Jam chuck burns my bowls

[Raif Harik]

Hi, I have had several situations where I have a jam chuck that messes up my project. I'm basically using just a cylinder of wood that I put in the chuck then put against the inside of the bowl sometimes/most times with a paper towel in between. Bring the tail stock in and that holds it in place while I turn off a tenon. However, some of the time, or most of the time, when I take it off there's a black ring where the block was touching the bowl. Sometimes I get a catch and it stalls the bowl while the block keeps turning. Some times I don't and I still get it. One solution would be to just tighten up the tailstock till it can't turn, but I fear putting a dent in the bowl. It may be the case that the solution is to find the right pressure and never get a catch, which would be a crappy solution but I get it. I guess I'm wondering how others do it, and if others have experienced this and over come it.
Thanks,
Raif

 

[Lyle Jamieson]

Hi, I have had several situations where I have a jam chuck that messes up my project. I'm basically using just a cylinder of wood that I put in the chuck then put against the inside of the bowl sometimes/most times with a paper towel in between. Bring the tail stock in and that holds it in place while I turn off a tenon. However, some of the time, or most of the time, when I take it off there's a black ring where the block was touching the bowl. Sometimes I get a catch and it stalls the bowl while the block keeps turning. Some times I don't and I still get it. One solution would be to just tighten up the tailstock till it can't turn, but I fear putting a dent in the bowl. It may be the case that the solution is to find the right pressure and never get a catch, which would be a crappy solution but I get it. I guess I'm wondering how others do it, and if others have experienced this and over come it.
Thanks,
Raif

Hi Raif,
I use a friction drive reverse chucking method on EVERY piece I turn. The use of a chuck is the first thing that could contribute to marks in your bowls. If you want to use a chuck make sure to true up the mating surface every time. The chuck will not put it the waste wood on running true and that wobble would leave a mark. With the blank running true now, just use a thicker padding element and tighten the tailstock down tight. Lock the spindle and try to turn the wood by hand. Cant move it?? good to go!! I suggest you get some help from your local club members and figure out what causes catches. We never need to get catches. Catches are not fun and not safe. That is not a crappy solution. You have your own solution. Eliminate that fear of catches and turning becomes a lot more fun. I have a ton of resources that will eliminate catches for you. Wish you all in AAW land a Happy and Prosperous and Healthy New Year.

 

[Raif Harik]

Hi Raif,
I use a friction drive reverse chucking method on EVERY piece I turn. The use of a chuck is the first thing that could contribute to marks in your bowls. If you want to use a chuck make sure to true up the mating surface every time. The chuck will not put it the waste wood on running true and that wobble would leave a mark. With the blank running true now, just use a thicker padding element and tighten the tailstock down tight. Lock the spindle and try to turn the wood by hand. Cant move it?? good to go!! I suggest you get some help from your local club members and figure out what causes catches. We never need to get catches. Catches are not fun and not safe. That is not a crappy solution. You have your own solution. Eliminate that fear of catches and turning becomes a lot more fun. I have a ton of resources that will eliminate catches for you. Wish you all in AAW land a Happy and Prosperous and Healthy New Year.

Hi, Thanks for the response.

So I do true up the the block every time.

I like your suggestion, maybe something like leather? I was using a mouse pad but that was getting burned in with molten plastic which was even worse. So If I use something like a leather pad, and I just clamp the heck out of it with the tailstock that should be ok?

Re catches, yes, I know I shouldn't but when I'm turning off waste wood sometimes I get too aggressive or don't pay as much attention, or maybe it's just kind of a weird angle and I don't approach it right. All user error I know. I don't get catches when I'm turning in general, it's mostly just when I'm finishing up the bottom. I'm probably too fired a that point and should turn off the bottom the next day, but I get excited to be done and just keep pushing. Lot's of issues. I know.

Good to hear you do it every time, that gives me confidence it can be done. Do you have any tips on how to get it centered? I always struggle with that too, and just get it close, figuring it's just the bottom.

