Discussion in 'Pattern making' started by PatJ, Feb 25, 2019.
I really admire the metallurgy in the new auto engines and what that means for the longevity of an engine.
For a steam engine, I will be using old school everything including custom-made fasteners that match the extra height and profile seen on the old bolt heads and nut.
I did purchase lead-free babbitt, and have eliminated lead from most of the metals that I use.
Most of the old steam engine bearings were poured babbitt, and sometimes the shell was tinned first so that the babbitt material would adhere to the shell.
The Speedy Twin main bearings appear to have been cast separately, since the bearings can be seen lying separately on the shelf.
I noticed that on the Cretors Popcorn engines, the babbitt bearing is not symmetrical in the shell, which tells me that a secondary use for poured babbitt bearings (besides their long life) was to allow some variation in the frame castings and still have a crankshaft that is in perfect alignment and exactly perpendicular to the bore.
And some bearing shells have recesses to prevent the bearings from spinning in the shell, and the molten babbitt flows down into these recesses when it is poured into the shell.
And remember that the definition of a "high-speed" steam engine back in the day was perhaps 300 rpm.
Steam engines do produce 100% of torque at zero rpm, and so the bearings need to handle a very large loading, and babbitt seems to be good at this if you put the right grade in the right place.
Babbitt does come in various grades (hardnesses), and as I understand it, a softer babbitt material will last longer in a given application as long as it does not deform under maximum load.
Another cool thing I learned about babbitt bearings a few years ago is that you can build up the surface using a torch and a thin piece of babbitt material as a filler, and you can add what looks like welds across the surface of a worn babbitt bearing, and then machine the bearing to the correct size.
You don't actually have to re-pour a babbitt bearing, assuming it is large enough to fill with the torch method (generally applies to larger bearings).
Edit: Also, the larger babbitt bearings can delaminate/separate from their shell over time, which causes hot spots, and then further separation.
Once separation starts, the only good solution is to melt out the old babbitt, clean and tin the interior of the shell, and then pour new babbitt bearings.
Piston rings on steam engines were generally very wide compared to modern engines, and that approach seemed to work well in a low-speed steam engine application, and I will keep that format for the rings.
I would like to learn how to make ductile iron for the crankshafts, and that is one area that I am lacking in at the moment.
The Speedy Twin offered two crankshaft options. One was in cast iron (not sure if that was some variant of ductile iron or what), and steel.
The steel crankshaft apparently was a superior unit, but the fact that it was optional indicates that it must have been significantly more expensive to make.
The Speedy Twin crankshaft counterbalances were cast hollow, and then filled with lead, which is something I have only seen in the more modern steam engines.
I started printing the hopper for the Galloway this morning.
Bore is 2".
Flywheel is about 12" diameter.
Nice discussion on babbitt.
A few comments. I've only poured babbitt around existing shafts, old cars had to be line bored after pouring to size the bearings. It really takes a high level of machine tool to use insert bearings, especially newer ones with very tight clearances.
Have you seen bearings that were in service built up, or only new pours which were incomplete? I would think it would be hard to get the oil off the existing bearing materials, very interesting comment.
Ductile iron was invented/discovered in 1943, although Meehanite had been developed earlier. It would be surprising if the Speedy Twin crank was anything except gray iron. The crank looks like it would be well suited for machining from a large steel billet.
Very cool stuff you're doing!
They had malleable iron quite a ways back, so perhaps the crankshaft was made from that.
Here is a photo of the bearing that was being filled.
I am pretty sure it was a used bearing.
Here are some bearings on a big 110 year old motor and water pump that were reworked because they were de-laminating from the shell.
We put back turbine-grade bearings, and they should last another 100 years.
The first Galloway hopper print did not go well.
It was quite cold when I started the print (40F), and even though I had a heater running, I think it was too cold.
I will go out and check on the second print in a minute.
Hopefully it went better.
Thanks for posting the old motor bearing pictures. Pawnee, Oklahoma, Steam Tractor Show has a generator that looks like that motor, driven by a Corliss steamer.
3D printers can make a mess when the print job comes unstuck.
The top of the hopper came out ok.
The purple filament seems to try and catch a bit; not sure why.
The temperature is fluctuating a lot outdoors.
A slight defect on the bottom side, but easy enough to repair.
I just started the print for the center part of the hopper.
Not all PLA filaments are created equal.... Could also be the print surface, im kinda old school when it come to them. I still prefer a glass plate with pva glue stick on it... Or its slightly under extruding??
I set my first layer height at .3 mm and the extrusion temp 5 to 10 c higher on the first layer then back it off to .1 mm or .2mm for the next layers and lower the extrusion temps to "normal"
The Soule Maker's Faire was a lot of fun, and quite a few people came through on Saturday and Sunday.
Lots of young people, so that was exciting. We need to teach the next generation of steam engineers.
Clarke's furnace ran well, but he was only able to do one iron pour due to the weather.
The finish on his cast iron parts is extremely good (he has the green sand thing worked out very well).
The kids all wanted to assemble something, so we played games with the flywheel patterns, and scrambled them, and then let the kids reassemble them.
Some of the patterns can be a bit tricky to align correctly.
The kids really seemed to enjoy the "flywheel challenge" as we called it.
A few photos.
Nice set-up. Looks kind of empty, did any others have tables and how many people came? I'm looking at local makers faire's, I just like to go see what everyone is doing.
The main event was in the foundry building, and it was packed full (I did not get pictures of that).
They even had a swimming pool with remote controlled submarines in it.
They put me in the main steam hall since there was a Speedy Twin in there that I could compare to the 3D printed frame I made for that engine.
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