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.
My jam chuck shape is based on the Oneway Drum Chuck shape. Long ago, I made an exact copy of the Oneway chucks in
wood. I used them for a while. I quickly gave up on them for hollow forms. Because the straight
walls on the inside of the Oneway shape only works on a very limited range of hollow form diameters
If a vase or hollow form drops between the inside walls of a drum chuck it is no good. I redesigned the Oneway chucks to come up with my jam chucks. The inside wall shape on my jam chucks tappers in over a long distance. Thus they work on more hollow form diameters and shapes.
People will not agree with me. Thus, I am not going to waste time debunking other methods used to finish the bottom of pieces. Cole Jaws, Longworth Chucks, etc. All I am going to say is they don't work for me. Often because the walls on my bowls are 3/16" thick and will flex to much on Cole Jaws, etc. How do you mount a live edge bowl or vase on Cole Jaws? If they work for you then great. Go for it.
Jam Chuck Size
One size does NOT fit all when it comes to jam chucks! You need a jam chuck that is a "Good"
fit to avoid trouble! See above drawing.
If a jam chuck is to big, you can crack the wall of a thin walled bowl with to much cutting and/or vacuum pressure. The walls of a thin walled bowl will flex to much. You may not be able to cut it cleanly and it may shatter.
If a jam chuck is to small, your work may slip on the jam chuck. If work slides on a jam chuck for just a FRACTION of a second it will break the vacuum and ALL HELL may break lose. The work comes flying off the lathe!
The outside dimensions of my "small", "medium", and "large" jam chucks are 5-1/2", 7-1/4", and
9-1/4". If you are just making bowls, then they are probably all you need. If you are making vases
and hollow forms then they are just a good starting point. I have several variations of my "medium"
size chuck with different inside dimensions for vases.
Oneway makes 3-1/2", 5-1/2", 8", and 12" Drum Chucks. Hold Fast makes 3-1/2", 6", and 8" Vacuum Chuck Heads.
Note: There will be people who disagree with me here. They will tell me: I only have one jam chuck size. I use a jam chuck that is to small all the time, etc. All, I can say is I hope I am wrong. Because, I think they have just been lucky. Sooner or latter all hell is going to break lose and I hope they are not seriously injured.
Make Your Own
The photos in this section show the making of the "Small" jam chuck on my blueprint drawings. It is based on a 3" PVC Coupling.
Most people would probably be better off making the "Medium" size one first. It is based on a 4" PVC Coupling. Then make the "Small" and "Large" ones as needed. I find that the "Medium" size one is the most useful.
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.
I use 3", 4" and 6" PVC Couplings to make my Jam Chucks. They are Schedule DWV size
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.
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.
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.
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.
Rough Turn Working Side
I start by turning the Working Side first. This allows me to kill two birds with one
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 a groove with a parting tool that matches the outside and inside diameter of your PVC
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.
Turn Faceplate Side
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.
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
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.
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.
Glue Faceplate Side
You need to use some type of epoxy to glue plywood to PVC. You can use hardware store epoxy if
I recommend good quality West System G/Flex 650 Epoxy. It is designed for an application like this. Designed for bonding PVC, metals, etc to wood.
G/Flex is thick like 5 minute epoxy so you don't have to deal with thin epoxy running all over the place. It sets up in 75 minutes. Cures in 3 hours. Two 4 oz bottles (4 oz of resin + 4 oz of hardener) of G/Flex cost around $20 on 12/4/2022.
Mix up the G/Flex. Prime the wood and PVC with G/Flex applied with an acid brush. Then fill the groove up about half way with G/Flex. Insert the PVC coupling and twist it back and forth a little.
There should be lots of squeeze out. I make a nice glue fillet out of the squeeze out with my finger. Fillets make epoxy joints a lot stronger. See red arrow in photo.
If you have left over epoxy see next step.
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.
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.
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!
Glue Working Side
Spin, Rinse and Repeat the above process to glue the Working Side onto the PVC Coupling.
See "Glue Faceplate Side" above.
Turn Working Side Shape
Mount the jam chuck on lathe and turn a nice shape on the working side. I use a 1/2" bowl
gouge. Plywood dulls your tools quickly. Sharpen early and often.
Leave room to AGGRESSIVELY sand in next step. At least 1/8" larger than finished size.
I recommend a 1/2" round over shape on the outside. This works good on cut edge or live edge bowls. See my blueprint.
I recommend turning the inside like it is a bowl. Take it out by starting from the center and work your way out towards the outside. DO NOT go all the way thru until AFTER you have removed most of the center.
I STRONGLY RECOMMEND you DO NOT part the center out and save it for something else. It is tempting. But, it can be very dangerous when you part thru. All hell can break lose. Then, you find that you don't really have a good use for the center. The risk is not worth the savings.
On the inside you need a shape that works good on vases or hollow forms. I have found that a long gentle round over shape works best. It works on more hollow form shapes and sizes. See my blueprint.
Note: My jam chuck shape is based on the Oneway Drum Chuck shape. Long ago, I made an exact copy of the Oneway chucks in wood. I used them for a while. I quickly gave up on them for hollow forms. Because the straight walls on the inside of the Oneway shape only works on a very limited range of hollow form diameters and shapes. If a hollow forms drops between the inside walls of a drum chuck it is no good. I redesigned the Oneway chucks to come up with my jam chucks. The inside wall shape on my jam chucks tappers in over a long distance. Thus they work on more hollow form outside diameters and shapes.
