Resin Casting

[iandt]

Hi all, new to the forum! Well, not new to reading it, but I hope now by posting that I can contribute to all the great information on this site!

I recently 3d-printed a prototype G43 gondola body in HO scale, and would like to make copies of this shell in resin. Unfortunately, I have tried my hand at casting a few times, and know that I do not have the skill to do it myself. Has anyone ever used a resin casting service, or had a friend cast for them, that they would recommend? I am not looking for a large order, just 15 or so good-quality shells, and being a college student I am sort of on a budget (this just means no $400-700 molds, like a few services I have contacted quoted me). The picture below shows the shell I'm talking about, to put it in perspective. Thanks in advance for any help!

[Green_Elite_Cab]

Why not just keep printing new models up? If its a cost thing, I don't think anyone is going to do this work for you and not charge you almost as much.


As far as your experience with resin casting goes, what happened? Have you tried to cast this model yet? What did you try?

It looks straight forward. I would pack the inside of the gondola with casting clay, but leave the edges exposed.

Then I would flip this over so that the underside was facing up, and put this in a mold box of some kind. This would let the bubbles travel away from the master. I would pour the rubber in a stream away from the model and let it fill in around the model. If you use a "thin" stream, you will reduce the bubbles you produce to almost nothing. Let this sit overnight or however long your rubber takes the cure.

Once this was done, I would peel out the clay, and put some mold release on the exposed rubber, and fill in the cavity with more rubber. the bubbles will again flow away from the deck of the gondola.

Once this is done, you're ready to go. Fill your mold with water and push the mold together, then measure the water volume that remains. Calculate how much of each part of resin you need, and pour them in separate cups to be sure before mixing them together. Like the rubber, poor in a long thin stream as soon as possible, and that will help reduce the bubbles. Microwaving the mold prior also helps.

You should have minimal defects.


Alternatively, rather than printing the whole gondola as one "master", You could just make the sides and the floor, essentially making a "kit" for yourself.

[nachoman]

Can you give us details about the 3-d printing? It looks like a clean print, and if it's possible to do the same thing 14 more times, that would probably be the cheaper and easier route. Is there a reason you can't just have more printed? I

[Sumpter250]

Hi all, new to the forum! Well, not new to reading it, but I hope now by posting that I can contribute to all the great information on this site!
I recently 3d-printed a prototype G43 gondola body in HO scale, and would like to make copies of this shell in resin. Unfortunately, I have tried my hand at casting a few times, and know that I do not have the skill to do it myself.

First: Welcome !!!
Second: That "printed" Gondola, looks GREAT!
Third: Give the first two lines of my signature some thought, and keep trying.
and lastly....... to our little bit of "Model Railroading Heaven" :mrgreen:
Looking forward to seeing a bit more of your work.

[iandt]

First: Welcome !!!
Second: That "printed" Gondola, looks GREAT!
Third: Give the first two lines of my signature some thought, and keep trying.
and lastly....... to our little bit of "Model Railroading Heaven" :mrgreen:
Looking forward to seeing a bit more of your work.

Thanks for such kind words, I will certainly be visiting this site often!

Why not just keep printing new models up? If its a cost thing, I don't think anyone is going to do this work for you and not charge you almost as much.

As far as your experience with resin casting goes, what happened? Have you tried to cast this model yet? What did you try?

3d Printing this one car cost $101, so there's no way anyone could justify printing multiple for that much. The problem is that the most common ABS 3d printers all "pixelate," in a sense, the model, and destroy rivet detail, subtle surface texture, etc. So the only way capture HO models cleanly is with a resin printer, which is expensive.

Basically the last few times I have tried to mold, it's been a number of issues. My mold designs have not worked, and the resin has hardened before it got into all parts of the model. I finally learned that I need to have an escape route for air to carry the resin through the model, but then I end up with bubbles. I would rather mold it as a single piece than in "kit form," as the last time I attempted casting thin panels I wound up with more bubbles, and resin did not fill the mold correctly.

I kind of boiled my bad experience down to one main issue: the last few times I have attempted molding I used Composimold, which captured the details well but was damaged with each successive casting and proved not to be very strong. Which mold material have you used in the past with success?

[sailormatlac]

Welcome aboard! This is a very interesting project. I face the exact same problem as you: making resin kit out of a 3D printed car.

Matt

[Green_Elite_Cab]

3d Printing this one car cost $101, so there's no way anyone could justify printing multiple for that much. The problem is that the most common ABS 3d printers all "pixelate," in a sense, the model, and destroy rivet detail, subtle surface texture, etc. So the only way capture HO models cleanly is with a resin printer, which is expensive.

