Click here for a PRINTABLE version of the above blueprint.

Over the years I have made and used a lot of different jam chucks. This blog entry documents the ones I like best. They are made out of good quality 3/4" plywood and PVC pipe couplings. They work good, are stable and vacuum tight.

My jam chucks are Drum Chucks that you can use with or with out vacuum.

I use my jam chucks to finish the bottom of bowls, vases, and hollow forms. I almost never, just part off a piece. I like to finish the bottom of my work with a nice smooth turned surface. I sign my name on the bottom and I want it to look good!

My jam chucks are stable. They do not warp when the weather changes because they are made out of plywood and PVC. Solid wood warps.

PVC pipe is water tight. Thus it is vacuum tight. Thus making a jam chuck that may be used in a "Vacuum Chuck System" out of PVC makes a lot of sense. The end grain in plywood is not vacuum tight, but it can be sealed. Plywood is more airtight than solid wood. Thus using plywood for the parts that need to be turned into a nice shape makes sense.

Faceplate

I like to use a permanently attached 3" steel or aluminum faceplate on my jam chucks.

There is NO WAY I would go with an expensive aluminum faceplate when I can get a really nice steel faceplate made by Nova from Home Depot for $34. See photo on right.

If you want to tap threads in wood. Go for it. I take my jam chucks on and off all the time. Wooden threads would not last long in my studio.

In my not so humble opinion. It is not worth screwing around with other solutions when a good steel faceplate is only $34.

PVC Couplings

I use 3", 4" and 6" PVC Couplings to make my Jam Chucks. They are Schedule DWV size (thickness).

You can easily get 3" or 4" PVC Couplings from your local Home Depot. The price is right. You may have to order 6" PVC Couplings from Home Depot with free shipping on 12/22. See photo on right.

I use PVC Coupling Fittings rather than a piece of PVC pipe to avoid the expense of purchasing a long piece of pipe.

The thickness of PVC pipe and fittings is determined by there "Schedule". The thin stuff is thick enough for Jam Chucks. Thus you can use any "Schedule" of PVC pipe.

The dimensions in my blueprint are based on "Schedule DWV" PVC Fittings from Home Depot in Wappingers Falls, NY on 12/2022.

You should measure your PVC Fittings and/or Pipe and adjust the dimensions in my blueprint to match what you have!

Note: "Schedule 40" has been around for along time. It is used in household plumbing. "Schedule DWV" is like "Schedule 40". Same OD and ID. DWV is lower quality PVC. 40 can handle pressure. DWV is not for pressure.

Rough Cut Plywood

I recommend the use of 3/4" good quality 7 layer plywood. See my "Good Quality Plywood" blog entry.

Rough cut the plywood a 1/2" larger than the required finished size. This will leave plenty of room for centering and truing up losses.

You need 3 pieces of plywood. One for the faceplate side and two for the working side.

Mark the center on plywood. Draw circle for faceplate on one piece. Draw the "inside" and "outside" circles on another piece. The "y" and "z" circles from the table on my blueprint. i.e. 3-1/4" and 5-1/2" for "Small" jam chuck.

Glue Up Plywood

I make the working side of my jam chucks out of 2 layers of 3/4" plywood glued together to make a 1-1/2" thick piece of plywood. You need 1-1/2" of thickness to make a nice long gentle curve on the inside of the jam chuck. See my blueprint.

I glue the plywood together with "Titebound II" yellow wood glue. Spread it out with scrap of wood or cardboard. More is better than not enough.

Clamp Plywood

I put the plywood together and move it back and forth a little to spread and set the glue. Then I put a drywall screw in the middle to prevent movement while clamping.

Use lots of clamps. I use at least 8 clamps. 4 on the sides and 4 on the corners. The "inside" and "outside" circles I drew earlier tell me where I need to focus the clamping pressure.

There should be lots of glue squeeze out.

Mark Circle for Groove on Working Side

I start by turning the Working Side first. This allows me to kill two birds with one faceplate.

After the glue is dry. Rough cut outside circular shape. Then attach plywood to faceplate and mount it on lathe.

Mark the true dead center with the lathe running. Then, PRECISELY draw a circle on the plywood that matches the OUTSIDE diameter of your PVC coupling. Red arrow in photo on right. Draw the circle with the lathe running so it ends up being true.

