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Thanks for the feedback, Chris, I'm sure there is a table somewhere tat gives the optimum dimensions. I like slow running engines too. Do you think that there is any drawback to having larger valves? Not that it matters in a model but in full size, you are running on boiler pressure until the valve closes to work on expansion. Bigger valves could close sooner and be more efficient. Am I picking my nitts in the right direction or just burning hot air?
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« Last post by crueby on Today at 03:11:06 AM »
Good stuff Cap'n! For the Ohio engine I did recently, which has LP cylinders roughly 3 inch bore and stroke, quite large, i was able to feed it with fairly small valve openings, in the 1/16" diameter range, as long as the speeds were relatively low. As you say, the ability to breath limited the speed. Fine for that engine, I wanted it to run slow. For a smaller model, even small openings at 40 to 60 psi can run quite fast. Bottom line, a good thing to calculate! 
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For any engine to function well it must be able to breathe easily and that means adequate valve ports. Full size Corliss engines generally had steam and exaust ports that ran almost the full width of the cylinder. In a rotary valve, long narrow ports can reach a full open condition in just a few degrees of rotation. All of the models that I have seen depend on four or five round holes that are drilled from the steam or exhaust chest reaching into the cylinder. On an engine this size the holes may be as small as 1/32" diameter or maybe 1/16".Five hole of 1/16" dia. give an area of .0153 sq. in. The ports in this design are rectangular 1/16" wide by 1" long for a total of .0625 sq. in. or 8.5 times greater. I'm not sure but I think that will make a big difference. One way to cut that port is to do it from the inside. I don't know how it was done in full size engines but I bet it involve some very sophisticated foundry work.
One way to do that would be to cut the block open, do your port work and stick it back together. I would start with two half size blocks. Mill all of the internal air passage including the val passages and the steam and exhaust ports and then join the two half blocks together. From theree, you can proceed with all outside operations as if you were working with a a sophisticated well designed casting.
Any questions?
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« Last post by Dave Otto on April 19, 2024, 11:33:17 PM »
Great idea on the swarf shield, I'm thinking I may make something like that for my mill.
Dave
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« Last post by crueby on April 19, 2024, 11:31:07 PM »
You might look at https://pcbway.com as well, they not only do printed circuit boards but also 3D printing and metal machining. My limited experience with parts for strength has been that 70% or so infill is surprisingly strong, esp. if you inrease the number of perimeters to 4 or something like that. Prusa slicer gives good guidance to infill for strength over speed.
gerrit,
(who is trapped in a cycle of tool making/refurb to get to the next part)
Cool, I had not known of them. Just took a quick look, will dig into them some more. Thanks!!
I think a printed bucket would be strong enough, though I don't have any experience with how it would wear when digging .
Uploaded the CAD file for an online quote - for a CNC machined version from aluminum they are quoting about $135, for 3D printed aluminum about $10 more, though those are online generated prices, they say it could change when they have a person look at it before committing to the purchase. Thats not bad for a part that size! Shipping is probably another $15 or more.
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« Last post by crueby on April 19, 2024, 11:19:50 PM »
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« Last post by crueby on April 19, 2024, 11:17:07 PM »
You might look at https://pcbway.com as well, they not only do printed circuit boards but also 3D printing and metal machining. My limited experience with parts for strength has been that 70% or so infill is surprisingly strong, esp. if you inrease the number of perimeters to 4 or something like that. Prusa slicer gives good guidance to infill for strength over speed.
gerrit,
(who is trapped in a cycle of tool making/refurb to get to the next part)
Cool, I had not known of them. Just took a quick look, will dig into them some more. Thanks!! I think a printed bucket would be strong enough, though I don't have any experience with how it would wear when digging .
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« Last post by cnr6400 on April 19, 2024, 11:02:29 PM »
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« Last post by gerritv on April 19, 2024, 10:59:45 PM »
You might look at https://pcbway.com as well, they not only do printed circuit boards but also 3D printing and metal machining. My limited experience with parts for strength has been that 70% or so infill is surprisingly strong, esp. if you inrease the number of perimeters to 4 or something like that. Prusa slicer gives good guidance to infill for strength over speed. gerrit, (who is trapped in a cycle of tool making/refurb to get to the next part)
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« Last post by Kim on April 19, 2024, 10:49:50 PM »
Sounds like a solid analysis (i.e. 100% infill  ) Go for it! I'll be cheering from the peanut gallery (or is that the popcorn gallery?)  Kim
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