"Catherine", a USA "Sweet Pea" engine build

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ironhorseriley
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by ironhorseriley » Mon Apr 03, 2017 7:34 pm

Great to see you back at it & that you survived the move! I am encouraged by your ways of getting the "bugs" out.
Jim, Former railroader, fascinated by wood working & “all things engineered”.

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Mon Oct 23, 2017 12:52 pm

Because the wheel/axle box assemblies are loose in the horns (the suspension springs are not installed yet), the wheels slid around and trying to measure the proper length the rods should be was tough. So, I kept the frame vertical on the floor which at least forced the axle boxes into the full “rear” position due to gravity. I used a long yardstick (which isn’t nearly accurate enough for measuring the rod dimensions, but since I hadn’t blocked the wheels and this was going to be a rough process anyway I just proceeded) and measured the axle-to-axle center spacing as the exactly 13+5/16” as called for in the plans.

I took a piece of the aluminum stock I bought and laid out holes exactly 13+5/16” apart. Being frugal, I oriented them on the aluminum bar so that if I could fit another pair of holes on the same stock if I needed to. Then, I drilled the holes in steps up to the 3/4" which is the diameter of the crankpins. The two bars were slipped on either side of the engine and I tried to rotate the wheels but they bound up. Clearly, they were either a little too long or a little too short. So, I cut each rod in half and then drilled/tapped the ends with a 5/8-16 tap. Some steel plates were then milled 5/16” to allow for slots and tightening bolts. I took one of the rods to Home Depot to size up some hardware and unfortunately must have left it there, because I couldn’t find it anywhere. I called and they didn’t have it, so I had to remake it.
Making adjustable rods.jpg
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Then, the rods were loosely bolted together and installed on the engine’s crank pins (which were for right now just essentially 3/4" diameter extensions from the wheels. Little by little, the wheels were rotated and the bolts adjusted and tightened until the wheels ran free with the rods in place. When we switched them around, they still rolled well. So, I tightened the bolts really well, tested the rods one more time to make sure I didn’t screw them up, and set them aside. It was, frankly, amazing that we hit the perfect length without so much as a measurement.
Adjustable rods.jpg
Adjustable rods.jpg (38.16 KiB) Viewed 898 times
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Mon Oct 23, 2017 1:05 pm

I have been pondering the crank pins for several years. The Sweet Pea designed called for marine style drive and connecting rods with the ends separate pieces that would bolt around the pins, which were shaped sort of like mushrooms. Thus, any incorrect measure of the rod length could be corrected by filing or shimming the rods. I didn't particularly care for the appearance of the round cross-section marine rods and wanted to build conventional, one-piece rods. These would slip over the crank pins and somehow be retained. This meant that I had to redesign the crank pins. The community here provided me a wealth of information (http://www.chaski.org/homemachinist/vie ... =8&t=95312). After looking at crank pins used for Allen Models' mogul, Little Engines' 0-6-0 switcher, and Kozo's A3, I decided to go with the LE design.

However, the passage of time has led me to instead go back to the original design of a three-piece rod and a mushroom end on the crank pin. Not only will be rods be more prototypical, but they should be easier to adjust for wear down the road.

There have been quite a few threads on the topic of what metal makes the best crank pins, and after doing some research online here, I ordered two feet of 4140 hardened steel rod from McMaster-Carr. http://www.chaski.org/homemachinist/vie ... hp?t=96360 This is more than I will need, but I have a track record of making imperfect parts.

I adjusted the specified measurements of the crank pins by allowing for extra thickness on the first flange of the pin where it fits into the wheel. Since the valve gear was shimmed out from the frame ¼,” I added ¼” to the crank pin dimensions. Once I have a more concrete numbers for the valve gear clearances, I can always turn away the extra part of the flange (on the inside portion) which will move the areas of the crank pins where the rods will ride in. Of course, that will also require shortening the crank pin or else it will stick out the back of the wheel. Anyway, I made that portion longer than necessary at this point too because it is easier to remove metal than add it back.

One of the things I decided upon early on was that the crankpins were going to be secured with Loctite instead of press fitting. If properly made to the correct tolerances, they should hold up well and not work loose. Key to that is accurately measuring the crank pin holes in the drivers.
Measuring Crank Pin holes.jpg
Measuring Crank Pin holes.jpg (37.49 KiB) Viewed 895 times
One tool that was especially useful was a round cutting tool. This allowed me to carve out the portions of the wheels where the rod bearings will ride and also smooth over the edges nicely. I guess it could be done with a round file, but that would take a bit more work. I also used various grits of emery tape (80, 140, 220) to get a nice smoother surface on everything.
Turning crank pins.jpg
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The ends of the leading crank pins were rounded over with a file to give them a nice smooth appearance. The ends of the driving crank pins have a shoulder turned to accept the linkage of the valve gear, which clamps on it. This not only functions as part of the valve gear but it also keeps the rod from falling off the crank pin. I don’t know yet if I will need to drill through the crank pin, but I likely will have to.

