I've gotten somewhat cynical (what me? never! - before GM3SEK says it!) about
tapping holes in aluminium unless there's plenty of thread depth available.
Another problem is using the wrong thread, and by far the 'most wrong' is
metric - ISO metric coarse is far too fine a thread for aluminium and the like.
For larger threads, use UNC, and for smaller threads, the UNC sizes below
10-28, i.e. 8-32, 6-32 etc. Metric threads are far too fine: BSF is too, and
BSW is a good alternative, al;though it only goes down to 1/8 inch or abour
6-32. Or use the steel coil thread inserts so you can use metric, with all the
cost and fuss of those.....The smaller sizes of BA trhead are just about OK if
you don't need too much torque, they being much stronger, size for size, than
metric - or ANC for that matter. Soft materials, such as aluminium and copper
are absolute b*&^%$s to tap, and need lubricant and much care. Plus, ideally,
access to a spark erosion machine to remove broken taps....suc
h access, by Murp[hy's Law, reduces the chances of tap breakage enormously.
But the caustic soda treatment I've used quite succesfully. Sure, you need to
be careful because it has its dangers. So does dfriving to work.......and just
look at the idiots you see on the road who manage that succesfully!
73
Peter G3RZP
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|