Discussion in 'Lost wax casting' started by Zapins, Dec 10, 2017.
He'll get it the next go around. That's a big pour with lots of pieces to this ceramic shell puzzle.
Yeah next go around should be easier. I've got better tooling planned for the next pour. Too bad its gonna take me months to get back up to CT for another attempt.
The video should process by morning. I'll post the fixed version when its done.
Sorry, been out of the loop for a while with house/workshop move and all the fun and games with the phone company that ensues in this country to get reconnected. Its not all sorted yet but another engineer is turning up this week to finally sort it out.
I guess ive missed some fun and games? I will have a quick look through your thread for a catch up and see i i can add anything to the mix.
Welcome back Art! Good to see ya. Zap kinda screwed the pouch and I'm not much help.
or am I?
Ive had a quick skim through the thread from where i last saw it and youve made some good progress. Im gutted for you that the bird didnt come out and you lost the other one on the coating process. That was really unfortunate.
The feet and branch are salvageable i would say with careful chasing and finishing. Im impressed you got it hollow.
Now, i havent seen the videos yet and i have only skimmed the thread so if im repeating what others have already said, sorry.
There are a few things i can possibly help shed some light on but im off out shortly so will just start by saying that i could have had a pretty good guess which orientation the feet were in when they where draining slurry, even if i hadnt seen the pour cup and sprue configuration.
Im guessing you stood the wax on the cup while the slurry/sand dried and hardened?
What you probably did was first you put on your face coat of slurry all nice and neat and even with no air bubbles then sprinkled sand. When it cured you re-dipped with more slurry and sprinkled again. Repeat half a dozen times til thick.
What i think happened is (a bit complicated to explain for me but bare with me!) after your first, even, neat face coat of slurry and sand had dried is you slurried again (possibly a bit thick but not necessarily), sprinkled and stood it on the cup to dry. If the slurry is too thick or not drained enough between slurry and sprinkling sand, the top coat can slough off (technical term alert!!!, meaning the top coat doesnt bond well with the coat beneath and detaches) or it sagged down to the lowest part of the wax as it is standing on its cup. This not only causes an uneven thickness of coating, weakening the shell but also causes the slurry/sand mix to trap air pockets, tiny air bubbles that make the shell like foam.
So now we have a neat face coat loosely attached to a foamy (not a technical term!) second coat on the lowest parts of the shell due to gravity. The upper parts are fine as they wont have foamy thick slurry as the excess slides down to the lowest points. This is repeated till the shell is finished. When it is fired, due to the uneven thickness and the very foamy back-up coats the face coat detaches (possibly causing a rattling shell and blocking air vents?!?) leaving the foamy back up coats exposed and ready to receive hot metal. This causes tiny air bubble texture on the surface of the cast, but only in the areas that will have had the slumped back up coats.
Not sure if this is what happened but it looks that way to me due to half of the surface having the bubbly texture and it being on the side nearest the pour cup.
If it is whats happened its an easy fix for next time. Thinner slurry, drain the slurry well before the sprinkled sand and make sure there isnt excessive build up of uneven coatings. It usually happens in crevices or when the slurry sinks to the lowest points.
I used to see the slurry as a mortar to join the sand, nice thick coats to build shell thickness quickly. Now i prefer to see it as a paint to bind the sand layers together. Thinner coats equals stronger for me, and i rarely go more than 6mm (1/4 inch) thick now.
Any questions let me know.
I will see what else i may be able to help with later when i get a chance.
That makes perfect sense. Strength is derived from good adhesion between layers and not necessarily from shell thickness. Who'd a think it?
Glad to have you back art! It's been lonely in the lost wax casting forums without ya!
Not to worry this statue had a lot of difficult casting problems to solve that I'm not used to dealing with. Huge piece, new 50 lb crucible equipment & handling of crucible, hollow cast, multi-part design, lots of thin & thick sections and round parts that can shrink & damage.
It was more a learning experience than anything so I'm not too bummed that it failed. Just a bit bummed I can't try again for ages.
Me too. The key was using my shopvac to dry the inside of it out. 5 coats seems to work well for inside.
I wish it was that easy of a fix. I had the piece lying down on the drying rack with the clawsfacing down not dryingon the pouring cone. It was in anatomic position (the way it would stand after welded onto the bird).
I can try thinner slurry mix for the first and second coat next time. Though half the claws cast perfectly its just the 3 or 4 closest to the tip of the branch that didn't work out.
Its just weird because half the claws cast perfectly and they were all spaced roughly the same distance apart and all would have had similar coating and filling experiences. The only thing I can think of that might have been different between them is the burnout and rattling shell inside.
I still haven't been able to find where the chunks of shell that were rattling around inside broke from. I wonder if they broke inside the hollow core at the tip of the branch, then metal filled that area up and created a very dense thick solid part near the tip of the branch. Then when it cooled it pulled the metal back from the claws and side of the foot and tip of the branch? So maybe we are seeing shrinkage porosity on the tip there and that's why the other claws cast fine?
Hmm thats interesting. So you use thinned slurry for thinner coats on all the coats? Like even coats 3-7 with coarse grained sand? Does that help to reduce cracking?
What is the final thickness you like to get before casting a large piece like the eagle?
Also, any chance of seeing your slurry setup? I need to redesign my high tech coating system (home depot 5 g bucket and wire shelf for drying). Because I lost about 2 gallons of expensive slurry binder from dripping as I coated the large shell.
Here is the better version of the pour (at risk of flogging my already dead horse to a 2nd death):
Found something for ya Zap. Take some time and snoop that website. There is some really nice stuff there. The hard part is trying to get your stuff up there to sell. It is SERIOUSLY NOT CHEAP to put stuff up on 1stdibs. We need to find someone sympathetic to our cause willing to post stuff for sale there on our behalf.
Here's another cock for your collection of feathered friends Zap.
That's one pricey cock-a-doodle-do!
If I ever get my sand ramming up to speed, I'm going to try to reproduce this...
Some mid-century crap I got for my chicken raising wife.
(Sorry about the thread hijack, Zap)
Super pricey. Man jesus. If I got 2g for my bird I'd be over the moon.
No hijack issue. Cool sculpture. Post pics when you get it cast!
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