Most broken threads and snapped taps in the workshop are caused by misaligned taps. It’s easy to check for these potential problems before starting work.
Check the Arm Is Truly Vertical
The majority of arm mounted tapping machines are configured up to run off the arm being truly vertical, so ensure that the workbench that the machine is mounted upon is square. Using a small square (engineer’s square) held against the arm, determine if it is vertical to the workbench surface.
Confirm the Tap Holder Runs True
Check for any wobble of the tap holder by rotating it slowly by hand when in use. Check for any burrs or debris in the tap holder’s collet and body that may cause the tap shank to wobble. If any damage is found, clean up as necessary before using the new tap.
Inspect Your Work-Holding Setup
Just as a workpiece that moves during cutting can cause just as much harm as a misaligned arm, the work must be held firmly in place, checked to be flat and for the tapping hole to be central to the tapping location on the arm of the tapping machine.
Check Entry Angle on Awkward Surfaces
When tapping into angled faces, for example in bent tubing or into curves of various radii, the entry point of the tap must be perpendicular to the surface to be threaded, not to the work on the bench. This can be checked by tilting the workpiece slightly and re-clamping, or by using an angled fixture to bring the hole in the workpiece square to the arm of the tapping machine.
For Electric Tapping Machines, see cotswold-machinery-sales.co.uk/roscamat-tapping-machines/electric-tapping-machines/roscamat-tiger-electric-tapping-machine/.
Repeat the Checks After a Tool Change
When swapping between taps (of different lengths and diameters) recheck the vertical of the arm and the runout of the tap holder for that new tap prior to cutting any more threads.
Checking your machine for these problems every time you use it takes less than a minute to do and will result in accurate threads and long lasting taps.
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