Basically the last few times I have tried to mold, it's been a number of issues. My mold designs have not worked, and the resin has hardened before it got into all parts of the model. I finally learned that I need to have an escape route for air to carry the resin through the model, but then I end up with bubbles. I would rather mold it as a single piece than in "kit form," as the last time I attempted casting thin panels I wound up with more bubbles, and resin did not fill the mold correctly.

I kind of boiled my bad experience down to one main issue: the last few times I have attempted molding I used Composimold, which captured the details well but was damaged with each successive casting and proved not to be very strong. Which mold material have you used in the past with success?

I do hate the cost of 3D printing, but some pieces don't come out as super expensive. I was hoping this might be one of them.

I've been using Alumilite with some success. They sell a variety of resins and rubbers with different properties that might help you.

The mold rubber will break down over time, but Stuff like HS2 and HS3 (tough and rubbery, respectively) can withstand much punishment.

[Mr Fixit]

Firstly iandt welcome to Big Blue as a poster not just a guest.
Your 3D model looks great, so well done there!
I cant comment specifically on resin casting as I have yet to try it, but I have cast concrete, done various types of welding and hopefully soon I will be casting aluminium and I have learnt a few things. It all comes down to learning the most correct technique to use and repeated practice. When you first try anything, unless you are a freak of nature, you are bound to only see partial success and you have to use that experience as a benchmark to project yourself further forward. Failure can be discouraging, no matter who you are. It just takes determination and a sprinkling of intelligence to see that with some minor changes, success is just around the corner. Even taking too much time off from a project or task can result in failure as your skills can and will degrade with time as you and your mind forget things. We were discussing at work, how even just having a holiday can put you "off your game" as far as trade skills are concerned.
Another thing to look out for is technique adoption, whereby you observe or use a technique in one part of your life and then see if that technique can be used elsewhere.
Check out people on You Tube who offer up resin casting techniques as that may help you to learn where your problems occurred.
Your problem with air entrapment in the mold is also a familiar one for people who try various types of casting, be they casting in plaster, foam, green sand, formwork or cake tins.
As far as bubbles in your resin mix, one tip I have seen used when casting water features is to use a stick or tool as a chute to pour the resin down to the molding surface to avoid air bubbles.
Another tip maybe to use a vibration device to help settle the resin into all the parts of the mold and float up any air bubbles.
If your resin is going off too fast before it reaches all of the mold, take note of how much hardener used and reduce it by say 10% in the next pour. If properly mixed it will still go off only more slowly.
Mark

[iandt]

As far as bubbles in your resin mix, one tip I have seen used when casting water features is to use a stick or tool as a chute to pour the resin down to the molding surface to avoid air bubbles.
Another tip maybe to use a vibration device to help settle the resin into all the parts of the mold and float up any air bubbles.

It's actually kind of ironic for me that you say this, the other day in studio we were attempting to cast models in Rockite (in case you don't know, basically just portland cement without any aggregate or other additives) and found out how to fix many of the techniques you mentioned. We even used an oscillating grout remover tool with a stick attached to vibrate the cement down into our molds! Very cool stuff, just never realized that I could apply it to resin casting.

I've been using Alumilite with some success. They sell a variety of resins and rubbers with different properties that might help you.

The mold rubber will break down over time, but Stuff like HS2 and HS3 (tough and rubbery, respectively) can withstand much punishment.

Is HS3 the pink or blue rubber stuff, like I've seen used in Model Railroader? Ever since I tried with Composimold I couldn't help thinking that my molds may work better if I tried this stuff. Especially since I want to repeatedly reuse the mold. I appreciated the step-by-step ideas you gave me in your first post, I have been thinking about how to make a better mold and try it again. The only thing I can't figure out is where to put the conduit to pour into and the conduit for air to escape without trapping some bubbles around the gondola body, or without having a significant area to carve away afterward, do you have any ideas for these? Questions like this are basically the main things that discouraged me from trying to cast again.

[AF350]

Do not give up too easy on casting just yet. I tried alumilite and it sets up too fast for me.

I use mold rubber and casting resins from smooth-on that I get from Blick art supplies, also have used EZcast or is it castEZ anyway there are more than one supplier out there. Micro marks starter set is a good place to start, but I would not buy the stir sticks and disposable measuring cups as you can save money by going to a dollar store to buy a big bag of wood craft sticks and clear disposable cups. If you use a 1:1 ratio by volume you do not need a marked measuring cup anyway.

Before investing in materials there is a DVD sold by micro mark showing the in and outs of one piece and two piece molds using rubber molds and casting resins I recommend that DVD and watch it a couple times then have at it(oh rubber gloves are highly recommended as uncured resin and molding materials are eye and skin irritants.).

My first attempt of molding was a gondola in S gauge it was simple compared to your model as undercuts can make the molds wear out quicker.

