Segmented turning

[JohnMessUK]

Hi All,

I have been trying my hand at segmented turning so that I could use boards to make peices. I started off by ripping them on the table saw, then cutting the angles.

I used an 18 degree angle so I had 10 peices to glue together which I held together with an elastic band to dry . The sections look great but I have broken 2 today one of oak and a test peice made from pine. I got a catch on both and they broke in pieces ( big up for eye protection)

My question is did they break because of poor gluing one was set over night the other for only 2 hours.

Was the choice of angle wrong?

if you have created segmented peices did anyone have an issue with breakages or if not how do you think you avioded them

Thanks in advance for any help.

 

[marcros]

chj is probably your man on this- he does a lot of segmented work.

It sounds to me that the glue gave up- did it break clean along the glue line? This could have been glue not going off- time, temperature, age of glue, storage conditions of the glue are all potential problems, or could be that the angles were a fraction off/concave across the face, so that the glue was being asked to fill a gap and didnt. Inspection of the broken joint with a straight edge will tell you about the latter. Was the tablesaw cut smooth, so that the pieces clamped up cleanly, with a maximum glue area possible?

My money would be on either a glue up that took too long, so it had started to go off before it was fully assembled, or glue that was old/subjected to frosting.

 

[JohnMessUK]

chj is probably your man on this- he does a lot of segmented work.

It sounds to me that the glue gave up- did it break clean along the glue line? This could have been glue not going off- time, temperature, age of glue, storage conditions of the glue are all potential problems, or could be that the angles were a fraction off/concave across the face, so that the glue was being asked to fill a gap and didnt. Inspection of the broken joint with a straight edge will tell you about the latter. Was the tablesaw cut smooth, so that the pieces clamped up cleanly, with a maximum glue area possible?

My money would be on either a glue up that took too long, so it had started to go off before it was fully assembled, or glue that was old/subjected to frosting.

Thanks Marcros, the table saw cut was good but as an added measure I gave each peice a light sand but something you pointed out may be the reason, the glue I am using PVA wood glue has been in the shed for months and I left the peices to cure in the shed so its possible that the glue is the problem as the peices both broke at a glued join not anywhere else.

I have another ring glued up at the moment I will bring it in the house to make sure it gets a constant tempreture and see what happens.

Thanks for the reply.

 

[nev]

IIRC Chas uses cascamite glue for his creations, though I'm not sure which flavour.
Have a gander at his website for hints and tips... http://quest42.co.uk/woodwork/html/projects.html

 

[Random Orbital Bob]

Sounds like the glue line was weak. But one thing...its not a change in summer overnight temperatures that's the risk, I think Macros is referring to the glue maybe having been left over winter and the frost damaged it??

This time of year the overnight temperature range is highly unlikely to cause problems. 2 hours cure time for pva is however nowhere near enough. Not for turning anyway.

Try buying some new pva and leave the cure time for at least overnight...pref 24 hours. You could also consider cascamite which is pretty cheap and so strong its used in boat building.

 

[tekno.mage]

I use Titebond Original for segmented work (it's an alphatic yellow glue which creeps less and sands easier than ordinary PVA) - your glue breaking either sounds like your PVA has had the frost in it and doesn't work any more, or you didn't leave your glue-up for long enough before turning it. I'd leave a PVA glue up at least overnight (longer in cool weather) before attempting to turn it.

 

[Phil Pascoe]

I always try to leave pva'd joints for 48hrs - even in the summer.

 

[CHJ]

Yes PVA on segments as opposed to just tenons needs to cure well before attempting any heavy turning.
If the joints are letting go then it's the glue.

Accuracy of segment angles is paramount, I cut my segments with a Chop Saw, I do not normally sand sawn surface as sawn gives better bond and better joint line.

For closed segments use a decent clamping pressure, I use large jubilee clips.

As said I don't use PVA now for segments only Cascamite, 24 hr min. if in hurry but several days are better to allow glue cure and glue moisture to dissipate. I normally work in batches of similar pieces so can be weeks before turning.

A thing to watch is moisture content of wood, if it's not below 8% expect the angles to change as it dries or moves around with the moisture from the glue.

These have been around since the beginning of June and are currently off the bottom of the scale on my moisture meter.

(as a matter of interest the green and rough turned apple awaiting finishing before the weekend is down from 18-20% to below 8% since Monday.)

 

[JohnMessUK]

Thanks all as usual you have all been a great help. I will try a different glue and make sure to leave longer between gluing and turning.