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some notes on Resin Casting

Started by JohnP, July 31, 2010, 09:51:22 PM

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Ray Dunakin

Fantastic series of posts! Thanks for providing so much useful information!
Visit my website to see pics of the rugged and rocky In-ko-pah Railroad!

Ray Dunakin's World

Hauk

#31
Quote from: JohnP on August 22, 2010, 07:28:57 PM
Class dismissed, any questions? :)

Yes, one rethorical question.
Is this the best tutorial on resin casting ever posted on the net? I would say so.
Thanks a lot for releasing such an amount of knowledge into the public domain.

And a question for Russ as well:
What Annual do you plan to run the article in?

-Haavard
Regards, Hauk
--
"Yet for better or for worse we do love things that bear the marks of grime, soot, and weather, and we love the colors and the sheen that call to mind the past that made them"  -Junichiro Tanizaki

Remembrance Of Trains Past

JohnP

Haarvard,
I was very frustrated with the info available for precision resin casting. So I started this thread and decided to share pretty much everything. There are still many fine points that come with personal experience as the modeler tries things their way.

Such as, I have found that when plastic-type parts are laser cut they can get a bit of an uneven edge. When that is made into the mold, it can create a tiny undercut in the rubber. So, for example, when thin parts like my lacing strips are pulled out, they catch and break. I now sand the edges of master parts to break the corner.

More later, and thanks,

John
John Palecki

finescalerr

HÃ¥vard, John has to tell me when he is ready and send me the photos. When the material is here I will schedule the article.

Guys, I am interested in publishing many of the things you work on but I don't "assign" articles. As I have said before, I need good photos and drawings; nothing gets done without them. There is never a deadline; when I receive the graphics I schedule the article. If you can't or don't like to write, we'll do it by phone: I'll call and take notes.

If you want to get published, please let me know. If I already have asked you about an article and you have finished the model, please let me know. If you need help with photography, please refer to the sticky on that subject.

I think Ken Hamilton owes me a lumber carrier article and, when he finishes the new lumber loader diorama, we'll publish that , too. Chuck's rapid prototype parts will appear in the upcoming Modelers' Annual and the whole diorama will appear next year if it's finished. Jacq will put together a very comprehensive article on his lumber mill layout. Nick owes me articles on a couple of things but he's standing in the corner so probably has been unable to work on them. Marc will do some articles. And there are others.

Just get them to me before I retire, okay?

Russ

JohnP

I need to make the rest of the bridge now, finish it and take beautiful photos of it. I want the resin casting to have a focus. Dave DaKra will be laser cutting some parts for his forum SBS. Once I have all the material in hand, I can edit the info into an article form and send it to Sir Editor and Publisher.

In the late '90s and later I wrote a number of articles for Hundman's N-Scale magazine. That was always satisfying, but if this project article is successful, hoo-wee I'm getting top shelf bourbon and anoint the book, the model and mostly myself. I'll post a You-Tube of the dance.

Russ, what ever happened to The Railroad Man and his ritual dancing, cheesepuffs, etc?

John
John Palecki

finescalerr

The Railroad Man is now 72 and has slowed down a little. Worse, he and his wife moved up to Tacoma so I rarely get to hang out with him although we talk regularly on the phone. At the moment his big enthusiasm is 1:20.3 scale live steam ... as a dilettante, of course. I don't know whether his wife lets him eat cheese puffs very often. I suspect he sneaks in the secret Railroad Man dance now and then. -- Russ

DaKra

Guys, I've just got some of John's parts in-hand, and I have to tell you, as good as they look in the photos,  the photos don't do them justice!  :o Everything looks exactly as it should, the rivets are all perfectly formed and spaced.   Some of the parts are paper-thin, but perfectly cast, no warps, no bubbles, and really strong and flexible.  Even the post office couldn't destroy them.   You can see on the thread the thought and effort John put into developing his techniques, and it really shows in the finished product.   Amazing work! 

Dave

finescalerr

Imagine the quality of the model(s) we could produce as a group were we to harness the talents of about a dozen of our contributors! -- Russ

JohnP

Dave is being nice. Of course, he shares my views, and the views of others here, that things in the model railroad hobby world have become stale. So we have gathered together to display our techniques and results.

Meanwhile, I am sure Russ has in mind a reality show with the 12 modelers living in an old Southern Pacific station in the deserts of Arizona. What could possibly go wrong?

Actually, what is amazing here is that the models and processes are accomplished with fairly simple tooling and hand-done techniques, or like with Dave using sophisticated tools in new creative ways (show them the pies yet???). It has been proven that the Chinese are capable of making very detailed models based on engineering drawings from US companies. But that is all done with automatic micro-precision EDM machines and whatever else they use to make molds. Precise, cold, lifeless models anyone can buy. We do it with imagination and personal determination, and the unique results speak for themselves.

John
John Palecki

marc_reusser

Wow! This thread and tutorial has been simply outstanding. Thank You!



Marc
I am an unreliable witness to my own existence.

In the corners of my mind there is a circus....

M-Works

JohnP

You are all welcome. I will get the entire bridge done soon. It should be a sweet, simple model. And if I think of any other casting stuff to write I will do it here.

John
John Palecki

sd80mac

This thread has been extremely informative and I really appreciate you taking the time to share it with us (and me personally!) I have a question regarding thin castings. How thin have you been able to get them with consistent results? I am designing a master who's wall thickness I am trying to keep between .020" - .030". Would you consider this unrealistic?

