Starting out in resin casting?

[gr.king]

My impression from use of the Rampf Raku-Tool resins, my one batch of Sylmasta resin, and my brief unfortunate phase of using Easyflo 95 is that in each case absolute thoroughness of mixing seemed to be of most importance in getting a fully cured casting. Being inexact, within reason, with the "equal measures" of the two components of the resin seems less important, although it probably matters if you wish to hit the theoretical maximum strength of the final casting. 

 

Apart from mixing thoroughly the liquid that has actually run down the sides of the mixing pot into the main bulk, I suspect it is also important to wipe the stirrer round the sides of the pot above the main liquid level or to tilt and rotate the pot to pick up any stray un-mixed residue from the upper parts of the pot sides - otherwise those traces of unmixed resin can get swept into the mould as the mixed resin is poured, creating areas in the casting that stay sticky and slowly bleed un-cured resin. I have however noted that a quick wipe over with runny superglue can do a good job of hardening small sticky areas and permanently stopping the bleeding.

Edited December 2, 2017 by gr.king

[chris p bacon]

I've recently been using mainly Sylmasta, to make it easier I did pick up a cheap small weighing scale for £4.00* which has made all the difference. No failed casts since and you can tell when it's mixed as it goes 'clear' 

 

 

 

*it was £3.99 as I'm a cheapskate.

[Albert Bridge]

Hi All

 

I am about to take up resin casting and I'm wondering what the minimum usable thickness is, as I would like the moulding to be 0.5mm thick if possible.

 

Thanks

[chris p bacon]

That's a difficult one to answer.

 

What resin are you using.

What is the casting to be.

How large is the area that is .5mm.

Is it bounded by other thicker areas.

If a large area, can you make an accurate mould.

 

I've cast down to 'paper' thin but it was only a small area. I smeared some Cyano on the rear afterwards to 'stiffen' it as it's very fragile.

[Albert Bridge]

The maximum width will be no more than 5mm bounded by a 2mm diameter semi circle, the internally is s hole 28mm x 18mm.

 

 

Above is a rough sketch of what I have in mind.

 

Thanks

 

EDIT: for clumsy fingers.

Edited January 12, 2018 by Albert Bridge

[chris p bacon]

It's possible to do, it does depend on your mould though.

 

If you do it as a 'contained' item (like a sandwich) then you have to think of how you're going to let the surplus resin out.   You could make a mould 'on the flat' so the thin part is uppermost when you cast, but you will get varying thicknesses.

[Albert Bridge]

Thanks

 

I am going to do it with thin part at the top, the variable thickness should not be too much of a problem as it's a window surround and thus will be supported once stuck to the wall. The wall is 1mm thick card, I could thicken that up by laminating if it proves to be a bit too flexible.

 

Thanks again

[gr.king]

I've been having an infuriating problem with some castings recently. Despite mixing accurately matched volumes of the two resin components as briskly and as thoroughly as I can, for as long as I can get away with it (given the need to get the stuff into the mould before the reaction rate defeats the process), many "important" castings have been displaying spot "weeps" of uncured resin well after the general mass of resin has set hard. Whilst it is possible to stop these leaks with a quick wipe of runny cyano superglue, and to do so permanently so long as subsequent cleaning up of the casting doesn't break right through the seal of superglue, this is not an efficient way to produce castings! I've considered all sorts of possible technical causes and tried to eliminate those, without complete success. I'm now tempted to blame the problem on the fact that I'm using up some resin that has been open for a while and I'm being a bit cheeky regarding the use-by date, but naturally enough, I've not had the problem with any unimportant castings produced at the same time with much less care from the same resin, and that makes no obvious sense!!!

[jonhall]

That sounds like the resin is off - Polytek easyflow 60 does this when its old - one of the parts gets yellow and starts growing crystals on monomer, which if they get into the casting remain un-reacted and 'weep'. I tried filtering and centrifuging them out, but in the end gave up, and I never user the last 10% of the resin bottle because there will always be a little in the bottom of the bottle.

 

Squeezing the air out of the tip of the bottle, keeping it cool, or using a nitrogen spray to displace the air all extend the bottle life, but after 12months the life if mostly over.

 

Jon

[gr.king]

Thanks Jon, that sounds as plausible as any other explanation I can think of at present. It may be that the "important" castings seem to have been the only ones affected because (being larger and hollow) they happen to have a lot more surface area available for the problem to display itself, the less important castings being smaller and generally solid, so any "trouble" with those, if present at all, may be locked in well below the surface.

 

If suitable smaller empty bottles can be found, perhaps it may be worth decanting larger purchases of resin into smaller bottles as soon as the stuff is received, so that each quantity of resin held in stock has minimal contact with air before it comes into use.

Edited October 17, 2018 by gr.king

[gr.king]

After a welcome period free of trouble, since November, using a new batch of resin, keeping it in moderate and dry indoor conditions, air squeezed out of bottles as much as possible, tops screwed down firmly on clean threads except when pouring out the resin, and all previously successful methods faithfully followed when using the resin, I was deeply dismayed about ten days ago when I started to notice new castings bleeding again after removal from moulds - and this batch of resin is "within date" until July of this year!

