Corrections, additions, and FAQs: 1) Thanks to Steve for the idea of a saddlepoint mirror, and giving me the excuse to bust out the silvering solutions again! ukposts.info/have/v-deo/q4Bhl62DrHuo1Ks.html 2) Yes, since I know people will ask, I have seen the HEN3DIRK channel that has some incredible videos of electroplated SLA prints. I haven't embarked on that challenge quite yet… ukposts.info/have/v-deo/saeBnWemqq9o0Gw.html 3) "use a resin printer!" yes, you're totally right! I have an old one in a box that I've never ventured to use. it's on my list! In this case, I still doubt I'd have achieved an optical surface, although if you read that paper I flashed up on the screen, they claimed to get something approaching diffraction limited with an SLA printer, which just feels impossible. I think their smoothing resin was also very different from what you can buy on amazon. 3b) Someone in the discussion below about resin printing said that you could buy one with 50nm resolution, and I highly doubt this. you CAN easily get one with sub-50um precision, but unfortunately 1 micron = 1000 nm. light is crazy small 4) z-axis wobble (or any inconsistency on the rails, belts, and screw) ABSOLUTELY could have been at fault for some of the wobblyness. I can't stress how small these changes are. It was difficult to film it in a way where you could tell there was a difference from layer to layer. For every purpose that isn't reflecting light, it was perfect lol. 5) I DID actually sand down my best-performing mirror prior to coating. you can see the sanded part in the "coating" close up, and you can briefly see the green jig with blue tape bubbles chucked into the lathe. for some reason I didn't actually film that?? I put the mirror on the lathe and use a few sandpapers. It made it look better to the eye, but didn't fix everything apparently. 6) I'm doing this crazy silvering process instead of some kind of chrome paint because I was initially trying to make optics, and for that the surface needs to be absolutely perfect. That's also why I didn't do vapor smoothing, which I think can leave a slightly porous surface.

Nice. They popped up on my feed next to each other.

Have you considered using a resin 3d printer? They can be bought rather affordably and have much higher accuracy. Given all the work you do with chemicals, a resin printer should not be an issue. All the best and keep up the good work!

"The Continuity of Splines". It's a good video. I find it cool that many of my favorite science channels know and/or watch each other.

The striations you saw in your 3D printed mirror are most likely caused by the infill pattern that you used. At 10:00 in the video you can see the deformation caused by the infill in the surface. From testing with PLA it takes about 8~10 mm of wall thickness to get rid of this bleed through tension. For small parts like this the easiest solution is to just print it solid.

I'm so glad you referenced Freya's video on splines. it's truly a remarkable video

The artifacts you were seeing on the Z is due to your lead screw not being 100% straight, MirageC has a few good videos on the subject and something you can print to help with it. Not sure if there is a solution for the Prusa mini but i would be supersized if there isn't.

You can electroplate the mirror with nickel on top and keep it from getting rubbed off! And in general you can plate any other plastic thing after you seed it with silver. There are also silvering solutions based on citric acid, ascorbic acid (yes, vitamin C), EDTA and silver nitrate that plate directly onto PLA. I don't have a 3D printer but I plate stuff, a neighbor gave me some stuff to try, and I couldn't get the silver to stick with Tollens-based alkaline solutions. I realized that NaOH and bases in general slowly de-polymerize PLA. I'm thinking that while it takes quite some time to dissolve a part completely, it's acting fast enough that the surface is getting dissolved too fast for the silver to stick. So I cooked up the silver lemonade I mentioned before. No respirator needed, no messy spray bottles, just soak the thing in the solution. If you wanna try it I can give you more deets :P

Freya's videos on splines are absolutely stunning.

You should try non-planar 3d printing, so that you are able to create the mirror surface as the last layer, without having layer steps or placing the part in a weird way. Same sanding may be required to obtain a completely smooth surface though.

Great collaboration, wonderful to see you two working together on this cool topic

I watched this video because Steve's video sent me here. Then I realized I was already subscribed to your channel. Nice!

Oh thank god…I was worried this was one of those video pairs things that happen quite often where similar UKpostsrs post similar videos within a few hours or days of one another and people accuse one or the other of copying the other. I love when y’all relate it to one another. Thank you for this awesome video and I hope y’all two can collab again sometime!

