Professionals and Amateurs Together

Tool Speeds

Question

Are there ‘rules of thumb’ to decide which speed to use on variable or multi-speed tools such as a drill press, router, power saw and now sanders? – Alan Saffron

Answer

Joe Barry replies: Regarding speeds and feeds, there is a lengthy section in The Machinery’s Handbook on this topic. However in working wood rather than metal, you can use this “adage” – the bigger the cutter the slower the speed.

To calculate the rpm for a given drill bit the formula is:

RPM = (12 x CS)/(3.14 x D)

CS = cutting speed in surface feet per minute. Generally 100 sfpm for low carbon steel & soft gray cast iron. 250 sfpm for aluminum or brass.

D = diameter in inches for drills and other circular tools

Use of power feeders for shapers and planers will also vary the speed required. If there is evidence of chips being pressed into the cut surface, it usually indicates a need to either increase feed speed or improve chip clearance. If you want another rule of thumb, it is that it is always safer to start slow and bring the speed up rather than start fast and have a catastrophic failure. Router bits usually have the speeds they are designed for in the catalog. Again, the bigger the bit, the slower the speed – and no hand held big bits!

Tags: Tools