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Vacuum Caster Machine question


#1

Hi Crowd,
I was thinking a lot trying to decide between centrifugal and vacuum casting.
I am a beginner/ hobbyist and i want to be able to cast at home at my garage.
I decided to buy or build vacuum casting machine. It looks like vacuum casting machine is smaller, and it doesn’t need any balancing procedure.
Now I have to decide between buying something cheep, or building my own.
I already have a decent ( I think so vacuum pump). It is 1/3 hp. 6 cfm, max vacuum 27HG
What else i need to build a vacuum casting device? A table with flat surface, with a hole in the center and some “rubber” washers to ensure vacuum.
I am sure that i am simplifying, as we all know devil is in details.
People, can you tell me what traps, and problems will i meet if i take the route to make my own casting machine.

Also, if some body knows cheep machine i would appreciate recommendations. I was looking at Vacuum Casting Machine T3 from Gesswein


#2

Vacuum is way safer than centrifical. And you need the vacuum pump any way to debubbelize investment. There are lots of reasonably priced machines on the market. The main difference is if they have casting chamber or just a table and the size of the pump. The chamber is better if you are doing larger castings with multiple pieces. It allows you to use a perforated flask. And as far as pumps go, bigger is better. Rio Grande’s VIC 12 has about the biggest pump available for the money. To go bigger you have to get into the big commercial machines. Also if you are going to vacuum cast you need a melting furnace to melt your metal. Operating a torch and a casting machine at the same time is very clumsy. It is way easier to have the metal melted in the furnace and ready to pour when you pull the flask out of the oven. With a torch you have to have some means of holding the torch on the metal to keep it molten while you do that.


#3

We have used for decades a home made vacuum pump machine to both invest and
cast. We only do small runs so we don’t use perforated flasks. All we do is
just switch the pad from rubber for investing to a heat resistant pad for
casting. We get great results every time.
Have fun and make lots of jewelry.
Jo Haemer
www.timothywgreen.com


#4

Thanks Jo!
Can you please tell me where to get heat resistant pad? Was looking on Rio couldn’t find.
Thanks


#5

Hi Boris,

You have it about right. Look in Google for a silicone pad for casting. Several of the jewelry supply houses have them. You might even find something in a silicone pad for cooking that would work and be cheaper, I don’t know, haven’t checked.

You can use a tin can with both ends opened for a flask and there are various pipes and such you can use, too. Or buy a purpose built flask. An alternative to a perforated flask is to hook pieces of wire shaped like a hairpin over the side of the flask, giving air channels deep into the surface of the investment. Another possibility is to use a wax mesh to line the inside of the flask, The jewelry supplies sell it. For simple castings you do not have to have these. You will need a valve in the vacuum line to turn the vacuum on and off.

You can use a thick glass bowl instead of a bell jar, if the glass is without flaw. IDK where you are, but such is available in the US at Walmart for under $10. If you look at how the vacuum tables are constructed, you can construct yours as a “jiggle table” with bolts and springs. You will need at least a metal covered wood table…a thick sheet metal table would be better.

I think that about covers it for starters. You can use a torch at first, esp. for small amounts of metal. An electric melting furnace is nice, but even the cheap Chinese ones are $400+ and you probably already have a torch.
Good luck,
royjohn


#6

Thank you, Roy John


#7

Hi gang,

Just a safety note here: do NOT use any sort of glass jar, especially some random $10 thing for a vacuum flask. If they break, they implode. Almost instantly, with staggering power. (15 pounds per square inch of surface. Do the math.)

I once had a real glass vacuum jar, from the bad old days when they still made such things. About the size of a 2 liter soda bottle. It finally cracked on me one day. Blew chunks through the drywall. It ‘squeaked’ a little just before it blew, which gave me just enough time to hit the deck.
The bigger they are, the bigger the bang when they break. I have a friend with one from the 1890’s, that’s about the size of R2D2. He won’t pump it down. He’s calculated that if it were to blow, it would have roughly the power of a stick of dynamite.

There’s a reason that nobody still makes vacuum jars out of glass, and hasn’t since the high strength plastics came along. For the $50ish they cost, just go get a real bell jar. You’ll live longer.

As for the rest, opinions differ. I’ve built a number of vac casting rigs, and worked with spin casters for years. For one-off, I prefer spin casters. You get better metal density, and you have more force to slam the metal into fine detail.
For large production batches, vacuum is the way to go. Much safer than trying to sling a few pounds of molten bronze around in a spin caster. (I once worked with one that could handle several pounds in a shot. Which was great…unless you had a blowout. At which time it got downright festive.)

The funny ‘rubber’ pads are actually silicon, and available from any of the tool houses.

If you do make one, remember to put a trap in the input side of the vacuum line. (dig through the archives looking for my username crossed with ‘vacuum’. I did a pretty solid rundown on homebuilt vac casting rigs at one point. I remember spelling out the details of the metal trap and the pump requirements.)

Regards,
Brian


#8

MY apologies for suggesting the use of a glass bell jar without using appropriate glasses and protective clothing…however, it is not true that glass bell jars are obsolete…just google and you will find them still for sale. Whichever bell jar you use, use appropriate goggles and aprons or protective cages to protect you in case of an implosion. If you use a glass bell jar, it would be prudent to use a metal cage or similar in case there is an implosion. While plastic is lighter, if it breaks, it can still cause damage, so use appropriate cautions, such as googles and/or aprons.