How have both Sebastian Lague and Alpha Phoenix released a video in the same day that includes a bit about Freya Holmer? Neat coincidence

Steve Mould? Man, it's such an honor to get to collaborate with such a high caliber creator, that Mould guy should be really happy.

Hell yeah! That spline continuity video is amazing. I think about it every time I see reflective surfaces now lol.

I swear I have never clicked a video this fast, this is truly one of my favorite channels. THANK YOU.

Two suggestions. One is to smooth the surface before silvering it. Sandpaper, glass beads, stuff like that. Or even hitting it with a heat gun to melt it so the surface flows together into a single surface. Also, the rotating technique makes a lot of sense, so why not keep doing that when using the spray bottles?

Haha that video by Freya is FANTASTIC! It brought a tear to my eye :) Awesome work on the mirrors!

I really love when my favorite educators interacting with each other

I come from steves video, because i was told to watch yours, now you tell me to go watch steves. This is a neverending loop.

It is amazing what things you know with such passion. I love it. The whole 15 minutes are filled with non-stop non-redundant information. The intuitive genius vibes I am getting might be why it is so good.

I have been subscribed to both you and Steve Mold for quite awhile. I love your honest approach to doing science.

You could print a negative of your shape, heat acrylic until it becomes soft, and pressform it between the positive and negatives of your forms. As a matter of fact, you could do that with thin aluminum foil and silver that. Perhaps glue the foil to acrylic or pvc sheets and pressform it. Or if you prefer, you could vacuum form it. So many options!

Try using a high resolution resin printer, even hobby grade machines can create voxels at 20µm!

Just found your channel through Steve's. Excellent combination of instructive and humourous. Keep up the content and collabs!

eyyy shoutout to the continuity of splines video!

polystyrene mirror sheets can be heatshrinked to form this saddle mirror with first surface. You could 3d print the saddle with small holes for the shrink bed. The polystyrene isn't viscous enough to mold to layer lines, so they disappear. Great stuff, thanks for all the vids!

man i love these collabs!

Jumped out of my chair when I saw the splines video's mention lmao I just watched it a couple days ago and it's such a great video

I was excited for a collab when I saw both AlphaPhoenix and Steve show up in notifications with the same subject. Great job guys!

Great to see you getting collabs from some of the big-time UKpostsrs

Awesome video! Such an interesting connection between manufacturing and optics.

Excellent crossover!

Amazing crossover episode!

I've been subscribed since before 2^12 and while I don't watch every video, you do deserve every view you get. You're amazing.

I've seen so much about saddles but no one ever goes past the 2-fold "Pringle" to the 3-fold "monkey saddle". Years ago I sanded and polished a dollar coin and bent it into shape using 2 3d printed 3-fold saddle surface forms. The result was quite good, especially after electroplating it with copper to give it a more uniform surface.

I remember my preliminary investigation into lens making and how fast I noped out of that as a thing I reasonably expected I could do 😂 Awesome job!!

That video on splines is fantastic

Channel growing well, glad to see it, you seem like a nice fella :)

Numberphile also released a video on Parabolic Mirrors! What a Convergence of knowledge.

OMG I totally love how you love what you do.

Here from Steve's channel. Very glad to be here, especially as someone with my surname.

Great video! I love the 3d printed mirror videos!

With classic FDM printer there is also a possibility of non-planar printing, creating G-code which moves printing head simultaneously in all three directions. How far one can put this technique depends, as I have read / watched videos about, on the clearance around the printing head. Much better surface for surfaces that are close to being flat. With saddle shape, as mentioned in Steve Mould video, you should be able to create a custom G-code that takes advantage of the fact that the $z = x*y$ shape can be composed entirely out of straight lines at different 3d angles.

Did you consider printing with ABS instead and them smoothing it? I've never done it myself but that should remove the layer lines on top, and then either the UV cure resin might work better, or you could just skip the resin entirely and put the silver straight on top of the ABS.

A collaboration between a couple of my favorite science edutainers.. Yes please.

I saw both thumbnails and my expectations were met.

