Tap Performance Troubleshooting - Part 4: Fractures

June 5, 2019 2:25 pm

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A series from Walter Tools USA

 

The following is one part in a series of articles regarding performance problems associated with the tapping process.  The solutions focus on specific actions to counter specific issues.

This article addresses remedies for the issue of Tool Fracture.  We are offering suggestions and changes that can be made to counter the effects of fractures.  For further information regarding chip control or tool wear, please see other articles in this series such as Insufficient Tool life , Chip Control, or Excessive Wear.

When troubleshooting broken taps, we must first identify where the fracturing is occurring on the tool.  Depending on where we see the fracturing occurring, it will affect the corrective action that needs to be taken.

 

spiral point tap and spiral flute tap

Anatomy of a spiral point tap and a spiral flute tap

 

Let’s take a look at the different areas that we can see fracturing.

 

Fractures in the Chamfer Area

fractures in the chamfer area

When the chip gets jammed between the tool and part while reversing, we see fractures in the chamfer area.

 

Cause

Chips can get jammed between the tool and the base material when the tool is reversed.

It is also possible for chips to get jammed while cutting (this is less common).

 

Solution

  • Improve the chip control (see the previous article on chip control).
  • Choose a tool with lower relief angle in the chamfer area to avoid the chips getting jammed between tool and component when reversing.
  • Choose a tool with a tougher substrate that will be less likely to fracture if compromised with less than ideal condition such as chips jamming.
jammed chip

When the tap is reversed, the last chip must be sheared off by the back of the tap land.  If the clearance is too high, the chip can get jammed and break the tap.

 

 

Fractures in the Guidance (non-cutting) Area

fractures in the guidance area

When the chip gets jammed between the tool and cutting teeth, we see fractures in the guidance area.

 

Cause

Long, stringy and loosely curled chips can get caught by the teeth of the tap.  When this occurs, we see fracturing of the tool behind the chamfer, in the guidance area, which is also the non-cutting area of the tap.

 

Solution

  • Improve the chip control (see the previous article on chip control).
  • Choose a tool with a tougher substrate that will be less likely to fracture if compromised with less than ideal condition such as producing long stringy chips.
  • Improve chip evacuation by using internal coolant, with axial exit for blind hole applications. Blind hole applications are normally affected the most by poor chip evacuation.

 

As you can see, chip control is the common cause of tools fracturing.  While the location of the fracture tells us what type of chip control problem exists, we still need to improve chip control to resolve the issue.

To improve chip control, modifications to make the tool specific to the workpiece should be implemented.  But, before designing a special tool, the standard range should be checked for suitable alternatives.  Many times, these solutions have been designed into standard product offering.

Higher material hardness and a lower breaking elongation percentage of a workpiece material allow better chip control by keeping the chips shorter and more manageable. For materials with higher breaking elongation percentage such as soft structural steels, low alloyed steels of low hardness and stainless steels, chip control can be more difficult and create greater challenges in controlling the chip.

 

Didn’t find a solution to your issue? For a remedy that does not involve such a direct customization, try a tap designed around a universal application range and can be appropriate for a wide range of materials.  You can also find additional details in this Threading Handbook.

 

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