Green Bowls: Leave the Tenon?

[Matt Schrum]

Hi guys,
Long story short, I turned my first decent sized bowl (only 10" OD) with green wood. To help prevent cracking, I let it dry in a paper bag for a couple of weeks.

Fast forward to yesterday, I used a jam chuck to mount the bowl on the lathe and sand the outside-- but since I removed the tenon on the bowl, there was no easy way to mount the piece and sand the inside. I ended up making a sanding disc attachment for a hand drill, but in the future I'm trying to figure out the best/easiest way forward.

I'm worried if I leave a tenon on the base a green bowl, that extra thickness (compared to the walls/sides) may cause issues when drying. However, removing the tenon makes it more difficult to finish up once it does dry.

Thoughts?

[Ryan Mooney]

I've been leaving them, but hollowing the inside of the tenon out a smidge under the theory than it helps relieve the stress. No idea if its the right thing or not, but my success rate has been more or less reasonable.

Your other option is to reverse mount it (in a jam or vacuum chuck or whatever) and then turn a smidge of a recess to re-turn it.

[Prashun Patel]

If I'm planning to re-turn the bowl, then I leave a tenon on the bowl. It's usually not an issue with cracking. 9x out of 10 cracking happens for me around the rim or close to pith (if it's going to happen).

You can sometimes get lucky on a bowl turned with a recess instead of a tenon: if it hasn't moved too much, it may still hold enough for very low speed spinning while sanding. I don't even mind sanding the inside with the bowl mounted but lathe off, using the chuck simply as a stationary vise.

[daryl moses]

I mount all of my green bowls onto the chuck with a shallow recess. Not sure if the chuck you have will allow that or not, I use a Nova Titan.
This makes it easy to remount for final turning and sanding.

[Josh Bowman]

I leave 'em on. Usually make the tenon a little larger on the green blank then reround it after it dries.

[Faust M. Ruggiero]

I always leave the tenon. Like Josh, I oversize it a bit because it will deform with drying. The only time I experience cracking at the tenon is when I turn cherry and allow sap wood to remain on the tenon. That will produce a guaranteed crack since the sap wood loses moisture quicker than the heart wood. Tulsa must be a really arid climate if you only dried the rough out for a couple weeks. Here in Eastern PA, I leave them a year per inch of thickness. My stash of rough outs probably exceeds 200 so I am not usually stuck for a dry bowl to turn.

[Reed Gray]

I always leave a recess. I agree that the extra thickness of a tenon could cause it to split. When sanding, I have an extended jaw set that I use, and expand into the oval recess. I keep lathe speeds way down. You don't need the grip on the bowl for sanding that you do for turning. I do power sand, so no added friction. I don't know how you could hand sand a warped bowl because any speeds of over about 20 rpm will catch air over the low spots.

robo hippy

[Matt Schrum]

Tulsa must be a really arid climate if you only dried the rough out for a couple weeks. Here in Eastern PA, I leave them a year per inch of thickness. My stash of rough outs probably exceeds 200 so I am not usually stuck for a dry bowl to turn.

Rough outs take quite a bit longer to dry, for sure-- however this bowl I turned fairly thin to speed things up. Even though I turned it to it's final thickness (it did warp some, but that doesn't bother me for this project), it did need some final sanding after drying out-- and that's what I was trying to knock out the other night.

[Thomas Canfield]

I like to have a tenon on green bowls and turn about 1/4" or more above minimum diameter to allow for truing before remounting in chuck to return. I try to always remember to leave a center dimple to center when returning and normally will jam then against the open jaws of the chuck. I find it hard to true up a recess on green pieces, but do sometimes use a recess with the #3 or #4 jaws that will allow me to have a larger mass in center for a dimple to use with jam and true up the oval recess.

[Fred Belknap]

If you are going to twice turn a bowl with a tenon it is a good idea to make the bottom of the bowl thinner than the rim. For an example if the rim is 1" I try to make the bottom 3/4" thick. Seems to work for me, but I still sometimes get cracks.

[robert baccus]

Green tenons and green dovetail recesses are asking for trouble in my humble opinion. I attach most vases/bowls with a glue block held by a single screw or a strong dry tenon to the piece. It's the last thing to come off before signing and selling? All shaping, sanding, finishing is done on the glueblock keeping everything in line. Seems to prevent splitting on the bowl bottoms as well. I do wax after rough turning --double on the rims and bases. I also dry for 4-6 months in wax like Faust.

[Reed Gray]

My once turned bowls are between 1/4 and 3/8 inch thick. They are dry in 10 to 14 days. It doesn't seem to make any difference what wood or what season here.

robo hippy