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CarterTG

Elegoo Mars: Tamiya Wheel

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Completion of this project has been almost a decade in the making...

Commercial-level high-rez resin 3D printers had been sitting beyond $200,000 for all of the nineties and even when smaller desktop units dropped below $20k by 2011, their build envelope was only large enough to cram 5 or 6 custom ring designs into... IOW, not terribly applicable for 1:10th scale modeling. Jewelry casting resin was $175 a liter.

Disruptors came on the scene with their $2500 resin printers. In 2012, this was a downright bargain compared to my first printer at $15k. Resin was "less" costly at $100/liter. Reasonable expense for paying clients, but remains extravagant for hobby tinkering -- and the build envelope stayed minuscule at 5.7 x 3.2 cm. The only way to fit a standard on-road 26mm wheel into this space is to orient it upright. I attempted this very exercise around 2014 but the end-result wasn't worth posting here. Problem? Vertical print position pooled and caused a resin imbalance. The build-envelope constraint permitted no other alternative attempts. The wildly off-balance wheel was only good for shelf display.

2019 is the next watershed year where resin 3D printers have started tickling the $200 milestone. How'd they achieve this? By utilizing super-inexpensive components from the cellphone industry -- deploying a relatively cheap 2k-resolution smartphone screen rather than building a 3D printer around a $1000 theatre projector makes all the difference in final cost. All the buzz became loud enough to take notice. At $200, there are indeed some cheap resin printers cost-wise but also cheap in quality; questionable design features abound. Experience proved invaluable in identifying features to avoid.

The standout winner worthy of a spot in the stable is the Elegoo Mars at $250. Jaw-dropping price point no matter how you cut it. Tons to like:

  • Stretched-film release design similar to my $15k printer suggesting low-maintenance workhorse reliability/repeatability.
  • Superb Z-axis rigidity using a linear-rail like design. A wobbly Z-axis arm can cause disastrous banding in the print.
  • User-replaceable critical components as demonstrated by their own instructional YouTube videos. Crack the masking screen? $40-ish replacement makes things right.
  • Considerable leap in the build envelope. The Elegoo is able to print what fits within 11.9cm x 6.8cm (x 15.5cm height) and still maintains a 50-micron resolution.
  • Color touch-screen control. Files read off a thumb drive. Prior resin printers mandated tethering to a dedicated computer to drive the projector. (itself limited to a bulb lifespan)

After running a few calibration tests (largely unnecessary and for my own satisfaction), it was time to address my long awaited project. 26mm width BMW Style 35 wheel fitted to a Tamiya hex hub.

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Elegoo Mars 3D printer. Quickly Glowforged a pedestal storage box for it and made sure there was resin on-hand. One liter of their resin is just $45. Third-party resins can be used as long as they're formulated for these kinds of masked-SLA printers. Laser SLA like Formlabs and Moai require different resin formulations. Still, not many are gonna beat $45/liter!

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The free support & slicing ChiTuBox software has quite a bit of nice features coming from this veteran resin jockey. The ways to identify & edit supports for undercuts or floating islands is praiseworthy. One nit is that there's no apparent publicly centralized data pot for exposure times for Elegoo resins. Possibly walled off in their Facebook page. The product box only provides a range -- thus my initial tests. Small-object test prints suggested that my settings for Elegoo Black Resin be 60 seconds for the first 5-6 layers and all subsequent layers can be at 6-seconds exposure. As shown here, the represented build platform has plenty of space to accommodate an on-road wheel.

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For reasons outside the scope of this hobby forum, a flat lay-down positioning of the wheel isn't necessarily the most recommended, but I've printed using two alternate ways and got away with successful prints. ChiTuBox goes as far as asking how much I paid for this batch of resin and can calculate the projected volume of resin used and total cost of parts put on the build platform. Let me do the math for you.. a liter of resin ought to yield around 66 Tamiya wheels.

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Toss the sliced file onto a USB thumb drive and feed it to the printer. Here's the angled & supported version...

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What kind of detail does 50-micron yield? Hex heads on the lug bolts resolved with a faithfully reproduced dimple at the center of every one! 

