Whether to Rip and Re-Glue Window Stool Stock

For a 6.5-inch-wide window stool, how should stock be handled to minimize cupping of the piece in service? May 6, 2009

I make a lot of 6 1/4" window sills for a large home builder in my area. Stain grade is ash lumber. I'm wondering if you guys would rip the lumber 31/4" or so and re-glue with the growth rings inverted. This is typically how i do it since Iíve seen some 6" wide cutoffs turn into some funny shapes. I don't do the finishing, so I don't know if they are sealing both sides. Should I keep doing it this way, or would I be safe to rip a 7" board to width and save a lot of labor? I'm already guessing the consensus will be to keep ripping and re-gluing.

Forum Responses
(Architectural Woodworking Forum)
From contributor G:
When I make wide panels I take my 12" boards and rip them below 8" because that is the biggest board my joiner can handle. Otherwise I will just flatten it on the joiner and continue on. If the wood has been properly dried from the kiln and subsequently sealed properly after installation, the board should remain relatively flat. Plus 3 1/4" is still kind of wide. If you were gluing up to prevent cupping you should be ripping down to around 2" wide. Conclusion, joint it flat, make more money.

From contributor R:
You know what you are doing is safe and works. The only way I would do the full thickness parts is to pre-mill the stock a bit oversize, sticker and stack it, then re-mill parts as they get used. Not exactly a time saver
Since you do a lot of these windows, why not look into making your glue up and milling more efficient? UV curing the glue speeds dry times a lot, efficient clamping setups reduce time there, and being able to gang rip the original stock will pay off too. There are a lot of fairly low cost options for streamlining an ongoing operation such as yours. Feel free to check out my website and contact me if you want to discuss specifics of your operation.

From contributor F:

Basically if the wood is going to move, youíre not going to stop it. Ripping and flipping merely allows the wood to cup in two directions instead of one. It's a handy way to keep wide panels from cupping excessively in one direction, like tabletops. For something as narrow as what youíre making I'm not sure there's going to be a whole lot of advantage for the additional work required. You'll have to decide what your comfortable with, but if the wood is properly dried you shouldn't see a whole lot of cupping over 6-1/4". Certainly not enough for all the extra labor involved.

From contributor O:
Do you have any feedback from the builder or are you just hoping to forestall any complaints in the future? If you were following the old construction books they would advise quartersawn stock. They tend to do so quite often, and here they would be right. A window sill is about the most hostile environment trim sees (damp/cold from above, the furnace duct below blowing hot and dry). If you don't order quartersawn, your cut and flip is not a bad idea.

Just a thought, mark all the sills to be laid ring side down so they would more likely cup down than up. Also I have seen sills with a relief cut about a quarter of the way through the wood vertically from the underside. I imagine that was to relieve stresses that might cause cupping. It would be hidden by the skirtboard.

From contributor D:
I'm confused on what is being discussed. I learned that a window sill is the exterior lower horizontal part of the window, usually canted or beveled for water run. They typically are 8/4 or so, and are separate from the window frame, since they are prone to worst of exposure and fail more quickly than the other parts - and can be replaced somewhat easily. White oak is the preferred wood for these, historically. I would think ash is not a particularly good choice, and gluing for width would only make for an even earlier failure.

The interior lower horizontal member is a stool, as I learned it. There are many regional differences in naming these parts, but most glossaries will bear out the above. Exposure and species selection would be quite different for the two parts.

From Gene Wengert, forum technical advisor:
Contributor F has some great advice. Flipping has a very small effect; minimizing MC change is far more important. Very few people flip.

From contributor O:
What I was discussing is properly the stool, although here in the Midwest I am sure that the common reference by folks dustings, kids leaving empty soda cans, and people with African violets is that these indoor activities happen on the window sill.

From contributor D:
The questioner mentions "stain grade" so I assume he is talking interior, and therefore stools, but then 6" plus sounds like exterior. I'm sure any window stool has felt like a sill with the African Violets and summer thunderstorms. He also mentions a "large home builder".

From the original questioner:
Thanks guys, I am referring to the interior stool/sill. An exterior window "sill" is kind of a thing of the past (new construction windows don't have a sill you can set flower pots on, or pies to cool), so I think the interior "stool" is more commonly referred to as the "sill". At least thatís my experience. I have not received any complaints about the sills/stools cupping and Iíve been making them for about three years now. I was just wondering if I am making more work for myself by ripping and flipping. Many times the homeowner does the finishing, so Iím not sure they are getting sealed on both sides. Ash was pretty cheap, but now has gone up some around here, so I may approach them about using a different material after my inventory runs out. Most new homes have central air, so I would not expect drastic MC's.

From contributor W:
I would use the ash full width and make relief cuts in the back side (like they do with flooring). I don't think there is much possibility of it cupping at all. Even glued up boards will cup if thye get wet on one side.