new molds

2Printbeta proudly presents: New molds for our casted parts.

Within the last months we casted lots of prusa and mendel parts. The molds are made of very elastic silicone rubber, but they suffer from the demolding process.
Some of our molded bridges broke away and thus the casted parts had to be redrilled:

This postprocessing progress is very time consuming, so we tried another method to get casted holes without any redrilling.
Smooth rods made of stainless steel work perfect as bridges:

Treated with a spray which makes demolding easier they can be removed.
Therefore we grabbed the ends of the rods with pliers and rotated them with force. After a loud click the rods come out easy.
With this procedure the demolding is a little bit harder than before, but the holes are perfect:


The second experiment was to cast in M3 nuts into the motor pulleys:

Many customers asked, why there is no hole for a M3 nut in the pulleys.
The casting process has limitations and as mentioned in the description the m3 nuts have been replaced by threaded holes.
Although the threading is made of plastic it is capable to fix the pulley on a one side flattened motor shaft.
Without flattening the motor shaft the screw has to be fixed very tight - the plastic threading cannot resist this forces.

So we found a solution for this by inserting m3 nuts in the right position inside the pulley.

After demolding the m3 nut can be used as described in the assembly manual by gary hodgson.
The nut is already locked inside the hole:

The experiment has been a full success - using this mold the first time.

But our expierience with these molds an with such small briges as the 2.5mm holes inside the motor pulleys says it will not last very long.
The briges will break after about 10 to 20 times and then there will be nothing which forces the nut into the correct position.

The next experiment will be a mold with m3 screws as bridges. They can be used to place the nuts and will not break away after some time.


Beta prototyping Robots

Some time ago, we used a special process to create our casted 3D printer parts in larger quantities. In this process, we printed master models with our 3D printers, very similar to what you would do for creating printed 3D printer parts.  Then we put those masters into fitting boxes and pour silicon material into it. This way we got a negative form when we carefully remove the master again. Finally we used the created negatives to cast new copys of the master model by pouring PU casting material into it.

During this process, we decided to find out how much time it would really need to get from a digital model to multiple casted copys of this digital model. We were interested in making other parts than 3D printers, so we started a small experiment to get from digital design to small scale series as fast as possible.

To make the project more fun, we started with designing a small robot model. It is split into body, legs and weapon parts with different variations of each so we can combine many different looking robots once they are casted.

The digital design of all those robot parts looks like this:

And digitally assembled, they can look like this:

After we designed those digital models overnight, we started the next morning with printing those parts. As all those parts are pretty small, it took us only a few hours on our mendel 3D printer to make master parts of these digital objects. The whole morning was spent with waiting and feeding the 3D printer so we got all parts ready. The chaingun with an added plate for casting can be seen here:

It was around midday, and we had the master parts for this robot models ready. So after a lunch break, we started with putting the masters into boxes and securing them so they don't float up while casting. Then we mixed the two part silicone mold material and filled those boxes carefully to create our negative molds. We made a foto during this process:

Again we had to wait, as the silicone mold material needs some time to cure and to become solid. Depending on roomtemperature between 2 and 4 hours. So later, near the evening, we could take the silicone out of the boxes, carefully remove the printed masters. After this we only needed to mix some two part PU casting material, add the desired color and cast robot parts one after the other. The PU cures really fast, so you can make new casts around every half an hour.

Unfortunately some parts of our models were too detailed and thus these features didn't look perfect when casted. But the robots still look very nice after assembly. We made them in different colors:

In conclusion, it is possible with this technique to get from a digital model to multiple casted realworld copys of it, in one day, from moring to evening. And most of the time is spent on waiting for materials to cure and for the 3D printer to finish its jobs. But there are also limits to this technique, as some details, like the rockets on the green one, are very hard to cast and it's very likely for them to have casting errors. So the process might be better for more simple parts than ours. But all together it's a great way to get a small scale production of digital objects into the real world without too much effort.

If you want to recreate some of this, you can find the stl and openscad files for this robots on thingiverse as object nr 23788

We also made a video about this whole project. Take a look here: