DIY Network

Wax Chasing and Attaching Sprue Bars A wax replica continues to be formed. From "Trade School" episode DTRS-310

In this segment, foundry apprentice Jeff Herndon transports the replica made in the previous segment, to the wax-chasing section of the foundry to repair slight defects left over from wax molding process.

advertisement

Jeff uses a variety of wax-sculpting tools to restore the artist's intended vision. From there, he further prepares for the bronzing process by attaching wax sprue bars.

Safety Note: Always wear protective eyewear when working with hot wax.

1. Using a hot penknife, Jeff carefully cuts the replica in two (figure A) to gain access to the inside of the shell.

2. Looking inside the shell, Jeff notices a slightly sunken area. He remedies this by softening the area with a hot air gun (figure B). He then carefully pushes it out from the inside to restore the contour.

Figure A

Figure B

3. For thin areas of the shell, Jeff uses pre-softened wax as a form of putty, and then builds up the areas to increase the thickness (figure C).

4. He fills in any leftover pockmarks by applying drops of hot liquid wax. Once all the repair wax cools, Jeff grates the surfaces relatively flat with a heated metal rasp (figure D).

Figure C

Figure D

5. With the main repairs complete, Jeff uses the hot air gun and a metal putty knife to remove any unwanted texturing (figure E). He dips an abrasive pad in mineral spirits, and then rubs the wax to achieve an extremely smooth surface (figure F).

6. Finally, he uses a penknife to remove excess bits of wax remaining in the more detailed areas (figure G).

Figure E

Figure F

Figure G

7. Having restored the replica, Jeff moves to another section of the foundry to learn another wax technique. He prepares for the bronzing process by attaching wax bars, called sprues, to the replica. The purpose of this technique is to create a hollow and therefore much lighter finished piece. After it's coated with a ceramic shell, the wax will be melted away, leaving behind several ceramic channels feeding into the mold itself. When the bronze is poured into these channels, they act to evenly distribute the bronze throughout the piece.

8. Because the relatively large size of this piece would make for extremely heavy work later on, Jeff uses a hot air gun and a penknife to carefully cut the wax replica into several manageable segments (figure H). He cleans up the edges with a scraper.

9. Jeff now cuts pre-formed wax bars to size with a hot knife (figure I). Onto one end of each bar, he cuts an angle that later serves to better funnel the molten bronze.

Figure H

Figure I

10. Working with one segment at a time, Jeff dips the angled tip of a bar into hot liquid wax, and then presses it inside and against the cut edge (figure J). He fuses the wax together using a hot knife (figure K).

11. With the main bars attached to the segment, Jeff dips the free ends of the sprue bars into hot liquid wax, and then presses them to a wax base, called a cup (figure L). The shape of this cup will help funnel the molten bronze into the sprue bar channels. To later attach a handle, the cup contains a rigid cardboard disc with a built-in threaded hole.

Figure J

Figure K

Figure L

12. To increase the bronze-funneling ability, Jeff builds up softened wax between the sprue bars and cup (figure M). To further increase the flow of molten bronze, he attaches several smaller sprue bars between the piece and cup (figure N).

13. Having properly attached all the sprue bars on each piece, Jeff completes the waxwork by sealing and smoothing all the connections with a hydrogen torch (figure O) .

Figure M

Figure N

Figure O