Cast Model Aircraft Canopies w/Clear Resin

[TheRealMrEd]

Hello,

 

While working on my YF-105A (over on W.I.P.), I managed to misplace the canopy.  After checking my two backup kits, only one kit had the canopy!  As these kits are rather hard to come by (Revellogram F-105D) these days, I decided to explore my options.  First I check around, looking for a vacuform canopy for the 1/72 F-105D.  Nada, which is not surprising, considering the "ear flaps" and thinness of the original.  Next, I looked for resin canopies. I found a really great one, but only in 1/32nd scale, and after all, we modelers must maintain some sense of propriety and not stray from The One True Scale!

 

The one I found in that scale was however, a beauty, from the F-105B correction kit, from the former Meteor Productions, Inc or Cutting Edge F-105B correction kit, as sold by Mr Dave Klauss:

 

 

This is a beautifully rendered masterpiece, and if I could buy one in my scale, I would!  But, since I can't, I thought to study the work of the masters.  Closer examination of the molder pieces (only the clear ones here, not trying to replicate the kit!)

revealed that The molded bases or resin reservoirs, as they are in real life, are both slightly tapered toward the canopy parts, and the corners of the bases are cut off.  This serves to aid in removal of the part from the mold after casting, and may save even a little resin, a concern more having to do with mass production, rather than the one-offs that I'm trying to do.  Secondly, and hard to see in the front main canopy, are the small bits added between the base and the canopy to provide clearance and material for sawing the finished canopy from the base as shown better below:

 

 

In my rough and tumble proof-of-concept effort effort here I have used a chunk of old pressboard for the base piece, but I have added some 10 thou card between the base and the part, for the afore-mentioned reasons. All these were glued together with RS watch cement, as CA glues have bad effects on some resins and some silicone rubber.  In the background is a box made of Lego blocks, on part of a Lego base that I cut to the size needed.  One can make the box from all sorts of things, but some kinds of plastic have the advantage that the silicone rubber won't stick to them.  The large piece of scrap blue silicone is there only to hold the main canopy at the correct angle while the glue dries.  You will note that in the first photo, additional material (denoted by the hatch lines) had been added when the master was made, to enable the cast part to be pulled straight out of the mold, while my first effort was left at an angle.

 

Eventually my masters were stuck onto a thin layer of clay that provides the bottom of the box, as well as sealing the lower edges of the box, to avoid silicone leaking out of the mold.  It should be noted that regular modelling clay won't do here, as the process requires sulfur free clay, or bad things happen!

 

 

For this casting effort, I'll be using the Amazing Clear Cast clear resin, which my bottles are around 2 - 3 years old, and OoMoo25, which is brand new.  Both of these were procured from Amazon.

 

The Oomoo 25 was properly mixed 1:1, and poured into the mold box, with the masters in place.  I took no special effort about bubbles because, I use pressure casting as a rule.  For those interested, I have provided a link to my set-up, and would be happy to answer any questions about it:  Ed's Poor Mans Pressure/Vacuum Casting Pot

 

The silicone was poured into the mold bob and allowed to set under 55lbs pressure, for 75 minutes:

 

 

Above right, after the Oomoo had set up, the masters were removed, and I was ready for a casting try.  You will note the total absence of bubbles, due to the pressure casting.  I then   mixed up the resin and poured it into the mold, and allowed it to set under 55 lbs pressure for 48 hours, as per the resin directions.  When that time was up, I attempted to de-mold the resin canopy pieces, and then ran into the problem:

 

 

First off, the resin is kind of yellow. I believe this is due solely to the age of the bottles. Normally, resin has a shelf life of 3 - 6 months, maybe more with a little care, like nitrogen shot into the opened bottles, to keep oxygen and especially any moisture, from getting to the resin, even in a re-sealed bottle.  Second, the parts were still tacky and flexible, not hard.  This could also be due to the age of the resin, but it could be that perhaps I shout have pre-cured the silicone mold in the oven at 150 degrees or so for a few hours.  This time, etc, vary by manufacturer and product.  Since I had used this very resin a couple of years ago with Oomoo 30 (which only varies in setup time) I didn't consider this.  Another factor is that the molding is very thin.  Castings less that 1/8" or so are problematic for many resins, many also requiring a post cure period in the oven to achieve maximum strength and durability.  I will investigate some of these issues in my next attempt.

