Another Paddleducks Build

[Maryak]

A full afternoon's work in the shop resulted in exactly one useable part:

I can probably make a valve in less than half an hour if I don't mess up.

See you gained quite a bit but sometimes it sure doesn't feel like it.

I decided that the lathe karma was lacking, and decided to move to the mill for a "simple" piece, the blanking plates. Well I messed up there somehow as the holes didn't end up centered. So I figured it was time to call it a day.

An excellent decision, trust you imbibed some suitable fluids to maintain your electrolyte balance.

Best Regards
Bob

 

[kvom]

Here's the summary pic of today's progress:

Got the other valve made, although it took longer than the half hour I estimated yesterday. I also reamed the steam chest bore to .375" to match the valves. Of course now it's a press fit at best, so some lapping is due there.

The same is true for the block, where I re-reamed the bores to .5" to remove the burrs caused by drilling the steam holes. I then drilled the holes on each end for attaching the steam chests. The afternoon finished with turning the pistons, which are likewise a press fit and require lapping.

 

[kvom]

I had a couple of "days off": Sunday my daughter had invited 15 or so of her closest friends to have a party to celebrate the end of the school year, as well as to inaugurate the playroom upstairs from the stop. Dad was "politely" asked not to run any noisy machines during that event. Monday we had a long afternoon invite with some friends. But today I had most of the afternoon to play in the shop.

The first task was to turn the top caps, after which I drilled and tapped both them and the block. I also tapped the mounting holes for the upper plate, allowing a test fit:

I then made a pair of blanking plates and tapped the mounting holes in the block. The DRO did manage to get the holes in all three parts to line up, so I was able to screw them all together. The only "glitch" is that one of the valve holes is slightly obstructed by the plate, but taking apporx .01" off that end should solve that.

Since I had the top section chunks lashed together, I was interested to see how it would look connected to the bottom. I'm going to make the columns during the summer CNC lathe class, so I decided to quickly make a set of plain columns from some 3/4" Al round I had previously scavenged. I had only enough time to finish two of them:

The soda can is included as a size reference.

Now it's time to get cranking on the crankshaft.

 

[Maryak]

Kvom,

Very nice it's really starting to look like an engine. :bow: :bow:

Best Regards
Bob

 

[kvom]

I finished the other two temporary columns this afternoon, and started on getting the sliding pieces to fit. First up were the bearings. Here's my alignment/lapping setup:

I ran it about a half hour with the toothpaste, cleaned it up and oiled it. The drill rod turns pretty smoothly now. I then did a bot of catchup by drilling and tapping the holes for the setscrews on the eccentrics. Next I lapped the bores of the crossheads in the same manner as the bearings. I discovered that one of my crosshead guide bars was slightly bent, so that's a job for another day.

 

[kvom]

I had the afternoon to play in the shop, and worked on getting the crankshaft and its attachments done.

The assembly does turn without binding, although I don't have the bearing blocks clamped down really tight. I discovered that I need to enlarge the central baseplate opening slightly, probably .01", as one of the crankwebs is hitting the corner.

If I can get the conrods finished next I can connect up the crossheads and get them lapped in.

 

[kvom]

Today I narrowed the heads of the conrods to fit the cross heads. I removed the top section and attached the crosshead guides to check for fit. The crossheads went on fairly cleanly, even without any extra "wiggle room" with the guide mounting screws. I did find that one of the guide rods was slightly bent, so I needed to make a replacement. I found that my rear temporary columns were too thick and interfered with the crossheads; so I needed to turn them down to clear.

Then I made one of the link pins to connect the conrod to the crosshead and put it together with the crankshaft, as shown here:

I am able to turn the cranksahft by hand and move the crosshead up and down, albeit somewhat stiffly. The conrod is still a bit wide and rubs the crankweb. Since I plan to taper the conrods this issue will go away.

Progress might be slow the next week as we will have houseguests.

 

[shred]

As I remember, my crossheads worked ok until I assembled everything.. then I had to enlarge the mounting holes a little , so don't be afraid to do that if needed.

