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Reverse chucking question

D

Dan Stromberg

Joined
May 25, 2010
Messages
124
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81
Location
Prince Frederick, MD
Hi all,

So, I turned the bowl in the attached picture last weekend. It's a shallow bowl with an undercut rim. I ran into a bit of an issue when I turned the bowl around to finish the bottom. Because of the curvature of the outside, cole jaws would have nothing to grip on, and a jam chuck would easily crack the thin rim.

What's the best way to reverse chuck something like this? I eventually ended up making a "loose" jam chuck just to roughly center the bowl and holding it in place with the tailstock, but I was still having trouble. Eventually, I took it off the lathe and hand-sanded what was left of the bottom.

This was just a practice piece, so I looked at this as just a learning experience. I'm just wondering what is normally done on a shape like this to hold things in place.

Thanks! And happy Friday...

Dan
 

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Centering on a jam chuck with tailstock support (as you described) should work fine. A vacuum chuck is perfect for this - that’s what I use.
Cole jaws need to have very long tangs to mount this shape leading to a dicey hold at best. Turn a jam chuck shaped to the outside of the form and use tailstock support with a wood cup over the center to keep from marking the bottom. It works, but for me its quicker to just setup the vacuum...
 
I think the wood cup over the center was the biggest thing I missed (although I thought of it the next day). All my live centers had at least something that would have marked up the bottom.

I hadn't thought of turning the jam chuck to the outside profile. For some reason I kept thinking of trying to fit it inside the rim.

Don't have a vacuum chuck (yet). This is the first project I've done that would have made me consider it, though.

Thanks for the quick reply!
 
I used Cole jaws for a while but quit because they don’t work with lots of rims.
Vacuum chucks are nice but I cracked a couple of thin bowl bowls.

So I mostly use jamb chuck like the one I show in demos.
Thick walled bowls on the vacuum if I feel like setting it up.

Fast forward to 32:45 minutes. To see the measuring of the bottom
Fast forward to 34:10 to see the jamb chuck.

Mounting and turning a dried bowl -
View: https://www.youtube.com/watch?v=sCZWsHB4vlM
 
I'm VERY new at this, but in a class the instructor showed doing this by making a loose fitting jam chuck (for the interior) mounted on a face plate, cover it with a piece of foam (we used 1") to snug up the fit, then just wrap a bunch of masking tape around the faceplate and the outside of the bowl. Use the tailstock as long as you can then finish with light cuts. It worked great..
 
I tried to make a Jimmy Clewes inspired dyed bowl and the dye didn’t come out so hot. At 12 inches wide and with slight arc it works perfect. I use a piece of foam draw liner to hold it in place.
 
Mike Peace said:
Looks like cole jaws would have worked with the buttons on the inside of the bowl.
Click to expand...

That would have been what I tried first.

A word about Cole jaws. The brand I most frequently see and personally own are Nova. The Novas are sold with a set of short round grey buttons which are not tappered. These are frankly terrible and may contribute to the poor reputation of Cole jaws.
There is an accessory set of buttons available which includes a set of 8 round and 8 square-ish buttons, both of which are tappered. These will turn your Nova Cole jaws into a useful work holding device.

If the piece is small you can use ordinary chuck jaws on the inside of the rim. I stretch a big rubberband around the jaws to keep the rim surface from being marred.
 
Thanks guys!!

You know, it's funny the way the mind works. When I considered the cole jaws, I was only thinking in terms of using it from the outside, and when I considered the jam chuck, I was only thinking in terms of using it from the inside. And obviously I was using the tailstock, but I never thought to add in an extra piece of wood to protect the piece from the tailstock point, so I was concerned with excessively marking up the bottom.

Lots of good ideas. I also don't do so well about leaving enough wood at the bottom for a true foot, which would have helped here as well.

Practice, practice...
 
Mark Jundanian said:
That would have been what I tried first.

A word about Cole jaws. The brand I most frequently see and personally own are Nova. The Novas are sold with a set of short round grey buttons which are not tappered. These are frankly terrible and may contribute to the poor reputation of Cole jaws.
There is an accessory set of buttons available which includes a set of 8 round and 8 square-ish buttons, both of which are tappered. These will turn your Nova Cole jaws into a useful work holding device.
Click to expand...

That's good to know. I have a Nova chuck and an older PSI Barracuda chuck. My cole jaws go with the PSI chuck, and the buttons are more cylindrical, not tapered.at all. Might be nice looking into the squarish buttons. I assume that's what Mike Peace is showing in is video.

Btw, I'm amazed at how quickly the replies roll in on this forum. Thanks again!
 
With Delrin or Nylon round stock you can turn any size/shape of Cole jaw buttons on a wood lathe. You can also turn a quantity of small wood discs with a center point to use for additional support when using the tail stock and also use them for glue on tenons.
 
I've posted some info on this before with a few pictures to better visually understand it, the big difference between the Oneway Jumbo jaws and others is the buttons are tapered and actually steel with a hard rubber covering.

Tried to link to the earlier post, but it isn't working, so a search for "that pisses me off" will get you to that.

It should help some I do think
 
Last edited:
Dan Stromberg said:
That's good to know. I have a Nova chuck and an older PSI Barracuda chuck. My cole jaws go with the PSI chuck, and the buttons are more cylindrical, not tapered.at all. Might be nice looking into the squarish buttons. I assume that's what Mike Peace is showing in is video.

Btw, I'm amazed at how quickly the replies roll in on this forum. Thanks again!
Click to expand...

Yes, Mike's video does show the squarish buttons. The sides are radiused which gives you some options for mounting, but the most important factor is that the buttons are tappered. This gives them much better grip. The cylindrical buttons compress when the screw head is tightened causing them to bulge and actually become reverse tappered. This tends to eject the peice-or at least that's what happened in my "personal research".
 
Dan Stromberg said:
You know, it's funny the way the mind works. When I considered the cole jaws, I was only thinking in terms of using it from the outside, and when I considered the jam chuck, I was only thinking in terms of using it from the inside. And obviously I was using the tailstock, but I never thought to add in an extra piece of wood to protect the piece from the tailstock point, so I was concerned with excessively marking up the bottom. I also don't do so well about leaving enough wood at the bottom for a true foot, which would have helped here as well.
Click to expand...
When you've turned longer and screwed up more, you too will have a large repertoire of ways to solve problems. :D
 
I now have a vacuum chuck, but before I made it, I would use a donut chuck most often. On natural edge bowls, or bowls with rims that might crack from the pressure, I just put a block on the donut chuck "face plate" that was a bit taller than the bowl and about the same diameter as the inside bottom of the bowl. That way, all the pressure from the donut was directed to the bottom of the bowl.
 
"Necessity is the mother of invention" is an English-language proverb. It means, roughly, that the primary driving force for most new inventions is a need.

"There are more ways than one to skin a cat," so are there more ways than one of digging for money.

When you have a lathe and raw materials you can usually fabricate just about any tool or jig for a needed task if you put your mind to it.
 
Leo Van Der Loo said:
I've posted some info on this before with a few pictures to better visually understand it, the big difference between the Oneway Jumbo jaws and others is the buttons are tapered and actually steel with a hard rubber covering.

Tried to link to the earlier post, but it isn't working, so a search for "that pisses me off" will get you to that.

It should help some I do think
Click to expand...

I think that this is the thread that you are referring to: That pisses me off
 
I use a vacuum chuck often on bowls and platters when I need to clean up the bottom. I've always been challenged with thin hollow forms until I recently bought a Reverse Chucky from Rubber Chucky. This has made reverse turning my hollow forms so much easier.
 
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