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Army_Air_Force

Max Holste Broussard 1/72 Scratch Built Masters & Models

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While cleaning up some castings today, I spotted that the forward door skin had popped off the master and that this must have happened un-noticed before moulding in silicone. As a result, the resin pattern is missing the door. This isn't a huge concern as I need to add panel line detail to this before re-moulding it again for the final fuselages. I can add a replacement door skin before moulding again.

 

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I did a bit more work on the decal graphics today too, and then did a greyscale test print to check on sizes. The graphics were all produced at four times actual size. Once scaled down, they fit the parts pretty well. I know some of you who are interested in "Bruce" already have decal sets, but I'll probably try and sell a few kits via Ebay, so a full set of decals would be included with those.

 

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The delivery driver turned up late in the day with the second bottle of silicone rubber. As it was my daughter's modelling day, I didn't get around to moulding until tonight. I had two moulds to make. The larger one was the two main wing panels while the smaller one had the fin and rudder pattern again, so I could cast two fins at a time. This mould also had the tailwheel and prop again. since they were small, fragile and fiddly, and could be prone to air bubbles if I'm not careful.

 

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Today I made a tool for scribing the fuselage former panel lines around the fuselage. The scalpel blade was glued to a block of wood with cyano. The block was measured from the firewall, which was also the front face of the fuselage casting.

 

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With the fuselage on end, the block and blade were dragged around repeatedly, applying gentle pressure. For the next panel line towards the tail, another block of wood was cut to length, glued onto the first block and the length checked against the drawing. When cutting the blocks, I made sure they were a fraction on the long side, so they could be sanded back to set the length correctly.

 

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For longitudinal panel lines, I used a piece of thin brass sheet, stuck in place with double sided tape. Once in place, the line was scored several times. Blu-tac was used as a base to stop the fuselage from sliding around on the bench.

 

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For the panels closer to the tail, I used a metal 'V' block to help support the fuselage.

 

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A new door has been fitted now.

 

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The wings and extra fin/rudder moulds were cured this morning and this afternoon, I poured more resin. I also poured some resin in the fuselage mould, but put a plate over the pouring end before turning it updide down. This should form a section of front fuselage which I want to cut up for another small mould for a piece to plug where the landing gear fits in. I cast several other pieces as it is easier to measure out and mix larger quantities of resin. Even so, I was only mixing 20g each of resin and catalyst. I'm going to have a go at the clear resin next.

 

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I popped the front section of fuselage out of the mould on Friday. The red marked area is the piece I want to make a new mould.

 

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The first set of wings were also popped from the mould on Friday too. They came out very well. Each newly moulded part is a step close to completion on what has been a huge undertaking! Several other small parts came out of the moulds too including extra fin/rudders from the new mould.

 

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The test cockpit in cream resin came out very well. The clear resin version not so good! The clear, cream and master pattern are seen below. The clear resin part isn't a large amount of resin, but appeared to have created too much heat during curing. When it was removed, the main screen was distorted and it looked like the heat had damaged the mould too. The main screen in the mould looked like it was distorted and wrinkled, matching the clear piece.

 

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After a more careful inspection of the rubber and gentle cleaning out with some white spirit, the rubber mould came up like new. What ever residue had outgassed from the resin had thankfully cleaned off. Mixing such small quantities of resin was difficult, requiring so little catalyst. The cockpit only required around 30ml of resin and so the 1 to 2% of catalyst had to be guessed by drops rather than weight or measuring out millilitres.

 

A second cockpit was poured later on Friday evening, with a little less catalyst and also, to try and reduce heat build up through the amount of resin, this one had a rectancle block of clear acrylic dropped into the mould to make up some of the volume.

 

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I had planned to do some more work across Saturday too, but having seen the weather, decided to take the family out playing in the snow "Carr Family" style!!

 

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After we got back and I'd given the Jeeps a good hose down, I took a look at the second clear cockpit casting. When it was first popped out of the mould, the front screens looked a bit frosted. I figured I would still be able to polish them a bit, though the resin instructions say to fully harden ready for polishing can take up to a week.

 

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I had another look at the cockpit this morning and this time it appeared to be more clear! Like me, improving with age!! I may leave the third version in the mould for two or three days before releasing it? I'm not sure whether removing it after a day and then letting it continue to gass freely, or whether leaving it undisturbed in the mould for a few days would be better?

