Starting out in resin casting?

[justin1985]

I've been meaning to make a start on some resin casting for a while now, mainly to replicate some custom wagon and coach roofs, detail parts etc for 2mm/N gauge - so nothing big - in fact some probably very small parts. I had a great chat with someone doing demonstrations at the St Albans show back in January (was it jonhall on this forum?) and was recommended Tiranti, who conveniently have a shop just around the corner from my current office at Warren Street in London. However, I still haven't got around to it, and I'm soon to move job, so I figure I should just get on with it and make a start while its still convenient! 

 

I've picked up quite a few little tit-bits and tips by searching the forums, but can't really find any general tutorials or recommendations on the basics. I can't remember which specific products were recommended at St Albans. Tiranti have a bewildering selection listed on their website, and while I'm sure they'll be helpful when I go in, it would be nice to have an idea of what to get in advance! I figure I need an RTV rubber for making the moulds, but which one? (can't seem to see one that matches the usual pink colour I see on threads on here?) And which resin? I think I've seen polyurethane F31 recommended? 

 

Do I need their mould release spray? And if I build mould boxes from Lego (looks surprisingly expensive these days!), is it normal to work on a Lego base plate, and then mount the master on a smooth base (plasticard, plasticine?) sealed in with plasticine, or just stick the "walls" to a plasticard base somehow? 

 

Is there anything else I should look out for? It looks like it is important to measure the resin by weight, rather than volume, so are disposable plastic cups on a cheap digital kitchen scale ok? Is careful pouring and/or jiggling with a sandpaper-less orbital sander sufficient for getting rid of bubbles on the kind of scale I have in mind? 

 

Thanks for any advice!

 

Justin

[Rabs]

It's not something I've done any of yet but when I last looked into resin casting I found this website, which seems to be a very thorough review of how to make fine detail parts, including specific recommendations for materials for moulds and for castings:

http://lcamtuf.coredump.cx/gcnc/ch4/

[jwealleans]

Have a look back through Graeme King's thread here. He's done some excellent casting work, as good as many of the professionals and you can see how he forms his moulds and parts to be cast as you look back through the thread.

[Tiptonian]

Regarding the materials used, I have taken the liberty of uploading an information sheet compiled and handed out by Graeme King at the Nottingham exhibition earlier this year. He was giving brilliant demonstrations at that exhibition and I hope he doesn't mind my actions. Many thanks, Graeme.

 

 

[Neil]

Late last year I started a thread on 'Narrow Gauge Railway Modelling Online' where I covered the topic of resin casting from making the master to the finished casting. It can be found here, but you will need to sign up to that forum to see it. I'm afraid that it's too long to cut and paste to here, but it is quite a comprehensive guide and you do have the benefit of seeing the whole process step by step.

[Stuart Birks]

A bit of information on some casting I have done can be found here -
 

http://myweb.tiscali.co.uk/sbirks/railway/construction/con_casting.html

 
I have used the following materials.
 
Bentley Chemicals
Silicone for the mould -
http://www.benam.co.uk/products/silicone/condensation/mold-max/
I used Mold Max 10.
Resin for the components -
http://www.benam.co.uk/products/plastic/smooth-cast-300/
I have used their mold release spray but it is not really necessary.

MB Fibreglass
Silicone
http://www.mbfg.co.uk/rtv-silicone/gp-3481-f.html
Which worked fine.
I used a clear casting resin from them but it remained tacky. Probably something I did wrong but I don't know what

Sylmasta
http://www.sylmasta.com/acatalog/Casting---Mould-Making.html
I have not used any of their products.

 

All my molds are made just using Evergreen plastic. The silicone will pick up the finest of details to the point where it will show the slight change in the surface of the mold where the solvent has made the surface go slightly gloss.

 

I did find it beneficial to de-gas the silicone and from the first link you can see the vacuum chamber that I built. Without doing this it is possible to get gas bubbles on the surface of the mold resulting in a bump on the casting. I do not think jiggling it will have any effect.

 

The resins will not glue with any of the normal solvent based glues. I used superglue for all miine.

Usual disclaimer I have no connection to any of these companies.

 

Stu

[jonhall]

unfortunately i'm on a very slow connection (if at all) over the next few days.

