Large Scale Central

Resin casting theory question

Modeling Technical Modeling
#1

OK I have not gone down the road yet of casting but I know I will be. I have a model car shell that is cast in resin but it looks as if the maker smooshed a more or less paste type resin into an open mold. The exterior had very fine detail but the interior is rough and has finger prints not that I care.

This has me thinking about an HO project that someday I would like to return to. It is a GP-9 low hood.

I would need three of them. How would one go about casting three identical shells after making the blank? None of the comercially available locos are right. Most all are high hoods and the few low hoods don’t have the correct fans. They are correct for GP-9s as first built but not the way St Maries has them. Instead of buying a whole bunch of detailing parts and bashing High hoods i was hoping to make shells to go on the high hood chassis.

Seems Walthers has a whole line of GP-9M which are the low hood version but still are not really very accurate so i would likely bash one of these for a blank then hope to cast three

#2

I have never done a loco shell myself, but I did do a uni-body mold for a caboose in HO scale. I would say what you’re talking about is possible. If you’re new to resin casting though, I would recommend starting with some simpler molds, then working your way up (to avoid some frustration). Two-part molds can be tricky.

#3

Burl Rice said:

I have never done a loco shell myself, but I did do a uni-body mold for a caboose in HO scale. I would say what you’re talking about is possible. If you’re new to resin casting though, I would recommend starting with some simpler molds, then working your way up (to avoid some frustration). Two-part molds can be tricky.

Thanks Bruce,

That’s why it is a theory question. Not something I want to do tomorrow but someday. I will do a lot of G scale casting before returning to my HO project.

#4

Get Mark to print them for you.

#5

John Caughey said:

Get Mark to print them for you.

I have thought about this already. I have a guy who is printing those wheels for me. I might see what he can do. definitely an option.

#6

Go to Raw Material Suppliers home page. They sell RTV monomer for making rubber molds and polyurethane resins for casting. These are non causitc enviromentaly friendly materials. Cost is reasonable price and so easy to work with I use it for cub scout projects. Email them about your project and they will reccommend the right products and walk you through to process. You will probably need their test kit(small volume).

#7

Just a teaser, but I did a webinar at the office today, and what is being 3D printed these days is UNBELIEVABLE. What we do is a spit in the ocean. They are printing fuel nozzles for jet engines, bio-medical stuff, there is a company in the Netherlands printing 1:1 housing out of sand.

What ever the mind of man can conceive and believe, it can achieve.

#8

Thanks for the suggestion Thomas, I will check them out. Maybe not for this project but I am going to get into casting very soon

Bob,

Technology is interesting. Over at that other site a project bloomed. I (living in Idaho) asked a question much like this one about a future need to print 1:20.3 ten spoke 48"drivers for a loco build. In that I find out that Kevin Strong (in Colorado) is in need of the same driver as he is modeling the same exact locomotive, not the same type, but the exact same loco after it was purchased from my prototype by his prototype. So the question was raised if these could be printed (I was naive of the capabilities). I member who lives in Holland who 3D prints for a living and as a hobby says he will do them for us just for the experience and a few bucks plus shipping. Now we need machined tires, so I jump on craigslist and asked if someone could make them. A gentleman who is teaching his kid how to use machining tools says they will do it for price of materials just to see if they can.

The Wheels are in production and the first one was printed. Looks amaing just like the real deal. So thanks to the computer age we have a turly international project and new friendships and further more I get to share it here.

Too cool.

#9

Devon,

To carry this a little further, your drivers could possibly be entirely printed, in metal (brass or stainless steel) using the Laser Sintered methodology. Not necessarily cheap, but they would be metal, and I understand they can hold toleranced in the .001-.002 range. No machining required.

I have just learned that the company I work for has a couple other divisions that have Additive Manufacturing equipment. I hope to learn what our capabilities and costs are.

#10

Are machine shops a thing of the past, or will they be like the blacksmith shoppe, just filling a boutique niche?

#11

3D Printing used to be called Rapid Prototyping, as the process got more refined and additional materials could be used the field got a bit wider.

Ed’s Gartenbahn started 3D printing some time ago — yes, RhB items are a specialty. He produces some of the items that many have been looking for in vain i.e. the big guys don’t see the mass market for that item. So someone comes along and fills the niche with items that are less expensive than the brass models, but more expensive than the injection molded items.

And then it’s back to: do I “need” it? do I like the price point? how much use will it get?

BTW I was surfing the model railway items on Shapeways, incredible how many items there are in the Z to HO range … and I only got to page 10 of 161 pages. Haven’t found the LS stuff, yet.

How much are we willing to pay for models (small to medium series items) produced by a “machine shop”?

#12

I was thinking of machine shops in the larger sense, not just as they apply to model railroads.

#13

Steve Featherkile said:

I was thinking of machine shops in the larger sense, not just as they apply to model railroads.

They’ll be around for a long time, but the skill set required to work there will change drastically e.g. used to be that a machinist used to run one machine. That went out the door as soon as automation started. As far back as 25 years ago running two machines and doing benching at the same time was getting very common in some tool rooms that were on my customer list.

i.e. the machines are getting smarter and there is less human intervention required, but they are still machine shops, as opposed to production lines.