Broken taps, torn threads and poor finish surface all stem from one basic problem – getting the wrong tap speed for your tapping machine.
Why Speed Matters More Than You’d Think
Remember, when you are using an Electric Tapping Machine, the speed of the tap is more critical than it would be when using manual methods to tap a hole. If the speed is too fast the tap can over heat and the material being cut can tear and cause damage to the tap. In extreme cases the tap can even break off in the hole. Conversely, if the speed is too slow then not only will the process be extremely time consuming, the tap will simply drag through the material as opposed to cutting it smoothly.
Match Your Speed to the Material
When tapping harder materials it is normal to require slower tapping speeds. For example, mild steel can be tapped at between 300 and 600 RPM for average tapping applications using standard tap sizes. Aluminium materials can be tapped at much higher speeds, up to 1000 RPM or more. Stainless steel, cast iron, etc. require slower, more careful tapping speeds in order to avoid work hardening of the thread material.
Go Slower as the Tap Gets Bigger
Bigger Taps to Cut Slower – Roughly Halve the Speed with Every Double in Diameter. Thus M4 can be used a lot faster than M12 in similar material.
Read the Manufacturer’s Speed Chart
The manufacturer’s speed chart supplied with the electric tapping machine will provide a list of recommended RPM ranges for various sizes of taps to be used in a variety of materials. It is recommended to start at the lower end of the recommended RPM range and work up as required.
There is more on Electric Tapping Machines at https://www.cotswold-machinery-sales.co.uk/roscamat-tapping-machines/electric-tapping-machines/roscamat-tiger-electric-tapping-machine/.
Listen and Watch While You Tap
If the tapping machine starts to struggle or makes unusual noises, or the tapped thread feels to be being cut rather than screwed into the workpiece, then the speed of tapping needs to be decreased. Chip formation should be smooth and consistent, as depicted in images of good quality tapped threads. It is also relevant to refer to HSE guidance on the safe use of work equipment and machinery. This guidance emphasises the importance of operating equipment within the specified parameters of the manufacturer’s instructions. This would include any pre-determined settings for tapping speed that are recommended by the manufacturer for specific taps.
Tuning up your tapping speed is a small trick of the trade that can have a massive impact on your finish and your life!
