Looks like the fun I had with casting also, slowly getting there tho, you should of seen my first few attempts, both in mould making and casting
Have made a note of the name of resin you used, and put it on the not to use list. I have used Easyflo 95, but dont reccomend it, in takes with my mentor Graeme, think I will just order what he has been using and pay the extra, his results are alot better, and lessons have been learned from the first foot steps i have taken, the nest moulds will be alot better (he says with crossed fingers)
Will look into Hobby Craft for rubber, got mine from ebay, so if there is one more local to me...
oOo
Brian
oOo
Brian
Garage Hobbit!!
Modelling in 00 on my heritage line, very GCR inspired
manna wrote:
Cast 2 seemed to be beginners luck with only a small bit of air trapping on the spigot of the hood........Morgan
I too have suffered the frustration of seeing results deteriorate again after apparently getting almost everything right at only the second or third attempt. It can be rather frustrating to say the least!
I imagine that those large air pockets have only managed to cling to, rather than rise up clear of, the sloping surfaces because of the rapid thickening of the resin. A runnier, and slower setting resin may well be the way out of that problem, as you imagine. In the meantime, if the mould design allows it you might be able to dodge the problem by filling the mould in a quick succession of smaller batches of resin. An idea I've not tried myself, which may seem a bit "off the wall" but which I think may actually help to dislodge the air pockets quickly, would be to do your "single fill" of the mould with the fast/thick resin as now, but to work with the mould on a vibrating surface*, say the top of the automatic washing machine on its spin-cycle!
* but keep Prince Albert well clear.
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mlgilbert30 wrote:I have found that the Alumilite resin is very quick only having a pot life of about 1 minute before it is starts to solidify. In fact I found that if I didn't pour it within 30 secs of mixing then it would not fully fill the mould. Air trapping and bubbles in the cast have also been a problem. Cast 2 seemed to be beginners luck with only a small bit of air trapping on the spigot of the hood. Cast 6 was also acceptable, after poking through some extra air holes, but not perfect. Cast 4 was a complete disaster as I tried to reduce the proportion of resin hardener to try and slow the solidification down. It didn't solidify at all and ended up something like warm caramelised sugar that was a sod to clean out the mould. Despite all this, I have learnt quite a lot in a very short space of time and on reflection decided that a slightly revised mould along with some slower resin should solve most of the problems.
Morgan
I think you would have more success if you changed your mould design. The trick is to fill the mould from the bottom so that the air is displaced upward towards the risers. You could do this by turning the mould upside down and filling from a sprue in the flat face directly above the spigot.
That's a useful idea. It would also ensure that any marks caused by surface retention of small bubbles are on the inside of the hoods, rather than the outer faces.
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Thanks for the comments you are both quite right. Turning the mould upside down was my first idea after thinking about it afterwards. Not sure why I didn't realise this when making the mould to begin with. Obviously had other things on my mind. I need to make a new mould anyway but in the interim I'll try filling the mould though the 8 small riser holes as this will probably eliminate the large air bubbles on the main body of the hood.
During the week I've been made a new mould for the smoke hood and this evening I tried casting a few parts from it. First off I tried using the Alumilite resin. Whilst the result were better than before there was still too much air trapping and non fill going on. I've now run out of the Alumilite stuff and good riddance to it. I guess it may be ok for small parts, not too complex, with thick wall sections and minimal undercut. Otherwise I'd avoid it.
The other resin I have tried this evening is a recommendation passed onto me by Graeme. This resin is called Mouldcraft A2000L and it is much slower with a pot life of about 5 to 7 minutes and demould of 30 to 60 mins. I waited the full 60 minutes and the results have been stunning. Perfect cast first time! I love it when a plan comes together. I now have to make another 20 something of these so it will take a while with only 2-3 per evening being possible.
Also, to finish the job off, I had a small artwork etched this week for the smoke hood side plates. A couple of photos of the first A2000L cast with the side plates fitted are shown below.
Nicely done indeed. One thing I appear to have discovered about the A2000L which is likely to severely limit its usefulness to me, is that the castings seem to be a lot more brittle / less tough than those produced by the resin that Phil atkinson supplies. I'm a bit reluctant to use it for thin / hollow / exposed pieces. On locos it will certinly do for solid domes, sandboxes and the like, but that's not solving the problem that I wanted it to solve!
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Thanks Graeme. I've now cast 24 of these blighters from 2 moulds (did little else this weekend). I made a couple of observations that might prompt some discussion.
1. After 2 or 3 pours the mould fill performance seemed to improve. The first few needed a small bit of spot repair with resin. Presumably this is due to the mould "bedding" in and closure not being quite perfect between the halves for each successive cast. There certainly seemed to be a correlation with the amount of flash being produced on later pours so is a pointer for making moulds in the future. I need more or bigger risers.
2. The retention of static in the bits of thin cured resin when demoulding ready for the next pour became an effing nuisance. I found that three demoulds was the most I could do without having to scrub the mould clean in soap and water followed by a dry in the oven.
I've noted your comments about the A2000L resin. I'm trying to get a technical data sheet from Quantum Supplies for comparison to the Amber Composites product. In places the smoke hoods have quite thin sections (< 1mm). So far they seem to be robust enough and once installed in the roundhouse roof they should be out of harms way.
Mornin' all (on a shitty day in Surrey)
Thanks Morgan for info on brake fitting.
I have just read your method of using tubing to make spigots for mounting brake gear.
It's very good and simple like all good ideas should be.
I did think of using brass tubing as loose spacers, but gave up the idea as the smallest tubing that I had was far too big.
Micro tubing with 0.7mm insert and the shoes fixed by varnish is terrific.
Expo tools advertise micro-tubing, so I can see a trip to Alton Model Centre is on the cards, as they stock the expo range. Also the Railway Bell (near the station) is the brewery tap for the FFF brewery.
The ideas that I get from all the expert modellers on this forum have greatly increased the pleasure that I get from modelling.
Earlswood Nob
