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Good luck with the inspection TS, you'll be showing that molten bronze who's boss in no time now!

 

CO, right back at ya!  Who knew? 

Born and raised in Ottawa, but now I'm technically a 15 minute walk South of city limits with a Winchester mailing address, so jury duty and missed UPS packages would actually mean a trip to Cornwall, Ottawa's Shelbyville...  Who wants to admit to that though, amiright?!  :)  It's all about where you meet up for game night.

 

Driving right through Ottawa daily to get to the office across the river in Hull still counts too! 

 

but I'm not trying to derail this thing, go Sens, carry on...

 

Kang

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I passed inspection and now have power, Power, POWER!!!!

 

Ahem, yes, so for the first time in 20 years, I don't need extension cords to power my studio and shop.  I am very excited.

 

I used the excited energy to set up the foundry:

 

(Click for larger pictures.)

post-140-0-58243300-1483567191_thumb.jpg

(Note the fully installed vent system; I still need to install the elephant trunk for the melt kiln)

 

 

I have also started collecting metal to use in casting:

 

post-140-0-27419400-1483567192_thumb.jpg

 

From left to right: Bronze (tin based) casting grain from Rio Grande (I bought a pound), pewter from a bunch of old/broken minis I melted down, and 1.25 lb of copper from all the tag ends from the electrical project.

 

 

@ Kang: I am toying with creating my own bronze using the copper and the pewter.  The pewter is 95-98% tin with the rest being some mix of antimony, copper, and bismuth (though the exact mix varies).  I assume then that I should be able to take 90% copper and add 10% of the pewter to make my own bronze, yes? How do you ensure it is all blended well into bronze, a carbon stir rod?  What flux should I use (I have borax)?

 

<Edit: I found the answer to the above on Alloy Ave.  Essentially, yes, but the antimony/bismuth will affect it a bit making it less toolable.  To paraphrase them, "It would be good for sculpture work."    :B): >

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Sounds like you are on the right track with the wiring (congrats) and alloying.  You say you got your answer over at AlloyAve, but I will give mine anyhow since you asked, and maybe in my babbling I will regurgitate something you did not see there.

 

Start with a "heel" of molten bronze, add the pre-weighed copper and do your best to push it below the surface of the heel to reduce exposure to the air.  Once that has melted, add the correct amount of pewter to go with the copper.  The pewter should melt in no time.  Graphite rod or ( should be cheaper) mild steel for stirring, both are fine and either will deteriorate over time, but graphite won't contaminate your melt. Contamination from mild steel should be minimal and likely within acceptable levels if you go that route, it's what you will likely use for skimming dross anyhow.  That is what I would and do use to poke at the melt.

 

Borax for fluxing copper alloys, check.  Right from the box you got in the laundry aisle, that is the stuff.  Some people add broken beer bottle glass to the crucible at the beginning; it melts first and floats, protecting your alloy from oxidization.  A tiny bit of borax can be added to the center of the surface of the glass cover just before a careful and gentle stir, followed by skimming and pouring.  This keeps the flux off your crucible walls so it can't attack them chemically (much), and the flux makes all the molten glass and dross glop together so it comes out in one easy to remove blob.  Ideally.  From what I have read... 

 

Then there is degassing.  Keep your furnace running as close to neutral as you can, maybe erring on the side of slightly oxidizing since you can deal with dross by fluxing, and it should not be an issue.  This of course will depend on your alloy of choice since different alloys misbehave under different circumstances.  But there are solutions for gas porosity in your castings too if it comes up.

 

Next step should be to streamline your casting work flow to eliminate extra movements and the need to be making decisions or hunt for tools during the melt and pour operations.  Make a checklist to go over before you start the furnace, and use it every time. Update it whenever you come up with ways to simplify things.  For example, I lay out 2 sets of heavy leather welding gloves in the same pace every time, in arms reach of my furnace, with lefties on the left and righties on the right, my main gloves go on top and the backups below.  That way when one I am wearing gets too hot to handle while I am skimming dross (it happens, I have gotten blisters on my pinkies from putting hot gloves back on even a minute later), its replacement is right there where it should be, without me having to think about where I left it or be tempted to finish the skim with a tool that is cold (aka WET) enough to handle barehanded.

 

That's all I have right now; good luck, and again, congrats on getting your wiring approved!

