Pullman-Standard Mini-Hy Cube boxcar in 1:29

[Burl]

Ray: in the thinnest sections, probably paper thin (0.005" ?).  Thicker parts might go up to 0.030" in the middle.

[Burl]

My revised underframe prints came in last week.  When I started to glue them in, I was having trouble keeping them even.  After some double checking, I realized I had some variance in the I-beams.  So I stripped out the old glue, and made up this sanding stick out of aluminum C-channel & 220 grit sand paper:



With that, I was able to fine tune the fit & get a fairly straight line.  When I got ready to try gluing them again, I made up a spacer to represent the sliding part of the centersill (cut the same width), and added .015" styrene for clearance:



With that in place, I could tack it from the outside, remove the spacer & finish gluing from the inside.



Now everything looks like it fits well.  I don't want to get in a hurry on this step, so I'll look at it for a while.  If I can't find anything wrong with it, I'll pour another mold tomorrow (I have found sleeping on it helps me avoid mistakes due to haste):

[Bill Gill]

Continuing to follow along with this impressive project. Very neat work.

[finescalerr]

I applaud you for sleeping on it. I'm at my absolute best when I'm asleep. -- Russ

[Ray Dunakin]

Very interesting!

What is the purpose of the small styrene strips outside of the frame? Is it to "lock" the two halves of the mold, or to permit excess resin to flow out? Or something else?

[Burl]

Ray: that's exactly what they're for.  It helps me get a more even thickness over the length of a large, open-faced mold.

[Burl]

Poured my molds for the revised lost wax parts yesterday, only to find the two I really needed had refused to completely cure.  I was about to write them off as a total loss, but then I realized I could still get patterns out of them sufficient to finish the underframe casting.

I think the last thing I need on it is the divots for the new mounting holes:





I will remake the lost wax molds later.  Still trying to figure out what inhibited the RTV, but they say platinum-based silicones are very touchy.  When this has happened before, I cleaned the patterns, applied a fresh coat of paint, remolded, and they were fine the next time.

[Burl]

Finished the centersill pattern & molded everything.  Made up some castings to check the fit:

[finescalerr]

That should suffice. -- Russ

[Ray Dunakin]

Sweet!

[Burl]

Sort of got derailed on this project.  Shapeways took their sweet time on my last order (3-4 weeks).  When it did come in, I got covered up at work. 

Anyway, I got back around to working on the sides again.  I've re-done some more work here.  What I had before was OK, but I felt like I could get it closer.  I had previously used my old trick of using Aluminum tape to imitate oil-canned sheet metal.  Sometimes it worked well, sometimes it was hard to control the effect.  And there was always un-evenness between the panels that made it hard to apply the weld bead decals later.

What I did different this time was to model the oil-canning in Fusion 360.  I started with an image like this:



I run this through a script that interpolates the z-coordinate based pixel lightness/darkness.  Sort of imitates the result a 3d scan, without all the expensive hardware.  I do some mesh reduction & smoothing on the raw image, and scale it to get the print to the thickness I want.  Which looks something like this:



To avoid obvious repetition, I had three prints made: one regular, one flipped horizontal, and one flipped vertical.  The prints came in with obvious scan lines, which I expected.  I sanded them with 220 grit sandpaper until they no longer looked like topographical maps.  Then I made an RTV mold, and cast copies in resin.  Using a combination of castings, some rotated 180 degrees, I built up the side pattern:

[finescalerr]

Satisfactory. -- Russ

[Bill Gill]

Burl, Rippled sheet metal panels has always been a detail I've wanted to add to my (HO) scale boxcars. Quite awhile ago I experimented briefly with lightly carving and sanding the faces of the thick panels on some kits or applying metal foil (real) duct tape with ripples on top of panels. Neither produced the desired effect. I thought about removing the panels between the ribs on some cars and replacing them with something that could be randomly rippled, but still stay strong enough that it wouldn't badly distort if someone picked up the model by its sides. Your panels have me thinking about trying something again. Thanks. 

[Burl]

Bill: I think the key will be removing the panels, or printing the whole side from scratch. 

The first project I did that I would call "successful" was a 1:29 scale Airslide, probably 15 years ago.  I used Aluminum tape to make the patterns, and the waves were somewhat exaggerated.  Every car I've done since then, I've tried to tone down the effect, and control the rippling more.  Difficult in 1:29.  I never felt like I had enough control over it to go smaller.

Up until now, I had tried to build the side pattern, then apply the sheet metal casting over that.  But freight cars aren't built that way.  When there's a wave in prototype car sides, if it pops out 1/2", it also cavitates 1/2" in the negative axis.  Not sure if I'm articulating that in English well, but here's an illustration:



I won't be able to say for sure until this project it painted & weathered, but I may still have the waves exaggerated too much.  On this one, I restricted the wave to [-.25", .25"], which may still be unrealistic.  Don't know how I could actually measure such a thing on a prototype car without getting in trouble for trespassing.

[Bill Gill]

Thanks for the additional information and ideas, Burl.