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?

Quote from: 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)

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.

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 .

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)

Hmm... interesting.  Will it be strong enough?  Interesting question.  I've heard that while PETG is a bit stronger than PLA, it is less rigid.  It has more flex than PLA.   So the benefit, as I understand it, is it will give a little rather than breaking, but that may not be the feature you're looking for on this part.  If you print it with a thicker shell and a stronger infill (like 3D honeycomb?  I've heard that's one of the strongest infill patterns) you might get a better part from PLA than PETG.  I dunno.

But it certainly won't be as strong as making it from metal.  Nor will it be as much effort!

The biggest concern I'd have is the latching mechanism for the bucket.  Maybe make that from metal parts?

Don't you love advise from someone who know's less than you about your project? 

Kim

Great comments!


The petg may give a bit more than the pla, but the pla will snap if flexed too far. Prusa, maker of my printer, actually prints a lot of the printer parts from petg, as solids with no infill. This part is fairly thick. My experience with the  parts I printed for the subs is that petg is a lot more durable if thick enough to be rigid, though pla gives much better details.


The door, struts to the boom, and the moving latch parts would need to be metal. I'm  thinking the bucket itself would work as petg, and as you say would take a Lot less work than metal, just a couple minutes to set up the printer and hit Go!      worst case, it gets remade in steel.


Just for laughs, I  went to places like Shapeways to see what they would charge to print/cast the bucket in aluminum. Even scaled down by a third to fit thier casting limits, the cost was about $800.     Just having them print it in plastic would cost more than another roll of filament  for my printer!