@@PotterybyKent The advantage of a little shake table would be that you could run multiple molds at the same time! Since you need at least 2 molds per handle AND you could use it for any of the molds you make in the future.
Nice video! Still I don't understand why you didn't use just 3d printed mold to cast directly. I do understand for other materials like resin or metal, where you just can't, but slip casting I saw lots of 3d printed molds.
You might want to look at the PrintWave technique used for making plaster molds for metal casting, as it solves a very similar problem. The key steps boil down to heating the plastic mold to the point where it becomes soft and can be removed easily, as well as using the build plate of the 3d printer itself as the parting line/mold bottom. While this method does destroy the plastic mold, these are usually just a thin light shell so it will probably still be a lot more economical than the added design effort of a multi-part mold, and does not limit the design (no undercuts or anything required)
Thanks. I'll need to take a look. But I've ver deliberately been looking at a process where the molds can be reused many times. Also, since the clay needs to be removed once slip cast, undercuts are still a fundamental issue.
Interesting idea. It might be hard to reach inside the mold (my hand barely fits in even the bigger ones). What is often done is an application of underglaze on the outside.
Instead of using PLA... you should try printing with PETG filament. PETG is a lot more flexible than PLA, and with thin walls like that it is nearly indestructible. Thin wall PLA tends to crack at the layer lines when you flex it too much.
Looks like extending the template by a couple of tabs that can be pinched together will make extraction much easier. That way the print warps inwards and away from the plaster for easy release.
I'd thought about something that stuck up, but then it couldn't be printed flat on the bed. The thing that is really preventing flexing is the curvature of the handle itself.
@@PotterybyKent mhm okay. In that case, maybe holes for dowel pins or wood screws could do the trick. Have you considered finishing the surface with filler, sanding and spray coating with lacquer?
I was going to add some screw bosses to hold it down to the bottom plate if plaster was leaking. Those could serve the double purpose of points to pull on. However the tape worked well enough so I left them out. As far as finishing the surface, yes I have several other videos showing how to smooth the surface. However for this handle it wasn't really needed. You already need to clean the (small) seam line so most of the handle is gone over in that process. Also by the time it transfers to plaster then to slip and then fired (and shrinks), and with glaze, pretty much most of the artifacts from printing go away.
@@PotterybyKentYou could have the handle part actually go past the bottom plate instead of stopping on it. Have some key holes that are open on the side that protrudes past the plate. Then you slide into these holes 3D printed keys that have a slight taper along the length so it’s actually a wedge. Think of how some old tables are held together with nothing but wedge pins. This would hold the handle part in tight, have more to grab from when removing, allow to be printed flat, and no need to use tape. Just slide out the keys and it should all easily separate.
@chadvoller Thanks! I was considering something like that - in particular as a way to not need the tape. However the other consideration is so plaster doesn't leak and I think the jog in the bottom is actually helping in this case. I could put that geometry in the handle part but that would increase the thickness.
Maybe it would be easier getting the plastic handles out of the mold if you add a couple of grip points on the insides. Like, just a nub or something that you could grab with the needle nose pliers.
I thought this too! inside the spur cups of the handle model you could put a rib across it, something you can grab with a pair of needle nose, since it's a little tough to get out with the fingers.
You wouldn't want a rib that spanned side to side as that would limit flexibility. What comes to mind would be pairs of horizontal tabs with a hole for something like snap ring pliers to get into. That would let you pull the walls together slightly. The downside of this is that this inner mold is printed rather thin so it can flex, and therefore those tabs might break easily (and adding reinforcement is counter productive given the need to flex). And it would likely require a new tool. For those who already bought the molds, I'd love feedback on this aspect of the design.
Most people can't print TPU easily and the surface finish is way worse which is a problem since it transfers into the pot eventually. My last couple videos (and the comments) go through a lot of the tradeoffs and considerations if you're curious.
Hi Kent! Your video showed up in my recommendations and I watched it because I recently made a metal mug with a handle. I don't know anything about slip casting, but I recommend watching the video "Print-Wave Metal Casting". Even though it's about metal melting, people have commented that it would be also great for slip casting. Cheers!
