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Minimize Tap Breakage –
A Simpler Technique
by Dwain Wilder
Bob Daley’s tap tip is ingenious! But there is a simpler method for cutting down on tap breakage while tapping in the lathe (and, analogously, some other machine setups).
All the tap wrenches I have feature a center hole in the butt of the wrench – some are even tapered. So, for accurate hand tapping in the lathe I follow this procedure:
- After drilling the tap hole in the workpiece, leave it mounted in the headstock.
- Mount a live or dead center in the tailstock.
- Draw the tailstock toward the work until you can gently insert the tap and tap wrench between the workpiece in the headstock and the tailstock, engaging the center hole in the butt of the tapping wrench into the tailstock center. This preserves axial alignment between the tap hole and the tap (crucial to smaller size tap longevity).
- Gently engage the tap by advancing the tailstock feed screw.
- Lube the tool and work (yet another mortality factor).
- Use the wrench’s cross T-handle to turn the tap, rather than turning the workpiece, to get maximum feel for the cutting progress. If necessary, block the lathe chuck or select a very slow speed to keep it still during tapping.
- Advance the tailstock screw feed as you go to keep the tap firmly but gently engaged in the workpiece and to avoid off-axis play in the tap (another cause of early demise in small taps).
- Reverse the tap a turn or two for every few turns forward, to break chips inside the tap’s gullet, making for cleaner cutting and to prevent tap jamming (the most frequent cause of tap breakage). Your fingers’ sense will be your best guide for when the tap is beginning to have difficulty.
- Double checking which tapping fluid is the proper one for your workpiece will also cut down tap breakage.
Click here for information on cutting fluids, broken down in a chart by material and operation.
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