Oak cupping

[luke1i1]

Hi all

So I have been working on a project to make a cake stand. I had some bad experience several weeks ago with some "green" oak which has led to me reading up on MC in depth.

I have now acquired some kiln dried oak rounds for the base and surface however I am still experiencing cupping.

I have bought a moisture meter and the MC in various places ranges from 9-10% which is very slightly on the high side but nowhere near as bad as before.

Let me explain my process for turning the wood.

First I mount the oak round to the faceplate and face the opposite side to create a flat surface (this will form the base to sit on the table). I then remove the wood from the lathe (with the faceplate still attached) and confirm this is flat (I.e. no wobble when on my table). I then remove the faceplate and mount this to the side opposite side which is now flat. I then turn the outer edge and opposite side to suit before sanding etc. However when I remove the faceplate the dam wood has cupped and does not want to sit flat on the table!

Has anyone any suggestions as to why the wood is doing this? Is it the internal stressors of the wood?

Thanks for your time

Luke

 

[Paul Hannaby]

This is not uncommon with kiln dried wood. The drying process creates stresses in the wood and if you cut much of it away or split the board, the wood cups.

 

[CHJ]

Ensuring removal of equal amounts from both faces sometimes helps.

If you are putting the round on a separate stand, then with the aid of a decent mortise and tenon and sound non creep glue you can use the stand joint to hold the middle third of the round reasonably flat. Similar to this

If the cupping is within 1-2mm across a wide round without a stand then fit three small button feet or small felt furniture pads equally spaced under it, it will sit comfortably on those.

You can always, reduce the base surface bearing diameter to reduce the rock potential.

 

[Mike Jordan]

If you use quarter saw oak the problem should not be evident. Quarter sawn is stable since the growth rings are at 90 degrees to the face, it also shows the medullary Ray's as a pattern on the face. The photo shows the face of a quarter sawn pair of boards

 

[luke1i1]

Thanks everyone for the feedback! I guess it's pretty normal then. It just gets frustrating when you spend so long turning something flat and it starts to warp!

 

[Sheffield Tony]

If you are going to put a moist cake directly on it, then you'll see some proper movement I'd guess, quartersawn or not.

 

[Simon_M]

you'll see some proper movement I'd guess, quartersawn or not.

Certainly the cake will disappear! The effect of movement can also be seen in ordinary PAR timber. Machining one side and then the other, is like planning one side and then the other, only to find the final shape is distorted.

Using a glue block and turn both faces together helps. Take small delicate cuts on each side over several sessions and bringing the workpiece into the house on the chuck in the meantime, can help achieve stability because you will iterate to the final shape in small compensating steps.