Stephenson's Rocket--Working Model

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Brian Rupnow

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Today I finished the assembly of the front portion of the chassis , including the front plate itself, a 1/8" spacer, the crazy smokestack support and the smokestack. That smokestack support is a monster. It required three different fixtures to machine that part. I could have designed it simpler, but I wanted to attempt all of the fixturing. I will post the finished assembly and the three fixtures required to machine the support.---I got lucky with the third set-up and was able to use the front plate as the holding fixture for the third machining operation.



 

Brian Rupnow

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Today was a major lurch forward. I started with a 3 1/2" x 12" long piece of aluminum, turned half of it to 3 1/4" diameter, cut it in half, and counterbored both ends to receive the end caps. There is lots of exciting machining yet to come on that main cylindrical body. I had to quit half way thru the day and fabricate some brackets for a new flower box that my daughter was given, then jumped back into the shop to finish the main body so I could make a "mock-up".

 

Brian Rupnow

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I just finished adding the "wood cladding" to my boiler. I used a small (3/16") center drill and set it up to interfere with the boiler o.d.x about 0.020". Set the table stops up on the mill x axis, and rotated the rotary table 19 degrees between each linear cut. It turned out nice.
 

Brian Rupnow

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This afternoon I put in locating counterbores and #10 threads in the "boiler" to accept the steam dome and the safety valve. I never knew until this afternoon how badly I sucked at freehanding a "dome". It turned out okay, but the finished result does not reflect the first two attempts. I am not tearing down the set-up on the mill, because the slots for the axles and pivot rods still have to be machined.
 

Brian Rupnow

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Today I finished the work on the milling machine, and was able to tear down my set-up. You will see in the picture the end of the motor-mount bar, which runs completely thru the boiler from side to side. I was able to drill and mill the slotted hole thru, but that of course left round ends on the slot. I drove across town and bought a 1/2" square file to make the ends of the slot rectangular. There was a HUGE amount of time required to make those rounded ends rectangular, and I have a new blister in the palm of my hand from filing. The main "boiler" is almost finished. The motor mount bar will be held in place by bolts which are hidden by the end cap on the boiler. My initial thought were to Loctite the boiler endplates in place, but I have figured out how to use a "thru-bolt" that is hidden inside the firebox and goes completely thru the boiler and is threaded into the endplate which sets at the front of the boiler. Tomorrow I will make the bracket which supports the rear axle and the pivot shaft for the eccentrics. Then it will be time to start transferring the engines from the test stand over to the actual chassis. The wheels will be left as the last thing to do.
 

Brian Rupnow

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I'm finished with the chassis of the Rocket, to the point where I have to start transferring engine parts from the test stand over to the Rocket. I ended up having to put rubber o-rings on both pistons. The machine is setting beside me as I type this, running on 10 psi. It still doesn't want to self start, and it should. May be a matter of how I have the timing set, or may be there is still some friction in the system that it has to work thru. It's getting rather exciting now. Tomorrow should see the engines moved, and then I have to start on those big drive wheels.
 

Brian Rupnow

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Okay, we're good now. After running the engine for half an hour, it self starts. A bit of explanation---I'm not using Viton rings, just plain old rubber Buna-N o-rings. These rings are fine because there are no high temperatures to contend with.--But---they have an amazing amount of "stiction" when first used in an engine. If you give the engine a few drops of oil in the cylinder and run it for half an hour, the "stiction" from the ring goes away. There was enough air getting past the un-ringed piston to prevent the engine from self starting. Now, with rings on both pistons and half an hour run time, there is no residual "stiction" and the engines self start fine. The crank throws are 90 degrees out of phase.
 

Brian Rupnow

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This is the threaded rod that holds all of the chassis together. It passes thru a clearance hole in the firebox and the rear "cap", thru a clearance hole in the "boiler" and threads into the front cap and smokestack mount. It will get shortened up and the nut will be hidden inside the fire-box. The next picture I post will be with all of the engine parts in place on the chassis.
 

