Resin casting intro

[Guest]

Hi All,
A few months ago I ran a tutorial on the Military Modelling website on my version of resin casting. I have been asked by one of the members if I would run it again on this forum as it is no longer available. So following on from this post I will commence......
All abuse, rotten fruit and general mayhem is welcome.......

[Guest]

John Race has asked about casting and moulding. Well to try to help him out and others that might want to take the plunge but are unsure given the expense of the items required, I have put down my experiences which might help. I am not going to go into clear casting, to be honest I have had varied success on that front for the little I have required it.
Almost everything you need is available on ebay, so whichever part of the world you live in, it can be delivered to you. There are of course craft and hobby shops, so the choice is yours.
I do not have any commercial contact with the companies in this ramble through the casting world other than as a satisfied customer.
Where do we start, and the answer is what do you want to replicate and do you really need it to be that difficult. For most of us it is extra wheels or replacement parts and in our dreams it is that ultra correct Sherman turret/ Spitfire fuselage.
The art of mould making and resin casting is really easy once you have sorted out the sequence and measurements. My first attempt at casting was a few years ago and involved a plaster of Paris two part mould and lead bars used in car repairs and only the basics of half paying attention to someone else’s conversation. It was a 54mm figure and the plaster moulding side went off without too much of a hitch. I then came to the lead side and duly started to add lead to a saucepan on my mother’s cooker, the first small bits melted, so in went much bigger pieces, and with nothing to cool the pan which was not really made for lead casting the pan, lead and the cloth to hold the hot pan handle soon ended up in the garden. The end result was one pan with a big hole in it, no lead, no figure, some dead flowers and a re-think.

[PaulTRose]

this will be useful for me as its something i keep thinking about trying

[Guest]

Today it is so much easier, it is all there for you, you can buy a kit of equipment to take you through all the that includes the rubber compounds and the resin mixture.
Other items are :
Moulding clay/ plasticine. From ebay or craft shop.
Extra mixing cups, both plastic with measuring guide printed on them and paper/card drinking picnic cups.
Small pill cups for rubber hardener.
Wooden spatulas for mixing.
Electric scales (get cheap ones, do not use the wife’s).
Lego bricks and their base, the base is optional. Again from ebay, a bag of about a hundred for a few pounds.
Used ice cream tub (1ltr) to store plasticine.
Old dining knife, or similar.
Old lengths of kit sprue.
Block of wood about 50mm square.
Finally somewhere to work and leave work to set.[ATTACH]299003[/ATTACH][ATTACH]299004[/ATTACH][ATTACH]299005[/ATTACH]

[Guest]

So where do you start, obviously you need a master part, here we will use a wheel as the common item.
First you need to build a box from the Lego bricks, build this so that you have about 10mm all round. Start to fill the box with plasticine starting in the corners and working up to the top. I have some of the bricks where I have cut of the locating pins so that I have a flat surface at the top of the finished box. With the dining knife I then level off the clay and check to see that the bricks are still in place. If all is well then start to cut up your kit sprue so that you will form channels for the resin to run through (more later). Next take your master wheel and press it onto the surface of the clay and NOT into the clay, so that it is sitting centrally. Next take the block of wood [ATTACH]299007[/ATTACH][ATTACH]299008[/ATTACH]and use this to press the master wheel about halfway into the clay, if you still have the original mould line then use this as a guide, if not you can measure or just use the Mk.1 eyeball.
Once you are happy with the sit of the master, gently trim away any clay that has been dislodged and check the lego box again. Now we start to add the sprue for the channels. I usually form two that will run from the bottom of the wheel to the top as shown and a third from the top to the top of the master but this has a larger cone shape and is used to pour in the resin. I also cut three lengths and place these one at the bottom and two at the top as guides for joining the mould halves depending on the size of the mould.
Now you will need to build up the wall of the lego box so that you have somewhere for the rubber solution to be poured. You would not believe the amount of times I have read about people that have forgotten and gone off and mixed the rubber up…..

