Starting around the time I was first getting my Webster to run, Brian Rupnow started a build thread on a vertical 1" bore by 1" stroke engine he was designing. I watched it within interest because I was trying to decide what to build for my second engine.
I spent a while looking at hit and miss engines, and talked about scaling models to get closer to what I was thinking of building, but in the end I decided to build Brian's engine from his plans.
Brian finished in a few months. That's highly unlikely for me. First off he's a much more experienced machinist, and second off, I'm working from 2D prints in pdf files. While I have both a manual and a CNC lathe, my mills are only CNC, so my work flow or processes are different from most folks. For parts that I want to CNC that will mean turning the 2D drawings into 3D models in CAD, and then using CAM or writing manual files to get the tool paths. There are other things the prints call for that I should do; heat treating O1 (oil-cooled) steel; silver soldering some steel parts together, and so on. These are things I think I know how to do in concept, but I'll need to test the details.
My CAD program (Rhino 3D, but ver. 5 while 7 is current) is supposed to import .pdf files, and it sorta does. It doesn't import the dimensions and some things it imports (like circles) don't behave at all Rhino's native version. It just puts lines on the screen, and the commands to create dimensions don't work for many things, so it's going to be a completely manual process. Before you machine a part manually, you need to study the drawings. That doesn't go away with reading pdf files in.
For my first experiment, I thought I'd import the crankshaft counterweights. These have a rather complex outline, with only three straight lines in the whole part. To do these on the rotary table would take multiple setups. I believe that the whole part would take seven setups. If I could do it in CNC, I thought I could reduce that to three setups. First, I tried to import the outline, scale it in size and then convert it to a solid. It went better than I thought. As a test, I printed it in PLA, and it came out looking like it should.
It seemed like the best way to make this would be to not do that rectangular cutout in the bottom until the outline was cut. Then I could drill a hole where the center of the large radius (top in that view) is, and use that to bolt the workpiece to a tooling plate. Starting with a roughly 2" x 6" piece of solid steel I'll drill two holes far enough apart to cut two of these counterweights; with the tool paths based on a 3/8" end mill that was 2.000" apart. The cutout would be done using what CAM programs call "waterline" cuts: constant depth passes around the shape. Once the outline is cut, I'll stand it up in a vise, and cut out that 0.500" wide rectangle. After that, there are two holes, a through hole from top to bottom (you can see it in the center of the plastic model) and its counterbore.
This shows the two pieces right after cutting them out. I like to say it came out almost as if I knew what I was doing. It was kind of cool watching the cutter cut the one on the right out of the steel without touching the one on the left.
Look between the two of them where the piece of stock that hasn't been cut away has a point that's pointing out of the screen. See the ledge between the left and right pieces? It's an arc from that point to the right side of the left counterweight. What you're seeing is the left one isn't cut to full depth while the right one cut through the steel into my scrap aluminum backing piece in places. The backing piece is visible on the front left.
All that irregular depth of cut meant was that when I took them off that fixture they're on, I had to do some file work to make the problem child match the other one.
Now we get to the real meat of this task. How do I hold those rounded parts so that I can cut out the rectangular relief that's under the mounting screw? I want something with a concave radius that matches the convex parts, to hold it upside down in the vise. I thought about using the rest of the steel that I cut them out of, but that's the wrong radius. That radius is 3/8" more than the part because of the cutter going around them cutting out the parts. At some point, it occurred to me to use my 3D printer to print a fixture. An hour and 30 cents worth of filament later I had a fixture.
The two parts squeezed together are .620 thick, and I made the plastic thinner - like about .575 - so that the jaws wouldn't just squeeze the plastic but would lock the parts in place. I made sure the bottoms of the blanks were parallel to the mill table with an angle gauge.
Once I cut the rectangular cutout, the printed fixture was a perfect way to hold the two parts to drill the through hole. Being backed by plastic and not my vise made it risk free to the vise so a no-brainer to do. They're not technically done in this picture, there was one more step, but they're pretty close to being done.
This is after the second setup of the three needed, with the two counterweights alongside the fixture and the 3D printed test counterweight I did to make sure the dimensions were right after I translated from .pdf files to a CAD drawing. To do the final setup, all I needed to do was stand the two parts on their legs and center the drill bit that made the holes in the parts. I did the 1/4" counterbore with an end mill held in the drill chuck. The only motion is the up/down of the drill.
I'm not sure what the next part will be, but I either plunge more deeply into porting the drawings into CAD files or do something where I can work off the pdf files. I had been thinking of doing the crankshaft because I've never done one like this. I noticed that in Brian's thread he had the mating piston connecting rod done first before getting into the crankshaft, so that points me toward doing the conn rod before the crankshaft.