 

[kvom]

Only had a couple of hours or less today. Turned the conrods between centers. I couldn't taper the entire shaft but got reasonably close:

Here's the setup:

 

[kvom]

Better progress today in a short 90 minute session. I finished the glands for the valves, where previously I had made the gland and screw. Tonight I drilled and reamed the through hole for the valve stem as well as the two mounting holes. I was apprehensive about this step, but all went smoothly.

Although I didn't see anything in the plan about where to drill the mounting holes in the steam chest, John's photo shows them fore and aft. That's a job for another day, as well as lapping the valves into both the glands and the valve bores.

 

[shred]

Although I didn't see anything in the plan about where to drill the mounting holes in the steam chest, John's photo shows them fore and aft. That's a job for another day, as well as lapping the valves into both the glands and the valve bores.

FWIW, I put the gland mounting holes in the orientation you have them in the photo. Done like that the holes will likely intercept the cross-holes for the valve block mounting, somewhat limiting the length of screw you can use, but it's not a big deal and it makes tapping easy with a 'gun'-type tap. Put 'em the other way and you may hit the steam inlet for the bottom of the cylinders, which I think would be worse.

 

[kvom]

Today I milled the steam slots that connect the steam chest holes to the block holes. As mentioned in a previous post, it's possible to mill the slots in the block rather than the steam chests, and that's what I did. I used a 1/8" endmill cutting .11" deep.

I also made V3 of the pistons, this time threaded 10-24 for a stronger joint with the piston rods. The other end of the rods are 8-32 for connecting to the crossheads.

I managed a better fit on the pistons by taking tiny cuts on the lathe. One is already a tight slip fit on one cylinder; the other will require some more polishing. If I can get the pistons lapped I'll drill and mount the glands next.

 

[shred]

Lookin good.. that block's growing holes by the day..

 

[Maryak]

kvom,

I'm with Shred. Looking good. :bow: :bow:

Best Regards
Bob

 

[kvom]

The only holes left to do in the block are for the steam glands for the pistons. I'll be glad when that's done as I don't have any material for a redo if I were to screw up.

 

[kustomkb]

Looks real nice, going to be a beauty!

 

[kvom]

I lapped the pistons so that I have a good sliding fit. I tapped the hole in the crossheads to accept the piston rods, and assembled the block and top plate to the bottom with one piston in its cylinder and the rod screwed into the crosshead. Although the mechanism operates fairly well (able to turn the crank by hand), there is an obvious issue: at TDC the piston protrudes through the top of the block. ???

Since I had made the piston rod to the same scale as the rest of the parts, I am wondering if the 75mm on the drawing is correct. I checked the rest of the critical elements (stroke, length of conrod, height of columns, height of bearing blocks), and all seem correct. Doing some measurement of the piston postions I concluded that my piston rod is .45" too long, corresponding to 7.5mm off the plan's size.

 

[kvom]

One step forward, two steps back. :'(

I drilled the gland mounting holes and the block, as can be seen. Why the missing screw? Because there's a broken 5-40 tap in the hole. :wall: So I will get a chance to try to dissolve it out a bit later. In the meantime it's not holding up progress.

After screwing down the glands my piston rod/piston assembly wouldn't go in; turns out the thread on the piston iend of the rod is slightly tilted, so scrap one piston rod. In addition, I had a bright idea that instead of cutting an external 8-32 thread on the crosshead end of the rod, I would drill and tap an 8-32 hole in the end and use a bit of 8-32 screw for the connection. In theory it should work, but the two I tried ended up with the hole slightly off center. At least the threads were straight. I still have enough 3/16 drill rod for 4 or 5 more tries at good piston rods.

It's getting "tricky" to figure the sequence for putting everything together. I believe the best approach to connect the bottom and top sections is to have the crossheads as part of the top, so that you need only bolt the crosshead to the conrod and the top plate to the columns (haven't made the eccentric linkages yet).

 

[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. ;D

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.

 

[ariz]

you are making a great work kvom, well documented and with many interesting points :bow:

I'm anxious to see the engine completed and running!