Clear printing - aircraft canopies

[Bangseat]

Afternoon,

 

I thought I would share some of my experimentation with clear printing. I have been fit-and-spurtingly knocking together some CAD designed general aviation aircraft, and have decided to try and print the canopies, both for ease of production if it ever comes to that, and also because for complex shapes, eg a windscreen that also blends into the leading edge of the wing (see Cessna family) it really seems the only way to go.  

 

I'm using an Elegoo Mars and Monocure Clear resin. Printing at 0.02mm layers, with 9 sec per layer cure time and 70 secs on the first 8 layers (clear resin takes a bit more UV to cure, and I did have failed prints when I first used on my standard settings). Anti aliasing 8, which I think helps and certainly doesn't do any harm. These are my best results so far:

 

 

The first thing I discovered is, with a clear part, if you clean it in IPA straight off the printer, it will become matt as the full texture is revealed. So, l Ieft the parts to drip dry on the build plate overnight, then I put them under a UV lamp to cure the thin layer of uncured glossy slime remaining. I think a proper curing station would be a boon here, like a Mercury wash/cure station - but I just used a £10 nail gel lamp, pressing the "90 sec" button repeatedly while tidying my desk in the interim. After about 9 minutes of cure they seemed solid. A dip in IPA cleaned the final traces of resin and did not result in a matt texture. A few dips in Pledge and the result has me feeling optimistic!

 

A few learning points:

• Pledge doesn't seem to like IPA, so make sure the part is completely dry before dipping 
• Layers will always be there to some extent - but the top canopy - for a PZL Koliber - seems to have weathered very well printed at 45 degrees, whereas my Grumman AA5 canopy printed nearly vertical has more pronounced lines. Diagonal is good. 
• Don't store resin in a jar! Mine seems to have yellowed a bit. (It was a painted jar so I thought I'd be OK, but clearly not!) But I know this stuff does print completely clear normally. 
• Hygiene and cleanliness is a must - if particles settle on uncured resin they will forever be preserved like the mosquito in Jurassic Park. And if you drop it in the floor - bin it and start again! 

 

I'd be interested to hear if anyone else has had any informative experiences. I'm a long way off printing camera lenses (which it is claimed is possible!) but for the sake of having snug fitting canopy parts with visible framework I reckon there's mileage in this. 

 

 

[Mike]

10 minutes ago, Bangseat said:

Don't store resin in a jar! Mine seems to have yellowed a bit. (It was a painted jar so I thought I'd be OK, but clearly not!) But I know this stuff does print completely clear normally. 

Could that have implications for the long-term clarity of the part, or is the yellowing arrested by curing?  

 

As a consumer at this stage, I would say that it's got a way to go before we can print or buy clear resin parts commercially, as even at 0.02mm the layers are visible, giving a "headlight" look to the finished glazing, rather than crystal clear stuff we've come to expect from clear styrene and vacformed PETG.  It's interesting to see how things are progressing though, so please carry on sharing

[Bangseat]

12 minutes ago, Mike said:

Could that have implications for the long-term clarity of the part, or is the yellowing arrested by curing?  

 

Thanks Mike - Impossible to say at this stage, as the oldest part I have is about 2 months old, that will have to be a long term study!

 

I think for me the bar of attainment can't be a Tamiya part from a diamond polished mould otherwise I would give up and turn to drink. But 1960s Airfix standard, that could be within reach. One other consideration for the discerning modeller is that these parts do respond to the micromesh treatment, although that is much easier to do without framing, so that is something for the designer to ponder...

[Mike]

2 hours ago, Bangseat said:

One other consideration for the discerning modeller is that these parts do respond to the micromesh treatment, although that is much easier to do without framing, so that is something for the designer to ponder...

That's sensible.  For larger scales you could consider printing separate frames, I guess?  Might be tricky in 1:72 or 1:48 scales, but I might be wrong... it's amazing what can be printed.

[wellsprop]

Hrm, certainly food for thought...

 

I'm hesitant to plunge mold the 48th scale canopy for my chipmunk, but equally hesitant about clear resin!

 

Maybe I will give it a go.

[ratsmitglied]

On 9/16/2020 at 1:59 AM, Mike said:

Could that have implications for the long-term clarity of the part, or is the yellowing arrested by curing?  