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Here 'tis mounted to the M-04L chassis... spins just as nicely as the Tamiya-made wheels. No off-balance issues.

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Giving the back part of the rim a squeeze shows that it takes nearly DOUBLE the effort over Tamiya's ABS plastic to start deforming. At roughly 1mm resin wall thickness, the toughness observed so far suggests it would fare no worse than manufactured wheels.

Once I get my hands on more resin vats, I'll dedicate each one to their own resin making for super-quick printing material changes... black, grey, white, translucent, etc

Now all the things that normally get scuffed up (side mirrors, body posts) can be easily and affordably re-grown on the high-res 3D printer. Onto the possibilities of fabricating all the details I only dreamt of decades ago... windshield wipers, light buckets, suspension arms, action cam mount...

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There are legions of YouTubers showing how their resin prints get painted. Some use a wax-based buffing method...

 

Others airbrush with lacquer based paint...

And still others who 3D print miniatures (Dungeons & Dragons, Warhammer, etc) like using acrylic-based paints

I suppose paint’s steadfastness to 3D resin might be about the same as painting an ABS or nylon plastic rim and expecting it to withstand daily bashing. This is why I’d rather re-print my wheels in grey resin before committing a set of rubber tires to them. For shelf display though, the lacquer Alclad metallic range might be in order.

 

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in terms of strength, how well do you think the resin prints will compare to ABS and PLA?

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7 hours ago, yogi-bear said:

in terms of strength, how well do you think the resin prints will compare to ABS and PLA?

I wouldn’t have pursued this if the initial attempt with the $3500 2nd Printer didn’t show promise with the black resin I was using back then. As stated above, I don’t have any hesitations if they served as moderately stressed components...and real-world tests might likely show it’ll go the distance.  I’ll leave it up to the professional engineers in the crowd to extrapolate Elegoo’s cured resin properties from their Amazon page:

Hardness: 84 D; Shrinkage: 7.1 %
Solid Density: 1.195 g/cm³F 
Flexure Strength: 59-70 MpaE 
Extension Strength: 36-53 MpaE 
Elongation at Break: 14.2 %C

Some figures for extruded ABS based on a quick Googling:

Hardness: 68-113 
Solid Density: 1.01-1.20 g/cm³S 
Flexural Yield Strength: 69.2 MPa  
Tensile Strength: 40.5 MpaE
Elongation at Break: 34.2 %C

To this layman, the two seem to be in reasonable ballpark for it’s given RC hobby use. Add the equipment value proposition to this mix and it should be a no-brainer for those craving superfine, detailed parts.

 

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I'm not sure how to decipher Elegoo's shrinkage number above... possibly as a measure of the volume when it transitions from liquid to a cured solid layer? It certainly isn't related to the finished dimensional difference of the physical print versus STL model. My custom wheel was 3D modeled in Rhino following measurements of the typical Tamiya on-road wheel; 52mm rim diameter and 26mm depth. I think the end results compare favorably. If I needed more stringency, I'd simply have the ChiTuBox software bump up the scale by a fraction of a percent -- no need to go alllll the way back to the CAD software.

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In resin printing, changing the layer exposure time can also help dial-in the accuracy. Going from a 6-second exposure to 8 or 9 seconds might be enough to bring that finished print to the target 52mm.

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2 hours ago, CarterTG said:

I wouldn’t have pursued this if the initial attempt with the $3500 2nd Printer didn’t show promise with the black resin I was using back then. As stated above, I don’t have any hesitations if they served as moderately stressed components...and real-world tests might likely show it’ll go the distance.  I’ll leave it up to the professional engineers in the crowd to extrapolate Elegoo’s cured resin properties from their Amazon page:

Hardness: 84 D; Shrinkage: 7.1 %
Solid Density: 1.195 g/cm³F 
Flexure Strength: 59-70 MpaE 
Extension Strength: 36-53 MpaE 
Elongation at Break: 14.2 %C

Some figures for extruded ABS based on a quick Googling:

Hardness: 68-113 
Solid Density: 1.01-1.20 g/cm³S 
Flexural Yield Strength: 69.2 MPa  
Tensile Strength: 40.5 MpaE
Elongation at Break: 34.2 %C

To this layman, the two seem to be in reasonable ballpark for it’s given RC hobby use. Add the equipment value proposition to this mix and it should be a no-brainer for those craving superfine, detailed parts.

