Author Topic: N Scale 50ft Coal Gondola  (Read 1587 times)

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Mark W

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N Scale 50ft Coal Gondola
« on: November 29, 2018, 02:05:00 AM »
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I had this file from way back, probably 8 or 9 years ago.  I printed it twice with Shapeways, both times it arrived crazy warped, and a single shell was $29 back when things were still cheap!  Because of that, the design was abandoned.  Flash forward to today, I'm ready to give it another go!


https://i.imgur.com/widXeQ4.jpg

There are two main things I wanted to test with this shell:
1. Printing rivet detail
2. Printing long flat walls.

Aside from overlooking the usual suspects and their resulting defects (reinforce supports in the corners to prevent peeling, and print at angle), I'm quite impressed once again!


https://i.imgur.com/fUb0Myy.jpg


The bottom is dead flat, and check out that rivet detail!  There is a bit of bowing out the side though, and just ignore those wiggley rods.  Brass wire for those in V2.   :facepalm:


https://i.imgur.com/0XKTPsI.jpg


That's not ghosting of the outside rivets showing through the inside, those are actual inside rivets!


https://i.imgur.com/vWChj96.jpg


A little bit of warpage down the length, but nothing compared to the early Shapeways print.

 
https://i.imgur.com/uC4x1eD.jpg


Very nice and crisp freestanding ladders and reasonable stirrup size.


https://i.imgur.com/m12Eixk.jpg


A few things to be refined, but I think there ways to make it work! 
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peteski

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Re: N Scale 50ft Coal Gondola
« Reply #1 on: November 29, 2018, 02:14:25 AM »
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While it is incredible what can be printed in a single print, I question the fragility of the stirrups.  I realize that this is just a proof of concept test print, but I think that to make this into a model you can handle the stirrups should be made in etched brass.  I can't see these super-fine resin ones surviving many operating sessions.
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Chris333

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Re: N Scale 50ft Coal Gondola
« Reply #2 on: November 29, 2018, 02:57:04 AM »
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Maybe some cross supports that taper at the walls will work. After curing you could just spin them to break loose?

narrowminded

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Re: N Scale 50ft Coal Gondola
« Reply #3 on: November 29, 2018, 03:27:00 AM »
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Looking good!  Maybe some inside bracing could be attached at rivet heads to hide on removal. :| 

This is going to be fun.  For much of my stuff I don't think I'll have the same issues to deal with as they are so small, minimal long flat planes.  I'm anxious.  I might try to draw up my monumental monument for the area next to the train station for my inaugural test print.  It should be an easy one drawing and printing.  That's assuming the machine ever arrives.  Fedex is giving it quite an extensive cross-country tour, zig-zagging all over the place.  I hope they're not charging them by the mile.  :)
Mark G.

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Re: N Scale 50ft Coal Gondola
« Reply #4 on: November 29, 2018, 07:54:40 AM »
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That's actually pretty sharp.  Use the warping to your advantage and print one "pre-dented" with bulging sides!

chessie system fan

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Re: N Scale 50ft Coal Gondola
« Reply #5 on: November 29, 2018, 12:10:34 PM »
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Those rivets are amazing!  How thick are the walls?  I'm sure thicker walls would lessen the warping. And tell me more about those grabs and ladders.  What size are they and is thinner possible?

I'm designing a RDG mill gon so this is all relevant info.
Aaron Bearden

Lemosteam

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Re: N Scale 50ft Coal Gondola
« Reply #6 on: November 29, 2018, 12:29:53 PM »
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I think the bowing is being caused by what we discussed.  Fluid in what is essentially a large, thin wall container pushing the sides out because there is nowhere to go.  if you added holes in the bottom, between the center ribs that could later be covered with 0.010" styrene, would let the fluid escape with each dip.

narrowminded

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Re: N Scale 50ft Coal Gondola
« Reply #7 on: November 29, 2018, 01:45:27 PM »
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I think the bowing is being caused by what we discussed.  Fluid in what is essentially a large, thin wall container pushing the sides out because there is nowhere to go.  if you added holes in the bottom, between the center ribs that could later be covered with 0.010" styrene, would let the fluid escape with each dip.

That's a legitimate concern and solution but in this case the print orientation is inverted per the photo of the completed part in the machine.  The cavity is open to the vat, not closed.

Edit add:  On further thought, the same issue may exist in this orientation but for a different reason.  This time there is air trapped within the shell and a fluid seeking its own level will apply pressure (+ OR - pressure) at anytime that the external and internal fluid levels are unequal.  The fix would be the same, add a hole.  This time it's a vent hole rather than a drain hole. 8)
« Last Edit: November 29, 2018, 01:52:31 PM by narrowminded »
Mark G.

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Re: N Scale 50ft Coal Gondola
« Reply #8 on: November 29, 2018, 01:56:04 PM »
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But the print orientation is inverted per the photo of the completed part in the machine.  The cavity is open to the vat, not closed.

The vat is below the part in the first picture, but the walls are in fact open until the first layer of the floor is printed.  The platen has to immerse the part and then return to the nex print layer and i think the fluid may be pushing the walls out.  So mi idea may not do anything till the first layer of the floor...

narrowminded

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Re: N Scale 50ft Coal Gondola
« Reply #9 on: November 29, 2018, 03:36:47 PM »
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The vat is below the part in the first picture, but the walls are in fact open until the first layer of the floor is printed.  The platen has to immerse the part and then return to the nex print layer and i think the fluid may be pushing the walls out.  So mi idea may not do anything till the first layer of the floor...

The platen is at the top, not the bottom.  The floor is generated first.  There's where the difference is.  It's closed the minute it starts generating the sides.  I think you're thinking of it the other way around.  Or maybe I'm missing something. :|

Edit add:  OK, I see.  I was thinking it was inverted.  That IS the top of the car up against the platen.  Sorry. 

The thought remains, though.  Any captured void, holding resin or capturing air, will see forces trying to distort the cavity.  I suspect worse when it's the resin captured and worse in either case when the void is large with flat sides.  Small cavities, it might be able to handle the forces.  And vents should help with either scenario.
« Last Edit: November 29, 2018, 03:43:48 PM by narrowminded »
Mark G.