How to drill and thread copper

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

Ralph, and others who may have had problems drilling 
copper for rotary gaps, etc.

I got this info from Tim Raney:

>
> Maybe you
> could pass this info to the folks having trouble drilling copper. I've
> worked with copper a lot and it's not difficult to do, but there are a few
> things you must consider. First off, as one person said, copper can be a lot
> like machining mild steel and that's correct. However, there are a few
> differences and I will focus on those differences in the following comments.
> Copper alloy C-110 is electrolytic tough pitch (ETP) copper. The "ETP"
> refers to the refining process. The "20% machinability" rating is compared
> to brass alloy C-360; its rating is 100%. The relative machinability of all
> metals and alloys are rated against C-360 brass. 
>
> Based on the comments about breaking the bit when drilling the copper, I
> think a few things probably happened; (1) the feed rate was too great; (2)
> incorrect spindle speed; (3) work piece was not clamped properly (never hold
> work piece with your hands); (4) no coolant or lubricant was used (WD-40
> works very good for copper, but don't use standard cutting oils -they will
> discolor the copper); and (5) drill bits may have been dull. Usually, the
> nominal hole diameter that results from drilling could vary by a few
> thousandths and depends on how accurate the drill is. If these drills were
> hand-sharpened and are not new, your holes sizes will be off. 
>
> There are readily available charts on the Internet that will give you
> nominal hole sizes for given drills; fractional (most common), number,
> letter and metric. Additionally, these same charts usually include the
> correct size drill for a given tap. These drills are based on providing a
> hole that will give you a 75% depth of thread. If the hole is a little
> larger, you're depth of thread will be less. Other common values are 60% and
> 65% depth of thread. In copper and stainless steel, you can probably go down
> to 50% depth of thread without adversely affecting the holding capacity of
> the screw fastener. There are tables that'll tell you the appropriate depth
> of thread for selected materials. Tougher and harder materials use the
> reduced thread depth. Machinery's Handbook is an excellent reference as
> mentioned.