An Anatomy of LEGO Train Tracks - a.k.a. Diamond Crossing Design Notes

djm · May 25, 2015

Context

The text within this post is based on an article I originally submitted in September 2014 to RailBricks for consideration to be included in a future issue of RailBricks. In the absence of any RailBricks issue since the article was submitted or recent communication from them, I have elected to post a modified version of the article to this forum.

Introduction

Figure 1 - Brick built Diamond Train Crossing

13 and 3. Two numbers which are key when building the diamond crossing shown in Figure 1 (the build instructions for which are available for download as a PDF document). Before explaining the numbers further though, a brief explanation of the reason for writing this article.

It's not hard to imagine that one of the success factors in LEGO being played with worldwide is the absence of words in their build instructions. Build instructions, such as those for the diamond crossing, are intended to stand on their own without the need for additional commentary. The purpose of this article is to pass on the knowledge gained in the construction of the diamond crossing to other AFOLs. It contains information that is not appropriate to place in building instructions. The desire is to encourage others to experiment further to see what can be achieved in providing alternatives to the standard LEGO PF/IR train track parts.

13 and 3 Explained

Figure 2 - Track Cross Section

Figure 2 illustrates a cross section of a LEGO standard straight train track, 160 LDraw Units (LDUs) wide, complemented with a couple of extra plates. The image was generated using MLCad [1] and LPub [2]. Each rail has a 20 LDU footprint. The yellow plate was moved from its "correctly aligned" position on the partially obscured stud to its left, 7 LDUs to the right. The right hand side of the plate is touching the left hand side of the top of the rail. Since the rail parts are symmetrical, there are 7 LDUs of "space" on the right hand side of the rail, meaning the rail width at the top is 6 LDUs. Thus aligning a brick to the inside edge of a rail requires an offset of 7 LDUs + 6 LDUs i.e. 13 LDUs.

Figure 3 - Solution Concept

Figure 3 illustrates the concept of what needs to be built to achieve the same spacing as that between the two rails on a standard LEGO track part.

Didier Enjary's advanced building guide [3] is a useful source of information about different techniques to obtain offsets. However, the offsets identified are even numbers, which won't combine to produce the desired offset of 13 LDUs.

One of the answers posed to a question about how to achieve a 1 LDU offset [4] identified that there is a LEGO part that provides an odd valued LDU offset. The Minifig, Neck Bracket with Back Stud (42446) [5], as illustrated in Figure 4, produces a desirable odd value offset of 3 LDUs.

Figure 4 - LDU Offset Bracket

Built from inside to outside

Figure 5 - 94 LDUs separation

The crossing is built from the inside towards the outside. A fundamental principle was to create the equivalent gauge to a real track piece by obtaining a separation between bricks of 94 LDUs. Figure 3 illustrates where this LDU measurement comes into play. Figure 5 illustrates a combination of pieces from the crossing that achieves the desired spacing. Other brick combinations exist that provide the same separation.

Potential for Re-use

The diamond crossing is built, fundamentally, as a straight through track with a diagonal track attached to each side using a Technic angled connector. This approach yields a high potential for re-use of the straight through section if building a differently angled crossing, as follows.

remove the diagonal tracks (see Figure 6)
replace the angled Technic connector (highlighted in Figure 6) with one of a different angle
for the hinge connectors' forming the internal diamond, alter their angle appropriately. This will also likely require a rework of the parts which form the diamond as a different length of track will be required for a different angle (see blue highlights in Figure 7).
tweak the bricks used where the tracks join to adjust the length where necessary (see red highlights in Figure 7).

Figure 6 - Straight Through Track

Figure 7 - Adjustments required if angle changed

Other Notes

The crossing is built by creating a brick separation of 94 LDUs, working from the inside of the track to the outside of the track. At one point during construction, an alternative approach yielded an offset of 13 LDUs when combined with a baseplate, as illustrated in Figure 8. This approach was not explored further but does offer the potential for constructing a crossing on the basis of from the outside to the inside. Readers are encouraged to experiment to see whether a suitable crossing can be built using this approach. There is no guarantee that the approach will yield a usable crossing.

Figure 8 - Candidate for an outside to inside build

The crossing uses one part that is no longer in production; the "Hinge Plate 1 x 2 with 3 Fingers" [8]. It may be possible to use the "Plate, Modified 1 x 2 with Handle on End - Closed Ends" [9] instead. During the design evolution of the crossing, both parts were trialed in different versions. In the end, the decision was made that the profile (see figure 9) of the hinge plate provides a better functional fit than that of the modified plate.