Subbed to both of you for a fair while and thought that it was odd that you both had saddle shaped mirrors come out at the same time. Turns out that it wasn't a coincidence.

Aww, I was kinda hoping you'd go into glass making like Huygens Optics... aaand I only mention it case I'd love it as a fallow-up / how-to thing. Neat stuffs.

That's a really great video on splines

Again a super entertaining video. Thanks man.

To get layer artifacts out you could try filler and sanding. If you want to avoid coating the 3D printed part, you could try slumping the acryllic sheet over the 3D printed part in a temperature controlled oven. Acryllic has a glass transition temperature of around 100°C. Polycarbonate 3D print filament has a glass transition temperature of 147°C. Alternatively make a plaster cast and then slump over that.

Amazing video bro

I was going to say "weird that you and Steve mould put out videos about weird mirrors in the same day." Makes more sense that this was a colab.

10:17 FREYA!!!! i loved her videos about bezier curves and splines!!

There are pre-coated acrylic first surface mirror sheets available that I've used for this kind of stuff before (making curved mirrors for ldgraphy). The surface is pretty sturdy and even survived putting into boiling water to get it easier to bend.

You may want to try vapor smoothing the 3d printed part with acetone before using your resin. Vapor smoothing, and perhaps pre-sanding, could help at the macro level, now that you have the micro level seemingly more figured out with the uv resin.

I had a very similar problem a while ago and realized that you can get surprisingly good optical quality double-curved mirrors by 3d-printing molds and then thermoforming a aluminium-coated polystyrene sheet. The melted/softened 1mm thick PS sheet does average out the layer steps of FDM prints while the mold is curving the AL layer in the sandwiched polystyrene sheet nicely. I used that for enlarging and redirecting pico laser projectors with an okay-ish quality. There is a video on my channel where I discuss the process and show some results.

That layer inconsistency was something I had to chase in my 3d printing journey for a while. I tracked it down to my v groove wheels (I had an ender 3 at the time), changing them from the TPU wheels to the firmer polycarbonate wheels almost immediately solved my issue. My stock TPU wheels also developed flat spots from preheating in my heated enclosure. With your one-sided prusa, I would blame the wobble and inconsistency on the lack of support.

Would love to see you try this again with a modified slicer for the printer. They have some that can modulate the z-axis at the same time so you have a nice smooth top surface.

Reasonably effective, affordable, expendable first-surface mirrors? Nice.

My guess on the issues with the 3-D printed mirror are because you used an STL. I don’t believe PrusaSlicer allows the use of STEP files, but some thing like Bambu or Orca Slicer does. That would likely get you less faceting and a smoother surface finish overall. I’m still not fully up to speed on this, but you might need a 32 bit printer to print step files with arcs in the G code instead of line segments. Maybe someone else who is experienced printing STEP files can chime in.

I would have rigged some variety of centrifuge to "smooth" the resin, with the "top" of the part facing the hub. You could literally make one with some twine or thin rope and swing it in a circle. The effect would be like putting the part under extra Gs, causing the resin to flow more quickly and strengthening surface tension. You could even do it in a sealed container for a "clean" environment.

Man . . . i also watched that 1 hour-long spline video around a week ago XD . . . youtube recommendation is surprising XD

Have you ever heard about vapor smoothing of 3D parts? You basically 3D print a part out of ABS or ASA and put it in a air tight jar with acetone on the floor. (heating up a bit gives quicker results) The finish is almost mirror like. The key is to let the part sit for a couple of days to reharden the surface for further coating with your silver applying method.

I need to make some elliptical mirror that has 2 focus length so that light passes through 1 will always pass through another. Thanks for the video!

That's crazy, Steve Mould just posted a video on the same topic!

wow it was the most extremely interesting vídeo i've see this week...

