I bought some stuff today..

[erospawn]

Welppers... I took the plunge today.. I bought a pressure pot and air compressor today.. and I found an Art Dealer here who is also a Smoot-on distributor and bought a gallon of rubber latex, a trial size of liquid rubber and also some casting resin..and a refrigerator! Yes, I said refridgerator. Woke up this morning to find my Ice cream and other stuff a little on the warm side.. Ugh! At any rate Im pretty excited!!


   
   
   
   
   

[modelnutz]

Well, looks like you're in business now ! ;-)
Got most of what you need....
(dump the latex...useless....you'll come to love Silicone )
Don't forget the Talc !

I might suggest a water trap between the compressor and the Pot.
You don't want any water in the system...it causes urethane to foam.

Can I ask...why Rebound instead of Mold Max 30 or 40 ? ( never mind...just went to Smooth-On's site...brush on stuff...right ;-D
If I remember correctly, Rebound is a platinum cure silicone..( could be wrong though )..be sure to avoid any sulpher based clays ( they inhibit the cure of platinum silicones )

Good luck with the learning curve...may it be mercifully short !

[DarthDuck]

Congrats!

Let the fun begin.

[erospawn]

(12-13-2009, 11:23 AM)modelnutz Wrote: Well, looks like you're in business now ! ;-)
Got most of what you need....
(dump the latex...useless....you'll come to love Silicone )
Don't forget the Talc !

I might suggest a water trap between the compressor and the Pot.
You don't want any water in the system...it causes urethane to foam.

Can I ask...why Rebound instead of Mold Max 30 or 40 ?
If I remember correctly, Rebound is a platinum cure silicone..( could be wrong though )..be sure to avoid any sulpher based clays ( they inhibit the cure of platinum silicones )

WHy the rebound?? It was there, I'm just playing around for now . He didnt have any mold max other wise I would have gotten that..

So, a water trap? What does it look like.. I got most of this stuff at Harbor Freight..

Good luck with the learning curve...may it be mercifully short !

Learning curve? Im a computer engineer .. I wonder if those learning skills apply here as well?

[modelnutz]

I think you'll do just fine ;-D

You can find water traps at Harbor Freight as well.

[JAWS]

Couldn't sit on the fence any longer could you? Very keen to see this brush on rubber. Whats that 'Mould Builder' tin? Im still a learner too!

[Recycle]

That "Mould Builder" tin is the gallon of latex. You may want him to take a few more pictures of that can so that he'll always remember "That time" he bought some. This is part of that "learning curve".

LOL!

I agree with Modelnutz, erospawn. You need to get some Mold Max. I don't use the 40, but have used plenty 20 and 30 with excellent results. You need to get a couple more pieces of equipment once you make the move to RTV's. Vacuum equipment so that you can de-gas RTV. It'll be a very important addition, especially if you plan to pressure the resin later.

[erospawn]

Yeah, I was going to get the vacuum pump too, but the guy at the store couldn't tell me if the pump pulled 29 HG.. it was 10 Pascal / 25 micron pump. As for the brush on stuff, you don't really need to degass that do you? The stuff I want to try is large for now.. the small stuff that will fit in the pressure pot should be fine though.. Also, some of the stuff I plan on doing will need to be hollow cast.. which brings me to my next question.. You need a rotocaster for that right? Or, can you sort of get away with out one?

Where do you get some reasonably priced vacuum pumps though? the vacuum chambers are pretty up there too.

[Recycle]

Here's a picture of a moisture trap. It'll go at your compressor outlet before any other attachments. That one is at Home Depot.....$12.99.

Most of the time, you need to get into the habit of de-gassing any mold making. I'm not sure about your latex, but it will NEVER hurt to degas your RTV.

For de-gassing RTV, you won't need 29HG. 29HG (Inches of Mercury) will ALWAYS mean big dollars. To put this into more perspective, 30HG is a perfect vacuum and is all that's possible, so 29HG, consistently of course, is big money AND hard to come by. In fact, if I bought equipment that was suppose to be able to maintain even the 29HG they claimed, I would have to see that.

You can get away with less than any 29HG of vacuum for de-gassing RTV and it doesn't have to be able to get it to max vacuum quickly either. You'll want to apply the vacuum in increments anyway because as your RTV releases (actually a type of boil), it will expand a great deal. If you do this too fast, RTV will expand and overflow the container you've got it in inside your vacuum chamber. You'll actually apply the vacuum and as it starts releasing the trapped air, you'll need to stop the vacuum for a bit, let it stabilize and then re-apply the vacuum a little more. Once you've done this a couple times, you'll see it slow down with the expansion and you can apply the vacuum and leave it on until you see very little action taking place.

