Sycamore bowls trouble

[mattsutton29]

Hi everyone. I’ve been turning some 11x3 sycamore bowls and the all have warped out of shape before they come off the lathe. They run perfectly true on the outside but start to warp when reversed and halfway through hollowing. By the the time I’m sanding the inside they are a lot out of true. Any idea what I’m doing wrong or is sycamore prime to warp?

 

[akirk]

how wet are they (moisture content)?

 

[mattsutton29]

I’m not sure. They are direct from yandles and snainton. Supposedly kiln dried. Haven’t got a moisture meter.

 

[Richard_C]

I've not found sycamore to be particularly difficult, everything moves a bit over time but I have made thin wall/rim platters OK. As it happens recently did one with a Snainton blank (sad to see they are closing down forever soon). Moisture might be the problem but if they are decent purchased blanks rather than home prepared that is unlikely.. One way to deal with it is to rough it out, leaving the walls c. 20-25 mm thick and leave it for a couple of months then turn to finished size you want. I can't see the bottom from the photos, but making the middle of the base slightly concave helps, so it sits on a rim then when it does move, as all things do, it won't wobble and few will notice.

 

[niall Y]

It could be the internal stresses within the wood. It is interesting that it does this whilst turning. Rather than some time after. In the latter case I would suspect that the timber wasn't fully dry.

In a perverse way I quite like the way a bowl changes shape when drying I have a small Ash bowl that has done precisely this, which I find to have a very pleasing shape.

I know it's very satisfying to turn a bowl in one uninterrupted session, but it might be more expedient to relieve some of the stresses, by rough turning the shape And then you can re-turn it, at a later date. I appreciate that this doesn't help with the present situation - but isn't hindsight a wonderful thing?

 

[Paul Hannaby]

Sometimes wood moves because you are removing some of the stresses as you turn it. Kiln dried wood is more likely to suffer as it's dried faster which can lock in more stresses. Also, just because a piece of wood was kiln dried once, doesn't mean it is dry to any particular degree now. It would depend where the wood has been stored. Wood will acclimatise to the environment it is in so the moisture level can go up as well as down.

 

[cmoops2]

As Paul mentions, where you store your blanks after receipt and how long you store them before turning can be a factor.

On the odd occassion whe I've bought a blank from Turners Retreat (end grain sealed or not) I always rough turn them first and store them for at least 6 months in the workshop before final turning.

Check out this clip from Richard Raffan on rough turning bowls: