If he was mine.. I would do 6 on the outside and try 4 inside him. I've been doing the drill thing on sprues and cracking shell has just about disappeared for me. I get that with shell, wayy less sprues can be used because the shell is actually gas permeable, I think my main reason for going ape shit is for dewax more than anything. If things are going to go sideways, it's gonna be at dewax. Patching the holes adds an extra day, but it's worth it.
5 to 6 mm is the ideal bronze thickness for small items (that dont need an internal armature to support them), the more uniform thickness the better to prevent uneven cooling/shrinking issues. As you say it is very difficult to do this with a hollow wax cast through the small entry hole to pour the wax. For future reference, in this case as your silicone mould is nice and evenly split in half (easy acces to all the surfaces) i would have made the wax as follows. i would put a large pan of wax on till it is all melted and just started smoking. Then i turn it off and start painting the first layer into the mould, making sure to get all the details, using a hair dryer on hot setting or heat gun to push the wax into all the nooks and crannies. After the first layer is completed i would start laying the next coat of wax (which will have cooled a bit since youve turned the wax pan off). After several layers built to an even thickness of around 5mm i would clean the wax from the edge of the silicone mould (using a warm spatula and modeling tools) so the 2 pieces could neatly join together. Bolt it all together and reheat some more wax. This needs to be fairly warm to stick to your existing wax but not too hot to melt it. Each wax has different melting temps so i cant give you an accurate temp im afraid. Pour in your joining wax, leave for a few seconds and pour out the exess. Leave to cool completely and pop it out. I think someone metioned earlier that it takes a couple of goes to get a workable wax. I tend to agree. Every mould has unique caracteristics that need to be learned. A couple of thoughts on the wax making. By letting the wax pan cool between layer application you are reducing shrinkage and distortion(the later cooler layers hold the hotter first coats in place). Not too bad on small pieces but gets noticable on larger ones. I tend to use virgin wax in the first coats and recycled wax (burnout mixed with a bit of fresh) for the joining layer. This is a different colour to the virgin wax so it makes it easier to spot when it comes to cleaning up the seam. Next up, i agree with external sprues. Far easier to clean up after. As for number of layers of slurry/stucco i cant say, different brands behave differently. Best to go on thickness. It depends how you are going to pour your bronze. If you have the mould packed in sand before pouring the shell can be thinner than if you were to pour it standing in your burnout oven but as a rule of thumb i'd be aiming for between 8 to 10mm unsupported on the external shell. Go thicker if its got sharp edges or reinforce the edges with glass fibre. Internal shell i usually go 4 to 5mm making sure its thicker where the outer and inner shells join together. This is the weak point and has to support the inner shell. Im with jason with the pressure vent holes, saves a lot of stress (both your mental and mould physical) Sorry for the novel. J
So what's the thickness if the shell is sitting in a plastic dollar store bucket layered with kaowool??? No one has given me any grief about that white plastic bucket... LMAO. Good stuff J on pouring into silicone. I've seen the shrinkage issue first hand and took it all the way to bronze. Still learning! Now if only I could master this open face wax mold stuff, I'd be cranking out lanterns. I'm stalled at the moment for some reason and cant wrap my head around it. Maybe if I get the hell off THF and park my butt at the bench, I could get back in motion. Anyone know where to buy a bottle of ambition?
i thought the bucket was some military grade composite kevlar tactical bucket...... If id known it was dollar store i would have been all over it!!! For dollar store i would recommend at least an inch thick ceramic on all sides just to maintain maximum heat, an maybe consider super heating the bronze!!! Ok, master-class on open faced moulds such as plaques (lanterns!?!) and other thin flat section castings. These are the PITA of waxes to make as you already know by the sounds of it, but there are a few things you can do to reduce shrink/warpage. My prefered method as follows. Heat wax in pan till it starts smoking (but avoid flash point as this can sometimes be a little disconcerting to the uninitiated) and turn it off. While the wax is melting i would paint a thin layer of petroleum jelly/grease over the surface of the (resin or plaster) mother mould that holds the silicone. Paint in hot wax with a brush and heat gun or hot hair dryer as usual. Continue to paint the wax over the edge of the mould. if we to use zapins chicken mould as an example i would continue the wax over all of the silicone rubber, across the resin mother mould and hook it around the edge of the resin. Almost like if you were to drape pastry over a pie dish before trimming it off. This helps to lock the wax in place. When the first layer is done start the second by laying the wax on with the brush rather than scrubbing, taking care not to remove the first layer of wax from the high points of the mould. Continue this layer to the edge of the mother mold too. Now you have about 1mm hooking the wax to the mould. For the subsequent layers you dont need to take the wax all the way to the edge, just layer as you would normally. Repeat until you are 1 to 2mm short of the full thickness needed using cooler and cooler wax as you go. This takes some practice to get the timing right but by the final layer your wax in your pan should be hard and cooled around the edge and the centre should be slightly slushy/liquid (a bit like one of them chocolate cakes thats still a bit liquid in the middle..... Sorry for all the food references, i havent had breakfast yet!) Take your brush and stir the slushy wax in the middle for a couple of seconds til it becomes a paste (it will probably change colour to a lighter shade too). Now spread this paste onto the wax to get the correct thickness of your wax model. It spreads fine with a brush. Aim for as flat as possible. The final layer will be not much above body temperature so shrinkage will be virtually nil. If youve got it right the wax model is good to go when totally cooled. Dont try n rush the cooling with water or air. As a extra precaution you can lay a sheet of baking parchment or greaseproof paper (there i go again!) over the wax and place a flat plate or sheet of glass on the back with a bit of weight on it till totally cooled. This isnt always necessary but can help. BEFORE you remove the wax from the mould, attach the sprues to the back of the wax with the pour cup. Then you can cut the excess wax that you used to anchor the wax to the mould with a warm spatular or dull knife. Now you can remove the wax from the mould. I have even started the first few coats of the shell while the wax is still in the mould if the wax is really thin and a good tolerance was needed. This helps support the fragile wax till it has some shell reinforcement. Thats about it. Sorry for the thread hijack Zapin and sorry for the novel sequal. J
Excellent suggestions J. Filling it and pouring has left me battered and scarred. I'm going to give this brush method a try. Thanks buddy. Now go get some food! It's 230am here and time for the rack.
I'll give that a go for my second wax copy. I used a bright light to check the thickness of the shell and patched the inside of the bird with thin wax sheets until it was the same thickness (brightness) all the way around on the inside. This way it should cast fairly well even if it is a bit thicker. One thing I'd like to figure out is how to get the wax to stay on sharp edges. It seems to settle into low areas and slide off ridges making it hard to get an even coating without first filling up all the troughs before finally the ridges can be built up. Maybe the painting on method will fix this? I'll give it a go. Good tips on the shell part. I'll see what I can do when the time comes in a few months. I might get a few models made with different sprue patterns and see which gives me a good copy. I may not have enough metal to cast more than 1 or 2 birds at a time but we will cross that bridge when we come to it!
Yep, this is always a problem area. What tends to happen when you use a heat source on your mould is it melts the peaks of wax and fills the troughs. Theres 2 ways to deal with it. On smaller stuff like your bird you can paint the detail layer and get the air bubbles out. Then cool some wax so its a bit thicker and add it to the ridges to thicken them enough so they hold up when you add the next layers. On bigger pieces i tend to not address the issue at first, letting the peaks be thinner than the troughs. Then before i assemble the mould to join the pieces together i get some pliable firm wax (like modeling texture) and thicken all the high spots like i was sculpting. This way i know that its an even thickness. Join the mould together and pour the joining coat. Good technique using the light to find the thin spots by the way. I think with ceramic shell all your sprue patterns will come out well. It is very forgiving! I have top poured, J gated, over sprued, no risers and the sucess rate is nearly 100%. The only flaws ive had are shrink tears with too thick internal shell (early days when i wanted to be sure the mould would hold!), uneven shrinkage through uneven wax thickness, not enough feed metal (too skinny runners cooling before the casting) and finally not putting a riser on an obvious high spot and getting an air pocket cos i thought that the porous shell would let all the gas out. Even with ceramic shell you still need risers on high spots or at the end of narrow sections such as fingers or 'thin feathers' for example. These risers dont necessarily need to run all the way to the top of the pour cup, they can be blind. This might be something for you to consider. J
Some photos of where I'm at. Not finished yet of course. 20180228_225448-1 by Zapins, on Flickr 20180228_225502-1 by Zapins, on Flickr 20180228_225454-1 by Zapins, on Flickr 20180228_225528 by Zapins, on Flickr 20180228_225631-1 by Zapins, on Flickr
He looks good. That's a big hole. Plenty of room to stuff HILLARY in there before you weld it shut. Are those legs look solid? If they are, I'd dig some of that wax outta there or sprue to them. I bet J from France will chime in a few hrs from now when he has his morning pig out and coffee.
They are hollow legs about 1 cm thick walls. I used one of them to pour wax into the mold. I've got to figure out a good toe position that doesn't look stupid then I can finish feathering the foot and properly fuse the bird to the wax wooden branch. It's tail comes down perfectly and tripods with the wood to balance it. Should be pretty balanced when cast. His tail needs repair too. Some feathers didn't make it out of the mold. Got to dig them out haha.
Looking good Zapins. Is the wood wax solid? And are you going to re-separate them for casting and weld later? If you are planning on an all in one cast it may cause you a few problems. That will be such a huge chunk of bronze attached to smaller chunks that on cooling it will rip the legs from the bird. You would have to do some jedi-fu selection cooling/heating to stand a chance of getting it out in one piece. If not casting them joined but the wood wax is still solid then you may end up with porosity/shrink issues with the casting without some BIG reservoirs. If both are hollow then there should be no problem and i'll go now and finish my soy-yogurt and fruit breakfast and soy chai latte. I really like the tripod design by the way, good solution for stability. J
I think I'd be tempted to cast the bird with his feet separate from the log. I'd probably pin and weld him to the stump when it's finished prior to closing up his chest. Plenty of room to weld at the bottom there. No way in hell will that log be solid! Someone told me fine bronze art is done thin.
Im liking the pinning and welding idea. I would have gone straight to the welding, trying to save me some time. Then spent twice the time trying to jig it into the right position. Good forward thinking.
Wood is hollow. But it's going to suck to dry the inside of that shell. I think I'll need a dehydrator machine to dry the ceramic shell inside it.
I use a computer fan directing air into cavities in box made from insulation foam and a lightbulb. Never tried a dehydrator machine, sounds interesting. Will have a look and see if i can find one cheap.
If you can ventilate as Artopsy says, that's simple and may be sufficient with enough time. For drying hollow cavities I've used aquarium pump and desiccant. If your pump has an inlet and outlet barb, and you can run the air closed loop through the cavity, this is best because that way the desiccant only needs to absorb the water from the cavity and not ambient air. If you cant flow through closed loop, pump through desiccant, suspend a tube into the end of the cavity so the air must travel back up and out the opening thus flowing through the blind cavity. You may need to change the desiccant occasionally if not closed loop. For your bird, I'd let the outside dry for a day or two, then if you put desiccant on a tray, place the pump and flow through desiccant filter (piped into the hollow) and the bird inside a tent......say made out of a dry cleaning bag weighted around the perimeter, you'll have a closed loop system. Add as much heat as you dare. Aquarium heating mats can be a good regulated source of that too. A cheap source of desiccant is crystal cat litter. It's mostly silica gel. It will absorb water as is but you may need to activate it to make it more effective at grabbing vapor. To activate it, just spread it on a cookie sheet, cook for a couple hours below 200F and then for a couple hours at 300F. Place it in a quart container and flow through it. You can reuse the desiccant indefinitely by reactivating it. Some just use a can for the filter cartridge and toss the whole thing in the oven to reactivate but it takes a little longer. The hollows don't dry because the water vapor pressure inside is high due to all the wet material. This is because the vapor must first diffuse out of the opening which is slow and dramatically slows the rate at which water evaporates out of the shell. So lowering the vapor pressure to the ambient level should make the inside dry as fast as the outside. So depending upon how much effort and fast you want it to dry: Flow ambient air through/around the hole shebang. Expose everything to desiccated air. This helps a lot because the bigger the difference in vapor pressure the fast water will evaporate and diffuse into the dry air stream Add as much heat as you dare. Like vapor pressure/diffusion this effect his is not linear. A little heat can increase the vapor pressure of water a lot. Each step or combination will significantly increase the rate at which it dries. Voila....dehydrator Best, Kelly
I have intake/outflow air pumps I can use like you discussed. That would be a decent option though as the log internal diameter gets smaller it might be hard to stick a tube inside to properly dry it. I might use both methods. First the air pump then when it's dry stick it in a box and vacuum pump it for 15 to 20 mins at like 20 mmHg to pull the water out of the internal area. This just means I have to weld up a steel vacuum chamber.... a perfrct job for my new mig welder.... muahaha.
Just a couple of points youve probably considered but thought id mention anyways. For drying in a heated fan assisted environment you need to be aware that due to the big difference in coefficients of expansion in the wax and shell material it is best to keep the temp below 78degreeF and as constant as possible. The wax expands with the heat, the shell hardens, the wax shrinks on cooling leading to a weakened shell. Ive even gone to the trouble to store the shell materials in the same hot box. Also a good idea to try and dry all the shell evenly (inside and out) for optimum shell strength. Im not a materials engineer or anything but having the outer shell dry before the inner shell might lead to weakness where they come together? Ron Youngs shell casting book also mentions some clever stuff about very low humidity causing cracks for some reason but its been a while since ive read it and i cant remember what it was. If youre interested i can dig it out for you. J
Sure I'd be interested. I know that the shell instructions say not to use a fan for the first 2 layers to minimize cracking. But after that it doesn't matter too much. All layers are temperature sensitive and need a consistent temp when drying.
Wow, you got instructions with yours? I need to get onto my suppliers, barrels with a sticker torn off is about all i get! Will have a look for the book and see what Ron has to say. Its a fairly old book (late 70s early 80s i would say) so the info may be a bit dated.
