Model Engine Maker
Help! => Specific Engine Help => Topic started by: chucketn on August 02, 2018, 12:26:50 AM
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I'm drawing up and planning to make the Woodson Vertical slide valve engine from Popular Science, 1947.
Has anyone built this engine? I having trouble understanding how to set up the eccentrics. There has to be a better way.
This engine has what I believe to be a Stevenson Link for the reverse part. It use 2 eccentrics that are riveted together. Is there a better way?
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It will need two eccentrics unless you make one with offset throws ( but that would be somewhat non-adjustable). Why not make the two eccentrics as called for but fix them to the crankshaft with grub screws. Do you have a pic of the engine?
Bill
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https://www.youtube.com/watch?v=-X7LswXveW8
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That looks similar to the VR75. From Elmer? I'm not sure.
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I'd do the same as bill and make two separate ones drilled for a grub screw. I have done the rivited type and it is not difficult, you just need to mark the position of the max throw and set that to the angles shown then drill and rivit. You then adjust the position of the pair as one unit. If you have CAD to draw it out it is quite simple to set the angle using a pin and right angles stop. The Rivited method mimics both being cut from one piece as you often find on full size but makes construction a lot easier.
If you do go for grub screws may be worth upping the thickness to 1/4" and doing away with the boss on both. The alternative would be a boss on both to take a grub screw which saves taking the strap off to adjust but you would need to move the eccentrics further out and have more crank in the rods
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On all of my reversing steam engines I have had a single eccentric with two throws which are located by the key way on the crank. They are not difficult to turn you just use a jig.
I would guess on the Woodson engine the idea is that you can use a single jig which locates the eccentric with a pin. Having turned both eccentrics on the jig one is simply reverse and a pin slid between the two to give you the required same angle in both directions. You still need to prevent the eccentrics slipping round so a grub screw would still be needed and that gives you a little adjustment.
Horses for courses - do which ever you prefer.
Jo
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You don't need a jig to machine the eccentrics just something simple to set the angles for riviting. You can use the back jaw of teh vice as the location block and just locate the eccentrics the set distance from that.
This is the drawing for my Fowler and the eccentrics drilled ready for riviting
(http://img.photobucket.com/albums/v156/jasonballamy/Fowler%20A7/PICT0103.jpg)
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Chuck there is an engine in .STEP format on Grabcad you can downlaod to save drawing it.