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With the last subassembly (electrical) removed, the only thing left is
an empty shell. Albeit, a very heavy empty shell. I had
hoped most of the weight was in the internals, but it turns out
the shell is remarkably heavy. It took 2 people to maneuver it
into the horizontal position, suggesting the weight is 300 lb or more.
Most of that mass seems to be concentrated in the solid cast iron
base plate. "Tip Day", as I've come to refer it, was a milestone in the restoration. At this point, almost everything that is coming off the saw is off, and the rebuilding phase may be considered begun as of 11/19/06. There are 2 things to be done with the saw in this position. First, I'll clean and paint the bottom of the plate. Second, I'll build a rolling chassis. |
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And here's a picture of the bottom. I'd like to think I'm the
first person to see this side of the saw since it was built in 1941. I was surprised to find the load is actually supported by only 4 small pads rather than the entire surface area. Also, you might notice there's some spots of light blue paint. I believe that's the official "DoAll Blue", but those spots are only here: the rest of the shell is painted a dark green (almost black) as a first coat. |
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Here's a drawing of the bottom plate features. These dimensions are approximate. Notice it's not quite symmetrical. The 4" pads at the corners are roughly 1/4" taller than the 2" "rails" are, so the entire weight of the saw is supported on those normally. I ran some quick "back of the envelope" calculations of the stresses involved at the critical points (with huge factors of safety) and it looks like A36 structural steel tube 2"x4"x0.12" will easily support this load with maximum deflections of less than 0.006". In order to be sure 2x4x0.12 A36 steel would be sufficient for the loads at the casters on the right hand side, I calculated the maximum stress and deflection of a cantilever 16" long with a 1500 lb load at the free end. Maximum stress was 9917 psi (giving safety factor 3.6) and maximum deflection at the free end was 0.0073 inch. Note that this calculation is extremely rough because the design for the chassis is complex and it's impossible for me to factor in the quality of my welding, but I believe I ran an unrealistically-worst-case scenario in my so there's absolutely no chance of failure with A36 steel of those dimensions. |
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Here's the base being leveled in preparation for welding the two
wheel-side casters in place. It's sitting atop a piece of
particle board that I carefully shimmed to level in 2 axes as a
reference plane for the base. By doing things this way, I'm able
to position the casters so as to minimize the need for shims. The tolerance for parallelism of the various outriggers on this base is only about +/- 1/4", owing to the crude technique I used to cut the steel. Ironically, I could have done much better if I had a large bandsaw. |
| Here's the base finished and installed! So far, none of the welds has cracked and the saw is remarkably stable and level. I stood on the saw and jumped up and down to put a little extra load on the base, with no effect whatsoever. I think the strength is adequate. Those washers on the bottom are large 2.5" cast iron load distributing washers to keep from crushing the box sections with the bolt tension. |
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| Here's the results of a couple hours pounding out the dents
in the front of the saw. These dents were definitely created
using some sort of framing hammer, as evidenced by the crescent-shaped
marks at the periphery of each depression. The metal here is over
1/8" thick, and there's a bracket inside the drivetrain bay that blocks
direct access to the largest dents. It's very difficult to tell from the photos here, but I've definitely improved things a lot. My method was to heat a small area until it glowed red using a propane torch. Then using a 3-lb sledge and a smaller body hammer along with either a block of wood or an iron anvil I pounded away at the metal. This was a very slow process: 3-5 minutes of heating with the torch, then 30 seconds or so of pounding. My goal was to flatten the metal until the remaining depressions were shallow enough that an automotive body filler could be used. By minimizing the depth and area of the depressions I can give the best chance of the filler material remaining in place over time. So what body filler should I use? I'm considering 2 options, both by Evercoat: Metal-2-Metal or Metal Glaze. Metal-2-Metal is an aluminum-reinforced filler, whereas Metal Glaze is a glazing compound (meant to be used as a topcoat for an ultra-smooth finish). Glazing compounds are not meant to fill deep imperfections. I believe the depressions that remain at this point are shallow enough for Metal Glaze. Metal-2-Metal is very strong, but difficult to work with relative to Metal Glaze. It will not produce the fine finish that Metal Glaze will, but it offers better adhesion and much better durability in an industrial environment. After much debate, I decided to go with Evercoat Rage. I came to this decision based on reading a number of car restoration and hot rod forums, where many people expressed satisfaction with the Rage family of products. Actually, I'd prefer to try Rage Xtreme, but its minimum quantity is 1-gallon (and that would be a waste for such a small job). I wasn't able to source this locally, so I got it from GoferAuto, who had the lowest price I could find and remarkably fast shipping. After applying 2 coats of Rage, it became clear that a glazing putty would be required to get a perfect finish so the machine can be painted without showing the repair. Evercoat Metal Glaze was therefore used atop the Rage to give a perfectly smooth finish. |
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| Stripping the entire shell was a time consuming, boring process. I
first stripped as much as possible using a strong chemical stripper,
then finished up using wire brushes on a 4.5" angle grinder and a 7"
sander/polisher. By far the hardest part to strip was the drivetrain bay. The amount of "goo" in it was astounding. I began by washing it out with a strong Lye solution (I used Castrol Superclean). I followed that up with some paint stripper (which also happened to be effective on the grease). From there it was many hours with a handheld wire brush, a slag hammer, and a dental pick. The slag hammer was used to remove the slag that DoAll never bothered to remove at the factory. As an aside, there is some of the worst welding I've ever seen in my life inside this saw. I would be embarassed to produce such welds, and I'm a complete novice. The picture at right shows the drivetrain bay. It's quite clean now, but not "perfect". There are just too many interstices, especially the area at the base of the column (right hand side in the photo; you can't really see it). Note the debris at the bottom of the housing - that's just some leftover wood chips from the dent pounding process. Since I couldn't get this area "perfect" (or at least "perfect enough"), I decided NOT to use the DTM Alkyd paint I'm using everywhere else. Instead, I'm going to paint this area with a couple coats of gloss white Rustoleum spraypaint. There are 2 reasons for this: 1. The drivetrain housing, fully assembled, is a dark place. Gloss white paint will greatly improve visibility. 2. If I had an abrasive blaster I could easily clean this area to my complete satisfaction. Since I plan to one day have such a machine, there's an excellent chance I'll want to go back and blast the area. Whereas DTM Alkyd is an extremely strong paint (and expensive), Rustoleum is very weak (and cheap). That means it will be much lower cost to blast away a couple coats of the Rustoleum. |
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| The first step in reassembly is painting the shell.
This should be done all at once, but the fact that I need to
body-fill the dents in the front drove me to use a 2-stage process.
Pictured at right is the first stage of painting, which covers
most of the shell except the very front. 2 coats of Sherwin Williams DTM Alkyd applied with a foam roller. Prior to painting, all the label plates (such as the serial number) were removed. These were held in place using small rivets, which were pounded out from behind. |
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These photos show the front and back of the shell completely painted and ready for reassembly. |
| Before | After |
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