Twice Turned Bowls?

[Tom Albrecht]

I watched a video yesterday showing a technique that I had never seen before and I am wondering if any of you use it.

The heavy walled and dried bowl was about 12" - 14" diameter. First, the turner re-mounted the bowl by using the tailstock to hold the inside of the bowl up against a large four jaw chuck in order to true the warped dovetail foot/ tenon. Second, the bowl was reversed and held with the four jaw chuck gripping the dovetail tenon in the standard fashion. Third, the top edge of the bowl was trued, and then a small dovetail recess was turned inside the bowl at about 2/3 of the depth. The the bowl was reversed again and mounted on the chuck with the jaws expanded into the recess cut in the previous step. Then the outside of the bowl was shaped and sanded.

Again, I have never seen this technique before and I am wondering how common it is?

 

[Mike Johnson]

That method gives you a little wiggle room to re-center the bowl after it has warped to even the warpage of the bowl walls and then true up the tenon or recess to reverse mount and finish 2nd turning the piece. It seems like more steps involved but you end up with a bigger bowl by not trimming away the outside edge if the bowl was warped too far to one side.

 

[hockenbery]

I have seen that method,

however once you have the bowl jamb chucked
Why not true the rim, true the out side, and true the tenon.
Sand it if you wish. If you line up the rims as I show in the work with wet wood tips you get the biggest bowl possible.

cutting a recess on the inside is only useful if you want to turn the face of the tenon for some reason.
It will likely increase any error in centering and returning the tenon.

If you have a really bad feeling from the jamb Chuck then it could be a good thing.
I play a little with how far open or closed the jaws are if I get a wobble.
Jamb chucking on the slightly open jaws is so rock solid that I don’t see any value to using a recess on the inside unless you want to turn something inside the tenon

 

[Roger Chandler]

I use the twice turned method a lot. When the wood is too wet, it needs drying time to stabilize. I usually rough turn to about 10% of the diameter ...example a 10” bowl is left with a 1” thick wall thickness, and then I seal the outside with Anchorseal, and a little on the end grain on the inside. I place in a paper bag, seal it up and weigh it, then write the weight and the date on the bag. I weigh it every month or two until it stops losing wight, the I know its ready to turn to finish thickness.

When time to finish turn, I always jam chuck and true the tenon first, then re-chuck it, true the rim and finish the bowl.

 

[Bill Boehme]

It seems that there is a lot of excessive flipping the bowl around. Usually I use the center dimples to true up the tenon between centers. Occasionally, I will make a small mortise on the inside that is approximately the same diameter as the tenon only for the purpose of truing up the tenon. Once I have the tenon in the chuck I turn the inside and outside. Flipping the bowl back and forth will always result in some shifting of the axis of rotation just because wood is a non-homogeneous material and woodturning scroll chucks aren't as high precision tools as are metal lathe scroll chucks.

The final step that Tom described seems to be an unusual way to finish the bottom. Is there another step to remove the dovetail on the inside. I can see this going on forever ... then it needs to be reversed again to redo the foot ... and on and on. I believe that there are a number of better ways to finish the bottom ... vacuum chuck, jam chuck, Cole/Jumbo/Bowl jaws, etc.

 

[JeffSmith]

most of my bowls are twice turned. When finish turning, I generally find the original tenon is not that badly warped that it can’t be fit in the chuck. I chuck it on the original tenon, turn a small dovetail recess inside, then turn the outside of the bowl while gripped by the recess. Particularly with large pieces, the inside recess gives a strong, reliable hold for truing and finishing the warped exterior. Sand the outside, then turn to grip by the trued tenon and complete the inside.
Tenon is removed/bottom finished and outside finish sanded in a vacuum chuck.
Might seem like too many turns for some, but I’m not in a particular hurry and I appreciate a reliable hold. An 18 - 20” bowl coming loose doesn’t seem like a good idea.

 

[Bill Boehme]

I watched a video yesterday showing a technique that I had never seen before and I am wondering if any of you use it.

Could you post a link to the video?

 

[Dennis J Gooding]

I watched a video yesterday showing a technique that I had never seen before and I am wondering if any of you use it.

I often use a dovetail recess and expanding chuck to reverse turn the outside of a bowl, particularly if the wood is cranky or it involves embellishments. Being right-handed I find it much easier and faster to finish the outside this way.

 

[Dave Landers]

I always jam a rough-turned bowl between centers. Sometimes on the chuck jaws, sometimes on something else (like a disk or whatever seems right for the job). I usually true up the tenon first, just in case, then finish turn and sand the entire outside of the bowl. I've never had a problem with that.

I have thought about a dovetail inside a bowl for doing the outside, but more as a what-if thought experiment (sometimes its useful to try different things just to learn something). But I got stuck on figuring out how I would get the chuck key inside the bowl to tighten it...

 

[Emiliano Achaval]

I always jam a rough-turned bowl between centers. Sometimes on the chuck jaws, sometimes on something else (like a disk or whatever seems right for the job). I usually true up the tenon first, just in case, then finish turn and sand the entire outside of the bowl. I've never had a problem with that.

I have thought about a dovetail inside a bowl for doing the outside, but more as a what-if thought experiment (sometimes its useful to try different things just to learn something). But I got stuck on figuring out how I would get the chuck key inside the bowl to tighten it...

Since I have some welding equipment I made a key with an angle. Vicmarc used to make one with a pivoting hex head, so it would give you more angles. I just cut up an Allen wrench and welded it.

 

[Tom Albrecht]

Could you post a link to the video?

Unfortunately, no I can't because it is a paid link with one of a series of videos by Ashley Harwood on the TWW Guild website.

 

[Dennis J Gooding]

I always jam a rough-turned bowl between centers. Sometimes on the chuck jaws, sometimes on something else (like a disk or whatever seems right for the job). I usually true up the tenon first, just in case, then finish turn and sand the entire outside of the bowl. I've never had a problem with that.

I have thought about a dovetail inside a bowl for doing the outside, but more as a what-if thought experiment (sometimes its useful to try different things just to learn something). But I got stuck on figuring out how I would get the chuck key inside the bowl to tighten it...

This is one of the reasons that I have stuck with chucks that use a toggle bar instead of a key. I keep a bar that is bent to a ninety-degree angle near the end.

 

[Don Wattenhofer]

That sounds like a lot of extra fooling around to accomplish what most of us have been doing all along to finish turn a rough turned bowl.
There is one point that seams to be ignored in that method, which when rough turning and using a dovetail tenon you must oversize the tenon so that when the wood dries with the inevitable warp there is enough material left to make a large enough tenon for the dovetail jaws being used.