A poor thread is rarely the result of mere chance. More often than not it is the result of minor faults in operator procedures that can be easily corrected once one is aware of them.
Wrong Pilot Hole Size
A pilot hole that is too small for the tap can break the tap, while a hole that is too big for the tap creates a thread that is too shallow and not strong enough. The recommended pilot hole size for common tap diameters should be checked before drilling.
Tap Not Running Perpendicular
If the tap is not drilled into the workpiece perpendicularly, then a bell-mouthed hole is created and subsequently threads that will not seat a fastener properly. Utilise the float or quill on your tapping machine to enable the tap to find its own axis. Also, ensure that the workpiece is properly positioned on the machine and that it is being clamped down correctly.
Wrong RPM for the Material
Harder materials need to be cut at slower speeds than softer ones and also can sometimes cause a material to work-harden whilst being drilled thus breaking a tapping tool.
No Cutting Fluid, or the Wrong Type
When tapping dry, in steel or stainless, excessive heat can be generated, leading to galling and torn threads. It is therefore very important to use a proper tapping compound or paste instead of general-purpose oil. It clings well to the tap and reaches the cutting edges in time.
Worn or Poorly Fitted Tap Holders
A worn or misfit holder allows any amount of runout to be transferred to the tap. For Tapping Machines, visit cotswold-machinery-sales.co.uk/roscamat-tapping-machines/.
Not Clearing Swarf on Deep Holes
Material swarf in a blind hole cannot fall out of deep holes and causes damage to newly formed threads. Remove the swarf from the hole by withdrawing the tapping machine’s cutting tool several times during the tapping process.
Changing habits takes minutes and instantly improves thread quality.