Bog's Paddleduck Engine

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ozzie46:
Thanks a lot Shred,

Mine turns over but it is stiff. I haven't made the spool valves and eccentrics or steam chest yet.

I have fiddled with it some but it needs more. I figure I will get the other bits made and try again to be sure I check everything.

Ron

kvom:
Some good advice above. Back in the shop this afternoon, I fiddled a little with this and that, but cam to the conclusion that I needed to back up to "square 1". I disassembled the bottom so that I was left with the base plate and the 4 bearings. Turns out one bearing was loose, so I decided to make sure that the entire crankshaft asssembly would be square and straight.

I pushed a 1/4" length of drill rod that I had checked for straightness on the surface plate through the bearings. I tightened down on end bearing and left the others loose. Then I clamped the plate on the mill vise, and using the edge finder zeroed the DRO on the drill rod at the fixed end. I then moved the edge finder to the other end and pushed the rod against it while tightening down the bearing's screws. Now I had both end bearings tight and parallel to the centerline, so I could tighten down the two center bearings. Now I had al 4 bearings lined up and parallel, but the rod was too tight to turn by finger pressure. The DRO indicated that the rod was parallel to the fixed jaw within .001" over its 6 inch length.

Next I applied some toothpaste as a lapping compound and hooked up the electric drill to turn the rod in the bearings. After some minutes it did loosen a bit. I then clamped the assembly vertically in the vise and used the mill to turn the rod, meaning I didn't have to hold the drill trigger down. I ran this for about 5 minutes, and while the rod was not loose I could just turn it with finger pressure. I reassembled the crank components along with the webs, but I still had too much drag. :hammer: So next time I will put it back in the mill and run the rod until I can turn it easily through all 4 bearings. I don't think any other adjustments make sense until the crank is straight with little friction.

As for the top side, I can manually slide the valves and pistons with the gland nuts loose or tight. I suspect part of my previous problem was that the crank pin was not square, causing the connecting rod to twist slightly as it rotates. I did verify with the height gauge that the top plate is parallel to the base plate. Once I have top and bottom reconnected, I can use the DRO to ensure that the block is both centered and parallel to the center line.

Not that much different from debugging software in a way. :scratch:

bogstandard:
This is always the worst part Kirk.

You have everything made within tolerances, but once those tolerances are added together it gives a problem.

It could be such a small thing as the bearing block heights, one on high tolerance and one on low equals trouble. Rather than trying to wear them in, take them off, put them on your drill rod as a block and pushing down fairly hard, swipe the blued up bases across a piece of smooth W&D resting on a flat plate. That will instantly show highs and lows. So then gently flat all the bases down (held as a block and mounted onto the bar in the same order as they are on the baseplate) until you have a nice complete matched set. It only has to have one 0.0005" higher or lower than the others and it will bind when you tighten them up.
Only then should you bed them in with the drill.

Logical and methodical is the way forwards.

You are very nearly there, don't let it beat you on the final straight.

John

kvom:
My brain might be a little weak this morning. What"s "W&D"? :scratch:

shred:

--- Quote from: kvom on July 12, 2009, 08:09:09 AM ---My brain might be a little weak this morning. What"s "W&D"? :scratch:

--- End quote ---
Wet & Dry sandpaper is my guess. A fairly fine grit-- the idea is to scrape the blue (layout die or magic marker would work; I use that a lot for fitting) off the 'low' one. Depending how much they're out, I suppose you could sand the assembled block-o-bearings into shape or flip them over and tickle them with an end mill; just make sure the bases and rod remain completely parallel.

Running-in works for some tight fits, but it will only make alignment problems worse by wallowing out misaligned parts.

A couple other things I forgot to mention earlier was when tuning the assembled engine:

--- I chucked the end of the crankshaft in a small drill chuck (use a tailstock chuck if you haven't got a loose drill chuck running around. I have no idea how I got so many loose chucks.. they must breed under the bench ::)). That is much easier to turn by hand and get a good feel for what's going on than trying to push the flywheel around.

-- Another thing to try when tuning is loosening the crank web on the #1 (awaymost from the flywheel) piston, disconnecting the front end of the engine from the other. If needed, you can make an extendo-rod for the front end eccentric and turn just the front end as well. The engine won't run like that without a much larger flywheel, but you can get a feel for where the problems are.

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