 

edit - yup, a ball valve here and there for emergency fuel shutoff is a great idea!  1/4 turn is just about like an on/off switch.  I have them as the last thing before my burner so I can shut off quick without changing the setting on the needle valve I use for fine control of the waste oil flow or the adjustable propane regulator that I use for preheating the furnace.  Although I don't like having the regulator open when I am not burning propane, it's still a comfort to know I can cut it off from the hot furnace ASAP if needed, it buys me time to get to the regulator and main tank valve.

 

Kang

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Sounds like you are on the right track with the wiring (congrats) and alloying.  You say you got your answer over at AlloyAve, but I will give mine anyhow since you asked, and maybe in my babbling I will regurgitate something you did not see there.

 

Start with a "heel" of molten bronze, add the pre-weighed copper and do your best to push it below the surface of the heel to reduce exposure to the air.  Once that has melted, add the correct amount of pewter to go with the copper.  The pewter should melt in no time.  Graphite rod or ( should be cheaper) mild steel for stirring, both are fine and either will deteriorate over time, but graphite won't contaminate your melt. Contamination from mild steel should be minimal and likely within acceptable levels if you go that route, it's what you will likely use for skimming dross anyhow.  That is what I would and do use to poke at the melt.

 

Borax for fluxing copper alloys, check.  Right from the box you got in the laundry aisle, that is the stuff.  Some people add broken beer bottle glass to the crucible at the beginning; it melts first and floats, protecting your alloy from oxidization.  A tiny bit of borax can be added to the center of the surface of the glass cover just before a careful and gentle stir, followed by skimming and pouring.  This keeps the flux off your crucible walls so it can't attack them chemically (much), and the flux makes all the molten glass and dross glop together so it comes out in one easy to remove blob.  Ideally.  From what I have read... 

 

Then there is degassing.  Keep your furnace running as close to neutral as you can, maybe erring on the side of slightly oxidizing since you can deal with dross by fluxing, and it should not be an issue.  This of course will depend on your alloy of choice since different alloys misbehave under different circumstances.  But there are solutions for gas porosity in your castings too if it comes up.

 

Next step should be to streamline your casting work flow to eliminate extra movements and the need to be making decisions or hunt for tools during the melt and pour operations.  Make a checklist to go over before you start the furnace, and use it every time. Update it whenever you come up with ways to simplify things.  For example, I lay out 2 sets of heavy leather welding gloves in the same pace every time, in arms reach of my furnace, with lefties on the left and righties on the right, my main gloves go on top and the backups below.  That way when one I am wearing gets too hot to handle while I am skimming dross (it happens, I have gotten blisters on my pinkies from putting hot gloves back on even a minute later), its replacement is right there where it should be, without me having to think about where I left it or be tempted to finish the skim with a tool that is cold (aka WET) enough to handle barehanded.

 

That's all I have right now; good luck, and again, congrats on getting your wiring approved!

 

edit - yup, a ball valve here and there for emergency fuel shutoff is a great idea!  1/4 turn is just about like an on/off switch.  I have them as the last thing before my burner so I can shut off quick without changing the setting on the needle valve I use for fine control of the waste oil flow or the adjustable propane regulator that I use for preheating the furnace.  Although I don't like having the regulator open when I am not burning propane, it's still a comfort to know I can cut it off from the hot furnace ASAP if needed, it buys me time to get to the regulator and main tank valve.

 

Kang

 

Excellent.  Not sure I fully understand everything yet.

 

Remember that my crucible as it is is 1" diameter x 3" (the ones in the following spoiler are shown at life size).  In that small tube, how would you go about skimming the dross. When do I skim, just before the pour?  I read somewhere that using a carbon rod the glass flux will stick to the rod and remove the dross, true?

 

How will I know if there even is dross to skim, when the whole shebang will be glowing white hot?

 

 

61vglw0nZIL._SL1133_.jpg

 

517vZ4TpNRL._SL1280_.jpg

 

 

 

 

 

I do not understand this at all:

 

 

 

Then there is degassing.  Keep your furnace running as close to neutral as you can, maybe erring on the side of slightly oxidizing since you can deal with dross by fluxing, and it should not be an issue.  This of course will depend on your alloy of choice since different alloys misbehave under different circumstances.  But there are solutions for gas porosity in your castings too if it comes up.

