Got a job on doing some small gear selectors in aluminium bronze, the drawn variety. The job calls for two M3 tapped holes 10mm deep into a bore.
Now for anyone not familiar with this material it's horrible. It heats up at the drop of a hat and then cools down gripping whatever it is you are trying to cut it with. It's also very abrasive and needs very sharp tools. Reaming this stuff shags reamers faster than rubbing them on the hard shoulder between junctions 15 to 17 on the M25 [ clockwise ]
Well tapping these is getting thru taps like one O unless you go over size on the tapping drill and finish up with a less percentage thread. Only broke one tap but it's costly as the component has a lot of work in it.
I picked some fluteless forming taps from Ketan at Arc Euro the other week and although they are fine in soft metals I have never tried them in ali bronze.
Delight of delights they go straight thru, and felt a lot better. With having no flutes they feel and are stronger, no heart in mouth feeling and I finished up power tapping these with the reversible air drill set to flat out.
-- Regards,
John Stevenson Nottingham, England.
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