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Hi, has anyone ever converted a woodworking lathe to make plaster models for casting? I'd like to try turning a few models in plaset, but reluctant to fork out £2.5k for the machinery. Curious to know if anyone has used a table-top woodworking lathe for this purpose and any tips on how to do it?

Becca

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I've never even considered the idea of turning plaster the way you can wood.  Actually, what's the purpose?  You're going to make the mold itself on the lathe out of a solid chunk of plaster?  I could see making an original model on the lathe, but why use plaster as the medium?  Seems like it would be very funky to turn, coming off in dust.

If this is a thing, please explain it.

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yeah he's got to be meaning making the model in wood and then using that to make the mold. I can not think of any benefit to making the model in plaster on a lathe.  You wouldn't cast plaster models? I don't even think you can.  

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1 hour ago, Stephen said:

yeah he's got to be meaning making the model in wood and then using that to make the mold. I can not think of any benefit to making the model in plaster on a lathe.  You wouldn't cast plaster models? I don't even think you can.  

Turning plaster on the lathe for masters is definitely a thing!  More of a European thing I think, but I've seen lots of videos of it

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Plaster lathes and plaster sledging are a thing you guys.

Its not uncommon in industry to make a master form out of recently set plaster that still retains some moisture and is soft, and take multiple casts from it. It's messy, but not particularly dusty. I didn't take an intense look at the lathe at Medalta while I was there because plaster isn't really my thing, but it looked pretty similar to my Grampa's wood lathe. 

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I'm somewhat confused by the terms, I think.  When Callie uses the term "master form", that's the positive, right?  Then you'd then make a mold off that, the negative.  So you're casting a plaster mold off a plaster turned object.  Some kind of super release agent would be required, I'd guess.  The plaster from a wood lathe could be pretty smooth, no grain, but otherwise I don't see why plaster on a lathe would be the material of choice.  I'll have to see what they are making.

Yep, it's on Youtube all right.  Makes some sense now.  It would cut super easy and be cheap.  Learn something new every day.

I have some experience with wood turning and in my opinion, I want to be careful attaching the plaster block to the lath.  The plaster, especially in an uncured state would not have much strength holding screws from the chuck.  A flying projectile from a lathe is no fun.

Edited by CactusPots
update

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54 minutes ago, Callie Beller Diesel said:

Plaster lathes and plaster sledging are a thing you guys.

Its not uncommon in industry to make a master form out of recently set plaster that still retains some moisture and is soft, and take multiple casts from it. It's messy, but not particularly dusty. I didn't take an intense look at the lathe at Medalta while I was there because plaster isn't really my thing, but it looked pretty similar to my Grampa's wood lathe. 

Yeah but he\she is talking about using the lathe to cut it and I think that will make a huge amount of dust. Having a dust system for a lathe only kinda gets the dust since the cutting span is so huge. Maybe tent the whole thing while you cut.

how do you get the plaster model to separate from the mold plaster? Will the cured one just separate?

 

edit: never mind the second question as I realize you could just spray the model with sealer and it should separate.  

Edited by Stephen

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26 minutes ago, liambesaw said:

It's not bone dry plaster, at least that I've seen.  It looks like it comes off in chunks and settles fast.  Plaster also has no silica and doesn't pose the same long term risks that something like clay would.

yeah and  guess you can soak fully cured plaster as well. I CNC molds directly so I can skip the whole neg/pos and rubber molds but I use a dust shoe. I will try one next time soaked. Just seemed like it would gum up but I worth a try. Hate plaster dust!

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4 minutes ago, liambesaw said:

Maybe somewhere between soaked and dry would be best. I'd imagine a CNC mill would probably have a hard time clearing soaked plaster

Yeah I just figured it wouldn't work well and why I haven't tried it wet. The lathe would have it dropping and falling. Still seems like a wood model would be better than plaster though. 

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1 minute ago, Stephen said:

Yeah I just figured it wouldn't work well and why I haven't tried it wet. The lathe would have it dropping and falling. Still seems like a wood model would be better than plaster though. 

I think it's just because plaster is very cheap and very easy to turn. 

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Also, there’s this old thread with a good video showing a vase positive being turned. It looks like there’s a couple of additional resources in there as well. In the video it looks to me like the plaster isn’t generating superfine dust when she’s doing the actual turning. Plaster is considered a low hazard material, but it does contain tiny quantities of crystalline silica. According to this MSDS , tests didn’t detect crystalline silica in plaster dust under most normal circumstances, but they seem to also encourage you to wear a proper mask anyways. 
 

 

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2 hours ago, Callie Beller Diesel said:

@terrim8 didn’t you take that plaster workshop at Medalta? How did they deal with the lathe? What was the dust like?

We made the tube shaped plaster forms right on to the lathe chuck. Then while the plaster was just set enough to handle, we put them on the lathe and started turning the shape, saving enough at the end to make a spare too. No dust, just crumbs of wettish plaster all over the place and the tools - lots of fun to clean up. There is a separate plaster working area where the lathe is- its kept away from the rest of the pottery - remember?

Wish I had that lathe!!!

Edited by terrim8
additional comment

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Of course plaster releases from plaster.  How else would you make multi-part moulds?

Using a lathe to turn plaster is easier than turning wood.  Different mess, different dust, but both are hazardous to health.

Take proper HSE precautions, no problem.

 

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6 hours ago, Chilly said:

Of course plaster releases from plaster.  How else would you make multi-part moulds?

Using a lathe to turn plaster is easier than turning wood.  Different mess, different dust, but both are hazardous to health.

Take proper HSE precautions, no problem.

 

ha ha showing my ignorance :rolleyes:

Haven't done any casting and just doing press molds but having a blast learning more. Great thread, have now spent a ton of time looking at videos I hadn't seen. 

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You still need to soap your master thoroughly. It will indeed stick if there’s not enough of a barrier. 
 

If you want some fantastic multiple part plaster moulds, Peter Pincus and Joris Link are both glorious madmen. (Links are to  instagram accounts.) Beware of rabbit holes!

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Final thoughts (maybe).  As to the original question, yeah, it's just a woodworking lathe.  The only caveat would be how to attach the plaster to the headstock.  Building a DIY wood lathe would not be a one six pack job, if you get my meaning.

I doubt if anyone here will try this, because really you can't do any form on a lathe that can't be done  on a wheel directly into clay.  Round is your form.  The only possible use I can think of would be trying to use some kind of clay that can't be thrown.  Bone China, maybe?  You need either throwing skills or wood turning skills.  Uncured plaster would cut nicely with a really sharp chisel, but there's more skill involved than you might think.  Easier to hurt yourself too.

The other reason no one here will try this is that you would need a completely separate studio to do it.  Any plaster chunks in the clay will blow out in firing.  Sure disaster.

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I wouldn't rely on a head stock alone.  I'd want a tail stock supporting the blank.  Plaster doesn't have the strength, I think, to be gripped by a jawed head stock the way metal or wood could.  Definitely wouldn't hold screws.  Let us know how it works out.

I still don't get why.  What can you make by turning that can't be a thrown form?  Rae's comment about using the turned form to make a silicon mold to cast plaster is giving me brain freeze.  You're making a plaster cast of a plaster model?  The only reason I can think of is if you want a slip mold ultimately, but have no access to thrown forms.  We are assuming clay is in here somewhere, right?

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