Raspberry Pi 4 Experimental Resin 3D Printer -- Episode 414

Hi Clem,

I found your youtube video very interesting, I am wondering why not use the low refractive index substrate with a silicone applied coating?

lots of laser resin folks are using acrylic like vats with a silicone coating. Would this maybe help? https://www.youtube.com/watch?v=RHTgHzDQbSY 
Also are you using polarize filters on each side of the LCD to help block the wave between slices?

Are the UV Cure lamps 380nm to 410nm?

Keep up the good work!

Thanks,

Paul aka Deadbe3f

Hi, thanks for sharing your ideas here. I will add some of them for the Q&A when I finally get to the second iteration.
O nthe separation forces: density of course is a factor, but the resin does not seem to be always at the same density from batch to batch and also behaves differently at different temperatures, over the course of a print it warms up a bit. For floating it was crucial to have unbroken surface tension. so I increased the density of the liquid but also had to make sure the surface would not get broken. which made removing air bubles areal pain.

to avoid having to deal with it the current plan for C.L.E.M. iteration 2 is to put it on its head and have avery deep floating liquid that supports a bigger amount of resin and the topmost layer wil lget cured not the layer at the seperation zone of the two liquids.
this avoids having to make sure for a perfectly clean separation and only needs it to be a uniform layer of resin that levels itself by gravity.

Hello! retyping my thoughts from my youtube comment:

I recommend you make a build tank out of solvent welded acrylic, and a base of thin plastic film. This will allow you to see how thick your gap liquid layer is from the side of the tank. a tub with rounded edges makes this impossible and has too thick a base. You want as little distance from pixels-to-resin as possible which means the gap liquid+plastic film needs to be as thin as possible.

As for bubbles, I pour the resin in the tank and then give it like 10 minutes to settle, then i use the build plate motor to stir it up and down but under the surface so you don't introduce further bubbles. maybe add the gap liquid only after the resin is well stirred & de-bubbled.

It seems like for this method to work you really have to avoid agitating the gap liquid which probably means running the thing super slow. as the build plate moves up there will be a strong suction force inward which will disturb the uniformity of the gap liquid. perforating the build plate should reduce this force in the early layers. also using a physically smaller build plate, like just the size of one benchy for starters, because the smaller the build plate the less it disturbs the fluid.

It will maybe also be necessary to glue down the plastic sheet to the display surface (like with a light dusting of contact adhesive like super77) to prevent it from pulling away from the display under the forces.

I'm not a chemist, I'd love to hear from one on how to increase the separating forces between the liquids, like maybe if the resin is less dense and gap liquid more dense then they will want to more strongly separate. If density is part of what makes the gap liquid fall and the resin float, then you should measure the densities of various resins and use the lightest one, and figure out how to increase the density of the gap liquid. I think i'm talking about the buoyant forces like what makes oil float on water.

Another maybe useful idea is to put a sort of plastic mesh or fine netting material against the display and putting enough gap liquid to *just* cover up the mesh material. it'd act as a baffle keeping the gap liquid mostly in place, in the case where the suction forces are disturbing the interface too strongly.

alright, that's all I can think of right now. Cant wait to see more experiments

mayermakes

Clem, you are welcome. this is what I call a WIP Work In Progress! I can't wait to see more of this thing.

I really can't judge your soldering technique though. So go over to my blog and look up "NexGen Soldering School"  and look at the bottom and see the NASA specs, especially the photos.

Good Luck!!

I say thank you! cant say anything else. very nice comment on this date!

mayermakes  Clem great work. cant say anything else. Your best effort to Date!!

Hi, welcome to the community.

I try to answer these questions, if I'm unclear please ask further and I hope I can clarify it for you.

"I assume the liquid needs time to settle down before starting the print, to produce perfectly flat layers." -- Yes, that is correct, but it does not take that long to settle, it is crucial to avoid shocks or impacts during the curing of a layer. in nanodlp you can set wait times for different steps in the sequence, i just gave it as much time as I coulkd effort in my experiments to make sure the waves have set before proceeding.

1. yes, like on most printers the plate lifts between 1mm and 5mm depending on resin and machine. while FEP based machines need that movement(or a sequence of moves) to peel the layer of the fep and let new resin float under the cured one. the CLEM system uses it to let new resin flow in ,but also let out possibly trapped airbubbles(these are a huge pain currently to deal with). Ic also thought about going down a mm and then up to kind of whash the cured layers in the floating liquid. but did not try that out.

2.yes, and I also reduce the movement speed greatly for the last 2-3mm of the move. it is less about disturbing, more about avoiding to break the surface tension. once the surface is penetrated a blob of resin sinks top the bottom. further advances in the floating liquid may solve that problem. for now the resin is not floating but more like balancing on the surface tension(if that makes sense) also the meniscus at the edge of the vat is kinda helping it stay above, but it also makes it very hard to judge the actual height by vision.

3. yes, but it is not that easy. As mentioned the surface tension has to be kept intact. so I have to be very gentle. what worked was removing the liqiud with a straw/pump/pipette and then dumping the resin in a bottle.

when reusing it you need to pour it very slowly so only the upermost resin leaves the bottle, there certainly will always be a rest of mixed resin at the bottom. the plastic tubs that i used for my experiment can only be thrown away once resin has come in contact with the bottom. another reason to turn the whole system upside down to make the liquid reservoir hold more liquid and sinking resin would just turn into waste that you'd remove from time to time, not every after print.