 

Either way, trying to photograph clear resin and pick up detail is a nightmare, and it took be several attempts from different angles, with different backgrounds and lighting to get these. Most of the pictures were just a reflected whiteout!

 

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Today, I did some cleaning up of some of the castings, as well as filling some tiny air bubbles in the new fuselage master.

 

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The piece of front fuselage was cut down to form the pattern for the plug that will fill the slot where the landing gear fits. I also cut down one of the wing centre sections, just saving the leading edge. This is the master pattern for the landing light glazing. I'm leaving it much larger than needed, probably enough for two landing lights. It allows for goofs or fitting an over sized glazed piece to allow filling around the seam, while just masking off the section which needs to be glazed.

 

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The original wheels were a fraction over size, but I found some better sized ones, so started preparing them to be moulded.

 

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Time for a feel good picture. The fuselage shown here is the new pattern with panel lines, which still needs a little wet sanding and priming before being moulded. It's quite an exciting moment to see the resin parts balanced in the shape of an aeroplane! Bar a few days, it's almost a year since my research trip to photograph and measure up the fullsize aircraft.

 

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Yesterday, I got the panelled fuselage casting rubbed down, primed and the panel lines cleaned up again.

 

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Also, out of interest, I took the first failed cockpit attempt and gave one side of the screen a light wet sand, followed by a polish. Being the first, it had the longest time to cure. The resin instructions say up to a week to fully cure before it can be polished, but I gave it a go anyway and it cleaned up quite well. It's still no use of course, but showed the better versions can be improved too.

 

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The landing gear fillet and landing light patterns were boxed up ready for moulding.

 

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The fuselage was also boxed.

 

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At the start of the project, I considered making a vacuum chamber for the moulding process, as I'd always used one back in the 1990's when working at the company making Ministry of Defence models. For the quantity of casting I do, I decided against it, as even with a workshop 23 x 12 feet, I'm running out of space!

 

So sometimes when mixing silicone, if I feel I've got a bit too much air in it, I'll use a palm sized orbital sander to vibrate the silicone pot and shake the air out prior to pouring into the mould. When I do pour the rubber, I add a small amount first, perhaps one quarter, and turn and roll the mould around to allow the silicone to slowly flow over the pattern, gently flowing into all the corners - hopefully. Once done, the rest is poured in.

 

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I've actually been pouring the silicone in the dining room. Over the last week, it's been so cold, even with the heater on in the workshop, I couldn't get the room up to the minimum temperature for mixing. I think this is the last three moulds finished.

 

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Something that has been a concern from the start was resin shrinkage. The polyurethane resin has got virtually no shrinkage at all, by the clear polyester shrinks a great deal in a big block. The first cockpit was distorted from the heat, so it wasn't obvious. The second casting had the clear acrylic block hidden inside and that didn't have any significant shrinking. Because I only had some 6mm thick clear acrylic sheet to do the test with, the line of the block can be seen through the resin windows. OK, so that was better, the right size, but the block inside showing.

 

I cast another all resin cockpit with less catalyst and that didn't distort, but it did shrink quite a bit - around 0.5mm on width and 0.75 to 1mm on length as shown below. The front end of both the clear polyester and cream polyurethane cockpits, are both pushed up against the face of the 'V' block.

 

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This is the second cockpit with the clear acrylic block inside, highlighted with the red dotted line. While this test block could be seen, it showed that the cockpit remained dimensonally uncompromised, as the lower quantity or resin around it, limited the effects of shrinkage.

 

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Armed with that knowledge, I began with the plan 'C' test!! The shrunken clear cockpit was sanded down on the belt sander to give around a 1 to 1.5mm reduction in size all round. It was then wet sanded and polished.

 

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It is seen on the original fuselage master, showing the clearance around the edges. This piece will be used as an insert in the next cockpit casting. It is the same polyester as the new casting will be, so should bond well. Its rounded, polished corners are a fairly close fit in the mould and so it should blend hopefully invisibly with the newly poured resin, not leaving eny edges showing. The limited thikness of the new resin should pick up the surface detail while minimising shrinkage to almost nothing.

 

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Here's the clear block test fitted into the mould. If it works well to give me a clear cockpit without shrinkage, I'll make a new pattern for the insert and take a mould. I can then just pour the insert in clear resin, let it cure and then transfer it to the cockpit mould for final casting.

