scale-model-concrete-blocks

 

 

CAD files dir in this repo:

Name	Top Plate	Bottom plate
Rect
Angle45
Circle
W

 

 

What is this?

• CAD files for concrete molds, to create linkable cement blocks. these are 3d printable and include the .STL and .F3D file
• sized for 80x40x40mm

How do i make them?

• these are 3d printed with your material of choice.

What is their durability?

• PLA does not seem to last so long when under water and in the presence of cement, which is a caustic material. My first printed form had a failure after roughly 10 uses, several more have chipped corners from me dropping the forms on the counter or in the clean-up bucket.
• ABS might tolerate the damp conditions longer , i have not tested this.

What materials can i put inside these forms?

• these can be poured using regular concrete mix
• plaster mix
• Sillicone

Where would i use these?

• I use these for parakeets, they like to sharpen their beaks on them and the material (concrete) is easy to wash and clean countless times
• RC cars, Model trains scenery and landscaping

The shape i want is not here, can you help?

• Open up an issue on this github repo and (i cant promise anything) i will take a look time permitting and come up with a design

These blocks are too small, are there larger ones?

• You can download the STL files and scale them up in your 3d printer to any size you want, just be aware the M4 holes in the forms scale up too.
• .F3D (Fusion360) files included as well in this project repo, if you want to make these out of metal or fiberglass as a professional numerous-use product

3d print info:

• avoid printing these in orientation where supports are laid across the features, it becomes incredibly tedious to sand the smallest of errors and any bumps or irregularities in the 3d printed surface can cause significant difficulties in releasing the forms after curing.
• once these are done printing, check the surfaces of all the features. a small manicure sand-file or scraps of sand paper wrapped around a crafting knife can help ckean up corners and remove any irregularieis

Hardware:

• these forms relied on me using an M4 socket head cap-screw. They only need to be about 20mm long, just enough to go past the first plate's depth and into the 2nd form component. the M4 screws/bolts do not need to be full length. Its only purpose is to lightly hold together the forms so they don't come apart when using a vibrator, and avoids the use of additional clamps.
• you can skip using the hardware and 3d print some cylinders or pins to slide through and keep the forms aligned just as easily, and maybe use tape or rubber-bands to hold the forms together instead of M4 screws/bolts hardware

 

 

 

 

Notes on mixing for small blocks

These are notes on how i get a 'somewhat ok' result out of using conrete mixture with limited tools:

• Note , lots of compromises needed for small scale at 80x40mm *

• Adjust the consistency of the concrete to be wetter than usual, but not excessively runny or dripping. Aim for a low or no slump. The mixture should be pourable, slightly thicker than pancake batter. Keep in mind that this compromises the strength, but for this particular scale and size, high strength is not necessary.

• Use a composition consisting mostly of sand, with approximately 50% sand, 30% cement, and 20% pea gravel. If you only have sand, you can omit the pea gravel and use a 50/50 mix of sand and Portland cement. You can also experiment with less cement and more sand, such as an 80/20 ratio.

• Prior to pouring the concrete, lightly coat the features of the form with a thin film of oil or grease. Use a small brush to ensure an even and light coating. While spray-on oil can be used, it tends to leave behind bubbles that may interfere with pouring. Brushing the oil on is preferable to avoid air entrapment.

• Secure the form using two C-clamps per form. Apply light tension to ensure that the 3D printed material remains flat and does not shift during vibration. Place a wide board or piece of metal at the bottom, and two smaller pieces at the top, leaving an opening for pouring. To protect the bottom surface from the caustic concrete mixture and improve the finished product, consider laying a piece of plastic or wax paper on top of the bottom board or plate.

• Use a shaker or a vibrator motor to vibrate the cement form. Due to the scale of the project, it may not be practical to use a small-scale vibrator. Instead, shake the entire form assembly to encourage the sand to settle out of the aggregate and into the recesses and feature points.

after mixing , vibrating to remove air pockets is critical. Once done, remove the clamps and top wood pieces carefully, let it sit for about 4-6 hours (depends on temperature and humidity). Once the concrete has dried enough to not be disturbed by a light touch, gently submurge the form in water deep enough to cover the concrete. Once it is underneath water, it will cure within 48 hours we can remove the forms. sometimes as soon as 24 hours if it is in a warm environment

To remove the forms:

• gently wiggle the forms side to side, it is a technique to learn and is difficult to describe, like asking someone to explain how to crack an egg without breaking the shell.
• if you aren't sure you can wait another additional day, ive found by the 3rd day of curing when submerged in water, the blocks are much more resillient.

Tips:

• it is better to UNDER fill the form, than over-fill. do not over-fill the form! the blocks will not fit together if they are too wide (over-filled).
• Shrinkage will occur, if you fill right to the edge and it cures, the final block will have some shrinkage and this is OK, but if you want closer tolerances and less gaps in the finished product, use less water in the cement mixture or a "water reducing additive" (superplasticizer)
• Always vibrate, its better to shake it too much than not enough. I run the vibration at least 10 seconds after the last bubbles rise. This compromises the mixture, sand precipitates out from the aggregate BUT results in a better finish and less errors.
• get the cement mixture level after, or during the final moments of the vibration. Sometimes there is a film of water or fluid ontop of the mold that gives a false sense of full, sometimes i pour in extra mix and let it over-flow so i am absolutely sure that it will be at the right high when cured.

Curing:

• Concrete (portland cement) needs water to cure. it does not cure when it is dry.
• Placing the forms underneath water while it is curing, ensures the mixture is strong enough to remove at 48hrs without ripping the features off
• the forms are very sensitive to disturbance when curing. Do not flex or bend the moulds, do not tap on them or bump them. Handle them like an egg
• if it is not practical to place the project underwater for curing, they can be placed in a plastic bag to retain humidity

 

 

 

 

examples of the final product

Surface irregularities:

• this was printed at 0.2mm "draft" resolution and the resulting layer-lines transferred through to the final product