Spiral Flute Tap

[llavalle]

I was at the "tap the tie down bracket" stage of my wings. I knew how to tap a hole, I've done it a couple of times before. Not that it's complicated but I've always found it awkward... A cheap tap will twist, you think it's going to break, etc etc.

My brother lent me a "spiral cut" tap. We started the cut with a regular 3/8x16 straight flute type. When a couple of thread were cut, we switched to the spiral flute tap.

Wow, what a difference. Instead of having to back up at each 2-3 turns, you screw it one way, all the way down the depth you want... then unscrew. The chips will go up through the flutes.

I'm told this tap is worth around $50 (cad) a piece... Not really worth it to tap 2 holes but if you can rent one, like I did, go for it.

 

[Jimd]

CNC ?

I wonder what the CNC machines use where they tap a hole? They probably don't start and stop like us humans with a regular tap.

Looks like one of those neat tools you might want to spend the extra money on for spots where you DO have more than a fe holes to tap.

 

[frankh]

The other way

with a straight flute tap (if you don't trust yourself) is to chuck the piece in the drill press vice and use a square to make sure its at right angles.

Put the tapered tap in the drill press chuck and hand turn the chuck as you pull down on the lever.

This will then give you a few turns (say 4) then back the tap out and use the hand tap handle to finish the threads.

Because the drill press started the threads in line the hand threads will be parfect too.

Better to start with the tapered tap and finish off with the plug (non tapered).

Frank

 

[llavalle]

I wonder what the CNC machines use where they tap a hole?

They use spiral flute taps... They were designed for this exact purpose. Drill all the way down with the tap then unscrew.

with a straight flute tap (if you don't trust yourself) is to chuck the piece in the drill press vice and use a square to make sure its at right angles. (...)

This is a really good alternative... and I was about to do this before my brother showed up. He works as a CNC programmer for a machine shop, that why he had this kind of tools available.

 

[Garage Guy]

They use spiral flute taps... They were designed for this exact purpose. Drill all the way down with the tap then unscrew.

A mill or drill press can also use an autoreversing Tapmatic tool and a standard (straight flute) tap. Not particularly cheap but they do work: http://www.tapmatic.com/

--Paul