Tina :- Engine and Boiler Build

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lordedmond:
Peter (Klank)

lathe back stop

http://madmodder.net/index.php?topic=4693.0

BTW boiler done, tested, lagged and test fired ( I did put in some stays as I intend to use it at its design SWP not the derated one ) now to get on and get my scale injector for the class 4 tank tested
cannot post any pic as they are 50 meg after they have been in PS5

Stuart

klank:
I decided to do the piston and its rod next.

A casting in gun metal for the piston is provided (with a nice chucking piece) together with a goodly length of 3/16 stainless steel rod. There is plenty of meat provided.

Here's the casting :-

The sides of the piston were all reasonably parallel, and after holding the main body in the three jaw, the chucking piece was skimmed down its length until running parallel.
I then held this in a collet for the main machining of the piston body to just oversize finished diameter and length.
It was drilled tapping size through, tapped 3/16 X 40 ME for the rod and counter bored half way through 3/16 for the un threaded part of the rod.

The rod is screw cut 3/16 X 40 ME for half the length of the finished piston whilst held in a collet with as little overhang as possible.

The chucking piece was then carefully sawn off, and the threaded end piston rod screwed on and held with thread lock and left to cure.

The rod with piston attached was then held in a collet, with the piston close to the collet face.
The final machining could then be carried out to bring the diameter to a good fit in the cylinder and length to what was required using very very light cuts with a very sharp tool.

A silicone O ring is supplied for the piston and precise dimensions given for cutting the O ring groove, to allow for a little bit of "roll" in the O ring lengthways in the groove when under power.
This was quite a fiddly operation to get exact, using a combination of a thin "pointy" tool to start, then a very sharp thin bladed parting tool.
The piston/rod should not be moved in the collet until all these operations have been completed (to keep everything concentric to the rod).
Here is the finished piston/rod with the O ring fitted. :-

Now to start the cylinder end - covers.
These are the castings supplied in the kit.
They are somewhat "coned" but with a reasonable anount of meat to play with.
The inner end cover casting has a rough "spigot" for the stuffing box. :-

Starting with this one - the inner cover - I firstly held the casting in the three jaw, using my chuck back stop, with the spigot outermost, so this could be lightly machined to get its sides parallel.
The spigot could then be held in the three jaw (with backstop) for turning the main body true (removing the cone) and facing off the outer skin/debris. :-

The casting could then be turned around and held in the reversed jaws, plus back stop, to machine the spigot true and the outer face of the cover.

It was then pilot drilled through and the spigot counterbored for the piston rod gland.

The spigot could then be held in a collet, the main body brought to length and a register cut on (what is) the inner face to be a close fit in the inner face of the cylinder bore. The cylinder was brought up to try the "fit" repeatedly.
The outer diameter was then finished to match that on the cylinder casting, and the pilot hole then reamed for the piston rod.
Once again, all of these operations must be carried out at the same set up to ensure concentricity and the register/face is at 90 degrees to the piston rod reamed hole. :-

The outer end cover next - a slightly more difficult item as it doesn't have a spigot - I'll do that tomorrow.

Thanks for the encouragement

Peter

klank:
Hi Stuart,
I just saw your post after finishing today's post on the build.
Thank you for giving the link to the back stop.

Wow, you didn't hang around doing your boiler - glad it all worked first time for you.

Good luck with the class 4.

Peter

lordedmond:
Thanks Peter

as I have said I am mobility challenged from the waist down but ok above the belt , as I gave up work ( retired ) at 50 that was 15 years ago I have plenty of time , but I do have to work when the pain is under control

BTW your build is coming along at a good pace also , I do agree with others it is sometimes quicker and cheaper to use bar stock , but as Doris came from GLR i am familiar with there castings with the loco build you have no choice ( i think when I got the cylinder castings they cost the same as your Tina kit but they were fully core as per full size ) nut of the OT I will not clutter up your thread

Stuart

loco:
In the latest copy of Model Engineer no 4404 vol 206 an article by the editor on machining a similar cylinder using a Keats angle plate. There is more than one way to cook eggs.
If you have one DO make sure that the base is square to the vee. If its not correct it before you need it.
Pete

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