 

How do I control this with those two torches?  How do I know what temp I'm running at?  I'm confused here.

 

 

Thanks,

 

Andy

 

My flame is in the form of two propane torches in the mini kiln.

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On Saturday afternoon, I decided to try the first part of the process, making a vulcanized rubber mold of a sculpt and casting wax copies of it.

 

I am using Castello yellow rubber (which is standard in the jewelry trade).  You make the mold by making layers of the very soft putty-like rubber in a frame and then vulcanizing it at 340 degrees F.  I tried using talc so my mold would separate (though I'd been warned in tutorials that this doesn't work well with this type of rubber); most jewelers don't bother and cut the molds.  Cutting a mold is an art form and skill that I really messed up as you will see. 

 

The rubber:

 

post-140-0-04015600-1484020881_thumb.jpg

 

 

Preparing the mold rubber:

 

post-140-0-66873100-1484020881.jpg

 

 

Cut rubber with mini in place (paper still needs to be peeled on the center piece:

 

post-140-0-23998400-1484020882.jpg

 

 

Top rubber in place:

 

post-140-0-76849200-1484020882.jpg

 

 

Heat plates added.  Note that the rubber must be thicker than the plates.

 

post-140-0-24562200-1484020883.jpg

 

 

Vulcanizing (1 hour and 15 minutes at 340 degrees):

 

post-140-0-83308100-1484020884.jpg

 

 

Melted rubber coming out of the mold sides:

 

post-140-0-42145800-1484020885.jpg

 

 

Venting the fumes with my new elephant trunk vent:

 

post-140-0-96362700-1484020885_thumb.jpg

 

 

Removing from the vulcanizer:

 

post-140-0-11944300-1484020901.jpg

 

 

Cooling:

 

post-140-0-61372600-1484020901.jpg

 

 

Vulcanized mold:

 

post-140-0-21613200-1484020902.jpg

 

 

 

Removed and trimmed:

 

post-140-0-78139000-1484020902.jpg

 

 

Now you can tell that the really hard part was cutting the mold, because there are no pictures.  I was very focused and made a lot of errors.  I have a lot to learn here.  Here is the cut mold:

 

post-140-0-32412800-1484020903.jpg

 

 

Injecting with hot wax:

 

post-140-0-81861800-1484020903.jpg

 

 

Final casts:

 

post-140-0-66667000-1484020904_thumb.jpg

 

 

Every one of them is flawed, mostly in the ankles and some fill problems. None of them are good enough to cast.  I also broke the sculpt, so will need to fix it if I ever want to try it again.

 

 

Lessons learned:

 

1. Cutting molds is hard. I am going to need a lot more practice and experience.

 

2. I tried way too complicated of a piece for my first.  I need something without a hole that has to be cut around (this one had 4). It also had very thin parts that I am not currently ready to cope with yet.

 

3. This is very fun and very frustrating all at the same time.

 

4. Vulcanizing rubber smells bad.

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well in my opinion, as small as that is,  you did a great job on your first attempt!  The results are fully recognizable and with some minor wax work would match the original. 

 

So ....

 

 

WELL DONE!

 

:poke:

 

Problem is, I still need to learn how to sculpt in wax.  :rolleyes:

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It is really fun watching you move through this process.  Don't be discouraged.  You're doing something new!  Anytime we try new things several things happen:

 

1. we get frustrated and feel overwhelmed

2. we question our sanity and choices

3. our brains slowly remodel as we build new "muscle memory"

4. we reduce our risk of dementia

 

seriously- pushing the brain beyond what is comfortable is actually good for us.  Plus, you have such a nice plan for all this it renews my faith in humanity. Don't give up!!

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well in my opinion, as small as that is,  you did a great job on your first attempt!  The results are fully recognizable and with some minor wax work would match the original. 

 

So ....

 

 

WELL DONE!

 

:poke:

 

Problem is, I still need to learn how to sculpt in wax.  :rolleyes:

 

I think as soon as you learn the way it behaves in comparison to what you are used to working with, you will have the wax sculpting part down in short order

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Tried to post a reply here yesterday but the internet ate it!  It was even longer than this so maybe you guys all got lucky.  I'll try to answer the questions you rasied in replying to my last post here.

