Shop Step Stool - [sketchup model]

That’s pretty neat, Brad, and awfully handy as well. We all need a step stool in the shop and this

-- Thos. Angle, Owyhee Design, Oregon

Excellent. Thanks for sharing.

-- We must guard our enthusiasm as we would our life - James Krenov

looks like a really sturdy stool . Great design and a great purpose!

-- "Functional WoodArt" by Debbie, Canada (http://www.execulink.com/~yohan)

Hey that’s quite a neat design, kind of like a sawhorse on two levels. Since I just built some sawhorses and was looked at several designs before doing so, it’s interesting that you went with something very similar to what I built – and they are very sturdy. So, how did you join the stretchers between the two steps? Edge grain glued together?

It’s cool that you shared the sketchup plans. That’s the beauty of it, eh, that you can not only show it but you can share a 3d plan…Now if we just had a sketchup 3d viewer plugin..everytime I see a pic of a sketchup model, I keep trying to rotate it!

-- Steve, New Zealand, www.steveracz.com

daltx,

Yep, jointed edges glued together.

I considered the question of front to back strength and possibility of needing a stretcher front to back. If this were a typical sawhorse I’d just screw a triangle of ply on the inside and call it done. I wanted something a little cleaner so no plywood and no screws. I still could have cut a dado and dovetailed the ends for a stretcher across the legs but I don’t think I need it.

The legs splay out at 10 degrees each, 20 degrees total inside angle. The force of me standing on the treads transmits 17% horizontally out to the legs front to back. So for a 200 lb guy holding another 50 lbs in his arms that’s about 43 lbs force prying the legs apart front to back. Off the cuff that sounds like a lot, and if I ever jump on it that number goes way up.

But, there are a couple of saving elements. The first is that the legs are not free at the bottom. If the bottom of the legs were wheels or if the stool was on a slick surface, maybe hardwood or tile, somewhere that the bottom of the legs couldn’t get a grip, then all of the lateral force would have to be held by the middle glue joints. For this stool, out in the shop on a concrete floor, the bottoms of the legs get a grip on the floor. Basically the floor pushes back on the legs to keep them together. The glue joint doesn’t have to hold the entire outward force.

When the legs can get a grip it’s kind of like having a front to back stretcher. The bottom of the legs “lock” into the floor and don’t get to splay out. The floor holds part of the outward force and the middle joint doesn’t have to carry it all. This is not perfect, and there’s always the possibility of a leg slipping, and so on. But even if the legs don’t get a perfect grip I think the wood and joint is strong enough.

The other saving element is that the vertical force is not transmitted just along the legs at a 10 degree angle. Basically the 17% number only applies if the legs are very skinny. With wide legs a significant portion of the load is carried straight down vertically through the legs to the floor. It is never seen as an outward force. So the the max outward number (43 lbs) only applies under very specific conditions. To get a better idea of this look at the stool and picture standing mostly centered or slightly out on the front step. Most of the weight is straight down through solid wood. Almost none of the weight is held at an angle. So almost no outward force.

And if it’s not strong enough, if it ever cracks, I’ll either just screw a stretcher front to back, or if I care enough I’ll cut a dado front to back with a shoulder plane, cut some dovetails at the ends, and put in a hardwood dovetail stretcher front to back maybe a third the thickness of the legs.

Good catch though, at first glance you would think about using a front to back stretcher, I did.