I think I'm ready to discuss this idea in public. Is this a practical
idea for fabricating small cylinders, or is this completely harebrained?
I was trying to figure out how I could fabricate a cylinder for a 0.500"
bore and a stroke of 0.750". While looking at various cross-sections, I
found myself thinking "Hmmm, you know, those look a lot like what you'd
get if you used three layers of telescoping tubing. Hmmm ..."
So I did a bit of cipherin', and came up with this idea: Take a length of
Schedule 80 pipe, which has an ID of 0.423" and an OD of 0.675". Bore the
inside to a nice, smooth 0.500", then turn down the outside to to about
0.623". Cut it to the length you need and notch the ends a wee bit to
form the steam ports. This forms the inner surface of the cylinder.
Take a piece of heavy-wall 11/16" telescoping brass tubing, with an ID a
touch over 0.625" and an OD of 0.688". Carefully mill a long, wide slot
to serve as the steam passage at each end, and braze that to the
aforementioned pipe.
Finally, take a piece of heavy-wall 5/8" telescoping brass tubing, mill
slots to allow steam to pass from the valve into the steam passages, and
braze that to form the outside surface of the cylinder.
For those of you who, like me, find it easier to see a picture instead of
trying to visualize this from words, I added a drawing of this idea to my
Web page at:
http://www.440american.org/Ideas/Cylinders.html
(The small image on that page is a bit coarse; click on that image for a
larger view.)
I did a quick check on the area that this provides for the steam ports and
passages, and it's comparable to both scaled prototype areas and the areas
in the G1MRA "Project" and "Dee" model examples.
If you're worried about corrosion in a steel cylinder, it should be
possible to use a length of brass or bronze rod for the inner cylinder
instead of steel pipe. You'd just have more work to do to bore the
cylinder, but it shouldn't be much different from boring a cylinder in a
block.
The overall idea can be scaled to other sizes as well. The dimensions
given above work for the cylinders I'm developing. You can either work
with readily available stock, as I've described above, or you can try
things like using strips of flat stock to create the steam passages. (How
ambitious are you?)
So what do you all think: is this a practical idea, or am I running with
no air in the brake line?
- - Steve