Don’t forget to score the ends of that handle and the pot where you want to attach the two pieces. The slip really doesn’t stick all that well to a smooth surface. But, if you score the handle and the mug, before adding the slip, it will make it that much more stable.
I haven't found that to be the case with the slip I'm adding, the moisture content, and proper drying. However if you've had issues or are concerned at all, it isn't a bad practice. For thrown pots and pulled handles it is very much a good idea since it reorients the clay particles.
The draft angle is what made the piece release with this iteration, they're absolutely necessary for casting like this as well as injection moulding. Also, if you take something like a palm sander and just touch it to the side of the mould with the fresh plaster, it'll vibrate all of those bubbles out immediately. Works for cement as well, that's ehat I usually do.
It very much is not only the draft angle as I had them in some of my previous iterations. This is different than injection molding because the plaster actually grows slightly. And yes there are several ways to help knock out the bubbles however with such a small mold I didn't have any issues here.
It's mostly about tradeoffs, your process and your logo. Currently I'm using an underglaze stamp I made (I 3d printed a mold and poured silicone in it). I've also used a 3D printed stamp to make an impression but my slip casting clay body isn't very plastic so getting the timing right was tricky and why I switched. I do use it on my thrown pots. I have videos on my channel for both. I have yet to cast in my logo - I think doing so would require a much larger logo than I'm currently using since plaster is pretty delicate. It is something I want to explore.
@@PotterybyKent just tried to make a casting with the logo into a single non-collapsible shape and the results are always different, so today I will print an blank mug and a separate stamp. Thanks for the answer!
At this point I don't use anything on them. My prints are in PLA but I'd imagine ABS would work fine. Make sure you have a good draft angle. And you can also try using a mixture of frozen wanter and isopropyl alcohol. This stays liquid at freezer temperatures and when poured into the print causes it to shrink just a bit so it is very easy to get out. I have a video on that in the play list and my more recent videos show it as well.
The thickness of the clay in the handle? Here it is cast solid so there isn't anything to measure. If you mean for a pot, that is determined through trial and error as it depends on your molds and clay body. But you can measure a freshly made pot and apply your clay shrinkage factor to get the final thickness.
@kbsorrells yes as I mention in the video you can also score in addition to slip. However with slip cast pieces (and correct drying) it likely isn't needed. And indeed I just pulled a bunch from my kiln and they are all great.
Yes it needs to be plaster, and not just any plaster, pottery plaster. It has special characteristics so it can absorb the water from the slip and transport it away.
1) I use a heat gun to soften the PLA mold for challenging designs, it lifts right out but is one-time use only. 2) I use Murphy's oil soap in a spray bottle (50/50 with water). Let dry about 10 minutes. Greatly helps with removal in corners and small text. Thanks for your continued experimentation Kent!
Thanks. Both have been suggested! On my large molds, Murphy's oil soap didn't actually help, so I havent tried here. But given the number of times it was suggested, more rigorous experimentation might be useful sometime down the road.
Nice vid! If you just throw the circle that you’re attaching the pot upside to on the wheel, then you can stick the pot in slightly and have no under cut. And use green ware cups for casting, then you can break the cup inside the mould for no chipping
Just 3D print the handle and pack it halfway into clay, make a flat slab by pressing clay into a container and flipping it out. I print aligned registers for mine. Then it can be demolded separately as the back and the handle. You can use silicon from there if you want it to be replicable, I’ve always damaged the 3D print getting it out so far.
Consider switching materials. Make a silicone copy of the handle model. Silicone works best for me with pottery plaster. Urethane is good too, and sometimes cheaper. I also tried and made my own reusable mold material out of gelatin, glycerine and water. Works too, but lower resolution.
Thanks. I've used silicone in the past and have a few videos here from a good while ago. Instead I'm working on a 3D printed only solution just like with the vessel forms made by Shape Cast. The intent is to go straight from print to plaster without extra materials.
May I once again mention boil molds? Release works great when boiling the mold - it only allows you one cast per mold, so there's that. But the finished plaster mold will of course work over and over again. The mold can be made very thin with very little inner supports which cuts down on plastic and printing speed.