There are several things that can be acquired that are fairly inexpensive that you can use to de-gas RTV. Here's an example that you can use to get started. At one time, there was a product for sale on an "infomercial" called a "Pump-n-seal". This item can STILL be bought online and only costs about $10 bucks. Get one of those and then go to Walmart and buy one of the clear acrylic containers they sell as a food container. There are several different sizes of these things and they have a seal around the lid with a snap-type closure that allows for it to be opened and closed quickly with a lever type lock. I'll search and see if I can post a picture of one.

This will get you started nicely:

http://www.kaboodle.com/reviews/pump-n-s...food-saver

I know I said $10 bucks, but it looks like they are NOW $29.99. That sucks. They WERE $9.99 just a few years ago when I bought one. These babies pull a GREAT vacuum. I even picked up a set of those sealing lids. You won't need those if you use the containers I mentioned from Walmart, but those lids come in handy on a variety of different bowls and such, so you may want to consider those?

The containers you should be able to find at Walmart look EXACTLY like these in this Walmart link, except that they are clear, thick plastic and WERE sold individually in the container aisle. I haven't purchased any in a few years, but they certainly used to be available.

http://www.walmart.com/catalog/product.d...id=7855714

These two items will EASILY work and keep you well within budget until you figure out if you even need way more expensive equipment.

On your large molds, de-gassing the RTV isn't as important if you can't get them into a pressure pot. The reason why is, when you place a mold into a pressure pot, you are compressing any gases (air mostly) in your resin to keep them as small as possible until the resin cures to the point that the bubbles they make won't be able to re-expand once you release the pressure. What happens when you don't de-gas RTV when you use a pressure pot is that when you leave those small bubbles in your RTV mold, the pressure pot wiil ALSO compress THOSE bubbles too, so that when you remove your parts later after the resin has cured, you'll have little marks all over your parts, sorta like the dimples on a golf ball only they'll be raised dimples. You won't be able to actually see these dimples in your mold either. They are voids under the surface of the RTV that the pressure you placed on that mold while you were trying to compress the gases in your resin also compressed in the RTV mold. This is why de-gassing RTV ESPECIALLY if you'll be placing it under pressure, is an important step. Generally, this won't be too big a factor in a mold that you won't be placing in a pressure chamber. It CAN happen though. If there happens to be a void in that mold that can flex from the resin (such as the simple weight), then it WILL show up in your parts. De-gassing RTV is a practice you can afford to get into no matter HOW you'll be using the mold.

On your hollow cast parts, yes, a rotocaster is a nice piece of equipment, especially for parts that are larger. They aren't cheap and will take some practice, patience and perhaps some special resins.

If you'll be keeping the parts to an average size, a two part mold will do the trick. Now, these will take some learning too because you'll need to put a little more thought into your mold creation than you would with an open faced (single part) mold. Indexing, liquid flows and venting will all have to be considered when you make two part molds, but you'll catch on to what is needed quickly.

[erospawn]

Thanks! Thats some serious insight in to all of this and I thank you very very much for that.. So, with that having been said.. I went ahead and bought the vacuum pump today..Along with the other mentioned items as well. But I just need something to create the vacuum in.. The thing I want to after that, is put a feather and a coin in it and see if they both drop at the same time.


Ended up getting this one.. http://www.harborfreight.com/cpi/ctaf/di...mber=98076

[JAWS]

Wow thats some great information Recycler. Thanks for that. Well in all honesty my vaccuum chamber was really just a big soup pot with a hole drilled in for the regulator & release valve. Very expensive soup pot.... The top however is a thick piece of acrylic with a rubber ceal.

[Recycle]

Not a problem. Trying to help.

erospawn, you said you wanted to try the old "feather-solid object" test. It'll work, if you remove enough of the air. If you trap a flying bug in your chamber and remove the air, he won't be able to fly. You might think being under a vacuum would kill him, but it won't because you can't remove enough of the air (nor fast enough, which is another key part) to make his fluids boil (which is what is suppose to be happening in "space movies" when they open their helmets).

