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Making plastic train parts?
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   Making plastic train parts?
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   Author  Topic: Making plastic train parts?  (Read 951 times)
fred_55
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Making plastic train parts?
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« on: Apr 27th, 2013, 3:51am »
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I needed some castings but couldn't find a helpful foundry so I tried casting them in plastic. (they are buffer stocks, but they take no load on the model.)
This is the kit. RTV2 casting silicone, sticks to itself but not to anything else.


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« Last Edit: Apr 29th, 2013, 3:39am by fred_55 » Logged

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Re: Plastic trains?
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« Reply #1 on: Apr 27th, 2013, 4:07am »
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The setup. (I'm single so I can use the kitchen bench)
The purple pack makes the mold, cast in a cup. The mold is quite flexible and will tolerate undercuts. It will withstand 300 degrees so can also take low melt alloy.
The picture doesn't show the mould mixing, but does show 1, the mould (grey tube), 2, the pattern (grey wood) and 3, the finished item (white).  In the back are the cups with coloured spoons, for mixing the polyester.


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« Last Edit: Jan 11th, 2014, 1:15am by fred_55 » Logged

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Re: Plastic trains?
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« Reply #2 on: Apr 27th, 2013, 4:14am »
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OK  I am starting again.
 
Having made the pattern, next is to work out how to fill it. I decided to use the mounting face which is easily filed flat. the pic shows the pattern suspended in a pattern box (cup) with the mount face upwards.
The RTV mould material is mixed as instructions (use a lollypop stick and take care not to stir in air bubbles) and gently poured away from the pattern and allowed to fill up around to the top face. There is minimal shrinkage and with a set time of several hours, some topping up is possible.
To get the right quantity, first hold the mould while filling the cup with water up to the spot, then empty the water into another transparent cup and mark the depth. Mix the RTV to this mark. Make sure everything is dry before mixing and pouring.


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« Last Edit: Jan 11th, 2014, 12:43am by fred_55 » Logged

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Re: Plastic trains?
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« Reply #3 on: Apr 27th, 2013, 4:18am »
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Leave for 24 hrs, then you can fill it with polyester. Like fibreglass it is a two part 50-50 mix that goes off quickly.
The orange pack is the polyester resin 50/50 pack. Note the colour coded mixing spoons. A quick stir and pour, then it sets in 100 seconds.
The pattern is grey and the plastic copy is white. The undercut was more than I thought, so I split part of the mold with a scalpel to release the product (simply duct tape it together for the next one)
 
To save guesswork fill the mould with water. This time I used a spoon and counted spoonfulls. Divide this number in half and thats your quantity of each part.
 
I measured part 1 ( with a green spoon) into the mixing cup, then added the same quantity of part 2 with a blue spoon, then stirred with stick. The soiled spoons will keep for several hours if they dont touch each other and are kept in their own cup.


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« Last Edit: Jan 11th, 2014, 1:14am by fred_55 » Logged

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Re: Making plastic train parts?
 
« Reply #4 on: Apr 29th, 2013, 6:00pm »
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wow!  nice work, pete.
 
now...can you make another casting and show us from start the finish?!  
would be nice to see how you started and what you had to do to replicate the part you used for the pattern.   if you can do it in your kitchen, then maybe we should be able to do it in our shops, garages...er' an maybe the backporch.
 
keep it coming, kindda gets the juices flowing again!
 
moose


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fred_55
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Re: Making plastic train parts?
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« Reply #5 on: Apr 30th, 2013, 6:59am »
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OK I skipped a bit. This is the mould in a cup recreated for the pic. Using the original mould box keeps the shape, in this case the mould was split to release the finshed item, then returned for the next one.
The polyester has a pot life of 100 seconds, so you have to have mould ready to go. Slow pouring down the side of the mould will minimise air bubbles, but if you set your mould in such a way that bubbles will be on the non-view side, then you get a better result.  