Thanks,
R

 

[Jim McLain]

Hi, Thanks for the response.

So I do true up the the block every time.

I like your suggestion, maybe something like leather? I was using a mouse pad but that was getting burned in with molten plastic which was even worse. So If I use something like a leather pad, and I just clamp the heck out of it with the tailstock that should be ok?

Re catches, yes, I know I shouldn't but when I'm turning off waste wood sometimes I get too aggressive or don't pay as much attention, or maybe it's just kind of a weird angle and I don't approach it right. All user error I know. I don't get catches when I'm turning in general, it's mostly just when I'm finishing up the bottom. I'm probably too fired a that point and should turn off the bottom the next day, but I get excited to be done and just keep pushing. Lot's of issues. I know.

Good to hear you do it every time, that gives me confidence it can be done. Do you have any tips on how to get it centered? I always struggle with that too, and just get it close, figuring it's just the bottom.

Thanks,
R

Leather should work fine. I use tanned deer hide and it works great.

 

[Lyle Jamieson]

Hi, Thanks for the response.

So I do true up the the block every time.

I like your suggestion, maybe something like leather? I was using a mouse pad but that was getting burned in with molten plastic which was even worse. So If I use something like a leather pad, and I just clamp the heck out of it with the tailstock that should be ok?

Re catches, yes, I know I shouldn't but when I'm turning off waste wood sometimes I get too aggressive or don't pay as much attention, or maybe it's just kind of a weird angle and I don't approach it right. All user error I know. I don't get catches when I'm turning in general, it's mostly just when I'm finishing up the bottom. I'm probably too fired a that point and should turn off the bottom the next day, but I get excited to be done and just keep pushing. Lot's of issues. I know.

Good to hear you do it every time, that gives me confidence it can be done. Do you have any tips on how to get it centered? I always struggle with that too, and just get it close, figuring it's just the bottom.

Thanks,
R

I have used a leather pad with paper towel backing to prevent the wet wood from getting color from the leather on the wood. Don't have to get perfectly centered. I turn the outside wall completely before reversing. Now we are just working on the bottom and never need to transition into the sidewall. I start and end everything I do between centers so the pin center hole is is still there when I reverse them.

 

[hockenbery]

like your suggestion, maybe something like leather? I was using a mouse pad but that was getting burned in with molten plastic which was even worse. So If I use something like a leather pad, and I just clamp the heck out of it with the tailstock that should be ok?

When i true up the jamb chuck I always round over the rim of the friction chuck to eliminate sharp edges.
I paper towel folded with even layers or use thin foam like 1/8” thick fun foam.
I use a 4” friction drive for most all the bowls

I use steady pressure to tighten securely.

Then light cuts sharp tool. I use the bowl gouge and a 3/8 spindle gouge.

Very important is having the tool rest high enough so my spindle gouge can’t run under the nub.

 

[Tom Gall]

Raif, not sure what your jam/friction chuck/block looks like. Maybe try one or both of the following ideas in addition to your cushioning material.
1. Round over the edge of your cylinder and make a slightly concave center - so only the rounded or radiused edge touches the surface.
2. Make the cylinder much larger (depending on the size of your project). This provides more friction area and less tailstock pressure is needed.
OR - invest in a vacuum chucking system!

 

[Mike Zip Hamilton]

I'm guessing that you are getting catches on that tenon from failing to support your cutting edge. Make sure that you are getting bevel support.

 

[Richard Coers]

Use a spindle gouge to remove the tenon. Dampening the end of the friction block will help on the fresh face of the wood block, but most importantly, don't have the center of the block touching the bowl.

 

[Don Stephan]

A few years ago I made jam chucks for each of my four jaw chuck jaw sets. For example, assume the minimum tenon clamp diameter of one set of jaws is 4”. I band sawed a ¾” thick plywood disc 5” in diameter. In the center of the disc I drilled a pilot hole and mounted it on a screw faceplate, trued the face flat, turned a 4 ¼” diameter tenon ¼” long, and trued the remainder to the maximum diameter.

