KalKat Posted August 16, 2015 Share Posted August 16, 2015 Cyanoacrylate works well for resin gluing ..... but mind your fingers! Are your moulds single part or two part? Could you post piccies? - There may be an 'easy' solution Link to post Share on other sites More sharing options...
justin1985 Posted August 16, 2015 Author Share Posted August 16, 2015 Moulds are single part - don't have time to sort a photo now but will try to later or tomorrow. I am tempted to try and carve a slither of the rubber off the mould to open up the overhanging section of the roof. Would probably result in a wedge shaped fillet, but easier to do it that way and file back the casting, maybe? Link to post Share on other sites More sharing options...
RMweb Premium Neil Posted August 17, 2015 RMweb Premium Share Posted August 17, 2015 Modifying the mould will work, a V shaped nick into the corners will allow air to escape, but will result in a V shaped addition to the casting which will need to be pared away. The best filler I've found for resin castings is a home brewed mix of pound shop superglue and talcum powder. Quite substantial holes can be filled in one hit. I'd rather repair castings than bother cutting and shutting those with a flaw at just one end. Link to post Share on other sites More sharing options...
RMweb Gold chris p bacon Posted August 17, 2015 RMweb Gold Share Posted August 17, 2015 The best filler I've found for resin castings is a home brewed mix of pound shop superglue and talcum powder. Quite substantial holes can be filled in one hit. I'd rather repair castings than bother cutting and shutting those with a flaw at just one end. I've seen a similar filler but they used Bicarb of soda instead of talc. Unless you're using up supplies of "Brut" or "Hai karate" talc. . . Link to post Share on other sites More sharing options...
Horsetan Posted August 17, 2015 Share Posted August 17, 2015 ....The best filler I've found for resin castings is a home brewed mix of pound shop superglue and talcum powder. Quite substantial holes can be filled in one hit.... Many years ago, I mixed superglue with filler. The result was rock-hard. One of the best accidental discoveries I've ever made (the other one was Belgian beer). 1 Link to post Share on other sites More sharing options...
lyneux Posted August 17, 2015 Share Posted August 17, 2015 (edited) Go and get some talc from Tirantis (cheap) and talc the moulds before pouring. This will help sort your problem. This is also where a lower viscosity resin helps. Guy Edited August 17, 2015 by lyneux Link to post Share on other sites More sharing options...
justin1985 Posted August 17, 2015 Author Share Posted August 17, 2015 Go and get some talc from Tirantis (cheap) and talc the moulds before pouring. This will help sort your problem. This is also where a lower viscosity resin helps. Guy Would the talc on the mould would help the resin flow, or help to ease the casting out and avoid snapping the thin edge? Would normal Johnsons baby talc do the job (have some kicking around at home), or is Tirantis stuff special? Justin Link to post Share on other sites More sharing options...
ajaxjones Posted August 17, 2015 Share Posted August 17, 2015 The talc is to help break surface tension on the resin so bubbles get their skin broken basically and pop afaik Link to post Share on other sites More sharing options...
lyneux Posted August 17, 2015 Share Posted August 17, 2015 The talc is to help break surface tension on the resin so bubbles get their skin broken basically and pop afaik I think that this is correct but I am no chemist. Perhaps Jon will explain why it works? All I can say is that I have had good experience with it when casting with moulds that were previously not filling properly. Baby talc should work fine too. It is perfumed so will make your moulds smell (nice?)! Guy Link to post Share on other sites More sharing options...
