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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 942 times)
Dan Watson
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Re: Making plastic train parts?
 
« Reply #20 on: Jan 18th, 2014, 7:33am »
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Sorry to hear about the mold failure. But I'm not following how you separate the two halves of the mold.  Is it cut apart after the pour?  
 
If so, why not pour half of it at a time?  First fill it half full to the midpoint of the pattern and let it harden,  Then put some kind of parting medium on the first half (could be cooking oil spray or wax paper) and then pour the top half. Would be much easier to separate the mold.
 
If not, then I'm not following your method.
 
As far as the cost of 3D printing, it appears to be way cheaper here than it is elsewhere.  What's really strange is that Shapeways (which I believe has their plant in the U.K.) charges a lot more for the same part there than they do here. I heard of one guy in England ordered a part from them, had it delivered to a U.S. address, then had it shipped it back to the U.K. for less total cost than having it shipped there in the first place (?).


« Last Edit: Jan 18th, 2014, 7:40am by Dan Watson » Logged
fred_55
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Re: Making plastic train parts?
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« Reply #21 on: Jan 19th, 2014, 6:51am »
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Part of the benefit of RTV is its stretch, so when cut partway (after molding) it holds registration real tight and leaves no parting mark.
However I have obviously found the limit and exceeded it. This mold for this item will have to be done in 2 halves.
I also discovered that incompletely cured RTV reacts with the plastic, look what happened to the test pour
Very sparing petroleum jelly stops the bond, but keeping the joint sharp is difficult.  Registration pegs will be  required.  A split top and bottom is probably the way to go, and would minimise air bubbles in the filter area.
 
3D printing is crazy expensive here. I enquired about a headlight, one quote was over $400 and had very  poor definition. Perhaps Moose could get a ballpark, then I might get him to make them!  
Pete


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Dan Watson
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Re: Making plastic train parts?
 
« Reply #22 on: Jan 19th, 2014, 12:24pm »
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The other trick in holding down on the cost of RP parts is to make them hollow.  Generally they charge by the number of cc's of material used, not by the size of the item, so if you make it hollow it costs much less.  It's also easier to mold if the pattern is made in halves.  Then it's easy to fill the cavity with something cheaper like plaster of paris, and mount each half on either side of a matchplate.

« Last Edit: Jan 19th, 2014, 12:25pm by Dan Watson » Logged
Steen_Rudberg
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Re: Making plastic train parts?
 
« Reply #23 on: Jan 21st, 2014, 6:31am »
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Hi Fred
 
Maybe you should split it up in smaller parts, and join them later.
 
 


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Steen Rudberg
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BobbyT
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Re: Making plastic train parts?
 
« Reply #24 on: Jan 21st, 2014, 7:28pm »
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Pete,  
So sorry about the mold issue. I really like the possibilities this has for our hobby.
 I had read an article once about using RTV molds. In the article they only filled the casting box half full, and placed 4 marbles, one in each corner into the still wet RTV. Once the first half hardened they removed the marbles, coated the first half with a release agent and then poured the remainder of the mold. The marbles provided a nice clean registration pin. Just a suggestion.  
 


« Last Edit: Jan 22nd, 2014, 10:16pm by BobbyT » Logged
fred_55
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Re: Making plastic train parts?
 
« Reply #25 on: Jan 21st, 2014, 10:40pm »
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The marbles idea has merit. Making smaller parts makes sense, but because there's no shrinkage, it only makes more work....we'll see.
Hollow parts is definately worthwhile. Balsa wood or polystyrene inserts  are OK I've been told,  perhaps here I could skewer them, like a kebab!
Meanwhile I have some axle box ends to copy that shouldn't cause too many dramas.
I'm liking the idea of RP a lot more. I'm not sure about scanning the pattern, why not just draw it from the original specs. Maybe someone who is digi-savvy could jump in.
Pete


« Last Edit: Jan 21st, 2014, 10:42pm by fred_55 » Logged

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Re: Making plastic train parts?
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« Reply #26 on: Feb 2nd, 2014, 12:17am »
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Went back to the shop and told my sad story. "Too much hardener" she said. Anyway she gave me a discount on the new kit.
Meanwhile I ordered a little kitchen scale from ebay for $7.99,    0-5000 grammes, just right.
So here's the new setup.  I need 650 grammes, so set up scales with empty container, and zero it..........


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« Last Edit: Feb 2nd, 2014, 12:45am by fred_55 » Logged

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Re: Making plastic train parts?
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« Reply #27 on: Feb 2nd, 2014, 12:19am »
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Pour in 600 grammes of goo  (scuse the "modern" measures, you'll just have to convert it to U.S. yourself  )
Note how is outgassing when left still. With a pot life of 45mins it can be left stand for a while


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« Last Edit: Feb 2nd, 2014, 12:37am by fred_55 » Logged

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Re: Making plastic train parts?
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« Reply #28 on: Feb 2nd, 2014, 12:23am »
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And add the 10% hardener.   That total is a bit more than I need, but it needs slightly more than the water used for calculations.
.


