- The discussion started with jam chucks. One member talked about a bowl flying off the lathe twice when using a jam chuck. A wooden jam chuck had been turned to fit tightly to the bowl and stretch wrap was wrapped around the jaws and the top of the bowl. The problem occurred when removing the very center of the base of the bowl.
- Pictures were shown to compare a wooden jam chuck and a universal jam chuck with foam over the edges for a greater friction fit.
- It helps to keep the tail stock up as much as possible. One member has a ¼” diameter live center that lets him turn down to 1/8” before removing the nib.
- Another member suggested moving the tool rest up perpendicular to the bottom of the bowl as close as possible to keep it from flying off (after the tail stock is no longer helpful).
- One member showed a jam chuck called a “bullet chuck” since the cylinder end was shaped like a bullet. The rounded chuck (or a cone could also work) goes into the opening of a vase, bowl or cup. A new edge is shaped for the application each time so that it’s round and true. Don’t bring it in too tight or it will crack the project. The project may burn while in contact if it spins but leaves a nice line on the inner edge. After turning, the nubbin is taken off in a separate grinding process.
- The material that’s placed under rugs or used as shelf liner can be used as padding to give extra friction when supporting a piece. Check first since some brands leave an oily residue.
- With a jam chuck, use the tailstock for support as long as possible.
- Turn at a slower speed and use a sharp tool. Sand off the nub.
- A friction chuck is similar to a jam chuck. It’s tighter so the bowl snaps in. One paper towel can be used to make the friction tighter. (But only one…)
- A member has a One Way brand live center and said it’s a good investment. It does poke a hole in the wood.
- A small piece of wood can be placed between that point and the bowl to keep it supported but prevent a hole in the project.
- The point can be taken out of a live center but it’s harder to align. It takes a guesstimate and then looking for a wobble after turning on the lathe.
Cole Jaws or Jumbo Jaws
- We talked about using Cole jaws to support a small bowl with the rubber stoppers inside rather than outside the bowl. Longer screws could be used to bring the stoppers out away from the base plates if it would help to get it out farther. Would it be safe to use only 4 stoppers if that were all that would fit the area? It was agreed that four would be the least that could safely be used. The conical shape of the rubber stoppers helps connect with the wood. Be careful not to expand the jaws into the bowl too far or it will crack.
- Synthetic corks work well with a longer screw.
- The stoppers that come with the Cole jaws are only ½” tall. Some members have some that are 1 ½” or 2” tall that they have added. (Some came from Penn State or Amazon)
- The stoppers have to be adjusted just right. It takes several times to adjust and readjust the wing nuts so it’s not as easy as Cole jaws. “A lazy man works the hardest.”
- A website was given as a source for vacuum chucks. The company takes pumps that were used in the medical field that are no longer reliable (possibly from small clinics) and reconditions them to be used for woodturning. The Super Frugal II is unassembled while the Plug n Turn II is mostly assembled (around $300-400). (https://www.frugalvacuumchuck.com/home.html)
- Several members of the club have vacuum chucks and can mentor on using them.
- A caution is that you can feel air through the bottom if it’s too thin and some woods may be too porous.
- A tail stock should still be brought up for safety.
- It’s used primarily for finishing the bottom of a project. Choosing between a vacuum chuck and Cole jaws depends on the project, shape and type of wood.
- How to align it: 1) make a center mark on the bottom of the project and line up with the vacuum chuck. 2) True it with a board at 90° from the lathe bed to the bottom of the project. Check for roundness when turning on the lathe.
- The website given above has bearings and parts also if you want to make your own.
- It’s important that vacuum pumps be oilless to keep oil and moisture out of the lines and off of the wood. A filter is also important to keep sawdust out of the lines.
- Could it be used with green wood? Not sure, it might suck moisture and sap into the pump.
- There are articles on how to make your own vacuum pump and some of our members have made them with standard black plumbing parts, Trex, bearings, tubing, etc.
- Segmented projects can be used with a vacuum chuck since they are tight with no holes (some might have intentional holes…) Projects with insect holes or cracks cause a problem with vacuum chucks.
- The amount of vacuum is lower at high altitudes. A smaller diameter vacuum tube is not held as tight as one that’s 4 ½-5” diameter.
- There are two different styles. One has bearings in an adaptor in the chuck; one has the bearings in an attachment outside of the headstock.
- One member uses these when making finials. It’s used between centers with a tenon that’s clamped in the chuck by the gnarled clamps in the device. It has a taper inside that will tighten around the tenon. A small cup center (<1/4”) is used to hold the top of the finial.
- One member said it’s fun to make your own collets and use some Yankee ingenuity.
- It has a face plate connected to a ring to hold a bowl in place. The two members who’ve used them have only done so once. It would take a series of rings to make it worthwhile. Cole jaws are easier to use.
- The book Fixtures and Chucks for Woodturning by Doc Green (he has a PhD in physics) describes many chucks and has information on making and using them. The PAW library has a copy.
- If you’re a member of AAW, the article “The Basics of Workholding” can be found at this link: (https://higherlogicdownload.s3-external-1.amazonaws.com/WOODTURNER/020e63a0-bff2-8223-91db-56213f5dce74_file.pdf?AWSAccessKeyId=AKIAVRDO7IEREB57R7MT&Expires=1626296745&Signature=unFFb06Xj1x1rVE%2FXcU927IS0Ak%3D)