 

As a consumer at this stage, I would say that it's got a way to go before we can print or buy clear resin parts commercially, as even at 0.02mm the layers are visible, giving a "headlight" look to the finished glazing, rather than crystal clear stuff we've come to expect from clear styrene and vacformed PETG.  It's interesting to see how things are progressing though, so please carry on sharing

Monocure3d clear resin does tend to yellow slightly when exposed to UV wavelengths of <405nm - it is particularly noticable if you post-cure in the sun.

If you have exactly the right settings for post cure and get the properly cleaned and cured then it doesn't tend to yellow (and yes this resin does print perfectly clear)

Getting completely clear parts out of a printer is a pain, I personally have found with the monocure resin that using their ResinAway with an ultrasonic cleaner, then rinsing in water and drying off prior to post-cure does get a much clearer result than using IPA

I'll have to see if I have any clear prints to photograph (I was printing in clear because someone wanted ghosts, I normally print in colours) to show the results I've had with my method

 

[ratsmitglied]

@BangseatFinally had a chance to find an item and get a photo - not the best in terms of showing clarity (nature of the object printed), but it does show the colour that the resin comes out at

 

And I due to the nature of the object (intended to be painted) I may have forgotten a step to clear up the cloudiness...

Edited September 21, 2020 by ratsmitglied

[Bangseat]

@ratsmitglied, lovely print, and thanks for sharing. Cloudy, but not yellow at least! 

 

My next plan is to try a 2k clearcoat to see if it has an edge on Pledge.. I've always been a bit scared of the stuff, but I shall be wearing my Darth Vader mask with the extractor turned to 11. Will report back!

[ratsmitglied]

@Bangseat That was post-cured under a 36W nail curing lamp purchased from Amazon, I can look up exactly which model it was if you're interested. 

but yes, it is a bit cloudy, I suspect it was because I forgot the wash step after cleaning in resinaway, so if I throw it in the ultrasonic cleaner with soapy water it will probably clear up nicely.

 

[plasticguy]

On 9/15/2020 at 5:48 PM, Bangseat said:

Afternoon,

 

I though I would share some of my experimentation with clear printing. I have been fit-and-spurtingly knocking together some CAD designed general aviation aircraft, and have decided to try and print the canopies, both for ease of production if it ever comes to that, and also because for complex shapes, eg a windscreen that also blends into the leading edge of the wing (see Cessna family) it really seems the only way to go.  

 

I'm using an Elegoo Mars and Monocure Clear resin. Printing at 0.02mm layers, with 9 sec per layer cure time and 70 secs on the first 8 layers (clear resin takes a bit more UV to cure, and I did have failed prints when I first used on my standard settings). Anti aliasing 8, which I think helps and certainly doesn't do any harm. These are my best results so far:

 

 

The first thing I discovered is, with a clear part, if you clean it in IPA straight off the printer, it will become matt as the full texture is revealed. So, l Ieft the parts to drip dry on the build plate overnight, then I put them under a UV lamp to cure the thin layer of uncured glossy slime remaining. I think a proper curing station would be a boon here, like a Mercury wash/cure station - but I just used a £10 nail gel lamp, pressing the "90 sec" button repeatedly while tidying my desk in the interim. After about 9 minutes of cure they seemed solid. A dip in IPA cleaned the final traces of resin and did not result in a matt texture.

 

 

 

Tip to avoid the cloudiness:

- when the part is printed, bath it in 99% IPA (first in a recycle bath, then in a brand new IPA).

- soak the part, use a airbrush on the part to get rid of IPA.

- immerse the part in a jar full of water and close it.

- then, cure the part in the jar.

 

The so called cloudiness is oxidation, so without oxygen, no oxidation.

 

[Bangseat]

6 hours ago, plasticguy said:

 

The so called cloudiness is oxidation, so without oxygen, no oxidation.

 

makes perfect sense, thanks!

 

Although, are you drying it off with the airbrush - or blasting it with water? Just so I'm clear (well, clearer than my clear parts anyway)

[ratsmitglied]

9 hours ago, Bangseat said:

makes perfect sense, thanks!

 

Although, are you drying it off with the airbrush - or blasting it with water? Just so I'm clear (well, clearer than my clear parts anyway)

I'm pretty sure it's blow the excess off with the airbrush - as per the resinaway instructions:
https://monocure3d.com.au/product-category/resinaway-cleaner/

the 'directions' section says 

Quote

Use this cleaning agent as is, do not dilute with water. For best results, start with a “pre-wash” of RESINAWAY® in a separate container to remove excess resin using a soft brush to assist. Then place the object into an ultrasonic cleaning bath. Keep printed objects submerged in RESINAWAY® until the uncured resin has been removed. Once clear of resin, remove the object from bath, use compressed air to remove excess liquid, otherwise pat dry with a lint-free cloth. Then post-cure the part using a recommended LED 405nm light until the surface is tack free (approx. 5 mins at 30 watts). The final process is to rinse under running tap water. For cleaning vats, build plates, instruments & surfaces, rinse/soak/wipe with RESINAWAY® then wash with fresh water.

