The Custom Part Blues

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Cregory Carr

Nov 16, 2022, 4:34:04 PM11/16/22
to Texas Brick Railroad
   I've started the first car of my Super Chief, the pleasure dome car.  I designed a custom dome frame and had a prototype 3d printed by Shapeways online.  After completing the roof and placing it on the car, I was surprised to find it was too long!  I took the custom part off and placed the forward and rear roof assemblies on the car.  I tried to attach the custom part and sure enough too long.
   Unfortunately, I had relied on Lego brick sizes in BrickLink's PartDesigner and Sariel's Unit Converter.  Both of these have a stud measuring 8mm. According to this the length of the custom part should be 208mm (26 studs) with the dome section being 192mm (24 studs).  I measured the opening between the roof sections.  The distance end to end of the opening is slightly less than 206mm and the opening for the dome is slightly less than 191mm. So it seems these both have the wrong sizes for actual Lego. Searching online I found several differing measurments/opinions.  

   I do most of my 3d design in a program called Anim8or , but relied on the measurment data in BrickLink's part designer and Sariel's online tools.  Now I have to figure out how to come up with an accurate way of designing custom parts.  FRUSTRATING!

   Here are some pics of the pleasure dome car:
The goal (software render) with 0.01" plastic sheet nameplates:
The forward lounge:
The lower lounge:
The Turquoise Room:
The dome lounge:

Matt Sailors

Nov 16, 2022, 4:41:56 PM11/16/22
to Cregory Carr, Texas Brick Railroad
I'm old-school. I use a caliper to get measurements when I'm designing and printing custom parts.  I mockup the size I need and break out my trusty dial calipers (I REALLY need to upgrade to digital ones) and find the measurement to the nearest 0.1 mm.  I also double check wall thickness so things snap together well.  So far I'm 9 and 6, but 4 of the losses came from brain farts during the design process (e.g., I made the outside dimension what the inside dimension should have been or missing the decimal point in a wall thickness).

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Nov 16, 2022, 5:02:24 PM11/16/22
to Matt Sailors, Cregory Carr, Texas Brick Railroad
Is the 3D printed part accurate?

Lego is nominally 8mm from *stud to stud*. Bricks will measure slightly less than that (like 7.8mm for a 1x1 brick, 15.8 for a 1x2, etc.) due to the need for some tolerance otherwise it would be hard to put bricks adjacent to each other. This is why you can do brick bending. But that difference should lead to slight gaps between bricks, not the overall length being too small - at least, I don't think it would be enough to explain how far off the part is, since you have fairly long pieces sandwiching the 1x2 bricks.

Probably the most fool-proof method would be to mock up the connection points to your 3D printed part and take measurements, instead of using digital models.

Cregory Carr

Nov 16, 2022, 5:29:43 PM11/16/22
to Texas Brick Railroad
This was my first custom part. Lesson learned the hard way. Just wish those prototype dome frames had been less expensive. Tempted to by a 3d printer and learn how to make my own.

Cregory Carr

Nov 16, 2022, 6:49:15 PM11/16/22
to Texas Brick Railroad
Ok, this is weird. I made a 26 stud long assembly of plates and it will not fit. I also made a 24 stud long assembly and it will not fit without forcing the roof sections up. Someting strange here.

Gareth Ellis

Nov 16, 2022, 7:00:25 PM11/16/22
to Cregory Carr, Texas Brick Railroad
you may find that the car has a slight bend in it, I have that with the intercity coaches, i have to forcefully encourage the roof sections in.

Cregory Carr

Nov 16, 2022, 7:03:52 PM11/16/22
to Texas Brick Railroad

Cregory Carr

Nov 16, 2022, 7:23:07 PM11/16/22
to Texas Brick Railroad
I'm ready to invent some new curse words #@%#^$($&$%$@^&#($($!!!!
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