Sand casting an odd shape - sprue, runner, gates and risers

Very interesting project MHJ and very helpful to see your techniques in action.
Thats a good result on such a deep drag. I did think of adding support battens like yours but I'm using green sand and was worried the timber may pull out moisture and cause a drop out (still had plenty of drop outs)

Each pattern sat on supports/wedges to keep them from moving during ramming. Pic below is of the last board with matching part of the styrofoam maquette on it. I've been following Jeff's thread; he did mention your patterns dropping out, so I took extra precautions.

As with your project, each was recast in plaster for ramming up. Only one pattern cracked during ramming, though the jute cloth reo kept it together well.
The two end pieces (pic) had no reinforcing jute in them so I just had to hold my breath while very carefully ramming.
All pieces will be cleaned up and TIG welded (4043 filler), then I'll use a tungsten blade (meat axe) to facet some areas and blending wheel to clean the rest. I'll also bead blast the exterior to finish off. Happy days...

 

Instead of using shims and supports, I am doing a pack of sand under the majority of my piece to stabilize it. Spreads the load. It acts as a partial false cope that I then remove before I ram the true cope.

Mine will be TIGged together where the panels were cut to accomodate undercuts, but also welded to 6061 to make hollow blocks for assembly in the final sculpture.

I am looking forward to seeing your final piece.

Best
David

QUOTE="Ando, post: 53247, member: 9638"]Very interesting project MHJ and very helpful to see your techniques in action.
Thats a good result on such a deep drag. I did think of adding support battens like yours but I'm using green sand and was worried the timber may pull out moisture and cause a drop out (still had plenty of drop outs)

Each pattern sat on supports/wedges to keep them from moving during ramming. Pic below is of the last board with matching part of the styrofoam maquette on it. I've been following Jeff's thread; he did mention your patterns dropping out, so I took extra precautions.

As with your project, each was recast in plaster for ramming up. Only one pattern cracked during ramming, though the jute cloth reo kept it together well.
The two end pieces (pic) had no reinforcing jute in them so I just had to hold my breath while very carefully ramming.
All pieces will be cleaned up and TIG welded (4043 filler), then I'll use a tungsten blade (meat axe) to facet some areas and blending wheel to clean the rest. I'll also bead blast the exterior to finish off. Happy days...
View attachment 24372 [/QUOTE]

 

Hey Jeff and David, here's a pic of the four parts. Next step to trim/clean up, tack and weld.
The exterior welds will be tiny, so as not to upset the look. I think I'll bead blast when complete to make the finish more uniform.

 

Process of turning the styrofoam to plaster patterns
Hot wire cutting the original into four pieces
Silicon applied to make negatives
Plaster backing/removal of styrofoam piece
Plaster positive in the mould

 

Good to know silicon doesn't stick to foam. Looks like it pulled very clean.

 

Yes and stretches to remove as well, so the plaster positive has that top edge/lip.
There may be a way to stop the plaster sticking to the foam but the silicon picks up all that detail. (see the plaster positive in the last pic)

 

Ando,
I've been following your post and excuse me if I've missed something but I'm wondering why if you are carving the pattern in foam that you just don't use lost foam casting to make the pieces. It seems to me that it would much easier, cheaper, and faster.

 

I'm not going to speak for Ando but I can think of at least a couple reasons for not using lost foam, first, this method gives you the option of making multiple identical copies, second, since all of the cast pieces are very irregular shapes and need to fit together, recreating the pattern for even one single failed lost foam casting would be very difficult, to the point you might need to start all over and re-sculpt and recast all of the pieces.

 

Wondering if a basic 2:1 no blush clear epoxy would work to coat the Styrofoam (EPS) originals to make them less porous and a tiny bit more rigid before silicone.
I don't have silicone for molding but could make a test piece of foam with and without epoxy coating for someone to try.

 

Hey all, I agonised for weeks over trying the lost foam method but just couldn't risk losing the original piece.
Would not be a good look, phoning the artist...."umm sorry can go back and do another one"

Haven't tried lost foam before so I thought I'd play it safe with green sand. I would definitely like to become proficient with the LF method in the future.
The foam maquette was painted with several coats of water based polyurethane to seal it before it was laid up in silicone.
I used supports to keep the original from flexing while applying the silicone and plaster.
Epoxy resin was an option though I had the polyU on hand.

 

Just to wrap this thread; the project is complete. All sections welded and blended and the customer is very happy.
I had intended in leaving the welds to the artist to take care of but she wanted me to make them blend in to the cast surface.
I took the needles out of my needle gun, sharpened them to about 60 degrees and went to work. The action of deformation with the needle gun worked quite well.
Pics don't do the blend justice, as they bring out the colour differential (not noticeable IRL) but if you look at the edge of the casting; that was ground flat then blended with the needle gun.

Some partial pics here of the weld blends and the tool.