Taps

[wrustle]

(10-03-2012, 09:29 AM)EdK Wrote:

(10-03-2012, 06:25 AM)PixMan Wrote: Hand taps have no chip control geometry, such as spiral point or spiral flute, which machine taps do have. As such, you have to reverse direction every 2 or 3 turns to break chips.

The number of flutes increases or decreases load "per tooth", though less flutes makes for a stronger tap. More flutes helps carry chips away better. I practical terms, you notice no real difference in how much pressure it takes to cut the thread.

NEVER use a hand tap for power tapping. You want to do a power tap cycle in one pass, and hand taps need that chip-breaking reversal every couple of turns.

Yes and no. If you have really abrasive material or have to do lots of holes, coatings help. There are TiN, TiCN, THL and more. The right coating can make all the difference in the world when you need to get it done. Rarely is this an issue in most home shop situations.

Enco has it all wrong then. Here's their description of a hand tap.

"Hand taps are popular in hand use, in general machine tapping, or CNC tapping. They are also appropriate for tapping the vast
majority of materials in through or blind hole conditions."

It doesn't surprise me though.

Ed

Ed,

You are spot on by stating "Enco has it all wrong then."

A "hand tap" is really best reserved for chasing damaged internal threads.......in my opinion.......at least.

"Hand Tap"



A hand tap in a CNC machine would most likely not make it past the first hole without serious consequences to either the tap itself or the part you are trying to tap.

Perhaps if you were to power tap in a knee mill where you could forward and reverse the switch to break the chip as you tap you may make it ok, but depending on the depth of the thread, those chips packing between the flutes will in all likelihood make a mess of your threads as they gall up inside the hole.

For thru holes, a "Gun Tap", or "Spiral Point Tap" is your best bet as those taps will drive the chips forward out thru the bottom of the hole.

"Spiral Point Tap or Gun Tap"



For blind hole tapping, a "Spiral Flute Tap" is the ticket as it draws the chips up and out of the hole by following the spiral flutes along the length of the tap.

"Spiral Flute Tap"




For small deep holes, I would recommend using a "Form Tap" as they will not produce any chips at all and are a very strong tap.

"Form Tap"



The key to a good thread with a form tap however is to use the correct size drill. They are not the same size as in cut taps. Any deviation from the recommended size will either break your tap if too small, or make your threads oversize if too big. There is a fine line between the two with form taps.....tread lightly......they are not as forgiving as cut taps if your hole is not spot on, but they have their place, and for me, it's on nearly every job. I use them all the time and cannot honestly remember the last anyone broke a tap in a machine.

These were some aluminum parts we made not too long ago. The tapped holes in the sides were #4-40 or #6-32 and were machined using form taps. Very seldom, in fact rarely do we ever use cut taps anymore.



As always........free advice is......well.......free!

Your results may vary.

Best Regards,
Russ