 

Since the resin was still soft, I managed to scratch this piece getting it out of the mold, and totally destroyed the windscreen part!  I was however, encouraged by the fact the that the thin wall section was able to be reproduced by the pressure casting method, and the detail was all faithfully seen, and given the old resin, still had good clarity.  After three days out of the mold, the casting is still hardening, but slowly.

 

I have ordered another brand of clear resin, and some 3/8 clear acrylic sheet for the base part. I will take everything I have learned from this effort, and make a second attempt.  Please stay tuned if interested, as it will take a few days for this all to be done, as well as more time in the mold and pre and/or post curing time.  You will kindly note again, the absence of any bubbles, due to the pressure casting!

 

I would dearly love to know the brand of the resin and silicone that Dave Klaus used for his pieces, if anyone out there happens to know, or any useful suggestions from others who have tried this process.  I'm certain I will succeed, just not sure how long it will take!

 

Back ASAP,

 

Ed

Edited April 29, 2019 by TheRealMrEd
added info

[uncletommy]

Very cool Eddie.  

 

But gee, you've come a long way from 25mm metal wargame figures molded from lead on the stovetop.  

 

Ahh... nostalgia.  It ain't what it used to be.  

Edited April 29, 2019 by uncletommy

[TheRealMrEd]

Yep UT,

 

I still miss those wargames...

 

Ed

[TheRealMrEd]

Okay, back again.

 

I tried another shot with the Amazing Clear Cast, in the same mold, but with 2 days more curing time.  Pretty much the same result as the first time, yellow and soft.  I re-read the Amazing Clear Cast data sheets online, and found way down in the fine print that epoxy resins yellow, theirs in particular, after about 2 months or so.  While this makes them okay for covering bar tops and the like, it is useless for this effort.  Scratch that resin off our list.

 

Using the sheet of 3/8" acrylic that I ordered, I used my cheapie band saw to cut some into smaller blocks, trimmed off the corners, and tried to cut a 3-degree angle on the sides.  Since my bandsaw doesn't have much capability, I had to run the pieces through without a fence or the like, so the edge taper works out to closer to 1 degree than 3 degrees.  Oh well...

 

I sanded the sides with a fingernail type sanding stick, to smooth up the saw marks a little.  With that ready, I turned to the last remaining kit canopies that I had used as masters earlier.  I cleaned them up, then attached them to a sheet of 15 or 20 thou plastic card, by brushing the plastic card with some brushed on Weld-On #3 liquid cement, then sticking the canopy parts to that. When this had tacked up, I put on some more liquid cement around the edges, using a micro-tube applicator, to make certain that none of the glue got on the parts of the canopy that were to remain clear:

 

 

Several hours later (after the glue had dried), I trimmed the plastic card down to just proud of the canopy parts, using tiny scissors, sanding sticks, and on the inner curves, finished up with some careful trimming with a #11 X-Acto blade:

 

 

I considered trying to add plastic material to the edges of the main canopy to enable a straight out pull to release the casting from the rubber mold, but in the end, that was to risky, considering that this seems to be the only canopy remaining for the three kits that I have.  I decided that the earlier trials had worked okay, even with the angled master.

 

The purpose of this step is, again, to provide an area of thinner, "throw away" material to saw through to separate the canopy parts from their molding block "reservoirs".  Next, I glued these assemblies to the prepared acrylic blocks, using CA cement, and allowed this to dry overnight:

 

 

After the CA had dried, it was time to address an issue that it caused.  Several resin manufacturers take the trouble to caution that the presence of CA glue will inhibit some resin's cure.  To side-step that issue, the entire assembly of each of the two masters were dipped into Future, or Pledge or whatever, and allowed to dry several hours, underneath an upside down plastic cup, to keep off dust, hair, etc.:

 

 

Now all I gotta do is figure out how to make the end product look as good as the masters!

