Resin Casting

[Angus Shops]

I also use Smooth On products, specifically Mold Cast 30 and Smooth Cast 300. Both seem to work very reliably. The 300 is the fast cure white; I've also tried Smooth Cast 305, which is a slower cure, but I found it to be less reliable. The 2 minutes or so you have to use the 300 is plenty of time for me. Decent products, with smaller quantities available at reasonable prices. And there is a retail supplier close to me.

Contrary to others, I have no trouble filling bubbles in my castings with additional resin. Once filled and cured it is as solid as any other part of the casting. Works for me anyway.

I also agree the pressure and vacuum is probably a really good idea, but for somebody interested in getting started in casting, they can probably get started without making the investment immediately.

Geoff

[peteski]

I also agree the pressure and vacuum is probably a really good idea, but for somebody interested in getting started in casting, they can probably get started without making the investment immediately.

Geoff

For an example of simple 1-piece open-mold casting (using Smooth-On products) see https://www.therailwire.net/forum/index.php?topic=28541.0 .

[jimmo]

I also use Smooth On products, specifically Mold Cast 30 and Smooth Cast 300. Both seem to work very reliably. The 300 is the fast cure white; I've also tried Smooth Cast 305, which is a slower cure, but I found it to be less reliable. The 2 minutes or so you have to use the 300 is plenty of time for me. Decent products, with smaller quantities available at reasonable prices. And there is a retail supplier close to me.

Contrary to others, I have no trouble filling bubbles in my castings with additional resin. Once filled and cured it is as solid as any other part of the casting. Works for me anyway.

I also agree the pressure and vacuum is probably a really good idea, but for somebody interested in getting started in casting, they can probably get started without making the investment immediately.

Geoff

Geoff, I'm not sure I follow you when you say that you found 305 "less reliable." The only difference in the 300 line of resins is the cure time. For small or quickie jobs I would recommend 300, but in my case I am always filling multiple small molds so a longer pot life is crucial. I have no problem with 305's reliability, especially since I pressure cast.

Filling bubbles in cast resin parts only works when the hole is deep enough to get a hold or the insides of the opening are concave enough to hold the fix in place. Another technique that helps is to rough up the inside of the opening so the new resin has a tooth.

Epoxy is fine if you have 24 hours to wait but I rarely have that option so filling with gap-filling CA and a kicker is instantaneous. I use Insta-Flex+ because I have found that the slight flex makes it less likely to shear under pressure or come lose if the resin is flexed.

Another thing that I often hear whenever there is a discussion about pressure and vacuum. Don't go half-a$$ on equipment when you consider a pressure pot. I have read in forums where the person giving advice tells about buying a cheap Harbor Freight pressure pot then attaching clamping points to the lid with JB Weld. Later he narrowly missed getting seriously injured when the lid blew across the room when the JB Weld failed. Good pressure pots are not expensive and are worth the investment.

[jimmo]

My casting equipment is finally out of storage. If you would like me to cast the parts, PM me.

Are you buying new rubber and resin or using stuff you had stored? If you had your old casting supplies stored, they are expired by now. It only has about a three month shelf life under ideal conditions.

[Lemosteam]

For an example of simple 1-piece open-mold casting (using Smooth-On products) see https://www.therailwire.net/forum/index.php?topic=28541.0 .

@peteski how did you prevent bubbles both when mixing the silicone and pouring it in the example above?  I REALLY struggle with this.  it is not as simple as what you show, at least from my experience-  I get very frustrated trying to get bubbles out.

[Doc Frankenfield]

getting bubbles out of the RTV is simply a matter of bringing to vacuum and then back to atmospheric pressure several time. the longer the setting time for you RTV the better chances that it will have fewer bubbles.
it looks like when you pioured the mold you poured OVER the master, trapping air.
 I usually pour froma far corner of the Mold box and do so slowly, allowing the RTV to seep innto the master, you can also manipulate the RTV as you pour by gently poking as you pour.

[Alaska Railroader]

......One well-respected modeler/manufacturer (not going to mention any names but his initials are DKS) gave me some great advice about what kind of device I could use for my casting challenges. The hotly debated subject of pressure or vacuum has been around for as long as I have been aware of such things. Simply put it was recommended to me to purchase a 2-1/2 gallon pressure pot and use that to make both molds as well as my resin castings. Since that time I have been able to make flawless castings regardless of atmospheric conditions.....

The loss of this same person is why I would like to find someone willing to cast from masters for me. Just small stuff that I can include with kits. A friend of mine is one heck of a skilled 3D drawer but Shapeways is still Shapeways. Resin is awesome. Let me know if any of you are willing and how much....

[Angus Shops]

Re Smooth Cast 305: I'm perfectly willing to admit that I've only used it once and it's possible that I should try it again. I ran into trouble with a slight foaming issue, similar what can happen when old products are used. Maybe it was old... Using the 300, I only cast the parts I know I can manage in the short setting time, but I do it repeatedly during a casting session. Also, I'm not really doing all that much; if I can produce the parts for 5 cars during the course of a day, that's pretty good for me.

As for avoiding bubbles in the RTV without using vacuum, I use an old paintbrush to 'paint' the RTV onto the surface of the master part, building up a modest layer over the part before pouring the rest over the master . This allows me to tease out any little bubbles on or close to the surface of the master. They are easy to see in the thin layers of RTV as it is painted on. Masters with a lot of surface detail tend to trap bubbles more easily than smooth surfaces, but even smooth surfaces can 'attract' little bubbles on their surfaces. Building walls with lots of tiny wndow mullions are particularly difficult as bubbles will get stuck between the mullions unlless they are carefully watched and the bubbles removed.

My purpose in expounding on my 'low tech' casting techniques is to encourage modellers to experiment in a modelling technique (resin casting) that can really produce great results without a huge commitment in equipment. I fully agree that vacuum and pressure makes the process more reliable, but pretty good results are still possible with the extra gear.

[peteski]

@peteski how did you prevent bubbles both when mixing the silicone and pouring it in the example above?  I REALLY struggle with this.  it is not as simple as what you show, at least from my experience-  I get very frustrated trying to get bubbles out.

@Lemosteam , I answered your question in the original bumper car thread.

[Lemosteam]

@peteski Did I ask the exact same thing then? 

[peteski]

@peteski Did I ask the exact same thing then? 

No, No! Relax, you aren't getting *THAT* forgetful.      I answered your question tonight. But for continuity I put the answer in my original thread and linked to it from here. 

[daniel_leavitt2000]

With all this discussion, do you think it would be worth it to do a start-to-finish how to?

[Lemosteam]

^^^^^^^^^THIS^^^^^^^^^ with detailed pics!!!!

[glakedylan]

^^^^^^^^^THIS^^^^^^^^^ with detailed pics!!!!

+1

would be a great learning experience
thx
G

[daniel_leavitt2000]

Ok guys. I tested my new equipment tonight and everything seems to be working. I'll start on the project over the next few days and post to a new thread.

I'll link that here.