Tapping with Taps & Dies - Hints

Hints on tapping with tap and die : Useful information - recommendation for efficient tapping by The Tap & Die Co

 A]   Hints on Tapping with TAPS :
 Success of any tapping operation depends entirely on the use of a correct tap aided by an ideal tapping setup for the job
 There are several factors constituting an ideal set up for tapping operation. Few general recommendations for satisfactory tapping, most common causes of inaccuracy and their cures are enumerated below:
 a.  In cored holes, presence of hard spots, scale, sand can ruin a tap when the first thread is cut
 b.  Use of dull drills or reamers can ‘work-harden’ the surface of the job
 c.  Multisided or oval holes give rise to uneven threads resulting in improper fit and is a common cause of breakage
d.   Use of worn out drills give a smaller hole which increases the torque required for tapping resulting in breakage
   Recommendations:
 1.  Select the correct type of tap to suit the job required
 2.  Select correct size of drill shown in our Tapping Drills for Taps Traditionally a thread depth of 75% has been the rule. An increase in the thread depth affects the tapping torque, while a decrease, results in weak threads
 3.  Hold the tap, if possible in a special purpose tapping attachment or chuck, ensuring that the tap will be presented to the hole squarely and there is no relative eccentricity between the tap and the hole. It is usual to allow some float to the tap to take care of misalignment
 4.  When the tap is to be used on machine without lead screw feed, ensure that the tap will be able to advance into the hole freely. This ensures that it will cut its own correct pitch
 5.  Efficient tapping has its optimum speed. Always start with lower speeds and increase slowly if works properly
 6.  Good tapping can only be done with copious supply of proper lubricant. Use of lubricant is as important as its choice.  Choose suitabe lubricant .  Keep it clean and direct the flow into the hole being tapped. An ample supply is needed on the cutting edges, not only to disperse heat, but to assist in the formation and disposal of chips
 7.  The tapping operation is ready to start. The tap must be started in the hole smoothly. Do not try to hold it back or push it forward or make several attempts to start it, as this will lead to bell mouthing of the resultant tapped hole. After completing tapping of the hole ensure that the flutes are cleared of any swarf before tapping the next hole
 8.  When the tap is used by hand, the above points are still valid and the tap should be turned smoothly
 9.  Proper care, correct size and use of drills, with equipment in good condition, is very important in producing holes for tapping.
10. Select nearest commercial drill by using the formula for obtaining ‘Tapping Drills for Taps’ (click on button on left) for fluted  Metric taps ( normally recommended for 75% thread depth) = Dia of Metric tap - pitch
   Note: refer point 2 above for our recommended chart of  Tapping Drills for Taps
 B]   Hints on Tapping with DIES:
 a) Always ensure that the die is presented to the bolt squarely and is concentric.  If this is not correct the die will not cut evenly on all the lands
 b) When adjusting a split die, try to avoid opening it out excessively, to avoid breakage
 c) When closing in, do not apply all the pressure on one position, but keep it even. Dies will cut well provided adjustment is kept in the range of approximately 0.4mm
 d) Threads tearing and teeth chipping are due to incorrect sharpening of lands or due to die hitting the shoulder
 e) Before starting a die always chamfer the end of the bolt at around 45o to allow the die to start cutting gently. Failure to do this throws a sudden jerkonto the cutting edge, causing chipping
 f) Size of bolt to be threaded should be basic size, as an oversize material will put extra load on the die
 g) When a die is used on machines without lead screw feed, ensure that the die will be able to advance into the hole freely. This ensures that it will cut its own correct pitch
 h) Efficient threading using a die has its optimum speed. Always start with lower speeds and increase slowly
 i) Good threading can only be done by using a lot of lubricant and choice of lubricant is as important. Direct the flow into the bolt being threaded, onto the cutting edges, not only to disperse the heat but to assist in the formation and disposal of chips/swarf
 j) When a die is used by hand, above points are all valid and die should be turned smoothly
 k) In order to achieve good results, the rake angle must be suitable for the material to be threaded. - Long chipping materials, materials having more tensile strength, requires more rake angle. Short chipping materials, ductile materials, materials having lesser tensile strengthened lesser rake angles. Our standard dies are designed for general purpose steel application, with 8o to 12o rake angle.
 l) Some customers need threads upto the neck of the component. Hence customers grind off the surface of the dies. This reduces the relief angle portion of the die. This is wrong practice as uneven grinding of the lands, leads to uneven cutting. Note: the chamfer-relief is to facilitate cutting which for dies is 45o on the stamped-side and 60o on the backside of the die
 C] Why in through-hole tapping TAPER taps give more life than BOTTOMING taps:
 As actual cutting takes place in the cutting-portion (chamfer or lead area) of the tap, the taper tap has longest cutting portion and hence cutting load is distributed on longer area, hence more life. It is found that bottoming taps give 50%-60% of the life of taper taps
 D] When is the life of a Tap or Die finished? Life is over when:
  - a Go-gauge becomes tight or does not enter.. although the tap or die still cuts threads
  - tap or die becomes blunt. Cutting edges of the tap or die wears out and does not cut threads
  - tap or die breakage

The Tap and Die Company website has a lot of other very useful 'Technical’ Data & Information for you to view