How To Cast Resin Models

Hi all.
This thread will evolve over the next few weeks as I try to explain how I make a mold and casting out of a master.
It will take a good few weeks unfortunetly due to my limited time to actually do this!
I hope to show how I take a master and break it down into parts for casting as well as do vacforms and make a mold and casting.
Here is the master I just received today. It is a 1/200 and 1/144 Blenheim Mk.I and Mk.IV.
Attachment 57839

Currently I am struggling with visualising how to make the vacforms for the 1/144 plane.
The 1/200 will be a 'wargamer' model and so will not have vacforms.
The easiest would be a single vacforming of the whole front of the forward fuselage including cockpit. And although this is what will happen with the Mk.I cockpit I have doubts that I can achieve this with the much longer Mk.IV cockpit and observers area.
Issues are:
1. my Mattel Vac-U-Form machine is limited in size and although I have modified it to work from a vacuum cleaner and the suction is much improved it is quite limited in making vacforms over too tall/deep a form.
2. I have to ensure a almost perfect match between the edge where the vacform meets the resin as shown in the following picture (The red line shows the surfaces that need to join).
Attachment 57840

Another idea is to do a intermediate cast of the Mk.IV cockpit and then cut off the fuselage section (as per the solid red line) and then vacform the top section and have the lower fuselage section part of the main fuselage (with a seperate vacform for the forward square windows (as in the Beaufort of mine)) OR cut down on the dotted red line and vacform that forward section with the observers vacform.
See diagram below:
Attachment 57850

More to come soon (after some brainstorming and experimenting).

ok,
So I have made a number of retaining formers out of Lego.
On the right you can see the cockpit sections of the 1/144 Blenheim seated on the base ready to be covered iin the Silicon RTV. When ready the master will be pulled out from the bottom and resin can then just be poured in to the correct level (this has the problem of the casting needing to be sanded back to the flat base in order to mate up with the front of the fuselage).
There are also a duplicate set of casting formers just to the left for another casting of these items but these will have a thin silicon base and then the master will be placed on top and again covered in silicon. This will allow the master to be totally enclosed in the Silicon and will need to be cut out (from the bottom). The idea of this is to give a perfect cast with NO part line and no need to sand.
Attachment 58895

Here is the silicon in the vacuum pot being degassed:
Attachment 58896

And here is the mold formers with the silicon poured in and again being degassed in the vacuum pot.
You can see that a lot of bubbles are still present despite having already been degassed once!
The degassing removes air bubbles from within the mold which weaken the mold and can breakdown over time causing resin to flow into them making the cast have 'pimples' on it!
Attachment 58897

ok some more progress.
Firstly Lego is MY own and no I don't share! The kids always think dad's lego is great to play with though

The plane(s) are CAD drawn by Roman (Kampflieger, prolific Shapeways 3D plane producer!) as well as milled on his CnC machine.

Here is one of the molds with RTV silicon starting to be poured.
On the top is the 1/144 fuselage which has had a half centimetre layer of RTV layed down (i will cut through this to get access to the master) and then when set had a small amount of RTV put in to fix the fuselage in the centre (as seen in the picture).
At the bottom are the 1/200 wings. Again a base layer of RTV has been layed down and then when dry, some more is used to hold the wings in position and further added to roughly cover them to the parting line at the leading/trailing edges.
The three small molds in the middle are the fully enclosed castings of the canopies (see further below for the results).
Attachment 59640

This picture shows another mold with at the bottom the 1/144 wings being made in what is basically a two part mold BUT with the area in front of the wings leading edge being joined (top and bottom halves joined by NOT putting any vaseline here and this allows the two RTV halves to fuse together). This means that there is NO join line at the leading edge and that the halves are perfectly mated without the need for making locating holes and lugs as wouldbe needed on a traditional two part/halves mold. You can just see the vaseline that has been applied to the top part of the mold on the RTV as well as on the area between the wing roots.
The top two smaller molds allready have the smaller 1/144 bits (horizontal tailplane, undercarriage legs, wheels) set in half the mold with another pour about to happen to fully cover them. Note I have marked with purple texta where they are in the mold near the edge. These smaller items I will then cut the mold at the edge hopefully near to where they are embedded (using the texta as a guide). This makes them into a fully enclosed mold with no seams (except for the very small one where they are cut out of).
Attachment 59641