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« Last Edit: Jan 11th, 2014, 1:01am by fred_55 » Logged

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Re: Making plastic train parts?
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« Reply #6 on: Jan 11th, 2014, 1:22am »
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You can demould in 60 minutes, so it's a quick production line. I did 8 of these in one evening
Meanwhile, this stuff has reasonable strength, but is best for "decorative" parts, especially underbody detail (generators, battery boxes, air cylinders,etc).  
Secondly, it is not neccessary to split the pattern, as for sand casting. Provided you can support the mold, say in a box or cup, you simply slice the mold partly or fully, through the middle and stretch it to release the part.
It's also great for repetition jobs or sharing with others. The mold  can even be mailed.
Note that there's no shrinkage to calculate, and the finished article can be machined with normal tools ( albeit a bit careful with the vice!!)
Pete


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Re: Making plastic train parts?
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« Reply #7 on: Jan 11th, 2014, 1:27am »
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Next job is quite a challenge, a 2" scale Westinghouse K valve and tank. I'll describe the mould process a bit more thoroughly, meanwhile this is your version of my valve.

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« Last Edit: Jan 11th, 2014, 1:29am by fred_55 » Logged

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Re: Making plastic train parts?
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« Reply #8 on: Jan 12th, 2014, 3:09am »
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And this is my version, turned in wood.  I had the choice of making it in two pieces, or laying it horizontally and filling on top of the air tank where it is out of sight.
In the end I decided that one piece was possible, and air bubbles would escape better if I stood it on end with the awkward tiny details near the top where the bubbles would release more readily


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Re: Making plastic train parts?
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« Reply #9 on: Jan 12th, 2014, 3:13am »
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Here it is with detail bits added.  The bottom end (sitting in duct tape roll) has less detail.  The moulding box has been cobbled together to give around 1/2" cover (min 1/4" in small areas) and then the joints sealed with bathroom sealer.

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Re: Making plastic train parts?
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« Reply #10 on: Jan 12th, 2014, 3:24am »
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Then I changed my mind and went for broke by adding the filter and a couple of pipe ends.  This meant that the box was too shallow so I extended it.  The box is best nailed together but leaving the nails just proud, so it is easier to grasp them when the box is to be pulled apart later.
The master has now had a coat of gloss to make it less likely to grab the RTV.
Finally it is suspended in the mould box. I used two batten screws in the ends as I want to later put a 1/4" bar through the mould to strengthen the finished article.


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« Last Edit: Jan 12th, 2014, 4:05am by fred_55 » Logged

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Re: Making plastic train parts?
 
« Reply #11 on: Jan 12th, 2014, 2:04pm »
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Very interesting post, Fred. I have been thinking about making some similar castings using RTV molds with low-temperature bismuth alloy. These alloys have melting temperatures between 120F to 300F (depending on the alloy) and the ones towards the lower end shouldn't harm the plastic mold. This one is a bismuth/tin/lead alloy:
 
http://www.rotometals.com/product-p/LowMeltingPoint212ALLOY.htm?gclid=COfsirup-bsCFSHNOgod0EoAzw


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Re: Making plastic train parts?
 
« Reply #12 on: Jan 12th, 2014, 5:49pm »
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Amazing what is available on the www these days!
When I was casting bits for "O" scale I used pewter scrap from printing press type. It was cheap, ran about 300 degrees and was hard as it had a higher tin content.
Here's a link to someone with better writing skills than me.  I notice he refers to polyurathane and not polyester (fibreglass) as suitable resin.
http://johnsblogworld.blogspot.com.au/2010/11/building-custom-usb-flash-drive-part-1.html


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Re: Making plastic train parts?
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« Reply #13 on: Jan 14th, 2014, 1:35am »
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Filled the mould with water to the desired depth then dumped it in  the tupperware measuring pot on the left.
It measured 1200 ml which is the exact ammount in the rtv kit. That made measuring easier as I mixed it in the kit container, but it only just covered the pattern, so I put in some scrap bits of wood where the rtv was thickest and by scraping the barrel, just made it.  
This morning I checked it and there is a soft spot, possibly from scraping the pot and getting mixture with less hardener.
I'll leave it a day or three as it could still cure.
 