 

For the mold this time, a larger piece of Lego base was used, and non-sulfur modeling clay filled the lower layer of Lego bricks.  This is easier done before the upper rows of bricks are added, and serves to both seal the bottom-to-brick wall join, and to steady up the masters for the pour:

 

 

At this stage of the game, I also decided to proceed with another project, while setting up the molds --  a cast resin windscreen for the Academy F-8 Crusader.  This need came about because I bought a couple of Muroc Models F-8A and F-8C conversion kits for the Academy Crusader.  The kit Academy kit represent a later mark of Crusader, that had the sensor mounted on the front windscreen.  This began, I believe, with the F-8D variant.  While Muroc provides a vacuform canopy for this conversion, it was so thin it gave me a lot of trouble when I built the F-8A, that I decided to try this approach for the F-8Cconversion, when I do that.

 

Anyway, I began that part of the project by filling the hole in the Academy kit windscreen with two or three thin layers of CA, then sanded to shape, and polished as I could.  Then, a couple of dips into the old bottle of Future, and I had a working master.  I could not use this part for the conversion, because as you can see below, the windscreen while smooth, is clouded:

 

 

Next, above right, I filled the kit canopy with non-sulfur modeling clay, and carefully trimmed it with a #11 X-Acto blade.  I then built on another "side room" to my YF-105A mold, mostly to save building one wall, and I can pour the silicone rubber for both molds at the same time.  The F-8 canopy will end up being a two-piece "squish" type mold, with the top half being poured separately, later.  The reason for this is that the "ears" at the rear of the canopy will not permit the simple one-piece mold, and using the narrow end to try that method would of course, never release from the mold.

 

 

I have just gone out to the garage to pour the OoMoo 25 silicone rubber into the molds.  After that sets up we'll move on to the next step.

 

Ed

 

 

 

 

 

 

 

 

[Jackman]

This is a fantastic tutorial. I appreciate the time & effort you took to explain the process in detail. Good work, sir! 

[TheRealMrEd]

Hi Jackman,

 

That's the purpose of this effort, to show the details and just hope I can figure it all out for all of us.  Pity that the folks who make money off kind of this kind of work won't share any details; they're missing a bet, because heaven knows, if I could have bought the canopies, I would have, and I'm only making the things I can't buy elsewhere!

 

Ed

[Stalker6Recon]

On 4/30/2019 at 2:35 AM, TheRealMrEd said:

beautifully rendered masterpiece,

The details in that 32 set are absolutely gorgeous, I must agree. Seeing how this comes together, makes me want to put this into my file system. There is the "explained/understood" file. Then I have the "magic" file. This is definitely the latter of the two!

 

Anthony

[Jackman]

I'm really curious of how you're going to pull off the F-8 Crusader piece. Those "ears" do look like they're going to be a challenge, especially in 1/72 scale.  Looking forward to more in-progress pics

 

Also, I too have been curious about the type of clear resin that Cutting Edge uses. It never seems to yellow and appears quite durable.  I did a bit of research and it seems the "ArtResin" brand of clear resin appears to stave off the yellowing process a lot longer than other clear resins.  ArtResin actually did a study comparing the various clear resins and found that ArtResin lasts longer than others:

 

 

https://www.artresin.com/blogs/artresin/why-is-artresin-more-expensive-than-other-epoxy-resin-brands

 

https://www.artresin.com/

 

**Not associated with this company in any way. Just wanted to share the info. **

 

 

 

 

Edited May 4, 2019 by Jackman

[TheRealMrEd]

Thanks for the info, Jackman

 

I hope others use some of the various kinds eventually, and update this research thread!

