Tapping hole in brass question

Hope someone can settle an argument: The part is a 1" long x 3/8" OD x 3/16" ID brass bushing that needs a 6-32 set screw. Tap drill goes all
the way through both walls for convenience. Hand tap with straight flute tapered tap and 'T' handle. Quick prototype level part, only making 2 of them, precision not required.
Questions: tap dry or use what lubricant? Backup the usual 1/3 turn to break the chip necessary on this part?
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RoyJ wrote:

I dry tap brass 5/16-18 fairly often . Works for me , a sharp tap works best (duh) .
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No lubricant, no backup (provided your alloy doesn't produce curly shavings - most don't).
Piece of cake.
-- Jeff R.
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That's what I said when a student was taking an hour to get 2 bushings tapped for the set screws. I got severely yelled at, subject of nasty e-mails.
Jeff R. wrote:

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RoyJ wrote:

There must have been a hundred students at school that have taped 3/4 brass "hammer heads" with 3/8-16 threads over the last many years without a drop of fluid and without a single "backup" of the tap. :-) Also a large number that have done a blind hole in 1/2-20 about 3/4" deep. If a material dosent make stringy cuttings, no need to back up a tap. Even if it does that is what a spiral point tap is for. :-) ...lew...
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Do yourself a favor and go buy 2-flute gun taps in all the smaller sizes you use, and 3-flute gun taps for the larger sizes. They throw the chips in front of the tap, which means you'll never have to back up in any material unless it's a blind hole, and then only to empty the chips when you're done. Tap brass dry, aluminum with kerosene or d-limonene (orange oil), and steel with Rapid Tap. Once you try gun taps, you'll wonder how they still sell the standard 4-flute taps.
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Ah ha. An improvement! Can you run those in 6-32 or 8-32 in aluminum with a low speed cordless drill?
If I can get it by the crusty old codger I'll do it.
Bruce Spainhower wrote:

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Just 10 minutes ago I tapped 16 10-32 through holes in 3/4" 6061 using a 2 flute tap and a cordless drill. Lube was a couple of drops of Alumi-cut. No backing up, just stick it in the #21 hole and tap 3/4" through.
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I like it!
BillM wrote:

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I do it every chance I get. My big problem is that the chuck can't grab the hardened tap well enough. Any thoughts or ideas? I'm not quite ready to grind 3 flats on the tap.
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DanG wrote:

That occasional slip has saved my ass a lot, I'm sure!

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Maybe a "tap socket"?? Chuck up a 1/4 hex by 1/4 square adapter, snap on the tap socket, insert tap. Find out just how good all those slip clutch settings really are on your cordless drill.
http://buy1.snapon.com/catalog/item.asp?item_ID 40&group_ID58
I've actually used these before to hold 3/8-16 taps and drive them with a 3/8 air butterfly. Worked well in 1/4 steel flatbar.
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    [ ... ]

    The 8-32 should be no problem. 6-32, however, is the thread from hell. Someone made a poor choice many years ago when they decided to stretch the 32 TPI standard all the way down from 10-32 to 6-32. By the time you get to a #6 screw, the threads remove such a large percentage of the overall diameter that the resulting thread (and tap) is quite weak for either side loads or over-torquing. With the tap in a hand drill (battery powered or with a power cord) it becomes hard to hold the drill motor in line with the hole for the whole time of tapping -- especially when you are trying to switch the drill from forward to reverse.
    What would be a much better way to go would be with a tapping head in a drill press -- but this can run into money if you aren't lucky about picking up an appropriately sized used one on eBay or at a swap meet.

    The gun taps -- pretty likely. The tapping head (if you don't already have one) --probably not. :-)
    Good Luck,         DoN.
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Just got back to checking this thread. Yes, I use gun taps in variable speed drills all the time. Don's right though. 6-32 is right on the ragged edge of sensible. It all depends on the alloy you're tapping, how far you're going, and which lube you use. 1/4" 6061 or thiner, through hole, proper lube, and a sharp tap, and you can pull the trigger all day long. Give it a try. At least the 6-32's are inexpensive. As with any tapping job, keeping the tool aligned to the hole is really important. It's just that much harder to do with the weight of a cordless drill.
- Bruce

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My experience has been that for 6-32 into aluminum, especially if handheld, thread-forming taps are the way to go. Lube the tap with sticky wax. I use Lenox saw wax. The thread-forming taps are stronger than cutting taps, and tend to follow the hole automatically rather than trying to go off at an angle.
Joe Gwinn

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