PM Research #4 Build Log

[vederstein]

Onto the main bearings:

These took several hours to do because there are two of them and the shaft hole positions relative to the mounting holes must be as exact as possible.

I started via milling the bottom face, but I quickly realized this was a bad idea because of the tool marks left on the casting. So I did my main facing on the lathe.

 

[vederstein]

Bearing blocks continued:

Then it was back to the mill.

Much of the time was spent milling edges (both parts at the same time as possible) to qualify edges. Then I could saw off the bearing caps from the body.

Note that I stamped the bearings "A" and "B" and filed a notch into each part to ensure the bodies and caps are matched and oriented to each other.

 

[vederstein]

Bearing Blocks Continued (2):

After cutting the caps from the blocks. There was more machining and cleaning up to qualify edges:

 

[vederstein]

Bearing Blocks Continued (3):

After milling most the edges, the bearing cap was drilled. Then the block was transfer punched, drilled & tapped. I could then assemble the incomplete bearings.

After more milling to size, I then drilled and reamed the bearing journal.

The journal wasn't perfect, but much much better than on my earlier engine. After a little deburring and working in the shaft, the bearings line up pretty good with very little perceptible binding or backlash (slop).

 

[vederstein]

Time for some internal reciprocating parts.

First the steam valve. I differed from the plane and used some 5/8" brass stock instead of the CRS bar that came with the kit. The reason for this is twofold:

1. I think the brass will wear against the cast iron better and will break in sooner.
2. I have several feet of 5/8" 360 brass round and can afford to screw up a piece or two.

 

[vederstein]

Onto the piston.

The piston's not too hard to make except for a couple of caveats:

1. Fit the piston to the actual cylinder bore. I over-bored the cylinder a few thousanths. So I measure both ends of the cylinder. When I got close to size, I continually fit the cylinder to the piston (while it was in the lathe) to check for fit.
2. I used my 2" Bison chuck to hold the piston for machining the opposite side so I didn't mar the piston walls.

 

[vederstein]

Sometimes you just can't win.

I guess I shouldn't be too surprised, because the same thing happened on the large(ish) Stirling - my cylinder bore is somewhat tapered.

It's strange though, the open ends match, but the center is a bit smaller. Perhaps it's due to the casting flanges or that my lathe is nearly 80 years old. I don't know.

Anyways, it's several hours with a cylinder brake hone to fit the cylinder to the piston. (The issue isn't the piston because is fits into each end of the cylinder, but gets stuck about 3/4" in.

At the time of this writing, there's improvement, but I've stopped for now (too annoyed: time to stop for the day).

 

[charlesfitton]

Sorry for this - but is the piston tapered?

 

[AlbertdeWitte]

Sometimes you just can't win.

I guess I shouldn't be too surprised, because the same thing happened on the large(ish) Stirling - my cylinder bore is somewhat tapered.

It's strange though, the open ends match, but the center is a bit smaller. Perhaps it's due to the casting flanges or that my lathe is nearly 80 years old. I don't know.

Anyways, it's several hours with a cylinder brake hone to fit the cylinder to the piston. (The issue isn't the piston because is fits into each end of the cylinder, but gets stuck about 3/4" in.

At the time of this writing, there's improvement, but I've stopped for now (too annoyed: time to stop for the day).

I had the same problem VED and I easily corrected it with a "Flap Wheel"disk grinder, was like in and out and 100%

 

[vederstein]

Sorry for this - but is the piston tapered?

The piston goes in either either end and either way, so I don't think the piston is tapered.

All evidence is that the bore is hourglass shaped.

It'll take time, but I'll get it to fit.

...Ved.

 

[willburrrr2003]

Ved, this is a great build thread! Thanks for all the pics of working parts in your lathe! Hope things go well with your cylinder bore. If you can't get the hourglass issue fixed, could you sleeve it?

Regards,

Will

 

[vederstein]

Week 4?

After about another 45 minutes of honing, I got the piston to flow freely though the bore. The bore was definitely hourglass shaped. Every few minutes I'd remove the part and check for fit. When running my finger inside the bore, I could feel the flared bore at the end.

Doesn't matter now. It's good.

Onto finishing the crankshaft. First the crank pin. The tolerances on this are tight and therefore I broke out my good micrometer for measurements.

The prints call out a sharp corners on the crank journal, but my carbide tips have what I consider a too large radius. So I used a small cutter and hand held the tool to undercut the corner a tad (fifth picture).

 

[vederstein]

Then using the earlier brass mandral, I pressed the crank pin to the crank plates.

Then I could machine the crank shafts. I don't have a keyway cutter, so I used an 1/8" endmill.

 

[vederstein]

Issues will arrise, I guess even with my careful measurements, one of the press fits for the crank pin wasn't strong enough and came loose. But instead of risking damage to the cast crank plates, I decided to fuse (TIG weld without filler metal) the pin to the crank plate.

After a little bit of working, the crank runs pretty good in the bearings (with the upcoming flywheel it free spins). Much better than my earlier engine.

 

[vederstein]

On to the flywheel.

It's both an easy part (not many dimensions are critical) and a hard part (those chips are hot!!).

 

[vederstein]

I don't have a broaching kit for the flywheel keyway, so I did an alternative that I've seen done, but never have had much luck myself:

Take a parting tool and clamp it sideways. With the lathe back gear engaged (to lock the spindle) "whittle away" at the keyway via running (by hand) the blade in and out of the bore.

For this I took 0.002" cuts.

This time was better than my previous tries, but I still had some issues. :wall: To compensate, I'll grind away the interference on the key. The rest is drilling and tapping the thread to lock the key in position.

With the upcoming U.S. holiday, I'll probably a couple week before I get back to this project. Have fun!

 

[vederstein]

Now onto the Connecting Rod. It's a brass casting and I'm sure quite expensive if I screwed it up. Therefore I took my time and measured two, three, four times before cutting. And I always "sneaked" up on the final dimension.

The biggest issue was once again my round column mill and Z-axis travel. For facing the sides of the Conrod to width, I used a extra long, spiral, two fluted, 3/8" end mill that I have. It deflects a lot, so getting the width correct was a slow process of 0.005" to 0.010" cuts.

In the end I'm pleased with it. When I tested it on the crankshaft, there's just a little bit of drag.

 

[vederstein]

Conrod #2...

At the small end of the rod, notice that I left material at the end. This was to support the small end's ears while drilling and reaming. After I took the rod out of the mill, I manually cut out the extra material with a hack saw and filed the surface smooth.

 

[AlbertdeWitte]

Hi Ved, its coming on just fine!

 

[vederstein]

Thanks Albert.

It will be some time before I get back to this project, but a working engine by the end of the year doesn't seem unreasonable. Painting won't happen until March or April when it's warm enough here to wash and paint the parts outside.

...Ved.