I know this suggestion is a little more labour intensive, but what about trying the wax holes in a smaller size, then drilling? Usually drills only have tear-out/break-out when their web can't fit through the material at the centre (most drill bits don't cut at the centre, and even those with a cutting web the centre spins so slowly that the cutting speed is effectively 0rpm), this is why it's common to first drill a smaller pilot hole in tear-out/break-out-prone woods and metals, usually just a little larger than the final drill bits web dimensions.
Standard 3D printer bowden tubes are 4mm OD PTFE, maybe you could find an appropriately sized screw (m2.5?) that would plug the hole and give it a head that would keep them from pulling through? Then put the printed outer mold for the plaster on to hold them in place rather than the tape?
The problem would be whatever plug the tube isn't PTFE and that would likely retain the slip so kinda defeating the purpose. As far as pulling through, my previous attempts had a decent tolerance and friction was enough so I think that is the real solution there. And even if not, no the outer mold wouldn't work since that is flush with the plaster surface. Pulling the pins from the outside wouldn't work since there isn't anything to get a hold of just as I had issues here with the wax pins that ended up flush.
If the holes you need aren't too small, you could try drilling the holes in the pot once it is completely dry using a small Forstner bit, rather than a twist bit. My guess is that would considerably reduce tearout. Another idea is to just go back to your original method of drilling the pot in the leather stage, and deal with the tearout afterwards by spinning the pot on your wheel and smoothing out the internal imperfections using a wet sponge mounted on a stick. Although you can't easily reach into your lantern shape using your hands, it seems to me that the hole is big enough to admit something like that. You could likely 3D print something that would be ideal for reaching all the interior surfaces where there are holes. Regardless of the final method you adopt for making the holes, it is likely that the end result would benefit from this sort of treatment.
After doing all of these experiments, and having time to reflect, I think the actual solution is to go a different direction. I think I need to change up my clay body so that it is more plastic.
You can get silicone jacketed electrical wire, which is for heat resistant applications. It's pretty cheap, comes in a variety of diameters, and you could just cut a bunch of whatever length you needed. It's flexible, which is not ideal, but at a larger diameter like you have, that probably wouldn't be a problem.
If the wax is not too consistent in diameter, perhaps pushing rods through slightly smaller holes will shear them to consistent size. That's common with wood dowel through a steel plate, but plaster may be strong enough for wax. Can you take advantage of slip thixotropy by swirling before you pour out the slip? That may minimize the amount of slip that remains on surfaces where you don't want it. Once the slip is demolded and dry, is it possible to effectively sand the inside surface by shaking with the largest soft ball that will fit inside? Something like wool dryer balls might work.
Thanks for the ideas. I don't think putting anything inside to sand the surface would really work. Either with the static friction it would just roll (and not sand) and if you had something heavy enough to impart force, I'd worry about cracking the bone dry piece.
What if, instead of drilling holes in the plaster mold, you cast the plaster mold in such a way that the holes are cone-shaped, with the inner diameter being slightly smaller than the outer diameter?Wax or silicone pins can be cast with the same angle at the cone tip, and a length such that they protrude a sufficient distance on the outside of the mold to be conveniently removed from the hole, and on the inside, they protrude 2-3 mm above the wall thickness of the casted slip. The cone-shaped holes will allow for a complete seal, preventing the slip from entering and also allowing light rays to travel parallel to the hole walls.
This has been really interesting to watch you experiment! When you were trying to pull out the wax pins I thought that you could melt the end into a blob that would prevent the wax pin from going too far into the mould. Good luck with the further design :)
Thanks! Yes I thought about that as well. However I'd need to get the tolerances correct first since some wanted to slide out and a blob on the end of the outside wouldn't help for them.
I think casting your own silicone pins would be trivial - you could design a "head" that prevented it from slipping too deep into the hole. A single 3d- printed mold could contain 10x10 pins and you could get 200 pins in 2 castings. Note that the silicone should probably be quite soft and viscous so that you could fill your mold without air bubbles. I could whip up a demo model if you're interested.
I think the trick with casting one's own would be getting a good surface finish so the geometry didn't pose any retention issues. And as with the other comments about adding a head - it wouldn't be that helpful for all of the orientations needed and if the tolerance was ok like my last videos I could just place it in the right spot.