I spent a while looking at hit and miss engines, and talked about scaling models to get closer to what I was thinking of building, but in the end I decided to build Brian's engine from his plans.
Brian finished in a few months. That's highly unlikely for me. First off he's a much more experienced machinist, and second off, I'm working from 2D prints in pdf files. While I have both a manual and a CNC lathe, my mills are only CNC, so my work flow or processes are different from most folks. For parts that I want to CNC that will mean turning the 2D drawings into 3D models in CAD, and then using CAM or writing manual files to get the tool paths. There are other things the prints call for that I should do; heat treating O1 (oil-cooled) steel; silver soldering some steel parts together, and so on. These are things I think I know how to do in concept, but I'll need to test the details.
My CAD program (Rhino 3D, but ver. 5 while 7 is current) is supposed to import .pdf files, and it sorta does. It doesn't import the dimensions and some things it imports (like circles) don't behave at all Rhino's native version. It just puts lines on the screen, and the commands to create dimensions don't work for many things, so it's going to be a completely manual process. Before you machine a part manually, you need to study the drawings. That doesn't go away with reading pdf files in.
For my first experiment, I thought I'd import the crankshaft counterweights. These have a rather complex outline, with only three straight lines in the whole part. To do these on the rotary table would take multiple setups. I believe that the whole part would take seven setups. If I could do it in CNC, I thought I could reduce that to three setups. First, I tried to import the outline, scale it in size and then convert it to a solid. It went better than I thought. As a test, I printed it in PLA, and it came out looking like it should.
It seemed like the best way to make this would be to not do that rectangular cutout in the bottom until the outline was cut. Then I could drill a hole where the center of the large radius (top in that view) is, and use that to bolt the workpiece to a tooling plate. Starting with a roughly 2" x 6" piece of solid steel I'll drill two holes far enough apart to cut two of these counterweights; with the tool paths based on a 3/8" end mill that was 2.000" apart. The cutout would be done using what CAM programs call "waterline" cuts: constant depth passes around the shape. Once the outline is cut, I'll stand it up in a vise, and cut out that 0.500" wide rectangle. After that, there are two holes, a through hole from top to bottom (you can see it in the center of the plastic model) and its counterbore.
This shows the two pieces right after cutting them out. I like to say it came out almost as if I knew what I was doing. It was kind of cool watching the cutter cut the one on the right out of the steel without touching the one on the left.
Look between the two of them where the piece of stock that hasn't been cut away has a point that's pointing out of the screen. See the ledge between the left and right pieces? It's an arc from that point to the right side of the left counterweight. What you're seeing is the left one isn't cut to full depth while the right one cut through the steel into my scrap aluminum backing piece in places. The backing piece is visible on the front left.
All that irregular depth of cut meant was that when I took them off that fixture they're on, I had to do some file work to make the problem child match the other one.
Now we get to the real meat of this task. How do I hold those rounded parts so that I can cut out the rectangular relief that's under the mounting screw? I want something with a concave radius that matches the convex parts, to hold it upside down in the vise. I thought about using the rest of the steel that I cut them out of, but that's the wrong radius. That radius is 3/8" more than the part because of the cutter going around them cutting out the parts. At some point, it occurred to me to use my 3D printer to print a fixture. An hour and 30 cents worth of filament later I had a fixture.
The two parts squeezed together are .620 thick, and I made the plastic thinner - like about .575 - so that the jaws wouldn't just squeeze the plastic but would lock the parts in place. I made sure the bottoms of the blanks were parallel to the mill table with an angle gauge.
Once I cut the rectangular cutout, the printed fixture was a perfect way to hold the two parts to drill the through hole. Being backed by plastic and not my vise made it risk free to the vise so a no-brainer to do. They're not technically done in this picture, there was one more step, but they're pretty close to being done.
This is after the second setup of the three needed, with the two counterweights alongside the fixture and the 3D printed test counterweight I did to make sure the dimensions were right after I translated from .pdf files to a CAD drawing. To do the final setup, all I needed to do was stand the two parts on their legs and center the drill bit that made the holes in the parts. I did the 1/4" counterbore with an end mill held in the drill chuck. The only motion is the up/down of the drill.
I'm not sure what the next part will be, but I either plunge more deeply into porting the drawings into CAD files or do something where I can work off the pdf files. I had been thinking of doing the crankshaft because I've never done one like this. I noticed that in Brian's thread he had the mating piston connecting rod done first before getting into the crankshaft, so that points me toward doing the conn rod before the crankshaft.
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