Grain and Cupping

Grain and cupping--

I have read in many places that quarter sawn lumber is much more stable than plain sawn. I know that it doesn't shrink / expand as much and therefor is a good choice for projects that will be exposed to large changes in humidity. Being the 'thrifty' sort ( not to say cheap ) I decided to make the screen door I am working on from 'quarter sawn' douglas fir that I milled myself from lumberyard stock. So I went to Home Depot and picked through their pile of premium douglas fir 2x12's , checking the ends of the planks for pieces that had been cut from the center of the tree so that the outer (roughly) third of each plank was nearly vertical grain.

[(((((o)))))] sort of like this.


I ripped them on my band-saw so that I had two roughly 4" v.g. pieces from each plank and a 4" center piece to set aside for other uses. Since I was busy making sawdust for another project. I put them up on my lumber rack to acclimate while I finished my other project. In my case this means a couple of months since, as a carpenter I once worked with liked to say, "I might be slow,but I do bad work". I like to think that the 'bad work' part is said with tongue in cheek.

Well, to make a short story long, I eventually got around to running the quarter sawn pieces over the jointer and through the planner and cut some of the other pieces of quarter sawn to length for the rails . They all seemed to be dry and, having had that much time in my climate controlled shop, there was minimal twist and cupping. After jointing and planning , I resawed them on the bandsaw to about 15/16" , thinking I could use the off cuts , which now had one true surface and one rough surface, to make glued-up pannels for the bottom section of the door. They were about 7/16" thick so I was hoping to get panels that were about 5/16" when finished, since I would only have to true the one rough surface. Well the next day when I went into the shop all of the thin pieces had cupped a serious amount. I was shocked because I didn't think quartersawn picece were that prone to cupping.

My question to the forum is - did I not let them dry long enough or is cupping that much normal in quarter sawn stock?

Framing lumber is typically only dried to 18%MC, whereas interior lumber is dried to 6% - 8% MC. When you resawed them, it appears that there was a delta in MC% between the core and the shell.

Which way did they cup - towards the resaw side or towards the planed side?

They cupped to the resaw side. So that makes sense-- they shrank to the freshly exposed surface which was wetter. This has moved me to buy a moisture meter. Thanks for the feedback.

Even with a moisture meter, you still have to take measures as the MC is never totally equal throughout the thickness.

I've found the wider and thinner the resaw, the more issues, if not from moisture, from stress relief.

I find it helps to sticker them with cauls and clamps to "hold" them while they acclimate.

Bill, I have tried making things using that same type of lumber. No matter how I handle it, it always ends up warping, cupping, twisting, etc., so I gave up.

Thanks for the reply. I've never had any real problems with moisture before. It seems counterintuitive since I live in the pacific northwest, but seasonal humidity swings here aren't large. I have wondered about clamping while the wood acclimates, but really never had the problem before. I think what caught me by surprise was that (essentially) quartersawn wood reacted so much. I guess the lesson here is 'it ain't dry 'till it's dry'.

Thanks for the info, Mark. I guess the combination of being cheap and thinking I could use a local species ( I live near Seattle ) caught me by the short hairs. I really love the look of the old growth vertical grained douglas fir pieces I have seen. I guess I will just have to spring for some that is reclaimed or something.

Douglas needs to be kiln dried for furniture or doors to set the pitch. Or when it get hot or very warm sap will weep right out of the face. Even through paint.
Dont ask me how I know this.:o
Good Luck