# Jam chucking 101



## Schroedc (May 19, 2015)

I recently acquired a bunch of bowl blanks that had been cored out of larger pieces by someone else and while I normally flip them over and put a tenon on the bottom while I'm coring using the larger bowl as a jam chuck these had some really thin bottoms so the 1/4 to 3/8 deep tenon I usually use won't work unless I'm going to make funnels. I thought some folks might find the following useful.

I started with a blank that was just a hair over 1/4 inch thick at the base so by the time I turned my normal tenon and a foot I'd be through the bottom. 



 

This jam chuck was made from a chunk of oak burl but you could even use a section of PVC with some rubber on the edge or a roll of tape clamped into your chuck for items with a flat face I've also used just a faceplate with some sticky back 80 grit sandpaper stuck to it. This one has a piece of children's play floor mat glued to the mating surface to give some grip and account for any irregularities in the surface. I've found 3M Super 77 spray adhesive works quite well. 



 

First I mounted the blank between the jamb chuck and the live center using the pressure from the center to hold it against the chuck. I'm using the cone screwed on over my center so the spike doesn't protrude into the blank as far and to give me a bit larger clamping surface. If you have the tap to match the threads for your center you could also turn a wooden ring to use as well. I then turned it to an outside profile I liked and turned a tenon much narrower than I'd usually use.



 

 

I then flipped it over and grabbed the tenon in my chuck and turned the inside keeping an eye on the wall thickness but most of all paying attention to take as little material out of the bottom as possible, just enough to true it up and give me a smooth surface. With the much thinner tenon I was careful to use very light cuts and take my time as there was much less holding it than usual. While it was on the lathe got almost all of the sanding done as well to make sure there wasn't anything else I needed to turn out.



 

 

Then I flipped it back over, and using the same jam chuck and the dimple in the bottom from my live center the first time we mounted it to line it up I cleaned up the tenon to create a foot and remove any chuck marks. Then I sanded the outside of the bowl.



 

 

Normally I'd use the depth of the tenon to turn a nice foot on the bottom but with the remaining thickness left on this bowl I chose to use my big flat belt and sand the bottom down to remove the dimple from the center and create a little flat foot. as you can see the bottom in the center is now about an 1/8 inch thick.



 

 


Please feel free to share any other setups you may have that would help or ask any questions. For anything even thinner than what I started out with you'd probably have to go with a vacuum chucking system. I will be adding that to my lathe in the near future but for now this allows me to use at least some of these blanks.

Reactions: Like 2 | Thank You! 1 | Great Post 2 | Way Cool 1 | Informative 4


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## NYWoodturner (May 19, 2015)

Great post Colin. I recently acquired some cored blow blanks form the same guy you did :Sarcastic: I Use the exact same setup and process except I use the vacuum chuck drum with a neoprene seal. If anyone makes their own out of wood or PVC (Which is every bit as effective, )You can buy 5 packs of neoprene replacement seals for Oneway vacuum chucks pretty darned cheap. One generally lasts me a couple years.

http://www.woodturnerscatalog.com/p...m-Cylinder-Neoprene-Seal-5-Pack?term=neoprene


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## manbuckwal (May 19, 2015)

You certainly made it seem easy

Reactions: Thank You! 1


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## El Guapo (May 28, 2015)

Thanks for the thread... I have a bowl tat busted on me recently that would be perfect for turning into a jam chuck!


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