Thanks,
Donnell

JohnP

SD80MAC- you from Mass? I saw those Conrail beauties when they were brand new on the B&A up the mountain. What a sound they made. Software sucked though at first- a train going by me stalled, the engineer was panicking on the radio, the dispatch told him to reboot the computer. After a restart away they went, starting on the hill and accelerating to track speed in less than one train length. Must have used Windows Vista.

.020" - .030" is pretty thin. I have many parts in the .015" - .020" range that cast very well when the mold is new. But, sometimes within 8-10 castings, the resin byproducts have already swelled up the rubber so I get thin spots. Your best bet is to design parts with edge areas that thin but beef up the body of the part so you can tolerate dimensional changes. The art of deception. Another thing to try is to apply a barrier coat first to the rubber before every casting. I am planning on running some experiments to see how DullCote works. The resin byproducts won't penetrate the rubber with the spray, and the spray creates the outer layer of the casting. I have read that mold release is useless for that, and all it does is grease up your fragile parts so paint won't stick. So if you are going commercial work it out first. For a handful of repetitive parts for you and friends, make the parts thin.

Meanwhile, for everyone keeping track of this, I had a nice customer post some good words about my bridge on a Yahoo On3 group forum. I have been inundated with orders and am booked through January. This volume, and the problem with the thinner parts, has lead me to try brass etching for the thin lacing parts on the next bridge.

And to think- I had just bought paint, salt and hairspray to take a break and try rust weathering. Someday, maybe, I'll finish that little Phoenix bridge so Unc Russ has an article....

John
John Palecki

sd80mac

#43
Hi John,

I'm actually in Southern California. I had some minor issues like that with early GEVOs  back in '06 (I'm a furloughed UP engineer).

The project I'm working on is a TT scale International wide-vision caboose. It's a farily small project at just over 3.5" long. The plan was to get an RP master printed and then make resin copies. Model was drawn in subsections that would be assembled into the final piece. The parts included the main body, roof, cupola, cupola roof, and underframe. However, I'm thinking of breaking the main body and cupola down into a series flat parts, about .040" thick with some sort of tabbed indexing to help align the many pieces.

I really like your idea of a two-part injected resin mold, and the results of your system yield professional quality parts with the ability to add crisp detail on both sides. Plus, it utilizes much less rubber than a more conventional, deep cavity mold.

Thanks again,
Donnell

Quote from: JohnP on November 10, 2010, 04:31:22 PM
SD80MAC- you from Mass? I saw those Conrail beauties when they were brand new on the B&A up the mountain. What a sound they made. Software sucked though at first- a train going by me stalled, the engineer was panicking on the radio, the dispatch told him to reboot the computer. After a restart away they went, starting on the hill and accelerating to track speed in less than one train length. Must have used Windows Vista.

.020" - .030" is pretty thin. I have many parts in the .015" - .020" range that cast very well when the mold is new. But, sometimes within 8-10 castings, the resin byproducts have already swelled up the rubber so I get thin spots. Your best bet is to design parts with edge areas that thin but beef up the body of the part so you can tolerate dimensional changes. The art of deception. Another thing to try is to apply a barrier coat first to the rubber before every casting. I am planning on running some experiments to see how DullCote works. The resin byproducts won't penetrate the rubber with the spray, and the spray creates the outer layer of the casting. I have read that mold release is useless for that, and all it does is grease up your fragile parts so paint won't stick. So if you are going commercial work it out first. For a handful of repetitive parts for you and friends, make the parts thin.

Meanwhile, for everyone keeping track of this, I had a nice customer post some good words about my bridge on a Yahoo On3 group forum. I have been inundated with orders and am booked through January. This volume, and the problem with the thinner parts, has lead me to try brass etching for the thin lacing parts on the next bridge.

And to think- I had just bought paint, salt and hairspray to take a break and try rust weathering. Someday, maybe, I'll finish that little Phoenix bridge so Unc Russ has an article....

John

JohnP

GOOD NEWS!!!

I have found a mold release that protects my RTV from the urethane secondary products.

Somewhere in this thread I explained that my casting process is great except for a mysterious expansion of the RTV. The rubber swells until it will not fit in the mold box and all the features are squeezed shut. With my thin designs, this was happening within 6-8 castings. That was intolerable at best and made the business doubtful. I knew a mold release would help as a protection but they all needed to be cleaned off for bonding and painting. My thin casting would not withstand solvent scrubbing.

But this product works like a charm: Ultra 4 Urethane Parfilm Paintable Mold Release by Price-Driscoll. http://www.price-driscoll.com/formulations.html

I have used it on a new set of molds and have multiple castings from each mold without any sign of the dreaded swelling. I sprayed it an all rubber surfaces the first time, then on the pattern surface every casting. The parts drop out of the molds within spec. It has also allowed me to use molds that were getting marginal, and I got about 10 more shots out of them so far.

I also sprayed parts with PollyScale acrylic paint. Water based paint performs the worst on a contaminated surface. The paint went on smoothly with no fish-eyes or creep-back. It adhered as well as any other PollyScale paint. It seems the Ultra 4 becomes part of the top surface of the urethane. If it is sprayed on lightly per the instructions, it is not noticeable to the touch like regular mold release is.

I am quite pleased with the product. I recommend it if you are doing even a few hobby castings. I bought it at The Complete Sculptor http://www.sculpt.com/. They have a good selection of casting supplies including the Ultra 4.

John
John Palecki