Memory foam to make a jam chuck

[Brian Deakin]

I would like to make a jam chuck using memory foam

Can anyone advise how I can cut the memory foam to form a dome shape similar to the one in the link below shown at 5 minutes 54 seconds

https://www.youtube.com/watch?v=qeAUp4rbeqk&t=353s

[Marvin Hasenak]

Glue up a stack of EVA foam and turn to shape with a sharp round nose chisel.

[Brice Rogers]

On the video, the foam looks like it is wrapped around a wooden form.

I use the medium density foam (rubber) from Harbor Freight. It is the stuff used for shop mats to stand on. It is about 1/2" (1.2 cm) thick. I usually cut it with a pair of metal snips. But a scissors kind of works too.

On my vacuum chuck I use the 1/8" or 1/4" craft foam (Hobby Lobby or Michael's). That stuff cuts easily with a scissors.

While neither of these foam items might technically be a "memory foam", they do take somewhat of a "set" over time from pressure.

I've used both products in conjunction with a jam chuck to avoid marring a piece. But since I put together a vacuum chuck system, I typically will use that instead for removing a tenon, or touching up a mortise.

[Don Jarvie]

I have a Jimmy Clewes dyed bowl that didn’t come out so well and use it with foam kitchen draw liners as a jam chuck. Since the bowl has an arc to it it can be used for up to 8 inch wide bowls.

[Michael Mills]

It worked there but I would suggest not making it dome shaped. Unless it fits the bowl perfectly you may only have about 1/2 sq inch of contact in the center and it is easy to wobble.
Instead make the end flat or slightly concave. Round the outside corners. I have several of different diameters and try to be just a little over the diameter of the base. It will self center in the bowl (using the divot in your tenon or recess with the tailstock) and provide friction around the entire circumference of the drive. Having it fairly close to the base diameter means the bowl will be supported just under where you are cutting. So with a 3.5" foot I may use a 4" inside or for a 6" foot on a large bowl a 6-7" inside.

A thinner but good gripping material is what I would suggest also. Is the memory foam like some beds are made from? If so you may have to apply a lot of pressure from the tailstock to compress it enough to keep it from slipping, possibly enough to crack the bottom of the bowl.

The stuff which goes under throw rugs to keep them from slipping on a hardwood floor works well and is cheap at Kmart. Probably a lifetime supply for $10.
The rubber thingies in the kitchen to help remove jar lids (bumpy side to the wood) works well also. Usually 3 for $1 at Dollar Tree.
An old mouse pad, desk side to the wood works great... about the right thickness and tremendous friction.

You want (IMHO) the highest friction with the least compression. You can keep one piece to throw over one each time but for the price... just wrap each around and hot glue it on the side for each drive. If it does get torn up some time just turn the hot glue loose and glue on a new one.

[Thomas Canfield]

Following Michael's post, I usually use a jam chuck made from construction 2x material with tenon and the face turned to provide a contact ring about 1/3 of bowl diameter. I also usually use the mesh rubber shelf liner from $ store and sometimes will go double thickness but no glue. The tool finish surface provides holding for the liner against the jam and tailstock pressure provides drive ability to the bowl. Simple and fast easily adjusted as required with no cost using scrap.

[Brian Deakin]

A huge thank you for your replies and suggestions

I found another approach in the video below( 1 hour 19 minutes to 1 hour 47 minutes ) which is probably the ideal solution

https://www.youtube.com/watch?v=N7BjRcSDurM&t=678s

[Bill Blasic]

I use 5" foam backed sandpaper with the foam side against the chuck and the particulate side against the piece.

[John K Jordan]

I would like to make a jam chuck using memory foam

Can anyone advise how I can cut the memory foam to form a dome shape similar to the one in the link below shown at 5 minutes 54 seconds
https://www.youtube.com/watch?v=qeAUp4rbeqk&t=353s

I don't know what memory foam is I've done that several times: turn a jam piece from wood to almost fit the inside then use a thin piece of closed-cell foam between the jam form and the inside of the bowl. I use the tailstock to support as long as needed then either finish the center nub by hand or on the lathe after first taping the piece to the chuck.

BTW, I just skimmed through a bit of Batty's video so I didn't catch what kind of tape he used, if he even mentioned it. I use a green tape that looks like that but it's nothing like the green painters tape from the hardware store. I use the 3M/Scotch Masking Tape for Hard-to-Stick Surfaces: https://www.amazon.com/gp/product/B000LNYE4E and https://www.amazon.com/gp/product/B00004Z4AY This stuff sticks FAR better than the painter's tape. Maybe Stuart is using the same stuff but it looked like his came off too easy.

JKJ

[robert baccus]

Over the years I have turned and used many types of jam chucks. One I find very useful is a mere tenon/glueblock of 3-4" in dia. faces with 180 to 60 grit sandpaper, depending on the finish or coarseness of the piece. Even a piece with a finished bottom can be grabbed and rebuffed easily. Easy does it with the cutting tool naturally.