 

yeah they are definitely within the same ballpark, so that good to know. Maybe the only other property to look at is shear strength. I have an AnyCubic Photon 3D printer, but haven't had a chance to setup it up yet. I bought it for the detailed print, but wasn't expecting much in terms of strength, so this has me a little hopeful. 

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Just doing some exploring for on-road touring car wheel designs I'd make for the TA04...

WheelCoffinSpokes.thumb.jpg.22b255631b2c9029c3694e4ecfedbe42.jpg

Integrated cross-drilled racing rotors. We all know by now that the resin printer should have no problems keeping the holes intact. In the traditional injection-molding process, the space between the spokes and rotors would be a nightmare. 3D printers will breeze through these layers like a champ. I'll save these for printing in grey resin.

B)

 

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That is a great little machine, and it overcoms the resolution problems of my 'classic' 3D printer.

Something for the christmas wishlist this year! ^_^

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OK.  I'm convinced.  I need one of these in my life.  If only I could find one at the $250 price mark...

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A deeper 2¢ dive into how I evaluated the field based on my professional use of resin SLA machines...

The current generation of super-inexpensive resin printers caught my eye around June.

The first one I saw getting buzz was the MonoPrice MP Mini at the $200 mark. The buzz was solely based on the price. I immediately spotted design problems like the dual-rod z-axis rail (linear bearings are a MUST for me), build platform attached by magnets (MAGNETS for a high-stress, absolutely-musn’t-shift region?? Seriously??), and electrical-actuated auto build-platform leveling (already sounds like a needlessly over complicated feature begging to break). These “features” almost caused me to paint the entire generation as bottom-barrel scraping cheap sludge. Majority of folk generating the buzz ended up returning theirs for one or more of the reasons I pointed out. This only served to testify the gospel that if you buy crap, you’ll always buy twice. Hard pass on the MonoPrice MP Mini.

The Anycubic Photon showed up on my YouTube feed, but as a $499 Printer, I batted it away. At that kind of price point, I’ll continue to operate my previous resin printers.

The Elegoo Mars at first glance looked like a clone of the Anycubic and in many ways it is, but yet in many good ways it’s not. Identical resin vat dimensions, identical LCD masking screen, identical z-axis mechanism. To be HALF the Anycubic’s price, it HAS to be cheaply constructed right?? I couldn’t find any consistent voices to shore-up this accusation... in fact, many Amazon and YouTube reviews were showering the build quality and materials with praise. For their supposed July-only sale at $250, I was willing to give it a shot. If the buzz were based on price alone without build reviews, I would’ve given it a cautious dismissal. I fully expected Elegoo to follow the razor-blade or inkjet business model. Doesn’t seem to be the case here. A litre of their black resin is now only $39 and they just announced a bundled set of FOUR (disposable?) resin vats will be dropping September for only $30! ~ $7.50 each vat! That’s cheaper and way more convenient than replacing the FEP film! My $500 stretched-film resin vat on the $15,000 Printer has been in service for the past 7 years. If I get six-months off a $7.50 vat, that’ll be a colossal win in so many, many ways.

Meanwhile, the Anycubic ecosystem had third-party replacement resin vats at $60-$80 (for each) listed on Amazon. With a bullet to their head, Anycubic finally relented and lowered the Photon’s $499 price to $299. These forced reactionary moves certainly doesn’t endear me to Anycubic. Because of the cloned dimensions, Anycubic users will fully be able to use Elegoo’s resin vats.

The $200 Sparkmaker is another race-to-the-bottom sludge-scraper that had me hammering the NOPE button with a mallet. No screen of any kind to report the print progress, 26 watt light engine (vs everyone’s 40 watt) for extra-slow printing, and a SINGLE button/knob to handle some very important controls. The dumbest feature design? It will only recognize a single specific “PRINT.WOW” file name for 3D printing. Oh, the fun of having to maintain a sub folder library of PRINT.WOW files. Who’s the genius that thought this up? The 673 cubic cm build volume is also half that of the Anycubic and Elegoo’s 1224 cu cm. Any two of the above deficiencies would negate the $50 difference for me.

