On 8/18/2012 12:09 PM, John Kasunich wrote: > > On Sat, Aug 18, 2012, at 10:59 AM, Kenneth Lerman wrote: >> On 8/18/2012 9:49 AM, Gene Heskett wrote: >>> On Saturday 18 August 2012 09:46:26 Kenneth Lerman did opine: >>> [...] >>>>> I have done quite a few 6-32 holes in 7078-T6 but can't claim a lot of >>>>> experience in tapping the common alu stock sold at Lowes/TSC, its >>>>> pretty soft. ISTR the last batch of 4-40's I tapped about 3/8" deep, >>>>> blind, took about 4 trips back out to clear the chips. Not much chip >>>>> room in a common hand tap. >>>> Try using roll form taps. They don't generate chips. >>>> >>>> Regards, >>>> >>>> Ken >>>> >>> Do they not require near breakage torque and EP lubricants? >>> >>> Cheers, Gene >> I've only used them in aluminum and never broken one. I usually brush >> the tap with a little motor oil. I don't know what is recommended. > My understanding is that you need to drill a slightly larger hole > for form taps. Trying to use standard tap hole sizes leads to > breakage. (Haven't used them yet, just bought a few last week > because I got tired of picking chips out of blind holes.)' > > I usually use gear oil for tapping - it has high pressure > additives. You are correct that you need a larger hole. Consult the appropriate tables. Cutting threads and forming them are different operations and I would not expect the same fluid to be appropriate for both.
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