Thread: Which Tap & Die set to purchase?

The dies with the slit in em ,make for adjustment of the cut thread.

Meaning you can make the cut male thread tighter or loose to custom fit the thread to the nut,within in a small range of course.

Yes are carbon steel but appear to be a good quality. I use the 6mm die on stainless rod all the time and its still cutting well after a year or so.


Here's some helpful stuff about dies

dies - ICS Cutting Tools


Grahame

Originally Posted by issatree

Hi Brett,
Have just come back from Aldi's, & I saw a set there.
Never took a great deal of notice, looked up their Cat. but there was nothing there.
My guess wood be that it maybe up to ½"- 12mm.

I've just recently bought a set of those from Aldi. The tapping size drills in that set are HSS and are split point. The taps seem to be HSS as well but don't have any indication on them, neither have the dies.

Other than that I've only used one tap from the set, M4 in BMS. It cut easily and left a clean, sharp in appearance thread. Having said that I would buy taps and dies as needed for repair work. Any new work I will stick to metric.

Geez Ewan, Ray Phil; you guys are just as warped as me.
I must be in good company.

Ken

Originally Posted by BobL

This method will produce holes that are generally too tight and can lead to broken taps.

The other commonly use ROT is Bolt Size - 10% of bolt size, but both are only ballpark figures

The Tubal Cain (TC) book recommends 5.35 mm holes for a 60% or loose fit down to 5.1mm for an 85% (tight) fit - the "British Standard" sizes are 5.3, 5.2 and 5.1 mm
So the -10% rule (5.4 mm) is too loose and the Size - Pitch rule (5 mm) will be too tight

M8 (1.25) TC recommendation is 7.2 mm for a 60% fit down to 6.9 mm for tight fits.
-10% rule (7.2mm) is on the loose side and Size - Pitch (6.75 mm) is too tight.

M10 (1.5) TC recommends between 9.2 and 8.6 mm. -10% rule is OK but Size - Pitch (8.5 mm) is too tight.

M10 (1.25) does not have an entry in TC but all sizes can be worked out using a formula on P92 of the TC book.

Diameter of bolt - 1.083*Pitch * % flank height/100

The % flank height is ~10% greater than the engagement, so a 60% engagement is around 50% flank height.
This will allow you to work out what ever you want.

I disagree....

Just sticking with the M8x1.25 for this calculation,

Drill Size = Basic Major Diameter of Thread - [% of full thread * Pitch] / 76.98 ..... ( Black Book page 22 )

So for a M8x1.25 60% ( loose fit ) Drill Size = 8.0 - [ 60 * 1.25] / 76.98 = 7.0 mm not the 7.2 mm quoted above.. 75% fit gives the standard drill size of 6.8 mm

Tubal Cains recommended drill size of 7.2mm gives only a 50% engagement flank.

Regardless of his errors, I'd dispute the assertion that tapping for a loose fit is a good way to stop breaking taps, starting square and not bending the tap seem to be more sensible approaches.


Ray

PS... On re-read I see that we might be swapping %flank height for %engagement when referring to fit? PC might be correct, this is getting a bit anal for home workshop applications...

Originally Posted by RayG

PS... On re-read I see that we might be swapping %flank height for %engagement when referring to fit? PC might be correct, this is getting a bit anal for home workshop applications...

Yep - that's what is happening - the BB and TC equations are the same if the same parameters are being used.

Warning - NERD alert!
These equations come from the ISO specification for the metric thread (see ISO metric screw thread - Wikipedia, the free encyclopedia)
A 100% contact has the equation Drill size = Diameter of bolt - 1.082532*Pitch
A less than 100% contact, Diameter of bolt - 1.083*Pitch * % flank height/100
End NERD alert

Here is the TC chart I use - only a range of tapping drill sizes for the coarser threads are provided but any others can be worked out from the equation provided.

Hi

A theory : If your spindle or chuck ( therefore drill shank )has any amount of runout, then the drill chart figures would not mean anything ?

It may be worthwhile measuring your drilled hole to see if it is actually the size you are wanting ... the smaller sizes may need one of those expanding ball devices ( small hole gauges ).

Mike