All this activity leaves Anycubic and Elegoo as standouts that has garnered an impressive critical-mass of users. This ensures availability of formulated resins, FEP film, resin vats, and spare parts will be available for a much longer span than anyone else.  Between the two, Elegoo has demonstrated their willingness to cut pricing deeper without sacrificing material quality. I also greatly prefer how the lid completely lifts away giving me easy access from all angles to the vat (for mid-print refilling or checking progress) versus Anycubic’s hatched access. Disassembly into the guts of the machine also goes to Elegoo. Either way, these two gets my thumbs-up compared to the rest in this field.

Not sure how it is elsewhere around the globe, but the US Amazon page for the Elegoo Mars is almost comical to observe. Refreshing at least twice a day, they seem to restock on average every three days. It sells out as fast as it restocks. Within an hour, you’ll see the page trigger it’s “only 5 left in stock” warning. I hope they can find reason to maintain their $250 pricing but would fully expect them to sell briskly even if bumped to Anycubic’s $299 price for the Christmas harvest.

Back to your normally-scheduled Tamiya-talk...

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wow, didn't realise resin printing have come down so much in price. really appreciate your insight. definitely piqued my interest.

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Well, thanks to the advice in this thread (and some very good online reviews) I am now the proud owner of an Elegoo Mars too.

Oh, and a few other bits I didn't realise I'd need - like a UV lamp, pickle strainer, few tubs of IPA and a huge box of nitrile gloves.  (Although I'm spent a lot of my life working with various resins and chemicals and cheap gloves that break, and so far none of my fingers have fallen off.  I got some resin on my hand on Saturday and didn't see any ill effects of it being there.)

Now I just have to practice until I'm getting print quality like the above.  I've had a mixed back of success so far, with some prints being absolutely how they were intended (the demo file is truly superb) and some that weren't supported properly and sagged in the printer.

Anyway - I'll stop derailing this awesome thread now.  Look forward to seeing some 3D designs from me uploaded soon :)

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Congrats Mad Ax

As a fledgling TamiyaClub usergroup of two, this thread can certainly be open to discussing the minutiae of tips and tricks in the name of producing great Tamiya-compatible parts. Since the last post, I’ve explored the r/ElegooMars Reddit forum and attempted to add to the conversation with a few helpful posts only to get a response like “...it’s such a wall of text..” Apparently, one should not post more than 280-characters in a forum dealing with the nuances of resin printing. <_< The rest of the reply also demonstrated a massive failure at reading comprehension. Not currently feeling the urge to go back and correct them. Best to just laugh it off and back away from that dumpster fire. Makes me appreciate the posts in here all the more..

On the resin hazard issue... as you’ve surmised, the hysteria and fear drummed up mostly by newcomers has been overblown to viral proportions. I and numerous pros have 3D printed with envisinTEC and B9 resins continuously for the past SEVEN years. According to some YouTubers, I should have died instantly from handling the uncured resin with my bare hands all this time. Not dead from the odor. My skin isn’t a cauldron of blisters. And I’ve no intentions to ingest nor vape 3D resins. Are there folks who may have skin sensitivity to resin? Probably. I’ll report that in all those years immersed in the B9 Forum exchanging ideas with fellow owners, I can’t remember anyone bringing up skin irritation issues... and the only time folks mentioned any sort of ‘stink’ was when they tried one of the few third-party resins available back then. The smell that comes from using Elegoo, B9, and EnvisionTEC resins is approximately equal to detecting someone unrolling a newly-printed vinyl banner from the graphics shop. Detectable, certainly not a gas-chamber scenario, and easily mitigated by flipping on the house fan or opening a window.

OK, onto successful Tamiya wheel printing...  

One of the first things to understand is how this and almost all other resin printers want to work. The general concepts of SLA (stereolithography) can likely be found across some YouTube infographics. The pertinent point I want to make is how crucial the first layers are. It’s imperative to overexpose the first layer to ensure it’s tenaciously cured to the Build Platform. ChiTuBox’s settings refer to these as ‘bottom layers’. Default settings might be 60 seconds for each of the initial 5-8 layers. Thereafter, the rest of the model layers might be exposed for 6-thru-9 seconds.

