Bog's Paddleduck Engine

Gallery, Projects and General > Project Logs

<< < (26/45) > >>

kvom:
After I posted previously I went and sliced off some 2" brass round and machined a square block from it. I'll start drilling the holes next.

kvom:
Today I started on the steam control block, which is the last component needing to be machined and the last assembly that can be completed until I am able to silver solder pieces together. Here's the block and spool, along with the elements of the eccentric linkage completed since the last photo:

I made several errors in machining the block, none of which I think (hope) will require remaking it.

The first issue was in drilling the mounting holes for the flanges. I was using the vise stop to center all of the holes on the edges, and apparently a piece of swarf or something got between the block and the vise jaw, causing these holes to be slightly off center. To work around this, I will need to offset the mounting holes in the two flanges, but this seems reasonably easy to do.

The second issue was in the size of the 4 steam holes. I just scaled these up from the 4mm plan spec, which means I drilled them 15/64. I should have realized that I would be soldering 1/4" tube into these holes. Since I machined the block out of 2" round stock, the block is slightly smaller than the plan scale would require (1.4" each side vs. 1.47"). This means that the holes are closer to the edge, and enlarging them would make them even closer. However, it appears that I can enlarge the holes to 1/4" while keeping enough material between the hole and the edge.

Finally, I made the center hole overlarge. I entended to drill it to 1/2" and then bore to .59". To save time I drilled the hole using a 1/2" endmill. At least the shank was 1/2" but the flutes made it a 5/8" endmill. So after boring, the hole ended up with a diameter of .645". This can seemingly be handled by making the spool larger to fit, and that's what I did. I also made the spool shaft slightly oversize at 1/4" as I need to find an o-ring with a matching ID. Once I get the O-ring the front and back caps can be machined.

bogstandard:
Kirk,

You might find that the valve doesn't operate quite how it should.

When I designed and made the control valve, the diameter of the spool and porting holes was rather critical when it came to swapping over the inlet/exhaust. Allowing just a small 'dead spot' when in the off position before going to a pressure on position.

You might find that your 'dead spot' will be a little larger before the engine starts to be fed with pressure.

Oh the joys of changing scales and having to wing it.

But at least what you have done is a good job.

The learning curve coming up. Just hope you can get the silver soldering cracked. But if you follow how I did it, and DON'T use too much flux and solder on the joints, you should be ok.

John

kvom:
John,

After studying the control block during machining, I now understand how it works. Before I mill the slots I will do some measurements to ensure that they properly connect the inlet/exhaust holes in both positions. I'm not sure right now, but I might need to angle the slots and/or increase/decrease the depth.

bogstandard:
You are quite right on that method Kirk.

When the engine is stationary, the slots sit against the dead area between the porting holes, so effectively blocking all movement of steam or air. As you move either way it connects the ports and depending how much it moves, depends on how much pressure is allowed thru, acting like a restrictor, like your finger over the end of a hosepipe.

John

Navigation

 Message Index

Go to full version