Casting With Tom Haltmeyer

April 19th, 2003

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This month's meeting was held at Tom's shop. Tom has been very generous in sharing his experience and providing demos for the club previously. We had a very large turnout for this week's meeting.



 

 

 

 

 

 

 

 

Here, the group is pictured around the mould-making table. 

 

This is the furnace and associated eqiupment. The furnace is a metal casing filled with refractory material on the sides and bottom. It has an opening to allow a propane fed heat source to enter and circulate around the crucible.  Shown also are a temperature sensor, cricible with initial material load, tongs, holders, weights and furnace lid.

 

We begin with Tom outlining the planning required. Everything is sequenced and timed as to allow the proper pieces to be in the right location at the right time. Especially important is the need to have a smooth motion of the crucible from the furnace to the mould. I'll get into this topic later, but first we fire up the furnace and begin the melt while we go back to the table to begin the mould-making process. 




Shown above is the template. It's a nameplate from  a Yates American mortising machine, brought by Marty as part of his restoration project.

 

Tom first placed the template face-up on the table and placed the cope over it.  A light dusting of talc is used to allow for seperation of the template from the casting sand following the ramming. Tom then began to pack the casting sand around the template as shown below. One tip was to not pack the sand too tight, and to let it breathe. Hence, he used the sifter to make a basic covering of sand material surrounding the template,

then continued to fill the cope with material packing lightly with his hand.   

     

He completed the pack with more sand and using a ramming tool packed the bottom of the cope somewhat tighter. There was no need to pack very tightly, as the moist sand held together well.

Following this, Tom flipped the cope over and mated the drag to it.

This becomes the back of the template, where the pour will be made through the spru. The process was repeated, with a spru sleeve in-place to form the opening for the pour. Talc was again used between the sand on the cope and drag to facilitate seperation.



The finished product can be seen below with the template removed and the cope and drag seperated.   

 Marty also gave a try at forming a second cope and drag around the same template.

In the end, 2 pieces were made, one from each mould. Now, on to the furnace, which is quite hot by now... 

This shot of the furnace with the lid removed shows the terriffic heat generated. The crucible is shown inside the furnace with the first load already being melted. We had a total of 3 moulds to pour, and this required additional material to be introduced to the crucible. When the metal is melted down, the crucible is only about 1/2 full from the first load.

Here, you may be able to see additional metal being pre-heated before introduction into the crucible to bring it's level up near the top. Once this second load is melted, and the proper temperature reached, the pour may begin.  

Tom is adding material very carefully, as it can have a tendency to out-gas somewhat violently. We all had to stand back a way and of course, Tom is wearing appropriate clothing for this task.

Here, Tom is removing the crucible from the furnace. This operation needs to be fairly quick as the metal will cool rapidly. The crucible is lifted from the furnace, using tongs, then placed in a circular holder from which it may be poured.

 

A small piece of paper is placed on the cement block prior to placing the crucible down, to form a burnt ash layer to prevent the crucible from sticking to the cement.  

Finally, here is the pour. There is some technique here which I cannot relate. It involves issues surrounding the molten material flowing through the spru properly and not clogging or hardening prior to reaching the outer cavities of the mould. To aid in this, Tom had prepared vents at various locations around the mould to aid in the pushing out of the air and introduction of the molten material.

Whew! Now, for the moment of truth. Tom lets the mould cool for about 5-10 minutes, then carefully opens the mould to reveal the results. Please note that these moulds are a single use only. They would need to have the sand recycled (re-oiled) and re-packed around the template for another run.  

Here's the part after sand-blasting. It's a beautiful piece.

We examined it closely and found that defects in the surface were actually reproductions of those in the origional template. Success, and the end of an excellent and informative meeting. Thanks a bunch Tom...