13 October 2021

LEGO® Element Development: the Porsche Bows – Interview with Stephan Breum Steen

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Tom Loftus (@inthert.lego) continues our series of LEGO® Element Developer Q&As today with Stephan Breum Steen, Senior Mechanical Engineer in the Novelty Element Development department at the LEGO Group. As explained in the first article, element developers are one of the many, many different roles in the LEGO Group who work together to create each new element. They receive the brief from the product designer or element designer, and when complete the mould developer continues the work. Today, Stephan answers our questions on a particularly curvy element, then Tom provides additional analysis and MOCs. Transcripts were edited for clarity, readability and narrative flow.

Commonly known as ‘Porsche bows’, having first appeared in 10295 Porsche 911, today’s subjects are Left Shell 2x10x2, Outside Bow, W/ Cut in White (6336752 | 77180) and Right Shell 2x10x2, Outside Bow, W/ Cut in White (6336754 | 77182). They have since appeared in 21327 Typewriter in Sand Green (Left 6359067, Right 6359068) and have just become available in Dark Red (Left 6359689, Right 6359690) thanks to 10290 Pickup Truck.

Stephan Breum Steen has been involved in the development of over 100 elements and is one of the marvellous minds who takes a new element design and makes it a reality. It's a process that involves careful consideration of countless factors, but most relevant to us today is how an element will be moulded and how well it fits in with existing LEGO parts.


New Elementary: What was your background before joining the LEGO Group?

Stephan Breum Steen: I have a formal education as a mechanical engineer, and before the LEGO Group, I worked designing elements for wind turbines (blades and other glass fiber elements), thermostats (plastic elements) and various other projects as an engineering consultant.

When did you start and which teams have you worked in?

Stephan: I started with the LEGO Group in 1997, in the LEGO Primo team. Since then, I have worked with most product lines.

Of the released elements you’ve worked on, which are you happiest with or most proud of?

: I am quite proud of a Bionicle mask element I designed in the past [Large Figure Mask Huna (Toa Metru), design ID 47308], where I managed quite a large bit of the visual design work along with the technical design.

Moving on to the bow pieces now, what was the original brief? Did it change during development? Roughly how many prototypes were in the Concept stage?

Stephan: I received a 3D file with the shape the element designer needed. My brief was to take the general shape of the element and work out how we could design it technically so it worked for its intended use. The 3D file shape didn’t need to change very much, so using a lot of prototypes was not really necessary,

Did you need to consider the design of other old elements e.g. for backwards compatibility, or maintaining a design legacy?

Stephan: Yes – we needed the bottom shape of the element to match element 44126. Developing this element was really interesting and satisfying, because the bow standard applies in many details and directions on the element, and among Element Coach, Element Designer and myself (Part Designer), we were all keen on getting to the very best result. So a very pleasant cooperation across departments helped finalize the details.

The underside of a Porsche bow can accommodate Brick 2x6 w. Bow (44126) and any element with the same 4x1 curve such as Brick w. bow 1x4 (61678, shown here in yellow). The tip perfectly lines up with 4x4-based rounded elements such as a 2x2 macaroni brick (85080, here in red), while its other end matches the curve of a 1x1x1 1/3 brick with arch (6091, here in blue).


Is it ABS or did you need a different plastic? 

Stephan: The element is made in ABS plastic. In spite of the curvy shape, this element is essentially a very traditional building brick with traditional connectors.

Did you include any features that deliberately prevent the builder using the element in a way that is not intended?

Stephan: The space between the 2x2 and the 2x4 connector area is a bit wider than on a usual brick, in order to prevent clutch in this area.

If you could make one more change to this element now, what would it be?

Stephan: From a moulding perspective, it is not ideal to have the gate point as far away from building functions (2x4 tube side) as they are on this element, so changing the inlet position would improve the moldability. But that would be a big change to the element, and I know we got the element right for its purpose in this case.

Analysing the LEGO ‘Porsche bows’ 77180 and 77182

Spurred on by Stephan’s insightful responses, I took a closer look at the bow to see how well it fits in with the current array of curved elements and slopes. 

It’s far from being the only interesting brick-based curved element introduced in recent times:

  • 1/4 Sphere 3x3x1 in White (6334524 | 76797) currently only found in 10283 NASA Space Shuttle Discovery
  • 1/4 Arch Brick 3x3, W/ Cutout, No. 1 (6294351 | 65617) appearing in 6 sets to date.
  • 1/4 Cone 5x5, W/ Cutout in White (6334516 | 76795) also from the 10295 Porsche 911 and available in pearl gold (6349623) in 76394 Fawkes, Dumbledore's Phoenix.
  • Brick W/ Bow 2x2x1 in White (6299937 | 67810) which appears in 5 sets.

As discussed earlier, its tip, inside curve and rear edge all line up with existing LEGO parts but a match for its overall curve eluded me. 

Its closest but more angular relative, Shell 3x8x2 W/Bow/Angle Right (41749) and Left (41750) here in red, comes close but is two modules too short. Other curved elements don’t hit the mark either. Shell 6x10x2 W/Bow/Angle (59195) pictured bottom right in yellow, is the only element I could find that precisely matched the Porsche bow’s curve and stud/anti-stud placement. 

What about the overall smoothness though? The Porsche bow with its featureless surfaces and rounded corners doesn't quite fit in with these angular elements.