Next I used a knife to cut a 6” disc in ¾” thick high density insulating foam. Using Titebond on hand I glued the form disc to the side of the plywood disc opposite the tenon. After a couple hours I clamped the plywood tenon in the four jaw chuck and with very light spindle gouge cuts turned the foam disc round and rounded over the top edge of the form disc.

Then I repeated the process with perhaps a 7” diameter ¾” thick plywood disc and an 8” diameter foam disc.

Because I make once turned bowls, I cannot sand with the bowl rotating. I will clamp the bottom tenon of the bowl in the four jaw chuck and power sand, in stages, the inside with the first grit, whichever is appropriate. Then I will unclamp the bowl, clamp one of my foam jam chucks without having to change jaws, position the inside of the bowl over the jam chuck, bring up the live center pin in the mark made when the tenon was being shaped, lock the tailstock in place and advance the tailstock ram to apply pressure through the bowl onto the jam chuck. I chose the largest diameter foam jam chuck, for that jaw set, that would fit in the bowl, for stability. I power sand the outside of the bowl, in stages, with the same grit used on the inside, then power sand the outside, in stages, with the next grit. Then I’ll flip the bowl and power sand the inside of the bowl, in stages, with the next two grits, and so on.

After the bowl is sanded to 220 inside and out, I’ll turn off the tenon, again using the foam jam chuck. I’ve done this for a number of years and can’t recall ever having the sanded interior of the bowl damaged by the foam while turning off the tenon.

I have 2 or 3 different diameter foam discs for each set of jaws. I’ve used them for years and haven’t realized any damage to the inside surface of my wooden bowls.

A 4’ x 8’ 2” thick sheet of high density form 10 years ago was about $35, and likely is more now. And a 4’ x 8’ sheet would make a whole bunch of these jam chucks. Partner with some others in the local turning group to same some money.

 

[Don Wattenhofer]

Hi, I have had several situations where I have a jam chuck that messes up my project. I'm basically using just a cylinder of wood that I put in the chuck then put against the inside of the bowl sometimes/most times with a paper towel in between. Bring the tail stock in and that holds it in place while I turn off a tenon. However, some of the time, or most of the time, when I take it off there's a black ring where the block was touching the bowl. Sometimes I get a catch and it stalls the bowl while the block keeps turning. Some times I don't and I still get it. One solution would be to just tighten up the tailstock till it can't turn, but I fear putting a dent in the bowl. It may be the case that the solution is to find the right pressure and never get a catch, which would be a crappy solution but I get it. I guess I'm wondering how others do it, and if others have experienced this and over come it.
Thanks,
Raif

The end of the wood cylinder should be turned to match the contour of the bowl such. I keep several blocks of basswood that I mount to the chuck with the wood worm screw then I can adjust the outside contour of the jam chuck to match the inside of the bowl. Note: the basswood I am using is low grade milled from locally grown basswood trees but of course I live on "Big Basswood Lake".

 

[Randy Anderson]

The black rubber mesh mat stuff you can buy in a roll used to line drawers with works well for me. A folded paper towel between the rubber mesh and the bowl keeps it from marking or staining the surface should it slip. I always take some 400 on my angle sander and go over the bottom of the bowl when done and before I add finish. If you look close you likely will see a burnished or shiny area where the jam chuck was pressing on the bowl. The paper towel will "polish" it a bit. Easy to get rid of. Never had one burn. As other have said, rounded edge on your jam chuck and slightly concave works well for me. I only have a couple and use the same ones on all my bowls. I tighten until it won't spin without a lot of effort and it doesn't wobble side to side. No more.

 

[Roger Wiegand]

Leather (undyed) on wood works well for me. I've also used a silicone hot pad on the bare chuck (no wood) and had no problems, except that after a while the edges of the chuck cut the pad. It's very quick and convenient though!

