Experiments in casting epoxy resin for detail parts.

[Guest baldrick25]

Experiments in casting epoxy resin.

 

I had a need to produce detail castings for a rake of wagons I was scratchbuilding here

 

http://www.rmweb.co.uk/community/index.php?/topic/31186-a-rake-of-hydra/

 

I saw a demonstration of RTV ( Room Temperature Vulcanising ) to produce moulds to cast a two part epoxy resin compound to make wagon sides etc.

 

Impressed , I decided to investigate 'Blue Peter' alternatives , preferably items I already had in the DIY cupboards. RTV reminded me of 'bath sealer' and the casting liquid of two part quick set epoxy so the experiments began.

 

First I needed to produce a mould, so in the 'spares' box was a Ratio wagon kit part which had the 'W' irons and springing arrangements. OK , I know I could scratchbuild it , but its non destructive and after cleaning has been returned to the kit , ready for it to be built ( one day!)

The part had detail lugs on the reverse, which I didn't want to remove, so I dug a couple of pieces of (black) plastic sheet out of the offcuts box and cut it to fit as can be seen here :-

 

 

Now I needed a 'release agent . Comercially I had seen wax furniture polish used , so I tried that. The cheapest ASDA wax polish was liberally applied after the mould part had been secured with a couple of tiny pieces of double sided adhesive.

I had the remains of some 'bath sealant' and a blob was placed on the axle bearing area. A small piece of wax sprayed plastic sheet was placed over the top , a couple of spacers inserted to maintain a distance of 4 or 5 mms, and it was left to cure for 24 hours.

It failed.

The bath sealant was too flexible, too sticky, and took some time to seperate afterwards. Now was it the sealant or the release agent? I tried lots of alternatives , until one day , whilst car cleaning , that eureka moment struck- Holts 'Back-to-black' seemed to have the properties I was looking for.

A quick spray of the wagon part etc, and after the solvent evaporated , sealant was applied again.

Signs of success!

The sealant parted without much problem- the detail on the potential mould was excellent. The problem now was the mould was like trying to use jelly to cast- much too soft and unstable.

I had always been impressed with 'outdoor' silicone sealant for its sheer tenacity when trying to remove excess, so why not try that.

Different brands and price ranges were tried , but the cheaper the better seemed to be the motto. The more expensive seemed to have much better adhesive qualities, something I didn't want.

Using a cheap 'market' high modulas acetoxy multiprurpose silicone finally produced a mould that had good potential.

I still have the moulds I made somewhere in the modelling box, and I'll add a photograph as soon as I find them.

 

So onto the second part - the casting.

 

With a mould looking like a licquorice 'pontefract cake', a quick spray with 'back-to'black' and a small quantity of quick set 'pound shop'epoxy was mixed and carefully teased into the mould with a wooden tea-stirrer. A piece of plastic card and a small piece of wood as a weight , and its left to cure for a couple of hours.

Success.! A clear casting like this at the top of this shot was seperated:-

 

 

 

A few more clear parts were run off , with a turn around time of some 10 minutes now... getting better every time with practice.

Being clear though has problems when it came to fettle to excess, it was difficult to see the part I wanted and the part I didn't.!

So I added a little 'filler' to the epoxy mix, in the shape of polyfilla-like dry powder substutues. Now the detail on the moulds became very visible , like the one in the bottom left hand corner of the above image.

As an altenative I tried a tiny amount of black acrylic paint added to the mix and ended up with a casting in the centre of the above image.

 

Production now began in earnest with a dozen moulds. One or two castings failed with air in the mix, or air in the mould that I hadn't managed to 'shake' clear , but personal techniques soon developed that saw the casting resin trickled into the edge of the mould and vibrating it.

 

This was the general setup of items used.

 

 

The 'heap' at the top left was a few of the castings straight out of the moulds- All need fettling to leave just the bits I want before using something like a 'UHU' clear to add them to the model.

 

Here's a close up of that heap.

 

 

I hope that has inspired others to have a go with something they've never tried, I did, and ended up with all the castings I wanted and more for a couple of pounds.

I've since used the techniques to produce GWR front and tail lamps , cab interiors for locos, and lots more.

[kandc_au]

Hi Baldrick, Just to add as a thought.