I was negligent in not specifying the thickness of the glass salad bowls. Take a look at the thickness of the plastic and the glass bell jars for sale and compare the glass “salad” bowls. Maybe you’d prefer to sling metal around on a centrifugal caster instead…caveat emptor. If you’re using vacuum, I wouldn’t get my face up right against ANY bell jar when pulling vacuum.


#9

Thank you, Brian - i never thought that glass jar can break. But your warning makes a lot of sense and I will follow it for sure. Can you please elaborate a little bit more about trap? What is it for? What exactly it is supposed to trap?


#10

I don’t understand. Don’t we use the bell cover ONLY for debubling? It doesn’t make sense to use bell when doing casting itself, correct? Sorry for a stupid question. I used vacuum caster at school and there were no bell on poring melted metal stage.
Thanks guys and girls!

Boris


#11

Yes you are correct. You only use the bell to debubble


#12

Do not ever use a glass container whether it is a real bell jar or some
random piece of kitchenware as a vacuum chamber. There are a very few
reasons one would need to use a real glass bell jar and none of them are
present in the jewelry making field. When a glass chamber implodes the
pieces are driven inward by the tremendous pressure on the jar and then
are thrown back outward by the rebound of impact with other pieces or
just pass right on through and off across the shop. All glass bell jars
that are in use in labs are shielded by heavy screen cages to contain
the missiles those shards become when the jar shatters. A glass chamber
that has worked fine for years can implode because of a minor scratch in
the surface. People have been severely injured by flying glass from
such events. Stick with commercially produced vacuum bell jars made from
plastic, much safer.


#13

I agree with almost everything said above. One thing I do recommend though is to line the flask with wax rods to just above the level of the wax pattern to facilitate the even draw of the vacuum through the entire flask. (Actually, you are not sucking the metal into the flask. You are using ambient air pressure to push the metal. A little more than 14 pounds per square inch) I bring up this point because visualizing this you may sprue a little differently. One other point, RIO sells a wax wire mesh to line a flask with. It really helps when casting finely detailed pieces.
Oops, one other point…Your vacuum pump should be able to boil water at room temperature within a minute or so if you are using a 9 inch bell jar.


#14

HI Boris,

Yes, the bell jar is only used for degassing the investment, not casting.
The ‘trap’ I mentioned is a safety feature that’s been omitted from recently made casting machines (or at least a few that I’ve seen lately). The idea is that it gives you a pit that molten metal flows into if you have a blowout, rather than getting the molten metal sucked into the vacuum lines, and into the sensitive guts of your pump.
Basically, it’s a plumbing “T” joint set sideways under the casting table, with a hunk of capped pipe sticking off the bottom. The vac line draws out via the center leg of the “T”, which is above the slug of pipe. If you have a blowout, the metal drops straight down into the pipe section, missing the vacuum port, which is high up on the side wall of the pipe. Wait for it to cool, then unscrew the bottom and retrieve your metal from inside the pipe. Vastly preferable to digging little globules of silver out of the guts of your pump while you replace the totally fried vacuum lines. Some of the old casting machines had them built in, but the last machine we bought for my old school didn’t have one. (Found that out the hard way…) Costs about $15 to build and install.
Plan for failure. It’s cheaper in the long run.

Regards,
Brian


#15

Thanks, Brian!


#16

Hi, need a little bit more help
I made a table from 2x4, i am planning to screw on a piece of ply as a table top,
Now i have several questions.

  1. Is plywood enough, or i should cover the plastic with steel, or something else?
  2. what material should i use to make the seal between jar and table surface more tight?
  3. I am going to use the same hole for vacuum casting and debubblinbg? Are there any problems with this design decision?

Hope to get help.

Thanks,

Boris


#17

Hi, need a little bit more help
I made a table from 2x4, i am planning to screw on a piece of ply as a table top,
Now i have several questions.

  1. Is plywood enough, or i should cover the plastic with steel, or something else?
  2. what material should i use to make the seal between jar and table surface more tight?
  3. I am going to use the same hole for vacuum casting and debubblinbg? Are there any problems with this design decision?

Hope to get help.

Thanks,

Boris


#18

I’m not sure what you mean by a piece of ply. But it really doesn’t matter. I made my own table and use it for both debubble and casting.

I first got a vacuum dome so I knew what size to make my vacuum dome base.

I got a piece of scrap steel plate 1/2" thick Ann mounted springs on each corner. This allows the table to be jiggled whe vacuuming the investment.

I drilled and pipe tapped a hole in the center to fit my vacuum line pipe. In hind sight I should hav offset from center to not cover the vacuum source with the investment canister.

I got a piece of silicone about 1/4" thick and the size of the steel plate. Cut a small hole to all the vacuum inlet.

When using it for debubble the silicone mat provides a suitable seal for the dome. When using it for casting I first put the canister on the silicon mat and pull a vacuum on the sprue hole to get any residual ash or containments out. Cut the vacuum turn the flask over and pull a vacuum at the same time I pour.

After investing and before burnout I always make the investment concave on both ends of the flask to ensure a good seal to the silicon mat. I can take pictures if that would help.
Regards RLW


#19

Thank you, pictures would definitely help. 1/2" of steel is huge and heavy. Do i really need such a massive piece of steel?

Thanks,

Boris


#20

At my age my memory may be off a little. I’ll take some measurements and pictures tomorrow and post. The real issue is vacuum is a very powerful forces a it needs to resist bending under the bell
Regards RLW