Advice on molding and casting my latest work

[mantrid]

Advice needed on mold making and casting the work below. Its not finished yet but Im thinking ahead.

Its the most complex shape Ive sculpted upto now and am not sure which way to go for making the mold.
Questions.
Should I cut it up and make separate molds for each bit?
Should I make a mold of several pieces from the whole. If so wheres the best places for the walls?
I thought of using a separate stainless steel rod for the pole inserted after the casting. But the bronze will shrink and so may not fit the rod, particularly at the clasped hand at the bottom. How to overcome this?
Would incorporating the pole into the mold, and casting in bronze as part of the sculpture be too tricky?
Should I cast it hollow or solid. Max thickness is about 2.5" at the hips.
Thanks for your time.

http://www.iddsoftware.co.uk/VFTPICS/sculpture/poledancer1.jpg


http://www.iddsoftware.co.uk/VFTPICS/sculpture/poledancer2.jpg

[racine]

there ya go, puttin the pussy on a pedestal....
from photo.....one mould maybe 3/4 pieces, start point at the bridge made by hand an foot. plaster piece mould or flexible [no hands yet...?..head off?] you may need to consider risers to let out air in traps. the main prob is where the funnel.
bronze shrinkage is variable to the thickness,suppose shrinkage between 5-10%. hollow casting gives the least shrinkage if the walls are thin..guessing 3mm for this. solid casting monkeys with accuracy, in a piece like this would be awful.

to be honest this is troublesome to mould and many would chance making direct in wax around a torso/thigh core. can free up the work nicely giving a sense of immediacy.

[Mold Man Mike]

mantrid

Are you sending the mold to a foundry to cast your bronze parts or are you going to mix bronze powder in a resin and cast your own parts?

Is the figure going to have a head?

I would tackle the piece making a brush-on mold, by using an armature to support the clay figure (a pole up into, but not through the model). Adding the pole to the finished casting. The use of shims (aluminum flashing works great) in between arm and leg holes (to have something to brush up against) is the way to go. The product I would use is PolyGel-35 (Polytek) urethane rubber. Self thickening once A and B is mixed. To make the mix thicker (if needed for a really thixotropic matrix for filling in a deep area or undercut) Poly Fiber II can be added in small amounts.

A plaster or plastic shell (1512 with Poly Fiber II) should be made on top of the mold in multiple sections (Depending on how "simplified " the mold is made).

Once the mold is made, a mold key knife or scalpel is needed to cut a seam along the needed areas (along the leg and arm, etc.). YES, this can leave a seam line on the casting, but can be cleaned up.
Hint: the cleaner the mold is put back together at the seam, the less the seam line will be seen on the cast)

Looking at venting for the bronze pour, I would pour through the head cavity and allow the natural vent from the one arm to the foot and back up again. A vent is necessary from the tip of the other foot back to the top by the head (Depending on the angle of pour). The other arm may need venting (again, Depending on pour angle).

I like to glue long, thin straws (I bought a box from a restaurant supply store)
to my model and make my mold around them for my venting. Straws pull out and the vent is there. If straws can not be glued, I cut a vent in the mold using a scalpel.

This is really hard to explain when the whole process is in my head, but I tried.

Another option is a block-mold, which seams will need to be cut in to get the part out. Venting also.

I wont get into the block-mold method now, I'm winded from thinking and typing this manual.

[Mold Man Mike]

For help in the UK

making silicone molds: Mouldlife
www.mouldlife.co.uk

making urethane molds: W.P. Notcutt
www.notcutt.co.uk

[mantrid]

Racine
Do you think 3 to 4 pieces could do it? Where do you think I should have the joins? My initial thought was along the line of the following.

http://www.iddsoftware.co.uk/VFTPICS/sculpture/poledancer3.jpg


Which would be 10 pieces. Do you think this is unneccessarily complicated?