RMweb Premium PaulCheffus Posted August 17, 2015 RMweb Premium Share Posted August 17, 2015 Hi I also warm the moulds in the microwave for around 10 seconds before adding the talc and pouring the resin. Cheers Paul Link to post Share on other sites More sharing options...
ozzyo Posted August 18, 2015 Share Posted August 18, 2015 To stop some of the bubbles forming you can add a vent hole, paint a first coat of resin in the mould, or use one of them vacuum bags to pull all of the air out of the resin. You may have to make a frame work to keep it off the part but it could help. OzzyO. PS. I've seen this done in a proper vac. tank and it looks like the resin is boiling with all of the air that is in the mix. Link to post Share on other sites More sharing options...
justin1985 Posted August 18, 2015 Author Share Posted August 18, 2015 Well, I'm not sure if its the talc, having poked around at the thinnest corners of the mould with a scalpel and tweezers to open out the thinnest bits, or removing the mould from its lego frame before trying to flex out the cast parts to get more flex and hopefully put less pressure on the mould. Either way, I've done another two batches, and all have turned out essentially perfectly! Well, apart from extra flash around the corners where I was poking with a scalpel and evidently created little slits into the mould - better too much than too little though. I can't see the EMU roof mould lasting very long after this abuse, but it will have served its purpose if I can get four "perfect" matching driving car roofs to produce 2 N gauge class 309 EMUs. Next up will be a 2mm pre-grouping covered sand wagon and outside framed van, once I get around to finishing the masters ... 2 Link to post Share on other sites More sharing options...
gr.king Posted September 17, 2015 Share Posted September 17, 2015 (edited) Does this help anybody? Sylmasta e-mailed me this link recently, which I find quite interesting, including the bit that reminded me of helping my mother to make jam tarts. http://www.sylmasta.com/acatalog/How-To-Videos.html I don't employ every detail of the method shown in the video, but it all looks like sound technique. The idea of swirling the mould and then back-injecting resin through the outlet hole could help in some situations, but careful thought about mould shape might be wise before trying that. A constant flow through of resin to carry air bubbles away might be more successful in some cases. Some resins don't leave you with enough time to pause and reverse when using an injection method anyway. Working on a tilted surface rather than a level one is a good way to get resin to flow steadily through some moulds without trapping air as it goes. Use of plasticine to make a dummy first-part of a two part mould isn't always the quickest approach, sometimes not even a viable one. Some items are better with a thin skirt of plastic or tape attached, anchoring them firmly to the base of a moulding box and preserving air-space underneath (and within if the item is hollow). After the first pour of silicone has gone off, the box can be inverted, the old base broken away, release agent applied and a second pour of silicone used to form the second part of the mould. Either method achieves the important goal of allowing air bubbles in the silicone mixture to rise away from the master rather than clinging to its surfaces. Edited September 17, 2015 by gr.king Link to post Share on other sites More sharing options...
peter220950 Posted September 17, 2015 Share Posted September 17, 2015 Does this help anybody? Very much so, thanks for that. I've not really got on with two part moulds but will give it another go I think, as it's a much more useful way of casting a lot of the parts I do. Not sure about injecting the resins though as I'm using stuff that's gone in about 60-90 seconds, I might give the more viscous resins a try, the G36LV I use would go off while I was trying to back inject it! Two other observations, I now always decant the resin parts into smaller containers first before mixing, then put the lids back on the big tins, bitter experience tells me it's only too easy to knock a tin over, and it's difficult to get out of the carpet/shed floor. (Yes, I did it twice) Nowadays I tend to work on an old polythene box lid which not only contains any spillages but is easy to get dried resin off. Finally it does show me where I've been going wrong, I should be wearing a suit to make the moulds and a lab coat to mix the resin. Peter Link to post Share on other sites More sharing options...
wagonman Posted September 17, 2015 Share Posted September 17, 2015 Would the talc on the mould would help the resin flow, or help to ease the casting out and avoid snapping the thin edge? Would normal Johnsons baby talc do the job (have some kicking around at home), or is Tirantis stuff special? Justin Talc is Magnesium Silicate and is available from potters' suppliers (e.g. Potclays etc) for a reasonable price: for the cost of a pack of Johnsons you could get a couple of kilos! I presume what Tiranti sell is also straight Mg3Si4O10(OH)2 without any added baby-friendly ingredients. Mmm. Tiranti autocorrected to Tyrant... Link to post Share on other sites More sharing options...
billbedford Posted September 18, 2015 Share Posted September 18, 2015 Always worth reading how other people do it Link to post Share on other sites More sharing options...