Discussion with the suppliers has led to the suggestion that for some reason, one or other of the components has managed to absorb enough atmospheric moisture to upset its behaviour. Certainly, the initially bright, transparent, pale-straw coloured isocyanate has become yellower and a little cloudy, but I'm at a loss to explain the early degradation compared to previous batches. Only slightly more than half of the original quantity has been used so the containers are not full of air. Very kindly, the suppliers have offered to send me a replacement batch.

Interestingly, in contrast with ideas discussed elsewhere, my suppliers suggest that both components should always be shaken before use, but they definitely advise against disturbing the stuff at the very bottom of the isocyanate by stirring it. While the other white "Polyol" component clearly has to be shaken (and sometimes stirred when new) because it otherwise separates into translucent liquid and a heavy white sediment at the bottom of its bottle, and the the manufacturer's information sheets state that the Polyol should be stirred before each use, the manufacturer's seem to say nothing about stirring, or avoiding the stirring of the isocyanate....

All a bit puzzling.

 

Edited February 2, 2019 by gr.king

[gr.king]

For possible use in a new project I've been considering clear casting resin but in view of my total lack of experience with clear resins I am deterred by a number of things. Firstly I couldn't find an easy, small quantity, on-line purchase option for a clearly identified resin for which I could find a data sheet, because I would have to be certain of negligible shrinkage during the curing process. Secondly, the clear resins I was finding seemed either to be "stinky" polyester, which I might not be able to use in the house, or a type of epoxy with a well-emphasized need for an extremely accurate mixing ratio. Not being at all inclined to mess about with extra equipment such as digital scientific weighing scales I wasn't sure whether I could get away with my careful volumetric technique which always seems to work with "ratio sensitive" RTV mould rubber.

If anybody has certain knowledge of a no-stink, no-shrink, mix-ratio-tolerant, clear rigid fast-cast resin that produces strong, faithfully detailed castings in typical RTV rubber moulds and can be bought easily in small quantities I'd be interested to know please.

[jonhall]

The clear polyurethane I tried was intended for encapsulation - making paperweights and the like, in thin sections it remained quite cool, and it turned out the exothermic reaction it should have had, in a thick section, was required to help the resin set - so in heat's absence it didn't!  Also heat and low-shrinkage don't go together.

 

Jon

[gr.king]

Thanks Jon.

 

Not sounding very promising on that basis. I do have a "plan B" if necessary, although it is a bit fiddly, and rather more "hands on" than I would have preferred. That is to cast in, in the right places, pieces of transparent plastic, using an ordinary white fast-cast resin around those. 

 

A convenient clear resin for the whole casting would still be preferable, if anybody knows of one that satisfies the criteria I mentioned above.......

 

Graeme King

Edited January 6, 2020 by gr.king
Added final remark

[gr.king]

Useful Info:

 

Today I needed to re-order the Rampf fast-cast resin that I've been using for some time.  John Burn & Co, in Birmingham, my usual supplier in recent years, now seems to have been absorbed fully into the Ellsworth Adhesives organisation, of East Kilbride.  As a private customer with no account, I've previously had to phone Burn to place an order. On trying that today, I think I got the Ellsworth automated switchboard instead and on selecting the "orders" extension found that nobody was available and I that could only leave a message - no option to simply wait for somebody to be free. Not wanting to hang around for a return call I looked up Ellsworth Tooling "Solutions" (apparently their preferred new style) on the web and found a full new on-line ordering facility, with the size and type of resin I wanted easily found. It all seemed to work very smoothly, including the credit card processing, with a very pleasing lower carriage cost than I've paid on most recent previous orders.

[Jamiel]

Hi

I am looking for a supplier of Polyol 23 as I have had good results for casting parts for both rolling sock and buildings with it in the past, but I am having some difficulty in finding it on-line.
 

A should have kept a scan of the receipt in my modelling folder, but I can’t remember who I got it from last time, about 5 years ago.

Does anyone know a good supplier of that resin?
 

Failing that is there a similar resin you could recommend?
 

I used to pay around £20-£25 for 1 litre pots I think.

 

Just to give a bit of life to the request, here are some examples of models where I have incorporated resin casts into them.

A few bubbles in there I know, but with a little filler they make really good parts for DMU underframes.

 

 

Here are a couple of photos on underframes in progress with a mix of resin, brass and white metal parts. The cab roofs are also resin casts.

 

 

A building in progress where I have cost off sections from a Kibri kit to make a much larger build.

 

Brickwork painted, and a cast dome at the far end too.

 

Jamie

[gr.king]

If you can't find a current source for that, you may want to have a look at the data for SG2000, supplied by MB Fibreglass. I switched to that last year, on grounds of cost, and so far it seems to me to be just as good as the Rampf Raku-Tool resin that I'd been using for several years. As I can now order rubber and resin from the same source, there's a saving not just on the product, but on delivery too, as just one delivery charge applies for the quantities that I get.