Resin Casting

[DKS]

Silwhite

What are the properties that makes it superior to other products, such as Smooth-Cast?

[randgust]

I'll second the motion that CR600 hates humidity.  I keep a humidistat right on the casting table, and if it hits 70% and the dehumidifier can't pull it below that, I shut down casting until it does.  Just not worth it, it foams, and the more humid it gets the worse it is.

The biggest single breakthrough I ever made (and it was suggested to me on a forum, so I pay it forward) was using fiberglass boat repair syringes for injecting the casting resin into the molds under pressure.  When you've got a 7-minute work time with CR600, you can't be dripping stuff out of a cup.  Injection, rather than gravity, solves about 80% of the problems on mold filling, bubbles, etc.  But the molds have to be designed to use bottom-fill gates and air bleed sprues to do it.  But wow, did it ever speed up the process and improve quality.

[LV LOU]

Randy,have you tried pressure casting? Few worries about humidity unless the resin is REALLY old.I use slow stuff,Smooth on Smooth Cast series,and a pot.I do maybe a dozen casting at a time in the pot,fill them up,put them,put the air to them,a few hours later,take them out,look like injection moldings.I only do really simple stuff by pouring.By the way,Smooth on resins are cheaper that Micro Mark,and the range they have on different resins is amazing.

[Lemosteam]

Do you guys add vent holes in the mold, or do you simply rely on pressure to force the resin into the mold?

[LV LOU]

John,I do put vent holes in the corner of my molds,just tiny ones to let air out.I cut from the edge of the cavity to the outside with a sharp single edged blade.On steam castings,I pour a little resin in the cab area,then I slowly work it toward the front,to fill those ignorant areas,stack,domes,bells.Then I close it up,and pour into a hole in the center of the mold with a TINY funnel.One thing you have to do,you need a definite reservoir of extra resin stored in the pouring hole.I have a decent sized cavity there.When you put the pressure to it,there needs to be extra resin to fill the voids you're compressing..

[peteski]

I do very little casting compared to some of the others here, so I'm also always on the lookout for the hints from the experts.

I currently use various Smooth-On products (already mentioned by others).  I also thingk that Micro-Mark resins are re-labeled Smooth-On products.  I have in the past used Alumilite 5-minute urethane resin and their RTV rubbers and I didn't notice any appreciable shrinkage (or other problems). Alumilite has expanded their product line in the last few years and I'm actually thinking of trying some of those products.

There are other resins mentioned which have odor even decades after casting, which to me smells to me like mothballs.  Companies such as Fine N Scale Models, Chooch Ent., and Magnuson Models (DPM) used those resins.  I never liked those resins (because of the smell).  I suspect that they are cheaper than other resins and they are probably easier to work with (less viscous in the liquid state). But I prefer resins which have no odor.

The other thing about those smelly resins is that they seem to shrink.  Maybe because they are constantly emitting that odor?  For example, I has an old model kit of the Pioneer Zephyr (by Fine N Scale), molded from the smally resin.  When I examined it(after it was probably over 10 years old), I noticed that the body castings were shorter than the underframe castings (their screw holes no longer lined up.  The underframe has a fiberglass/epoxy circuit board encased in the resin.  Fiberglass/epoxy is pretty stable so I suspect that it prevented the underframe from shrinking as much as the body casting.  In the end, Dick from Fine N Scale ended up replacing the bodies (and the new ones were still a bit short but acceptable).  I still don't care for the stinky resin.

[wazzou]

I have in the past used Alumilite 5-minute urethane resin and their RTV rubbers and I didn't notice any appreciable shrinkage (or other problems).

I would imagine it depends on what you're casting for you to pay much attention to appreciable shrinking.
I scratch build a lot of freight cars and have had cause to mold roofs, ends, doors, under frame components and such and when measured against the masters with digital calipers, the castings shrunk.
In fact most if not all resins have stats for percentage of shrinkage and if memory serves, Alumilite has a pretty high percentage, too high for that kind of work as it turned out.

[peteski]

I would imagine it depends on what you're casting for you to pay much attention to appreciable shrinking.
I scratch build a lot of freight cars and have had cause to mold roofs, ends, doors, under frame components and such and when measured against the masters with digital calipers, the castings shrunk.
In fact most if not all resins have stats for percentage of shrinkage and if memory serves, Alumilite has a pretty high percentage, too high for that kind of work as it turned out.

Specs for Alumilite "regular" shrinkage and elongation are stated at http://alumilite.com/ProdDetail.cfm?Category=Casting%20Resins&Name=Alumilite%20Regular

[zephyr9900]

Randy,have you tried pressure casting?

Lou, I have never tried RTV/resin molding.  I made the masters for the Fine-N-Scale/ProtoTrains Pioneer Zephyr, but Dick Billings did the moldmaking and casting and marketed the actual kit.

I know it'll probably ignite a whole new debate, but the only casting I've done, years ago, was casting 1:1 gears out of epoxy under vacuum.  I have a vacuum setup, and know that you need to vacuum the RTV before pouring molds, but do not have any sort of pressure equipment.  This is all new territory for me, and I am open to learning from other people's experineces.

Logically to me, it seems that vacuum casting will pull out any air/vapors/gases but pressure casting would only pressurize entrained gas bubbles, which could cause problems later.  But again, I only have 20+ year old experience to go on...

Randy

[wazzou]

Specs for Alumilite "regular" shrinkage and elongation are stated at http://alumilite.com/ProdDetail.cfm?Category=Casting%20Resins&Name=Alumilite%20Regular

Just confirming my point, I'd assume?

[peteski]

Just confirming my point, I'd assume?

EDIT: Mike was quite right - my response was improper. Correcting...

Um, that depends on what amount of shrinkage was too much for you.    You mentioned inferred that Alumilite hides those specs - they don't.  At least that is how I interpreted your post.

[Sokramiketes]

Um, that depends on what amount of shrinkage was too much for you.    You mentioned that Alumilite hides those specs - they don't.

Welcome to the twilight zone, Wazzou.  Where people think you said things you didn't. 

[johnh35]

EDIT: Mike was quite right - my response was improper. Correcting...

Um, that depends on what amount of shrinkage was too much for you.    You mentioned inferred that Alumilite hides those specs - they don't.  At least that is how I interpreted your post.

I am not sure how you reached that conclusion.  I saw nothing about the specs not being available.

[kornellred]

On eBay, aeromarineproducts markets a rather complete line of molding and casting products that are comparable to those of Smooth-On, Alumilite, and other better-known brands.  Just an FYI for those who might like to engage in some comparisons.

[peteski]

I am not sure how you reached that conclusion.  I saw nothing about the specs not being available.

You know - I really dont' know that anymore.  Seemed clearer last night. 

Wazoo:   Alumilite Regular shrinkage is 0.005, SmoothOn Smooth-Cast 300 is 0.01, Smooth-Cast 310 is 0.0065, Smooth-Cast 380 is 0.0025 (all in in./in.) Alumilite doesn't seem all the terrible compared to the popular SmoothOn resins.  What is the acceptable shrinkage value for you?