REMEMBER: PRINT – RESINAWAY® – BLOW – POSTCURE – WASH

I didn't follow these exact instructions with my print, hence the cloudiness

 

Actually, those instructions are probably good ones to follow with IPA

Edited September 23, 2020 by ratsmitglied

[plasticguy]

20 hours ago, Bangseat said:

makes perfect sense, thanks!

 

Although, are you drying it off with the airbrush - or blasting it with water? Just so I'm clear (well, clearer than my clear parts anyway)

 

Dry it off with the airbrush.

 

11 hours ago, ratsmitglied said:

I'm pretty sure it's blow the excess off with the airbrush - as per the resinaway instructions:
https://monocure3d.com.au/product-category/resinaway-cleaner/

the 'directions' section says 

I didn't follow these exact instructions with my print, hence the cloudiness

 

Actually, those instructions are probably good ones to follow with IPA

Exact.

 

[Bozothenutter]

Though high marks for trying, I think this is the wrong process for canopies.

Tbh I don't think there is anything better than vacforming.

[Bangseat]

I said I'd follow up on this. Since my initial prints, I have done another batch, this time I followed more or less the post cure process recommended by @plasticguy . Curing in water does work well, thank you - the result was a part with a nearly gloss/satin sheen.

 

I then coated with 2k clear coat:

 

 

 

 

The parts now have the high gloss that I want in a clear part, but yes, there are still visible lines with optical distortion. It is possible that multiple coats of high build clear coat would reduce this further, so I will have to investigate next time I am in my hazmat gear spraying.

 

In the interests of science - bearing in mind these images are all way oversize depending on your screen, taken with a camera phone - here is a printed Socata TB canopy side by side with some other canopies.

Socata first, bit wobbly, although incidentally the top has been lightly sanded which has removed the lines and improved things somewhat (the side windows not):

 

Here's a PETG vac part, from Czech Master Resin's Supermarine Attacker:

 

 

Here's a really naff injection moulded part, from the ancient VEB Plastikart An-14:

 

 

And here is a really nice injection moulded part, from a Hasegawa F4:

 

 

What does this prove? Well, probably not much. But I reckon this process at least gives lower quality IM moulded parts a run for their money. Agreed a PETG vac part is a fine thing, although as the CMR part shows, they do yellow a bit with age, and of course you have to chop the damn things out with a scalpel..

[Kushan_Farsight]

really great writeup @Bangseat, and your getting some increasingly clear results! 

What is your layer height when printing? is it a case that we could reduce the stepping if made smaller? or perhaps the inverse is true and larger layers gives better clarity (i have found this when printing transparent and translucent materials in FDM) 

 

another question is what were your Anti-Aliasing settings when printing? this is something ive chatted with other designers about in the past for reducing stepping on parts.

 

Either way i think it certainly shows that while its not going to replace top tier injection or vac forming, with a bit of tweaking its more than suitable for some transparencies. I think that the smaller 1/72 and 1/144 models, will do great for this (im thinking things like airliner windows etc) 

[Bangseat]

@Kushan_Farsight thanks, these have been done with .02mm layers with anti aliasing on 8. To be honest I think the real trick is angling the part correctly on the build plate. Any near horizontal or vertical surface will show the wood grain type lines, but when surfaces are closer to 45 degrees the layers will be closer together and much easier to smooth out with a clear coat.

[Pouln]

Yes, layer heigh5 is not the cause (certainly not at 0.02). It is the X-Y resolution of about 0.05 (for most printers) that cause it. 
Angling the print should help.

[Bangseat]

13 hours ago, Pouln said:

the X-Y resolution of about 0.05 (for most printers)

That's interesting, I never realised that. I guess that would improve with one the new 4k printers, like a Phrozen Sonic (he says rubbing knees in delight)

[Pouln]

For the new printers you need to check, however it all comes down to resolution and size of the LCD screen. 

I think that Phrozen will have a printer with something like 0.035 X/Y resolution. But most others will still work with 0.05. Even the new larger 4K screens will still have this dot pitch.