I'm not sure I'm understanding the question. If it is about my slip, it is a bit tan when a liquid and fires off white in the glaze firing as just the raw clay body.
Love the video! I agree with the comments on the layer lines - on your larger moulds you sand and prime - basically filling in the layer lines. I assume you do not want a mould release (does it affect the plaster absorbency?) and so think the 'optimum' way would be to sand/prime the inner face of the handle and the base f the mould - which is what the plaster is gripping onto. Even at 'high' settings, each layer has a rounded edge sat on top of another rounded edge and I have found when using 3dprinting to make moulds (for casting concrete - via silicone) I need to do the sanding/priming that you do for your bowls (as I also do not want to use a mould release). However - I do then resort to some silicone (just the handle) and build a regular mould box around that.
Priming/sanding my larger molds or not doesn't make any difference really for getting them to release. Here the part is much smaller and therefore the tolerances are as well. Given additional testing I've done, changing the mold form is the way to go (somewhat in line with your last point, but I want to keep it all PLA). I think the other key factor that is causing some of these challenges is actually the slight expansion rate of the plaster.
Because the experiments I've done show that isn't the right direction. I tested it while developing Shape Cast a bit, and the improvements here were all about the mold form. However given the number of comments here, doing some more rigorous testing could make for some interesting videos!
I think it's because the plaster is surrounded on all four sides inside the handle and when the plastic shrinks, it shrinks around the breaking part. You can make the ear itself separately, applied in the same way as the separate wall, or maybe a semi-circular ear will be easier. I have the impression that all squares are problematic in ceramics. I'm waiting for the next videos. Now your video blog is better for me than any action series.
Love the scientific experimentation here. I'm interested to see you try TPU. I'm fairly sure my printer can handle it but I haven't invested the time or money to try. And I'm a bit worried about the filament messing with my PLA hot ends. I might just get a hot end just for TPU though.
Thanks! More of that is coming for sure! As far as TPU, I havent done much with it for awhile, but the modern printers do multi-material on the same hot end, so I'm not sure that's a huge concern.
I haven't done any plater molding so take my suggestion with a grain of salt. I think using mold soap would keep the plaster from sticking so much that it will not release without chipping.
I'm not sure mold soap works that way. It really prevents the plaster from bonding with itself, but my tests when making Shape Cast didn't show it did much with my 3D prints. To really dig in would require more testing.
Even a high detail 3d print is still a relatively grippy surface for a mold. I think if you just printed out the handle section itself, then put that on a silicone mat, that would allow you to separate it into two pieces
I'm trying to avoid silicone if I can. And strait up PLA prints have worked for my vessel molds. However breaking the mold into more parts is the way I'm going.
I don't think compressive and tensile strength are related much other than they are more when the plaster fully cures. I'm having similar issues, but seems to me that having a perfectly sharp edge is the reason, especially when the plaster isn't fully cured. A sharp corner is inherently a weak point. maybe adding a fillet around the edge would help negate this? Seems like doing this with plaster at a smaller scale like this is part of my issue. In other materials this would be less of a problem. I just now cast a part using a 50/50 of potters no.1 and ultracal.30. The ultracal would probably make a perfect mold as it's very much stronger, harder, and more durable. But I was concerned with using this sort of plaster because it has lower porosity, as its more for casting foundry stuff. I talked to another potter who has run a production slip casting shop for decades and he said doing a mix is what he normally does, as it makes the molds last much longer. He said they also maintain good porosity to absorb water during slip casting. I'm hoping this helps. My molds are similar to yours and don't have a massive undercut or anything weird. Middle part of the handle is probably just locking because of the plaster's expansion. Potter's no.1 has .21% and ultracal 30 has .08%. I'm betting that mixing the two will create a fairly linear change in properties. If so it'll drop the expansion to .145% Seems like a tiny number but, with a mold a tiny number is the difference between locking and popping it out. 😂 On simpler shapes or more rounded shapes like a pot (or a wing skin), it's pretty straight forward demolding. Thanks for the info, i hope you find some more insight into the issue.
