Mill engine

[Pete49]

the problem is the way the valve is supposed to operate. The valve is worked by the motion of a eccentric lifting and dropping as it rotates....no problem there, the problem is the beam (on an eccentric)driven by the overhead crank is meant to drive the valve eccentric and I can't see how this would work. The site I went to explains that the eccentric movement can't be made to rotate the other eccentric at the valve end. Hope I explained it right, basically the bar with the holes in it has an eccentric to drive it and needs to convert that to rotary motion at the other end to turn that eccentric 
Pete 

[steamer]

Does the second eccentric have to make a full revolution to operate the valve up and down?

To answer this , is the valve travel equal to TWICE the second eccentric eccentricity?.....or just 1X or less?

If it's 1X or less, the second eccentric is just a lever.......with a big pivot pin mind you...

If it's 2X then your right.....it won't work as designed.

Dave

[Pete49]

I will double check in the morning Dave but I'm pretty certain its x2 as the bar is on the circular part and the valve actuator is on the eccentric.  It seemed odd at the time and now not so odd but I'll check first
Pete

[Groomengineering]

Dave, thank you for pointing out the obvious possibility.    Several years ago I spent hours (days?) staring the drawing thinking 'no way will this work', never occurred to me it might be a 'rocking arm'.  May have to dig the drawings back out and build one. 

Cheers

Jeff

[Pete49]

Well I checked it out and yep still looks like x2 to me. The actuator has to lift and drop and the eccentric has to do a full revolution to do that. The way it is designed it can't do it as the bar can only rock the shaft not spin it. Maybe Jeff can explain it better.
Pete

[Don1966]

Pete I don't know if this will help, but on the Beam engine I built the eccentric arm moves a pivot arm on a fulcrum that lifted the slide valve.

Don

[steamer]

Pete,

You could move the pivot for the arm forward towards the cylinder and make it a true belcrank lever.....that would be in keeping with practice.  You will have to lay out the throws, but if the arms on the bell crank ar different lengths, it shouldn't be so bad.

Dave

[Pete49]

Thanks Don & Dave for the suggestions but I know diddly squat about this stuff except what the plans show. I don't come from a machining background and am self taught (not vewry well it seems  )
Pete

[Groomengineering]

Ok I'm baffled again  Time to dig out the plans and crank up Solidworks.  I need the practice anyway.

Cheers

Jeff

[Bearcar1]

Pete, I have to agree with your very first statement that you made regarding getting the valve to operate properly. In the drawings that you sent to me, it shows eccentric #1 fastened to the crankshaft and driving a shaft (a flat bar actually) via a driving strap, which is all well and good. That is how most all standard steam engines handle driving the valve. The problem herein lies at the steam chest end of the equation. Here, that same bar has an identical 'strap', exactly like the one on the crankshaft end, that gets attached to a double-wide eccentric #2, riding on an idler shaft in that location. On this 'double wide' eccentric is the driving rod end and another shorter  strap that drives the valve. Picture two identical eccentrics connected by a long bar that has a driven strap around each eccentric at both ends of the bar. The idea being that when one eccentric turns, the other will follow the same movement. It won't. Not unless the idler shaft is physically being driven at the same speed as the crankshaft. The two eccentrics will have a tendency to want to bind quit easily unless they are synchronized accordingly. Your best course of action is to figure out a method of driving the eccentric at the cylinder, through some sort of chain/rope/gear drive, thus eliminating the crankshaft eccentric or change the design and utilize a bellcrank/lever arrangement at the valve chest instead of a second eccentric. I may be wrong here, but I just don't see this design will function very well unless it is altered in some form.


BC1
Jim

[Pete49]

Jim you nailed it exactly. With my limited knowledge however it looks like it will now be a static model as I haven't the ability to sort it though I will continue to try.
Pete

[Arthur Dent]

Did you get this sorted?

[Pete49]

I think I have I am sorting out the mounting of the lever and the angle. I have decided to take Bearcat's suggestion and use a bell crank so it will be a little different to the drawings but will hopefully work.
Pete

[Pete49]

While I was waiting to finnish the RT I was puzzling over the problem I have with this engine and decided to make this little one to see if it will help me understand the problem I have and yep it has solved the problem. I am now in the process of assembling the original engine and will make a similar valve system so watch this space. (not too often as I need to dodge the heat.) anyhow I have attached the pic of the little model I started on. Its 5" long overall and 3" high
Pete

[steamer]

Good for you Pete!...glad you sorted it out!


 
Dave