Sources for tools and parts

There are a few vendors that every engineer ought to be familiar with whether you do design, fabrication, or operational support. These vendors carry a wide variety of parts or tools within their particular market niche. They have good web sites and good paper catalogs. Personally, I recommend getting a copy of their paper catalogs and browsing them. Every time I browse their catalogs I find something new and think “I didn’t know they made something that did this!”

McMaster Carr – tools, maintenance and repair operation support, materials. Need a pneumatic bolt cutter, threaded rod, plexiglass sheet, bolt? This is the big boy of this list. Definitely get their paper catalog! Unfortunately it’s not free for the asking. You have to buy it. You might be able to scrounge one up. Mine is seven years old but the part numbers are still good. www.mcmaster.com

Newark – If you do anything with electronics you need this catalog. Lists resistors, connectors, cable crimpers, oscilloscopes. www.newark.com

Grainger – a competitor to McMaster Carr. They have a product line similar to McMaster Carr. Personally I prefer ordering from ordering from McMaster Carr. Grainger, however, has local outlets. Being able to pick up your parts locally can be very useful. www.grainger.com

W.M. Berg – are you designing low power mechanical systems needing couplings, gears, belts, bearings, shafts, pins? Get their catalog. I have found I refer to their catalog almost as much as McMaster Carr’s. www.wmberg.com

Small Parts – as their name suggest if you are building small things take a look at their catalog. They carry items such as hypodermic tubing, miniature screws, miniature tubing connectors, glass ball bearings, micro drill bits (down to .002” diameter, yes, .002”).www.smallparts.com

CarrLane – this one is bit more specialized than the others but I refer to their catalog often enough to be worthy of inclusion. They carry handles, knobs, hoisting rings, locating pins, fixturing clamps, fixturing bases, leveling feet, and T-bolts. www.carrlane.com

MSC Direct – A competitor to McMaster Carr or Grainger. I include them because their catalog has a good selection of machine tools, cutters, and inspection equipment. When I’m looking for a specialized set of micrometers, or an optical comparator this is where I go look first. www.mscdirect.com

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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