Jamb Chuck question

[Mike Vickery]

A question for you jamb chuckers out their.

For making jam chucks for bowls can you use MDF or is that a really bad idea?

What do you use to make yours? Well I have tons of scrap lumber around most of it is not big enought to jam chuck a 12 inch or bigger bowl.

Thanks in advance.

[Don Orr]

MDF is fine for jam chucks.

[Paul Engle]

I make mine out of plastic pipe parts as the 3 in fits my G3 just right , i cover em with untreated cowhide using CA glue

[Jim Stoppleworth]

A question for you jamb chuckers out their.

For making jamb chucks for bowls can you use MDF or is that a really bad idea?

What do you use to make yours? Well I have tons of scrap lumber around most of it is not big enought to jamb chuck a 12 inch or bigger bowl.

Thanks in advance.

Mike, I get the sense from your post that you believe the jam chuck has to be as big as the full inside of your bowl. Is that correct? If so,your jam chuck does not need to be the same size as the bowl to be effective.

Jim

[Patrick Taylor]

I use a reject bowl that still has the tenon. The one I'm finishing either fits inside or outside the jamb-chuck-bowl.

[Mike Vickery]

Alright I think we have a terminology problem here. I think Don and I are talking about the same thing, but I get the immpression the rest of us are on different pages.

I am not saying that my terminology is right but I think some of you are talking about what I call a friction chuck.

Friction chuck - where you have something that just goes against the bottom of the inside of the bowl and then the tailstock is brought up into the tenon. The friction of the piece of wood of what ever against the bottom of the bowl drives the piece. This is actually the most common way I finish the bottoms of my bowls.

Jam chuck- A piece of wood (or something similiar) is installed on a faceplate of chuck. The end of the edge is turned so that it will fit snugly inside the lip of the bowl. Then once you can seet it you cut the next section on the jamb chuck equal to the outside diameter of the bowl and wrap masking tape around it (to stop it from creeping off not to drive the piece). You can spin the bowl without tail stock support. One of the supposed advantage (per a Stuart Batty video and demo) is that the hollowed out bowl behaves as if it were a solid piece of wood. You can actually re-turn the outside if you so wish. I did it last night with a little bowl and it worked quite well.

I tried to find a picture on the internet but could not.

Feal free to correct my terminology if it is wrong. Often what I call things are not what they are really called.

I am familiar with most of the methods used to finish the bottom of bowls but want to explore this method further.

Edited in - I found a picture http://www.woodturns.com/articles/tools/mounting_wood.htm the first picture on the page.

[Brett Baldwin]

Hey Mike.
It seems like there are two different things that I've seen called jam chucks around here. One is what I would call a friction chuck which is just an extension on the drive spindle that spins the piece by pushing it into a live center and using the fristion to make it spin.

The other is what I think you are talking about which is a piece of wood that just barely fits inside the rim of the bowl and has a lip so that the bowl is more or less pressed onto it and you secure it to the chuck with tape or soemthing like that or you can bring the tailstock up to be sure to keep it on for most of the turning. The first one of these I saw was an MDF disk on a facplate that was custom fit with a parting tool to the bowl in the demo. The reasoning was that scrap MDF was easy to get and easy to work.

BTW the Palo Verde is in newspaper right now but I'm leary of it coming out well since there were major cracks in the blanks I cut.

[Mike Vickery]

Yes Brett we are on the same page
http://www.channelislandswoodturners.org/SBattyDEMO.htm
This is a link that has pictures of Stuart Batty demo with two really good pictures of his jam chuck. This is exactly what I am talking about.

On doing a little more research Jam chuck may be the most generic term in woodturning. I should have been more specific in my origianl post.

[Martin Braun]

Mike,

I ran into a similar problem that you mentioned. I also found that after jam chucking a number of larger bowls, the sacrificial big piece of wood I used to jam chuck was getting turned down to the point where I had less options for jamming. As a result, I went with a home made vacuum chuck. There are a couple of plans on the internet and Paul Porter had some great tips in his demo last year. I chose the "Lowes shopping trip" style, and after purchasing a used Gast pump on eBay, I was all setup. The one advantage to regular jam chucking though is that with a vacuum chuck it can't have any significant voids/holes in the surface in contact with the wood. My $0.02.

Martin

[Richard Madison]

Mike,
MDF is fine if thick enough. For ref. have never taped a piece to the JC, but use tailstock to center the bottom and hold in place. Only leaves a little nub to be removed w/ chisel and sanded. Suggest edge glue scrap lumber to desired size, bandsaw round, and turn jam chuck.

[Malcolm Tibbetts]

Mike, I use MDF for all my jam-chucking. A lamination of two layers makes a real solid disc. For extra security, and to avoid using the tailstock, I also often use a "keeper ring" as shown in this photo.

[Jim Stoppleworth]

Mike,

Thanks for the clarification. I was on the wrong page. Learned several new things though!:D :D

Jim

[Mike Vickery]

Thanks everyone I think I got what I needed to out of this. I am lazy and cheap so have never gotten around to making a donut chuck or vacum system.
I will probably continue to friction chuck most of my pieces to finish the bottom. Jam chucking is just something I want to play with a little, mostly to return the outside at the bottom to make a very small foot for some pieces.
Just trying to get a few more things in my arsenal. Thanks for the input.