LINEAR
TOLERANCES
The chart below can be used for most applications.
 Grade
MD 1: for dimensions with no tolerances required.
 Grade
MD 2: for functional dimensions which require specified tolerances.
The
general rule for linear tolerancing of investment castings is usually
expressed as ± 0,5 % of the nominal dimension. Tighter tolerances
can be made available for a few selected design characteristics.
However, one should know that tighter tolerances usually require
special procedures and/or secondary operations which can increase
the cost of the casting.
DIMENSIONS
(mm)

PRECISION
GRADE

MD
1

MD
2

from

to

deviation
+ or 

tolerance
range

deviation
+ or 

tolerance
range


6

±
0,10

0,20

±
0,08

0,16

6

10

±
0,12

0,24

±
0,10

0,20

10

14

±
0,15

0,30

±
0,12

0,24

14

18

±
0,20

0,40

±
0,14

0,28

18

24

±
0,25

0,50

±
0,17

0,34

24

30

±
0,30

0,60

±
0,20

0,40

30

40

±
0,36

0,72

±
0,25

0,50

40

50

±
0,42

0,84

±
0,30

0,60

50

65

±
0,49

0,98

±
0,35

0,70

65

80

±
0,58

1,16

±
0,42

0,84

80

100

±
0,68

1,36

±
0,48

0,96

FLATNESS
A flatness tolerance is the total deviation permitted from a
plane and consists of the distance between two parallel planes between
which the entire surface so toleranced must lie.
Degree
of flatness in an investment casting is almost always determined
by the volumetric shrinkage of wax and metal during cooling. This
problem is typical of the casting process, and can be controlled
but not avoided.
General
flatness tolerances cannot be quoted because they vary with configuration
and alloy used. Wall thickness of the plane is, for instance, a
significant parameter: with the same surface extension, the higher
the wall thickness, the larger the flatness error.
Morover,
the flatness error of an uninterrupted plane will be higher than
the flatness error of a plane with holes or other things which interrupt
its extension (basically, to calculate the tolerances, an interrupted
plane must be considered not only one plane, but as many planes
as those definited by the interruptions). The following tab reports
a general indication:

Areas
under
2500 mm2

Areas
over i
2500 mm2

Section
thickness

Allowed
dish

Allowed
dish for every 3800 mm2
over
2500 mm2

Up
to 6 mm

Not
significant

Not
significant

from
6 to 13 mm

0,25
mm

0,10
mm

from
13 to 25 mm

0,25
mm

0,20
mm

over
25 mm

0,25
mm

0,40
mm

PERPENDICULARITY
When specifying perpendicularity, use the longest plane for reference:
the allowed deviation to be specified will be the deviation of the
shortest plane against the longest one.
Perpendicularity
tolerance of a plane is generally 0,8% the plane lenght. Basically,
when A is the dimension of the shortest plane and B the dimension
of the longest one, plane A will be perpendicular to surface B with
a tolerance of 0,008 x A.