 

Meanwhile, it's time to look in on the molds.  Below, a picture of the OoMoo 25 cured with the masters still in place.  This all set up in the suggested 75 minutes:

 

 

Then, before the resin pour, I wanted to finish the F-8 canopy mold, so I covered all the areas (the green stuff in the photo) that will have silicone rubber to silicone rubber contact, with a mold to mold release agent, but Vaseline would work as well.  Note that this is different from a resin-to-mold release agent, which is generally not needed for acrylic or styrene plastic items. Some folks use it however, for extremely complex molds, or simply extend the life of the mold for production purposes.  Although I have some of the latter also, I probably won't use any on these limited use molds.

 

 

Normally, the master is left in the mold for this step, but I removed mine so as not to get so much mold release agent on the master.  The trick is to remember to put the master BACK into the mold, BEFORE pouring the top batch of silicone rubber, and to make certain that it is perfectly re-positioned into the mold!

 

Interestingly, the resin I happened to choose was #4 on Jackman's list, The Super Clear Resin Epoxy Resin from  Resin Obsession

 

Even though it is an epoxy resin, it is said to have additives to combat the yellowing problem. Time will tell, but if I'm successful with this project, it will be a simple matter to cast another, should it be needed in future -- and also if I'm still around then...

 

Another factor for choosing this resin is that it was claimed to be able to set up in thin sections, something that many resins, clear or not, do not do well.  It takes a lot longer in most cases to cure a thin section than a thicker one, such as in the "reservoir" blocks shown above.  Anyway, here is the Chosen One:

 

 

But, before doing the actual resin cast, I followed the advice given in on the Resin Obsession website, and put the finished silicone rubber molds into a 150F degree oven for 4 hours to make any excess silicone oil go away, which can, in some cases, inhibit the curing of the resin. This is a one-time procedure for any given mold.   During  the actual casting process, I also set a small heater near the casting pressure pot to keep the ambient air at around 90F degrees, to also help eliminate the need for a post-curing process. 

 

The resin was mixed using 2 parts resin to 1 part hardener, by volume.  This is as opposed to by weight, which then requires a digital scale weighing grams.  I have such a scale, but dumping the stuff into two incrementally marked containers is a little easier.  Using two containers, however means you have to dump both halves into a common container, scrape out the materials from both cups, etc.  The advantage of two cups lets you pour a little excess of one or the other back into the bottle, which of course happened to me.  This resin has a 25 minute or so "pot" life before it starts to set, but I needed only three minutes, tops.

 

EDIT: Let me add here, that after the rubber mold came out of the oven, I let it set for a while, Meantime, I put the two sealed bottles of resin/hardener into a sealed plastic ZipLoc style bag in a bowl of 100-degree water for ten minutes, as the resin maker recommends.  This was also to help assure timely and complete hardening of the resin.

 

I might also add here that while the pressure pot/vacuum chamber combo I use can do either task, over my two years or so of using it is that I pretty much NEVER use the vacuum process any more, as the pressure casting process takes car  of the bubbles for you.  I used to mix the resin, put it in the vacuum chamber, de-gass the resin, the pour it carefully into the molds, then pressure cast.  Now, I just mix the resin, dump it into the molds, maybe squeeze out a larger bubble or two, put the lid on the pot and add the pressure.  The bubble look out for themselves, something like the old joke "When I eat an apple, the worms look out for themselves"...

 

The "de-mold" time on this resin was around 8 hours, but the full hardening time is 24 hours.  I gave my casting about 20.5 hours to see how the heated ambient air around the pressure pot (which is located in an unheated garage -- about 65F degrees at night, this time of year) would fare.

