New to Casting and need Help... Please

[Makrel Johnson]

...acusatory responses too many times from them when asking questions (IE: Question: Im having inhibition with your plat silicone, what type of primer can I seal my parts with. Answer: It must be something that you are doing on your end that is causing the inhibition. We can not guarantee our parts to work with the type of primer your using. .... But never an answer.

Stormrider:
At least you GOT an answer. I've shot several an email and never heard back until I used Reynolds Advanced Materials who partnered with Smooth-on. I get fantastic service from them. (Smooth-On recommended them to me for cheaper shipping as they were closer, and now REAL close in Denver!!) If you call one of their stores directly they'll likely have an answer or at least a suggestion. The fellow I dealt with at the Denver store was enthusiastic an knowledgeable. So I hope they will help out more. Also they have cured samples of most of the products so you can get a hands on feel for what it [should] be like when properly mixed/cured/etc.

I know this thread is likely old and crusty, but if I stumbled on to it, someone else may find it helpful.

...So I stumbled upon The RPF looking for help with my Task4 woes and I'm glad to see some answers. I look forward to contributing if I can and learning all I can cram in my head!

 

[Beaker]

Sorry for your poor responses... if you need anything I can try to help... issue with bonding primer that isn't ours... it is all chemicals and most companies have their preparatory blends and not real receptive in sharing their compositions so it is hard to say X will work because there are a whole lot of X's on the market and each have different degrees of chemicals. When someone is having issues with inhibition they are talking about a product that has gone through much R&D and countless man hours of testing to make sure it is as close to bomb-proof as possible so it then becomes a detective game to see what is going on... I have personally been down this road numerous times with customers and have usually found that it is something that is being done that was overlooked (and the longer one goes as a mold maker, the more we can become lax as things become second nature... I for one have been guilty of this and indeed it is the person calling in who qualifies they been a mold maker for 30 years before they start as the person that simply overlooked something) usually a little detective work and it is finished... this stuff is science it doesn't do things differently simply because it has a mind to do so, a chemical reaction such as these type of products do what they are supposed to do, it isn't by chance...
Inhibition in platinum isn't uncommon... sulfur, latex are the biggest offenders (in this environment at least) but there are other things also... if you are using a sulfur bearing clay or latex anything, no matter what barrier you use be prepared for inhibition.. at that point switch over to a tin-based silicone... Krylon Crystal Clear works for most things as a good sealer but even that can't seal sulfur or latex that well...
As for you Makrel, you got some good advise here from people about post curing or waiting 7 days before you qualify the Task 4 as either junk or the right product... urethane resin, no matter if it is ours, or someone else's all have common issues... a room temperature cured plastic urethane needs 7 days to reach it's ultimate physical properties. If it is to brittle you could try a lower durometer plastic but be aware that at such a thin section you could run the risk of the part not holding it's structural integrity. I am glad Mike from Denver helped you...
If you need anything you can always look for me on here.
~beaker

 

[Mostly Fantasy]

Have you thought of lamination? I don't know if I'd trust any resin by itself for a moving propeller...

 

[Makrel Johnson]

Thanks, Beaker. I appreciate the offer. I'll certainly take you up on it!

Last night I experimented with keeping my Task 4 in my 'oven' - which is a work lamp mounted to the top of a pink foam, reynolds non-stick foil-lined, 1.8 cu ft box. I have a dimmer on the light to control temp via a thermometer stuck through the wall. Kinda proud of it as it cures Tamiya acrylics pretty damn fast!

As for the Task 4, first thing I noticed is the viscosity dropped and the bubbles from 'shaking vigorously' completely dissipated in the container in under 3 minutes. Also the cured color of Task4 went from opaque white to a translucent white. Lastly I had SIGNIFICANTLY fewer bubbles in my cast (a mold of Mold Max 20).

The possible kicker is I'm working with 6-12 GRAMS at a time as my pieces are small. Really small - I'm replacing known fragile parts in some 20+ year old Robotech/Macross/GoBots models. (Hey, I like to play with them! ) I use polypropylene pipettes to injection mold in a 2-piece block and also to 'squirt-massage' the resin into the crevices of the open face mold. My lingering trouble is micro-bubbles in the undercuts of the open face. If I can't use heat to remove them, I'll try pressure next. (Big Lots, here I come for my pressure cooker).

Thanks for your help, when I pull the pieces, I'll post-cure and report back.