IF that initial crucial first layer isn’t sufficiently bonded to the Build Platform, the successive pulling of this growing model from the FEP membrane (throughout 1000+ layers) might eventually cause layer 1 to detach prematurely where the model stays planted at the bottom of the Resin Vat and no further growing occurs. Is there any penalty to cranking ‘bottom layer’ exposure to the sky? Aside from just the time penalty, not really. If you are getting detachment failures, don’t be shy about cranking the exposure to 120 seconds. In older resin printers that used a PDMS release in its vat, nailing an area with 2 minutes of exposure repeatedly is guaranteed to cause clouding on that PDMS material and thus cause premature degradation. No such worries or problems with the FEP film used in the Elegoo & Anycubic vats. Whether 5 seconds or 3 minutes of UV light exposure, cured resin on that film will still peel away at a consistent given force — so all that remains to ensure is that the OTHER side of that cured resin layer (attached to Platform) has seen enough exposure time to out-grip the FEP side. The Platform and layered object lifts up, more resin flows in, the object is lowered just shy of the FEP film (leaving a 50 micron ‘underwater’ gap) and next layer’s exposure commences.

Next opportunity for failure is demonstrated by my very first wheel attempt (not shown or detailed above). My initial wheel was 3D modeled years ago. It was faithfully detailed to the point where the BACKSIDE of the rim lip had a delicate rolled profile to it. The problem with positioning this wheel flat on the Build Platform (in ChiTuBox) was that the rolled lip was BARELY presenting enough surface area to the Platform at layer 1. It became apparent that I was effectively trying to grow a pyramid where layer 1 is the top vertex point and all the subsequent layers got larger and larger pulling with successively greater force on that initial weak anchor point. Imminent failure regardless of how much curing exposure it got. As this backside wasn’t visible to the audience, I had to compromise and rework the 3D model to have a flatter profile. Where the initial contact point was maybe 0.25mm wide, the revision planted a full millimeter to the Platform surface.

One additional reason for that failure was that I was trying to grow a cylinder on the Build Platform. In order to understand why this is generally frowned on, analyze what’s going on at each layer... a circle shape is ‘projected’. This is supposed to cure as a ring layer. In the seconds that this occurs, it’s possible that there may be a difference of some type inside that ring versus outside (pressure? suction?) If this difference causes trapped resin to unexpectedly flow, exposure curing might fail and the layer is compromised. All the subsequent layers building on this compromised layer might not fare well either. This is why experienced users will suggest positioning the wheel at a 45-degree angle (with generated supports). The initial layer profiles avoid the ring shape. (Moreso crescent shapes) As we travel up the layer stack and profiles do present rings, it’s not an issue as the established initial layers have provided open breathing spaces and avoids the trapped resin scenario.

The test Rook prints successfully because it as a large surface area base to establish that crucial initial anchor.... and although it appears as a cylinder, the ‘windows’ provide relief of trapped resins.

If users can internalize these fundamental things, it’ll go a long way towards not just troubleshooting failures but successful planning and layout of models.

Cheers and congrats again

 

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4 hours ago, CarterTG said:

Congrats Mad Ax

As a fledgling TamiyaClub usergroup of two, this thread can certainly be open to discussing the minutiae of tips and tricks in the name of producing great Tamiya-compatible parts.

consider this a user group of 2.5 :rolleyes: I have the Anycubic, and may not contribute a whole lot, will certainly read with interest.

4 hours ago, CarterTG said:

...

If users can internalize these fundamental things, it’ll go a long way towards not just troubleshooting failures but successful planning and layout of models.

 

thanks for that info.

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The more the merrier in this resin jacuzzi, Yogi! Elegoo and Anycubic are brothers from another mother. :lol:

If time allows, the next post might cover dialing-in resin settings with calibration prints.

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Thanks for the long reply, @CarterTG - long posts are quite welcome!  I'd rather have all the info than some cut-down 120-word Twitter post that omits all the vital stuff and leaves plenty of scope for ambiguity.

