Not so successfull first atempt at segmented turning.

[Terry B]

The pictures tell the story. The wood is KDH for the middle and decking timber allegedly "spotted gum" around the top. I had essentially finished turning it when one of the joints let go. This let another one let go and the piece broke free. I had turned the lathe off before this happened. The glue was polyurethane and is what I use on pens with very good success. The spotted gum is incredibly hard and took the edge off my gouge within a minute or two but seems quite pretty. A shame really. Oh well back for take two next week if time permits.

[DJ’s Timber]

What a bummer heh, better luck next time.

Some nice looking timber there

[powderpost]

Terry, it is indeed a shame, from the photo the glue joint has failed. The spotted gum looks more like black walnut to me. If it is black walnut, it will have a high silica content and that would account for the tools loosing their edge quickly. I wouldn't use polyurethane adhesive on a job like this. There are a number of reasons for glue failure, lack of pressure to close the joint properly, timber dry enough or not enough time for full cure (my biggest problem). They are the most common causes in my experience, there are of course others, that would take up too much space here, not evident from a photo. I have used successfully for a while now, selleys tradesmans choice, and exterior aquadhere.
Jim

[dai sensei]

Looks like you were well on your way to a very nice piece. Can you not just re-glue and re-finish?

[Terry B]

Terry, it is indeed a shame, from the photo the glue joint has failed. The spotted gum looks more like black walnut to me. If it is black walnut, it will have a high silica content and that would account for the tools loosing their edge quickly. I wouldn't use polyurethane adhesive on a job like this. There are a number of reasons for glue failure, lack of pressure to close the joint properly, timber dry enough or not enough time for full cure (my biggest problem). They are the most common causes in my experience, there are of course others, that would take up too much space here, not evident from a photo. I have used successfully for a while now, selleys tradesmans choice, and exterior aquadhere.
Jim
I had clamped the piece with a circular clamp but I think some of my joints weren't quite the correct angle. It was tight but there was a slight gap. I think this was the problem. How do you clamp your pieces together?

[Terry B]

I had clamped the piece with a circular clamp but I think some of my joints weren't quite the correct angle. It was tight but there was a slight gap. I think this was the problem. How do you clamp your pieces together?
I thought of that but it is pretty thin and I didn't think it would hold.

[powderpost]

Terry, the joint I was referring to was the horizontal joint between the light and dark timber. In this case, I would have used a disc of thick (19mm) ply or particle board, against the darker wood and used the lathe as a press. Not sure that less than perfect joints in the top darker layer caused the problem. To me it looks like the poly glue has bubbled and the two wood surfaces were not in contact. It looks like you may not be able to use the lathe as a press. I have made a few small wooden presses that use a 12mm threaded rod to apply pressure. Tree or four concrete blocks may provide enough pressure.
Jim

[Mick C.]

There is an interesting read on the Hal Taylor site www.haltaylor.com that has a reference to the same failure that your turning has shown. I know this is only one persons opinion, but its still interesting to read, and also gives you a way of testing to prove to yourself if it is worth useing in the future.

Nice bowl also!!!

[joe greiner]

A slight re-design may help. The segment joints are endgrain-to-endgrain. This is very weak for any kind of glue. The only thing really holding it together is the glued joint to the backing wood. Even a very light push on the rim toward the headstock imposes very large prying stress on the joint because of leverage. I'd suggest increasing the size of the backing wood to get more overlap, i.e. a wider glue joint. You had an excellent idea to use a simple design for practice, so as to minimize prep time and effort.

Joe

[martrix]

Doh! Looks like a nice piece, should be repairable though with some epoxy?

As for the timber, definitely looks like Queensland Walnut to me. Very high silica content, an absolute b!tch on tooling.

[Rum Pig]

Do not know a real lot about the problem of falling apart but it sounds like your getting good advice. I can see what you are trying to do and I think it is worth the effort of a second go. Best of luck if you do give another go:2tsup:

Cheers Justin:drink2:

[Skew ChiDAMN!!]

Personally I reckon you did well. It's a bummer that it let go, but it happens to even the best of us.

The reasoning as to why it let go seems fairly sound to me and the suggested fix (increasing the area of glue joint) is probably the best way to go next time... but somehow it feels wrong saying "leave an area thicker." :D

[Gino]

Hi Terry.

I once did a similar thing except it was a base for a foot stool that I never finished.

I effectively made up two circles of segmented pieces and then glued the two circles together. But the twist here is to offset the two cirlces so the segmented pieces overlap each other. ie the joint of the bottom piece ends up half way on the center of one of the top segmented pieces.

This way you will make it stronger as you are not reliant on just the end grain joint.

in your case your timber would have to be half the thickness otherwise it would be out of proportion.

Hope this helps

regards

gino

[joe greiner]

More than one ring, offset as Gino suggests, is the normal way. That's pretty much how running bond works in brickwork. As for leaving it thicker, not really necessary exactly. Assemble with the wider joint as I suggested, turn the outside to your desired proportions, sand it, and then don't touch it again. Turn the joint region to the desired proportions, and proceed to the centre.

Joe