_Makrel

 

[Beaker]

Not sure a pressure cooker can achieve 60lbs of pressure (maybe but not sure)... 60 is what you want to achieve... Harbor Freights does have a pressure pot for cheap (Paint Pressure Tank - 2-1/2 Gallon) but here is my huge disclaimer: Harbor Freights has a some what 'rep' of getting what you pay for... I have had people sing praises of this stuff and have used it for years without issue and others that have run the opposite way when they hear the name... a pressure pot is essentially a live bomb that has the potential energy to cause massive bodily harm or death! Use the link at your own judgement...

 

[Beaker]

oh and yes, there are two choices for your above senerio, either vent the mold in the places that air is collecting or use a pressure pot... powdering the mold may help to some degree but if it is simply an issue where the air has no place to go then it is one of the two options.

 

[Steamtech]

When using the pressure pot do you pour your resin into the mold and then place the entire thing in the pot? Put the unmixed resin in? The mixed resin?

I'm interested in getting a pressure pot for some upcoming jobs but I'm really clueless as to how you actually use it in the process! Can anyone give me a quick explanation?

 

[Beaker]

When using the pressure pot do you pour your resin into the mold and then place the entire thing in the pot? Put the unmixed resin in? The mixed resin?

I'm interested in getting a pressure pot for some upcoming jobs but I'm really clueless as to how you actually use it in the process! Can anyone give me a quick explanation?

If you are going to cast under pressure, first make your mold under pressure! Very important step... once the mold is made under pressure then yes, pour the uncured, mixed resin into the mold and place the whole thing into the pressure pot, clamp shut and cast at 60lbs of pressure

 

[Makrel Johnson]

Beaker, understood about Harbor freight. I've gotten adept at picking through the BS tools there. I think I'd only need slight pressure as my bubble count was 3-4 and they were really small. It's a shame I'm such a perfectionist... I'll try a few tests with a shot of primer prior to molding, using a powder and just plain poking the crevices with a pin. BTW my block does have an air vent and I make sure I fill that completely when I inject. I think it's just one of those things where you needs the planets aligned and the dog on the right side of the couch.

I'm going to try to attach some images...
Mold, Originals (right) and pulls (left)

Closeup of original and pull:

and 3rd that works well enough...

 

[Makrel Johnson]

...in the post above the swing arms (top images are ~2.5" long and the bottom image, the mounts are 1" wide. Just a note for scale. The arms are from this model: https://picasaweb.google.com/meffen/VR052F and are the first to break. The mounts are from a Revell Robotech Changers Axoid kit I inherited from a friend... naturally missing some parts but I have about 7 or so in various states of decomposition that I can mold parts from and rebuild.

I'll have to get my butt in gear and snap pics of my current project for that thread. (this molding issue/intermission is what I do while paint cures and putty dries)

 

[Beaker]

pressure pot will help this... next time you could try a squash mold also... I made a very successful motorcycle tail light lens doing this
http://www.smooth-on.com/images/gallery/232/table_shot_of_molds_product_and_castings1.jpg

 

[Makrel Johnson]

Beaker, I had better success squashing the mounts from above by pre-filling, closing then injecting. The swing arms will have to wait until I get pressure going.

I did cobble together a vacuum system consisting of an old 2qt nonstick pot, 1/4" acrylic, a PMC 121-30 gasket and a Harbro Freight 3cfm pump with ball valve. I'll post pics later tonight. It's small and suits my needs well. Next I'll look into pressure.

Thanks again for your help.

 

[Steamtech]

If you are going to cast under pressure, first make your mold under pressure! Very important step... once the mold is made under pressure then yes, pour the uncured, mixed resin into the mold and place the whole thing into the pressure pot, clamp shut and cast at 60lbs of pressure

I never would have thought to make the mold under pressure too! That is a fantastic tip.

Thanks for the advice, can't wait to try it out soon

 

[Makrel Johnson]

Beaker, one last question... Smoothcast 300 and 321 and Task4, do these need to cure in room temperature or cooler? I have tried placing these in my hobby oven and I notice foaming... it's ~100 F. Maybe a sticky on resin tips would be a good thing.

Update - I had extremely good luck with Smoothcast 321 (which I forgot I had). The viscosity was super low (like water) and I pulled very well from all molds. I'm going to chalk trouble with the 300 to being old and the Task4 to needing pressure and being too viscous for the tiny molds.

Hopefully someone can use this info and save some time

 

[Beaker]

Makrel,
Glad you had luck with the SC321... foaming is simply moisture, about the only thing that causes foaming... in fact any urethane foam is simply urethane resin with a controlled amount of moisture built into the catalyst.