 

First, sorry TS, I really did not mean to overwhelm you with extraneous details about the degassing stuff - thinking more about it, your torches are probably pre-tuned to run a close to neutral mix of air and gas with not a huge amount of adjustability, so porosity in your castings resulting from an overly fuel-rich mix burning in your furnace should not be an issue unless you leave molten metal in your furnace to stew for some reason.  I tend to think of these things from my own perspective - my gear is all homemade and so my burner requires careful adjustment in order to stay lit at all, much less burn neutral, or slightly oxidizing or what have you (depends on the alloy in question, but always close to neutral).  Furthermore, the type of porosity defect I was talking about should not really even matter much for sculptural casting because the little bubbles show up on the inside of the casting, not so much on the surface if you are not grinding on your castings too much or polishing quite aggressively.  There are lost wax casters on the other forum who really know a lot more about that stuff (as it applies to casting bronze into small molds) than I do, if you want to find out more.  Your tin bronze should be fairly well behaved to work with in terms of dross and gas porosity from what I have read.  So you are lucky there - the bronze I have been working with a bit for its extra toughness (making bronze axes, well just one so far but more coming) is notoriously eager to become dross at the slightest provocation, so my molds have to be carefully designed with a pressurized gating system intended to reduce turbulence from the pour, etc., as well as taking care to control the atmosphere inside the furnace. 

 

There will always be some dross, no matter what alloy you pour or how careful you are.  The surface of the melt will look smooth and reflective even when it is glowing brightly from the heat once it has been skimmed properly.  (I am not sure 'white' hot is accurate for bronze pouring temperature,  maybe bright yellow?  Cast iron is close to white hot at near-3000F pouring temps, and the glow alone can actually sunburn one's eyeballs.  Bronze is hella hot compared with aluminum, but not quite that level hella hot.  But this can all be looked up)  Dross is lumpy looking and not so reflective, you will be able to see the difference.

 

Honestly I do not know how people running those little furnaces for tiny object casting deal with the skimming of dross - some videos I have watched don't even seem to do a skim, though fluxes are often used.  Maybe that is normal, but I tend to think about 50% of youtube videos are made by people who are still figuring out how to do what they are showing, so YMMV imitating them unless you watch a whole bunch of different tubers to get a handle on how to figure out which ones to trust... But someone at Alloy Avenue will be able to steer you right on that count.  Yes, skimming should happen right before pouring though.  Dross on the surface of your melt actually protects the clean metal underneath from coming into contact with the air and turning into more dross - skim early and you'd just end up having to skim again before pouring; you'd only be making more dross than you would otherwise.  Your thought about a carbon rod sticking to the glass & flux as a way to skim that tiny crucible sounds right to me but again I have not worked with the tiny crucibles, I look forward to learning more, vicariously, through your posts!

 

To really be sure you are at pouring temperature, a pyrometer is the tool you want.  You can make one on the very cheap with some ebay components and a hollow graphite sheath to protect the thermocouple from the molten metal which the probe end gets dipped into.  The backyard workaround is to dip a preheated mild steel rod into a clean spot (ie. push the dross aside for a moment) on the surface of the melt.  If it pulls out clean or anything stuck to it knocks off easily, you are good to pour.  If the metal sticks to it when you try to knock it off into your dross bin, you're not there yet.  Obviously the pyrometer is the way to go if you want to perfect your casting technique and achieve reliable and repeatable results.  The size and shape of your castings also affect the ideal pouring temperature.  Maybe not noticeably at the small scale you work at though - they are all tiny.  I'm still dipping the steel rod to gauge pouring temp in my furnace and it has worked OK for both aluminum and al-brz, so far it has not taken me too far astray but it is not foolproof - sometimes you do get a bit of dross stocking to the rod which can trick you into overheating the melt. 

 

Controlling the temperature of your burners precisely is possibly not practical outside of high volume production foundries where a huge crucible is held molten all day while people dip pouring ladles into the melt and add more ingots etc; when pouring whole crucibles at a time, it's best to throw as much heat as you can at the crucible to make the melt proceed as fast as possible - the less time the metal stays molten, the less dross and gas it will pick up, the better your castings will be. 