Since MOST vacuum is measured in "microns" now, the lower the number, the better (of course). How many CFM's can be important too. The faster it can remove those microns, the better if you're working against the clock.

The concept of microns (as it relates to vacuum) is easy to understand. Atmospheric pressure measures around 760,000 microns. 0 microns would be a perfect 30 inches of mercury, or 29.97 HG. A perfect vacuum is practically impossible on earth simply because it would be almost impossible to remove 100% of the air. The weight of the air pressure around us, give or take for altitude, is 14.97 PSI at sea level. That being the case, 760,000 microns=14.97 PSI, so calculations for microns to PSI equivalents can fairly easily be worked out if you want to get that deep into it. For all intents and purposes, a vacuum pump is a micron remover.

This next part is simply for fun. The closest you'll ever get a piece of equipment to pull a full 30 HG of vacuum, without spending TONS of money, is as simple as a quality syringe. Try this if you want to. Get a good syringe (30, 40, 60cc's will work) and fill it about half full of slighty warm tap water and remove the air in the head space. Hold your thumb on the opening and pull back the plunger on the syringe WITHOUT letting any air in. The water will actually boil at room temperature. Hook the same syringe up to a vacuum gage and it will consistantly bottom out a 30HG vacuum gage. A standard good quality syringe pulls the absolute BEST vacuum of anything I've ever tried and I have access to some VERY heavy duty vacuum equipment.

[erospawn]

Which would explain why you know so much about vacuums!! Awesome! Thanks for that bit of technical knowledge.... Maybe I can offer some up if ever you need it.. I work in NAS and SAN server storage among other things.

[JAWS]

Wow that was actually a science lesson I understood! That was great I even feel smarter. Its amazing how some people can explain things in a way in which the subjct is very clear & some just can't. You my friend can & thanks for that!

[DarthDuck]

(12-15-2009, 05:41 PM)jasonwright.1972 Wrote: Wow that was actually a science lesson I understood! That was great I even feel smarter. Its amazing how some people can explain things in a way in which the subjct is very clear & some just can't. You my friend can & thanks for that!

Waitaminute!

Is he saying that a duck can not fly in a vacuum?
Well that explains my bruises.

Dang, I'll have to remember that one.

[bwayne64]

Ducks CAN fly in a vacuum. They just need someone to throw them,

[JAWS]

Hhahahahahahahah! Thats funny.

[Recycle]

You could still do a lot of flappin'?

[bwayne64]

Flying in the vacuum wouldn't be the real problem, it would be stopping,

We love ya Duck, just joshin' ,

[dbhs]

If you see an out of control duck about to fly into someone's head do you yell "DUCK !!" or "DUCK !!" ?

[bwayne64]

(12-17-2009, 08:27 AM)dbhs Wrote: If you see an out of control duck about to fly into someone's head do you yell "DUCK !!" or "DUCK !!" ?

Depends on who's head it's flyin' towards, sometimes you say nothing at all, LOL.

[DarthDuck]

(12-17-2009, 08:27 AM)dbhs Wrote: If you see an out of control duck about to fly into someone's head do you yell "DUCK !!" or "DUCK !!" ?

Personally, I yell Bonzai!

[treker2557]

Can anyone suggest a vacuum pump size for a 5 and 10 gallon pot? Any help would be appreciated

[Recycle]

(03-16-2010, 03:10 PM)treker2557 Wrote: Can anyone suggest a vacuum pump size for a 5 and 10 gallon pot? Any help would be appreciated

One thing you may want to keep in mind when considering pulling a vaccuum on a vessel made for pressure......

Pressure vessels are NOT designed to handle vaccuum and could very well end in disastrous results.

I know this doesn't answer your question about what pump you should choose and I apologise for that, but this is something some folks DO NOT realise.

Your question about pump selection will be more a matter of how much you are willing to spend.

The amount of vaccuum you would like to pull and how quickly you would like to reach that vaccuum point will give you a reasonable selection of pump choices......and a price range.

[erospawn]

Wouldn't you be using the vaccuum pump for the vaccuum chamber for degassing the rubber? The 5 and 10 gallon pot is for pressure casting. Ie, you pump air into them, not suck it out.