Here is a picture of the Mk.I and Mk.IV canopy molds that were just sitting on the plasticine originally. This show the hole where they fit and how the exposed end can be either sunk in if not enough resin is poured in or slightly bulged if too much is put in. Neither a real issue but just means more work to correct!
Attachment 59642

And here is the fully enclosed version of the Mk.IV canopy. It shows the cross-cut needed to get the part out but also the perfect reproduction of the end of the canopy just as the master actually is and no need for much tidy up.
Attachment 59643

moving on.
Here is the first cast of the 1/144 wings still in the split mold.
Attachment 59841

And here are the wings simply pulled out. You can see the excess 'flash' on the trailing edge of the wings and although it looks rough and uneven the actual trailing edge is straight and with a little sanding will be perfect (see further down for picture).
Attachment 59842

This is the 1/144 fuselage coming out of the one-piece mold. See how I have made a simple cut down the middle until I gently hit the master and the extend the cut the length of the master to allow easy removal.
Attachment 59839

Here is the complete fuselage.
Attachment 59840

AND here is the 1/200 models with the wings lightly sanded and push fitted into the fuselage.
I may well have a go at making a one piece casting of a fully assembed model (like AIM models) to see how it goes!
Being White they don't photograph well and so I will paint them up in a week or so and then re-photograph them.

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I will post a picture of that. BUT basically I mix the two part resin (by weight) in a small flexible plastic container and just pour it in the mold!! Sometimes I use a small (2-5ml) syringe (I am a doctor so have access to these as well as the blunt drawing-up needles) to inject the resin into the tailplane (on a enclosed mold) or engine area(on a split mold) to try to ensure that it gets into the furthest corners!
Attachment 60588
A simple picture of the plastic container with (dried) resin in it and how I literally pour it in! Remember I have a pressure pot so no air bubbles.

There are many types of resin. There are some that are very flexible but I don't use them for planes. Yes resin is brittle and more so in cold weather. However, things like props can be done and there is enough flexing that they come out of split molds easly enough (80% success rate I guess). I also have a hard perspex two part mold for one of my props and that works well with some mold release sprayed on and a scalpel blade to ease the prop out once set. Pictures to follow.

Again different resins with different properties. I work in a steel two car shed and in summer I can't mold as the resin cures or gels too quickly and it has gone off before I can even pour it into a mold! In winter it needs a lot of mixing in order to get the two components to mix. Again different resins can be bought that have varying 'work' times and 'cure' times and 'de-mold' times.

Yes you can, BUT again there are different RTV silicons and some are better than others. You would need to talk to your local supplier about what they have. The resin I use is NOT designed for white metal/lead etc and although it works the life of the mold is VERY much reduced.

I have read that thread and very good idea too!
I have used plasticine for this as well! BUT a bit messy and not great casts.
To improve your casting a smooth mold material is needed. You could try liquid silicone or hot glue gun glue and they work great. Also there are reuseable mold material on Ebay such as 'omeryu' (I think) that is solid and becomes soft in hot water and then sets again and can be reused over and over. Great for small and limited number of castings but then the mold can be remade again easily!

Hope this helps and ask more as needed?

So I plan on making a new fuselage for the 1/144 Gold series plane that will have vacform canopies.
In the first post above I showed a plan of where I was going to trim the cockpit area.
I have now made some progress and decided to make a vacform of the upper half of the crew area.
The picture below is how I have decided to go ahead.
Attachment 60580
The Green line indicates were I made a cut to seperate the upper glazed area and this will be used as the 'plug' for the vacform and everything above this line will be vacformed. I will then trim off (or the modeller can do it) the small area under the red line at the rear to conform to the edge of the cockpit coaming as indicated by the Red line.
The Red line is were I took a second resin front casting and cut out the bottom solid (non-glazed) fuselage section. This bottom area will then be hollowed out to allow detailing and will be glued to the current fuselage and another mold made for a complete fuselage for the Gold series model.
The Blue stripes indicate the actual area that will be made by vacforming and there will be a small area (between the observers canopy and cockpit) that needs to be painted fuselage colour.
Finally, the two flat windows at the front are hollowed out and a vacform made to fit (with trimming).