These are great insights! Agreed that compressive and tensile strength aren't directly related but the hope is that the increase in strentgh over time is somewhat similar? But that is totally a guess. From what I understand, yes the other big difference between hydrocal and pottery plaster, besides strength, is porocity. Hydrocal is less pourous so behaves worse with slip casting (since it doesnt absorb and transport the water as well). However this is probably a matter of degree, so maybe the mix is just slower to form the solid clay? You're right that plaster doesnt like sharp corners. However adding a fillet would also make the seam line worse! And the point about plaster expansion is also a great one. It is tiny, but with something small it could be just enough to cause the binding.
@@PotterybyKent So I just got done pouring a first half of the mold with the blended plaster. It's definitely much harder much sooner. I'm gonna move to the second half but will try a few other parts i have that were too delicate for potter's no.1. The strength definitely increases over time. Not a linear rate but we know it takes a while to dry out to the full value, which is toward the end of the curve. The seam line would be worse with a fillet but then there is better draft. a 90 meeting of the two surfaces creates a section with little or no draft. A fillet could help but you'd have to rub off the seam afterward. Most injection molding things have similar issues but plastic is softer and more flexible generally. Even the composite parts i've made have some flash, all molds do i guess. Seems like with clay it's hardly an issue as you can rub your thumb along and take off flash. If it saved you hassles of breaking a mold... you already have to attach the handle. Im not a clay or plaster expert so i'm figuring out what works 😄
Best video yet! I am always in a similar position as you on my building journeys. Im not a fan of 4 part molds or overenginerd complexity...simple is best. I agree on Tpu not being the #1 choice not because of ease of printablity (its getting much easier with 95a high speed overture) but the end result aesthetics would not be pleasing to me. Tpu has to be melt smoothed and im not interested in burning tires if i dont have to lol. I think the "C" shaped design ending in the pour sprues causes contraction to the inside of the "C" this could makes it pinch as the ends come together especially with the large end sprues. With that being said I would.... Have a pour sprue on the outside/backside of the C. (Uncomplicate the breaking zones) and make a draft angle for the inside of the Cup handle. Tangentially widen the opening distance to create a better overall shape draft instead of so much focus on radial chamfers (those seem to make a new pinching problems also). Since this is not true slipcasting yet. Maybe spray a mold release agent. I have seen affordable ones at $10 a can for cement. The shape combined the detail of part needed renders the Freeze removal process unsatisfactory. If in a bind I recommend heat to soften the PLA and remove. Use a heat lamp for example. Keep doing a great job 👍 Also i have no idea 2hat im doing half the time either lol 😂 All i know is forward lol must go forward. Make them pots 😅
I also think the inside of the D shape might be constricting. But I think the challenge is actually the rounded bit, not the part near the sprues. The goal is the have this work with a multitude of handle shapes so I'd rather not impose design constraints if at all possible. Some will be needed, but the fewer the better!
Your shrinkage method usually avoids the need for any type of mold release, but in this case it's less effective, as you note. Perhaps a thin coat of soap or slip would do the trick.
Thanks. I'll keep that in mind, but I'm pretty sure it's the shape of the mold components that is the issue. The iterations here slowly improved things and that was the really change. A few more steps to go and I'll get there!
I echo that. When casting plaster, I found that two thin coats of Murphy's Oil Soap work great as a release agent. It's cheap and already comes in a spray bottle. Just one spray and then wipe into the problem areas with a paper towel. Let dry and apply a second spraiy and wipe. Then, after the plaster is set, you can sponge the surface with a warm sponge to clean off any residue. With your large forms, you have filler-primed the centerpiece to eliminate layer lines that create a bunch of micro overhangs. You may want to at least sand the edges a bit. Lastly, it requires a bit of post-processing of the slip-cast item, but you could filet the edge between the mold box and the handle form. Then after the slip is cured and removed, you can clean off the added clay flash to the handle.
@mrfochs Something on my backlog of things to test is Murphy's oil soap. I used it on my early Shape Cast molds, but found it could mess with the palster surface and didn't actually help with releasing. It is great for keeping plaster from chemically binding to itself though!