DOUBLE CHECK your circle by holding PVC coupling up to the circle after you draw it.

Note: The photo on the right leaves a lot to desire. You can not see the faceplate. I did not hold up a PVC pipe near the circle. I have those ugly confusing screw holes in there because I screwed up and mounted the faceplate on the wrong side.

Cut Groove on Working Side

Cut a groove with a parting tool that matches the outside and inside diameter of your PVC coupling.

Make it just 1/8" deep. Like in photo. TEST FIT your PVC coupling. It should be snug, but not to tight. You need room for glue.

Make it 1/4" deep AFTER you adjust it to be the right size.

Remove it from faceplate. It is time to back up and work on the faceplate side.

Note: We will come back latter and turn a nice shape on the outside of the working side and remove the middle. This should be done AFTER everything is glued together so it runs as "true" as possible. See "Turn Working Side Shape" below.

Seal Faceplate

If you want to use your jam chuck in a "Vacuum Chuck System" then the joint between the faceplate MUST be airtight.

If you don't have a Vacuum Chuck System today then you can skip this step. But, then you will be sorry if you get a Vacuum System latter.

Over the years I have tried all kinds of things to seal this joint. Calk works, but it may dry up and crack. Plumber's Putty works good and is not to messy.

Start with a golf ball size lump of Plumber's Putty. Roll it out on a flat surface (table saw table) with the ball of your hand, into a long pencil shape. Then install it on your faceplate. See photo on right.

Note: Anything that is airtight is vacuum tight. Anything that is watertight is airtight.

Attach Faceplate to Faceplate Side

Attache the Faceplate with SHEET METAL screws. I use #10 screws that are 1-1/2" long. Yea, they are a little to long. The points just barely stick thru. I sand them off with some 80 grit sandpaper.

There should be lots of Plumbers Putty squeeze out. The faceplate should be almost flush tight against the plywood.

You can see in the photo that I drilled 4 more holes in the Nova faceplate. I like at least 6 holes. Nova faceplates only come with 4 holes. Drilling 4 more is the best solution if you want them evenly spaced.

Note: I believe, if you are going to do a job, then do it right. Lots of long screws.

Drill & SEAL Center Hole

If you want to use your jam chuck in a Vacuum Chuck System then you need a center hole that is AIRTIGHT. If the hole is not airtight then you will lose vacuum when it is pulled thru the end grain layers of plywood.

I have found the easiest solution is to drill a 5/8" hole in the center of the plywood with the lathe running. Then install a 1" long piece of 1/2" CPVC pipe in the hole with 5 minute epoxy.

BEWARE! 1/2" CPVC is 5/8" (0.625") OD. It is Almond color. 1/2" PVC is 0.840" OD. It will not fit in a 5/8" hole. It will fit loosely in a 7/8" hole. I use a scrap piece of what ever pipe I have. I drill a TEST HOLE in SCRAP WOOD.

Note: All of this sealing of things for Vacuum Chuck System is a pain in the back side. I would not be doing it, if not REALLY necessary. I have learned the hard way it is necessary.

Cut Groove on Faceplate Side

Cut a groove on the faceplate side that matches your PVC Coupling. Same procedure as above.

See "Mark Circle for Groove on Working Side" and "Cut Groove on Working Side" above.

Seal Faceplate Plywood

I seal the faceplate plywood with any extra epoxy, I have left over in the last step.

This is necessary if you want to use your jam chuck in a Vacuum Chuck System. You only need to seal the plywood on the inside of PVC fitting.

If you don't have any left over epoxy. You can skip the is step now and seal it with paint latter. See "Seal the Plywood" below.

Clamp It Overnight

I glue and clamp ONE SIDE at a time. This way I don't end up with glue all over the place.

In this photo the Working Side is in place to make clamping easy. I will glue it on latter.

Cut PVC to Length & True Up

If you are using a 3" or 4" PVC Coupling you can skip this step. The factory length is good.

If you are using a 6" PVC Coupling they are typically 6-1/4" long. If you leave them 6-1/4" long then they make a jam chuck that is to long. In my blueprint. I recommend making them 5". Thus you have to cut the PVC coupling and true it up.

BEWARE! Turning PVC is VERY DANGEROUS! It likes to catch and grab your tools. Be very careful!