[Guest]

So now you should have a lego box which is half filled with your clay and master in place and air/fill channels and locators as per the sketch. At this point you can brush on some of the release agent that comes with your casting kit on the surfaces and master, but I do not bother at this point as the rubber compound I use is pretty forgiving.[ATTACH]299009[/ATTACH]

[Guest]

Taking your rubber, Catalyst, plastic mixing cup, a spatula, a pill cup and your scales (electronic) and not forgetting kitchen towel to clean up with. Place your mixing cup on the scales, set the weight to grammes and then you should see a weight displayed, this is the weight of the cup and you now need to zero the weight. Pour into your mixing cup on the scales the amount of rubber you think you will need, in this demo we will use 100 grammes. But always word in parts of a hundred ie 25, 50 75 etc. You will get to know from experience roughly what you will need.
Into the pill cup add drops of the Catalyst (small blue bottle) you will need, which in our case is five parts or 6 mil Do not forget to change the scales or use the measurement on the pill cup as a guide. Then when you are happy pour the catalyst into the rubber and taking a spatula mix until the rubber is a light blue colour throughout, be very thorough with your mixing, with the mixing pot being clear you will see if there are any areas that are missed. You have plenty of time for this, so do not rush, with the product I am using to illustrate it is up to two hours.
Once you are happy with the mix, start to pour it into the mould in one corner of the mould and allow the rubber to find its own level, just a slow gentle pour should do the job. Once you start to get near the top of the mould and the master is fully covered, ease off pouring and allow the rubber to settle, you will see air bubbles start to form and come to the surface; gentle tapping around the edges of the mould should dislodge any bubbles that are sticking. Do not throw away the rubber that is left in the pot, this is your guide to let you know that the rubber is hardened, I usually pour last thing at night, this removes any disturbance of the mould and gives it a clear 8 – 10 hours to set. The following day check the rubber that was left in the pot by trying to pull it away and out of the pot, it should come away clean and if it is thick enough will have a use for when you are folding etch etc.
Taking your mould, start to remove the first layer of bricks and you will notice that there has been a slight bleed through of rubber, this is not a problem and can be cleaned off after you have released the mould and master.
Now place the master back into the rubber mould along with the pour/air sprue guides and the locating pegs and set aside while you remove the clay form the lego bricks/base and clean them up, you will be using them shortly.
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[Guest]

Rebuild your mould from the now clean bricks and place the rubber mould carefully into the area where originally you had the clay. Build up the sides of the mould to the same height again ready for your second pour. Make sure that everything, master, air/pour sprue guides etc are in the same place, this is important. This time use an old paintbrush to coat all surfaces with the release agent, rubber, master etc. It will dry quickly so you can now prepare your second pour just the same as the first, and once poured place away to set. Once set again remove your first layer of bricks and gently start to separate the two halves of the rubber mould, remove the master and the air/pour guides and you should end up with a perfect mirror of your master. The Bedford wheels I am using in the demo here are from my first mould made and were made to show the flattened area rather than the totally round wheel that came with the kit. The only adjustment made was to open out the pour holes wider to allow the resin to run into the mould faster after the first try failed due to the resin not getting into the mould, but that will come with experience.
The item you might want to replicate may not warrant a full two part mould and in this case you may just want to build your box, place the item to be copied as with the Challenger and chieftain final drives. Which were placed on double sided tape in the box and mixed rubber poured over them and left to set.
Again with the Centurion Mk.12, I made the box, half filled with clay and used masters of all the items to imprint the clay with a stamp made of each item I wanted to replicate and then coated the clay with release agent and poured in resin to just fill the imprints, To make masters of each part, make a split mould, pour holes was a non productive method when the alternative was some wet n dry sanding.[ATTACH]299012[/ATTACH][ATTACH]299015[/ATTACH]

[Guest]

Casting.
By now if this was Blue Peter, (which for those who do not know was a tv programme where they took rubbish/trash and turned it into an object using loads of sticky tape and white glue). We would all be sitting waiting with moulds at the ready or trying to extricate ourselves from the mess in the kitchen.
But casting is a different operation, much faster and gives end results, hopefully happy ones.
So to begin, we need one mould that is clean and free of dust etc, open it up to expose the two halves and paint or spray the halves with release agent and leave to dry, which is minutes, paint all of the inner faces that are going to either touch or hold the resin created by the master.
Once the release agent is dry, join both halves of the mould together, and here you will notice that they will not hold together. I usually cut some old foam board to match all four sides with the longer sides measured to overlap the end pieces so forming an outer box and also support the mould. The whole mould is then wrapped with either masking tape or elastic bands, but be careful when doing this in case you distort the mould, just finger tight is all you need.
The mix of the resin is in two halves, and with the resin I use it is an easy 50 – 50 mix. Give both tins a good shake to mix the chemicals together and then you can either weigh out in separate cups what you need or use a cup with measurements on it, but remember the cups once used will be thrown away. These are the disposable picnic cups listed earlier.
Take the hardener and pour this into the resin, then with a spatula start to mix the two together, you will start to feel the cup get warm and that tells you that it is time to start pouring.[ATTACH]299016[/ATTACH][ATTACH]299017[/ATTACH][ATTACH]299018[/ATTACH]

