Sintering vlog - p.1

Part one of my experiments with sintering. Might not seem like it from the video… but this footage spans several weeks

A few key points the video shows

  • printing
  • sintering
  • castable refractory
  • filawarmer/no warmer
  • bowden printing
  • infill testing

duuuuuuuuuuuuuuuuuuude. Your kiln controller is like, 6,000 times better then the lab ones we have that probably cost as much as a Lamborghini.

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nice vid! plus, can I try to print your upa?

:grin: I spent a while looking at a lot of options.
Although it took 4 months for my kiln to be made and arrive I’ve got no complaints (especially for the price).

My requirements were

  • gas vent
  • 120v power
  • ~2400 Fahrenheit
  • <2k usd

Thank you, and for sure (not actually my upa) but here’s the link

Found that the one without the tail support is the way to go (the tail rarely makes it anyways)

I replaced the tail with a pikachu’s and am printing it now in vasemode

I think it should work okay except for the leg and ear’s connection, which does not use enough material. Let you know in a few days.

Very cool. I was talking to my brother and he mentioned splitting it in two halves and packing refractory in the halves. Might also try it soon…

That’s also worth a try. I was going to just pour it in the hole at the top. I have a suspicion that it’ll be fine as long as you don’t sinter at too high a temperature, but the proof will be in the pudding…

I just printed it, 2 layers side and top, the legs and tail threaten to fall right off. The thing is very light, only about 5 grams.


Looking forward to see what happens :+1:
I’ll share as well. Also that print looks real good, what layer height you running?

0.15 mm layer height, 0.4 mm nozzle on creator pro.

Here it is after sintering: definitely way too thin! cracks all over and no facial features to speak of. It did hold the bulk shape though.

It is still pure metal and makes a satisfying “ting” when you hold it close to your ear.

Again this is with a 0.8 mm thickness. (edit: actually it was 0.4 mm) Maybe double that for a chance of success with vase mode.

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Noice! I had a hunch the deformations of mine were from gas blowing out the top (normally separating the ears) which the hole on the top of yours addressed. The little upa’s I printed held their shape too but didn’t really polish up (although I didn’t let soak in vinegar first)

The gas expansion (during debinding step) is definitely something I’ve been noticing more and more. The gas has to leave the part somehow and for large flat areas it can create a sort of “bubble”. Maybe we can address it with pinprick holes designed regularly into the part. Haven’t seen one explode at least yet :slight_smile:

from your pictures and video I really think the big big big thing with your upas is running out of carbon during the sintering step. Essentially, they are getting cooked by the oxygen! I say this because even on this failed print, the part “smoooshes” or bends rather than crumbles if you hit it with a science hammer. The only time I’ve gotten a copper part that was brittle (as opposed to melting or immediately falling apart) was also when I ran out of carbon.

It is probably okay to use charcoal or woodchips like you are doing but use like 5 times as much or cover, cover, cover during the sintering step (leave uncovered during debinding). It’s a really simple change that I think hopefully could make a big difference.

Thank you for the explanation. I suppose that may be also why this last part I did doesn’t seem to polish up from it’s black patina (oxidation I suppose).
The “cooking” of the part would be something I’d like to know a bit more about. Do you have some details on what chemically occurs when not enough carbon is used?

I’ll try to cast a lid of sorts for covering since that seems like an easy win to try.

On the pinprick idea I actually was going to drill small holes into the tiny upas… but I’ll need a little more precise drilling utility…

no problem, I myself am just learning this very recently. When you get a good upa you will absolutely know it without question.

Oxygen is a thug. It’s missing two electrons in its outer shell, and it will take them from other elements whether they like it or not. Unfortunately for us, most metals to some degree would like that. They have too many electrons, and will give them up quite willingly to anything that wants them in the slightest. When this happens to iron in the presence of oxygen, we could say the iron has been oxidized, or we could say it has rusted.

Copper is actually pretty good for several reasons in this respect. For one, it has a better hold on its electrons. For two, the layer of copper oxide that forms doesn’t flake off, like in the case of rust, and forms a barrier to further damage. The problem is, it’s still not immune to oxidation, especially at high temperatures. And when you sinter, you have a huuuuuuuuge amount of surface area, so that protective layer doesn’t do a whole lot of good.

Carbon is the solution, because carbon is something that also gives up its electrons to oxygen, making carbon oxides (monoxide and dioxide). The latter one is denser than air and both are much less reactive than regular oxygen, which it displaces. as long as black, unreactive carbon is still present at elevated temperatures, the area should be void of oxygen and the copper should remain unharmed.

In industry they go the extra step and use hydrogen gas, which actually donates electrons, reversing any oxidation already present. This is what copper parts come out of the oven looking like when you do that :wink: it’s almost like cheating.

hope this helped. in practical terms I think the lid is absolutely the best way to go, try that!

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Very much so :+1::100:
Lid it is

Slightly better success after buying some coconut shell carbon and doing a partial cover with a lid. I forgot to mention… I’ve been trying to get good prints without a 2-phase debind (hence the partial cover).
I believe I need to drop the peak sinter temp a bit but… clearly copper here

The nozzle on the left was in its own sinter tray while the other two parts were together in a larger one, same burn.

Two things to note:

  • the part on the left was in a smaller tray where carbon ran out during the sinter (no deformation but no shrinkage, so oxidation definitely prevented the sinter)
  • the other two parts while warped, came out clearly being copper and polished easily

nice! definitely in the right direction. Good example showing the difference between shrink vs. no shrink.

When are you going to hook it up to your rocket?

First step… get one that’s solid and not warped :sweat_smile:
So for now I can use the failures as samurai hats for my upa

You didn’t fail to make a rocket nozzle, you succeeded in printing a goomba

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