Maybe try SLA 3D prints next time? They have a much finer layer resolution! Either that, or vacuum forming acrylic sheets over a buck! - (You can even buy mirrored acrylic, granted it is second surface!) Awesome video as usual by the way, really enjoyed watching it! 🤓😎

The filament can vary enough to do that. Also heating fluctuations in the bed and hot end. There is also this cog teeth on the extruder that cause this. I think a post process would be the easiest way to remedy the issue. Unless you want to buy a resin printer or a Bambu labs X1C. Jamie Mantzel did a video on making a clay dome mold from a pendulum. I think this same sort of method could be used to smooth or iron the surface out to a perfect flatness. I haven't put much though into the mechanism for the other shapes of mirrors. The con cave pendulum could use a ball that is heated at the effecting end. With a nonstick sheet between it and the surface of the 3d print. The joint would be the key to making it smooth. There are high quality ball joints for RC cars out there that might fit the bill. You could also smooth something else out on the surface. Like body filler. Jamie's video - ukposts.info/have/v-deo/baqYiJmCaoialWg.html

Silver tarnishing: Mirror stereoscopes - for 3D viewing of aerial photography, have first- reflection silver mirrors on glass, and if kept in their case last for many years without tarnishing. Most degradation is from students fingerprints when the pick them up by grabbing the mirrors, rather than the handles

If you wanted to do this better, you could use the 3dprinter to make abrasive forms, basically make a form to hold your piece and a form to hold sand paper or a guide for some sort of rotary tool and use that to polish away all large imperfections using a higher grit sandpaper, and from there you can coat it with the uv resin and have a much less wavy surface.

Get ready for 2^20. Lots of Steve Mould viewers coming in.

Just a suggestion, Why don't you use vacuum-forming to get your flat "whatever is feasible" to follow the shape of a 3D printed part. Printing small holes might not be possible, but you could drill the last few millimeters with a 0.5 to 1mm PCB drill . The difficult part might be to geta sealing edge between the flat material and the printed shape, without causing tension deformations.... But for that I would suggest a bit of heating at the sealing flange to relieve the stress.

UV cure resin is also used in resin printers in a similar way to the process you described, a mask is put on the LCD and then a UV backlight cured the resin through the mask. More advanced printers don’t use LCDs or anything like that though.

When you pulled out the cast acrylic, i thought you were gonna use one of the 3D-printed saddles as a vacuform buck! That'd potentially be a good way to transfer the macroscale surface profile to the piece of acrylic while retaining the microscale smoothness of the acrylic sheet and mitigating the mid-scale lumpiness of the form.

Should look at nonplanar 3d printing teaching tech has some good videos on that. Would have help a tun with the surface finish on the printed ones, and it seems like an ideal use case for the tech. Might also look into vacuforming for your reflectors. Should be able to make a form on the lathe and just form a sheet to it to get the ideal surface.

Maybe you could get better surface quality via some kind of lapping between two or more prints? The prints are decently dimensionally accurate at a large scale, but they're wildly inconsistent at small details. This makes individual prints really bad, but it's very unlikely that two different prints would have the same errors. If you took the average of the two prints, it'd be closer to the shape that you want. Average out enough prints, and you've got a perfect surface. But because these would both be concave surfaces, you can't just lap one against the other, so you'd need to print out some matching convex versions to use as an in-between. It's like a weird version of the Three Plates Method for making flat surfaces. While this method would hopefully/probably/maybe work for telescope mirrors that are axially symmetric, I'm not sure if it would work for the saddlepoint mirrors. I guess while you couldn't rotate them all the way around, you could jostle them back and forth a little? Still a lapping action, but with movement measured in millimeters.

Wow, I watched that old video yesterday!

I saw an anti bird device that was to be hung from the branch of a fruit tree that was a 10 turns helix made of a strip of acrylic. Part of that helix looked like a saddle, my reflection in it was turned 90°. I assume the difference of focal distance between orthogonal directions is controlled by the pitch of the twist. Search “Swivel Bar Bird Repellent Reflective Scare Sticks Spiral Deterrent” to find the thing. The scale is wrong for Steve’s application of course. That could be an inspiration to produce a larger saddle mirror from a larger twisted strip of acrylic. Making a longer strip and doing turns would smooth the holding clamp irregularities.

now THIS is the most ambitious crossover of all time (and this joke is soo old...)

I saw a video on toroidal fans that were 3D printed BUT they used Acetone Vapor on *Printed in ASA(?) Material* for a period of time. This resulted in a smoother surface of the 3D print. Their method seemed unrefined, but with a little mathematical tweaking might do a decent trick.

