Im working on the valve and its operating parts. Ive made the eccentric straps and valve rod bearings so now Im on to making the eccentrics. A week or two ago I started making one of the eccentrics. I was midway through when I realized, NO!, make the part thats bored out first, then turn the other part to fit. I finished turning the part to its nominal size but then when I went to separate it from the rest of the barstock I cut it 0.030 too short. It was almost like when I first realized I was making the wrong part first, it was destined to end up in the recycle bin.
So I made two eccentrics this week that differ in minor diameter by 0.001. I turned each one to fit one of the straps. I like a nice close fit here, probably closer than necessary. Ive begun to realize making this two cylinder engine that a new challenge arises in a multi cylinder engine, ie, keeping track of what pairs of interacting parts go together. Im using witness marks to keep track of mating parts. Maybe that will be my next engine a multicylinder with completely interchangeable parts. Sounds easier than it probably would be.
With 2 drilled/tapped holes for 10-32 set screws the eccentrics are finished.
Here, the straps are fitted onto their corresponding eccentrics.
Next, I fished some ¼ steel scraps from the recycle bin for making two valve arms. Ive deviated from the original plans in making these. Plans call for filing a ¼ square hole in the arm and pinching it onto the valve end with a 4-40 screw. My design is all machine work which is easier to do for me. I milled a ¼ slot in the arm, then made a cap that fits over the slot to hold the valve in place. The slot is milled 0.010 undersize on the vertical dimension so the cap actually clamps the ¼ square valve end. The valve arms are pictured here clamping a piece of ¼ square steel bar to test for fit.
Valves were made from ½ brass rod. I turned them down to a diameter of 0.374 to fit the 3/8 reamed hole in the cylinder block. Then they are milled to produce two flats near the middle to act as open steam ports for each end of the cylinder, thereby producing a double acting mechanism. The completed valves are shown here:
Installed in the one of the cylinder blocks with the valve arm attached to the valve
I had one of those Aha! moments this evening. Im sure this has happened to some of you out there. Machining an engine or other mechanical device requires quite a bit of concentration at times. Ive been working on this engine for over 2 months and Ive been in the trees for so long I wasnt paying attention to the forest! By golly, I dont have that many parts to complete. Steam inlet flanges, crank pins and the baseplate and Im done. Im having déjà vu all over again because it was just about a year ago when I completed my first engine (of this design actually).
I made two sleeves for the valve rod bearings. Learned a good lesson making them too. Wasted time is wasted, no matter how trivial the part. I turned the minor diameter of my first sleeve to a diameter of 0.249 to fit the ¼ reamed hole in the bearing. Next I center drilled it in preparation for drilling a clearance hole for a #10 screw (#9 drill). Then, since I wasnt reading the plans I put a ¼ drill in the tailstock chuck and started drilling away!. If anyone needs proof that 0.249 0.250 is a negative number, I have the proof in the chip pan under the lathe.
Heres a pic of the valve trains, one assembled, the other in parts.
My next post will be a completed engine. Im making a baseplate from wood to test out my dimensions, then later Ill use a piece of aluminum plate. Once I get the dimensions correct, Ill pin the crank webs to the crankshaft with some #8 set screws.
Cheers,
Phil