Why not cast the ribs on the same mold as the larger carbody? The carbody looks like a good sized mold to make. Two part or three part mold? Is it hollow inside? I’m guessing the roof is a separate casting?
There are too many undercuts to cast the sides and the body as once piece.
The body is one, hollow piece.
It would probably have to be a multipart mold then. Besides, its easier to have one side mold and cast it twice, then to make a multipart mold with all the issues associated with it.
I’d like to see how you cast the body as one hollow piece. You’re the master caster Burl! 
I built a rotational casting machine to do it. Will try to post a video later.
(http://burlrice.com/_LS_PS2CD4427/rotational_casting_machine1.jpg)
(http://burlrice.com/_LS_PS2CD4427/rotational_casting_machine2.jpg)
(http://burlrice.com/_LS_PS2CD4427/rotational_casting_machine3.jpg)
This is the rotational casting machine I built. I started out with cordless rotisserie motors, but they couldn’t handle the load and began to fail. I upgraded to gearmotors (from McMaster-Carr). The primary motor is AC. The secondary is DC, driven by rechargeable AA batteries.
I also started out with pipe flanges on everything, but the one on the primary axis failed due to the stress. I ended up having a bracket fabricated for it (the welder thought I was stamping grapes?).
This was like re-learning everything I knew about casting. It took a lot of experimentation, and 2 or 3 gallons of resin, to figure out how to reliably cast this mold. It takes 8 separate pours to get one body casting. You’d think you could dump all the resin in, turn it on, & have something finished in 20 minutes, but it pulls away from the mold and turns into one, big, messy glob in the middle. So the pours are small, and 15 minutes apart, to keep the heat from building up and making the resin kick too soon.
The rotational aspect is all new to me. I would say it took me 6 months or so of design & testing before I finally had something settled.
BTW, the mold you see took 3 gallons of RTV. There’s a top to it (not pictured) with two plugs cut into it. One plug is for a funnel (for the resin), the other is an air vent. I have about 20-30 seconds to get the resin in & get the mold buttoned up, or I get an uneven coating in the mold. I’d say I’m getting usable castings out of it 90% of the time now.
Wow. That’s impressive. I’m still working on trying to master single faced open molds…
With this new method of casting are some of your older projects going to come back to life? I recall you saying how hard it was to cast the centerbeam flats. Would this method work for those?
This is a spectacular model. Great job Burl.
The 2 big differences between the AML car and this one by Burl is:
-
The low sides (low hip) on the 4427 makes it quite different in appearance that the higher hip 4740’s and 4750’s
-
An even bigger difference is that Burl’s model is an accurate version of a real 4427 whereas the AML car is not an accurate reproduction of any real specific car (A sore spot since it came out…I was hopeful til I bought one and discovered all the flaws/faults)
That said, I’m ready to build a kit Burl. When will it become available?
Brian Briggs said:
- An even bigger difference is that Burl’s model is an accurate version of a real 4427 whereas the AML car is not an accurate reproduction of any real specific car (A sore spot since it came out…I was hopeful til I bought one and discovered all the flaws/faults)
Brian,
Every time I’m tempted to spend money on the AML model I come back to this very issue, the AML model has major flaws… Now that Burl has a actual 4427 hopper I need to figure out how many ended up on the sub I’m modeling. I wish that manufacturer’s would design accurate models based on real prototypes instead of combining this with that to make their ‘version’ of what it should look like. But then again maybe I’m too much of a prototypical modeler! 
I’m still trying to work out issues with Shapeways, and its taking forever. A significant part of the detail parts will be 3d printed in nylon, and they keep telling me the print breaks in the cleanup process. Its forcing me to redesign the sprue around certain parts – and every time I do, it takes another two weeks to find out if it worked or not. And of course, I’m stumped by all this because they have printed it successfully before.
Are you designing it and test printing with abs or pla first to see if the design works, abs is a lot cheaper for testing. Do you have a 3d printer available?
Mark: no, I don’t have a printer of my own. Still waiting for prices to come down on the high-res machines.
