As mentioned in the previous entry, at the suggestion of my instructor, I modified the design such that the whole top would be a torsion grid. This approach did present its own problem though. Since the design called for the ‘leg’ to act as a massive tenon seated in the underside of the top, I would need a lot of bulk around the leg. I considered laminating solid wood pieces to build it up. I decided against that; I can’t recall why.
Instead, I opted to take what I call the weight machine approach. I would laminate several pieces of dense materials together like the stacks of weights on a machine at a gym. The thought was I could get 1) a solid area to bore out a mortise and 2) more weight by putting together several pieces of MDF together (nasty, toxic material, I know). I knew I would be making some jigs for this so I went with it and Willie confirmed it would be an okay approach.
I modified the SketchUp file so I could refer to it later for actual measurements on the cut list as well as knowing what the dimensions would be so I could scale it accurately. I was off an running.
Willie, our instructor, wasn’t particular about the materials to use for the model or how ‘tight’ the model should be. I told him I wanted to build the model pretty accurately because I thought it would give some good insight to the actual process. He suggested Basswood since it’s tight grained even though it is soft. Actually, he thought I should build the torsion out of Basswood too since it was so light and would not be seen. I was surprised but did a little research and discovered it weighs 26 lbs per cubic foot making it one of the lightest domestic woods readily available. It’s also pretty cheap. I went to Rockler and got a small stick.
As it turned out, building a detail model was a great idea. The first realization I made was the number of cuts that would be necessary. Lots. Also, the realization that there were going to be a lot of setups. Not only were there few right angles but there were few parts with the same dimensions. The cutting of the parts for the model was tedious but necessary to see if this concept had a chance of succeeding. I really didn’t want to invest the funds in expensive wood and cut it all up only to become firewood.
Why so tedious you ask? Well, this was in February and being in Minnesota, my shop doesn’t get used between September or October through April because its in a detached, unheated garage. So, the bulk of all this fun and games was being done with exacto knives, exacto saws, a small bench hook and a block plane… I could have gone to the shop at school and used the bandsaw but by the time I got out of work, drove to Minneapolis from St. Paul in rush hour traffic I had about an hour and a half of shop time. Between gas prices, lack of familiarity with their machines, and competing with full-time students for ‘open shop’ time, it was problematic.
The situation was what it was. Here is the result of a weeks worth of evening work on the kitchen counter:
When I was working on the leg/main support, I second guessed myself on the thought of a simple friction fit between the top and the leg. I for some reason thought cutting an actual tenon at the top of the leg would be a good idea. I think I reasoned it would make fitting it in the stacks of MDF easier.
In my previous post there is a detail shot of the tenon inserted in between the stacks. All in all, despite my experiment with the tenon, the model was solid! I got brave and tried squeezing the top/torsion frame from both the sides and the end. I even tried twisting it. It was stable. The one part I couldn’t test was the beam/stretcher strength. I didn’t actually cut a through mortise for that on the leg. I just glued it so technically it wasn’t completely accurate for judging the physical strength of the design. I felt relatively confident with it though…
My iPod weighs 14 oz. I didn’t do any math to determine it’s real world weight. Frankly, I don’t know the necessary formulas to accurately calculate what the real-world weight of an object that size would be. I do know that the deflection of the top from level was minor and I attributed a lot of that to the fact that the fit between the tenon and the stacks was not as snug as it would be when actually built. Also, I did put my 17oz #90 shoulder plane on the model but didn’t have the camera close by at the time. (I know. No pic, didn’t happen…) The model supported the plane but I was nervous about the glue holding the beam to the leg so I didn’t push my luck more than 10 seconds or so.
In summary, I truly believe building a model is a valuable undertaking when the design before you is involved or unproven. Were I to do it again, I would perhaps make it at 1/3 scale so the process was less finicky. At that size, a person could also use something like corrugated cardboard or foamcore but that might not provide accurate feedback as to the physical abilities of the design but would likely be adequate for seeing the piece in 3D so you could do as many walk-arounds as it took to be sure you were satisfied.
As always, thanks for following along and your critique is truly invited.
-- Jeff, St. Paul, MN