[TowerTalk] Tapping or cutting copper

[Its from Onion]

Bacon fat or lard is best. If you use milk then clean everything 
nearby as soon as you have finished, milk splashes stain and rust steel 
very quickly. 

Use a very sharp (or roll-form) tap, and some arrangement to keep the 
tap vertical is almost essential - a drill press or the like will do at 
a pinch. Without some such arrangement it is very difficult to tap 
copper, even a slight misalignment from vertical will cause the tap to 
stick. 

When (dry-) turning or drilling copper I find high speed helps, but 
that's a bit impractical when tapping. 

As with all tapping, a slightly oversize hole will make life much easier. 

As to taps, carbon taps are plenty sharp and hard-wearing enough, but 
HSS taps are tougher and break less easily - and toughness counts, 
especially if you are hand tapping and aren't using a tapping machine or 
drill stand etc. to keep the tap absolutely vertical. 

Lee
KE4VYN