Anyway - onto my prints!  I'm understanding that I get great success with top-down prints.  I've recently been working on a servo mount for a Clod Buster axle that is a bit like an open ended box.  I printed one yesterday and it came out really well.  Only issue was some lugs that protrude from the side - which had generated supports - were a bit distorted at the bottom (the first bit to be printed).  I think I have issues with things 'drooping' as the build plate lifts out of the vat.  I'm using default settings (8 seconds cure time, 0.5mm layers).

Previously I was working on some CC01 battery clips.  My own design with an additional clip to hold the lipo wiring away from the shell.  I experimented with various different angles, from flat on the build plate to vertical and all ways in between.  Results were, hmm...  Variable.  Sometimes it was 'ok', sometimes it was distorted.  What I'm seeing almost every print is if something is hanging off supports, it will be pimpled where the supports are.  I expect some marking exactly where the supports clip on - that's unavoidable - but the surface is rippled.  Just like pimples under facial skin.  It seems to me that the first layer after the supports will sag just a bit.

Temps are starting to go off here in the UK, my studio is currently around 19 degrees but it has been colder.  I know the resin says it's happier between 20 and 25 degrees.  I can get that kind of temperature with an electric heater but at the expense of being able to work in here - 19 degrees is comfortable, 21 degrees is baking.  It's my home office and where I do a lot of work.  Anyway, right now I'm experimenting with a 10s cure time on some scale accessories I downloaded.  I might have made a mistake in not adding some relief (I couldn't persuade ChiTuBox to cut a hole in my cylinder no matter how hard I tried) but I'll see what happens.

The FEP film on my vat already looks pretty bad.  I've had problems with builds coming unstuck but only because I had my feet too small, an obvious mistake and easy fix.  But it looks like the film gets rippled quite easily when sliding stuck prints off.

I intend to buy some more vats now they're available, they come with new FEP, and I'll try to look after my new ones a bit better.

How long do you keep resin in the vat before disposing of it?  I've had some in there for over a week now (although it's constantly being topped up as I add more).  I'm wondering if it goes off when exposed to air.  The printer lid always stays on, and I assume the lid has a UV filter.

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Kudos @Mad Ax on the insight to hone your suspicions toward layer-droop. As you gain more experience with resin printing, you'll immediately be able to identify areas that may be susceptible to this issue. In a mostly-text forum, it's a bit challenging to describe this without liberal image-posting allowances... let's see how far we can get..

There is never one single must-follow way of orienting a print on the Build Platform and I'm happy to hear that you're trying various methods. It's exactly these early prints that will give you the valuable experience seeing the results for yourself.

Exercise 1: The Levitated Cube

Take a cube, raise it up off the Build Platform, auto-generate supports. Expected end-result? That underside might look like a buttoned sofa cushion. The best way to see why this would be the case would require going back to the ChiTuBox slicer. This and almost all slicers out there reveal a feature that lets you step through the model slice-by-slice. This isn't just some fancy visual. It's a very important tool to illustrate exactly what will happen in the printing process. Step through the model. You can use the mouse on the slider, but I'd suggest using the keyboard arrow keys to tap through the layers.  Tapping through the initial forest of supports from the Build Platform, you WILL reach that juncture where all those little dots of support columns suddenly explode into a huge square sheet. AT THIS VERY LAYER, keep in mind that what the printer is attempting to expose/cure is a sheet of resin that's 0.050mm thin -- roughly half the thickness of typical office copy paper. The Build Platform lifts this structure off the FEP film and as you should now imagine, the super-thin sheet is... 

  • sparsely supported here and there
  • only cured enough (at 6 or 8 sec exposure) to maintain a fast model growth -- thus quite pliable as a 50-micron sheet
  • weighed down (drooping) a bit from the uncured resin it has effectively ladled up away from the resin pool

...continuing our growing procedure, the Build Platform lowers this sheet layer down and intends on stopping 50 microns short, but in reality this sagging sheet has either drooped all the way down contacting FEP -or- it's netted FAR MORE than the intended 50-micron layer of resin against the FEP surface. 8 seconds of UV cures the cushion-shaped layer. Lift away. Lower. Expose. This is a plausible way the cushion surface manifests itself. Familiarize your mind's eye with this simulation and you'll quickly learn to detect it and account for it. Account how? Raise the flat cube up off the platform. Tilt the cube so that only a knife's edge of the cube gets a head start... the parallel length of that horizontal edge might still be susceptible to some bowing/sagging... so rid yourself of any parallelism to the build platform and have the layer assemble starting at one vertex corner. Visually stepping through these layers in ChiTuBox should show supported areas GENTLY growing -- none of the very-little-to-very-big explosions observed in the initial scenario.

