Author Topic: Casting bench upgrade  (Read 2487 times)

Online Dan Rowe

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Casting bench upgrade
« on: October 29, 2015, 04:49:34 PM »
I bought some production flasks several years ago and the price of a vacuum pot to go with them was over $1000 at the jewelry shop so I said NO thanks I would build my own.

Well, that I finally got around to making a vacuum pot for the flasks. I ordered a 7" long piece of 6" steel pipe and a couple of 8" x 8" x .5" steel plates for the ends. I bought the conversion flanges so the vacuum pot can be used with either 4" or 3.5" production flasks when I originally bought the flasks.

The first step was to cut the edges of the square plates closer to size for the lathe. I used my Butterfly die filler with the saw overarm for the work with a normal hacksaw blade.



Then I cut a V-notch in an old cutting board so it could be used as a guide to trim the 4 corners of each end plate.



I taped a 1/2" hole in the center of both plates and trimmed both plates round with a bevel for welding to the section of pipe. The end for the adapter plates needed a 5.5" hole in it. I went to set it up in the mill and I found out that I did not have enough Z space to chain drill to remove the center section. I just got a mini mill base for my Servo drill press and it had enough Z space for the job but, the chuck will only take a 1/8" drill so I had to drill a lot of holes. Drilling 144 holes in 1/2" plate was a real work out for the Servo drill press but, it got the job done.




The final step before welding was to finish bore the top plate.



It has been a while since I have done much arc welding, and some of my bead was in the wrong place. This made me have to mill the face of the vacuum pot. I used the 1/2" bolt to clamp the pot to the mill table and used a pull-down vise on either side for extra stability. The weld bead did not respond to a file so I used a carbide milling cutter to save wrecking a good HSS cutter.



I made up a tree of 30 Shay truck parts for the test pour in the smaller 3.5" production flask.




Here are the flask and vacuum pot just after I poured the bronze.



And finally here is the tree of bronze parts ready for clean up.



A successful casting bench upgrade.

Cheers Dan
ShaylocoDan

Offline RMO

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Re: Casting bench upgrade
« Reply #1 on: October 29, 2015, 07:27:35 PM »
Dan,

Would you mind explaining a bit more about the vacuum pot, its uses and how this improves your castings?  I am just starting on the concept of casting and am interested in learning more.

Thanks

Mike

Online Dan Rowe

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Re: Casting bench upgrade
« Reply #2 on: October 30, 2015, 12:34:48 AM »
Mike, I learned how to do lost wax casting from a book, which I still use when I have to make the calculations necessary like water to investment ratio for flask size and how much metal to weigh out for the pour. It is a really good reference book for the subject Centrifugal or Lost Wax Jewelry Casting by Murray Bovin.

The reason I moved to production perforated flasks was not really to get a better casting it was so I could get more parts in a single flask. Here is a photo of my operation using solid flasks:



The electric graphite crucible is white hot in the photo, as I just poured the solid flask on the vacuum table. There is a red silicon gasket under the flask that can just be seen as it is mostly behind the splash guard. Several other flasks can be seen in front of the kiln. The solid flasks are 2.5" SS muffler pipe that I cut to length. It would have taken me about that many flasks to do the 30 parts I did in a single pour with the perforated flask. So I saved time and investment and had to heat less metal because there is a large sprue button on each solid flask. I only needed 200 grams of bronze for the 30 parts and most of that was for the premade sprue base that all the parts were attached to. I like all my parts to keep the wax injection sprue from the rubber mold, so all I have to do is use sticky wax to glue then to the base structure.

Here is a shot of the vacuum table with a bell jar and the flasks are vacuumed to remove the bubbles before setup.



The vacuum pot I made has a gasket below the pot and there is a red silicon gasket above and below the aluminum adaptor plate. The holes in the perforated flask allow the vacuum to be drawn from all directions, not just at the bottom with a solid flask. The perforated flask seals on the bottom of the rim so I do not have to trim the flask to get a good seal, and it has a much wider surface to seal with. The solid flask only has the wall thickness of the tube to seal. I have worn out two good files draw filling the base of the tubes to make a flat sealing surface. I now use a muffler tube expander as a chuck so I can true the tubes on the lathe safely.

The reason I chose vacuum lost wax casting over centrifugal casting is I can do a larger part than can be done with a centrifugal setup, and the number of parts I can do with the new vacuum pot is much greater that what can be done with a centrifugal setup.

If I missed anything just ask more questions and hopefully I will have a good answer. (Everything I explained and more is in the book.)

Cheers Dan
ShaylocoDan

Offline RMO

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Re: Casting bench upgrade
« Reply #3 on: October 30, 2015, 03:05:06 PM »
Thanks Dan, that clears it up somewhat.  I will have to take a look at the book.

Mike

Online Dan Rowe

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Re: Casting bench upgrade
« Reply #4 on: October 30, 2015, 04:53:40 PM »
Mike, after you read up on this ask questions if you have any. I started casting with a handheld crucible and a rosebud tip on my OA torch. That works fine for small pours and getting started with solid flasks. I helped on a few centrifugal pours as I had a lot of experience with an OA torch when I took a class in jewelry.