[treker2557]

I purchased a 16x16 sheet of 1/2 inch Lexan and then drilled a hole with a drill press through the center and tapped it. I then bought just standard black pipe fittings, shut off valve, and a vacuum gauge. Lastly I ordered neoprene gasket material 1/8 in think and will cut and glue it to the underside of the Lexan so it lips over the pot and have a viewing circle cut out from the neoprene material to see inside. Alot of people do this and it is cheaper than buying a vacuum pot or building your own since less material. I have this setup with a 2.5 gallon pot and has worked fine for a few years now. Your other option is to purchase 2 sheets of 1/2 in Lexan, 1 for top and 1 for bottom. Then purchase stock PVC coupler fittings. A 12 in couplet runs about $42 at Home Depot and then just drill and tap through the PVC for fittings.

[erospawn]

Ok, I understand now.... I just don't think I would feel safe with something like that though.

[modelnutz]

Trekker...what you are describing is a ticking time bomb.
First, I have an industrial pressure pot ( 7.5 gallon chamber ) and the lid for that is a piece of 1 inch thick acrylic.
No holes.
Even at that thickness, I get a deflection of nearly 1/8 inch in the center of the lid during use.
By drilling a hole in the center of your acrylic lid, you have introduces a stress point in the plastic. I may not have failed yet...but, trust me...when it does...you do NOT want to be anywhere near that thing.

Let me elaborate... I once purchased at an auction, a large bell jar type of vacume chamber.
Worked great...for a while...then, the sub-standard base that the previous owner made decided to give out while under 29 inches of vacume ( a LOT of vacume)....when the base cracked..it caused the bell jar to shatter ( implode actually...think...submarine diving too deep)

Now, keep in mind...this bell jar was 1/2 inch thick TEMPERED glass....damn near indestructable.....

Well, when it went off, the jar sucked inward and then rebound outward with enough force to sink a big piece of that heavy glass about 1/2 inch into the ceiling over my head. Took a pair of pliers to dislodge it.

Please....always use only the proper equipment to do this casting stuff...and never forget that we're working with BOMBS !

[427 Cobra]

(03-17-2010, 06:43 AM)modelnutz Wrote: Trekker...what you are describing is a ticking time bomb.
First, I have an industrial pressure pot ( 7.5 gallon chamber ) and the lid for that is a piece of 1 inch thick acrylic.
No holes.
Even at that thickness, I get a deflection of nearly 1/8 inch in the center of the lid during use.
By drilling a hole in the center of your acrylic lid, you have introduces a stress point in the plastic. I may not have failed yet...but, trust me...when it does...you do NOT want to be anywhere near that thing.

Let me elaborate... I once purchased at an auction, a large bell jar type of vacume chamber.
Worked great...for a while...then, the sub-standard base that the previous owner made decided to give out while under 29 inches of vacume ( a LOT of vacume)....when the base cracked..it caused the bell jar to shatter ( implode actually...think...submarine diving too deep)

Now, keep in mind...this bell jar was 1/2 inch thick TEMPERED glass....damn near indestructable.....

Well, when it went off, the jar sucked inward and then rebound outward with enough force to sink a big piece of that heavy glass about 1/2 inch into the ceiling over my head. Took a pair of pliers to dislodge it.

Please....always use only the proper equipment to do this casting stuff...and never forget that we're working with BOMBS !

Hello,Holton! I'm glad to see you're part of our community. It's been a while since I've talked to you last. I had to nuke my projects that I was going to have you make for me. It's just not something that can be cast in resin. Either way, while we're on the subject, does anyone know of a supplier that sells cold cast aluminum that looks like aluminum, and not just a dark gray?

[treker2557]

Thanks for all the comments and I understand what everyone is getting at. I'm a Chemist and understand all the basics about pressure and implications. My research is done actually in a closed system under a vacuum around 10^-6 torr and at ~20 Kelvin studying the movement of electrons in a system. I know 2 other casters along with myself that have used the setup I mentioned for years with no problems and I have industrial pots that can handle both pressure and a vacuum. The only thing I'm not sure on is the size vacuum pumps I need to purchase. Ideally I want to just purchase 1 pump that I would be able to use for both. I have a 6 cfm pump currently that I use for my 2.5 gallon pots. Any help from anyone that knows the proper size cfm would be very appreciated.

[erospawn]

9cfm is probably the best choice, if you have to get one. Although, 6 cfm should suffice...

[427 Cobra]

It depends on what type of silicone you're using, and how much space is between the pot,and the mould. Ron's right - 9 CFM is your safest bet. That's a lot of pull for this type of use. It's better to be safe than sorry.