Thursday, July 5, 2018

Need help: accurate and reasonably precise measurements of Duplo bricks

~ Background ~

So, for some ungodly reason, I decided to get the 30 day Alibre Design free trial.

This was, for the record, a horrible idea.  Right now depression is bad, I'm having trouble with the vitally important eat/drink/sleep trifecta, and since I'm not about to buy a $1,000 or $2,000 licence (depending on the version) I've basically saddled myself with sense of "If I don't do ¡Everything! in 30 29 days I'm an failure!"

(Yes, I did make an effort to indicate that "everything" is getting double exclamation.)

I . . . may not be the best at making decisions that are conducive to a non-catastrophic state of mind.

But it's just . . . I like Alibre.  With some exceptions here or there it's exactly how I would design a 3d modeling.  It's like a perfect fit.

And I've been having design ideas that I'd like to do more than just write about, since that comes with the constant caveat: "Of course this serves no practical purpose now, but if I ever get into 3d modeling again, maybe I could do something with this."

~ The issue at hand ~

  Short version:
It's a lot harder to get the specifications of Duplo bricks than it is for Lego bricks.  The dimensions that aren't easily derived are the studs on top (height and outer diameter) and the tubes on bottom (inner diameter, outer diameter), and the size of the splines that make the wall actually wide enough to hold the studs.  (Most of the wall is Lego-wall thickness to allow for compatibility with Lego studs)

Obviously knowing a radius is as good as knowing a diameter, and also some things can be derived if others are known.  Knowing stud outer diameter will allow one to calculate the spline size, or vice versa.  Stud outer diameter should allow calculations tube outer diameter (in theory, at least.)
  Long version:

The basic Lego and Duplo patents expired ages ago.  It's why Lego keeps on making new specialty bricks (it creates new, non expired, patents) and why Lego is so into stuff that's under copyright* (Superheroes, Disney princesses, a thousand original Lego IPs) these days.

Thus a thousand companies build Lego and Duplo compatible system bricks and don't even need to file off the serial numbers.

However, Duplo bricks don't get the same attention to detail outside of of the clone manufacturing centers.

Lego specifications can be found all over the internet.

Duplo not so much.

Now, Some dimensions of Dplo bricks can be worked out pretty easily by comparison to Legos.  The standard Duplo bricks are twice as high, wide, and long as Lego bricks, for example.  The short ones are the same width and height as the standard ones, but only as high as a single standard Lego brick.

Other things are harder.

The studs (round things on top, hollow cylinders in this case) are not simple multiples of Lego stud sizes.  Their height, inner diameter, outer diameter, and wall thickness are all unclear.  However the tubes under a regular Lego (which have known sizes) fit inside the the studs so we can thus work out inner diameter.  The wall thickness can be found from subtraction once one has the outer diameter.

Thus for the studs, the missing dimensions are height and outer diameter.

The tubes underneath have similar stuff going on, albeit with less to reduce things.

The height is a simple calculation in theory.  It's a Lego stud height less than all the way to the bottom.  The inner and outer diameter not so much.

If we assume similar construction practices to Lego bricks than the inner diameter will be equal to the stud outer diameter and the outer diameter can likewise be calculated once the stud outer diameter is know.

It is not clear that those are good assumptions.

So, for the tubes on the bottom, the missing dimensions are inner diameter and outer diameter.

~ conclusion ~

If anyone has superior google-fu, prior knowledge, or Duplo bricks + really good calipers:

I would be really appreciative if you could tell me these dimensions (plus any others you feel like sharing) of Duplo bricks:

The outer diameter of the studs on top.  The height of the  studs on top.  The outer diameter of the tubes on the bottom.  The inner diameter of the tubes on the bottom.  Anything else that you think one needs to know to create Duplo compatible objects.  (Primarily bricks.)

~ Footnote ~
~ (on copyright law vs patent law) ~

* Copyright law is fundamentally flawed and this is, in large part, due to corporations wanting to have stuff in perpetuity while simultaneously saying, "Fuck You!" to the people who actually made the fucking stuff in the first place as well as the entire extended family and circle of friends + acquaintances of those people.

Short version:
Patent law is designed to balance the importance of creators getting what they're due with the competing interests of the common good of society in general and the people within society in particular.

Copyright law is designed to make Disney (and others of their ilk) richer than God.  I know that, as a classicist, I'm supposed to say, "Rich as Croesus" but the truth is that Croesus couldn't even imagine this kind of wealth.
~ Giraffe ~

When we asked for the location of the AMC at Assembly Row (which was a field of dirt before they put in the Orange Line stop, but a mass transit stop is like really good irrigation and fertilization: It makes commerce grow with a vengeance) we were told, "Around the corner right by the giant Lego giraffe," or something to that effect.

All this time later I still snap photos when possible.  (It's been in multiple open threads at Ana Mardoll's because of that.)

Why is it here?  It's made out of Duplo bricks.  (Which makes sense, it would take eight times as many Lego bricks to do the exact same thing.)


  1. Stud height: 23.7-19.15 = 4.55
    Stud OD: 9.4mm
    Tube OD: 13.5mm (I am not tremendously confident in this measurement because there isn't enough clearance around it for me to get a solid grip with my caliper)
    The inside of the tube is not round, but an irregular octagon made from the superposition of two squares, one 10.7mm and one 11.25mm


    1. Awesome. I hope it helps too. There's a lot going on (which is another reason it wasn't the best time for a limited time run with stuff) but it should help and even if it doesn't:

      Thank you so very much.

  2. Meh. Trial periods are cool. If they're free, you have something to gain but nothing to lose.

    (If they cost something, Sunk Cost Fallacy means it's basically free, or do I have that backward? Anyway, basically free, nothing more to lose than you already decided you could stand to lose without harm.)

    The crappy thing is when they turn the free or cheap trial into taking money from your card or account if you don't cancel it, so best to set it up ahead of time so that won't work...