Cheers Dan
ShaylocoDan

Online Dan Rowe

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Re: Casting bench upgrade
« Reply #5 on: November 08, 2015, 02:34:42 PM »
I made my second pour with the larger new flask and I could not get the vacuum gauge to read. Now this was really disappointing as this has happened to me a few times with solid flasks and attempting a pour without vacuum does not work as the mold will not completely fill resulting in useless parts.  I poured the metal anyway as it was ready and I had to get it out of the electric crucible. I did not expect to see any of the 42 parts I had on a wax tree. To my surprise, I got 36 parts out of 42 parts. I carefully checked the flask and tried to get vacuum up when everything was cooled and I found the flange was warped when they welded it onto the tube. The best I could do was make the gasket blow a raspberry. I will have to turn the flange true on the lathe and now I know to check brand new flasks before use.

Dan
ShaylocoDan

Offline maury

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Re: Casting bench upgrade
« Reply #6 on: August 01, 2017, 01:52:06 PM »
Y'all, I just ran across this thread. I have a need to make sime bronze valve and pipe castings for a steam engine project I'm working on with a couple of other guys. I've been sand casting for years, but the parts I need to make have too much depth detail and are too small for sand casting. I need some basic help on the details for investment casting these parts. I do understand the process.
1) I want to cast using a plaster mold. Is this reasonable for bronze? Is there a high temp plaster I can use.
2) There is a lot of info about making the waxes and molds, but very little info on burnout. What are the requirements here? I assume the molds will be poured while still hot, is this necessary?
3) maybe a word about venting the mold.

Thanks,
maury

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Online Dan Rowe

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Re: Casting bench upgrade
« Reply #7 on: August 01, 2017, 04:45:53 PM »
Maury.
1) The plaster is called investment and I cast silicon bronze.
https://www.riogrande.com/Product/Kerr-Satin-Cast-20-Investment-2kg/7020992KG

2) Burnout requires some type of controlled furnace capable of reaching 14000 F. The flasks are gradually brought up to 13500 F with a 5-12 hour cycle. The time depends on the size of the flasks small flasks take 5 hours large ones take 12 hours. I usually pour after the flask has been ramped back down to 8000 F.

3) The usual method for investment casting does not need vents. With vacuum casting the vacuum is used and the investment is porous so no vents are needed. Some times a second sprue is used for complex parts. Centrifugal casting uses the pressure of the of the of the flying metal and again vents are not necessary.

Have you considered Shapeways for the parts? They have a bronze that is 90% copper and 10% tin. It is easy to machine, I use them for my masters these days and if they were around when I started I would not have casting equipment.

Dan
« Last Edit: August 01, 2017, 04:57:58 PM by Dan Rowe »
ShaylocoDan

Offline maury

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Re: Casting bench upgrade
« Reply #8 on: August 01, 2017, 06:48:51 PM »
Dan, thanks so much for the quick reply. I looked up the link to Riogrande, and wow, what a good find. I will probably be ordering supplies and investment from them.

I think I have or can make most of the stuff to set up except for the burn out oven. Don't have an answer for that yet.

A couple of questions, is a 4" flask large or small for burnout?
I guess stainless is best, but what would the issues be if I made the flasks from steel pipe?
Why do you let the flasks cool to 800 deg before pouring?

I could consider Shapeways or just making the parts on my CNC, but I need about 200 parts all totaled.

If you are still in Dripping Springs, we are close, I am in Leander. Perhaps we could get together and chat sometime.

maury

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Online Dan Rowe

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Re: Casting bench upgrade
« Reply #9 on: August 02, 2017, 01:56:43 AM »
Maury, all the answers I have given come from the book I mentioned. I consider it an essential reference for this work. Used copies are cheap and my copy is well shop worn.
https://www.amazon.com/Centrifugal-Lost-Wax-Jewelry-Casting/dp/B006DVIZ2A

The book says 8 hour burnout for a 4" flask. It also says 9000 F for bronze I was posting off the top of my head. I have my programs set for 8500 F. I am not really sure why but it works most of the time. I did a demo at a steamup and I could not see the oven temp. and it went below 8500 F the parts were small and did not form completly which is what the book says will happen.

A steel pipe will work fine and so will a soup can, They will not last as long as SS.

How are you planning to make the wax parts. I use a rubber mold and a wax injector. I try to arrange the wax sprue to be used as the sprue to attach to the base or a wax tree.

Rio Grande has the rubber bases for the flasks and they are handy as the tree is built on them and they seal the base so the flask can be filled with investment. I use masking tape so I can fill to just slightly above the top with out spillage.

The working time for the investment is 10-12 minutes and that includes mixing then vacuuming the mix pouring the investment into flasks and a second vacuum. You need to have everything organized for this process. The investment comes with a time chart and I use a kitchen timer to keep on track.

I have my casting bench in the garage and it has been way way to hot to cast this summer but we can get together and chat about the process. (I am still in Dripping Springs)

Dan
ShaylocoDan