//* {Bandsaw Iron Castings} ::
*//{2010.11.20 ~ Professional Work : Loisos & Ubbelohde}

Design :: Matthew Bitterman, George Loisos
Foundry :: Matthew Bitterman, Mike Feeny, George Loisos,
Special Thanks to: Tom Fox, Kyle Milligan, Darren Cockrell & Diablo Valley College
Image Credits : George Loisos, Eleanor Pries

This project represents the first phase of restoring a 1930's 36" bandsaw made by American Machinery Corporation, for the Loisos & Ubbelohde boat shop. It is a large cast iron machine with a pivoting table that was lost in a move, so we set about designing and casting a replacement for it along with a series of supporting components.

The table was designed in Digital Project parametrically using the solid modeling tools for a variety of subtle but important reasons. One such concern was that the center of mass of big 300# table needed to be located directly over the pivot point so a human could lift it. This was made a little more difficult because the table itself was necessarily asymmetric based upon the blade location, mortising fence track, and joint with its sister table. Another was the need to have all the vertical surfaces drafted (angled) for releasing the pattern from the sand during the molding process, which is actually really easy to do in Digital Project and allows these things to be redefined and updated downstream. It was also important to continually be able to change the designed thicknesses based on feedback from the total weight/volume of iron that would be required to pour the components, as there were tipping points regarding how much metal we could heat and pour within an acceptable time frame necessary to cast the parts. After design the the patterns were CNC routed and meticulously coated, and prepared for molding.

The cupola-casting of iron (especially in an art foundry) is a pretty crazy process compared to crucible casting - it is mayhem - metal is flying everywhere, people are everywhere, and the pouring temperatures are much greater than that of bronze or aluminum foundry work (around 3200ºF +). The high side is the process yields a whole lot of cheap metal really quickly - the cupolas we were using put out about 120# of hot iron every 7 minutes. It is sheer chaos until the last mold is poured off or the iron runs out.

From a design perspective grey iron has a smaller contraction allowance compared to bronze, however is prone to heat distortions, slag inclusions, and other inconsistencies that should be considered in the design of the gating systems in particular. Keeping the cupola running smoothly and consistently is also not a given for a variety of reasons and some taps of metal can be very hot, others quite cool, and there tends to be a lot of impurities in the metal as a result of sourcing it by breaking up old pipes and bathtubs.

This was actually a really challenging project due to the sheer scale and weight of these castings, and working with cupola casting and art foundry made things much more difficult. The sand molds from the large table alone weighed 1200lbs; we had to do the molding under a crane so we could lift and flip the 600lb half-molds. The iron kids from San Diego had to drive up a quarter-ton capacity bull-ladle just to pour the large casting, it was really an all-out effort.

We ended up nailing and all the components on the first try, and also the smaller half of the tabletop with only minor defects (still an 125# casting!). We lost the huge mold because we were not able to keep the iron hot enough in the bull ladle, which was a disappointment. The pattern however I believe is in route to an iron conference in New Mexico; there is a group of iron kids that want to see if they can cast it.

The raw castings of the tabletop will be heat-treated to relieve internal stresses created during the solidification process, and then blanchard-ground flat to a ten-thousandth’s of an inch tolerance before installation on the saw. The two-part tabletop will weigh 455lbs in grey iron, and measure 40" across.