Figure 9 - Hinge Plate and Modified Plate Profile

The key measurements 13 and 3, identified in this article, may be usable to build straight tracks suitable for use with the curved "narrow" rail track [7]. This has not been explored.

Conclusion

The primary purpose of this article has been to disseminate the knowledge gained about significant LDU measurements applicable when building a custom PF/IR train track diamond crossing. Armed with these measurements, the AFOL train community may be able to derive further track piece alternatives.

References

[1] Mike's LEGO CAD

http://mlcad.lm-software.com/

[2] LPUB

http://sourceforge.net/projects/lpub4/

[3] The Unofficial LEGO Advanced Building Techniques Guide. 2007, Didier Enjary.

http://photos.freelu...B/SBv1.pdf.html

[4] How to make a 1 LDU offset

http://bricks.stacke...-a-1-ldu-offset

[5] Catalog: Parts: Minifig, Body Wear: 42446

http://www.bricklink...tem.asp?P=42446

[6] Catalog: Parts: Technic, Plate: 4262

http://www.bricklink...Item.asp?P=4262

[7] Catalog: Parts: Train, Track: 85976

http://www.bricklink...tem.asp?P=85976

[8] Catalog: Parts: Hinge: 4275

http://www.bricklink...Item.asp?P=4275

[9] Catalog: Parts: Plate, Modified: 60478

http://www.bricklink...tem.asp?P=60478

Edited May 28, 2015 by djm

**zephyr1934** · May 25, 2015

Thank you for sharing what you have clearly worked hard to discover about the lego track geometry and how to work with this pre-system design feature. I found it to be a very neat background. Your solution is very impressive and looks great. That is an incredible work of snot in a very tight space.

Looking at Figure 8, I'm not sure that would work as sketched, I thiink the studs from the neck bracket and the technic pins might conflict. Of course there are other ways of doing that, e.g., use a longer technic beam and alternate holes for the studs and for the pins.

Another thought that comes to mind is that you are aiming for symmetry in the track design, which is critical if you ever want to connect to conventional lego track pieces. There are quick and dirty solutions that would be much simpler for pure straight track. If you do not care about transitioning to a lego track piece that opens up a myriad of possibilities, e.g., from p21 of [3], you can get a 10 LDU offset from a jumper plate and a 4 LDU from a headlight brick (or most brackets, etc.), which provides a lot of ways to get to 94. The lego gauge is an artifact of pre-system thinking in lego parts from the 1960's. I think another one of those ancient designs offers a very simple solution to getting 94 LDU, though it does look very hokey. Specifically, using part 3633 (1x4x1 fences) for the rails. I believe the fence is 6 LDU wide... but it might be 7 in which case this only gets you 93 LDU. Of course any of these non-symmetrical solutions would be difficult to impossible to connect to a lego track piece.

djm · May 26, 2015

The pin and neck bracket are okay (refer to the picture below which I screenshot from LDD). I probably had DGBDBG-itis when I mocked up the build in Figure 8, so picked the wrong pin colour. "1" below shows the longer pin while "2" shows the shorter pin.

Nice illustration with the quick and dirty solution. It's interesting because it gives me food for thought - in the build of the diamond crossing, I'd always thought to make the track separator have similar parts and orientation on both sides. The quick-and-dirty illustration reminds me to not to forget to think outside the box.

David

Edited May 26, 2015 by djm

djm · May 27, 2015

Given the build instructions are a PDF file, provided below is a parts list suitable for use as a BrickLink Wanted Items list. The list can be copied and pasted into BrickLink if desired.

Regards,

David

</INVENTORY>

**zephyr1934** · May 27, 2015

Ah, okay, you used the stud on the half pins to connect to the technic beam in Fig 8. Sneaky. Yes, the dimension of the fences are a quirky artifact. Looking again at the image I posted, I bet one could use a pair of 1x4x2 fences to get the right gauge for lego track while still being symmetrical. Of course it would be strange looking rails that are way too tall, but???

baard · May 28, 2015

Thanks for the inspirational article (and numerous posts about the WIP) using SNOT!

In a current project I am using the The Minifig, Neck Bracket with Back Stud (42446) to fill in the gap under a 2x1x1 old window with plate on top to make a 3 stud high (sideways) window with frame in a snotted wall of headlight bricks. I had thought of using the normal brackets, but these are 4 LDU, not 3 as you mention.

