Rail Car for Dirranbandi and Toowoomba Light Railway

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Re: Rail Car for Dirranbandi and Toowoomba Light Railway

Post by -steves- » Thu Apr 11, 2019 9:53 pm

Oily Rag wrote:
Thu Apr 11, 2019 6:03 pm
Hi Steve,
Well Ahem! Those dummy "springs" were turned from brass rod. I used a tipped tool with a triangular insert which is straight on and usually used for cutting threads. Cut in concentric rings to a common depth moving the saddle along the bed quite simply by measurement with a steel rule. I should n't say this as the health and safety are not happy with it but some careful jusicious dressing with a needle file finished the tops. Part them off to length ( I did fractionally over) and then file the back off to a full diameter, that means when assembled the pattern will come out of the mould with no undercut. A bit over length means you can adjust the fit. I did cheat and milled the back off.
The worst part of that job was getting the thing to solder up without previous bits falling off again. You can see quite clearly the flood of solder towards the back of the recesses. I should have used differing temperature solders or solder paste and warmed the whole lot through. There might have been less expletives.
it's actually nice to know you have issues doing things like that sometimes too, makes me feel a little less useless when I can't get things to go right when I do things, lol. Like solder a few things to something, then watch them all drop off when I solder something else on, these days I use engineering clamps for all soldering work as I got fed up on the Peckett build with everything dropping to bits again, lol.

I do love those brass springs! Very impressed with the molds, what are the molds made from and what resin or ? do you use to make the casts?
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Re: Rail Car for Dirranbandi and Toowoomba Light Railway

Post by Oily Rag » Fri Apr 12, 2019 10:00 am

Hi Steve,
Thanks for your interest. Firstly the patterns do not have to be brass, they can actually be anything. I have stopped using wood and either my patterns are metal or plastic or plasticard often with balsa cores all sealed up. I use silicon rubber for my moulds. There are a number of grades but simply I use two. The red one is higher temperature resistant which I use for my whitemetal castings and white/grey fro resin work. These are obtainable from a number of sources but the best success I have had is from W.Hobby or a firm called Alec Tiranti. The white stuff is more flexible than the red but of course does not have a high enough temperature rating.
first half 01.JPG
first half 01.JPG
My mould boxes are made from LEGO bricks they are incredibly accurate and there is bery little flash from the mould to be cleared off. A couple of things, silicon rubber is VERY seeking and will find every nook and cranny hence my stopping of using wood for patterns as even sealed off with varnish the gran picks up quite badly unless you have been really good with the finish. Secondly silicon rubber does not stick to anything (except glass found out using a glass jug for mixing) except itself generally. Using polythene utensils means that to clean up you just leave the excess to set overnight and then just peel it off your tools even metal ones. If you try to clean up whilst it is still liquuid you will get one terrible mess------ don't ask.
The resin I use is polyurethane "FASTCAST" from CFS in Redruth. You can get relatively small quantities from them even if it is a few pennies more so waste is less. If find yourself short for a mould, you can mix some more and pour extra in without problems. I have had not much success with the same using polyester resins, somewhat cheaper but has shorter pot lifes.
Hope that helps a bit.
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second half 02.JPG
Regards
Ian
Dirranbandi & Toowoomba Light Railway

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Re: Rail Car for Dirranbandi and Toowoomba Light Railway

Post by Jbs » Fri Apr 12, 2019 10:25 am

Ian,
Thank you for your very interesting posts about your pattern making and resin casting. I have done some preliminary searching for suitable mould making and casting materials, but it helps to have a firm recommendation of types and sources that have been found to work as is evident from your photos. If you have the time, I would appreciate a bit more information about white metal casting as I would like to have a go at both resin and white metal casting at some stage.
Regards
John
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John Smith

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Re: Rail Car for Dirranbandi and Toowoomba Light Railway

Post by Oily Rag » Fri Apr 12, 2019 10:56 am

Hi John
The mould above in the pics is for a whitemetal axle box I used on the Dinorwic slate wagons I used to make. Again the pattern you can discern is brass. The rubber is the high temp version i.e the red one. i am pretty sure that that particular material came from Alec Tiranti. In general their rubbers are are better than the Swiss stuff from W.Hobby. although both have proved more than good enough for the stuff I turn out. The only downside to Tiranti material is the catalyst. It is very thick like teacle and they advise standing the bottle in a mug of hot water, then go off have a cup of coffee, come back and do your mix.

