Axle pump

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BryceGTX
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Post by BryceGTX » Thu Feb 12, 2009 12:13 am

Jack.. your excellent threads including this one and your frame construction thread motivated me to create a thread myself. Your decriptions and pictures are absolutely top notch. And your techniques are novel.

I can see why you 3/4 inch guys like the scale. Parts are a more resonable size.
Bryce

srrl5
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Post by srrl5 » Thu Feb 12, 2009 12:27 am

Jack,

That is a great trick, I did the same thing to make some eccentrics for a rock crusher I made. What I found was it takes more spacer then half the throw you want, as you open up the jaws to grab the bigger dia. the shim makes the starting point for the shim moves so you don't get the full amount. On the 2" dia. eccentrics I was making a 5/16" shim only produced .430" throw. I believe if you measure the actual travel you will find it less then the 5/16" you were trying for.

David
We the willing, led by the unknowing, have been doing so much with so little for so long that we are now qualified to do anything with nothing.

prlawiii
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Post by prlawiii » Thu Feb 12, 2009 4:02 am

Live Steam did an article on this back in 1980 or 81. They have a table of corrections to apply to the shim thickness, depending on the size of the jaw width and the ratio between the eccentricity desired and the overall radius. They say that the correction isn't necessary where the exact eccentricity is not crucial. For this application, it will almost certainly work perfectly well enough, but for something like valve action, you would want to apply the correction to get it precise.

Herman

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Andypullen
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Post by Andypullen » Thu Feb 12, 2009 6:49 am

prlawiii wrote:Live Steam did an article on this back in 1980 or 81. They have a table of corrections to apply to the shim thickness, depending on the size of the jaw width and the ratio between the eccentricity desired and the overall radius. They say that the correction isn't necessary where the exact eccentricity is not crucial. For this application, it will almost certainly work perfectly well enough, but for something like valve action, you would want to apply the correction to get it precise.

Herman
I remember the article....Dick Bagley also mentioned shimming under a jaw on his brake valve article.

I just shimmed under the jaw to get the approximate throw I wanted on some solid pump axles I made recently.

Andy Pullen
Clausing 10x24, Sheldon 12" shaper, ProtoTrak AGE-2 control cnc on a BP clone, Reed Prentice 14" x 30", Sanford MG 610 surface grinder, Kalamazoo 610 bandsaw, Hardinge HSL speed lathe, Hardinge HC chucker, Kearney and Trecker #2K plain horizontal mill.

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ccvstmr
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Post by ccvstmr » Thu Feb 12, 2009 8:10 am

...trigonometry my dear Watson!

David, you're absolutley right. Those tables are needed if someone wants an "exact" offset of a particular dimension. When shiming the one jaw on a three-jaw chuck out a specified distance...the other jaws will not provide the full offset. Using a CAD program would be another way to determine how much shim would be needed for the one jaw.

Jack did a superb job of showing how to make a relatively complex machining project doable for us laymen. I do have one question for Jack...after your eccentrics were done, what were the next steps you used to install the shaft? ...and how do you keep the eccentric assembly from shifting? Once again...inquiry minds would like to know. Thanx in advance. Carl B.
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steveleatherman
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Post by steveleatherman » Thu Feb 12, 2009 5:42 pm

That's a pretty trick set-up, Jack. It's really nice to see you make quick progress on your 3/4" locomotive. It should inspire all of us to make more chips in the shop. Funny you started this post because this week I started my valve gear eccentrics for the mogul.
Pennsylvania Live Steamers Regular Member

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rwmorris
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Post by rwmorris » Thu Feb 12, 2009 8:09 pm

That's the neatest damn thing I have seen in quite sometime.... That concept for machining the eccentrics is so slick... I wonder if the same idea would work with machining a complete set for stevenson gear? The 120 degree concept is not applicable but the machining of flats still holds true? Just would need to machine the flats at the right spot? I wonder if that's easier than taking the Kozo crank shaft route???? i.e. the adaptor plate with the appropriate centers bolted onto the end....

I dig it....

Robert M.

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JBodenmann
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Post by JBodenmann » Thu Feb 12, 2009 9:48 pm

I have never had the nerve to machine valve gear eccentrics on the axle for Stephenson valve gear. Neither have I had the nerve to key them on. I like to be able to fiddle with them (rotate them), and fiddle with them some more, and run the engine on air, and LISTEN. And then sleep on it, and listen and fiddle some more until they are, JUST RIGHT! This includes adjusting the length of the link blades and valve stem until the engine runs dead square in forward and reverse. And then lock them down with set screws into drilled divots in the axles. Just my way. I am very mistrusting of numbers and formulas. Like the little eccentrics for the axle pump. If they had to be of a certain precise throw I would turn a round bit on the end and measure the throw and adjust it with shims until it was JUST RIGHT! I might use a table or some math to get close but I would never trust it.
As to locking the eccentrics on the axle. Same thing, I will use set screws into divots on the axle. But I won't put the divots on the axle until I know that everything is running smooth. Fiddling is a major part of what we do, and that is often what it takes to have a smooth running dependable engine.
Jack

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rwmorris
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Post by rwmorris » Fri Feb 13, 2009 12:24 am

I'm with ya on the fiddling.....

I have had several conversations with Andy Clerici about machining a complete set of eccentrics and it always amazes me how eloquent and simple he makes it sound....

"Just take a bar and slice it, then face it, then solder it, then turn it, then grab some Studebaker Connecting rods and then, and then...." Whamo! A perfectly square little loco..... Personally it makes me wet my pants to think about getting one right and all in one piece but it is fun to think about.... I remember talking to one of the ultra groovy machinist back at HP for several days about machining a big wobbly lump but we never really got after it. Your approach just rattled the brain again!

I do hope you will come up the Tilden with this masterpiece and possibly share a glass of vino while High Balling the 3/4" main line.....

Cheers,

Robert M.

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JTolan
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Poppet Valves

Post by JTolan » Mon Feb 16, 2009 7:08 pm

JBodenmann how do the poppet valves work?

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JBodenmann
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Post by JBodenmann » Mon Feb 16, 2009 10:31 pm

Hi J Tolan
A poppet valve is the sort of valve that is in an internal combustion engine for the inlet and exhaust valves. In an internal combustion engine they are held closed by a heavy spring, and they are opened by the camshaft, lifters, push rods and rocker arms. In the axle pump there are no springs. On the inlet side the valves are opened by negative pressure and the action of the incoming water, and closed by positive pressure, just as in a ball check valve. On the outlet side they are closed by negative pressure as water is drawn in by the piston, and opened by the action of the out going water. One reason that I like poppet valves and O rings is that the machining of the valve and seats is very forgiving, allowing me to get by with my haphazard and sloppy workmanship.
Happy Model Building
Jack

bobb
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axle pump

Post by bobb » Tue Feb 17, 2009 12:24 am

What Jack calls sloppy the rest of us call perfection.

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