My search for elements with a similar aesthetic led me to windscreens, specifically one of the largest released by LEGO: Shell 16x8x5 W. Bow/Circle (16477) originally from 75060 UCS Slave 1 in Transparent (6072861) but shown here in the easier to photograph and significantly cheaper Transparent Bright Bluish Violet (6253665) from 70828 Pop-Up Party Bus.

Rummaging around in my box of windscreens, I began to wonder if any would integrate nicely with the curved slope. 

The outer curve of Cockpit 10X4X3 (10312) here in Flame Yellowish Orange (6177918) is a reasonable match for the inner edge of the Porsche bows. The screen from 27275 UCS A-Wing Starfghter, Wall 4X6X10, W/ Arch, 1/2 Circle in Transparent (6288568 | 66606) caught my eye too. Its curve doesn't quite match that of the Porsche bow’s but it's close enough for an airtight cockpit seal, or perhaps a smooth transition from wall to glass for a luxurious Paradisa-style window?

Running out of legal part combinations to experiment with, I couldn't help but take Stephan’s comment about eliminating any clutch in the centre underside as a challenge to see what might fit in there - we are nothing if not thorough at New Elementary after all! 

As is often the case with wacky connections, none are especially strong but I feel they hold a certain aesthetic value. The row of visors might be my favourite of the bunch, I could see them as engine exhausts or once again as extravagant windows on a futuristic building, though probably microscale this time. I was amazed to find the escalator link can just about squeeze in there too (69900, another element we discussed recently and will publish an Element Developer Interview about soon).

Tom Loftus’ MOCs using the Porsche Bows

Fun though it is to find bizarre parts combinations, I used a more robust pairing as the basis of the mocs I made. 

Brick W/ Bow 2X2X1 (67810) has the exact same curvature as the studded end of the Porsche bow, and together with a 1x2 tile (3069) the trio of parts create a continuous flowing shape I ended up using twice over.  

Neo-Space Police III One-Man Speeder


First up, a one-man speeder inspired by the Space Police III line from 2009. The element’s sweeping curves are just perfect for achieving the sleek shape any intergalactic enforcement vehicle should possess. I was rather pleased with the headlight clusters framed up with a couple of small tyres (50951). 

The Life of Pussi 

This unfortunate kitty is the subject of my second build. Evidently it thought the graceful curves of this small sailboat would make it the perfect place for a cat nap. I originally intended to merely present the vessel way out to sea but I couldn't resist making the situation that bit more dire with a few circling sharks.


Elements that are ‘too specialised’ have always been a bone of contention amongst LEGO fans and some were quick to place these bows into that category. My initial reaction upon seeing them fell somewhere between the excitement of spying new elements and a nagging feeling that something about them seemed off. The lack of a defined chamfer, considerable size and general ultra smooth appearance all made them feel a wee bit un-LEGO-like.

However, a combination of time, appearances in other sets and cobbling together this article has definitely quietened any reservations I had. Is it a little bit specialised? Undoubtedly so. Is it too specialised? Well to that I’d say there’s a bigger picture to consider when discussing what qualifies as a specialised element!


Our thanks to Stephan Breum Steen, Niels Bundesen, Jordan Paxton and Sara Skahill at the LEGO Group for making this interview happen. Let us know if you enjoyed hearing from this employee, so we can feed back to the teams.   

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READ MORE: The 4+ Wheelbase – Interview with element developers Niels Bundesen & Jonas Stubager

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  1. I think you might be missing a photograph: you mention 16477, the UCS Slave I windscreeen in trans violet, but it's not in any of the surrounding pictures.

  2. There's also a tiny typo in the intro; "It's a process that involves careful consideration of countess factors". I doubt there are any nobles involved so it should be "countless" instead. :-)

  3. EwanCartwright13 Oct 2021, 16:38:00

    The only way to really know if a part is too specialised is to see if other designers can't find a use for it, and this piece 77180 has already been re-used in the Typewriter and the Titanic, so it's fine in my book.

  4. I am surprised there's not a decent match for the overall top surface curve. Perhaps we'll eventually see a Brick w. Bow 1x8 or 1x10 to go with it.

  5. All lego Bows are made as a section of a circle, as in they are tangent at the top and then run to an intersect point a "half plate" from the edge of the piece. The cousin of the 'Porsche bow', the 3x8x2 left and right shells have a bow that is 6 modules long and 5.5 plates tall, that works out to a radius for the bow of 9.3 modules, the 4 module bow has a radius of 8.5 modules, so they line up very close when they're next to each other. The 'Porsche Bow' is designed with the same principle in mind, so its curve runs 9 modules and up 5.5 plates, this radius matches the theoretical shape of a 1x6 bow (This is not to say that this part will ever be made) because the piece has a left and right we thought it was important to have the option in the future to fill in between the parts. That's why there is only 1 module of 'straight' at the top of this bow, then the overall length falls back into even modules, which we LOVE.

    1. Awesome info thanks! Do you know is it ever discussed to NOT put the notch for a stud in the outer radius of the 2x2 tube section?

    2. because the part has relatively low clutch (11 tubes compared to its 2x10 footprint) we wanted to have a way to lock it in from the top. We had versions with a stud on top and with a sunken stud. Since the whole purpose of the piece is creating extra clean curves we decided to sink in the stud, since we figured it then also lines up well with the classic 'R' brick.

  6. The part is fantastic, and great article overall. It's fun when familiar pieces from childhood pop up (Great Huna mask) and the cat boat MOC is perfect!