The experts say that a vacuum chamber will reduce bubbles dramatically, but this lump is way too big for my home made vacuum setup. Instead, that bit of coiled wire is a bubble catcher, waving it around and under the pattern very gently tends to pursaude the bubbles to let go and rise.
Pete


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« Last Edit: Jan 15th, 2014, 2:22am by fred_55 » Logged

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Re: Making plastic train parts?
 
« Reply #14 on: Jan 14th, 2014, 4:50pm »
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on Jan 14th, 2014, 1:35am, fred_55 wrote:       (Click here for original message)
Filled the mould with water to the desired depth then dumped it in  the tupperware measuring pot on the left.
It measured 1200 ml which is the exact ammount in the rtv kit. That made measuring easier as I mixed it in the kit container, but it only just covered the pattern, so I put in some scrap bits of wood where the rtv was thickest and by scraping the barrel, just made it.  
This morning I checked it and there is a soft spot, possibly from scraping the pot and getting mixture with less hardener.
I'll leave it a day or three as it could still cure.
Pete

 
well? inquiring minds want to know!  how did they turn out?  and btw...gonna do some in 1/6 scale?  i need 5 of them.
 
keep the pics coming!
 
moose


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Re: Making plastic train parts?
 
« Reply #15 on: Jan 14th, 2014, 9:45pm »
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Holy Crap Moose!  5!  where ya goin to keep all the equipment?
 
Tom C.


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Re: Making plastic train parts?
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« Reply #16 on: Jan 15th, 2014, 2:06am »
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Hi Moose. Bulk RTV costs $10 litre, this kit cost $90 for 1.2 litres. Two days out in the sun has seen it get much stiffer,  I think I'll wait a bit longer.
This item is at 1:6 or 2" scale, so would suit you.  I'll keep an eye on costs in case its worth making them for you . Either that or I can mail you the mould and you make your own and then return it.
Tom.   Holy Crap Moose!  5!  where ya goin to keep all the equipment?.  He can put two of his cabooses on one of your flatbeds .  Have you found any bedposts yet?
Pete


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Re: Making plastic train parts?
 
« Reply #17 on: Jan 15th, 2014, 2:13pm »
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As far as a vacuum chamber, how about putting the mold into the clean tub of a shop vac, putting a plug into the inlet of the vac, and let it run for five minutes?

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Re: Making plastic train parts?
 
« Reply #18 on: Jan 17th, 2014, 10:11pm »
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on Jan 15th, 2014, 2:06am, fred_55 wrote:       (Click here for original message)
Hi Moose. Bulk RTV costs $10 litre, this kit cost $90 for 1.2 litres. Two days out in the sun has seen it get much stiffer,  I think I'll wait a bit longer.
This item is at 1:6 or 2" scale, so would suit you.  I'll keep an eye on costs in case its worth making them for you . Either that or I can mail you the mould and you make your own and then return it.
Tom.   Holy Crap Moose!  5!  where ya goin to keep all the equipment?.  He can put two of his cabooses on one of your flatbeds .  Have you found any bedposts yet?
Pete

 
 
hi pete!
 
after having a day or two to think about it, all i really need is 1 (one).  for a modest fee, i can have it scanned in as a 3-d shape and then printed in one of several materials.  hi-res printing is coming down in price and there is now a handful of choices for printing materials.  once scanned, the object can be scaled to any desired size.  if this interests you, pm me and we'll work out the details to your satisfaction.  you've done the work, you'll own the file.  you've saved me a lot of work!   keep it coming, this is a wonderful project.
 
to tom c: i'll have to build an elevator.
 
to brian t:  all stations alert...i'll be on the high seas through 1/23, she's in your hands...take care of her.
 
moose


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Re: Making plastic train parts?
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« Reply #19 on: Jan 18th, 2014, 3:36am »
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Vacuum in a shop vac....might just work.
Moose, whatever works... it must be a lot cheaper to do 3D in U.S.  I have a fail in the mold, which is frustrating. The air tank end is good so I might do a test cast. It could take a little while to save up for more RTV material to try again.  
Pete


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