There is an RTV rubber that is red. Not being in the UK makes it hard but I would think that you could source it quite readily there.

The beauty of that as a mold is that you can also pour in white metal if you wish.

just a thought.

 

Khris

[kandc_au]

Hi Baldrick, Just to add as a thought.

There is an RTV rubber that is red. Not being in the UK makes it hard but I would think that you could source it quite readily there.

The beauty of that as a mold is that you can also pour in white metal if you wish.

just a thought.

 

Khris

[Guest baldrick25]

There is indeed and YouTube has many videos showing its use. There was nowhere locally I can source anything like it , and the minimum cost to do it 'properly' was £20+ for the RTV then another £20 for the resin, add on the release agent etc plus postage and I was looking at the best part of £60 to produce small items that are at best just cosmetic decoration. OK , I churned out many many more bits than I wanted , but it was very cheap, replaceable and easy , so the best were selected. It gave me a lot of experience of the techniques and problems, and I might have a go in future with these materials.

What I tried to achieve was something on a budget , and that wasn't available to even buy , except as a releatively expensive white metal product. In future and I need a couple of some small items , there's no problem making them in an evening whilst doing other modelling. As I said in the original piece , I'm from the Blue Peter' school of modelling and it gives me much enjoyment to make things out of ( relatively) nothing. I hope it inspires others to have a go at casting as a means of making small items.

[hayfield]

Baldrick

 

Thanks for the link, would 2 part filler work? or would it dry too quickly.

 

In Hobbycraft I saw a 2 part compound for making moulds (would it be by Crystal or some similar name) , any Ideas as it might come in handy for making small moulds quickly.

[Guest baldrick25]

Hayfield ,

I'm not sure if you mean 2 part filler for the mould, or for the castings. I presume you mean for the castings , using something like Tetrosyl or car body filler.

I haven't tried it, but I see no reason why not as long as its not too 'stiff, because the mould is flexible, and would give you dimensional stability problems with the finished casting. I did try 2 part quick set epoxy with as much dry 'pollyfilla' type powder mixed in as it could support, ie the casting compound was something like hard custard. It didn't fill the mould properly as air bubbles became trapped.

I'm not familiar with the Hobbycraft compound, although I have searched the shelves in the Coventry store before without finding anything that looked suitable. I will investigate next week.

Thanks for the comments.

[kandc_au]

There is indeed and YouTube has many videos showing its use. There was nowhere locally I can source anything like it , and the minimum cost to do it 'properly' was £20+ for the RTV then another £20 for the resin, add on the release agent etc plus postage and I was looking at the best part of £60 to produce small items that are at best just cosmetic decoration. OK , I churned out many many more bits than I wanted , but it was very cheap, replaceable and easy , so the best were selected. It gave me a lot of experience of the techniques and problems, and I might have a go in future with these materials.

What I tried to achieve was something on a budget , and that wasn't available to even buy , except as a releatively expensive white metal product. In future and I need a couple of some small items , there's no problem making them in an evening whilst doing other modelling. As I said in the original piece , I'm from the Blue Peter' school of modelling and it gives me much enjoyment to make things out of ( relatively) nothing. I hope it inspires others to have a go at casting as a means of making small items.

 

 

Points taken.

Given also the fact that they are cosmetic it's not a worry.

I was also thinking of whitemetal for weight but have since realised that they are already weighted fom memory.

 

Khris

[hayfield]

Hayfield ,

I'm not sure if you mean 2 part filler for the mould, or for the castings. I presume you mean for the castings , using something like Tetrosyl or car body filler.

I haven't tried it, but I see no reason why not as long as its not too 'stiff, because the mould is flexible, and would give you dimensional stability problems with the finished casting. I did try 2 part quick set epoxy with as much dry 'pollyfilla' type powder mixed in as it could support, ie the casting compound was something like hard custard. It didn't fill the mould properly as air bubbles became trapped.

I'm not familiar with the Hobbycraft compound, although I have searched the shelves in the Coventry store before without finding anything that looked suitable. I will investigate next week.

Thanks for the comments.

 

Baldrick

 

Yes either Car Body filler or one part filler like Green Squadron which is very fluid when new. Also glass fiber compound is very runny when first mixed.

