johnmcc69--the cam is rotating at the same speed as the crankshaft, but you have to watch it on Youtube at full screen to see it.
Inspiration for new air motor
- Thread starter Brian Rupnow
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I've just realized that my valve sequence may seem a bit funky because with the pivot in between the crankshaft and the actual valve, the valve action is reversed from what the original motor was. Now I have to try and decide what that information actually means to me. Last night I printed out five pages of valve positions from the original motor, to determine where the valve was when the piston was at top dead center, bottom dead center, halfway thru its stroke going up and coming down, and what things looks like at 45 degrees past dead center travelling counter clockwise. I'm 99% certain that if the cam, valve, and valve body worked on one single acting engine, it should work on another single acting engine, even though the piston stroke may change from on e engine to the next.
I'm pretty sure I have the valve sorted out, thanks to some help from Jason. Now if I get really, really, really bored this summer, I have something to work on.
Sometimes it is a bad idea to make too much of a change from whatever engine inspired you in the first place. I didn't like the look of the feet that I had on the model, so I changed them to be more or less the same as the flame-eater engine in the first post of this thread.
I have a theory on engine building that goes like this. Take the awfullest, most miserable part on the whole job and do it first. If you can do it successfully, then anything that comes after will be easy. The block that holds the crankshaft bearings and the pivot shaft is the hardest part on this engine. I rooted around in my box of aluminum and found a piece big enough to do what I wanted. This is kind of a trick, because you need a considerably larger piece to start with than what you finish with---especially if there are radii near the perimeter of the piece. You can't drill half a hole, so the stock needs to be large enough to leave about .100" beyond any holes that are drilled to give these radii. there are four holes to be drilled here. A 1" dia. hole on the right to give the radius I want. A reamed 3/16" hole in the upper left corner for the pivot shaft, a 3/8" hole below that to give another radius, and the center hole, bored to 0.906" for a bearing fit. You can actually see the bearing setting in there in the shot on the mill. I drilled that hole to 27/32" and bored it the rest of the way.
Some quality time with my friend the bandsaw yields a part that is starting to look like the drawing.
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I would like to see how you do the outside radi on the pivit pin holes.
will you file them to size or will you machine?
will you file them to size or will you machine?
I have 3 choices, I can use milling machine-rotary table, or my big belt sander, or make a couple of filing buttons and use them. The Filing buttons are the least work with no danger of cutting too much.
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I remember the filing button trick from the universal joint build you did. thanks for reminding me about that one.
This morning I cut the center out of the bearing support I made yesterday, and to finish it up nice I've made up a pair of filing buttons. These are made from 01 steel rod, cut to the finished diameter you want on the part you are going to file ,and have a hole in the center same size as the shaft you will be using. Then they are heated to red/orange and dropped into a can of oil. They are now harder than the devils horn, so a file won't cut them. You mount them as I have shown, and then use a file to cut the aluminum part, and the filing buttons keep your file from going where it shouldn't.
Now is that a beautiful thing, or is that a beautiful thing!! Using the filing buttons sure makes for a nice round pivot shaft boss. I keep making and saving filing buttons for applications like this. Much of the time if the radius is large I just use my stationary belt sander and "eyeball" it. I have a 3 jaw chuck permanently attached to my rotary table, so it's rather difficult to do radii on the rotary table.
I turned two pieces of aluminum to the correct width, i.d. and o.d. to become bearing caps. This used up two "short ends" out of my stock bin. If I do this right, when the caps are holding the ball bearings correctly, there won't be a visible gap between the caps and the main part they bolt to.
And now you know how I spent my day. Dang!! There's a lot of work in them bearing caps.
Today's work was this rather elegant little piece that looks a bit like a wishbone out of a metal chicken. Form follows function--the gap between the two arms is to allow room for the connecting rod big end to pass clearly when it rotates. There will be a second part to this linkage which runs in the opposite direction from the 3/16" steel shaft and picks up the eccentric cam movement.
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looking good, question on the bearing caps. when drilling off center of a circle like that, what do you do to keep the bit from walking? do you use an end mill to start the hole downwards and switch to a drill when you have a flat? or whats the trick to a drill like that?
I always use an end mill to cut just deep enough to have a flat spot to start a drill/countersink. After I have "touched" the flat enough to make sure my drill doesn't "walk", then I drill the hole. Many people say you don't need to use a drill/countersink to start your holes, even on a flat surface, but I get much more consistent results by using one.---Brian
I had high hopes of getting the first assembly of my crankshaft completed today, but I just plain "ran out of gas". I bought the material, cut it to length drilled 3 of the four holes in the crankshaft webs--and that was all I had energy for. I like to do the initial assembly and Loctite it, then let it set for 24 hours before cutting the center out and adding the dowel pins. Ah well--tomorrow--tomorrow--
We have a crankshaft---at least a darn good start on one. I just got it assembled with Loctite. After it sets up for 24 hours I will dowel all the joints and then cut the center out.
Nothing says class like brass!! Con rod is finished other than a visit from the bling fairy.
Well, that takes care of most of the major linkages. Crankshaft has been drilled and dowelled. The link that goes over to the elliptical cam is a bit odd, so I may do it next.
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