Brian Rupnow

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Oh Wow---If I just had some wheels, I could almost go for a drive!! All of the engine parts bolted right up where they were supposed to go. I have a few simple cosmetic detail to figure out, but I'm happy with the way this is looking.
 

Brian Rupnow

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--I'm setting here with everything assembled, trying to decide what to do next. There is an assembly of flat-bars that run parallel to the boiler and out in front of the engine from the rear of the driver platform. I have the material so I probably will build them next. I'm also thinking about how I am going to anchor the stay rods that act as braces on the smokestack and drivers platform. I would like to make them from 1/8" diameter aluminum round rods, but that creates a problem at the ends where they transition from round to flat. I might make them from 1/8" diameter steel cold rolled, which would let me silver solder a very small flat bar to each end. I checked to see what size socket head capscrew would work to attach them, but the only size that has a head diameter less than 1/8" is a number "0". That is almost smaller than I can comfortably work with.
 

Brian Rupnow

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I've started taking applications for "Train Driver". This guy showed up last night just after dark!!!--I also have a five year old grandson visiting for a couple of days. He should have a card like Paledin---"Have Toys--Will Travel".
 

Brian Rupnow

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I'm coming right down to the wire on this thing. All I have left to build before tackling the wheels are the bands which go around the boiler (Which will probably be cut from some aluminum tubing) and the piping below the boiler, and the fire-box door. Since the piping below the boiler is only for show and not for go, I think I can bend it up from round bar. I will make up a welding jig as shown in red, then heat the rod until it is cherry red and bend it around the posts in the jig.

 

awake

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That jig will allow you to avoid post processing.

Okay, terrible pun, but once it popped into my head, I couldn't resist! :)
 

Brian Rupnow

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This is the piping that runs below the boiler in it's first stage of development. A simple jig was made from scrap 1/2" plate and four 1/4" dowels mounted in it in the correct position. The "pipe" is designed with 1/8" inside radius at the bends, and the easiest way to achieve that is to bends the "pipe" around the 1/4" dowels. Of course the "pipe" is really 5/16" diameter cold rolled steel solid. It is going to require some more "finessing" before it is installed in place. It was heated to bright red in the bend areas with my oxy-acetylene torch and bent by hand.
 

Brian Rupnow

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Hah!!!--even the old and ugly get lucky sometimes. I had to go by my metal supplier today, and he had a cut-off of aluminum tube just about exactly the side I needed for the rings on the outside of my boiler. A little boring on the inside, and a clean up pass on the outside, and I have a lovely set of rings for the outside of my boiler. They will eventually be loctited in position, and the one ring that sets between the engines is going to have to be cut, but I'm so much happier making the rings this way than trying to form them out of aluminum strips bent around a form.

 

Brian Rupnow

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---Now, jumping back onto the project I started much earlier today. The piece has been removed from the jig, ends sawed off to correspond with the fire-box width, and a vertical section silver soldered on. The vertical piece has a hole drilled and counterbored thru the center, and a #4 shcs will go thru it and screw into threads in the bottom of a hole in the boiler. Although I have never shown it in the solid models, I want the sawed off ends to have a flange where it meets the sides of the fire-box. I'll do that tomorrow morning.
 

Brian Rupnow

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Today I added the "flanges" to the piping which sets below the boiler, and I built what passes for a fire-box door. What a crazy lathe set-up to turn the 9 degree tapered face on that "door". The only way I could make it work was to reach across center with the cutting tool and run the lathe in reverse. It worked fine, but was a really strange set-up.
 

Brian Rupnow

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This afternoon, while I had everything disassembled, I decided to paint. I've been dithering for a month, trying to decide whether to paint this thing or not, but finally decided to go with more or less "traditional" colors. Semi gloss black on everything except the boiler and wheels, which will be "Knock your eyes out yellow". So I painted--cleaned up---found another part---painted--cleaned up--found another part. I went thru about 5 or 6 rounds of this before I had most of the black parts painted. Damn, there are a lot of parts!!! Haven't painted the boiler yet, because I haven't Loctited the boiler rings in place, but maybe tomorrow. The only thing left to fabricate are 6 "stay rods" of various lengths. I know the engines run, because they ran on the test stand.
 
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