 

Had not thought about releasing agents, though did someone mention Talcum powder ?

 

I want to make a loco step mould using a repaired casting from a kit (where the Manufacturer no longer exists as it would be cheaper and easier to buy a new spare if it was available), I was wondering about strength of the part, my thought is that providing the spigot which goes into the hole in the floor is metal the part (embedded into the filler before setting has occured) will be strong enough once the body is on the chassis.

 

Would not adding plaster or any other powder to the mix weaken it.

 

I must go back into Hobbycraft and check it out, I was hoping they would sell a starter kit for resin casting.

[Guest baldrick25]

I used a spray aerosol of Holts 'Back-to-Black' as a release agent , allowing 10 minutes for the propellant to evaporate, and a quick dab with paper towel to remove any excess. Topped up every four of five casts.

The 'filler' I used was a very small amount on the end of a blunted toothpick which doubled as a stirrer, and was simply to make the detail more visible when it came to fettling etc. Working with a clear casting , as two part epoxy dries , is difficult to see where to cut and sand. I didn't notice any change in the strength of the castings - even the very thin sections stood up to being rubbed with 'wet and dry'. I did try a few experiments with larger quantities of filler , but it made the epoxy too 'stiff' to flow into the detail on the mould.

As well , I tried a tiny - end of a toothpick again- amount of acrylic black paint , which also improved the detail visibilty , with no other apparent changes to the strength of the finished cast.

The finished castings need a good wash in warm water with a drop of washing liquid added before any gluing or painting.

[hayfield]

I used a spray aerosol of Holts 'Back-to-Black' as a release agent , allowing 10 minutes for the propellant to evaporate, and a quick dab with paper towel to remove any excess. Topped up every four of five casts.

The 'filler' I used was a very small amount on the end of a blunted toothpick which doubled as a stirrer, and was simply to make the detail more visible when it came to fettling etc. Working with a clear casting , as two part epoxy dries , is difficult to see where to cut and sand. I didn't notice any change in the strength of the castings - even the very thin sections stood up to being rubbed with 'wet and dry'. I did try a few experiments with larger quantities of filler , but it made the epoxy too 'stiff' to flow into the detail on the mould.

As well , I tried a tiny - end of a toothpick again- amount of acrylic black paint , which also improved the detail visibilty , with no other apparent changes to the strength of the finished cast.

The finished castings need a good wash in warm water with a drop of washing liquid added before any gluing or painting.

 

 

I guess any spray polish would do then as a release agent. Car body filler may not be runny enough then, pity as it is pre coloured. I do have a pack of Epoxy Metal from B&Q, its a pre-coloured epoxy glue.

 

For 1 off castings some use plasticine any thoughts

[Guest baldrick25]

Plasticine and its pound shop equivalents, I tried those and found that two part epoxy was inseperable from the mould once cast . Any sort of release agent that I tried re-acted with the surface of the plasticine leaving a horrible gooey mess. Spray polish worked as long as it had 'wax' in it ( look on the label) but needed topping up after every or nearly every casting.

Note- these are all my experiences , maybe someone can suggest so different materials that do work, without costing a weeks income!

I did try using some 'candle' wax to make moulds , but shrinkage when cooling was a big problem.

[Phil Traxson]

 

Baldrick

 

Yes either Car Body filler or one part filler like Green Squadron which is very fluid when new. Also glass fiber compound is very runny when first mixed.

 

Had not thought about releasing agents, though did someone mention Talcum powder ?

 

I want to make a loco step mould using a repaired casting from a kit (where the Manufacturer no longer exists as it would be cheaper and easier to buy a new spare if it was available), I was wondering about strength of the part, my thought is that providing the spigot which goes into the hole in the floor is metal the part (embedded into the filler before setting has occured) will be strong enough once the body is on the chassis.

 

Would not adding plaster or any other powder to the mix weaken it.

 

I must go back into Hobbycraft and check it out, I was hoping they would sell a starter kit for resin casting.

 

For a starter pack for resin casting try "Hobby Holidays", I haven't got their website to hand at the moment but I'm sure you'll be able to find it with Google.

 

Phil T.