All of my whitemetal moulds are two or three part giving total enclosure whilst resin I use a lot of single sided moulds. The whitemetal. Very variable stuff from any number of suppliers but I now only use material from a military modelling supplier in Ireland called Prince August. They have a basic casting metal, a bit cheaper and another product called "Model Metal", more expensive because of alloy differences. The casting temperature of Model Metal allegedly is lower than the basic but in discussions with their techies there is not much difference. Model Metal will do much finer detail however but temeber in all these you are operating pretty close to the temperature limits of even the red rubber. A smoking match in the ladle is the time honoured method of temperature control. It does work after a fashion but in the end I built a bit of kit based on a "craft melter" (an ammunition melter in the States) but the temp control is poor so looking at the home brewing crowd I took the ideas and knocked up a proper genuine PID temp conmtroller with Chinese bits off e-bay and the box from a defunct computer power supply. K-type thermocouples are easy to get UK made.

I I learned all my basics from a series on the internet by an 009 modeller named Nigel Lawton. they were "A beginners Guide to resin casting or whitemetal casting.
I think they are still around but maybe under a differing title now.
To improve my moulds I also built a vacuum chamber to degas the rubber mix. It got badly damaged in the last house move GRRRRR! but not having the time or faclities any longer to turn 10" diameter Alloy tube with 5/8" wall thickness I spoke with an old contact in the high vacumm industry and bought one of his as a replacement. Machine Mart sell paint pressure pots if you want to go that route to improve your resin castings in the moulds. I have the smallest one and it suffices for the small parts like those suspension units and the coupling buffers.
Regards
Ian
Dirranbandi & Toowoomba Light Railway

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Re: Rail Car for Dirranbandi and Toowoomba Light Railway

Post by -steves- » Fri Apr 12, 2019 1:42 pm

Ian

I would just like to thank you for your very clear and helpful posts which are always packed with useful information. :thumbup: I look forward to reading them when I see them come up in the New Posts section :thumbup:
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Re: Rail Car for Dirranbandi and Toowoomba Light Railway

Post by Big Jim » Fri Apr 12, 2019 3:29 pm

Outstanding,
I am off to raid my son and heir's Lego box.

I was aware of the fine tolerances of Lego after I watched a program about it. Apparently, it has to be very accurate or it won't work. The knock off or copied versions are not nearly so well made.
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Re: Rail Car for Dirranbandi and Toowoomba Light Railway

Post by Oily Rag » Fri Apr 12, 2019 4:51 pm

Thanks guys. I am here to share what little knowledge I have and am more than happy to share the failures as well. Hopefully others will be able to sidestep some of the pitfalls.
vac chamber 01.JPG
This was the home build vac chamber. I did buy the pump new but they can be obtained quite cheaply on the dreaded auction site.
basic equipment 01.JPG
This how I started with whitemetal.
PID Controller 01.JPG
This is the kit I put together. I had to do some real mods to the melter. Allegedly they are temp controlled but are very coarse being really designed just to melt scrap lead for bullets. Not allowed to do that here please note.
casting 01.JPG
And some moulds. Release agent is talc preferably baby powder or the unscented kind if you can get it.
casting 02.JPG
Moulds ready for pouring.
casting 03.JPG
Finally some parts!!! No waste just put the sprues back in the melt along with some fresh as it will deteriorate. Oh and by the way don't worry if at the start of a run the mould doesn't fill or there are flaws. A couple or so need casting to warm the mould up.
Regards
Ian
Dirranbandi & Toowoomba Light Railway

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Re: Rail Car for Dirranbandi and Toowoomba Light Railway

Post by Oily Rag » Fri Apr 12, 2019 5:03 pm

Sorry I terribly remiss. Whilst you can get Prince August materials for whitemetal direct through the website, it might be easier to get it from W.Hobby who seem to stock pretty much the whole range. Either way I have come to the conclusion that I know what I am getting when I buy this way.
Regards
Ian
Dirranbandi & Toowoomba Light Railway

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Re: Rail Car for Dirranbandi and Toowoomba Light Railway

Post by Oily Rag » Sat Apr 13, 2019 9:16 am

Just realised another omission. I haven't mentioned Plasticine. I use genuine Plasticine for setting patterns into upto the split line decided upon in enclosed moulds. You can also press in locator recesses which will mould in the rubber giving the location for the second half.
I had problems early on because I thought that "PlayDoh" was a similar product as it is the readily available product in toy shops these days. Please note it is not! It is a corn based product that actually shrinks if left overnight. I did try a number of times but my moulds always came out with flash everywhere. The other alleged alternative is a modelling clay with the same claimed properties as Plasticine came from W.Hobby. It is much harder than the genuine stuff and I had problems getting it to seal at the pattern split line. I know I have difficulty in kneading the stuff due to arthritic hands aching after a few minutes that may be the problem. However eventually found the genuine stuff in the SMYTHS toy store chain we have here in the UK. Life became so much easier.
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Ian
Dirranbandi & Toowoomba Light Railway

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Re: Rail Car for Dirranbandi and Toowoomba Light Railway

Post by Big Jim » Sun Apr 14, 2019 10:55 pm

This looks very interesting. Thanks for sharing it with the forum.
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