Chucking Punky wood

[Kirk Amidon]

I've searched around but have not found the right combination of words to get results for this query.

This week, I cut down a standing dead tree - not sure what it is, some sort of New England hardwood. The first inch under the bark is punky, and the next inch or so has quite a nice spalting effect.

I turned a bowl, well started to. Started with a faceplate on the flat face on the pith side, and turned round with a center. Got down through the punky wood, and into the spalted wood. Added a dovetail recess 1/4" deep for the chuck, and swapped ends.

Long story short, it quickly broke off at the chuck. From reading, I merely snugged it up, and also ensured the jaws were at a 45 to the grain to make sure each was acting on the same wood. The recess had more than an inch of wood outside it.

My plan as of now is to put it back on the faceplate, and turn it down another 1/2" or so, making it shallower. At that point I'm hoping to be in more solid wood for a recess. Would it be better to turn it down 7/8" or so and make a tenon on that end? This wood is quite green, and this will be a twice turned bowl, or at least that is current plan.

What is the right way to approach chucking softer wood? Can a sacrificial plate be glued to green wood? Is it simply use the tailstock as long as possible when hollowing? All this said, I'm sure that sharp tool and light touches will also be necessary.

 

[Lou Jacobs]

I’d make a tenon. It’s hard to know when a recess provides enough strength to support the bowl on the chuck. With punky or compromised wood, you’re dancing much closer to the edge.

 

[hockenbery]

A tenon will hold better it almost always will.
Fundamentally you need solid wood for a hold.
Saturating the tenon with thin CA will strengthen the tenon.

the strength of the tenon needs to be up to the stresses you put on the wood.

I use a screw driver test for punky wood. If a flat bladed screw driver easily pushes
a 1/4” -1/2” deep into the wood I don’t turn it.

 

[hockenbery]

Can a sacrificial plate be glued to green wood?

Glue blocks on green wood is a somewhat advanced skill. You have to be able turn before the wood moves fracturing the glue joint.
I have turned lots of Green NE bowls in glue blocks using thick CA glue.

Turn a concave on both faces.
Thick bead of glue on the bowl accelerator on the glueblock a thick wire for alignment in a center hole in the glue block. With the wire in the center of the concave bowl mount area slide the glueblock into position and give a little twist to spread out the glue. With the two shallow concave surfaces the glue will spread toward the the center in making nice wide joint.
Hollow the bowl in less than 30 minutes. When finished a flat chisel in the glue joint splits the glue. (CA is a glue not stronger than wood)
With solid wood you have glue on the bowl and the glueblock. With punkynwood you likely have some fibers pull out.
Lyle Jamieson has a nice video on making a glue block.

 

[Donovan Bailey]

A tenon will hold better it almost always will.
Fundamentally you need solid wood for a hold.
Saturating the tenon with thin CA will strengthen the tenon.

the strength of the tenon needs to be up to the stresses you put on the wood.

I use a screw driver test for punky wood. If a flat bladed screw driver easily pushes
a 1/4” -1/2” deep into the wood I don’t turn it.

These words would make a danged good wall poster for the shop of every new turner.

 

[robo hippy]

I use a recess on 99% of the bowls I turn. As near as I can tell, there is no difference in holding power as long as they are made correctly. Given that you had a big shoulder on your bowl, I would guess that the wood was still rather punky. If it cuts too easily, then the failure was probably due to the wood. I like Al's screw driver test idea. Give it a little poke and see how firm it feels. A glue block might be the better choice for a piece of wood like you describe. The thing about spalting is it is one of the processes of rotting wood. If you catch it soon enough, the wood is still good. If you get it too late, it isn't worth the effort. If you have enough experience, just picking up the piece of wood can tell you a lot. If it feels like balsa wood, throw it on the compost pile. Not even worth burning....

robo hippy

 

[Kirk Amidon]

Thanks for all the advice. Went back at it last night, and ended up with a bowl I'm reasonably happy with. Removed a bit more stock from the bottom side of the blank, and created a tenon. Hollowing went fine, and decided to do a once turned bowl, rather than just rough it out. Ended up losing the spalt from one side of the bowl, but enough is left on the other to add interest.

I'm not nearly fast enough to risk the glue block on green yet, but speed is definitely improving. Here are a couple of views of the bowl post turning.





There is still a bit of tear out in the spalted area I can see on the outside, and some tool marks inside, but much happier with the overall shape and result. The thickness of sides is the most consistent of any bowl I've yet turned.

The good news is there is still another 20' of this tree trunk left! So lots to practice with.

 

[Ron Solfest]

Kirk - pretty wood, and it looks like you cut cleanly for the most part. Nice job. The shape is a little 'square' at the bottom as opposed to a more flowing curve, that might have contributed to the reason you have the ring near the bottom on the interior. By the end of the 20ft of this tree you'll be turning out heirlooms. If you get coring tools you could double, or triple, your fun

 

[robo hippy]

Well, you did a good job of saving this one. Looking at the tear out you have, I am thinking a good shear scape with a burnished burr on the outside, and a finish cut with a gouge that has been sharpened on a 600 grit CBN wheel could clean up a lot of that. Too soft, most likely, for a NRS. If you don't have a 600 grit wheel, honing the bevel on your gouge may help.

robo hippy