"Shapely" Chair Design from WoodCentral

Maybe you've thought about chair design, but have you ever thought about it in terms of shapes -- literally, shapes, the kinds you learned about in kindergarten? This woodworker has. - Editor

"I know there are a number of requirements in good chair design. Comfort, appearance, strength, durability, etc. Triangles are strong in an engineering frame of reference. Many chairs seem to use rectangles or trapezoids. Rungs enter legs at approximately right angles. This requires exceptionally strong tightly fitted joints to resist the racking and twisting forces on the frame of the chair. So, why not use triangles? Are chairs supposed to be somewhat flexible?" - Barry I.

While the original poster talked triangles, the first response addressed squares. - Editor

"I've made 'triangular,' i.e., three-legged, stools. They sit reasonably well. Why make four-legged chairs? Several reasons. Tradition, looks, easier to make (especially drilling the holes), etc. You have more wood on each side of a tenon if it goes in closer to a 90 degree angle -- so strength is also a factor. Another thing to think about are stress points. How does someone sit in a chair? Where does the weight go as they are sitting or getting up? With two legs in the front and back, you have something to take the strain. Many chairs are somewhat flexible. There is often a slight spring to the undercarriage. The 'give' to the chair makes them more comfortable (in my opinion). Flexibility is also important in the upper portion." - J.L.

And this one thought the shape was a function not necessarily of design, but of the woodworking process. - Editor

"I suspect that a large part of it is the difficulty of executing [mortise-and-tenon] joints at anything but near right angles. You see triangles in engineering applications because it's not difficult to weld them together. It would be interesting to see a chair designed like a wood truss, where the angles are made by sandwiching truss members rather than cutting joints." - John

This next post addressed the query about whether chairs are supposed to be flexible. - Editor

"'Are chairs supposed to be somewhat flexible?' I'll try to take that one. I recently attended a short class by Brian Boggs at Woodworking in America. He addressed that very issue. Traditional 'green wood' chairs were made with wet legs and dry stretchers, so that the mortise in the leg would shrink around the tenon in the stretcher, making a tight, but flexible fit. He demonstrated by holding down the rear part of a chair and lifting the right leg. It went up fully one inch with no noise and snapped right back when released. Only problem is that this doesn't work with tenons with shoulders. Another issue is that we like our chairs to be light and graceful, not big chunky affairs. So that limits the amount of real estate available in any one leg for joinery. Four legs spreads out the stress." - Jesse C.

And there were a couple more woodworkers with thoughts about triangles. - Editor

"I'm not an engineer, but thinking about your question caused me to come to the following ideas : Triangles are ultimately more stable than rectangles. That's one reason why the pyramids have been around for millennia.The problem with using a true triangle as a chair support is that, if you set the triangle on its base, at the top is a point. If you look at the chair from the side and the legs form a triangle, you would have to teeter the seat on a point (which might make a good amusement ride). Many chair designers in history have come to the use of a trapezoid, which is a truncated triangle, and with the best features of a triangle and a rectangle. That is, the top is flat for seat attachment, and the legs are angled for stability. The idea is to get the best compromise trapezoid shape." - Yonak

"I think Yonak has the right idea; it would be rather painful to sit on top of a pyramid."- Moses Y.

OK to Leave Batteries Uncharged for Long? from WoodCentral

Battery storage is a recurring question for woodworkers whose shops are subject to temperature extremes, but this snowbird woodworker has a bit of a twist on the battery storage question: how long, he asks, is it OK to leave a rechargeable battery uncharged as he travels between shops in Michigan and Florida? - Editor

"I have a winter workshop in Florida. I will no longer be hauling tools back and forth from Michigan. I know I can use a corded drill motor, but I have become used to the cordless. Does anybody know of a rechargeable battery than can stand not being re-charged for 9 months?" - Jerry

The first respondent said "absolutely not." - Editor

"No. If you will be using the tool, you will need to recharge. If you don't use it, you won't need to recharge as often. I've had batteries last for a good six months without recharging - but if you use them ... " - J.L.

But others said, with the new lithium-ion batteries: well, maybe ... - Editor

"The lithium-ion batteries are said to have a long shelf life; not sure if it's that long. The real question, I guess, is whether a battery that's allowed to sit that long will go stale and fail early; you can always put it in the charger the day you arrive. I'd contact some of the manufacturers and see what they say about their batteries in your situation." - Bill H.

"Lithium-ion batteries should do that OK. I have several, some of which do not get used very often, like an impact driver. They seem to hold up very well." - Jesper

"Just don't store them at 100 percent charge and don't let them get too hot. Li-ion cells live best stored at 40 percent charge. Not sure how you can measure that easily (you need access to the cells). We buy and store thousands of Li-ion batteries. They come from the factory at 40 percent and will last months. Not ideal, but we can't manage our demands/needs any closer than that." - Tony

And this poster had some thoughts about lithium-ion capacity, and the effect of the storage temperature. - Editor

"Li-ion batteries operate in mid-range of maximum theoretical capacity. Below a certain percentage of total capacity the battery is irreversibly compromised, and above a certain range there is risk of spontaneous discombobulation (smoke and fire if the safety features fail). Hence, all lithium-ion batteries and chargers have battery management electronics to keep the battery in this mid-range of total capacity. So, for example, a Li-ion battery doesn't become completely discharged in use; rather, the battery is shut down at a certain minimum charge and similarly shut down at some percentage of total charge.Hence, there are two possible percentages, one for the total capacity and another for percent useful capacity.

"The bottom line is that battery life will be shortened at a greater rate any time the battery finds itself outside the optimum charge range. But, as Tony said, there isn't anything practical that can be done about it except storing the battery cool, or better cold, to minimize the effect of the battery-destroying chemistry that occurs more or less at any percent capacity. As important to battery life as storage is the temperature that the battery is discharged at and the temperature it is charged at.

"About any modern tool is going to have a lithium-ion battery. This is a fairly new battery technology, so there are many variants to the details of their construction and materials, and no doubt some may be better at one attribute than another, but how would anyone but the technical staff of the battery company know which is better at this task or that, for example, storage? Indeed, there are other battery technologies that have better shelf life, but they don't make them to power drills. Lithium-ion batteries (NiCd and NiMH too) will typically have better life if they are stored in the mid range of charged capacity. All battery types have better life if stored cold, poorer life if used cold." -Bill T.

And one respondent had a suggestion that completely avoided the issue of storing and recharging long-unused tools. - Editor

"I assume you fly down to Florida; otherwise you wouldn't have this problem. Why not just ship the batteries to Florida via USPS, UPS, FedEx, etc.? Ship 'em back when you leave, and have year-round use from the same set. I know this doesn't answer the question you actually asked, but based on the limited info provided, it seems like a solution." - Henry H.