 

 

Jon

[justin1985]

Many thanks all, really helpful replies. I feel like I've got a much better idea of how to set about designing the mould, and what to look for choosing a resin. Graeme's thread on the LNER forum is seriously impressive! I've ordered some Lego and I'll try to collect the resin etc later in the week.

[Phill Dyson (onslaught832)]

Many thanks all, really helpful replies. I feel like I've got a much better idea of how to set about designing the mould, and what to look for choosing a resin. Graeme's thread on the LNER forum is seriously impressive! I've ordered some Lego and I'll try to collect the resin etc later in the wCC

Could we have a link please? 

[Rabs]

The link is already in the thread.  Post #3

[Horsetan]

....I've ordered some Lego and I'll try to collect the resin etc later in the week.

Good brick resource here, I think

[jwealleans]

SWMBO acquired a great deal of Lego from our local Sally Army shop when the kids were small.

[ajaxjones]

I started with the kit from MB fibreglass - http://www.mbfg.co.uk/category-186/polycraft-moulding-casting-resin-kit-small.htmland it worked great. Fine detail and bubble free moulds with a bit of vibration applied to the mould. Quite addictive once you start. Gradually buying larger quantities each time. A combination of lego and plasticard for the bucks mixed with wooden sides for larger moulds. Need to make sure the moulding material is well mixed to avoid any sticky patches and with the resin careful weighing of the components otherwise you could end up with tacky resin results. When you get it right, perfectly hard and quick drying results within a few minutes. 

 

Adding in some parts from http://www.62cmodels.com/for valves,poppets and chimneys etc

Edited August 9, 2015 by ajaxjones

[Neil]

...... and with the resin careful weighing of the components otherwise you could end up with tacky resin results. ....

 

That's unusual. I use Slymasta resin, which I pour into a pair of matched transparent throw away plastic tumblers (30 for a quid from the pound shop) before pouring one into the other and stirring for the obligatory 30 seconds. I measure by eye and don't worry if there's a slight inequality between the two components. I've yet to produce a tacky cast. Though the Sylmasta resin has a specified demould time of about 25 minutes I invariably give casts about an hour. After 25 minutes the casts can be a bit green and thin walled items like the railbus components in the photo below can distort when taken out of the mould.

 

[ajaxjones]

That's unusual. I use Slymasta resin, which I pour into a pair of matched transparent throw away plastic tumblers (30 for a quid from the pound shop) before pouring one into the other and stirring for the obligatory 30 seconds. I measure by eye and don't worry if there's a slight inequality between the two components. I've yet to produce a tacky cast. Though the Sylmasta resin has a specified demould time of about 25 minutes I invariably give casts about an hour. After 25 minutes the casts can be a bit green and thin walled items like the railbus components in the photo below can distort when taken out of the mould.

It might be that the SG2000 is faster drying perhaps?  about 2.5 min pot time and ends up pretty hard too. Can't use it by measuring it by eye so a cheap set of kitchen digital scales is needed. It dries to a nice white finish that takes paint well and I've inlaid brass rod where castings are very thin walled and long. I like the railbus you've done, about to embark on a 016.5 railbus/van myself.  

[Il Grifone]

Wilkinsons do pattern Lego bricks in bulk* and pound shops usually have small selections in kits to make up cars, aeroplanes, dinosaurs etc.

 

*£5 for a cupful the last time I was there - chose the bricks you want.

 

The supposed high precision of the genuine article is not required for a mould.

[jonhall]

A few comments since i'm back in the UK.

 

The mould box - Lego basic is pretty cheap - I bought quite a big box from Woolworths before they closed, but buying a bulk collection secondhand from ebay ought to get you what you need, and if you are luck sell the remainder off can cover most of the cost. A tip is to wrap the lego in brown tape so rubber cant get between the gaps, and its less likely to break up.

 

Mixing volumes and weighing - this is where you need to follow the instructions of your own supplier, the resin I use is a 50:50 mix by volume and is quite tolerant of being not quite  right - other brands will be a lot more demanding or require weighing - as with everything else you pays your money and takes your choice. Personally I think a 50:50 is easier than a 10:1 and by volume is easier than by weight. you can buy all sorts of measuring cups from art supplies and the like.

