The speed of a drill is usually measured in terms of the rate at which the outside or periphery of the tool moves in relation to the work being drilled. The common term for this is "surface feed per minute," abbreviated to S.F.M.

In general, when operating a drill at a speed anywhere within its range for the particular material involved, increases in speed result in fewer holes before regrinding becomes necessary, and reductions in speed permit more holes before the tool is dulled. As a result, on every job there is the problem of choosing a speed which will permit the highest rate of production without entailing excessive drill costs or down-time for tool sharpening. The most efficient speed for operating a drill will depend on many variables, some of which are listed below;

1. Composition and hardness of material.
2. Depth of hole.
3. Efficiency of cutting fluid.
4. Type and condition of drilling machine.
5. Quality of holes desired.
6. Difficulty of set-up.

Indication Of Extreme Speeds And Feeds

A drill split up the web is evidence of too much feed or insufficient lip clearance at the center, due to improper grinding. The rapid wearing away of the extreme outer corners of the cutting edges indicates that the speed is too high. A drill chipping or breaking out at the cutting edges indicates that either the feed is too heavy or the drill has been ground with too much lip clearance.

Material-------------------------------------- Recommended Speeds in Feet per Minute

Aluminum and alloys---------------------------------------- 200-300
Brass and bronze (ordinary)---------------------------------------- 150-300
Bronze (high tensile)---------------------------------------- 70-150
Die casting (zinc base)---------------------------------------- 300-400
High temperature alloys- cobalt base,
Hs25,s816,v36---------------------------------------- 10-20
Iron base
Inco 800, a286,n155---------------------------------------- 10-20
Nickel base
Inconel 700,u500, rene '41----------------------------------------- 7- 15
Iron-cast (soft)----------------------------------75-125
Iron-cast (medium hard)---------------------------50-100
Iron-hard chilled---------------------------------10-20
Iron-malleable------------------------------------80-90
Magnesium and its alloys--------------------------250-400
Monel metal or high-nickel steel -----------------30-50
Plastics or similar materials (Bakelite)----------100-300
Steel-mild .2 to .3 carbon-----------------------80-110
Steel .4 to .5 carbon----------------------------70-80
Tool 1.2 carbon---------------------------------50-60
Forgings------------------------------------------40-50
Alloy-300 Brinell---------------------------------20-30

High Tensile (heat treated)

35 to 40 Rockwell c-------------------------------30-40
40 to 45 Rockwell c-------------------------------25-35
45 to 50 Rockwell c-------------------------------15-25
50 to 55 Rockwell c-------------------------------7-15
Managing (heat treated)---------------------------7-20
(Annealed)----------------------------------------40-55

Stainless Steel

Free machining group

303,303se,430f,416f,420f--------------------------30-100
Chromium-nickel group (non-hardenable)
(300 series) (1) (400 series (2)-----------------20-60
Straight chromium group heat treated
(400 series (3)-----------------------------------10-30
Titanium alloys-----------------------------------50-60
Commercially pure---------------------------------50-60
Wood----------------------------------------------300-400