I’m about to drill the steam passages from the ends of the cylinders to the ports on the valve face. On the drawing they are drawn offset to the centre line of the cylinder bore but no measurement as to how much or why. Looking at other cylinders of different locomotives they are sometimes off set too. Why? If you can help I would be most grateful as I am bemused and not sure what to do. Also how much should be removed at the ends of the cylinders to allow the steam to enter and exit freely. Again little or no information given. Is this the reason for the offset - to help with the passage dimensions? hoping someone can help me I would be most thankful! yours
AS it happens there is a big one on one side and a smaller one on the other.
There's another thought, which might come into play. Many loco valve gears are to the side of the primary motion - the outside in Walshaerts. Even with an offset in the valve spindle/buckle, the valve chest and ports may not be centrally above the cylinder bore. So the transfer passages will arrive at one end of the port. Not really significant, but the designer might want to bias things slightly one way? Clutching at straws here.
The main problem with the cylinders is that the Exhaust hole is far too close to the valve face 1/16" A wrong drill and it is onto another cylinder. You have to remember that these passageway faces need to be quite far in as when the covers are in place they can be covered. Keith Wilson tested me very early on by handing me a cylinder and asked "Why did the locomotive not work very well?" 2 reasons including the non drilling out of the Draincock vent holes. Many failed the obvious.
On my new cylinders I am aiming to have the valve spindle central which I can as I am using new solid blocks from College Engineering. I am doing central valves on my Jessie.
Have seen a guide described like an old Micrometer which slides like a calipers but engages in the port slot. And the other end on the flat at the end. A single rod protrudes at the correct angles to line up with the drill chuck.
David and Lily.
Builder of far too many projects, but I love them all. The more Locomotives you have building, the more solutions to other Projects Problems get Solved. Reworking Simplex into a Fowler Complex. Making a Jinty more to scale. And going up a size in the shape of a Jessie.
On both the drawings for the Simplex and the Super Simplex, it looks like the steam passages are not on the center line on the cylinder. This is because the drawing is drawn poorly. The center line of the cylinder bore is 1-5/8" from the reference side of the casting, which is the side that bolts to the frame. The center line of the port face is also 1-5/8" from the reference side. The steam passages should be machined equally on each side of the center line. The drawing makes it look offset from the cylinder bore, but, it is not.
The bolt hole pattern in the cylinder end is really a 13 hole pattern with the top hole not drilled because it is on center line with the bore and the steam passages. The bottom hole of the pattern should be exactly on center.
The valve spindle is offset from the cylinder bore by 7/16". The offset for the valve spindle groove in the slide valve is also 7/16". If you machine the port face and the slide valve exactly like the drawing they will be in perfect alignment.
DO NOT SCALE the drawing, just use the written dimensions and the cylinder, steam chest and slide valve will align perfectly.
One thing not to do, is to use the bolt pattern for the steam chest. One of the bolts will be exactly in line with the valve spindle! This bolt should be move toward the frame, or reference side, to just clear the valve spindle. If you drill the steam passages close to the cylinder bore, there is still plenty of material for bolts for the steam chest to screw into. The bolts will not collide with the steam passages, just don't drill them deep enough to break through. There is plenty of material for the bolts to screw into.
The cylinder bores should also be reduced to 1-3/8". This will still give you plenty of power and the boiler will be able to more easily keep up with the demand of the cylinders. At 1-3/8" bore, this is a very powerful locomotive. This also puts the steam passages farther away from the port face which gives you more material for the steam chest bolts.
Thanks. That really helps. I have done my best and as you say follow the dimensions not the drawing. I did move some of the steam chest bolts to ensure no clashes and hopefully not marring the symmetry of the bolts too much. We will wait and see though! My next issue is tapping holes deep enough in a blind hole. Plug taps that don’t seem to be much of a plug - rather a taper end. Ground the end off to assist the plug characteristic! It helps. Got some better taps coming too as the carbon tap is prone to fracture I’ve discovered! Even with good lubrication.
You are welcome! Yes, I often grind the end of a tap to create a better "bottoming" tap! The bolt pattern on the steam chest will end up being not exactly symmetrical. This is okay as it is the only way to avoid the valve spindle. The steam passages should be far enough away from the bottom of the bolts to not be a problem.