Covered Topics

Please see the list of the topics I've covered. It's located near the bottom of the page. Thanks for stopping in!!

Wednesday, July 21, 2010

A Few Thoughts On Obtaining Custom Machined Parts

If you do much building, creating, or inventing, you will have need of custom made parts that simply cannot be bought off the shelf. Many an inventor or engineer turns to a machine shop to make such parts. This solution is not without problems, however, and is usually out of reach of the average home hobbyist or tinkerer.

Despite the sorry state of the economy, machine shops charge a king's ransom these days even to do fairly simple jobs. This is, in part, due to the 'set-up' cost, any special tooling or jigs, ... required for doing a job. Much of the time and labor cost to fabricate something is taken up with preparation: laying it out, precision measuring, and readying the machine tools to do the work. Many machine shops concentrate on volume work and don't want to mess with "small" jobs, as they don't consider those profitable. While volume shops can amortize the set-up and tooling costs over a large number of widgets made, a prototype or short-run oriented shop must charge for that along with the materials and labor of making one or handful of parts. On a "one-off" job, the set-up often takes longer than making the part itself. Even in the unlikely event money is no object, try to find a local machine shop: it's nigh to impossible in many parts of the United States, given the off-shoring of manufacturing in the last 30 years. Sadly, very few young folks today are going into this trade. This is in part due to market forces, coupled with the general low esteem modern society has for "working with your hands" or "getting dirty".

Fortunately there are ways around the problem in many cases. Here are several ideas I've used:
1) If possible, change the design to use something that doesn't require expensive machining. Lots of things can be "re-purposed". One example: People have made wind-powered generators using a front brake rotor, wheel bearings, and spindle removed from a junked car.
2) If you must have something made 'from scratch', try to simplify your design to require as few machining steps as possible. Every step in the process of making a part requires more tooling and set-up, and thereby adds cost to the total project.
2) If you have access to a local community college or high school that offers a metal shop class for adults, you can take a course and gain access to the tools you need to do your project. As an aside, many people take auto shop classes in order to gain access to facilities and instructional advice for rebuilding classic cars.
3) Don't overlook resources at work. I was lucky enough for several years to work at a small engineering company that had its own machine shop. With the permission of my boss and the staff machinist, I was able to get some stuff done during lunch breaks and/or after hours.
4) Finally, you would be amazed at the stuff one can do in a pinch using simple hand tools, some skills, and much patience. For centuries prior to the advent of lathes, drill presses, and CNC machines, people made many things by hand that, to modern folk, would seem impossible. A couple examples include clocks that kept excellent time, and 10' long wooden blowguns with nice, smooth, straight bores.

I've mentioned Lindsay Publications in a previous blog post. These folks have reprinted many old, "outdated" manuals that detail long-forgotten skills that folks used to get things done prior to the modern era. They're online, or you can still order their books the old fashioned way by phone or 'snail'. Any inventor, engineer, hobbyist, tinkerer, or one interested in a more self-sufficient lifestyle would do well to regularly peruse Lindsay's book selection.

A "Simple" Project - Overcoming Some Challenges:

The photo above is of a 1.25" pipe plug I tapped for 1/4" NPT pipe. I pilot-drilled the hole to 1/8", then worked up in small drill size increments to a final hole size of 7/16". I tapped it using a Greenfield 1/4NPT TPR pipe tap bought from McMaster Carr. Note I tapped from BOTH ends, leaving a small unthreaded section in the center. I needed to be able to thread a pipe nipple into each side of the plug for a project I did a while back.
Sounds simple, right? Problem was I didn't have a tap handle that properly fit the tap nor did I have a good, bench-mounted machinist vice.
For a "tap handle" I used an adjustable "Crescent" type wrench to grip the square end of the tap. I turned the wrench with one hand, while using the palm of my other hand to press downward upon the "gripping" end of the wrench to drive the tap in straight. When I threaded the bottom side of the pipe plug, I was able to clamp it in an inverted position by its hex flange in my drill press vise, just as I had for drilling the hole. The threads in the top side were a bit more challenging.

As I mentioned previously, I didn't have a machinist bench vise available.
My drill press vise's jaws aren't deep enough to hold the plug's hex flange while I tapped that side. If I tried to clamp onto the threads I would ruin them and they would leak, assuming the plug would still even screw into a fitting afterward. So I bought a 1.25" pipe cap that I could clamp into the drill press vise. With the cap clamped securely, I simply screwed the plug into it and tapped the other side as before.

Not including the trip back to the hardware store to buy a pipe cap, this took about an hour to do all this. But it was MUCH cheaper and quicker than hiring a machine shop - ASSUMING they would even do a small job like this. I still did this myself in LESS time than I would take just to DRIVE to the nearest machine shop to pick up the work when it was done.

Granted, there are indeed some things, such as building a scroll type refrigeration compressor, that ARE impossible to do without some major machine shop tools. The original idea for that was conceived nearly 100 years ago, but it took the development of computerized machine tools to make the parts to the exacting tolerances needed for it to work. That said, many things can be and have been done under quite primitive - almost 'impossible' - circumstances.

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