Prevent Tap Breakage on Tapping Machines!
Most broken taps are broken for the same reasons. To help save your time and money by getting more threads from your tools, we go through the common reasons and the solutions to them.
Drill the Correct Pilot Hole
Broken taps are often the result of an undersized pilot hole. As the tap is driven into the workpiece, it has too little metal to cut and soon comes to a stop. In many cases the tap will then snap off. When making threaded holes, always check the required tolerance for such holes according to the relevant thread standard. For drilling the pilot hole, use a proper tap drill chart.
Match Speed to Material
Tap speeds for tapping aluminium and soft brass such as C838C can be in the order of 100 to 150 meters per second whilst mild steel and stainless steel should be tapped at a slower speed of around 20 to 30 meters per second. Higher speeds in harder materials cause excessive heat to be generated which can cause the work to become work-hardened. This in turn causes the chip to become stuck in the thread of the tap, placing sudden and extreme forces upon the tap which can cause it to break. Reducing the speed allows the machine to cut more efficiently and produces a cleaner cut.
Set the Torque Clutch Correctly
A tapping machine worth using will have a torque limiting clutch, which you must set to a little more than the required cutting torque to allow it to slip before breaking the tap. Most operators simply set the clutch to maximum torque and hope for the best.
Apply Cutting Fluid Consistently
It’s also very important to use a cutting fluid and to apply it to the tap before drilling each hole. There are many different types of lubricants on the market and the correct one for the material being tapped should be used. A sulphurised oil is very good for steel whilst a light lubricant is suitable for aluminium.
Replace Taps Before They Wear Out
A worn tap may feel as though it is cutting satisfactorily until it breaks. It is worth regularly inspecting the cutting edges of tapping tools for signs of wear, such as chipping or blunting. Tapping Machines is covered in more detail at //www.cotswold-machinery-sales.co.uk/roscamat-tapping-machines.
Clamp the Workpiece Firmly
Workpieces that move during cutting can also apply side forces to taps. These are often enough to break them. Use proper clamps and fixtures and check that they are square to the spindle. Holding parts by hand is not good enough.
These few simple practices will ensure your cutting tools are always in good working order and ready to complete the job in hand.
