Straight edge…twisted cut! Help

[Saddleworthian]

Hey everyone!

I’m making plantation shutters at home and have previously posted about cutting from timber to get perfectly straight untwisted/warped workpieces.

I’m cutting Sapele wood, which comes in rough cut 8” x 4” lengths.

I have built a jig to get a square edge, and am happy that the edge is as flat as a mirror.

I cut two or three 3/4” thick lengths which will come off the saw flat, and then the next cut will bind on the saw and come off the saw twisted (winding).

I’m guessing this is due to tension in the fibre/grain of the wood, but am wondering what I can do to stop it?

Advice please?

 

[Droogs]

Your wood is still too wet or has been kilned too quickly and case hardened. Take a couple of strips off each edge and then leave the remainder a couple of days. Reflatten and then take some more off each edge.

 

[Saddleworthian]

I’m not sure they’re still too wet…I’ve had them on my shelf for over two months now in good conditions.

I’m interested in your theory about rapid drying though - perhaps I’ll try another source next time.

 

[baldkev]

It can take a long time for thick pieces to equalise right the way through.... and were they stickered to allow air to all 4 faces of each piece?

But yep, sometimes internal tension is to blame

 

[Saddleworthian]

Yes, they were correctly stored.

I picked them from the warehouse myself.

Thanks for the reply, for all the replies!

 

[Jacob]

Depends what size your components for the shutters, I assume smallish so I'd look at ripping 8x4" to 4x4" to 2x4 if that'd work. Just rip in half or thirds etc. not take off slices like carving a joint. Then cut to length according to cutting list, before ripping any further.

 

[Saddleworthian]

Jacob

This is an approach I’d not thought of before, and am intrigued.

Is there a scientific or logical basis to your idea? Is this something you have experience of? Or is this just something you think is best practice?

Either way, I shall give it a try as it is a fresh perspective.

On the size question, my biggest component is normally the stiles for the shutter, between 900mm and 1250mm x 70/75mm x 3/4”.

(Sorry about mixing my measurements…old habit!)

 

[peter-harrison]

All timber adopts a shape which is a compromise between all the opposing forces in it. Unless these forces are identical on either side of your cut, there's going to be movement. The difference between seasoned and green timber in this circumstance is that the seasoned timber will move once, while the green will move a bit when it's cut and more when it dries. It's well worth looking carefully at your timber before you buy it and again before you cut it. If you want tall doors, you are going to have a lot of trouble with timber that doesn't have straight regular grain that is parallel to the edges of the boards in both ways. On the other hand, if you want the door panels to be wild and interesting, you will probably get away with it.

 

[Hornbeam]

The problem you have is caused by tension within the piece of wood being released and the risks associated with deep sawing. In its 8" X 4" state the tensions are roughly balanced out, or there is mot enough tension to cause the piece to bend.
The tension could be caused by the grain in the timber and could just be one of those things or more likely the centre of the piece has a slightly higher moisture content than the outside. This is extremely likely as during drying the moisture has furthest to travel out from the centre and the drying actions work on this moisture gradient. This doesnt mean your timber hasnt been kilned correctly, just that it is a large piece. Many timber merchants only do air drying above 3 inches
If you adopt Jacobs approach you will generate the maximum moisture variation across the piece and create the largest forces, however the pieces will still be quite thick and able to resist bending while the moisture gradient settles down but it could all go horribly wrong
Droogs approach is much less risky. Take a slice or 2 off each side and then leave it to settle. That way you are doing the same to both sides . It is for exactly the same reason that when you thickness a piece of wood you take equal passes off each side .