Sometimes, our clients will be wondered how to determine the rough casting tolerance. According to our experience, the standard of BS6615:1996 and SFSA 2000 can be used for solving this issue.
Please see the following standard BS6615:1996, this standard is also as same as ISO 8062:1994, which has been taken as the standard for the rough castings. In addition, please see the following standard SFSA 2000, although this standard is for steel castings, it is also suitable for iron castings.
Actually, we also have Chinese standard, which is as same as the description in this SFSA 2000. From these two standards, you can see that investment casting is 5-7 degree. The highest tolerance for sand casting is 8-10 degree, which means shell molding process can reach CT8 degree. The machine molding and automatic molding can reach CT9 degree. The resin sand casting can reach CT9 to CT10 degree. The manual green sand casting can reach CT10 to CT12 degree.
However, this standard can not represent all dimensions. Sometimes, as for some mounting dimensions, the clients will have special requirements. Then the foundries should consider it, and can try to meet the special tolerance by grinding or machining.
The deviation of rough casting dimensions are related with the strength of molding sand, compactness of sand mold, liquid iron temperature, chemical components, moisture of sand and workers’ operation. Any small factor may cause the deviation of dimensions. Sometimes, too strict requirements are not realistic. Some level of deviation is inevitable although we also try our best to control the deviation as small as possible.
The following is the ISO 8062 1994 inches and SFSA 2000 standard. Please click here to see the ISO 8062 1994 millimeter (mm).
Table 1. Casting dimensional tolerances adapted from ISO 8062-1994, (inches), also used for SFSA 2000 steel casting tolerances.
| Raw Casting basic dimensions (inch) | Total casting tolerance (inch) | ||||||||||||||||
| Over | Up to and including | Casting tolerance grade (CT) | |||||||||||||||
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | ||
| – 0.4 0.6 |
0.4 0.6 1 |
0.01 0.01 0.01 |
0.01 0.01 0.01 |
0.01 0.01 0.01 |
0.01 0.01 0.01 |
0.01 0.02 0.02 |
0.02 0.02 0.02 |
0.03 0.03 0.03 |
0.04 0.04 0.05 |
0.06 0.06 0.07 |
0.08 0.09 0.09 |
0.11 0.12 0.13 |
0.17 0.17 0.18 |
– – 0.24 |
– – 0.32 |
– – 0.39 |
– – 0.47 |
| 1 1.6 2.5 |
1.6 2.5 4 |
0.01 0.01 0.01 |
0.01 0.01 0.01 |
0.01 0.01 0.01 |
0.01 0.01 0.02 |
0.02 0.02 0.02 |
0.03 0.03 0.03 |
0.04 0.04 0.04 |
0.05 0.06 0.06 |
0.07 0.08 0.09 |
0.1 0.11 0.13 |
0.14 0.16 0.17 |
0.2 0.22 0.24 |
0.28 0.32 0.35 |
0.35 0.39 0.43 |
0.43 0.47 0.55 |
0.55 0.63 0.7 |
| 4 6 10 |
6 10 16 |
0.01 – – |
0.01 0.01 – |
0.01 0.01 0.02 |
0.02 0.02 0.02 |
0.02 0.03 0.03 |
0.04 0.04 0.04 |
0.05 0.06 0.06 |
0.07 0.08 0.09 |
0.1 0.11 0.13 |
0.14 0.16 0.17 |
0.2 0.22 0.24 |
0.27 0.32 0.35 |
0.39 0.43 0.47 |
0.47 0.55 0.63 |
0.63 0.7 0.79 |
0.79 0.87 0.98 |
| 16 25 40 |
25 40 60 |
– – – |
– – – |
– – – |
0.03 – – |
0.04 0.04 – |
0.05 0.06 0.06 |
0.07 0.08 0.09 |
0.1 0.11 0.13 |
0.14 0.16 0.18 |
0.2 0.24 0.28 |
0.28 0.32 0.35 |
0.39 0.43 0.57 |
0.55 0.63 0.7 |
0.7 0.79 0.91 |
0.87 0.98 1.14 |
1.1 1.26 1.46 |
| 60 100 160 250 |
100 160 250 400 |
– – – – |
– – – – |
– – – – |
– – – – |
– – – – |
– – – – |
0.1 – – – |
0.15 0.17 – – |
0.21 0.24 0.28 – |
0.32 0.35 0.39 0.43 |
0.39 0.47 0.55 0.63 |
0.59 0.67 0.79 0.91 |
0.83 0.95 1.1 1.26 |
1.02 1.18 1.38 1.58 |
1.3 1.5 1.73 1.97 |
1.65 1.93 2.21 2.52 |
Table 2. SFSA 2000 for steel casting tolerance long-production series
| Production Conditions | Select Tolerance Grades |
| All sand molding process fully capable, most appropriate for large castings | CT 12 – 14 |
| Appropriate for most casting types and sand molding processes | CT 10 – 12 |
| With in process capabilities, but not appropriate for all casting types and sand molding processes | CT 8 – 10 |
| Investment Casting | CT 5 – 7 |