[Guest baldrick25]

I just happen to have a leaflet of theirs next the computer , from their stand at Midland Railex>>

 

http://www.hobbyholidays.co.uk/

 

01427 848979

[2ManySpams]

The resin can be found here: http://www.hobbyholidays.co.uk/products.php?cat=115

[Guest Natalie Graham]

With regard to the flexibility of your mould: Are you just putting a blob of sealer over the pattern? If so Make a 'fence' round it. That is a box of thick styrene or something similar, maybe 12-15mm high so that your mould ends up as a solid block. You can then put it back in the box to use it which should help keep it in shape. If it is still too flexible, then put a thin layer of your sealant over the pattern and once that has gone off fill the remaining space in the mould box with plaster or polyfilla. Then once that has set turn the whole thing over, remove yor pattern and you should have a rigid mould.

[t-b-g]

My friend Ken and I have recently had a play with a starter kit, which is really for white metal casting but the two part rubber moulding compound would probably do very nicely for epoxy type castings. We got ours via the "Hobbies" catalogue. I have looked at the online version but there isn't very much information on there compared to the paper book! The wargame people really are several steps ahead of model railway folk when it comes to home casting.

 

It is ever so runny when mixed, goes nicely into every nook and cranny and sets to a nice "semi hard" consistency. The whitemetal part of it was ever so easy too. We made a dozen chimneys and domes in no time at all and with a slight clean up they are as good as many a commercially bought item.

[davidw]

My friend Ken and I have recently had a play with a starter kit, which is really for white metal casting but the two part rubber moulding compound would probably do very nicely for epoxy type castings. We got ours via the "Hobbies" catalogue. I have looked at the online version but there isn't very much information on there compared to the paper book! The wargame people really are several steps ahead of model railway folk when it comes to home casting.

 

It is ever so runny when mixed, goes nicely into every nook and cranny and sets to a nice "semi hard" consistency. The whitemetal part of it was ever so easy too. We made a dozen chimneys and domes in no time at all and with a slight clean up they are as good as many a commercially bought item.

Do you remember the name of it?

[Campaman]

As to a release agent I suspect your back to black spray has silicone in it, we use cans of silicone lubricant at work as a release agent, so any sort of polish with silicone may work.

[shortliner]

Davids ( the Isopon people) Fasglas resin and hardner is good for casting - It comes out an orangey-red colour - and Plasticine from a toyshop for the mould - if you mess it up just squash it back together and make another! - but put the plasticine on a solid surface or it will "bend" slowly! A bit of formica or contiboard works fine

[hayfield]

Further to my earlier reply I went into Hobbycraft and brought a 2 part silicone moulding paste called Siligum, a bit dear at £12.50 per 100g but 300 gram packs are about £20. Can be used up to 50 times with plaster, resin and whitemetal. So I will try and make some steps up for old locos where the parts are not available now.

 

Hobbycraft had run out of resin, could I use the resin from a glassfiber repair kit just to try out?

 

link http://www.trylon.co.uk/products/mouldmaking.htm

 

Also the Remeltable PVC Compound - looks interesting. The melting point is higher than whitemetal so metal masters needed, but can be reheated and reused.

 

Anyone had any experiences with these products

[t-b-g]

Do you remember the name of it?

 

http://hobby.uk.com/.../result/?q=6407 was the one we used for the moulds. We also got some casting whitemetal which may have been this but I cannot remember for sure and I don't have the packing any more.

 

http://hobby.uk.com/...metal-250g.html

 

And the chimney and dome on this are what we cast.

 

As you can see, the mould resin is described as being suitable for resins, plaster and whitemetal. e just made a small plasticard box (make sure there are no gaps, to gets into every crook and nanny).

 

Good luck,

 

Tony

[hayfield]

Had a quick play with the Siligum tonight

 

 

I mounted 2 steps to some plasticard (I have tried to buy new parts from the maker but the model is not in production and no plans to reintroduce it, and there are no spares left, These steps are for my own use only and are a quick way of trying out this method)

 

 

I painted Vaseline over the top of the castings and plasticard, then quickly mixed the 2 parts together. You have to work quickly but there was time enough to have a second go at putting the silicone on to the mould. Next time I might put sides around the master to make a box

 

 

Not bad for a first go, the smaller step has a slight defect at the top, but the casting can be filed square.