I have found the best method is to glue the PVC to the faceplate side then cut it with a parting tool on the lathe.

Use the tailstock and working side plywood with groove to jam the PVC between centers.

Then cut a groove with a parting tool. DANGER! DANGER! DANGER! DO NOT GO ALL THE WAY THRU! Stop before you go all the way thru the PVC. Cut the PVC off with a hand saw with the LATHE STOPPED!!!

Bring the tool rest in close across the end of the PVC. Use a scrapper with a VERY LIGHT CUT to true up the cut side.

Cutting PVC pipe on a band saw is a GREAT way to CUT YOUR FINGERS OFF! I do not recommend it. The PVC grabs, pulls to the side and pulls your fingers into the saw!

Inside Shape

This photo shows the finished inside jam chuck shape.

You can see in the photo that you can get nice tight looking end grain on plywood IF you sand it aggressively.

I start with 80 grit Red Siasoft sandpaper. Then 120 Siasoft. I just hold the Siasoft up to the plywood while lathe is spinning.

Then I power sand with 180 and 220 grit Blue Flex Sanding Disks.

The brand of sandpaper here is a don't care. Use what you known and love. 80, 120, 180 and 220 grits.

Note: Check out my "Sanding Cheat Sheet" if you don't have a something you love.

Outside Shape

This photo shows the finished outside jam chuck shape.

I round over all edges on everything in my studio. No sharp edges to cut me.

Seal the Chalk Paint

I made a beautiful white chuck and then realized I was screwed. All white, would not work in photos. Thus, I decided to pain the plywood parts with Yellow Chroma Craft Wood Dye over the chalk paint.

You can skip the color and sealing if you want.

Chalk paint dries flat with a sort of open porous surface. I sealed it with two clear coats of Miniwax brand polyurethane. Any brand will work.

The jam chuck is mostly all done now. We just need to add some foam in next step.

Purchase Foam

You can use 1/8" Craft Foam from local craft store with or without adhesive back. If no adhesive then you just jam it in there. I like foam with an adhesive back better. You don't have to round it up. It lasts for a while. But, eventually you have to replace it.

I ran out of foam during the Pandemic. I had to purchase a roll of 1/8" thick neoprene rubber sheet with adhesive back from Amazon. I like it better than craft foam. It is a little softer than the craft foam, but not to soft. Finding wide stuff is easy. It costs less, because there is less scrap. See photo on right.

Green bowls warp while drying. When dry you often need more than 1/8" thick foam to deal with the warp. I add a layer of 1/4" thick neoprene foam on top of the 1/8" stuff. I cut a doughnut of foam and jam it between things. No adhesive. If 1/4" is not thick enough. Then add 2 layers of 1/4" thick foam. See photo on right for 1/4" foam.

Note: You can purchase really good quality neoprene rubber foam from McMaster, etc. It has a textured surface like a wet suit. It is really tough and will last forever. This IS NOT what you want here. The cheap, softer stuff from Amazon with a smooth surface works better.

Measure Foam Doughnut Outside Diameter

I use to just guesstimate the outside diameter of foam doughnut. I now measure it with a soft ruler. The kind they using for sewing clothes. They sell "Clothes Measuring Tape" in fabric stores.

The foam should wrap around the sides. See photo on right.

Cut Foam

Use a compass to layout a doughnut shape. Then cut it out with scissors.

Install Foam

Getting the jam chuck centered on the foam can be tricky.

I remove the paper backing on the foam and then lower the chuck onto the foam. See photo on right.

Tape Outside Edge of Foam

The foam lasts longer if you tape down the outside edge.

I use "3m Scotch #600 1" Wide Transparent Tape". See photo on right.

The Inside Edge of Foam

Taping down the inside edge is like impossible. I cut a scrap disk of 1/4" plywood that I use to hold down the foam when the chuck is not in use. After a while, the foam gets the idea and stays in place on it's own. See photo on right.

The 1" hole in the disk is a finger hole. I use it when removing the disk.

The tears in the foam visible in the photo suck. That is the way life goes on my small chuck. They are ok. Most of the surface is covered with foam. It will work ok.

The foam does not tear on my medium and large size chucks.

Note: Oneway ships their Drum Chucks with a fancy lid that holds the foam in place and makes it confirm to drum chuck shape. Making one of those is not worth my time.