A Semblance of Precision with the Tools at Hand

This panel has been sitting around too long; it’s time to put wheels on it. I want the panel to be relatively high up, so that neither the wheels nor the cyclist (me) will cast a shadow on the panel. That’s not the best design from the standpoint of stability or wind resistance, but that’s life. I also would like to make a structure that can be leveraged onto a narrower panel if I ever get one.

I settled on 1″ x 1/16″ aluminum angle stock as the least expensive material that would do the job. After sketching out on paper what the pieces would need to look like, it was time to fabricate.

So I needed pieces 23.125″ and 32.08″ long. A cutoff saw would have been the ideal tool, or maybe a bandsaw. None of that stuff in my amateur shop, though, and I’m too cheap to rent out shop time at $80 a month. Hacksaw? That would work, but I’d have to file to the final dimension. It turned out that I was able to get a 7″ abrasive blade at a flea market (by now, you might notice that flea markets figure heavily in my material supply) for a dollar, and fit that onto my table saw.

Table Saw with Abrasive Blade
A 7″ abrasive blade on my regular table saw cuts aluminum cleanly.
Drilling support with center punched dimple
Next, I needed to drill 3/8″ holes, 3/4″ from the ends. This would have been simple if I just had a CNC milling machine, or even a drill press with a good vise on the table. All I had was a hand drill, and a cheapo press that I got from a garage sale for $5. I needed a means of holding the angle aluminum level for drilling. As I didn’t have a vise, I improvised by using a second piece of aluminum, and a small bar clamp from Harbor Freight. While at Harbor Freight, I also picked up a center punch, to help locate the hole.
9/64" pilot hole
A good drill press with a step drill would have been able to drill the 3/8″ holes directly. But with my drill press, a 3/8″ bit has a tendency to skate and wander on the surface. To help things along, I first drilled pilot holes. 3/32″ turned out to be a good size pilot.
cheap drill press
This is the $5 drill press I got from the garage sale. Unfortunately, my variable speed hand drill only had a trigger lock in the max speed position, and to drill a clean hole of that size, I needed a slower speed. By carefully positioning everything, I was able to use my right hand as a vise to hold the workpiece, and my left hand to squeeze the drill trigger to just the right speed, while simultaneously pushing down the lever of the press. I used cutting oil, so the operation went quickly and cleanly.
finished holes
Good enough for the intended purpose.
makeshift triangle
The final pieces wouldn’t fit together unless a corner was cut off at 45 degrees. As I didn’t have a triangle on hand, I made a 45-degree angle by folding a piece of used printer paper.
after cutting
This is how the pieces will fit together. The bolt in this picture is just for illustration – in the final assembly, the axle for the wheels will go through those holes.
Update: 04-MAY-2014
diagonal brace mockup
Who says we don’t use math after graduation? I used the Pythagorean Theorem to calculate that the hole-to-hole distance for the diagonal brace should be 41.79″. However, I wanted to check with the real thing before drilling, so mocked up the geometry using the real struts, but threaded rods as a proxy for the width of the solar panel and axle. The actual measured distance was 41.75″ as near as I could tell, so that’s what I used.
wheel fit check
All the wheel support struts are in place. I needed to make sure there everything fit together, and that there was enough clearance for parts like nuts. For this quick check, I omitted practically all regular cut washers and lock washers. The structure is as sturdy as I had hoped it would be.
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