Top down DLP 3D printers normally need a lot of resin to fill the vat. I am always on the lookout to find a way to reduce the resin required to fill a vat.
In the past I tested floating resin on salt water, but it had too many downsides.
I read about using glycerine at that point in time and also other chemicals, but I just didn't have time to do more tests. I heard about it again this week and decided to find some glycerine and start testing.
I had some FunToDo Industrial Blend Black in the cupboard for a few years now. I knew I was going to need it for something. I also kept the beaker I used in the past to experiment with the resin in the cupboard.
Most of the pigment dropped to the bottom in the glass.
I still had some pigment in the beaker. I just added the glycerine to the beaker and mixed it as well as I could
I mixed the resin in the glass for a bit until all the pigment mixed well with the resin again. It was like the first day I pored it out of the bottle.
I pored the resin into the beaker and I could see it was floating on the glycerin.
The date today is 2017/01/18. I will take photos for a couple of weeks to see what happens with the resin and the pigment
The date today is 2017/01/22. The glycerin is very clean. The resin itself still has all the pigment floating in it. I can't see any pigment dropping to the bottom yet. I mixed it by shaking the whole beaker for about 20 seconds to see what will happen if we mix everything. The resin and glycerin mixed completely and it was black from top to bottom.
I left the resin for about 2 hours and it started to separate nicely again. At this point in time I can't see a downside to using glycerin to reduce the amount of resin needed to fill a vat.
It is 2017/01/29 and the pigment settled on top of the glycerine. Shaking it for a few seconds everything mixed completely again as before. It will probably take another 2 hours for the glycerine to settle. The important test still to do is to print with resin that has been mixed and have had the glycerine settle.
Someone on the forums did actually print with glycerine. He mixed and didn't let it settle for a long enough time. His prints failed. I actually like that I can mix and be able to print instantly. Less time lost and less management.
In the past I tried to mix the resin by moving the build plate up and down. That didn't work because the pigment was on the bottom of the vat.
In this case if the pigment is in the middle of the vat maybe using the build plate to mix the resin might work if you go through the layer between the liquids. The problem that I can see is that the machines use a gearbox system and the build plate might not move fast enough to actually mix the resin enough so a mixer system might still be needed.
We probably need a top down mixer and not a magnetic mixer anymore. We might also only need a very short shaft on the mixer since you will probably not fill the vat with that much resin. On the biggest vat you might fill it with 5L - 10L of resin. That might only be around 200mm of resin.
The more expensive resins seem to use something else to block the UV. They don't use pigment. So if you go with a much more expensive resin you don't need to worry about the mixing. Maybe go with an expensive resin and glycerine. Then you get best of both worlds.