ajaxjones Posted October 15, 2015 Share Posted October 15, 2015 Based on this I've got some t28 and f31. First impression is that the t28 is good, although I paid the extra 61p to switch to a fast catalyst and threw some quick moulds together but did experience some bubbles. Going to pay some more care in talcing, and pouring and mixing for the next moulds. Resin was ok, but not perhaps as good as the previous but again going to try and take some more time with smaller batches so as to be able to remove bubbles by vibrating the mould more. Although it's softer than than the MB resin so easier to trim. Also laying a glass sheet on the mould now to get a nice smooth base which I've forgotten to do before. Link to post Share on other sites More sharing options...
RMweb Premium richierich Posted October 18, 2015 RMweb Premium Share Posted October 18, 2015 (edited) I've being thinking of making some resin parts for unobtainable parts for Hornby Class 56s and 60s. I've found the following is a possible place for materials:- http://www.mbfg.co.uk/polyurethane-casting-resin/easyflo_60.html http://www.mouldlife.net/ekmps/shops/mouldlife/resources/Other/easyflo-60-data-sheet.pdf http://www.mbfg.co.uk/rtv-silicone/2462.html http://www.mbfg.co.uk/mixing_sticks/7083.html http://www.mbfg.co.uk/measuring/3234.html?var=1 http://www.mbfg.co.uk/release-wax-agents/bonda_afh_spray.html http://www.mbfg.co.uk/liquid-plastics/3053.html I think this little shopping list would get me started? Edited October 21, 2015 by richierich Link to post Share on other sites More sharing options...
RMweb Premium Neil Posted October 18, 2015 RMweb Premium Share Posted October 18, 2015 I'd recommend this kit from Sylmasta; it's what I started out with. Link to post Share on other sites More sharing options...
ajaxjones Posted October 18, 2015 Share Posted October 18, 2015 The Polycraft GP-3481-F and sg2000 from mbfg I would also recommend Link to post Share on other sites More sharing options...
ajaxjones Posted December 28, 2015 Share Posted December 28, 2015 just changed to axon f19 from tombs.com, much slower setting, far superior casting, longer cure time means casting surface is flat Link to post Share on other sites More sharing options...
RMweb Premium richierich Posted December 28, 2015 RMweb Premium Share Posted December 28, 2015 just changed to axon f19 from tombs.com, much slower setting, far superior casting, longer cure time means casting surface is flat Do you mean this supplier? http://www.tomps.com/axson-fast-cast-resin-c-55_42_64.html Link to post Share on other sites More sharing options...
Horsetan Posted December 28, 2015 Share Posted December 28, 2015 just changed to axon f19 from tombs.com, much slower setting, far superior casting, longer cure time means casting surface is flat Not F32? Link to post Share on other sites More sharing options...
ajaxjones Posted December 29, 2015 Share Posted December 29, 2015 Ooops, sorry .yes http://www.tomps.com/ Its the F19 I'm trying. Got fed up with the shorter potlife times of the other resins of 2 mins or thereabouts, so I've got 5 more mins to mould a few things at once. The F32 looks to have a lower viscosity, but shorter potlife. I'm laying a waxed glass sheet on top after pouring, and it seems to be better to get that nice flat finish. Mainly because it isn't already going thick when the sheet is laid down and a chance to move it around a bit. Just a little more patience is needed to get things out of the mould. I leave them overnight now Link to post Share on other sites More sharing options...
raymw Posted December 29, 2015 Share Posted December 29, 2015 Many years back, I used to cast white metal direct into a Sylastic (G?) silicon mould. I made a simple chipboard box, covered outside with polythene sheet, sellotaped at the edges, with a hole in the side for a vacuum cleaner nozzle, and I used a glass sheet as a lid on the box. This crude vacuum chamber removed all the air from the silicon mix, and would do the same for your resins. Initially, it will foam up, but then, after the air is removed, it will collapse down again to a smooth surface. Link to post Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now