Resin Casting

[johnh35]

Just wanted to get some opinions from those of you who resin cast. I have done a fair amount of casting in the past, but haven't done much since moving to California 5 years ago. I have always used the Micro-Mark 1 to 1 Rapid for making my molds and like it, but have tried several resins with mixed results.

As far as resins go, I have used the CR-600 from MM, Easy Flo 60 from Bare Metal Foil, and Smooth-Cast 321. I have typically had the best results with the CR-600, though the 321 seems to be about the same (I have heard that Smooth-On makes the CR-600 for MM but do not know it to be a fact).

What resins and mold material do some of you use and why do you favor those?

[kornellred]

It seems as though you have chosen three of the more popular casting resins on the market - from my own experience, I would conclude that Smooth-On supplies Micro-Mark with their own products which are separately labeled and packaged (and sold for a slightly higher price on a volume basis).
You should get a wide variety of responses to your questions since there are so many chemical companies with skin in the molding and casting game.  And there are many types of two-part resins, epoxies, and RTV rubbers, their differences having to do with Shore A or D hardness, cure and de-molding times, and the like.
Resin casting is simple in theory, after the science of selecting the appropriate materials is accomplished.  But then, there is the art of producing quality castings, and that takes practice.

[randgust]

I'm using the 10:1 high strength (pink stuff, not blue), with the Ease release 200 spray, and CR600.  I also use the thinner when the 10:1 gets too thick to pour.   I have a high-precision digital scale I use to get the mix right with the pink catalyst

Frankly the entire thing works so darn well that I'm not interested in expirimenting.   I don't have problems with the CR600 shrinking and it seems like everybody else using other materials is having to design in a shrink factor.

If I'm really careful on mold design I'm getting well over 50 parts per mold before I have to replace the mold.  I was lucky to get 15-20 out of the 1:1 before something tore.

I'm running a LOT of parts, guys, about as many as you can make without stepping up to a machine process.   With all my kits, multiple molds, etc. I probably have over 200 molds developed and make parts almost every evening in the winter.

[DKS]

I've found the Micro-Mark 1:1 Rapid mold material to have very limited use. It's OK for quick test molds, but its lack of strength makes it pretty much useless for production molds. My mold material of choice is Smooth-On Mold Max (10, 20, 30 and 40, depending on the application); depending on the complexity of the mold, they last for 50-100 castings or more.

For resin, I use Smooth-Cast 305 and 310 the most, but I have about a dozen other types on hand depending on the application. I never use mold release, thinners, or any additives (other than Smooth-On So-Strong dyes) as I've found that they compromise the casting quality.

[zephyr9900]

Back when Dick Billings cast our Pioneer Zephyr bodies, he used a resin that was the color and viscosity of skim milk (which would be 3 or 4 cps).  He literally put part A in one small paper cup and part B in a second small paper cup, and poured them back and forth together to mix before filling the molds.  All I know of the resin was that a group of Southern California small manufacturers did a cooperative buy of one or more 55-gallon drums of the stuff.  Parts I have kept boxed up for the last 17 years still smell "resiny".

I see that the EasyFlo 60 has a mixed viscosity of 60 cps and the Smooth-Cast 320 has a mixed viscosity of 80 cps, which is significantly higher and around 5 wt. motor oil.

Just some musing because I never found out what Dick's resin was.

Randy
http://www.prototrains.com

[DKS]

I see that the EasyFlo 60 has a mixed viscosity of 60 cps and the Smooth-Cast 320 has a mixed viscosity of 80 cps, which is significantly higher and around 5 wt. motor oil.

I used to be concerned about the viscosity of Smooth-Cast, but once I started high-pressure casting, all of those concerns have gone away. The exhaust stack is .015" wire, and the control levers are .010" wire. After hundreds of castings, I have yet to have the mold fail to fill properly.

[superturbine]

Silpak...... There is nothing better.

[johnh35]

Silpak...... There is nothing better.

Which resin do you use?

[zephyr9900]

That is one sweet casting, David, given your reference dimensions!  And a nice photograph of a tiny subject.

After hundreds of castings, I have yet to have the mold fail to fill properly.

Is that hundreds of castings from a single mold, David?  If so, I'm amazed (and impressed).  Dick could only get 25 or so castings from a mold before it absorbed enough solvents to swell out of tolerance.  The design of the PZ incorporated printed circuit boards as the chassis, and the upper body shells had to remain within .005-.010" or so in length to screw on properly (and for the details of the upper shell, which was free, to match with the details of the underbody, which was cast onto the PCB)

Randy

[DKS]

Is that hundreds of castings from a single mold, David?

No, that's across several molds. This particular casting is a bit on the complex side, and that takes its toll on the mold. I have some other simpler molds that have produced over a hundred castings and are still going strong.

I have one mold that produces a part which must exactly fit into an injection-molded piece. The castings fit precisely, so I don't have much concern about shrinkage, at least for castings in the range of less than 3 inches or so.

[LV LOU]

I've found the Micro-Mark 1:1 Rapid mold material to have very limited use. It's OK for quick test molds, but its lack of strength makes it pretty much useless for production molds. My mold material of choice is Smooth-On Mold Max (10, 20, 30 and 40, depending on the application); depending on the complexity of the mold, they last for 50-100 castings or more.

For resin, I use Smooth-Cast 305 and 310 the most, but I have about a dozen other types on hand depending on the application. I never use mold release, thinners, or any additives (other than Smooth-On So-Strong dyes) as I've found that they compromise the casting quality.

Couldn't say it better,1:1 mold material is useless.It's the difference between hardened silicone rubber,and cheese.I also use Mold Max,and Smooth Cast resins.I really like the 322,it's really "wet" fills out really well.I also use the So-Strong dyes,very potent stuff.I do occasionally use their silicone thinner,but only if my Mold Max is getting old.Better to have a mold that will only cast twenty pieces than throw the stuff away.I do use a touch of Smooth On Mold release between castings.

[LV LOU]

I used to be concerned about the viscosity of Smooth-Cast, but once I started high-pressure casting, all of those concerns have gone away. The exhaust stack is .015" wire, and the control levers are .010" wire. After hundreds of castings, I have yet to have the mold fail to fill properly.

Pressure casting is the only way to go.It's almost impossible to get perfect castings without it,especially on something like a locomotive shell.I get very close to 100% on my castings,also.I probably get 40 or more castings out of my molds before they start to show signs of wear...On this shell,it usually starts on the stack lip,because it has such a sharp edge..

[wazzou]

Whatever you do, don't use any of the Alumilite products.  They are notoriously bad for shrinkage.
I never was able to determine if the mold shrank or the resin castings or it was a combination of the two.
CR-600 was finicky with respect to humidity, for me. 
I'm definitely interested in learning more about pressure casting.  It looks like a lot of detail can be captured without risk of incomplete fills and distortion.
I've certainly experienced some frustrations and probably have batted .500 or less on usability, on two part castings, anyhow.

[pnolan48]

I've used very hard polyurethane molds (S60-80) for simpler parts without undercuts, and run 100s of casts before any degradation. These require mold release, and still can be murder to break from the mold, especially if the mold is deep. With silicon molds (S30 and 40), I've run up to 30 casts so far without any degradation. These experiences are for small details; casting large ship hulls is a whole different world. The casting material seems to be fairly consistent in behavior no matter the supplier.

[superturbine]

Which resin do you use?

Silwhite