Glue recommendation

[John Shillabeer]

What type of glue do you recommend when dealing with green (sappy) wood?
I'm planning to turn a hollow form with a narrow neck so will enter from the bottom. I'll first cut out the end containing the tenon, hollow the interior and then replace the end, gluing it back in place. I've used this technique several times before with kiln dried wood. This time I am planning a little larger piece, The cherry blank I'm starting with is about 6x6x12. Its quite sappy and will take years to dry naturally. I don't have a kiln.
The instructions on the labels on all my different glues begin with words to the effect "make sure the surfaces are clean and dry".

So what would you do?

 

[Don Wattenhofer]

For what you are doing it is best to let it dry before plugging the bottom. Cherry can be difficult to work with especially near the bottom where any uneven wall thickness will result in checking.

These 5 small black cherry hollow forms were all made from a small live & healthy tree cut when the snow was still covering the ground and the sap had not started to rise yet. The five were rough turned before they had a chance to dry so the ends never had any checking. The one on the far left was done first, placed in a brown paper bag for about 2 weeks, weighed regularly and it developed the radial checks that are clearly visible. The other 4 were then rough turned and I bored a 1 1/8" hole into the tenon to within 1/2" of the inside bottom. The 4 were placed in the same paper bag as they were rough turned and the weights were recorded on that piece of paper. The 4 were removed from the bag after about 2 weeks but still were weighed regularly and within another 2 weeks the weight change had stopped. The weight has slightly increased with the summer humidity but they all could have been finish turned about 2 months ago. Note: These were turned with the pith so that is much more prone to checking then without but the lesson is the same "large thick masses of wood can not move to accommodate the shrinkage therefore they check usually radial".

 

[Jason Meneely]

I turn green end grain hollow forms from the bottom very frequently (pics attached). Medium CA glue works just fine on most species. If you are consistent with your wall/base thickness and careful with the positioning of your pith you can avoid most checks. Also, if any small checks appear they more often than not close back up as the piece dries due to to the directionality of the drying forces pushing back toward the center (this assumes you are turning in end-grain and that your pith is dead center top to bottom).

 

[John Shillabeer]

Thank you both for your comments.
To clarify, the pith is not present in this piece. It's a chunk from a much large log that was more than 2 ft diameter. I will be hollowing into end grain.

I think I can turn the hollow form thin enough ( and the base plug thin enough too) to be able to avoid cracking as it dries after assembly. But there will be some distortion during drying and consequently the taper on the base plug wont be a good fit against the taper in the bottom of the hollow form. In my experience CA glue needs a good mating surfaces to form a strong joint.

The joint between the plug and the base must be stronger than normal. The top of the hollow form will be quite large and there will be some eccentric loading during a subsequent turning stage.

Is CA glue the best glue for this application?

I can either:
1 hollow thin and glue the pieces together while they are still green and a good fit, or
2 wait a while after hollowing to let the pieces dry, try to trim away any distortion and then glue in the plug.

What would you do?

Thanks

John

 

[Jason Meneely]

John,

Titebond 2 wood glue an 24 hours is another option. Also when I use CA I put it on quite liberally. Instead of a taper I use a step (like a box lid) which gives you an extra surface for glueing. I should have also clarified that I use a steady rest and a rotating jam chuck on the tail stock to finish turning / sanding the outside after glueing. Final step is to turn the inside of the top in the study rest with tail stock removed and very light cuts. With the pith not in your piece you may see some slight bending toward where the pith would have been.

 

[Don Wattenhofer]

Thank you both for your comments.
To clarify, the pith is not present in this piece. It's a chunk from a much large log that was more than 2 ft diameter. I will be hollowing into end grain.

I think I can turn the hollow form thin enough ( and the base plug thin enough too) to be able to avoid cracking as it dries after assembly. But there will be some distortion during drying and consequently the taper on the base plug wont be a good fit against the taper in the bottom of the hollow form. In my experience CA glue needs a good mating surfaces to form a strong joint.

The joint between the plug and the base must be stronger than normal. The top of the hollow form will be quite large and there will be some eccentric loading during a subsequent turning stage.

Is CA glue the best glue for this application?

I can either:
1 hollow thin and glue the pieces together while they are still green and a good fit, or
2 wait a while after hollowing to let the pieces dry, try to trim away any distortion and then glue in the plug.

What would you do?

Thanks

John

Titebond is a better glue to use with a carefully fitted taper fit so you will need to dry it first then true up and if necessary make a new plug out of dry wood. The taper as you probably already know will compress the glue as it is inserted rather then scrape it off like a straight fit would. The method I have developed to fit the taper is to first make the female taper then measure with a bevel square and transfer that to the plug. The final fit can be checked by putting pencil marks on the plug then insert the plug and rotate it and see where the pencil marks smear and lightly scrape as needed until the smear is uniform throughout the contact area.

 

[Doug Freeman]

I use thick CA for blocks to wet blanks, and it holds fine through pretty aggressive cuts. A polyurethane glue would be a better choice for long term strength, but it doesnt sound like you need it.

 

[John Shillabeer]

Some excellent tips
Thankyou
John