Here are the two pieces as described above:
Attachment 60590

Attachment 60591

Here is the Mk.I cockpit and rear cockpit glazing plugs having been vacformed.
Note that there are always small areas of folding or webbing were the hot material has stuck to itself whilst been drawn down by the suction. The webbing does not go onto the area needed for making the canopy useable thankfully.
Attachment 60592

And here is the Mk.IV cockpit vacform. As you can see there are large webbing runs that run up the sides of the part and these prevent it from being useable. This is because the resin plug for the vacforming was too high for my machine to handle. So an alternative method of making the vacform glazing for the Mk.IV cockpit had to be found as in the above post.
Attachment 60594

Sorry for the delay in updating this.
Here are the two resin cockpit sections. I have sawed them in half and sanded the cut section to reduce the overall width of the sections. This allows for the thickness of the acrylic used to make the vacform so it won't be wider than the fuselage (hopefully)!
First the Mk.I sawn in half with a original behind:
Attachment 61307

Then the Mk.IV which has been sawn down the middle, sanded and glued together again. You can hopefully see from the picture the reduction in width: Attachment 61308

The top of the cockpit (above the pilot's head) glazing will also be reduced in width as well.
Tommorrow I will try the final vacforming for these sections.

A small update.
Here is the reuseable mold making material as discussed above called Composimold.
It melts easily in the microwave with no smell and stays fluid for 20+ minutes. I put one of the poured molds in the freezer for 10min to speed up the setting with good effect.
There are a lot of airbubbles within the mold and not just on the surface. They do sell a spray-on 'bubble breaker' that is just watered down PVA(!) to spray the master with to reduce bubbles next to it (reduces 'stress' they say!! ). Antway, I tried to de-gas it by putting it in my vacuum chamber but the amount of trapped bubbles caused it to bubble like it was boiling! and I lost a bit over the edges of the Lego walls. It did work mind you but I sugggest having a large container if you plan on degassing! You can see the bubbles in the material below even after partial degassing.
My next mold (the 1/200 Blenheim as a complete casting) will be done soon and I will try pressurizing the mold as it sets to try to reduce the bubbles to microscopic size.
The resin cast came out fine but there were a number of quite small blobs of resin on the surface that needed to be scrapped off and then lightly sanded.
Attachment 62578

Attachment 62577

The transperancy of the mold allows you to check how the mold is as well as make one piece molds were you can then carefullly cut the master out at the appropriate place which can't be easily done with a solid RTV mold as you can't be sure of exactly where you are cutting in relation to the master that is enclosed.

Again sorry for the slow update! I have actually been busy making and painting the various finished models
Rob Yes a vibrating plate would help (as does tapping the mold before the material solidifies.
Pressurizing also is effective and as seen here there are hardly any noticeable bubbles.
Attachment 64269

However the material is then forced into every crack of the master and so it has to be well sealed!
I did note that when cutting out the trapped master (remember this was a one piece cast) that the Composimold is easily 'torn' and that I had to add more material to the top half were it bends to allow the casting to be removed.
Again, I think this material is really only suited for quick one-off castings to make say a duplicate for a missing part.

So I now have seperate molds for 1/200 Mk.I and Mk.IV planes as a single piece with only the horizontal stabilisers being seperate pieces:
Attachment 64270
Attachment 64271

I have molds for 1/144 'Wargamer' Mk.I and Mk.IV fuselages (solid canopies molded on) with seperate wings, horizontal stabilisers and parts for closed undercarriage (flying position) and gun pack if wanted:
Attachment 64272
Attachment 64273

And I have the molds for 1/144 'Gold series' Mk.I and Mk.IV fuselages (hollowed cockpit area) with seperate wings, horizontal stabilisers, wheels, undercarriage, tail wheel, props, vacform cockpit, turret and gun pack if wanted:
Attachment 64274
Attachment 64275

AND the finished planes will be shown in their own thread tomorrow!

Here are the first three castings of my new 1/200 Petersplanes Blenheim.
1.
A 55 Sqn plane based in Egypt in 1941:
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2.
A 90 Sqn RAF plane based in the UK September 1938:
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3.
A 254 Sqn RAF plane based in UK 1940:
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