One thing to consider is that a handle shrinks far less than a pot or mug or whatever. Say PLA shrinks 1% with the alcohol slush (completely made up number, recalculate with a real one) it'll pull 1mm away from the walls of a 10cm wide pot which gives you a great chance of it releasing. But if your handle is only 5mm wide, it'll shrink 0.05mm, maybe not enough to "unlock" the PLA layer lines from the mold. This is definitely a job for flexible TPU filament, that can deform and let you peel the mold out of the plaster. TPU works on most printers so I wouldn't immediately rule it out - direct drive printers do a better job of it, Bowden printers will tend to have uglier start/stops because of the filament squishing in the tube but still print walls fine. If you have a "ugliness here doesnt matter" feature on your mold and tell your slicer to start/stop there, you should be OK - I use this trick to print TPU on an Ultimaker. Also it makes your molds disposable which isn't ideal, but you don't need to heat PLA to a high temperature to make it flexible - you could bake the mold in the oven to soften the PLA, then carefully peel it out of the plaster. I was doing this with my mug molds before I stole your alcohol slush trick.
Yes I totally agree about the percent shrinkage given the smaller form. I think the shape is also causing issues. In addition printing with TPU, another consideration is the ability to improve the surface finish (eg with priming like I've done with some PLA molds). I am happy to use the prints straight off the printer, but several folks have concerns about doing so. Having said all of that, just like I was stuck for a while with the pot forms for Shape Cast, I think I can get just PLA to work for handles too with a few more iterations!
Thinking about it some more... ultimately what's going on here the PLA and the plaster are getting mechanically interlocked. It's not happening on a macro level since you've got no undercuts + draft angles to boot. It's happening on a microscopic scale, and 99% chance it's the layer lines creating a whole lot of tiny undercuts into the plaster, locking it in. Plaster is great at capturing layer lines, the layer lines even end up visible in resulting slip casts. It's a pretty high resolution process, honestly. And yeah once it's locked in... Plaster is hard, and PLA is hard, and to get them apart one of them has to deform. The PLA probably deforms enough most of the time, but in spots like corners in the plaster (where your plaster is breaking) the PLA wins. This could be caused by mechanical force distribution reasons - sharp plaster edges/corners favor the PLA, maybe. Or it could be caused by a bad force put on the thing when you're prying the plastic out with a scraper. Someone else on here had the idea of making an ejection mechanism that can pull the PLA straight out of the plaster and avoid any twisting - I'd consider that. You can probably get real creative using threaded inserts in the back of the mold so you can attach some sort of removal jig to yank the thing out of the plaster. Also if you can get the plastic out of the plaster as quickly as possible (so it crumbles at a small scale, vs having large chunks fracture off) that may minimize mold damage. But the most direct solution is gonna be to either reduce/eliminate the FDM layer lines, or use a softer plastic than PLA, or use a urethane/silicone middle step.
It's also possible the 3D print isn't perfect, and it could even be the heat from the plaster setting is having some effects (plus the plaster expansion mentioned elsewhere here). I am counting on the PLA flexing some to get out of the plaster, and am having luck with breaking the mold into more parts.
I had thought about that as well. However these prints are on high resolution settings and are very smooth coming off the printer. And with the draft angle I added, I don't think that is the issue. I'm pretty sure it is a combination of the geometry of the handle and the bottom part of the mold box.
@@PotterybyKenthave you researched injection mold design? They have basically ejectors that push out the parts. Obviously you don’t want to have holes in the handle portion.. but what if you included a few holes in the base plate and plugged them during casting and then 3d print a base with posts where those holes are.. you could then unplug the holes and press the whole thing down on the base with posts to apply even pressure across the plaster during removal
@@youtubemkhayes1136It is likely overkill for his application, but air release can work. The plaster is sufficiently porous that compressed air can go through to push off the mold. Search molduct tubing for leading references.
@@youtubemkhayes1136 makes the mold a little more complicated but could work. The easier solution is to make the mold split more. I'm having the same issue and was working to design a more complicated mold but the CAD work is getting more complex and I'm not an engineer. On the handle mold, if you added one more piece that could be removed from the inside of the D part where it's sticking, it would probably be less of an issue? I have a feeling it's the very corners where the flat back meets the curved shape are actually creating an undercut or at the least a stress riser for the cracking. Taking any inspiration from high rate molds is not a bad idea!
