captain Eddie was very instructional. I can see I need to learn this technique. It seems to have some advantages over a tenon.
fmr

[Thomas Canfield]

Faust,

You have been given a lot of good advise, expecially by Leo. I think that deeper recesses are the way to start until the confidence factor is developed with the holding ability and turning skills and sharp tools help to keep from pulling the bowl off the chuck. A recess works well for me for dry wood only, and I perfer a tenon for green wood that will warp and distort. It is hard to reseat a chuck in a warped recess when remounting a dried bowl to finish. You can return the warped tenon between centers and then mount to finish turn.

[Leo Van Der Loo]

Faust,

You have been given a lot of good advise, expecially by Leo. I think that deeper recesses are the way to start until the confidence factor is developed with the holding ability and turning skills and sharp tools help to keep from pulling the bowl off the chuck. A recess works well for me for dry wood only, and I perfer a tenon for green wood that will warp and distort. It is hard to reseat a chuck in a warped recess when remounting a dried bowl to finish. You can return the warped tenon between centers and then mount to finish turn.

Of course you can do the same with a recess, with the proper tool :)