 

[Dave Landers]

From your original post, it sounds like you may be burning a ring in the bowl. When it slips, it'll generate friction and heat and leave a burned ring. Or will transfer some of your padding (like rubber from a mouse pad etc) onto/into the bowl.
As others have suggested: make the contact point wider is the first step - if your friction chuck is just contacting on a corner, round it off so it more closely matches the bowl contour so there's more in contact with the bowl. And then adding something in between - maybe just a paper towel, or maybe some 1/8" fun foam (white is my usual choice) or mouse pad or leather etc. You are either going for padding or grip or both (basically experiment and see what works best for you).
Even when the bowl doesn't slip and burn, you might still get a burnished ring (not burned, just burnished compressed fibers). Finding the balance of tailstock pressure is a bit of an art - too much and you're compressing those fibers, too little and it doesn't hold. The burnishing is easy to remove with a bit more sanding.
And finally we all just have to reign in our enthusiasm for those last cuts on the bottom. No matter what you use, the hold is less good than while you turned the rest of the bowl. And you've invested all that time on the rest of the turning. Sometimes, it's helpful to take a break and reset mentally before tackling the bottom.

 

[Aaron Harris]

Hi, I have had several situations where I have a jam chuck that messes up my project. I'm basically using just a cylinder of wood that I put in the chuck then put against the inside of the bowl sometimes/most times with a paper towel in between. Bring the tail stock in and that holds it in place while I turn off a tenon. However, some of the time, or most of the time, when I take it off there's a black ring where the block was touching the bowl. Sometimes I get a catch and it stalls the bowl while the block keeps turning. Some times I don't and I still get it. One solution would be to just tighten up the tailstock till it can't turn, but I fear putting a dent in the bowl. It may be the case that the solution is to find the right pressure and never get a catch, which would be a crappy solution but I get it. I guess I'm wondering how others do it, and if others have experienced this and over come it.
Thanks,
Raif

Raif-A couple of months ago I made the https://www.woodcraft.com/blog_entries/universal-jam-chuck from the Woodcraft website, and it works far better than anything else I have used. I use it on everything from my little 6-inch square bowls to a big, heavy live edge maple bowl that I originally made it for. Make it exactly to their specs and you will be amazed how well it works. You can apply some tailstock pressure and the neoprene won't mar or leave a mark. I need to do as suggested above and make them in graduated sizes from my 35mm jaws up to my 130mm/5-inch ones.

That, and always find your exact center point as you bring in your live center. I have found that using the Robust cup center with the point protruding maybe 2mm helps me get trued back up easily almost every time (occasionally with a little fiddling and adjusting). If you use a detail spindle gouge to make a series of push cuts towards the spindle/head-stock and true up with scraping cuts as you go, your bottoms will improve dramatically. When I get close to the center and the tenon nub I back off the tailstock pressure a little, and once I have sort of a cone I start coming in under it with the bevel riding and parallel to the bottom. There are videos on this, and practice makes it easier to tell when you are ready to separate from the tailstock, of course.

But those three things: a well-constructed and padded jam chuck, finding your center accurately, and changing how I cut the tenon off all together totally upped my game and give me more professional looking bottoms (which are the 1st thing fellow turners look at as we all know). I hope this helps. Aaron

edit to add: Before I made the jam chuck above, I was using a well-padded round potholder I appropriated from the kitchen against the chuck jaws. This works very well for smaller stuff. There are many methods of reverse-chucking. Seems like I am learning something new in that area all the time!

 

[Kent Reisdorph]

Because I make once turned bowls, I cannot sand with the bowl rotating.

Could you elaborate? I pretty much only turn wet, once turned bowls. I microwave dry them and then sand.

 

[Ron Solfest]

What @Randy Anderson said, his post is exactly what I do as well without any issues.