By the way did you print the model your self or was it from shape ways? Desktop 3D printers are getting better capabilities wise but the price range varies from a few hundred to a couple thousand dollars per machine and can take a long time to print out larger items (even commercial 3D printers are slow). Hope this helps some. Also check the all other hobbies section of big blue there is a thread on casting and molding and one on 3D printing that may be of interest as well.

[Mr Fixit]

Getting hold of that DVD sounds like a good idea to me, then watch it until it drives you crazy, take notes, make crib notes and then do some pouring. Examine the pours afterward, then re-watch the DVD again to problem solve the issues.

I do similar sorts of things with my welding, practice, do small jobs, examine every weld and the overall job, watch my favourite welding channel regularly, closely examine welds on everything. I dont claim to be an expert by any means but my welds work and look fairly good, so I am now known for my welding skills.

Mark

[Green_Elite_Cab]

As far as bubbles in your resin mix, one tip I have seen used when casting water features is to use a stick or tool as a chute to pour the resin down to the molding surface to avoid air bubbles.

This is also recommended. This is how I do things in the laboratory to avoid splashes or bubbles.

You can also get a pressure cooker style device (though it costs $180) that removes the bubbles, but this is more for clear castings like window.

Is HS3 the pink or blue rubber stuff, like I've seen used in Model Railroader? Ever since I tried with Composimold I couldn't help thinking that my molds may work better if I tried this stuff. Especially since I want to repeatedly reuse the mold. I appreciated the step-by-step ideas you gave me in your first post, I have been thinking about how to make a better mold and try it again. The only thing I can't figure out is where to put the conduit to pour into and the conduit for air to escape without trapping some bubbles around the gondola body, or without having a significant area to carve away afterward, do you have any ideas for these? Questions like this are basically the main things that discouraged me from trying to cast again.

Its a specific type of casting rubber sold by alumilite. HS2 Is "Tough and Strong", very stiff but difficult to damage. HS3 is strong and highly flexible and stretchy, good for smaller molds with lots of details. HS3 is probably find for small stuff but HS2 will hold its shape better for bigger stuff.

All of it comes out light Pink. The only rubber I've seen that is blue (but I haven't seen all!) was the Micromark rubber, which I don't necessarily recommend for this project. Its fine for small simple stuff, The Alumilite is a better product for larger and/or more complex pieces.


You don't really need to worry about conduits or anything. The type of mold I suggested is called a "Squish" mold. You quickly pour the resin into one part of the the mold, then squish down the other half. When you squish to the two pieces together, it completes the mold and excess resin flows up into the seams between the two parts making some flash. If there aren't a lot of bubbles in your resin when you introduce it to the mold, you will probably not introduce to many additional bubbles, if any. Even if you do get some bubbles, they shouldn't be impossible to fix with some filler and polishing.

"Injection" molding can really only be done under high pressures, and that is not going to be the kind of molding you'll be able to do at home.

[iandt]

So, thanks to your guys' encouragement I ordered an 8oz starter RTV mold kit off eBay, I figured this was enough to get started and if not I'll just order more. But, I will keep in mind all of your tips (thanks very much! ) and update y'all as I go!

I didn't know that I could mold by simply pouring the resin on top and then smashing it down, I tried doing this before and had a problem with bubbles. Though I had equally bad luck with having two sprues for circulation, so I'll try the "smash" method first by simply squishing the top of the gondola down into the bottom.

Also, I do have a few articles on resin casting clipped from various magazines that I have been studying over the last day or so, but I feel like a DVD may be even more useful as well and will probably get one soon. I'm a "learn as you go" person though so I may try first anyway and then, when I fail, go learn the right way to do it lol.

Anyway, thanks for all the encouragement, and I will certainly post updates as I go!

[dave1905]

For casting your gon I would do a "squish" mold. It consists of a frame that hold the "female" half of the mold and then another frame that is keyed into the other mold that holds the male portion of the mold in alignment.

You put resin in the female portion then insert the male portion and "squish" the resin be tween the two mold halves.

I have used it to make "wooden" gondola shells.

If you look at different resins they have different set times. For a two part mold you need at least a 2-3 minute time. Alumilite sold a resin like that but not in small quantities, so I went to Hobby Silicones and got the equivalent from them.

I use a pressure tank to minimize bubbles in my castings. Its one of those pressure tanks for a paint sprayer, about a 2 gallon tank. I pressurize it to about 40 psi. I also have an incandescent spot light I shine in a container. After the castings come out of the pressure tank I put the molds/casting in the container with the spotlight, which warms up the casting and makes sure the thin sections fully cure.

[dave1905]

Here is a picture of my frames I use for my squish molds:


the master is put in the mold upside down and and keeper rods inserted:


The RTV is poured into the lower mold:


The mold is turned right side up and the upper frame is placed and poured:



Remove the upper portion and the mold and you have a completed mold. Removing the keeper rods allow the molds to be slid out of the frame: