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What is taper?

"Taper" refers to the slant in the edges of material that are cut using a waterjet or an abrasive waterjet. Because this method of machining erodes the material, it naturally leads to taper where the cut occurs.

What are the different types of taper?

V-shaped

V-shaped taper is where the top of the cut is wider than the bottom. This is a result of the jet spending enough time over an area to erode the top of the material more than the bottom. Also, "splashback" as the jet is bounced back from the material will tend to erode the sides.

This is the most common type of taper.



V-shaped taper


Reverse Taper

Reverse taper is where the top is narrower than the bottom. This tends to happen in soft materials where the material is rapidly eroded or when cutting very slowly. Because the jet stream expands the farther away from the nozzle it gets, it removes more material from the bottom than from the top.


Reverse Taper


Barrel Taper

Barrel taper is where the middle is wider than the top or the bottom. Barrel taper tends to occur in very thick materials.


Barrel Taper


Rhomboid or Trapezoidal taper

Rhomboid taper is actually normal V-shaped taper that has been tilted because the nozzle isn't at right-angles to the material.


Rhomboid Taper

Note:
The taper in these figures is greatly exaggerated. Typical taper is barely visible to the naked eye and is best detected using micrometer measurements.

The amount and type of taper is mostly affected by the thickness of the material and its hardness or "machinability." Although it's somewhat counter-intuitive, thin materials actually suffer some of the worst taper. This is because the jet stream spends little time over each area, so there's no opportunity to evenly erode the material.

How can taper be minimized?

There are a variety of ways to minimize taper:

• Stack thin materials to reduce taper
  If you need to work with thin materials, you can stack them to reduce the amount of taper. (The Make software includes a "Stack Height Calculator" to determine the optimum number of sheets to stack to make the most parts in the least time.)
  
• Use a new nozzle and jewel
  A nozzle and jewel in good condition will produce less taper.
  
• Use the best quality abrasive
  Lower quality abrasives will tend to have a wider spread of particle sizes. Different particles sizes will result in uneven edges and increased taper. Higher quality abrasives will produce more even edges.
  
• Use a nozzle with a smaller jewel diameter
  Nozzles such as the Mini-Jet nozzle, produce less taper simply because the jet stream itself is smaller in diameter.
  
• Use a tilting nozzle head
  Use the Tilt-A-Jet® to eliminate taper, resulting in nearly vertical edges on the parts and increased taper in the scrap, where it doesn't matter. Because only the angle of the machining is changed, parts can be made as quickly as before.

The Tilt-A-Jet nozzle eliminates taper and provides maximum accuracy with a single click

• Use a low stand-off
  The closer the nozzle is to the material, the less it will spread, and the less taper it will produce.
  
• Slow down cutting
  A slower cut will have less V-shaped taper. The OMAX controller can predict the proper speed to automatically slow down and compensate for taper in critical areas by simply assigning a portion of your tool path to a Quality of Minimum Taper.