Bog's Paddleduck Engine

Gallery, Projects and General > Project Logs

<< < (25/45) > >>

sbwhart:
Ho that annoying breaking the tap :bang:, are you going to try alum to desolve it out ?.

The builds looking very good though :clap: keep up the work, and the post are excellent.

Cheers

Stew

kvom:

--- Quote ---are you going to try alum to desolve it out ?.

--- End quote ---
That's my plan.

In the meantime I managed to screw up another piston rod (too short, measure twice, cut once). I think I have enough drill rod for one more shot at getting them right before I need to order another stick. I'm waiting for another "free shipping/$25" offer from Enco.

So I switched to something less stressful and milled out the sides of the top plate in order that the steam chest can join the block now that the glands are in place. Other than the piston rods, the main pieces I need to finish for a first run are the valve linkages to the eccentrics and some temporary inlet flanges, like shred made.

kvom:
Here's my results for the day's activities. Rather than worry about getting straight threads on both the piston and piston rod using my crappy dies, I decided to experiment by turning the piston and rod from one piece. The first one worked well so I made the second. :thumbup:

Because there are fairly tight fits on both the cylinder bore and glands, any deviation would tend to bind. By turning them together, they're concentric and (hopefully) straight. I still have to thread the ends for the cross heads, but any issue there can be adjusted by enlarging the mounting holes for the crosshead guide rods to allow "wiggle room".

In any case, I have a good sliding fit on one cylinder, while the other needs a small amount of lapping.

kvom:
I spent some time in the shop today on "fiddly stuff". First order of business was getting the second piston to fit its bore. A few seconds turning on the mill with some fine-grit emery cloth and some scotchbrite got that done. Then I made another temporary column to replace that one I sacrificed to turn one of the pistons. Then the boring job of cutting down screws to attach the top plate to the block. Next drilled and tapped the forks for the eccentric connection, and also milled and drilled the little blocks that go into the slots. Finishing the eccentric linkage will require me to get ready for silver soldering, which is still on the todo list.

I then spent some time looking at the drawings for the steam control. I don't have any flat brass stock thick enough to make the block, but using 2" round the block will be only .06" small. I could possibly use aluminum, although it's not on the "recommended material" list.

Earlier I was cogitating on how the valving works. It would seem that the main points are as follows, assuming the top holes are steam and the bottom are exhaust:

1) For the power portion of the stroke, the piston is near the top and the valve moves lower, opeing both holes. Steam or air enters the valve bore and can go in only two places, the cylinder or via the bore in the valve into the bottom of the valve bore. Since the exhaust hole is blocked from the bottom of the bore by the lower valve disc, all of the work will done by the steam pressing on the top of the piston.

2) For the start of the exhause stroke, the piston is at the bottom moving upware and the valve moves upward. Now the air or steam is forced by the piston back into the valve bore, where its only path is through the hole in the valve piston to the bottom of the bore. Now the exhaust hole is exposed so that the steam can escape. During this time the supply hole is also open, but the stream is confined between the two valve discs.

1)

bogstandard:
Kirk,

It is because of that swap over period that the distance between the two spools has to be spot on. Otherwise you would be having both pressure and exhaust trying to go into the same chambers. That is the reason I showed how to measure the distance between the porting holes and transferring it to the piston valves. Any more than a couple of thou out and you can start to run into timing problems.

Aluminium would be a difficult material to use for the fwd/rev valve casing because you would have to use mechanical fixings to join the pipes to it rather than silver soldering. You should get away with using a mild steel, if you can get the internal finish good enough. The soldering flux I sent you will cope with anything up to stainless steel, so it should easily join copper to steel.

John

Navigation

 Message Index

Go to full version