Exercise 2: Grow it directly on the Build Platform

There are instances where it makes the most sense to rest an intended flat surface on the Build Platform and NOT raise it up via supports. Most obviously this removes the cushion effect. The main downside is that it SLIGHTLY compromises the Z-dimension accuracy. Factors that contribute to this may include how layer 0 is effectively thrown away due to how the Build Platform gets leveled. The other factor might be due to how the "bottom layers" get overcured. The resin jockeys that 3D model their own goods can certainly compensate for this by extending the side that makes contact with the Build Platform. Perhaps add anywhere from 0.05mm to 0.10mm of additional thickness to compensate for an expected loss in those initial "Bottom Layer" growth. And what of additional structures that jut out of the sides? Again, it will depend on those layer portions that explodes outward... 

Example? Go seek out my Driver Sculpt in the other thread. The intention was to grow this bust resting directly on the build platform. I immediately started worrying about whether the overhanging earlobes, nose, and chin would present a problem. Visually stepping through the layers in ChiTuBox, the critical areas in question was extending outward at a gradual-enough rate where I could possibly get away without supports -- and thankfully I did. However, if my ears were more like Yoda's and exploded outward at an alarming rate, I would absolutely play it safe and manually dot that bottom edge with as many supports as I could fit. 

If you are doing your own CAD work, it might even be prudent to build your own supports into the model. It's perfectly acceptable to do it this way for certain structures rather than be at the mercy of the auto-support algorithms. In this route, you are the one who ultimately knows which surfaces are "safe" to harbor support pock-marks and which surfaces need to be blemish-free. Designing in-situ like this also gives you the freedom to lay in some very imaginative support shapes. A support doesn't always HAVE to be strictly a column tipped with a cone pointer... A few examples can be found in this thread (posted before auto-generated supports came to the B9 printer)...

https://forum.b9c.com/viewtopic.php?f=22&t=235&start=100#p5944

The "free" support-generating software still have a ways to go, IMO. I've played with a great deal of them (B9 Studio, ChiTuBox, Formlabs Preform) and for the most part, they ALL feature the same style of support. The ONLY stand-out in this field is Materialise Magics. It is marketed with a plug-in they call Support Generation. It's claim to fame was the intelligent way it would analyze a model and lay down a repertoire of different support types that I've yet to see others offer. The downside? Only one. An insane $14,000 price tag. A bespoke version of Magics came bundled with envisionTEC printers. CAD jockeys should take a look at the various support types and be inspired to manually model them directly into the target print. Every time I see an impossibly dense forest of supports sprouted by ChiTuBox, I long for a future where they may be enlightened to switch to a wall/curtain type of support.

Resin Vats and FEP

The spare vat kit from Elegoo arrived last week. Two factory metal frames and four sheets of FEP. As a kit, none of this is pre-installed, but in following Elegoo's video, it's a very simple straightforward task that ought to take no more than 20 minutes. The bonus is that familiarization takes away the apprehension from future FEP changes and may even invite experimentation with the alternative "non FEP" film from EPAX. I've only had one occasion where a failed print required fishing from the bottom of the vat. With a gloved finger, I detected the fail and nudged it from the side and it offered little resistance in sliding off. I might suggest using an old credit card or business card to sweep the FEP. This temporarily squeegees away some resin to see if anything has stuck without scratching at the film. Sweep only, not a shoveling/scraping angle. The black plastic scraper should only be used to push objects cured onto the Build Platform. I'd never use it on the FEP. Soon enough, you'll dial-in the optimal exposure settings for your preferred resin and it should greatly extend the longevity of the FEP film.