Thanks for all the technique Mike. Do you mean apply the rubber then cut after its set? What I have done up to now is build walls on the model where I want the joins and apply the rubber section by section letting each dry before moving on to the next. I may try your approach on this one to see if its easier. It certainly looks quicker. Do you think piece mold as in the pic above is the right approach or do you think it could be simpler ie less parts?
About the casting. I have my own little back yard set up for casting bronze, I'm still learning, but its going well and is perfect for small pieces like this.

What approach would you take to make it hollow?

About the head. Im doing that separately. Its easier to work on it the right way up and stick in on later. Cloths will go on later too, so no pussy on a pedestal, at least none on display anyway.

[racine]

try this. why not do a plaster piece of this, if u just want a couple of waxes????
help learn the fundaments of mouldmaking first.... cheap too and quality that the ancients understood.

[Mold Man Mike]

One way to get your model out of the mold is to cut it out after the mold is made,
Using shims, or doing as you said, making the mold in sections is another.
Yes, it is faster to make the mold then cut it out. Focus on where you would cut it before making the mold. Looks like just down both sides along the arms and legs to the shoe. If the part doesn't come right out, cut a bit more.

Send her over to me. I'll have a mold and shell made in 24 hrs.:D

I have no experience making plaster molds, but sound like Racine knows what he's talking about. Much cheaper using plaster. His 4 section idea looks less complicated than the 10 section.

As for hollow parts. Being so thin in the arms and legs, my experiences hand and machine roto-casting parts like this is the material does not slush well. Maybe someone else has more luck. I prefer to fill the mold solid to ensure no voids are in the casting due to incomplete surface coverage from roto-casting.

I forgot to mention. Make the rubber thicker where you intend to cut. The thickness will allow the rubber to key or register back nicely.

In my picture of the bonded bronze part, I brushed rubber over the entire model (which was a plaster model) and cut up the one side and between the legs.

[Scout]

Oh yes, I did see this.

Mold man, how do you key it if you cut it out?

I find the smaller the sculpture, the harder to mold. Scout

[obseq]

Mantrid,

Unless I'm off on the dimensions, I don't see why you would want to to cast hollow-- Your piece is small enough that you'd probably be saving only tablespoons of bronze in the end. Warping will also be less of a problem than it would be if you were to cast hollow.

Racine's 4-part mold seems feasible. (And his plaster suggestion is on the money) You might be able to cast it in fewer sections depending on your sprue system.
The key is creating a mold that will ensure the shortest distance for the metal to travel.

[mantrid]

Mantrid,

Unless I'm off on the dimensions, I don't see why you would want to to cast hollow-- Your piece is small enough that you'd probably be saving only tablespoons of bronze in the end. Warping will also be less of a problem than it would be if you were to cast hollow.

Racine's 4-part mold seems feasible. (And his plaster suggestion is on the money) You might be able to cast it in fewer sections depending on your sprue system.
The key is creating a mold that will ensure the shortest distance for the metal to travel.


By my estimate looking at the hollow waxes today it would take a quarter of the bronze and a bit more than a tablespoon. The sculpture complete is larger than the pictures suggest.

I opted for hollow to minimise shrinkage as the figure has to fit around a pole with the hand at the bottom clasping it and the pole fitting precicely into indentations in the thigh, calf and waist, any kind of shrinkage would throw them out of alignment and make them too small for the pole diameter.

By having larger numbers of smaller parts the metal will have a shorter distance to travel as you suggest. But more importantly than this it has to fit in my very small home made furnace.

I will also do a solid at some point to see how it works out

[Brendon Tohill]

Hi my mouldmaking skills are limited and I often get frustrated with smaller peices. With a piece like this I usualy coat with a rubber and thixotrpic then make a either plaster jacket or fibre glass.After taking the jacket off then cut the rubber open enough for the peice to come out.I know this is not ideal but it works for me but I do have to wait untill the wax is totally cold often over night before I take it out.
About the s/s pole I often leave s/s in my waxes and cast the bronze around it and have found no problem and often make a armiture of s/s wire to build wax around, once a peice of wire ended up being visable but for that piece it suited it.