McMaster-Carr has what you are looking for in PTFE, though some of the "off sizes" can be a bit pricey. If you pick the right diameters you'll pay way more for the shipping... And if you should go this route, or any other, get your self a Poly Pipe Cutter that uses a blade for cutting smoother ends, any cheap one will do. Also, spin the pins before pulling them out to help release the clay gripping them. Maybe a little coating of petroleum jelly on the pins to both seal any oversized holes and help to hold them in position. Use a high quality masonry drill bit for your holes in the plaster and YES, drill from what you want to be the good side.
That is a good idea. I'd need to make some good molds but then I wouldn't have the tolerance issue I had here in that case. And I could make them any size I wanted.
I was originally trying to make them when it was leather hard and my clay body wasn't happy which lead me here (I've got several other videos on that). I don't think I have the patience to do it when it's bone dry. I hadn't thought about doing it once it was bisqued.
I'm not sure if there'd be space for the clay to release in that case. When I use air for regular parts, the shrinkage of the clay is in my favor - pulling away from the plaster walls. Here the clay wants to constrict around the pins.
@@PotterybyKent I was thinking blowing canned air from the inside of the pot to just move the wet slip away from the pins before the clay shrinks away. Also wondered about the material you use to 3D print. Does that come in a spool? Would it be more consistently sized than the wax rods, and nonstick for the slip? Printing pins would be tedious, but might be splendid if the material works well. I’m a beeswax worker and would likely mold pins if the wax was the best option. Beeswax is durable and reusable. Alternatively, I use canned spray silicone on molds which would repel pretty much anything wet. Spraying your original metal pins should work well. One final thought on the metal pins is Plasti-Dip. There are both spray and dip options. It forms a long lasting chemical resistant plastic coating on tools, etc. it’s not expensive to try…
Ah I see. The newly formed clay is still very wet so any focused air blast could easily and inadvertantly disrupt the pot. I did briefly think about spinning the mold to get the slip off but didn't have an easy way to try that. Silicone spray was discussed in the comments previously and the worry there is about coverage and the coating coming off. Printing a pin wouldn't work because of the texture of the print (I have a 3d printed funnel and there is some slip that sticks to it). And the filament itself is too small to use directly. I'm not sure if it is slippery enough or not to shed the slip.
Why not try inflating a rubber balloon inside the mold to push the wax pins out enough so they can be easily removed from the outside? Additionally, this could help smooth out the internal surface.
How about 2.85mm diameter 3D printer filament? OD is well controlled + cheap, and plastics like PETG should be fairly smooth surfaced and hydrophobic. Exoeriment with 1.75mm filament first and see where you end up.
Also another idea - push the end of each pin against a warm surface to "mushroom" the end to a larger diameter, this'll keep it from going through the mold and it'll give you a bit of a handle to grab onto from the outside. For the tolerance issue, you might be able to make a gauge to sort your pins and eliminate the fattest/thinnest ones.
The idea of making one pin fatter is in another comment here, but that doesn't work since the orientation also matters with the pour tolerance. With a good one, it wouldn't matter.
How about using dry spaghetti or linguine and just leaving it in. Then when you fire it, the pasta could just be consumed by the heat. Kinda crazy but it might lead you in another direction.
I have seen (dry) beans mixed into throwing clay to leave cavities as they burn out. It's a very rough look! I think part of that is due to the amount the clay shrinks. I'm guessing the same issue would happen here - the clay still shrinks.
I know this suggestion is a little more labour intensive, but what about trying the wax holes in a smaller size, then drilling?
Usually drills only have tear-out/break-out when their web can't fit through the material at the centre (most drill bits don't cut at the centre, and even those with a cutting web the centre spins so slowly that the cutting speed is effectively 0rpm), this is why it's common to first drill a smaller pilot hole in tear-out/break-out-prone woods and metals, usually just a little larger than the final drill bits web dimensions.
Great point about the drills and yes that is an interesting thought! It's worth a try to see what happens.
