I'm looking for three of the pictured component from a Heywood-Wakefield walkover seat. It supports the seat cushion and allows it to move when the seat's direction is reversed. This part has 68244 cast into one side. It's 16.25" overall. The pins that hold the seat cushion in place are 10" o.c. Please email me directly at np5070@charter.net if you can help.

NPaul,

If you have trouble finding these castings, have you considered recasting them? We have a local Foundry that we have railroad parts recast at, Cast Iron, Cast Steel, Cast Aluminum and I think some cast Brass. The reason I mention this is the part is relatively small and looks like the part it's self could be used as the pattern given its shape. My guess you could have rough castings in hand for I'm guessing $30 or so Dollars each. Just an idea if you can't find any and it might be holding up that project.

The main problem with using a mechanical component as a direct pattern for duplication of itself is shrinkage. Due to the temperature of the molten metal when poured, the finished part is roughly 3.5% smaller than the pattern used.

A proper pattern is made 3.5% oversize, so that the shrinkage results in a properly sized part.

Jeff

Jeff,
While I welcome your comments, We (Our various Local Preservation Groups) have be making patterns, casting and manufacturing parts for our railroad equipment for decades. Now I will say you do bring up a valid point with making most parts but there is so much that can be done taking shrinkage and other material aspects into consideration. To us this is a simple part (Bracket) that when cast properly would yield parts that would look and work just fine for needed application, yes there would need to be some machining to dress up and shape the casting but operations wise it should still function as designed. Now once you do get into what would be considered more critical mechanical parts there are many variables to consider with shrinkage being one of them.

I still feel that casting duplicate components if handled properly off an original is a valid option for this application given that original components remain unavailable.

In my free time I volunteer for local preservation groups, To pay the bills I'm an Industrial Engineer dealing primarily with Research & Test and Material Science for a Class 1 Railroad.

So that my wife (who's my partner in this restoration) will stop giving me grief- I hereby apologize for the billboard-sized photograph attached to my original message. I'm better with tools than with a computer! ...now perhaps I can sleep in the house tonight. :)

Uh, 3.5%? Like the commercial says, "not exactly..."

Different metals/alloys have different shrinkage ratios.

http://www.nonesuchtools.com/pmkr/shrink.html
(If you're not familiar with basic foundry/patternmaking, poke around this site - some good stuff is listed, including suppliers).

Proper patternmaking utilizes "shrink rules" -- customized rulers that provide the appropriate compensation for the specific casting material, without causing the patternmaker to fry his/her brain computing all the compensated dimension sizes while trying to make a pattern. Such items are usually available from a foundry supply house.