I wrote this up to answer a few questions on another forum, so while I have the photos out, I figured I'd share it here. This is old hat to some of you guys, but hopefully it'll help a few of the newer members...

Here's the basic idea...the shallow bowl that's mounted in the chuck is a roughout that I don't plan to finish. It's got some hairline cracks that I don't think are worth the effort to fix. The bigger bowl on the right is the one I need to finish the bottom on:

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I put a sheet of rubber shelf liner/router pad in between the two, and used the tailstock to hold the bowl in place:

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At that point, I'd typically turn the tenon down to a nub, do any finish turning to the bottom of the piece, then turn the nub down to a cone and remove it, doing any final sanding of the foot off the lathe. I've used this method for a lot of bowls, and have been happy with the results. You can use a similar method for finishing the bottoms of hollow forms. To do that, the "chuck" bowl needs to be bigger than the hollow form, so the vessel fits inside of the bowl.

But with this particular pair of bowls, I didn't really like the way the big bowl fit over the smaller bowl. So I went back to the scrap bowl pile and picked out another, larger bowl to use as the friction chuck. If you look closely at the photo, you can see I've re-trued the rim of the "chuck" bowl:

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Here again, I used some beat-up rubber shelf liner as an interface pad:

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And used the divot in the tenon from when the piece was first roughed out to center the bowl on the friction chuck:

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Giving me this:

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And from another angle. I should point out that the blue line near the bottom of the bowl shows me where the inside bottom is. Before reversing the bowl, I use the laser pointer on my hollowing rig to accurately determine the bottom thickness, so I know how much I can (or should) remove from the bottom as I finish it:

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Then I do any final shaping of the bottom 1/4 of the bowl, as well as start whittling away at the tenon on the bottom:

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Once the tenon was down to about 3/4" in diameter, I decided to take out a little extra insurance in the form of plastic stretch wrap. I wrapped it tightly around the joint between the two bowls, making sure to wrap in the same direction as the lathe rotation. (I don't want the lathe's spinning to unwrap the plastic.):

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Here's another view. You can see that I've done some initial sanding of the concave foot area (by hand, with the lathe running):

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The I go about turning the nub down to a cone. Here's a spinning shot:

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And another photo showing how I hold the detail gouge to get a shearing cut on the cone. I'll point the gouge the other direction to make similar shearing cuts on the foot itself. It was a bit exciting taking this shot one-handed, while holding the gouge in place right next to the spinning wood:

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And, the "free at last" shot. Notice that the bowl is still turning but the cone is not.

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Here, I've stopped the lathe and moved the tailstock back a bit. You can see that the cone stays stuck to the live center:

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At this point, any of the work I've done on the bottom of this bowl could have been done without the stretch wrap. As I mentioned earlier, it was there just for insurance. But since it was there, and since it was holding the piece securely, I decided to do a little bit more tooling on the foot after moving the tailstock out of the way. Here's the finished bottom after the extra tooling and final sanding:

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Although I didn't get any decent photos of it, the inside of the finished bowl did show some marks (they looked almost oily) from the rubber pad. Those marks sanded away easily with 400 grit sandpaper after I took the bowl off the lathe. The stretch wrap, however, leaves no trace on the finish-sanded raw wood.

This isn't the only way to finish off the bottom of a bowl or hollow form, and it's not even one that I use very often (I usually skip the stretch wrap part), but it's one of many ways that works well.  smiley=thumbsup.gif

Questions and comments are welcome and appreciated.

Robert Harper wrote on Jul 11^th, 2011 at 6:17am:


I used to use various solid stubs, and still have a bunch in the drawer, but I've gotten to where I prefer either a wood bowl or the cup from my vacuum chuck. Using something close to the rim to support the bowl instead of something close to the middle seems to keep things more stable and less likely to get off-kilter. It also gets rid of the potential problem of having the contact point being right in the center, which can happen if the radius on the face of the stub is smaller than the radius of the inside of the bowl.

Great tutorial Vaughn, I will have to add this to my tool box.  Now if I only had two blanks that big.

Rev. Doug Miller wrote on Jul 11^th, 2011 at 9:59pm:


If the bowl is only resting on the center spot, there's more opportunity for it to wobble. (Think of sitting on a one-legged stool, as opposed to sitting on an overturned bucket.) The wider the support, the less chance for wobble. This is especially important as you're making the final parting cuts on the tenon stub. Unless the jam chuck face exactly matches the curve on the inside of the bowl, you're probably better off turning a bit of a depression in the middle of it.

The burnt bottom is another symptom of the center spot. That's happening because the surface area that's making contact between the bowl and the chuck isn't enough to overcome the torque of the lathe, so the friction chuck is spinning out. If there's a 1" diameter spot in the middle making contact, that's only about 0.8 square inches of contact. On the other hand, if you have a 6" diameter bowl rim as a contact point, and it's making contact 1/4" wide all the way around, that ends up being about 4.7 square inches of contact area. Much less likely to spin out and burn.

Does that help explain things?

Maybe I'm not envisioning this right, but doesn't the wrap need to go in the oposite direction to lathe rotation, eg, clockwise around the piece (when viewed from the tailstock end) to keep it from unwinding when the lathe rotates counterclockwise?
Except for that point of confusion, that was a very instructive slide show; a picture really is worth a thousand words (give or take a few)!
BOB

Vaughn McMillan wrote on Jul 11^th, 2011 at 8:33am:


Great write up and pictures Vaughn.
I use small sections of 2X and try to have the transfer of power just outside of the foot. If necessary it only takes a small cut if the friction chuck needs to be re-trued when reused.  The bowl would work well also but I assume less pressure could be used for fear of cracking the bowl that far out.  If the "bowl/cup chuck" warped between uses would it limit the number of reuses?  A 2X4 would provide support for a foot up to 3.5" and a 2X6 for up to 5.5" and still keep the transfer of power concentrated at the bottom of the bowl where there should be less flexing?
A 2X is not even necessary for smaller items, a 1X should suffice.  Or if you don't have 2X material handy, glue up some 1X and alternate the end grain?

Hi Vaughn, great tutorial. I haven't tried this yet as I'm still new to these things but how about the plastic wrap over the top of the router mat? Would that stop the marks on the inside of the bowl?

You know I never had good luck doing it this way. It always seemed to wobble.