 

Now to make a casting, but that will have to wait till tomorrow. I think the steps may be too thin to cast in whitemetal, anyway I do not have a small ladel to melt the whitemetal in. Runny resin may be the first option.

[Guest baldrick25]

Is the mould semi-flexible like the bath sealers etc, or is it solid , like epoxy putty etc. What was the mould material like to mould- it obviosly wasn't pourable. Was it a sort of plasticine texture?

[hayfield]

Is the mould semi-flexible like the bath sealers etc, or is it solid , like epoxy putty etc. What was the mould material like to mould- it obviosly wasn't pourable. Was it a sort of plasticine texture?

 

 

Its a bit like a soft rubber, may be a bit stiffer than bathroom sealer. Very easy to use. And if doing a lot the 300g is far more economical. Having said that I have used less than 10% of it.

 

Dont know what epoxy putty is like, it was very soft and workable and the reason I said about sides to the master is to help push the putty into the mould and keep the sides square. Different to plasticine as much softer at first.

 

I am very impressed with it, not bad for a first go and a quick lash up in between doing other things. The liquid Vaseline though a bit pricey at £5 is very good, master came away very easy. I guess it will be a bit harder with the mould and the thin slits, will use s nearly dry brush so not to fill the slit up with liquid Vaseline. I think I will have to work the resin into the slits.

 

The larger step will need a brass strip (with a brass rod soldered to it as a locating peg) stuck to it. I may try to stick it to the rsesin whilst it drys on the second casting, providing the first one comes out OK

[bertiedog]

For resin casting I use vinamold or equivalent Ebay product, which is meltable vinyl, that pours over the master, one or two part. The assembled mould can then have epoxy resin poured in or specialist thin resin from Tiranti etc. Vinamould's advantage is total re-use, and the moulds can do plaster casting as well for walls etc, along with other building details. The mould must be waxed to work properly, domestic spray wax will work.

 

For metal moulding then flexible silicone must be used if tin/lead whitemetal is used. Commercially vulcanised rubber is used, but this is unsuitable for home use.

 

The problem encountered with the metal moulding in thin sections is there is no real pressure to get the metal into the mould spaces, so make sure the feed from the pour to the details is a very large cone, this appears wasteful, but the metal is re-usable afterwards.(Also there must be air escape holes which leave a spot of flash, but without them the mould will not fill properly.)

 

The second way is to use the lost wax way, the hot mould is put on a chain and filled, and then swung around, the centrifugal force will fill the mould. This is very tricky to learn to do.

 

The next way is to use a plunger in a cylinder to press the molten metal into the mould, a design like the bolt on a gun is used, the open hole allows hot metal in and closing the bolt injects it into the mould. The whole cylinder is heated to near whitemetal melting point to allow the whitemetal to flow to the colder silicone mould. Some designs use a spring, with a trigger release, but a hand press will work as well. You have to work with heat proof gloves! The bolt and chamber should be stainless steel, and will require lathe work to make.

 

The third method is a turntable, the metal is poured into a hot container at the centre and runs outwards into the moulds, a 78 rpm clockwork record player will do fine!. The spinning provides predictable pressure and flow.

 

Do not forget with all pressure moulds, the air has to escape, and wires must be embedded in the master to leave exit airways. This is vital with pouring metal into any mould.

 

Also you must make sure any mould is dead dry, no water, or steam results which will blow the mould.

 

For simple pouring moulds you can use lower temperature whitemetal, or add low melt solder to the normal whitemetal to lower the casting temperature. There are ranges of different temperature whitemetals available from various suppliers.

 

Straight lead is not really suitable for pouring into silicon, it flows badly, it would be all right in a hot brass or steel mould, so it must be a whitemetal type for home silicon casting.

 

For one off castings don't forget plaster of paris, bury a wax master in it, burn it out and pour molten brass in, this is actually the easiest way, done for hundreds of years by artists and sculptors, but see it demonstrated first.! For home use you can cast in lead or white metal into plaster, a bit safer! Open backed mould work well with lead, just pour straight in to the plaster, very good for sideframes of bogies. The wax masters can be made in Vinamould from the original master.

 

Stephen.