Recently I finally uncovered what material is used to do this:
Because yes, it says “PVC” in the label, but what is the liquid they use? Well, as it happens, it’s called (doh!) “PVC ink”, and one of the most avaliable commercial names is PLASTISOL. It is used in the shirt printing industry around the world, so it should be fairly easy to find locally wherever you are.
I know, silicone rubber can be used for that purpose, but it has shelf life and any leftover mix will be lost if not used, whereas the heat curing (150ºC/90secs – 170ºC/30secs, special aditives to reduce temp to 130ºC exist) material will just stay as it is, and any non-contaminated excess can be just dipped back into the container for future use.
When I first uncovered the material name, I was not sure it was the right one, so instead of bitting the bullet, as emotion would want, I just bought a 1Kg black can to test for about 23€ shipped.
Damn that’s messy…
To properly mix the ink the first time I used a knife, but that was far from ideal. I knew I wanted a different tool for the job. Something called a cream spatula (had to learn that from Twitter, I only knew the shape until that point):
The thing is, I bought the cheapest one I could find, but upon further inspection at home, the edges where really bad, very coarse and dirty:
I knew I didn’t want any edges to rub and cut the inside of the plastic plastisol container, so I quickly went to town with the scotch brite pads to smooth that out. The result was good with a lot less effort than I had anticipated:
As a test piece, I would use this CNC test I did years ago. A nice curved shape on an aluminium block:
And my trusty hotplate. It does not have a huge amount of heat capacity, so the temp can drop once putting a big enough mold, but for the small things I usually do, this should be more than enough. Remember this stuff curing temp is between 150ºC/90secs and 170ºC/30secs, but it won’t fully harden until you cool it. That means that poking it to see if it cured while still at high temp, will not give you an adequate answer. Don’t worry though, it’s easy to get the knack of it, you just have to totally avoid it smoking (closer to 170ºC), because, like with all burnt plastics, the smoke is highly toxic.
An important detail is that you can also gel the ink at about 50/60ºC so it doesn’t run around, but still adhere to any other inks you put on top later, very useful to do double sided things, for example.
As always, since you are reading this, you know it worked. Shame, there’s no way to surprise you anymore…
So, next try was doing a mold on purpose, and I settled for a keychain-esque piece:
But the thing is, I hadn’t touched my CNC in a fucking long time (maybe…about 1.5years…yeah, too much time) and I kinda made rookie mistakes all the way on the first test. For srtarters, I assumed the stock thickness, but I was wrong, instead of 4mm it was 3.
And I also forgot that the piece would be mirrored…and forgot to mirror the mould instead:
Nothing some phohoshop can’t fix:
Joking apart, this material has sooooo many uses I don’t know where to begin, but in the meantime, I decided I wanted to do a nice keychain to sell. After a meh poll on twitter, I finally settled on a Nixie tube…because you know, if you do something, do something cool, right?
After fiddling a bit, I arrived at the following design, kinda okay, but of course, totally missing the grid:
Much deliberation later, I decided I would add the grid to the main mold, and sort the addition of the number in between steps, to get something like this (grid not to final size, that’s just a test):
So, how would a mold for that look like?
At this point I didn’t have any 0,1mm engraving bits, but decided to do a test anyways, because you know, cool molds and experiments, and I sorta could not wait to see something other than a crappy inverted text keychain.
This took a while…
The 2mm ball endmill could not reach the smallest details, I was fully aware of that, but this was a test of the capabilities of the 3020 cnc anyways. I might also have overreached with the heat capacity of the hotplate, but it worked in the end, it just took a while longer to reach temp.
And…this came out. The cad program didn’t pick up the fine detail of the grid with such a big endmill, wich is a shame, but nevertheless the wall finish was quite acceptable.
It’s definitely not perfect, BUT, it’s a promising start. I’ll get rid of the bubbles by using a more liquid plastisol, and once I have the fine cutters, I should be able to reach many more details. Buying all the colors I need for it, is a different matter, though. ^^U
Anyways, the keychain thingy is just an excuse to play with the technology. My own ulterior motives will be seen later on.
See ya!
The Electronic Mercenary 