Tuesday, July 03, 2007

How do I make this?

I am designing a material storage container. One of the design requirements is that it can latch closed to prevent inadvertent opening. I came up with a design that utilizes the locking pawl shown in the picture above. There is a locking pawl at one end, an actuation arm on the other end, and a shaft connencting the two ends. The question now arises, "How do I have such an odd looking part made?" If it can't be made the design isn't worth pursuing.

This is not a mass production part. I will only need about twenty of them. This eliminates processes such as casting, forging, or powder metallurgy.

I concluded that it could be made on a CNC milling machine. It can be machined out of a solid block of material. The shaft of the part will be parallel to the milling machine spindle. The trick is to locate a milling cutter that will allow cutting on its top, side, and bottom surfaces. I show how envision it being cut in the second picture. The stock from which the part is being cut is in red. The cutter is shown in blue. The clamping fixture and the spindle are not shown.

A more elegant way of making this part would be to use a lathe with a C-axis and live tooling, or perhaps a swiss-screw type machine. I am, however, constrained by what is commonly available in my area. CNC milling machines are common but only one shop locally has a lathe with a C-axis and live tooling.

Postscript: My original design which used the locking pawl shown above was discarded in favor of a much simpler mechanism that uses a bent sheet metal tab.

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