Tolerance

Dimensions on one side of parting
Dimension Tolerance
 0″ – 3″ +- .030″
 3″ – 6″
+-.045″
 6″ – 9″ +-.060″
 9″ – 12″
+-.090″
 12″ -24″
+-.090″ +-.003 in/in
24″ and up +-.126″ +-.002 in/in
Dimensions across partings
Projected Area Tolerance
1 to 10 sq. in. +.020″
10 to 50 sq. in. +.035″
50 to 100 sq. in. +.050″
100 to 250 sq. in. +.065″
Core Dimensions
Dimension  Tolerance 
0″ – 3″ +-.015″
3″ – 6″ +-.030″
6″ – 9″ +-.040″
9″ – 12″ +-.050″
12″ and up +-.050″ +-.002 in/in
Dimensions Between Two Cores
Dimension  Tolerance 
0″ -3″ +-.030″
3″ – 6″ +-.060″
6″ – 9″ +-.090″
9″ and up +-.090″ +-.005 in/in
Wall Thickness (One Side of Parting)
Wall Thickness Tolerance
.125″ – .375″ +-15%
.5″ and up +-10%
Wall Thickness ( Across Parting)
Dimension Tolerance 
.125″ – .375″ (Small Casting) -.03″ + .09″
.5″ and up (Large Casting) -.04″ + .12″
Mismatch – Mold And/Or Core Shift
Core or Parting Line Dimension 
Dimension  Tolerance 
0″ – 8″ +-.030″
8″ – 18″ +-.060″
18″ and up +-.090″
Warp Or Twist As Cast
Dimension  Tolerance 
0″ -3″ +-.030″
3″ – 12″ +-.060″
12″ – 24″ +-.090″
24″ and up +- By Agreement
Parting Line Fins
0″ to .04″
Ground Gate And Riser Connection
+-.06″ To True Surface

 

 

Typical Minimum Machine Finish Allowance-Does Not Include Draft
Casting Dimension Drag Cope
Up To 8″ .125″ .156″
Up To 14″ .156″ .1875″
Up To 18″ .1875″ .25″
Up To 24″ .25″ .3125″
Up To 30″ .3125″ .375″
Up To 36″ .375 .5″
Allowances For Finish Are Not Covered By Fixed Rules Because They Involve Many Variables And Should Be Agreed Upon Between The Foundry And The Manufacture.

Machining allowance is like a blanket covering a number of uncertainties and variables in the manufacture of a casting. 

Some of these are as follows.

1. Casting Roughness

2. Core Variance And Placement

3. Surface Defects

4. Change In Mold Dimension During   Casting

5. Pattern Inaccuracy

6. Variances In Shrink During Cooling Of Casting

7. Molding Variance

It Is Important That All Machining Location Points Be Clearly Defined On Casting Drawing.