Per Shapeways email:
"Our nylon materials are printing with a process known as “selective laser sintering.” During this process, a layer of powder is pushed out by the printer, and only the areas specified as solid per the 3d file are lasered. The product, therefore, is composed of hundreds of microscopic layers joined together.
The areas of powder not melted by a laser are left as loose powder. At the end of printing, we have a vertically built print job, having solid models encased by loose powder. We remove the solid models from the loose powder by hand, then we use sandblasting and compressed air to achieve a fully cleaned surface.
When the product is encased in loose powder, it is similar to as if it were encased in a snow bank. The powder, especially that closest to the model, can be tough or difficult to remove. To avoid a breakage in this stage, it is important that the structure of the part be sturdy.
In this particular design, the structural integrity broke at the above mentioned stage of handling. The wires were too thin to withstand the pressure of the loose powder around them and the attempts at freeing it from the powder cake. The design may be more successful if the broken areas are thickened in diameter. "
Burl Rice said:
I’m still trying to work out issues with Shapeways, and its taking forever. A significant part of the detail parts will be 3d printed in nylon, and they keep telling me the print breaks in the cleanup process. Its forcing me to redesign the sprue around certain parts – and every time I do, it takes another two weeks to find out if it worked or not. And of course, I’m stumped by all this because they have printed it successfully before.
I’m not sure I know completely how Shapeway works, but don’t they decide where to place your part in the print? I’m guessing that multiple prints are printed at once where shapeway adds a sprue from customer A’s part to customer B’s part. Depending on where your model gets placed it either gets printed well, or it has this problem. Is there any way to find out ‘where’ you print is placed?
With SLS Nylon, there are no added supports. The powedered nylon IS the support material.
Craig Townsend said:
Brian,
Every time I’m tempted to spend money on the AML model I come back to this very issue, the AML model has major flaws… Now that Burl has a actual 4427 hopper I need to figure out how many ended up on the sub I’m modeling.
Craig,
Especially the era you’re modeling. This particular 4427 was produced in large quantities in the 60’s. The PS-4750 (AML’s alleged inspiration) started being produced in 1971/2.
Brian Briggs said:
Craig,
Especially the era you’re modeling. This particular 4427 was produced in large quantities in the 60’s. The PS-4750 (AML’s alleged inspiration) started being produced in 1971/2.
I’ve got evidence of at least two PS4427’s on the sub but at a later date (mid 80’s?), so it’s possible that these cars were roaming the sub at an earlier date.
(http://www.theinsidegateway.com/SooLIneCH2.jpg)
Isn’t prototype research fun?
Craig Townsend said:
Brian Briggs said:
- An even bigger difference is that Burl’s model is an accurate version of a real 4427 whereas the AML car is not an accurate reproduction of any real specific car (A sore spot since it came out…I was hopeful til I bought one and discovered all the flaws/faults)
Brian,
Every time I’m tempted to spend money on the AML model I come back to this very issue, the AML model has major flaws… Now that Burl has a actual 4427 hopper I need to figure out how many ended up on the sub I’m modeling. I wish that manufacturer’s would design accurate models based on real prototypes instead of combining this with that to make their ‘version’ of what it should look like. But then again maybe I’m too much of a prototypical modeler!
Craig I am by no means a rivet counter. But if something doesn’t look right to me, then I don’t “need” it. So if it doesn’t look right to you, then its not good enough for your railroad. Call it what you will.
Craig Townsend said:
Brian Briggs said:
- An even bigger difference is that Burl’s model is an accurate version of a real 4427 whereas the AML car is not an accurate reproduction of any real specific car (A sore spot since it came out…I was hopeful til I bought one and discovered all the flaws/faults)
Brian,
Every time I’m tempted to spend money on the AML model I come back to this very issue, the AML model has major flaws… Now that Burl has a actual 4427 hopper I need to figure out how many ended up on the sub I’m modeling. I wish that manufacturer’s would design accurate models based on real prototypes instead of combining this with that to make their ‘version’ of what it should look like. But then again maybe I’m too much of a prototypical modeler!
Craig, oncet you get the number of rivets accurate, and in the right place, then you have to decide what date you are modeling, so you can get the chipped paint and rust just right. The price of perfection is insanity! 
Ain’t this fun? 