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« Last Edit: Feb 2nd, 2014, 12:36am by fred_55 » Logged

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« Reply #29 on: Feb 2nd, 2014, 12:30am »
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And I can report that the half mold has hardened and the second layer is going off nicely.
While I was messing about I tried another SMALL item, a dummy axlebox.  It has a taper, and the tin bowl also has a taper, so it should release easily.  It did and the test piece is nearly right,(needs a bit more trimmig of the joints).
On the plus side the tapers mean the mould doesn't have to be split, but I won't use tin bowl again as it needs to be flexed to release the RTV.
Pete


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Steam290
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Re: Making plastic train parts?
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« Reply #30 on: Feb 2nd, 2014, 9:57am »
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on Jan 19th, 2014, 6:51am, fred_55 wrote:       (Click here for original message)

 
3D printing is crazy expensive here. I enquired about a headlight, one quote was over $400 and had very  poor definition. Perhaps Moose could get a ballpark, then I might get him to make them!  
Pete

 
I've been going down the 3D printing path. My casting masters for the Burlington # 7 truck have used this technology. And some parts on the truck are plastic and metal 3D printed. I have used Ponoko and Shapeways. Sometimes their prices align, other times there is a large divergence. I have found the most cost effective approach is have your longest dimension on the X axis, next Y, and shortest dimension Z. Cost is substantially different depending on part orientation. And then overall volume matters.
 
Not trying to hijack the thread. But here is an example. The side bearings on my do not need to be metal. They hold a block or roller. I put the 3D drawing together during a lunch hour. Cost for the plastic or aluminide (plastic with aluminum filler) was $4.11 and $4.76 respectively, plus shipping. they are about 0.5" by 0.4 x 0.5". Picture of each below. The pedestals, in rough numbers, 6" x 4" x 1" in plastic are low $50. My brake hanger brackets (red part upper right in second photo) in bronze impregnated stainless were $8+. I see the quote now is $9.48. But it is a little part that would cost about that by the time I went through the lost wax silicon bronze casting process. And that would have a sprue on it that I would have to cut/machine off. It's a small part, hard to hold. I might have to get a casting quote on it, just to compare.  
 
Back to the thread at hand. Here in Atlanta, GA USA, there is a place that carries all kinds of casting materials. http://www.theengineerguy.com/ I have used some of their stuff to do reproduction locomotive trust plates for a full size locomotive.


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Steam290
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Re: Making plastic train parts?
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« Reply #31 on: Feb 2nd, 2014, 9:59am »
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Here's the truck jpg with the brake hanger.
 
Dale Grice



Image exceeds display size of 900 pixels wide. (168250 bytes, 1428x612 pixels)


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fred_55
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« Reply #32 on: Feb 4th, 2014, 2:45am »
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No highjacking, it's all relevant to plastic parts.
I did some comparison from your link. My RTV costs $90 litre,That's a bit over a quart. Engineer guy's platinum cure BC 9060 is $50 a quart. Big difference, especially when you think that the westinghouse mold took over a litre(without considering the epic fail cost)
My polyurathane is $75 a litre ($325 a gallon), engineer guy has Smooth Cast 320 for $40 a Gallon, which makes the excercise worth while on your side of the pond.  
So my finished Westinghouse is $25 for plastic, $90 for mold.
Your link would be about $3 for plastic, $50 for the mold.
Dang..
 
Meanwhile it's fill-em-up and move-em-along


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« Last Edit: Feb 4th, 2014, 2:47am by fred_55 » Logged

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« Reply #33 on: Feb 4th, 2014, 2:51am »
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And pop-em-out at 30 minute intervals.   Some of the bolt detail could be better, but I figure anybody lying down looking up at a passing wagon might not notice
I gave up on kebab-ing the interior to save material, it just wasn't worth the agro. (although one of them has a mixing stick dropped in it! doh)
Maybe the RP method is better for higher quality stuff.
Pete


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« Reply #34 on: Feb 4th, 2014, 6:47pm »
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Not much on TV tonight

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BobbyT
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Re: Making plastic train parts?
 
« Reply #35 on: Feb 4th, 2014, 7:47pm »
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WOW Pete, you keep this up and you will have to build more cars to put these on. From the photos they look like they came out real nice.

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tomc
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Re: Making plastic train parts?
 
« Reply #36 on: Feb 5th, 2014, 11:03am »
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Pete,  looks like your trials and tribulations have paid off.  Glad hands next?  Rare Earth Magnets work great to hold and let apart.
 
Tom C.


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moose_the_caboose
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Re: Making plastic train parts?
 
« Reply #37 on: Feb 7th, 2014, 8:57pm »
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on Feb 4th, 2014, 7:47pm, BobbyT wrote:       (Click here for original message)
WOW Pete, you keep this up and you will have to build more cars to put these on. From the photos they look like they came out real nice.

 
heck!  keep it up pete...i'll pay the freight on a couple!  i know a couple more guys that would love to have one or two.  just sayin'...they are looking good, when they meet your approval, let us know.
 
moose


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fred_55
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Re: Making plastic train parts?
 
« Reply #38 on: Feb 8th, 2014, 3:04am »
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on Jan 17th, 2014, 10:11pm, moose_the_caboose wrote:       (Click here for original message)

 
 
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.
 
 
moose

 
Back to playing trains, eh
 
Result is good enough for me, but not good enough to sell. I don't need any more, and I have the mold, so if you want the pattern, I'll give it to you so you can RP it.  PM me with your address if you interested.
Pete


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moose_the_caboose
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Re: Making plastic train parts?
 
« Reply #39 on: Feb 8th, 2014, 5:50pm »
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on Feb 8th, 2014, 3:04am, fred_55 wrote:       (Click here for original message)

 
Back to playing trains, eh
 
Result is good enough for me, but not good enough to sell. I don't need any more, and I have the mold, so if you want the pattern, I'll give it to you so you can RP it.  PM me with your address if you interested.
Pete

 
pete, pm sent!  thanks!


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