In one of the old Lego picture books from the Blue era, there is a roller coaster model pictured, where the curved rails are mounted sideways with 5 studs in between, so in my mind the dirtiest way of obtaining straight stretches is simply mounting tiles on plates sideways, usinge a jumper plate solution to attach to Lego rails. This is not a sturdy solution, but definitely quick :laugh:

Keep up the good work!

djm · May 28, 2015

If someone has (a) the Emerald Night and (b) the parts to make the crossing, I'd appreciate it if you would trial the crossing with the Emerald Night. My "stress" testing of the crossing was done with the 7939 Freight train and the 60051 Passenger train. My understanding from a few sources is that the Emerald Night can be sensitive to bumpy track. It would be nice to know whether or not the crossing is too bumpy.

If you do trial it, please post your diagnosis to this thread.

Regards,

David

Edited May 28, 2015 by djm

marook · May 28, 2015

If someone has (a) the Emerald Night and (b) the parts to make the crossing, I'd appreciate it if you would trial the crossing with the Emerald Night. My "stress" testing of the crossing was done with the 7939 Freight train and the 60051 Passenger train. My understanding from a few sources is that the Emerald Night can be sensitive to bumpy track. It would be nice to know whether or not the crossing is too bumpy.

If you do trial it, please post your diagnosis to this thread.

Regards,

David

I'm thinking of building one, and test it with my large HE tran (6 cars, 2 locos).

Quiestion: Why do you use these at two rail-ends??

Dark Bluish Gray Brick, Modified 1 x 1 with Headlight

Why not simply two 1x1 bricks?

djm · May 28, 2015

I'm thinking of building one, and test it with my large HE tran (6 cars, 2 locos).

Quiestion: Why do you use these at two rail-ends??

Dark Bluish Gray Brick, Modified 1 x 1 with Headlight

Why not simply two 1x1 bricks?

Refer to this picture (generated using mecabricks.com) combined with the explanation below,

The bracket attached to the fence gives a 4 LDU offset. I needed another 4 LDU offset to fit the tile. I achieved this by using the 8 LDUs under the stud on the Brick, Modified 1 x 2 with Studs on 1 Side, and using the hole on headlight brick rotated by 180 degrees to turn the studs back towards the centre. This then gives 8 LDUs on which the tile is placed.

One of the reason wanting to make the build instructions available is to gather improvements for them. I've got no ego attached to the design (hopefully!) and welcome suggestions for improvements. It will help to have other people's eyes other than mine looking/critiquing the design.

Regards,

David

Legopold · May 29, 2015

Thanks for this interesting topic and the well described examples, djm. I might start playing around with brick built rails, too.

In one of the old Lego picture books from the Blue era, there is a roller coaster model pictured, where the curved rails are mounted sideways with 5 studs in between, so in my mind the dirtiest way of obtaining straight stretches is simply mounting tiles on plates sideways, usinge a jumper plate solution to attach to Lego rails. This is not a sturdy solution, but definitely quick

Keep up the good work!

I think this gives rails with a width of 92 LDU, which is slightly narrower than the 94 LDU you have in the original.

Edited May 29, 2015 by Legopold

**zephyr1934** · May 30, 2015

If someone has (a) the Emerald Night and (b) the parts to make the crossing, I'd appreciate it if you would trial the crossing with the Emerald Night. My "stress" testing of the crossing was done with the 7939 Freight train and the 60051 Passenger train. My understanding from a few sources is that the Emerald Night can be sensitive to bumpy track. It would be nice to know whether or not the crossing is too bumpy.

Wouldn't it be better if they sent you an EN for you to do the experiments yourself? (grin)

I think this gives rails with a width of 92 LDU, which is slightly narrower than the 94 LDU you have in the original.

Yes, exactly. It looks a lot better, it does work well enough, but it is a little tight and not as robust.

djm · May 30, 2015

Wouldn't it be better if they sent you an EN for you to do the experiments yourself? (grin)

A fair point. So if anyone has a spare EN which they were wondering what they should do with, I'm willing to spend my time trialing it on the Diamond Crossing. Drop me a message and I'll provide you with the shipping address. And I promise I'll post back to this thread about whether or not the trial is successful. Oh, and I'll assume that you won't want me to return it to you :wink:

Edited May 30, 2015 by djm

djm · June 1, 2015

So it looks like I've got another itch to scratch:

This is a legitimate build in LDD. It achieves the necessary 112.5 degree angle with two hinges, eliminating the Technic connector altogether. A deeper exploration of this will be required but I fear that the itch may result in version 11. Dang.

djm · June 1, 2015

I put some flesh on the bones: That was fairly straight forward.