[Guest]

Pour into the middle wider hole gently so that the resin has time to flow to the bottom of the mould. The trapped air will release through the other holes on either side and some may come back through the pour hole, this is natural, just a slight squeeze of the sides of the mould should help, Keep pouring until no more resin is getting into the mould, you may see the overflow appearing out of the air release holes this is telling you that the mould is full or filling depending at what stage of the pour you are at.
Again keep the cup with the mixed resin in it as a guide to let you know when the resin has set. This saves you from disturbing the mould. Unless I am casting more parts, by the time I have cleaned up and put away everything, had a cup of tea it is time to open the mould. Check your waste resin in the cup, if it is hard and cold then you are ready to open the mould. Release the elastic bands/masking tape and then gently open the mould and in this case what you should have is a perfectly cast wheel with three runners coming off it, remove the wheel and snip off the runners. The wheel may feel a little sticky to the touch, stand it in a warm place such as an airing cupboard for a couple of hours and it should be ok. And once dried you can wander round and proudly show off your new found skills.[ATTACH]299019[/ATTACH][ATTACH]299020[/ATTACH][ATTACH]299021[/ATTACH][ATTACH]299022[/ATTACH][ATTACH]299023[/ATTACH]

[Guest]

Problems.
The resin has not set.
Check your mixture quantities. Less hardener than resin can cause this.

The wheel has not cast correctly and is partly formed.
This usually leaves the bottom part of the cast but has not formed the top half.
The resin has been left to stand instead of a direct pour.
Open the air/pour holes using a sharp knife by cutting the channels deeper into the mould. You can see this on some of my moulds.
These are the most common problems and are easily rectified.

Lastly, the ‘stamp’ moulds, again paint with release agent, allow drying, then mixing up your resin quantity and pouring over the open mould so that the resin runs into the open areas filling them. A slight tilting of the mould during pouring will help here with the object being to just fill the indentations with just a slight overfill.

And that is all I can really tell you about casting in resin. Experimenting can lead you to all other forms of casting, with either clear or tinted resin. To date I have not had that much of an experiment although there are ideas forming.
I hope I have helped you to overcome the horrors of casting, I know when I started it was like the mad scientist at work, as with my soldering, but you learn through use.
The company I use for my product is Sylmasta in the UK, there are other companies which are just as good or even better but this is the product I am comfortable with, again if one does not work for you then try another.
Happy casting

Happy Casting.[ATTACH]299024[/ATTACH][ATTACH]299025[/ATTACH][ATTACH]299026[/ATTACH][ATTACH]299027[/ATTACH][ATTACH]299028[/ATTACH]

[Guest]

Hi Paul,
I have just been through and numbered the posts, got the idiot head on today. Once you get the process clear it really is easy, the main thing is to take your time, plan and then do it. Main points are the scales setting, zeroing the cup and the measurements.
Cheers, MikeC.

[JR]

Mike .
Was there fire envolved with the saucepan !
The things I think I would be interested in doing would be tools, weapons , that sort of thing. I have taken a seat and waiting with glee .
John

[Guest]

Hello John,
I wondered if you were around. No fire but a thick ear, hurt for days.....
Weapons - lay on the side, and then gently press into the clay. a dusting of talc on the clay first will help the part go in halfway easier. Then dust off and cast in rubber as per tutorial.
Tools - And I bet you mean spades/shovels, these take some planning due to the shape of the shaft. The spade need to be placed face down and then as if looking at it in profile the clay is shaped to take the spade first and then the shaft. I will do a sketch and put it on here in about an hour. But the process is still the same as for all of the other moulding in that you will make two halves.
Cheers, MikeC.

[JR]

Thanks Mike ,
Sounds good, yes spades , jack's , that sort of thing.
John