Bog's Paddleduck Engine

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kvom:
As Sunday was Mother's Day here, most of the day was spent on family doings. Plus I was starting a minor repair to reweld the fenders on my car hauler trailer. However, at the end of the day I decided to cut off the metal for the block using the big horizontal bandsaw from the 1940s that I recently restored.

The metal was a chunk of 1x2x7" bar of coppery alloy. When cut the surface looks like a new shiny penny, but the patina is a dark brown chocolate color. My goal was to cut a 3.25" piece. This was the first time I tried to use the saw on anything other than a test on some 1/2" brass bar (which took 2 seconds to cut through).

The first and second attempts to start the cut saw the blade pop off of the drive wheels. I finally got the tension tight enough and was able to start the cut, but had the feed adjusted too slow. I left it to run while sweeping up a weeks' worth of swarf, but after 20 minutes it was only halfway through. I let off on the hydraulic cylinder a touch and it sawed through the next inch or so in a couple of seconds, then slowed. Another touch off and it cut through. In conclusion, these old saws need a lot of manual adjusting to cut, but once it's right they can really rip through the material. The resulting cut was quite straight as well.

I need to do some measuring, but I am hoping to get the steam chests and bearing blocks from whats left over.

kvom:
I spent a few hours today starting on the engine block. It took some time to square it all up as the material doesn't like big cuts or fast feeds. Too fast and it throws off dark chips and smoke. In addition it creates a lot of tough burrs, so lots of filing to debur the edges after milling each side was necessary.

The dimensions ended up right on for thickness, and about .100" large on height and width. Based on the material I have, the steam chests may be somewhat thinner than spec, so I am planning not to adjust the block width until I can measure them.

In any case, the cylinder bores are positioned relative to the center lines, so I proceeded to drill these. I am going to leave the bore at .500, which although somewhat less than scaled, is the size of my largest reamer. Were I to bore it to .590, the displacement would be 3.375 times greater than the original. As it is, the displacement will be 1.907 times.

I was concerned that scaling up the steam holes from 1.6 mm might not work, as I would presumably want the area of the opening to be approx. twice as large. Since a hole with twice the area is .089" in diameter and a hole 1.5 times 1.6mm is .094", it seems irrelevant.

kvom:
After milling the main block, I was determined to make the rest of that bar serve for the steam chests and bearing blocks, as I have no other thick brass.

The piece destined for the steam chests was just wide enough for two, but I was afraid that if cut on the bandsaw one piece would be too small. So I used the slitting saw to slide it in two on the mill. I can say that the level of "chatter" was more like a scream, but feeding at less than 1 ft/min at 300 rpm finally got the job done. After squaring the two resulting bars, I found that the height would be less than scale, but still enough for the computed valve bore with a decent amount to spare. I then milled one side to the proper width, but left the depths unchanged. Given that the datum lines are center lines, I can drill all the holes and clean up the depths at the end (I might possibly need to reduce the depth of the block slightly as well).

The remainder of the material was 1x1", meaning that the depth of the bearing blocks will be slightly smaller than scale. Before I mill the width I need to calculate an allowance for the smaller than scale crankwebs.

So not a lot to show in finished parts, but a lot of time spent on the mill.

The scale for the valve bore is between 5/16 and 3/8, so I will need to order some drill rod. Luckily Enco is running a free shipping + 10% discount the next two days. :beer:

kvom:
Not having any bar stock large enough for milling the crossheads, I did some calculations and found that I could get a block cut from some 2" round stock. I still has a chunk of mystery brass alloy that Cedge gave me, so I cut off a 1" slice on the bandsaw and milled it into an ablong block. This was yesterday; today I decided to continue. I didn't get far. :bang: As I was drilling one of the holes for the guides, I noticed a hot spot on the side of the block. Seems this metal gets hot when drilled, and actually melted at the bottom of the hole:

Since I also had a piece of 360 brass 2" rod, I went to Plan B and repeated the milling operation. Once I had the first block, I calculated that it was 62% of the original disc:

Here's the machining sequence for anyone that's interested. First, since the sides of the disc are reasonably straight, I chuck the disc in the vise with one side flat against the fixed jaw and mill one face flat to remove saw marks. Next I reverse the disc with the flat face on parallels and mill the other face. Now I can clamp the two flat faces on the vise jaws and mill one side (after calculating how much to cut). This flat side is then clamped flat on parallels to mill the opposite face. I now have something that looks like this:

I then use a square to clamp it vertically.

Once I had an oblong block it was a matter of carefully drilling and milling the crosshead out of it. I didn't find the optimum milling sequence, but all was fine in the end.

Hopefully I'll finish the other one the next time in the shop.

kvom:
Rather than finish the other crosshead, I decided to work on the bearing blocks that I had roughed out last week. It was tedious work, but nothing fancy. The vise stop saves a lot of time in repetitive operations on multiple parts. I did drill the oil holes before reaming the bores so as to avoid burrs.

For turning the bosses on each side, I used the same fixture I used for the eccentrics: a piece of aluminum round drilled and tapped 1/4-20. The first one turned out poorly, with a lot of tearing. I was using a medium speed and slow machine feed on the crossfeed. This alloy needed just the opposite: lots of RPMs and fast feed. Here's the results:

I did discover a potential problem. I drilled the holes for mounting the blocks on the base plate according to the plan. However, the material I had for the blocks was smaller than spec, so the blocks ended up .18" shorter in the longest dimension. Fortunately the blocks cover the holes, but using the planned 8-32 screws to attach them will mean that the tapped holes in the base of the block will be extremely close to the edges. I think I will just use 5-40 screws, leaving more "meat" around the holes. However, I'm going to sleep on it before making any decision. I could conceivably drill a second set of holes in the plate inside the ones I already drilled. In any case, I have not drilled mounting holes in the base of the blocks.

Any other ideas are welcome.

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