With a bit of luck and carefully thinking through everything before doing it, I managed to make all four crank pins on my first attempt. (Well, my "first" attempt at making crank pins to the original plans). The four in the front are the "keepers", but the ones in the back are my previous attempts.
Lots of crank pins.jpg
Lots of crank pins.jpg (30.68 KiB) Viewed 895 times
I won't secure the crank pins to the wheels until the rods are done, in case something else must be modified.
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Wed Mar 21, 2018 7:47 am

I have been working on the coupling rods for the past eleven months. I wish I had more to show for it, but I am not a master machinist. As was mentioned previously, I reverted back to the original plans for marine style rods with multiple pieces of steel and bronze that bolt around the crank pins. So, I first bought some steel and some brass online. Let me tell you, bronze isn’t cheap and it is a bad feeling when you order “just enough” and then worry about what you will do if you make a mistake. Thankfully, these rods came out okay but I hate having to shut everything down to order more stock. The bronze for the coupling rods alone was over $80!
Brass and steel parts - pairings.JPG
I had purchased some cold rolled 1018, 0.500” diameter, steel rods for the middle portion of the rods. I also bought some cold rolled 1018 bar stock for the rod ends. As can be seen in the picture, there are 9 pieces of metal per rod: each crank pin is sandwiched between two pieces of brass and two pieces of steel, with a steel rod connecting them. Once the metal was cut to length, I milled it in matched pairs, and later in matched sets of four, so that all four pieces of metal per rod end would be the same height and thickness.
steel and brass sets.jpg
steel and brass sets.jpg (22.36 KiB) Viewed 404 times
Then, I had to somehow hold the four pieces for each rod end together in the drill press and drill through all of them for the bolts which would tie everything together. It didn’t help that there wasn’t any easy way to secure all four pieces while holding them perfectly perpendicular to the drill press. Some adjustment was required after the holes were drilled, but I finally managed to get everything bolted up.
coupling rod ends with bolts.JPG
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Wed Mar 21, 2018 7:54 am

Then, the inside pieces of steel for each rod end had a ¼” diameter hole drilled through it. The half-inch diameter steel rod ends were turned down to ¼” diameter to slip into the holes on the end steel pieces, and everything was welded up. Maintaining true parallelism on both rod ends at the same time was also a fun experience, but it was managed. Thankfully, my machinist friend is a very good welder (and thinker!) and once we cleaned up the weld joints things were looking good. We used the mill to round over the joints, as well as spinning the rods in the lathe.
welded rod ends.jpg
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Welding had causes the end pieces of steel to slightly warp, so the ends were milled taking extremely light passes until it was perpendicular again.
machining rod end square.jpg
machining rod end square.jpg (20.88 KiB) Viewed 402 times
Next, I had to measure the length that the rods needed to be, and wouldn’t you know I didn’t have access to calipers long enough. So, using my adjustable aluminum rods (which I tested yet again extensively on the chassis to confirm that it was still bolted to the correct length) I measured the distance in two passes and then roughly cut the steel rods to length. Then, one end of each rod was assembled around crank pins set into the adjustable rods and the other end was clamped around the pin. I marked on the adjustable rod where the inner edge of the steel piece should be, then removed the un-welded end and swung the rod around so that it was over the line I had just marked, and I transferred it to the rod end. It was all highly scientific, as you can see.
measuring length of rod.jpg
measuring length of rod.jpg (31.71 KiB) Viewed 403 times
Then, the rod end was turned down and double checked.
end of rod diameter turned down.jpg
end of rod diameter turned down.jpg (23.49 KiB) Viewed 402 times
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Wed Mar 21, 2018 8:11 am

Once middle half-inch diameter steel rod was the right length, it was cut and welded onto the other end, with both ends being held in perfect parallelism. Next, I took the bronze sets out from each end of the coupling rod and just bolted them up together. I inserted paper spacers between the pairs which gave me a slight cushion for wear down the road. I marked the center point for each pair, which was then carefully drilled out and up to the final diameter of about 0.750." Then, each pair was bored out on the milling machine to match the exact diameter of the crank pins I had made.

