How Automatic Back Spotfacing Tools Can Improve Your Machining Efficiencies

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Automatic back spotfacing is an operation that provides a seat, counterbore or flat surface.

Automatic back spotfacing tools may be used to save a set-up or because there is no other practical way to access the machined feature. Common components requiring automatic back spotfacing are castings, weldments, valve and pump bodies as well as power generation components.

How Automatic Back Spotfacing Tools Can Improve Your Machining Efficiencies

Automatic back spotfacing enhances the machine/operator safety by automating manufacturing processes and eliminating a manual interface with the operator using a manual back spotface tool. The automatic process is also faster, which reduces machining time and improves profitability on the machining process.

Different Types of Tools:

Swing Out Style:

This style of tool is manufactured by Heule Tool and is their BSF series allowing for a maximum back spotface diameter ratio to the pilot bore of 2.3 to 1. When the RPM of the spindle hits the recommended activation speed, the blade swings out in working position. The pressure of coolant controls the retraction of the blade. This internal coolant pressure system gives optimal cutting performance, resulting in consistent spotfaces and fewer scrapped pieces.

Another style of swing out tool for back spotfacing is the Steiner Autofacer. The Autofacer is a swing out style that uses a mechanical activation to move the blade out and back in. There are several styles of Autofacers and several activation methods which we’ll describe later in this article.

Dual Blade:

Heule Tool’s GH-Z style back spotface tool is a dual blade design and uses an anti-rotation positioning pin to activate the blade movement perpendicular to the workpiece bore. The two blades of the tool are radially extended and retracted by forced action when the direction of rotation of the spindle is reversed, providing high stability and rigidity. It is designed for machining large work pieces in heavy manufacturing applications, and producing large spotface diameters.

Centrifugal Force:

Cogsdill Tool manufactures a simple back spotfacing tool known as FlipCut. For this type of tool, the blade extends with right-hand rotation of the tool to cut the back spotface. Left-hand spindle rotation initiates positive mechanical closure of the cutter; the closing action is assisted by centrifugal force. When the cutter is fully enclosed within the arbor pocket, the tool can be easily withdrawn from the bore.

Different Workpiece Features:

Back Spotfacing:                     

Back spotfacing is the machining of large spotfaces and counterbores without turning the work piece over, or spotfaces and counterbores that are inaccessible from the opposite side. This means that the machining is done on the same side as the drilled hole.          

              Back Spotfacing

Automatic Front and Back Spotfacing:

Automatic front and back spotfacing is used when there are two bores to reach through and it is necessary to spotface the front and back bore of the piece. This operation allows the work piece not to be turned over, saving you valuable time.

Automatic Front and Back Spotfacing

Back Counterboring:

The process of back counterboring creates a cylindrical cavity with a larger diameter at the head of pre-drilled hole. The pre-drilled hole is meant to contain the fastener and prevent the two work pieces from separating when their two surfaces are joined. This method allows the fastener to be completely hidden.

Back Counterboring

Different Ways to Actuate the Tool:

There are several ways to actuate the cutter blade for back spotfacing and back counterboring.

  • Cone or Bump: The cone style actuation is incorporated on the shank of the tool and contacts the front of the workpiece. The contact activates the blade to open and close mechanically.
  • Flywheel: The flywheel uses the inertia generated during the rapid acceleration of the spindle to open and close the blade.
  • Pad: The pads grip the inside diameter of the pilot hole to open and close the blade.
  • Torque Bar: The torque bar utilizes an anti-rotation device during spindle reversal to open and close the blade.
  • Air or Coolant: High-pressure coolant drives the blade open. Spring-pressure closes the blade when coolant is shut off.
  • Extended Range: A rack and pinion gear opens the blade.


All automatic back spotfacing tools have limitations on how large diameters can be machined. Typically, the Max Ratio = Ød x 2 – 1mm. In some cases, this ratio can be exceeded for example the Heule BSF series with a ratio of 2.3 to the bore diameter

Triumph’s Supplier Partners:

Our suppliers of back spotfacing tools include:

When you are challenged with a back counterbore or back spotface machined feature, Triumph Tool can help with a solid, secure and predictable solution from one of our supplier partners that specialize in back counterboring and back spotfacing tools.  If you are looking to improve your machining operations or need more information, please contact us!

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