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.
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 Plywood
I like to make my jam chucks look pretty. Why live with ugly crap day after day?
If you want to use your jam chuck in a Vacuum Chuck System then you need to seal all plywood. You can easily pull a vacuum thru the end grain on plywood.
Over the years I have sealed the plywood with all kinds of things. Bondo, clear poly, milk paint, etc. Clear poly looks good.
My current passion is Chalk Paint. It dries fast and easy to use. I used "Folk Art Home Decor Chalk" paint. See photo.
I spread on a thick coat of chalk paint with a paint brush, with lathe stopped. Then dip the brush in a little water. Turn the lathe on SLOW and spread the paint out with wet brush. Add water as needed.
If you add to much water you will get a face full of paint! If it hurts when you go like that, then don't go like that!
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
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.
You will screw up a finished piece of wood if you just jam it against another piece of wood.
You will scratch it, etc. Thus, you must install a piece of foam between the two to avoid making a
mess. A doughnut shaped piece of foam works good. See photo on right.
When I was learning to turn, I was taught to use a thick piece of soft foam. This did not work well for me. My piece moved around to much on the jam chuck. It was very frustrating. I could not get a clean cut, etc.
I now use a 1/8" thick piece of firm foam. Like they use on the Oneway Drum Chucks.
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.
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.
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.
The foam lasts longer if you tape down the outside edge.
I use "3m Scotch #600 1" Wide Transparent Tape". See photo on right.
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.
Smaller Jam Chucks
I make smaller jam chucks as needed out of solid wood. See photo above.
I wrap small jam chucks with shrink wrap plastic if I need to make them airtight for "Vacuum Chuck System". However, vacuum does not work well on small things! Not enough surface area.
Larger Jam Chucks
My "large" jam chuck has a 9-1/4" outside diameter. See my blueprint. I really don't see any need to go larger than this for bowls. Big
bowls will still work on the outside of this chuck.
You may need a larger jam chuck if you want to mount a hollow form on the inside. The inside diameter of my "large" chuck is only 6-1/4". HOWEVER, this does not mean it is limited to hollow forms with an outside diameter of 6-1/4". You can mount larger hollow forms on this chuck. How big is hard to say. It depends on the hollow form shape. See page 2 of my blueprint.
I have used 8" PVC Sewer & Drain pipe to make larger jam chucks. See purple chuck in above photo. The inside diameter of chuck is 7-3/4".
Starting at 8", most PVC pipe is "Sewer & Drain" rather than "Schedule 40". The pipe comes with a built in bell coupling on one end. You can not get (or afford) 8" PVC stand-a-lone coupling fittings. Purchasing 20' of pipe to get 8" is not practical. Thus you need to find a scrap at a road construction site or what ever. Thus you are on your own.
I am not a big fan of "Hollow Form Mandrel Chucks" but they are probably the way you need to go for really big hollow forms. See next section.
Note: Oneway makes a 12" Drum Chuck. Think big bucks!
Hollow Form Mandrel Chuck
I known some people use these all the time. I am not a big fan of them. They can be tricky.
The piece can come lose. There is no access to the ENTIRE bottom for sanding and painting.
The bottoms of my vases are OFTEN painted gold with a nice swirl in the middle.
Solid Wood Jam Chuck
A solid wood jam chuck mounted in a 4 jaw chuck is a good quick solution for bowls.
They DO NOT work in a "Vacuum Chuck System". Four jaw chucks are NOT vacuum tight. Air leaks between the jaws, etc.
You can not mount a vase or hollow form in a solid wood chuck. Well, ok. If you screw around with shape, maybe you can. But, they don't work in the "classic" shape show in books, on the web, etc.
Note: There was a good "Universal Jam Chuck" article in Issue 78 of Woodcraft Magazine written by Michael Kehs. It is available on the web. Google "Woodcraft Magazine Universal Jam Chuck".
Tailstock Jam Chuck
Time for some radical ideas. But, they are only radical because you have not seem them before.
I turn the INSIDE of my green bowls FIRST. I then turn the outside to match the inside. Why? Because it is EASIER!
You can push out hard with your bowl gouge on the inside and get a nice clean cut. The thick outer walls support the cut. No problems with thin walls vibrating. Aggressively sanding the outside of a bowl is easy. Sanding the inside is harder. Thus, getting a nice clean cut on the inside is more important than the outside. Thus you should TURN THE INSIDE FIRST!
I install a jam chuck on the inside of the bowl after it is finished. This allows me to turn the outside of a thin wall bowl with less vibration problems.
I install the jam chuck on my tailstock via the "Oneway Live Center Adapter".
I strongly recommend installing a set screw in your jam chuck. Because, it is going to be running in reverse and can unscrew off of your tailstock. ALWAYS make sure the jam chuck is in CONTACT with the wood on the headstock side BEFORE starting the lathe!
Why do you turn the outside of your bowls first? Because that is what you see in demos? Dare to think outside of the box! There is more than one way to skin a cat.
Turing the outside SHAPE first and getting the SHAPE right is easier for beginners. This is probably why you see outside first in demos. But, after you get a little experience, I think INSIDE first makes more sense.