 

Bubbles - there will be some bubbles added during mixing, and some air trapped where the resin can't get into the mould well. A low viscosity resin will help deal with both. I was advised to pour the resin into the mould from a relatively high level, and allow it to come out in a stream - this elongates the bubbles which are more likely to burst - I also dust the mould with a tiny amount of talc to help break the surface tension, and if I know there are areas which will trap air, I will encourage resin into those holes using a wooden probe (eg a kebab skewer)

 

Jon

[justin1985]

Many thanks for all of the help and tips! I called into Tiranti today and on their advice got some G26 resin and T28 silicone moulding rubber. I'll try and start experimenting later this week by copying some ready made parts before moving on to using my own masters.

 

Justin 

[peter220950]

Many thanks for all of the help and tips! I called into Tiranti today and on their advice got some G26 resin and T28 silicone moulding rubber. I'll try and start experimenting later this week by copying some ready made parts before moving on to using my own masters.

 

Justin 

 

 

Good luck with it, I think you'll find it addictive. - If you have very fine detail to cast, and if Tirani stock it, try G36LV next time, LV is the low viscosity product, and I find it pours better into moulds, it's almost like water.

 

Find somewhere to store your moulds and castings, I predict you will soon have loads of them!

 

Peter

[ajaxjones]

Was going to say that looking at the specs the T28 looks very close to the silicone i've had lots of success with and just about run out of, so might well drop in their shop next week too. Interested in the results of the resin, but its a lot to try out. 

[macgeordie]

I've been using Tiranti silicone rubber for moulds for quite a few years and found the T20 version easy to use http://www.tiranti.co.uk/edgeimpactshop/product.php?Product=1259&Content=T20+Silicone+Rubber+%2B+T6+Catalyst+1.05kg+kit+Mouldmaking+Silicone+Rubber+T20+Silicone+Rubber+

 

I like their F23 fastcast resin as moulding material, it has always given me consistent results http://www.tiranti.co.uk/edgeimpactshop/product.php?Product=3012&Content=Axson+F23+Fast-cast+Resin+1.2kg+Casting+Polyurethane+Resin+Axson+F23+Fast-cast+Resin+Supplied+in+a+1.2kg+kit%2C+mixing+ratio+1+part+%28A%29+to+0.2+parts+%28B%29+by+weight.

 

Ian

[lyneux]

I use T28 and F31 resin with good results. The F31 is the lowest viscosity resin that Tirantis sell (IIRC).

[justin1985]

I asked about viscosity, but the staff in the shop said that for small moulds the difference would be negligible (and if I had trouble bubbles, paint on a first layer before pouring) so I might as well start with the cheapest one! I wasn't 100% convinced by this, but figured it might be better to start with the cheapest, see if there is a problem, and if necessary work up, rather than start with the most expensive (and viscous) and carry on using it if its unnecessary. 

 

I'll make a start over the weekend and post progress!

 

Justin

[NickL2008]

Sounds a good idea, glad found this thread, Im making some class 442 mouldings in 4mm for my project, so something a bit larger

NL

[justin1985]

Right, I made my mould for a pair of EMU roofs and a hopper wagon roof on Saturday, and had three shots at casting from it today.

 

The first attempt seemed to go quite well, but in each of the casts there was a large bubble in each of the corners - inevitably. On later attempts I used a cocktail stick to poke around, which brought a few bubbles to the surface each time, which improved the result no end. First attempt on the right. Is it even worth trying to fill holes this big that penetrate through both sides, or just bin it? I imagine Miliput would work better than Squadron Green putty or similar on resin? 

 

 

After a bit of hacking to the bottom where the master hadn't quite been in contact with the base of the mould causing a bit of a lump underneath, they fit quite well (noticed after took picture that this one isn't sitting quite properly on the left, probably just needs a bit more filed off the underside).

 

 

The main thing I wanted to cast turned out slightly less successfully - roofs for a class 309 EMU. I had laboriously filed and sanded an existing Mk1 roof into shape for the domed end with corridor connector that is characteristic of this type, and didn't fancy repeating it. Again first time around I had bubbles in the corner, but in later attempts I never seemed to end up with both the domed end and the (wafer thin) projecting corridor end of the roof both cast cleanly. Clearly the master was just too thin to cast reliably on the corridor end. On the third attempt there were no bubbles, but I managed to snap off a small amount of the corridor end as i wiggled it out of the mould

 

 

Is it worth trying to "cut and shut" the castings to combine the good end from one with the opposite good end of another? (which glue would work best for this? epoxy?) Or keep trying/alter the mould?

 

Cheers

 

Justin