Maand: juli 2026

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3D printed PLA mold for concrete casting

Hi, a new project and I’ll be adding to the documentation coming weeks. I hope it gives you useful information or inspiration.

Usually for casting concrete a wooden form is made which is filled. For simple shapes that’s easy, but some shapes are hard or time consuming to make of wood. I wanted to try this already for some time, so I decided to make a 3D printed mold. Interesting study project but for such a simple shape way over the top 🙂

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This is what I want to make: a sign for use at competition days at my athletic club

(Tion Herfstloop)

We thought of a simple wooden cross with a weight (three tiles or a bag filled with sand) placed on it, a bucket filled with sand (or concrete). It has to be transportable, not too heavy, and it will be decorated (painted).

Rather simple, and it could well be made quickly without any problem. But for learning I’ll use 3D printing. The added value might be: nice shape, own logo, durable.

Questions:

-How thick should the mold be

-Will the concrete release well? Release agent or grease necessary?

-How many times can it be used.

-Aluminium or Portland cement ? Alu is much faster and fine for details. Portland is cheap.

A block with a center hole for a post, 2 handles to pick it up easily and two holes to put a rope through.

These parts would form the sides of a wooden mold. However, I abandoned this idea of separate parts and adjusted the plan for 3D printing the mold.

The 3D print design. The walls are still 9 mm thick, remnant of designing for wood 9mm.

The resulting shape. Looks nice to me. Print it

27 hours printing.

Settings: 0,20mm Standard @BBL A1M (Bambuslicer):

0.2mm layer height, 15% fill, , gyroid.

Nozzle: 0.4mm.

PLA: Basis PLA (Bambu), printed at 100% speed.

The next print ( the shape to form the opening for the hand) I printed at 160% (ludicrous). It turned out well.

Next: sanding before appling a coating.

K120 sanding paper, primer spray paint, 2 coats applied

I bought this material:

Gietsteen (casting stone). You can also use aluminiumcement mortar with sand. Alu cement is not sold everywhere like portland cement. I found it at sculptors supply store Beeldhouwwinkel. Others that have it: Keramikos and Hazelaar. 20 kg costs about 40 euro, transport 12,50 euro. That is much more than 25 kg portland ( around 8 euro / 25 kg mixed with sand (3x 25 kg, less than 10 euro). It better looks awfully nice for such a price. Bought it anyway. If this works well there will be follow up projects.

https://www.beeldhouwwinkel.nl/nl/caltra-gietsteen-standaard-snelwerkend-801

For the through holes I use a PE tube around a metal rod, so I can remove it easily: just pull it out, it is flexible and does not stick to concrete. Metal tubes or wooden rods might get stuck. Then you have to do a lot of work to get them out and keep the mold intact.

For the big hole I cut a 2-piece foam core with the hotwire cutter (smoother than with the belt saw), made a 2-piece foam core (might be easier to remove than a 1-piece core). Taped around it to keep it together. I can, I suppose, remove this core quite easily with a piece of metal, a screwdriver or other sharp tool. We’ll see 🙂

The mold parts. Now: applying release agent ( bekistingsolie (NL), Schalol (GE) ). Oil or vaseline can also be used as well but is not recommended as it may stain the concrete. I found a jerrycan with still 3L in it at Marktplaats for a very reasonable price. That will do for many molds to come.

A thin coat of oil applied, 1 liter is good for 20 -30 square meter, that means a layer three times as thin as a paint layer, so apply sparingly. I applied it with a dry-ish brush and removed excess with a paper towe

Cement and water. Ready to go

Mixed. Now tapping against the bucket with a stick, to get the air out

I waited 5 minutes before casting, following the instructions. But it set very fast, I could hardly poor 80% into the mold and it got to stiff already. Probably too hot today (over 25°C). So I quickly prepared another batch, mixed, did not wait 5 minutes this time and still it set very quickly. But now I succeded to fill the mold to the rim and hit it gently with the plastic hammer to get the air out and level the surface. Even filled a couple of small test molds. Covered it with wet cloth and a plastic bag to prevent that the concrete dries out. Tomorrow we’ll see how it ended up. Will it release properly, will there be a visible separation between the first and the second cast? I must go home now and not have a look (and rip the fresh concrete apart)