[mantrid]

Hi my mouldmaking skills are limited and I often get frustrated with smaller peices. With a piece like this I usualy coat with a rubber and thixotrpic then make a either plaster jacket or fibre glass.After taking the jacket off then cut the rubber open enough for the peice to come out.I know this is not ideal but it works for me but I do have to wait untill the wax is totally cold often over night before I take it out.


This is exactly the aproach I took with this one.


About the s/s pole I often leave s/s in my waxes and cast the bronze around it and have found no problem and often make a armiture of s/s wire to build wax around, once a peice of wire ended up being visable but for that piece it suited it.

I though about doing it this way. I was concerned that the metal pole would expand and crack the shell. I may give it a go when I feel I can risk a shell. But they take so long to make I might chicken out. Do you know if the stainelss steel rod would tarnish badly in the furnace (burn out of wax and preheating shell), and is it easy to clean up afterwards?

[Brendon Tohill]

I aways use s/s core pins now I used to use silicon bronze welding wire and havnt had a problem with the metal expanding.As for tarnishing it is only a patina and is easy to polish off but if you are going to sand blast your bronze prior to patining it then I would mask the rod with rubber electrical tape otherwise your pole will have a satin finnish.

[Mold Man Mike]

Scout

I use this mold key knife: http://polytek.com/cart/index.php?target=categories&category_id=312 to make a positive on one side and a negative on the other. This helps with registration. I don't cut all the way into the rubber to the model with this knife. Just enough to get the curved part of the knife in. I finish cutting the rubber to the model using a #12 curved scalpel blade.

That's why I mentioned before to make sure to "beef-up" the areas with rubber when making the mold where you intend to cut later. Thicker rubber helps make registration hold better.

If I can not get a mold key knife into an area, I use the scalpel and cut in a jagged form (like alligator teeth) to help prevent slipping of the rubber when registering.

[mantrid]

Scout

I use this mold key knife: http://polytek.com/cart/index.php?target=categories&category_id=312 to make a positive on one side and a negative on the other. This helps with registration. I don't cut all the way into the rubber to the model with this knife. Just enough to get the curved part of the knife in. I finish cutting the rubber to the model using a #12 curved scalpel blade.

That's why I mentioned before to make sure to "beef-up" the areas with rubber when making the mold where you intend to cut later. Thicker rubber helps make registration hold better.

If I can not get a mold key knife into an area, I use the scalpel and cut in a jagged form (like alligator teeth) to help prevent slipping of the rubber when registering.



That mold key knife looks an interesting piece of kit, whats the wdth of the hump bit?

[Mold Man Mike]

mantrid

The width of the mold key knife is: 1/2 inch
The depth is 1/8 inch

[mantrid]

Decided to cast solid afterall as a more straight forward option initially, will try the hollow approach later.

Below are images of the wax after the primary slurry coat. I tried to keep it in as complete form as possible but had to remove the extended leg to reduce the height so it woulf fit my furnace, also the metal would have less distance to travel. I also always fill from bottom up now as I was getting problems filling from the top.

http://www.iddsoftware.co.uk/VFTPICS/casting/cs1.jpg http://www.iddsoftware.co.uk/VFTPICS/casting/cs2.jpg http://www.iddsoftware.co.uk/VFTPICS/casting/cs3.jpg

[mantrid]

Some pics of the wax just prior to cleaning up and applying ceramic shell. Quality is poor as using camera on phone. It shows the head that was missing in first pics

http://www.iddsoftware.co.uk/VFTPICS/sculpture/pd1.jpg http://www.iddsoftware.co.uk/VFTPICS/sculpture/pd2.jpg http://www.iddsoftware.co.uk/VFTPICS/sculpture/pd3.jpg