Standard 3D printer bowden tubes are 4mm OD PTFE, maybe you could find an appropriately sized screw (m2.5?) that would plug the hole and give it a head that would keep them from pulling through? Then put the printed outer mold for the plaster on to hold them in place rather than the tape?
The problem would be whatever plug the tube isn't PTFE and that would likely retain the slip so kinda defeating the purpose. As far as pulling through, my previous attempts had a decent tolerance and friction was enough so I think that is the real solution there. And even if not, no the outer mold wouldn't work since that is flush with the plaster surface. Pulling the pins from the outside wouldn't work since there isn't anything to get a hold of just as I had issues here with the wax pins that ended up flush.
If the holes you need aren't too small, you could try drilling the holes in the pot once it is completely dry using a small Forstner bit, rather than a twist bit. My guess is that would considerably reduce tearout.
Another idea is to just go back to your original method of drilling the pot in the leather stage, and deal with the tearout afterwards by spinning the pot on your wheel and smoothing out the internal imperfections using a wet sponge mounted on a stick. Although you can't easily reach into your lantern shape using your hands, it seems to me that the hole is big enough to admit something like that. You could likely 3D print something that would be ideal for reaching all the interior surfaces where there are holes. Regardless of the final method you adopt for making the holes, it is likely that the end result would benefit from this sort of treatment.
After doing all of these experiments, and having time to reflect, I think the actual solution is to go a different direction. I think I need to change up my clay body so that it is more plastic.
You can get silicone jacketed electrical wire, which is for heat resistant applications. It's pretty cheap, comes in a variety of diameters, and you could just cut a bunch of whatever length you needed. It's flexible, which is not ideal, but at a larger diameter like you have, that probably wouldn't be a problem.
Any ideas for sealing off the cut end as well?
If the wax is not too consistent in diameter, perhaps pushing rods through slightly smaller holes will shear them to consistent size. That's common with wood dowel through a steel plate, but plaster may be strong enough for wax.
Can you take advantage of slip thixotropy by swirling before you pour out the slip? That may minimize the amount of slip that remains on surfaces where you don't want it.
Once the slip is demolded and dry, is it possible to effectively sand the inside surface by shaking with the largest soft ball that will fit inside? Something like wool dryer balls might work.
Thanks for the ideas. I don't think putting anything inside to sand the surface would really work. Either with the static friction it would just roll (and not sand) and if you had something heavy enough to impart force, I'd worry about cracking the bone dry piece.
What if, instead of drilling holes in the plaster mold, you cast the plaster mold in such a way that the holes are cone-shaped, with the inner diameter being slightly smaller than the outer diameter?Wax or silicone pins can be cast with the same angle at the cone tip, and a length such that they protrude a sufficient distance on the outside of the mold to be conveniently removed from the hole, and on the inside, they protrude 2-3 mm above the wall thickness of the casted slip. The cone-shaped holes will allow for a complete seal, preventing the slip from entering and also allowing light rays to travel parallel to the hole walls.
I was able to get a good seal in previous attempts with the right size hole - no need to use a cone.
This has been really interesting to watch you experiment! When you were trying to pull out the wax pins I thought that you could melt the end into a blob that would prevent the wax pin from going too far into the mould. Good luck with the further design :)
Thanks! Yes I thought about that as well. However I'd need to get the tolerances correct first since some wanted to slide out and a blob on the end of the outside wouldn't help for them.
I think casting your own silicone pins would be trivial - you could design a "head" that prevented it from slipping too deep into the hole. A single 3d- printed mold could contain 10x10 pins and you could get 200 pins in 2 castings. Note that the silicone should probably be quite soft and viscous so that you could fill your mold without air bubbles. I could whip up a demo model if you're interested.
I think the trick with casting one's own would be getting a good surface finish so the geometry didn't pose any retention issues. And as with the other comments about adding a head - it wouldn't be that helpful for all of the orientations needed and if the tolerance was ok like my last videos I could just place it in the right spot.