It's safe to leave the resin in the vat for back-to-back printing IF you know for absolute certain that your last object grew fully intact and that no unsupported islands left floating bits of cured resin in the vat. Jewelry and other simple curvilinear objects are easy to account for. Missing portions of a ring, or gear, or suspension arm are glaringly easy to detect at the end of a print. This can be a very different story for the figurine printing crowd. The new legion of noobs discovering resin printing for their detailed Dungeons & Dragons, Warhammer, and anime are over the moon at the new found detail, but I'd wager a large portion of them are not supporting every last detail or overhang that I'm seeing in many of the poses out there. Figurines that harbor unsupported islands only provide that many more opportunities for a chunk of resin to be cured... perhaps for a few layers.. and then left floating somewhere in the liquid resin. At the start of the next print session, the user initiates the start sequence where the clean Build Platform lowers into the "dirty" resin. If a sizable chunk of cured resin is in the way, that Platform is NOT going to care and continues to its ZERO Home Point effectively pressing a solid into the LCD Masking Screen. Destruction abound.

This was not an issue with my previous Resin Printers as they used a true projector design leaving a required air-gap (and safety zone) in place. In this generation of cheap Resin Printers, the FEP film rides bareback directly on a super-delicate LCD masking screen. My suggestion for people printing a mixed variety of objects, strain the resin between prints to double-check for "floaters" until you've developed some measures to mitigate unsupported islands. 

THAT issue aside, there aren't further problems leaving resin in the vat. Just be sure to keep the Red (or Orange) acrylic dome over it. Its coloration DOES block the UV that reacts with the resin. I'm not certain the same can be said for Anycubic's use of BLUE acrylic windows on the Photon. Virtually all the other manufacturers use something in the Orange-Red color range. How long can it survive? I've left resin in my other printers for MONTHS in a room with shaded windows. No direct sunlight. Within a week, the resin's color pigment settles to the bottom, so before starting a print agitate, mix, and fold the resin in the vat using a business card -- again, a back and forth sweeping motion... no angled digging into the FEP. Resin is NOT like water... it doesn't evaporate or dry into a thicker viscosity... it is ONLY affected by strong exposure to 405nanometer wavelength UV (blue-ish). I've seen people post photos of a FDM-printed plate that fits over their vat while in the machine. Unless their machine lives in direct sunlight, I'll reiterate that it's perfectly OK under a Red/Orange translucent dome. The spare Elegoo vats do come with fitted covers furthering the possibility of leaving resins in there, but if storing outside the printer, just make sure the vat bottom is accounted for.

This is my method for storing my spare vats:

https://community.glowforge.com/t/elevated-elegoo/43655

During my B9 era, I would strain the resin every so often... or sometimes would empty the Vat contents into old resin bottles. I really don't recall ever throwing out resin for "going bad". I've always presumed I'll be treating the Elegoo resin in similar fashion.

From the way you're describing your FEP film, I'd concur that you should get that spare kit. Of the four sheets of FEP, two will be designated to the Metal Vat Frames. One goes to rejuvenate the factory Vat leaving a single back-up sheet. When following the video instructions, do not be afraid of putting as much slack as possible (wedged sponge) during the sandwiching operation. This assembled frame (with loose FEP) is placed inside the bigger housing and when the large screws are installed, there's a great amount of drum-stretching that goes on. I'd also suggest that the screw-installation order be done the same way a REAL vehicle's wheel gets mounted... sequentially jump to the opposite-sided bolt from the last one fastened.

I hope much of the above provides clarity. Let me know where elaboration is necessary.

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@CarterTG that is absolutely awesome, so many questions answered, including ones I didn't even know I had.

So I'm pretty pleased with the results I've got recently and I've been considering adding my own supports in CAD.  Glad to know that's not weird.  I've also had some successful prints directly on the build plate - for what I'm doing the loss of a bit of Z-axis accuracy isn't a big deal, especially if the benefit is a super-smooth mating face.  That's how I did my clod buster servo mount.

I need to get my head around the next thing I want to build - so many ideas I barely know what to work on next!  The UK Scaler Nationals is just under 2 weeks away which realistically I think is too soon to print any scale parts off for my trucks.  It's not the design or print time - it's the time I'll spend painting them!

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