 

Never seen a vulcanizer in action before, that was a treat!  Other wax injection molds I have seen were made with RTV silicone products.  I guess your non-room temperature vulcanized molds are more durable, or cheaper to make or something?  Not my area of expertise at all, in fact I have only ever heard of non-RTV molds being made for making pewter spin-cast minis.  You ought to post the vulcanizer pix over at the casting forum, those guys would probably love to see that, and your new waxes as well!  They probably can also help you figure out what went wrong with the wax injection.  Maybe you just didn't have the first two toes on your left foot crossed for good luck or something.  The waxes look great from what I can see in the pix, so I'd say you came pretty close...  You will get there.

 

Kang

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One thing that can help with cutting into a rubber-type mold is to embed some small ball bearings into it along where you envision the two halves of the mold to meet.  After vulcanizing, those bearings will help you find your centerline as you cut through the thick rubber and will later act as indexing points to help the two halves of the mold align when you go to cast!

 

Keep up the great work, and don't get discouraged!  Almost every attempt I've ever made at casting has necessitated a bunch of tweaks to get things just right!  I frequently found myself having to cut thin air vents into the mold to help with fill issues.

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I wanted to thank you guys, Kang and Kuro, very helpful.

 

Continuing the Saga:

 

So I decided to try sculpting something simple.  I need to sculpt some skulls for a couple minis I am working on, so I thought I'd cast them and have pewter ones on hand.  At first, I sculpted two skulls and a primitive spear for my son.

 

I put them on a sprue and prepared them for vulcanizing:

 

post-140-0-12565000-1486437550.jpg

 

 

I put a liberal coating of talc on these, hoping to be able to separate these, then covered them and put them in the vulcanizer:

 

post-140-0-66318400-1486437550.jpg post-140-0-19246000-1486437551.jpg

 

 

When done, I pulled them out, trimmed the excess and began cutting the mold.  They did separate, but not as easily as I'd have liked:

 

post-140-0-66309100-1486437551.jpg post-140-0-22190200-1486437552.jpg post-140-0-82938300-1486437552.jpg

 

 

I then injected the mold with wax, over and over and over, but could not get a good casting to save my life.  I tried cutting vents, adding talc, and everything I could think of, but in every case the skulls failed to consistently fill. I decided that the long nails were just too long and the wax was getting too cool by the time it got to the skulls.

 

post-140-0-36343700-1486437553.jpg

 

 

I sculpted a couple more and made a new shorter sprue, then made a whole new mold of that.

 

post-140-0-90618500-1486437553.jpg

 

 

This time I didn't even bother with the talc.  The cutting went a lot better (I am learning a lot with each mold):

 

post-140-0-41934700-1486437554.jpg

 

 

I then injected them and got a perfect wax cast the first time!

 

post-140-0-53384600-1486437568.jpg post-140-0-95180100-1486437554.jpg

 

 

I started making loads of casts.  Not all of them were perfect, but at least one skull was good on each try.  After a while, I dialed in the right pressure on the injector and with my hands on the mold and got good casts most every time.  It takes about 2 minutes per cast due mostly on the need to wait for the wax to cool before opening the mold.

 

Next, I inserted a wax rod into the rubber flask base.  Using a flame and sculpting tool, I heated up the tool and welded the wax skull sprues to the rod in a tree formation:

 

post-140-0-05995800-1486437569.jpg post-140-0-59273600-1486437569.jpg

 

 

When done I put this in my perforated flask and prepared it to receive the investment. Investment is a silica based plaster used to make the mold.

 

post-140-0-15003800-1486437570.jpg

 

 

I weighed it and mixed it with water.  I looks a lot like pancake batter.

 

post-140-0-73618200-1486437570.jpg post-140-0-25815300-1486437571.jpg

 

 

I put the bowl in the vacuum chamber and put it under vacuum to remove all of the air.

 

post-140-0-81197700-1486437571.jpg

 

Then I poured it into the flask and put that in the chamber, vacuuming it. When done I let it harden for two hours.

 

post-140-0-38285200-1486437572.jpg

 

 

To my great horror, I had not inserted the wax rod far enough into the base and it had come out during the vacuum.  I could not remove the cured investment without ruining the wax tree, and so this attempt came to a disastrous end.  I was very despondant at that point and left it sit for a week before looking at it again.

 

post-140-0-02040400-1486437573.jpg

 

I did learn several valuable lessons, and I still have a good skull mold, so all I needed to do was to make more wax copies and build the tree again.

 

Live and learn.

 

The next post will be a bit more positive.

 

 

 

 

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