Standard matches
can usually be found between stock bearing sizes and the
diameter of shaft steel that can be bought. In the UK
close tolerance, smooth surface finish steel round bar
for uses such as shafting is usually differentiated from
rougher unfinished steel bar by the use of the terms
"bright" and "black". For shafting look for bright bar -
a, say, 12 mm diameter bright bar will usually fit a 12
mm diameter bearing because the 12 mm bright bar is
usually about 11.95 mm actual diameter and the bearing will
be 12.00 mm (+ a wee bit) hole diameter.
There are other
specialist shafting steels that can be bought usually
described as "ground" or "precision ground" bar with
even tighter tolerances (+0,-0.015 mm) and better surface
finish (0.6 microns) than standard bright bar. One of
the most commonly available of these in the UK is
"Silver Steel" or more precisely high carbon bright
steel to BS1407. This is commonly available in short
lengths and is suitable for hardening (it contains about
1.1% carbon) but is also considerably stronger than mild
steel in its unhardened supplied state and can often be used
as bought. (I understand UK Silver Steel is
approximately equivalent
to US ground tool steel SAE 0-1.)
Bright
steel bar comes in many steel specs with, in increasing
strengths, mild steel, medium carbon and low alloy
steels probably of most interest to DIY-ers. For your
more heavily loaded shafts and axles look at through
hardened, low alloy steel bright bar (UK EN24(T) , US
4130 and 4340 specs or similar), these are common and are just
about hacksaw-able when hardened moderately although
getting the supplier to cut to length in diameters of
1/2" upwards helps a lot. In common heat treated forms
they have strengths about 3 x that of mild steel and are
drill & tap-able - but they are more expensive.
There are intermediate
strength steels available too; in the UK EN8 (or BS970
080M40) medium carbon is quite common with stockholders and
in the US SAE1040/1043 shafting may be found for duties
where the stresses (eg bending) or surface hardness aren't
quite so onerous.
The image on the
right shows a shaft machined from "black" steel bar. The
mounting areas for the bearings, sprocket and pulley are
the only parts of the shaft machined to close tolerance.