 

One last thing here, is while the F-8 canopy was an afterthought, it is good to have something like this alongside your main project, as the "squish" mold can be used for excess resin from the main pour, as well as offering a "bell-weather" as to how well the thin sections of the resin have cured.  So, we'll open that mold first:

 

 

Above, you can see the "flash" from the squish action of this type of two-piece mold. To use, you just fill the cavity side of the mold about 3/4 full with mixed resin, and then "squish" the top half of the mold together, allowing excess resin to "squish" out of the mold.  The excess on the OUTSIDE of the mold is wiped off before putting the entire mold into the pressure pot.  The excess "squish" left on the INSIDE of the mold becomes the thin mass in the photo above left.  In the photo above right, I have just picked off the still-flexible VERY THIN flash with my fingers.  Some minor trimming or sanding later will remove the rest.  In these pictures, nothing has been "cleaned up".

 

Next the "reveal" of the main pour, the canopy for the YF-105A:

 

 

Note the finished product (still in the mold) has no bubbles, I think due to the pressure casting method.  I would welcome any brave soul trying the same with just vacuum, so that we could compare results.  That person, however, will NOT be me!

 

Next, the finished product, removed from the mold:

 

 

The top row are the original masters (the main canopy master came apart from the casting block -- no problem as it will someday be used on a model), while the bottom row are the finished castings.  A little later today, I will saw them off, clean them up and see how it went, and post a picture here.  So far, I am very pleased with the results, and I wish I had known how to do this before I made my Mach2 B-45 and the P2V-3 Neptune mod!

 

Except for those last pictures, my work here is done. I have learned how to solve a problem I had, and I hope any viewers will have learned something of value.  I also hope others will experiment with this and any other methods of casting clear canopies, and help educate all of us!  Hints, tips and general "spec-a-lations" are welcome!

 

Thanks for looking.

 

Ed

Edited May 10, 2019 by TheRealMrEd
Additional info

[TheRealMrEd]

As promised, here are the last pictures.  Below, ready to saw the parts from the casting blocks"

 

 

And after sawing them off:

 

 

Above left -- if I were doing these masters again, I would make the "sawing excess" fit much closer to the actual canopy shape, to lessen clean-up efforts.  I did not do that this time, because these masters were the only canopies I had for 3 boxes of models, and I did not want to risk damaging them!  Also, I would give them another 24 - 48 hours drying time.  They were hard enough, but very slightly sticky  -- acetone may remove that, but we'll see another time.

 

Above right, after trimming and sanding, the parts need only final cleanup, attachment, and painting for their respective models.

 

I can see an F-100 Hun, an F3H-1 Demon, and a re-mastered F-8 canopy in my near future!

 

So long 'till the next project...

 

Ed

 

 

Edited May 5, 2019 by TheRealMrEd
spelling

[Stalker6Recon]

7 hours ago, TheRealMrEd said:

the parts need only final cleanup, attachment, and painting for their respective models. 

That is just phenomenal work Ed, true artisans work! On another thread, Tony has just got his hands on a dental vacuum former for 30 quid, that is a steal and a fantastic little machine as well.

 

You guys have raised the bar, it's a wonder just to watch you work!

 

Anthony

[Schwarz-Brot]

Ed, this is very valuable information. Thank you for sharing. I guess my next diy project should be a pressure chamber... This seems to work really well.

 

Also thank you to Jackman for digging up that infomercial.

[TheRealMrEd]

Thanks guys.

 

Swarz-Brot,  all you really need is a regular commercial paint pressure pot, and a compressor capable of sustaining 55 psi, or a larger one, with a reserve tank that will activate less  often.  Trick is, you have to maintain the pressure until the resin sets up.  In a perfect world, there would be zero air leaks after the initial charge, but even after extensive leak-checking, I found that on my rig, the compressor has to come on about once or twice an hour.  as I also said above, I almost never use the vacuum side of the rig at all.  IIRC, in the mentioned pressure pot article of mine, I linked to the original guy who converted a paint pot.  If not, the video is on Youtube.

 

Ed

[TheRealMrEd]

For those who may be interested, here is a link to the model that uses the F-105 canopy made above:  YF-105A Done At Last

 

Ed