Two other points: regarding centering make sure you leave the center point from the tailstock to realign (if tailstock is centered and inside is round mating onto a round friction drive it will find its center); and, make sure you use lighter cuts when friction driving to clean up the base, especially the last cuts as you separate the very last of the center (and hence the tailstock support - very light cut using remaining center wooden point on tailstock side, and the bevel of tool to keep bowl pressured lightly onto the friction drive as you turn off the lathe)

 

[robo hippy]

Kent and Don, I also only once turn my bowls. Check out my Articulated arm for bowl sanding video. I do need to redo that one as I don't explain exactly what I am trying to accomplish with it. Having a lathe that goes down to 15 or so rpm will allow your lathe to spin slow enough that you are able to spin the bowl by hand for the coarser grits, and keep the lathe on while sanding the finer grits. My Vicmark 240 goes down that low without changing anything. My Robust AB now goes down that slow with Brent's help.

robo hippy

 

[Don Stephan]

Could you elaborate? I pretty much only turn wet, once turned bowls. I microwave dry them and then sand.

As the bowls slowly dry, the differential shrinkage causes them to warp. After they are dry, if I mount on the four jaw chuck and rotate at a coupe hundred RPM's the unevenness does not allow uniform sanding.

 

[Dean Center]

All good suggestions above. I use white eva foam from the craft store, or foam drawer/shelf liner, or a 'rubber' lid gripper, which is my favorite for this purpose.

The ones I have were promotional items from car dealers, but they can be bought as well.

 

[David Croxton]

Great suggestions for Raif on how to improve the process of jam chucking, such a wealth of knowledge here! After reading all the posts, I got to thinking that perhaps a set of Cole Jaws might be a viable alternative method to jam chucking that could help in some situations. Over the years, I have found Cole Jaws to be very useful - especially with my more recent work. However, they also have limitations and cost some $$. Granted, it is always good to learn more than one method to accomplish a task - I do utilize the jam chuck method as well.

 

[Darryl Fective]

Try to contour your jamb chuck piece closer to the shape of the inside of your bowl. Imagine a disk with a very sharp corner, your only contact area is just that circle. Round the corner get the shape a bit closer, suddenly you have a lot more shared surface area between the two; way more drive friction is possible with the same pressure.

Also keep in mind, a larger jamb chuck provides more drive torque than a smaller one, but matching the contour gets tougher (going up the inside of your bowl) and it will put more stress on the bottom. If your piece is very thin, you might crush it, or if the bottom is very thin, you might punch thru. A very tiny jamb chuck could be flat and you could crank up the tailstock pressure with no fear, it just won't have enough diameter/friction to transmit any torque. It's all a compromise.

 

[Kent Reisdorph]

As the bowls slowly dry, the differential shrinkage causes them to warp. After they are dry, if I mount on the four jaw chuck and rotate at a coupe hundred RPM's the unevenness does not allow uniform sanding.

Different woods have different T/R shrinkage ratios. Some warp worse than others. Red oak, for example, has a T/R ratio of 2.2. That's pretty high. Dogwood is 1.5, as a contrasting example. You can find all of this and more at The Wood Database.

I think someone already mentioned this, but true up the tenon after drying. That should smooth things out.

I spend too much time sanding. I'm still working on getting the smoothest finishing cuts.

Edit: Don, I apologize. I somehow had in my mind you were someone else. Far be it from me to be giving advice to the experienced folks here.

 

[Kent Reisdorph]

matching the contour gets tougher (going up the inside of your bowl) and it will put more stress on the bottom. If your piece is very thin, you might crush it, or if the bottom is very thin, you might punch thru.

I blew a bowl apart by using a jam chuck that was a little too big. The wood was punky as well (heavy spalting). Tightened the tail stock and it split right in two. Good lesson, fortunately on a crappy piece of wood.

