Cutting slots for slider pots

[R.G. Keen]

>>The only good way I ever found that turned out consistent slots for 
>>sliders and was (relatively) cheap was to chuck up a small side mill
>>bit in a drill press ($200) and clamp the work into an X-Y vise ($50)
>>to make a poor man's mill. The X-Y gives you control and truly straight
>>lines. I've only done this in aluminum.
>>
>
>A safer solution that should work would be a router on a router table. I
>know that they are meant for woodworking, but aluminum is quite soft and
>easy to work. With clamps and wooden guides, you should be able to 'route'
>multiple slots that would be perfectly parallel.
That ought to work, too. I just hate to use router tables and hand feed
them. I liked the X-Y vise because it actually held the aluminum clamped
to the table of the drill press, not freehand. Also, I could watch the
slot being machined as it cuts from the top, not the bottom.

>
>Question would be:  If it cost $100 or so to buy the tools, would it be
>cheaper for you to have them done by a metal shop???
Sure ... the first time. I tend to buy tools rather than services as a 
habit. If the service cost is roughly comparable to the price of a
tool, I look at it as learning how to do it and getting the tool as a
byproduct of the work for free. Obviously that does not hold where the 
cost of the tools is much more than the cost of the service. It
depends, I guess on whether you just want a widget made and don't
particularly care how you get it, or whether you want to learn the
technologies. I like the technologies, perhaps more than the use of the
end result. Quoting "The Sensuous Gadgeteer", "the finished product is
just the garbage of the work."

Hey. I just thought of another way to do the slots - etching. The
reason they tell you not to pour ferric chloride into aluminum pans to 
etch circuit boards is that it eats aluminum MUCH faster than it eats
copper. (Some day you can hear the story of how I know that...)

If you mask off the area of the slots you want to cut with 
something like plastic tape and spray the whole panel with lacquer, 
then remove the 
plastic tape when the lacquer is dry, you should be able to immerse the 
whole panel in a ferric chloride bath. Failing that, you could build a
parafine wax dam around the area to be etched and pour in the etchant. 
It would take a while, but the slots would get eaten. There would be
some undercutting, but the area at the top should be well defined. A
two- or multi-step process would probably minimize undercutting.

This process releases some really nasty fumes, perhaps even chlorine
gas, really bad news; so for safety's sake, don't just rush out and try
it. In fact don't try it all unless you know and can take the proper
safety precautions and have all of the right equipment. If you don't
know whether or not you have the proper knowlege and equipment, you 
don't have them.


R.G.