Tolerances control whether your parts fit together correctly, whether your project stays within budget, and whether the final product performs as designed. When you set tolerances too tight, you pay for precision that isn’t necessary for your specs. When you specify tolerances that equipment can’t reliably hit, you get higher costs, longer lead times, and potential quality issues.
Achieving tight tolerances in metal fabrication requires a thorough understanding of each production phase. You must choose the right material, select the most suitable equipment, and conduct inspections at multiple stages throughout the production process. The solution begins with a reputable fabrication partner who reviews your drawings before quoting, identifies areas where tolerances can be optimized, and explains how different fabrication methods impact what’s achievable.
Why Tolerances Matter in Metal Fabrication
Tolerances define acceptable variation in a part’s dimensions. Some CAD software programs pose challenges by automatically generating precise measurements, even when they are not needed. While these numbers may appear professional on drawings, they sometimes represent precision levels that metal fabrication can’t consistently achieve without secondary processes or additional costs.
When your drawing specifies machining-level tolerances for sheet metal parts, fabricators must either quote based on those tight specs or contact you to discuss realistic alternatives. Either way, the mismatch between specified tolerances and fabrication capabilities usually results in wasted time and money.
Material Tolerances vs. Fabrication Tolerances
Many raw materials come with built-in tolerances before fabrication even starts. Steel mills produce sheet metal through rolling processes that create variations in thickness and flatness.
- Hot-rolled steel: This material is processed at high temperatures to facilitate easier forming. The high-heat process and room-temperature cooling create larger thickness variations and a rougher surface finish. Thickness typically varies plus or minus 0.010 inches or more.
- Cold-rolled steel: Hot-rolled steel undergoes additional processing at room temperature, which produces tighter thickness tolerances and smoother surfaces. It costs more than hot-rolled but delivers better consistency. Thickness typically varies by 0.005 to 0.008 inches, depending on the material’s thickness and width.
Fabrication tolerances are added to these material variations. You can’t reliably hold plus or minus 0.005-inch fabrication tolerances on material that already varies by plus or minus 0.010 inches in thickness.
Geometrical location also affects achievable tolerances. Features like holes, edges, and cutouts on a flat surface maintain much tighter tolerances because they are created by a single machine in one operation. Variations in features across multiple processes increase with each forming step.
How Fabrication Methods Affect Tolerances
Different processes can achieve varying levels of precision:
- Laser cutting: Laser cutting holds tight tolerances on flat surfaces, typically plus or minus 0.005 inches for hole-to-hole or edge-to-edge dimensions. The CNC-controlled laser cuts exactly where programmed.
- Bending and stretching: Metal forming introduces more variation due to material spring-back and thickness inconsistencies. CNC press brakes typically hold plus or minus 1 degree angular tolerance per bend and plus or minus 0.015 to 0.030 inches on linear dimensions across bends.
- Multiple bends: Multiple bends increase variation with each additional machine pass. A part with four 90-degree bends might accumulate plus or minus 4 degrees total angular variation and plus or minus 0.030 inches or more in dimensions measured across all four bends.
The Hidden Costs of Overtolerancing
Specifying tighter tolerances than necessary creates problems like:
- Higher quotes: Shops must account for additional setup time, inspection frequency, and higher rejection rates when bidding tight-tolerance work.
- Longer lead times: Tighter tolerances require more machine setup, more frequent inspection, and careful handling throughout production.
- Increased waste: Parts that function perfectly within realistic tolerances are rejected for minor variations that don’t affect performance.
Many parts with overly tight tolerances would work perfectly fine with standard sheet metal tolerances of 0.020 to 0.030 inches. The tighter specification doesn’t improve the function — it just increases cost. Implementing a design with materials tolerances and equipment capabilities in mind helps eliminate many problems before production begins.
Mid-Atlantic Steel Fabrication’s Approach to Tolerances
At Mid-Atlantic Steel Fabrication, our equipment and processes deliver consistent results within realistic tolerance ranges. Our TruLaser 3030 and TruBend 5130 provide the precision and repeatability that today’s manufacturers need. Our D1.1 Structural Certified fabricators understand how tolerances accumulate across multiple operations and how to optimize parts for manufacturability.
When we review drawings with unrealistic tolerances, we will contact you before providing a quote. This proactive approach identifies opportunities to modify designs slightly while maintaining function. Minor adjustments often achieve the same performance at significantly lower cost.
Operating as a one-stop shop for laser cutting, CNC forming, welding, and 3D CAD design gives us control over the entire process.
Contact Us Today for More Information
Need help optimizing your specs for fabrication? Call 717-687-7313 or submit a quote request today. We can review your drawings and help you find the most practical and effective solution.