 

[Leo Van Der Loo]

Hi, I have had several situations where I have a jam chuck that messes up my project. I'm basically using just a cylinder of wood that I put in the chuck then put against the inside of the bowl sometimes/most times with a paper towel in between. Bring the tail stock in and that holds it in place while I turn off a tenon. However, some of the time, or most of the time, when I take it off there's a black ring where the block was touching the bowl. Sometimes I get a catch and it stalls the bowl while the block keeps turning. Some times I don't and I still get it. One solution would be to just tighten up the tailstock till it can't turn, but I fear putting a dent in the bowl. It may be the case that the solution is to find the right pressure and never get a catch, which would be a crappy solution but I get it. I guess I'm wondering how others do it, and if others have experienced this and over come it.
Thanks,
Raif

I very seldom use jam chucks, just the occasional uneven natural edge, where as I use a recess on most turnings, I can and will turn the bottom to a finished shape and condition so seldom need to revisit that later.

On most turnings I will use the Jumbo jaws that will accommodate all sizes and are held securely, even off-shapes and if very large I have made Mega Jumbo jaw extensions.

If one does not have the Jumbo jaws, they can make bases to hols pieces securely, shown in the picture below.

I can hold inside or outside depending shapes.


Black Wanut & oval Apple turning.


A Norway bowl held in place in the shallow recess and 6 frogs, and the bottom side of a 3 bowl special shape turning.


If my Jumbo jaw extensions won't reach, I have made special size disks to turn/return those pieces.

 

[Wyatt Holm]

What you are describing is not a jamb chuck. It is a tension drive, or friction chuck. I had the same problem I tried neoprene, it left black marks. Soft leather was the best padding material I found. However I learned a new technique from an Australian wood turner, hot melt glue. Shape your friction chuck with a concave surface, add 3 dabs of hot glue on the rim of your chuck. Bring the tsilstock in to center your bowl. Finish turn the base down to a small nub. Then remove the tailstock and the glue will hold your bowl in place so you can turn away the nub and sand the base. It doesn't always work, but it's a good cheat for a vacuum chuck.

 

[Vicki Hayden]

A few years ago I made jam chucks for each of my four jaw chuck jaw sets. For example, assume the minimum tenon clamp diameter of one set of jaws is 4”. I band sawed a ¾” thick plywood disc 5” in diameter. In the center of the disc I drilled a pilot hole and mounted it on a screw faceplate, trued the face flat, turned a 4 ¼” diameter tenon ¼” long, and trued the remainder to the maximum diameter.

Next I used a knife to cut a 6” disc in ¾” thick high density insulating foam. Using Titebond on hand I glued the form disc to the side of the plywood disc opposite the tenon. After a couple hours I clamped the plywood tenon in the four jaw chuck and with very light spindle gouge cuts turned the foam disc round and rounded over the top edge of the form disc.

Then I repeated the process with perhaps a 7” diameter ¾” thick plywood disc and an 8” diameter foam disc.

Because I make once turned bowls, I cannot sand with the bowl rotating. I will clamp the bottom tenon of the bowl in the four jaw chuck and power sand, in stages, the inside with the first grit, whichever is appropriate. Then I will unclamp the bowl, clamp one of my foam jam chucks without having to change jaws, position the inside of the bowl over the jam chuck, bring up the live center pin in the mark made when the tenon was being shaped, lock the tailstock in place and advance the tailstock ram to apply pressure through the bowl onto the jam chuck. I chose the largest diameter foam jam chuck, for that jaw set, that would fit in the bowl, for stability. I power sand the outside of the bowl, in stages, with the same grit used on the inside, then power sand the outside, in stages, with the next grit. Then I’ll flip the bowl and power sand the inside of the bowl, in stages, with the next two grits, and so on.

After the bowl is sanded to 220 inside and out, I’ll turn off the tenon, again using the foam jam chuck. I’ve done this for a number of years and can’t recall ever having the sanded interior of the bowl damaged by the foam while turning off the tenon.

I have 2 or 3 different diameter foam discs for each set of jaws. I’ve used them for years and haven’t realized any damage to the inside surface of my wooden bowls.

A 4’ x 8’ 2” thick sheet of high density form 10 years ago was about $35, and likely is more now. And a 4’ x 8’ sheet would make a whole bunch of these jam chucks. Partner with some others in the local turning group to same some money.

Could you post a couple of pics of these? TIA