Now to think about tweaking the separator (the bit circled in red) to allow the connection to the normal track part.

djm · June 2, 2015

This is a legitimate LDD build which provides for the separator and the connection to the track a la version 10.

I'll need to integrate this back into the straight section but on (digital) paper it's looking promising. I am now also wonder if it can be leveraged to eliminate what would be the only remaining "illegal" LDD part of the build - the separator on the "straight through".

djm · June 2, 2015

First draft of version 11. Fully LDD legal.

I'll try the actual build perhaps within a week, stress test it and, if all is good, produce the build instructions.

David

**zephyr1934** · June 6, 2015

Wow, that is very impressive, I can only imagine your head must be turning inside out to get all of the dimensions to line up.

Prairie · June 6, 2015

I'm entertained by how similar this is to the kinds of things one does when crafting cycle-perfect machine code, trying to super-optimize it, or trying to get it to fit within a particular number of bytes or some other severe constraint. Having done way too much of this kind of thing in the past, I see the effort going into something like this in the LEGO realm and just scurry away.

marook · August 12, 2015

Seems the instruktions still point to version 10.. any idea when version 11 will be up?

I have build version 10, and some points break apart when I run trains over it with speed.. ;-)

Edit: Or maybe it's just some of the old parts that does not hold together good enough.. :-/

Edited August 12, 2015 by marook

djm · August 12, 2015

Seems the instruktions still point to version 10.. any idea when version 11 will be up?

I have build version 10, and some points break apart when I run trains over it with speed.. ;-)

Edit: Or maybe it's just some of the old parts that does not hold together good enough.. :-/

Version 11 is on the back burner at the moment and is probably 6 weeks or so away. I've been working on a GBC - Akiyuki''s Cup to Cup (also available [shamless self plug] on Rebrickable). The reverse engineering of that then and writing suitable build instructions for it took a lot of time.

When I stress tested version 10, I got an hour of continuous running without the crossing falling apart. The test was a simple figure of eight with each loop taking 8-9 seconds. Does yours fall apart only when the trains are travelling at speed? Roughly how long does it hang together before falling apart?

Regards,

David

marook · August 12, 2015

Version 11 is on the back burner at the moment and is probably 6 weeks or so away. I've been working on a GBC - Akiyuki''s Cup to Cup (also available [shamless self plug] on Rebrickable). The reverse engineering of that then and writing suitable build instructions for it took a lot of time.

When I stress tested version 10, I got an hour of continuous running without the crossing falling apart. The test was a simple figure of eight with each loop taking 8-9 seconds. Does yours fall apart only when the trains are travelling at speed? Roughly how long does it hang together before falling apart?

Regards,

David

No problem. Take your time!

I will have to test some more, but it was not that long time.

Maybe it's the long HE train... but it was also in a 8-figure shape, with the one side normal Lego curves, the other ME Models r72 curves.

Maybe the trains speed on those curves pull a bit to much...

djm · September 5, 2015

Here we are, version 11:

Files that may be of use related to this are;

the build instructions. These include both a BOM as a diagram and as XML suitable for use as a BrickLink wanted list
the part list as a BrickStock file, should you prefer that format for managing parts.

Brief descriptions of significant differences between version 10 and 11 are;

The angles are now achieved using hinges rather than Technic angled connectors
The connection between where the track pieces attach and the crossing is more secure

Other items of note include;

The centre diamond rail for the "cross arm" is better aligned with the corresponding entry and exit rails. It turns out that in version 10 there was a 2 LDU misalignment. Version 11 eliminates the misalignment.
This build is not quite LDD "legal". Though it can be made so, the change to do so "feels" like it slightly weakens the strength of the assembly. The only "illegal" joins are as part of the 94 LDU separators. The following picture illustrates the "illegal" as-built solution (on the right hand side) and the corresponding "legal" equivalent (on the left hand side).

I successfully stress tested this build with a train running for over an hour in a figure of eight. The structural integrity of the crossing remained sound at the conclusion of the test and no derailment or carriage detachments occurred.

Hopefully marook will conduct his more challenging :"marook test" at some point and post the outcome.

If anyone feels like working out a suitable ballasting design for the crossing, please go ahead and post your design.

Regards,

David

An Anatomy of LEGO Train Tracks - a.k.a. Diamond Crossing Design Notes

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