Hope that helped! if you have ideas please share them!

That's a clever idea, the resin floats on top of another liquid. That reduce wear and tear on the vat screen. Thank you for experimenting with this technology. That's how things evolves.

I assume the liquid needs time to settle down before starting the print, to produce perfectly flat layers.

1. Do you have to lift the part higher than a layer thickness after each layer? Is the resin able to naturally flow under the cured layer or you need to lift the part higher to ensure the resin cover the entirety of the previously cured layer?
2. Do you have a "settle down" time delay before each layer or the lifting of the part is slow enough to not disturb the liquid underneath?
3. Are you able to easily recover unused resin? Does it matter if it get mixed with the liquid underneath? I assume it would separate easily. As long as you reuse it in the same printer with the same separating liquid, it probably doesn't matter if you get some of the separating liquid while recovering the resin...

Sorry, I have so many questions...

Hi thanks for posting yxour ideas! welcome to the community.

I go through this one by one to give some feedback of mine, but I hope others join in on these topics too:

I see all these Ideas keep the FEP film-> that was one thing I wanted to get rid off , for the reasons of cost (strips of FEP are not crazy expensive but wide sheets are) and the problem wit hpeeling forces at scale that make it more likely to rip/tear or just not peel that well. this holds true even for the thickest FEP I could find(the wider the build volume_> the bigger the lift-> the higher the force ->the more sever  distortion).

I tried to combine lcd masking with techniques more used in DLP machines.

1. I not sure if i understand that idea correctly please chime in if i get it wrong.
Every section gets built ,peeled(the lift in general is between one and five millimeters depending on resin and machine) the next one exposed and so forth until a layer is completed.
I see a simple mechanical problem here, in which as one section is exposed the gantry cannot go back to it the exact position for the next section without pressure to the Foil.
But on the other hand if this would be a Non-FEP but liquid system no such problem would arise. the pixel density of the whole screen is the same as if it would be exposed at once, speed is slower( divided by amount of sections). I think you are aiming to get the peeling forces lower, but the sheet would still have to be in one piece, which means the same stretching problem over wide areas would occur, but the forces would be lower per peel.

2.I could see this idea viable for very high resolution machines! two gantrys are needed :
Z for liftuing the part and X/Y for the screen underneath the build volume or in a top down configuration(which I think would work better) vice versa.
I'm intrigued to give this one  a shot, not for a big printer like in the video but for a reasonable small but very high resolution one.
the biggest challenge here is the firmware& pefectly aligned mechanics! to get everything in snc I'd tend to use a beaglebone for its PRUs and later spin off a board based on it. another variant is to use a TMC5161 driver and load off a lot of the movement calculations by setting it dynamically to the loading times of the image..but I'm currently not confident that I could pull off a machine like that in a timeframe reasonable for a video.

3.I also like this idea, not sure if formlabs or anyone else has a patent or similar on this technique. it basically works like a photocopier. peeling forces are highly reduced.
what bothers me is there is stil FEP involved and the firmware would be very tricky. to get the screen in sync with the movement i think a beaglebone would be a good option, the PRUs could act as synchronized stepper drivers that get triggered on the image bbeing displayed. (synchrionizing the movement to the image , not the image to the movement.)

Hope this sparks soem more discussion!

Hello! I wrote some ideas about a large format MSLA printer in the youtube comments and was asked to post em here. I've thought about three ways, each with their advantages and disadvantages:

1. Easiest and simplest to implement would be to just expose each layer in sections instead of all at once. It can be done with the current rig from the video, you would just need to separate the large bitmap into several  sections, then expose each section and peel it without advancing the Z axis. It may be possible to split the bitmap in various ways like alternating checkerboard patterns to optimize them for easy separation from the FEP film. Main downside from this method is that although it's simple, the resolution is still relatively low, and i doubt we'll be seeing any improvements in the near future for off the shelf LCD monitors.

2. Use one of the standard small 1440p smartphone LCD screens from Sharp which printers like Anycubic's Photon use, but put it on a gantry that will allow it to move on the X or X/Y axes. To cure a layer you would split the bitmap into sections like in the first method, but physically move the LCD and backlight into the correct positions and expose them one by one. Though slow, this would keep the nice ~50x50micron resolution no matter how large the build volume is.

3. An approach similar to Formlabs's "Low Force Stereolithography", but using the LCD screen instead of a laser scanline. The whole unit would need to be placed in a gantry and for each layer it would sweep the layer while creating a small bulge in the FEP film. The idea is that the resin would cure only in the area where the bulge contacts the buildplate and then quickly get peeled off as the contact point moved away. Formlabs has a very nice video on how their Form3L works here:

https://www.youtube.com/watch?v=dLIRAkXa6t8

Not sure how feasible it is to do this with an LCD, it would require some way to synchronise the displayed bitmap with the motion of the LCD gantry such that the image remains "still" with respect to the buildplate. I'm guessing this would require an HDMI-to-MIPI converter board since the bitmap would be animated.

So that's basically what i've come up with. I'd love to hear any feedback on these ideas, and perhaps hopefully we'll get to see something interesting come of them