Your channel has been fun to come back to! I haven't seen it for a while and then heard you mention in Steves video! And even got this in my recommended right after! Is that old phone your using a iphone 7+? I have one for a similar function myself... And also Freyas video on splines was a funny thing to see mentioned here! I have followed them on twitter for a while and neat seeing that back around here! Anyways I don't really know how different in quality a higher resolution resin printer could do! I have a 4k resin printer and even at that scale it is crazy, but still visible, the layer lines

Dont know if it resin based, but the stuff they fix holes in teeth (other than the older quicksilver thingy) is also UV-hardened. It's awesome doctor fills the whole, puts on the UV light 10 seconds later its as hard as teeth.

Might be time for you to watch Peter Brown polish regular epoxy with micro mesh. Your printed base shapes with epoxy coatings would've been perfect.

A comment I didn’t see scrolling through: Other common causes of those sorts of banding is subpar filament. Either differences in melt rate, though that causes more subtle changes, or more seriously, inconsistent diameters. 3D printers meter their filaments via distance - how many millimeters to advance the filament per non-travel move. If the diameter of the filament is varying even as little as +/- 0.03 mm, that’s still a 3.3% difference in diameter, which is as much as a 10% swing in volumetric extrusion, if my math is right. There’s ways to make the Klipper and other firmwares for 3D printers use a filament width sensor for exactly this reason, but an easier option is to just buy high end, tighter tolerance filament. Edit: I don’t suspect the Z screw simply because the banding doesn’t look very consistent, and you showed a Prusa printer. They’re not very “high spec” as far as features but they’re well built so I doubt that’s the issue. A bent/loose Z screw usually results in a regular pattern.

have you tried adding multiple coats of resin? maybe applications of averaging the surface works better after all.

Surely SLA / resin / whatever we're calling it now is the way to go for 3d printing mirrors. Saturn 2 can manage ~20um layer heights and you can use the same resin to smooth it.

Have you seen applied sciences video on optical polishing? Print your part, then smooth the surface, and finaly resin coat. That should give a very decent surface. Although much more labor intensive

Recently I have been working with aluminium and nickel plating and I'm sure you could have achieved this effect with that. But I would really like to see a video where you explain what happens to the grain structure of aluminium during the process of burnishing and polishing as I don't really understand it and think it's an interesting concept.

If you can get me a mirror base that won't outgas. I can see if I can coat the parts with a physical vapor deposition. This can be done in bare silver, gold, a high reflective stack of materials (opposite of an AR coating we stack two clear material in layers and it becomes more reflective than silver and aluminum), or add a thin top coat of quartz to seal in the silver and prevent oxidation and scratching. I do think we have done plastics before but I would have to beg to do a one off specialty run lol.

I would give acetone smoothing a try. Also, even probably not gonna work, centrifuge at constant speed UV resin while cure, so it take the shape. Problem is that it should happen basically instantaneous

amazing material science.

Hi nice video and nice idea. Regarding the surface issues: have you considered vapor smoothing? I know for PLA it is a bit nasty but with ABS it should work fine and rather save.

"... a perplexingly patchy patina." Haha! ... Brilliant! This episodes sponsor! ... maybe ... dunno, but brilliant all the same! :)

Have you tried non-planar top layers, it might help with the medium scale smoothness by laying down a final layer of pla all at once onto the top of your print

From my own personal experience with 3D printing, I'd say your best bet is probably using ASA, ABS or something like that and acetone smoothing it. If done correctly acetone smoothing can give you a surprisingly good mirror finish. Perhaps printing the part with non planar 3D printing, would also help making the part a little smoother to begin with. In that case you'd also be printing it flat, so the z wobble wouldn't have such a pronounced effect. Obviously you also want the smallest layer height possible, the Prusa Mini should be able to go down to 0.05mm, which is probably worth the quadruple print time in this case...

I'm wondering if you could even heat some glass sheets to warp them into a custom shape, that way the silvering solution is being used as intended and would hopefully be more stable

If it doesn’t stick very well to acrylic then you could maybe try polycarbonate as well. It is clear too and you can get it in sheets just like the acrylic.