Next, the bronze pairs was inserted in the lathe in a four jaw chuck and carefully adjusted so that the hole was running true. I had originally thought that chucking a piece of 0.750" steel in the tailstock and running it into the chuck would be sufficient, but it wasn't precise enough. So, I used the measuring tools.
brasses with crankpin holes chamfered - measuring.jpg
brasses with crankpin holes chamfered - measuring.jpg (22.36 KiB) Viewed 398 times
Then, a specially ground rounded cutter was used to chamfer the outside edges of each crank pin hole. We used one of my spare crankpins that had also had the slots rounded over as a go-no go gauge to see where chamfering was still required. When one side was done, the bronzes were flipped around, re-centered, and the process done again.

When we thought we were close, we chucked a crank pin in the lathe and then put some polishing compound on the slot where the rod bolts around. The rod was then clamped around the pin and held with a wrench while the lathe slowly rotated the crank pin. This ground away tiny areas where there had been interference, and after multiple times of removing the bronzes and cleaning it up, and then applying new compound, the bronzes looked really good and fit around the crank pins well.
brasses with crankpin holes chamfered.jpg
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"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

Harold_V
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Harold_V » Wed Mar 21, 2018 3:48 pm

Benjamin Maggi wrote:
Wed Mar 21, 2018 8:11 am
When we thought we were close, we chucked a crank pin in the lathe and then put some polishing compound on the slot where the rod bolts around. The rod was then clamped around the pin and held with a wrench while the lathe slowly rotated the crank pin. This ground away tiny areas where there had been interference, and after multiple times of removing the bronzes and cleaning it up, and then applying new compound, the bronzes looked really good and fit around the crank pins well.
A note of caution.
Bronze, being soft, will tend to trap abrasive particles, creating a lap. The imbedded abrasive doesn't wash off, and will create unwanted wear on the pin. You most likely would have been better served to have bored the holes for the desired fit. Might not hurt for you to comment on the method you chose to ensure that you didn't create a lap, if you didn't. Could prove to be useful for others.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Wed Mar 21, 2018 3:55 pm

Harold_V wrote:
Wed Mar 21, 2018 3:48 pm
A note of caution.
Bronze, being soft, will tend to trap abrasive particles, creating a lap. The imbedded abrasive doesn't wash off, and will create unwanted wear on the pin. You most likely would have been better served to have bored the holes for the desired fit. Might not hurt for you to comment on the method you chose to ensure that you didn't create a lap, if you didn't. Could prove to be useful for others.

H
Harold,
we bored the crank pin holes to fit the pins. But, when we chamfered the edges we didn't perfectly round over the crankpin holes to match the radius of the crankpins. So, we clamped the bronze around the crankpin and then ground/polished away any areas that interfered. The pins themselves fit the main bored holes fine, it was just the mismatch of the chamfered areas. We could have used the rounded cutting tool and removed more bronze on the edges of the holes, but that would likely have resulted in removing more bronze than necessary just for the tiny (and I mean tiny) areas where the pin squeaked in the bronze.
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

Harold_V
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Harold_V » Thu Mar 22, 2018 1:33 am

Assuming no abrasive invaded the journal area, all should be good, but it's not always possible to keep it out. It would pay for you to examine the surface for signs it migrated. It should be obvious.
So you have a better understanding for the future, you could have used a three cornered scraper for the task, and eliminated the risk I mentioned. Three cornered scrapers are (or should be) a part of any machine shop equipment, as it's commonly used as a debur knife. Kept sharp, they cut quickly, with little effort.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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Benjamin Maggi
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by Benjamin Maggi » Tue Apr 24, 2018 7:47 am

FIVE YEAR ANNIVERSARY!

4/24/2012: that was the day I ordered the plans for the Sweet William from Blackgates Engineering. Five years ago. Time sure has gone by. I had hoped to have a running chassis by now but that is not to be. However, I am working presently on various valve gear parts and they are progressing nicely. I will post some pictures soon.

I wonder what my locomotive will look like in another 5 years?
"One cannot learn to swim without getting his feet wet." - Benjamin Maggi
- Building: 7.25" gauge "Sweet Pea" named "Catherine"

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FLSTEAM
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Re: "Catherine", a USA "Sweet Pea" engine build

Post by FLSTEAM » Tue Apr 24, 2018 7:53 am

" I wonder what my locomotive will look like in another 5 years? "

Done I hope.......

John B.
http://www.ngshay.com/
Shay drawings and castings

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