First, we need to discuss how to choose the right spindle speed for Electric Tapping Machines, so that you can create clean threads and avoid having your tap stuck in your workpiece.
Match Speed to Tap Diameter
A larger tap diameter means more material removal per revolution. Therefore the spindle speed must be reduced with increasing tap diameter. A rough guide to follow is to halve the RPM when doubling the diameter of the tap. Thus a 4 mm tap in mild steel could be run at 600 RPM, but a 12 mm tap would require approximately 200 RPM or less.
Adjust for Material Hardness
A hard material can generate a lot of heat. Reducing the speed of the spindle is the best option. Materials such as aluminium allow higher speeds than mild steel. Other metals such as stainless steel and cast iron require a slower tapping speed. Recommended cutting speeds for common metals are a good starting point for suggested tapping speeds for specific materials.
Account for Blind Holes
For Blind Holes reduce speed by 20 – 30 % and use a Spiral Tap to remove swarf. The tap pulls the swarf up and out of the hole instead of packing it in.
Read the Manufacturer’s Speed Chart
These speed charts for tapping machines often detail suggested speeds for common tapping operations in various materials and for different types of tap. These charts are usually found on the side or back of an electric tapping machine and are typically one of the first references to consult for speed information.
Electric Tapping Machines is covered in more detail at cotswold-machinery-sales.co.uk/roscamat-tapping-machines/electric-tapping-machines/roscamat-tiger-electric-tapping-machine/.
Spot the Warning Signs
Squealing, a poor surface finish and swarf which comes out as dust, instead of curly shavings, are all signs that you are running at too high a speed. A tap which drags or stalls could be running at too low a speed or perhaps more likely, it may not be adequately lubricated.
Setting the correct spindle speed for new materials can take a little practice but once you have established the correct settings for your materials these can be easily re-run for future workpieces.