McMaster-Carr has what you are looking for in PTFE, though some of the "off sizes" can be a bit pricey. If you pick the right diameters you'll pay way more for the shipping... And if you should go this route, or any other, get your self a Poly Pipe Cutter that uses a blade for cutting smoother ends, any cheap one will do. Also, spin the pins before pulling them out to help release the clay gripping them. Maybe a little coating of petroleum jelly on the pins to both seal any oversized holes and help to hold them in position. Use a high quality masonry drill bit for your holes in the plaster and YES, drill from what you want to be the good side.
I looked at PTFE on McMaster - and it was way too expensive. The problem is the quality of holes and therefore material needed.
Kent, could you melt the wax and make custom pins to fit the holes that you can drill and make in the plaster?
That is a good idea. I'd need to make some good molds but then I wouldn't have the tolerance issue I had here in that case. And I could make them any size I wanted.
Maybe make the holes when it is leather dry, or even when it is totally dry. Alternatively you could drill them after a bisque fire
I was originally trying to make them when it was leather hard and my clay body wasn't happy which lead me here (I've got several other videos on that). I don't think I have the patience to do it when it's bone dry. I hadn't thought about doing it once it was bisqued.
Would a quick blast of air before pulling the pins remove the extra artifacts?
I'm not sure if there'd be space for the clay to release in that case. When I use air for regular parts, the shrinkage of the clay is in my favor - pulling away from the plaster walls. Here the clay wants to constrict around the pins.
@@PotterybyKent I was thinking blowing canned air from the inside of the pot to just move the wet slip away from the pins before the clay shrinks away.
Also wondered about the material you use to 3D print. Does that come in a spool? Would it be more consistently sized than the wax rods, and nonstick for the slip? Printing pins would be tedious, but might be splendid if the material works well.
I’m a beeswax worker and would likely mold pins if the wax was the best option. Beeswax is durable and reusable.
Alternatively, I use canned spray silicone on molds which would repel pretty much anything wet. Spraying your original metal pins should work well. One final thought on the metal pins is Plasti-Dip. There are both spray and dip options. It forms a long lasting chemical resistant plastic coating on tools, etc. it’s not expensive to try…
Ah I see. The newly formed clay is still very wet so any focused air blast could easily and inadvertantly disrupt the pot. I did briefly think about spinning the mold to get the slip off but didn't have an easy way to try that.
Silicone spray was discussed in the comments previously and the worry there is about coverage and the coating coming off. Printing a pin wouldn't work because of the texture of the print (I have a 3d printed funnel and there is some slip that sticks to it). And the filament itself is too small to use directly. I'm not sure if it is slippery enough or not to shed the slip.
Why not try inflating a rubber balloon inside the mold to push the wax pins out enough so they can be easily removed from the outside? Additionally, this could help smooth out the internal surface.
The balloon would move to fill the area of least resistance.
Why pull the wax pins at all? Just melt them or let them burn off?
Because I need to get the clay out of the mold. Beyond that, the wax would prevent the clay from shrinking as it dries and would likely cause cracks.
put a sacrificial material on the opposite side you are drilling from to support the clay as you drill through should stop the break out
Unfortunately it does not. And even if it did, that would be hard to do in the full sphere form.
How about 2.85mm diameter 3D printer filament? OD is well controlled + cheap, and plastics like PETG should be fairly smooth surfaced and hydrophobic.
Exoeriment with 1.75mm filament first and see where you end up.
I'm really looking for something closer to 4mm. I don't want to go below 3 for my particular use.
Also another idea - push the end of each pin against a warm surface to "mushroom" the end to a larger diameter, this'll keep it from going through the mold and it'll give you a bit of a handle to grab onto from the outside.
For the tolerance issue, you might be able to make a gauge to sort your pins and eliminate the fattest/thinnest ones.
The idea of making one pin fatter is in another comment here, but that doesn't work since the orientation also matters with the pour tolerance. With a good one, it wouldn't matter.
How about using dry spaghetti or linguine and just leaving it in. Then when you fire it, the pasta could just be consumed by the heat. Kinda crazy but it might lead you in another direction.
I have seen (dry) beans mixed into throwing clay to leave cavities as they burn out. It's a very rough look! I think part of that is due to the amount the clay shrinks. I'm guessing the same issue would happen here - the clay still shrinks.
Press them out from the inside so you can pull from the outside
I can't get to the inside of my sphere mold which is my target form.