Ok, some positive and some negative points:

1 cast came out easily,

2 tubes and center hole worked out well

3 overall shape and weight are convenient

but:

4 shrink cracks,

5 characters were damaged

6 casting in two times gave an ubly joint

next cast:

Working at lower temperature or using a slower setting cement so I have enough time to fill the mold in one time

adding sand against fracture

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marble run 2026 drawings and manual

(you can also download the files from github here)

Manual for the workshop (German)

murmelworkshop manual duits 5 20260716Downloaden

workshop manual Nederlands

knikkerbaan workshop manual nederlands 5 20260716Downloaden

Making the schablone:

Cut the PDF with a laser cutter or print them on paper and cut them with a knife and scissors. use cardboard of about 0.5 – 1 mm.

Alternatively they may be 3D printed.

straight track schablone:

schabloon rechte goot karton 20260708Downloaden

curved tracks and support schablone:

mal bochten en pylon 920260630Downloaden

Using the schablone:

copy the lines on 200- 300 gram paper, using a ballpen, which gives suitable folding lines. when tracing: skip the triangles, they are only ment for holding the schablone together. draw / cut a straight line

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Marble run maker in residency

Augustusburg, june – july 2026

I have been invited as a maker in residency in Aufweiterflur in Augustusburg, close to Chemnitz in Germany. A major objective was giving workshops marble run here and also representing AWF at the Chemnitz maker fair. And also collaborating with other makers at Makers United (link to Makers United 2026 here)

I developed a marble run made of paper. Trial and error and interaction with children was part of designing. The first ideas of the marble run were very much rooted in smoothly running tracks made of wire, or referencing the German – Ertzgebirge toy tradition. For example here: spielzeugmuseum-seiffen

Very nice things, but I wanted to create something else than the than marble runs that are available on the market (not so easy though!). Why? A couple of reasons: some need specialized tools to construct them. Or require much work. Or are just expensive. I would like to connect to the German toy making, but still had to find out how.

Paper

Paper is a material that I like a lot, and it can be worked with quickly. So it felt comfortable to follow this paper road and see what could be done with that material for a good workshop, wherever it might go.

Ultimately i arrived at a very simple solution: two curved tracks, a straight track and a support that can be combined. All made of easily available, either new or recycled, paper. It runs with standard glass marbles. It requires nothing more than scissors, a pencil and some tape. Optional were bamboo or paper sticks and (ready made) 3D printed supports for the tracks that fit on the sticks. For drawing the tracks I produced schablones, cut with a laser (optionally with a scissors and a knife) and I also printed these

The shapes are included in the workshop manual (aimed at instructors) and all are available digitally here as well as on Github.

The sticks and supports turned out to work well. The support design is not perfect ( too stiff), but it is used successfully anyway. An improvement may follow later.

You can find the support 3D design (VV2-TPU) here on Github, you can download and print it, or improve it (keep me informed!) yourself.

Other marble tracks were also prepared (more about them here). These use 3D printed supports and wire ( either ABS , bamboo sticks or rattan; a natural fiber). Building them requires more time and dexterity than the paper tracks. Most of all, they are more permanent and components can be used over and over again in new marble runs. Built marble runs now reside in the AWF garden and are used frequently by children. It obviously is not necessary for them to build a new marble run from scratch. Much of the fun is playing with a marble run, not only building it.

Looking back.

And, did I connect to the tradition of toy design? 
Specifically, Erzgebirge toy design? 

Frankly, not really. 
But I did connect to toys and toymaking, when you ask yourself: 

What is a toy (for)? 

If there is a specific goal, I would put this on the first place: 

Make children (and also adults) explore, cooperate, try for themselves, get interested, learn not to give up.....

That, rather than making a nicely looking toy (even though that certainly helps a lot in accepting the toy), is what unites toys all over the world. Not a design-goal maybe or something to advertise on a website, but certainly a deeper understanding of what toys mean and what they can do.  The good thing is: you get it because you are working with it. 

I have this result now and kick it into the world. It is not perfect and it is limited in its use but it works and it broadened my understanding of marble runs.

Gluck auf!