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

[finescalerr]

Those little rivets along the top and side -- printed or applied later? If printed, can you shoot a close-up? Your posts are providing a good tutorial. -- Russ

[Burl]

Is this close enough?



Everything is printed on.  The tops of the ribs (the easiest part to get to) got a light sanding to remove the layer lines.  Then I cleaned, sealed and primed.

[Greg Hile]

Very impressive! I have a three-month old grandson who was on life support for a couple weeks and I haven't been able to do much work on my own stuff, so I have been living vicariously on all the wonderful projects you and the others here have been up to. The little guy is now on the mend and doing much better, so hopefully I can get back at it. I am especially interested in your use of Fusion 360 and how that is working out.

Thanks!

[Burl]

Greg: sorry to hear that, but glad he's getting better.

[finescalerr]

Thanks, Burl. That photo works well and answers some questions I've had. I guess I should try a test print one of these days.

Greg, glad the little rascal is getting better. You, he, and the entire family must have been wrecks for a while. I hope that's the last time his health is a concern.

Russ

[Burl]

Progress on the underframe pattern:








The printed parts are only there for reference right now.  I will be making resin copies of them later.

[Bill Gill]

Burl, the rivets look good even in the extreme closeup view and the underframe is coming along nicely.

[Burl]

Poured the molds for the underframe this weekend, and I immediately saw some things I wish I had done different.



Since this car has a cushioned underframe, it has four beams for center sills, instead of the usual two.  I had planned on making the outside center sill as two pieces.  I could see right away they were going to be too floppy to glue in place and get a proper alignment.  My goal was to make the sliding underframe operational, so this would be critical. 

I also had all the bearings aligned to take vertical load only.  I can see now, it will function better if I added some to maintain the clearance between the inner & outer center sills.



The other problem I see is that one beam has to be cut to make clearance for the trainline piping.  I'm afraid this will be easily broken if its made out of resin.  Brass would be much better.




So, I think I'm going to revise it to make the outer center sills part of the floor casting.  Just wish I had figured this out before I used four pounds of RTV, but you live & learn.

[Lawton Maner]

All is not wasted.  Chop it up and add it to the rubber for the new mold.  When you do it,  first pour a fairly thin layer of new rubber and then add the chopped pieces, then as soon as the mold is poured, evacuate it to remove the remaining air.  Old molds can be repeatedly diced and reused over and over.

[finescalerr]

In a model as large as your, do you find it necessary to reinforce the frame by embedding brass rod or bar? A friend has built many 1:32 scale cars and felt it necessary to do that. -- Russ

[Burl]

I generally find some other way to brace it up internally, with resin bulkheads, or similar.  I have always shied away from embedding metal in castings because of the differing expansion coefficients.

[Burl]

After stewing on it a couple days, I have found a design I like better.  Funny how simpler designs seem like they are harder to come up with.

The outer center sill (green) will now be part of the main floor casting.  It will have a channel that the bearings will ride in.  The inner center sill (pink) will have slots for the bearing shafts.  This should lock the whole thing in & keep it from sagging vertically.  It also means I only have to reprint the center sill, and I can use the rest of the floor pattern with no further modifications.




This also allowed me to change the orientation of the pattern in the (eventual) RTV mold by 180 degrees.  Now I can also model the spring for the cushioning unit as part of the casting.

[finescalerr]

Simpler always is harder. Excellent engineering. -- Russ

[Burl]

While I'm waiting on my revised underframe parts to come in, I decided to work on the side patterns.  Started with the vertical panels.  Looks odd right now, because the glue shows through in places where the castings are very thin.  It should all even out when its painted though.

[Ray Dunakin]

How thin are those castings?