 

It's all part of the fun and challenge of scratch building and working with new materials.

 

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Around 6pm, the silicone moulds for the fuselage, gear infill, landing light and wheels, had been cured for around 24 hours, so the plastic boxes removed the the master patterns pulled from the moulds. I'll probably leave them until tomorrow before casting any resin in them.

 

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I did some casting late last night so the first panel lined fuselage came out of the mould this morning. The landing gear filler and the new set of wheels were also cast.

 

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Other than the landing gear which will be brass strip and the wing struts which may be brass, aluminium or styrene, then this is a full kit of parts. The small clear part to the lower left is the first clear landing light casting.

 

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Here's a close up of the landing light casting. There's probably enough for three landing light glazings. This will allow for mistakes when cutting and fitting, or would allow a larger piece to be let into the wing to fill and blend the join, then just masking the piece that needs to be clear. Making it over size was easier than thinking about shrinkage.

 

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It's difficult to catch the fine panel detail, but here's the new fuselage casting.

 

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Going back to the cockpit glazing, I cast a new one last night with the polished resin core prepared earlier yesterday. I was hoping the solid core would prevent the shrinkage and the polished rounded corners would help to keep the block invisible in the new casting.

 

It was released from the mould today and left to cure a while longer, then out came the vernier calipers to check the dimensions. It would appear that I won the battle and both the fuselage and cockpit widths matched!

 

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For much of today, I've been trying to finalise the decal artwork, shown here larger than model size. The two registration black crosses at the top of the image should be 2 inches apart for the image to be the correct scale.

 

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While casting the main airframe parts is a moderately quick process, casting the clear pieces is much slower. Too much catalyst in the clear resin to try and speed up the cure, causes heat build up, distorsion and discolouration. There's no quick way. Also, once the resin is cured enough to be removed from the mould, it still isn't fully cured, and takes several more days in the airing cupboard to fully harden.

 

I need the canopy core completely hard so that it can be fine wet sanded and polished before going into the cockpit detail mould. The three moulds below show the final cockpit mould on the left, the clear core cockpit infill in the centre and landing light glazing on the right.

 

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Between working on the castings, I've also been working on instructions. This has involved setting up the model in various positions, with different sections of airframe positioned together. The different poses are then photographed and a line drawing produced from the photo on a new transparent layer.

 

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Each different line drawing could then be transferred to a step by step instruction sheet. Of course, instructions are just a suggested order of assembly and we all know that some stages get moved around depending on paint colours, schemes and order of painting.

 

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I'm waiting for clear casting numbers to catch up to the cream castings, but this as already mentioned is slow going. I'm also waiting for the postman to bring some brass strip and aluminium tube for the kits. Half an hour ago, I popped out to the rather cold workshop and set up the six kits cast so far. Two of these are the pair I was originally commissioned to build which started this whole project off.

 

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Casting continues with the kit count at eight now, but the cockpits are a few behind. There's two moulds for wheels for an N scale GMC 2.5 ton truck in this shot. Mixing the correct  quantity for the moulds is getting better, but still difficult to estimate, so I have a few other moulds so any excess resin doesn't go to waste.

 

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Here's number seven out of the moulds first thing this morning.

 

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The postman brought a package with brass strip and aluminium tube. The brass is for the landing gear. I need to experiment with the round section aluminium tube as I want it an elliptical section. I may need to anneal it, but the plan is to squeeze it in a vice with a piece of 1.2mm material also in the vice to limit the travel. This should crush the tube to the required section and thickness, without going too far and squashing it flat. Each strut is only about 43mm long.

 

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The final draft of the decal graphics was finished and test printed onto paper today, before emailing the files to the printers. I was told I should have the finished decals back tomorrow!

 

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A few of the paper decals cut to size and placed on the master patterns. The 5-ML fuselage code is printed in black on the model, as the white ( with black outline ) of the colour test print was too faint to see to cut out. 

 

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The destructions are pretty much complete, bar any tweeks as a result of the build. With the decals sorted, and that took some effort to find someone who could print them, they way is clear to get on with building the first two commissioned models. I'll get at least one airframe glued together before releasing the others for sale. After all, I'm still cockpit moulding as fast as the resin will let me!

 

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