Simple tap project

[Evan]

I have need to tap a lot of holes. Most are 1/4x20 or 1/4x28 plus some smaller sizes. I purchased some very good quality spiral point taps to tap under power. I have already tapped about twenty holes with no problem but I am using an 18 volt battery drill to do it. It has a keyless chuck and doesn't hold the tap quite frimly enough. So, I made a tap holder that will fit in the drill without slipping so I can take full advantage of the adjustable slip clutch on the drill. Allen key shown on purpose.

This is a simple project but I was suprised to find that the shanks of the 1/4" taps are not standard. What's up with that? They (the six new ones I bought, two different brands) vary from 0.254 to 0.2555. Huh? So, I had to drill the tap holder with an F drill to accomodate the variations. It works.

[JIMofalltrades031]

Evan, have you noticed any canted threads?

[matador]

hi,evan,i found the same thing with a couple of 6mm taps.the plug tap's square is quite a bit larger than the taper item(like yours different brands.i don't know if this is intentional,e.g. more torque required for plugtap?so ichecked my other taps,and they're all over the place.no rhyme or reason.i'd be curious to know the answer too.nifty idea about the adapter,but how do you manage to keep it straight in a battery drill.last time i tried that,i broke an expensive 2.6mm tap(odd size) .

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Hans

[Evan]

Hans,

Years of drilling holes in aircraft skins teaches you to hold a drill square to the work. It's practice, practice, practice. When you drill 10,000 holes per day you eventually become fairly good at it.

I am puzzled about the shank diameter. I have never bothered to measure it on a tap but I would have expected it to be 0.250 for a 1/4" tap. It isn't.


Canted threads? I assume you mean off angle? No. The 20 or so I tapped so far were in 1.5" aluminum and if they were off angle the tap would have broken. It didn't. It was just a pain that the tap kept slipping in the chuck.

The adapter uses a standard 1/4" hex screwdriver bit with the end ground off. I drilled the one end of the adapter to about .006" under the size of the hex bit across the points and pressed it in with a vise. Works fine. I have been giving some thought to a jig to hold the drill dead straight to the work. I can do that just fine by myself unless I twitch and then it will be SNAP goes the weasel (not so far). My hands are becoming a bit twitchy in my old age.

[This message has been edited by Evan (edited 01-02-2005).]

[wierdscience]

Nice job Evan,the only brand of taps I have seen with tight tolerances on the shanks are OSG and Melin,the rest who knows.

I suppose the CNC qualified taps will be tighter,but I don't know.

[JCHannum]

Machinery's Handbook gives 1/4" hand tap shank diameter as 0.255" +0.015" -0.005".

Manufactured tap holders like Tapmatic, Jacobs or Procunier use a floating arrangement to grip the flats and a collet to center the tap.

[This message has been edited by JCHannum (edited 01-02-2005).]

[Allan Waterfall]

<font face="Verdana, Arial" size="2">Originally posted by Evan:
Hans,

Years of drilling holes in aircraft skins teaches you to hold a drill square to the work. It's practice, practice, practice. When you drill 10,000 holes per day you eventually become fairly good at it.

[This message has been edited by Evan (edited 01-02-2005).]</font>

Must have been a long day,if you worked 12 hrs none stop that equals less than four and a half seconds a hole including moving to next hole and locating the drill. 833 holes an hour by hand is more than I would want to do to earn my pay.

Allan

Allan

[ibewgypsie]

I am too puzzled about the non-standard. I have several smaller Klien screwdriver like drivers made just for holding small taps. 6/32-4/40 All brands seem to fit equally well in them.

Just how many tap profiles are there? I know of starting taps, bottom taps. Two-flute, three flute,four flute cutters, I have a drawer full in a old silverware sink drainer that about all are different. The ones with the long starting taper seem to work best, last the longest when you know you are going complete through a piece. They self align or self straighten a whole lot. You can stand the tip up in the hole, others are more aggressive on the tip and will "cant" easier with you.
I recently got on ebay about ten pounds of a pretty well known brand (union butterfield) in 3/8"x16 for $9 that look like nothing in a profile I have ever saw. If you need a bunch, I'd shop there first.

The two flute seem to work best on the ALuminum you love so dear Evan. I am working on dies today. HARD metal I have been welding on w/7018 rods. I have to tap about a dozen 3/8" holes.

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David Cofer, Of:
Tunnel Hill, North Georgia

[Artpro]

Blended trifocal eyeglasses give me fits when trying to use hand drill. I have a Craftsman drill alignment attachment that I now use to stay square to the workpiece.

[Paul Alciatore]

I've done hundreds of 1/4-20 holes in aluminum and copper with standard taps in a cordless drill w. keyless chuck. I had no problems with slippage. I used Tap-Magic and Tap-Magic for aluminum and backed the taps out for clearing chips frequently. I set the clutch to prevent excessive torque. I brushed on or dipped on more Tap-Magic after each chip cleaning. No slippage, no broken taps.

Instead of making special sized holders for each tap size, why not get a standard tap holder, remove the T handle, and turn it down for chucking. Add three flats on the turned down diameter to prevent slippage. The standard tap wrench will grip a lot better than a set screw. I have a tap wrench that has a smaller diameter at the rear for a guide sleeve when manually tapping. My homemade one works better in this application. But, it could be easily chucked as is or with the three flats added.

Paul A.