7 ways to improve tolerances to make better parts

Sheet metal tolerances describe the acceptable deviation between features on sheet metal parts to ensure correct and consistent fit in installation or integration.  As requirements for sheet metal components becomes more complex, companies demand tighter and more precise tolerances.  It is also essential to work with a sheet metal fabricator who has expertise in tight tolerance assemblies and components

 

Here are seven ways to improve tolerances to make better sheet metal parts:

 

Critical Information

Always call out information not available on models—datum planes, tolerances (block and critical), material type, finish requirements, hardware specifications, hole tapping, welding requirements, surface requirements, and edge requirements, just to name a few.

 

Standard Tolerances

Although the machinery and tooling will repeat within 0.005″, it is a mistake to simply engineer all mating parts, to be within +/-.005″.  This excess forces additional labor in sorting and inspection.

Tolerances that are too tight result in higher costs and lower productivity.  Correct tolerance will still produce excellent fit and function, with the added benefit of manufacturing efficiency.

 

Hole Size Tolerances

Whether the hole is being laser cut or punched, a general rule of thumb is the hole diameter must be no small than material thickness.  Some high powered fiber lasers have the ability to make holes with diameters smaller than material thickness, but this increases processing time and adds labor to inspection.

 

Hole to Hole Tolerances

Accuracy of the distance from one hole to another is dependent primarily upon the machinery used to process the sheet.  Greater tolerance allowances for this feature allow for easier assembly and fit up as well as reducing potential sheet distortion by holes being too close.

 

Hole to Edge Tolerances

Part profiles are either punched or laser cut just like any other feature.  When adding a hole close to an edge (less than double the material thickness), the edge can be pushed out by the stress of punching the metal.  This edge movement can introduce variables in the accuracy of the hole location in relation to the edge.  There are techniques to minimize this problem, but whenever possible, engineers should allow +/-.010” hole-to-edge. Tolerances
of +/-.005” should be used only when absolutely necessary.

 

Hole to Bend Tolerances

Precision press brakes will position and repeat within the +/- .003” range.  Skilled brake operators are able to load the parts for forming
consistently from bend to bend.  Nevertheless, consideration must be given to the natural variation in material thickness (5%
of nominal thickness), the +/-.005” from the turret press or laser cutting machine, the effects of cosmetic sanding, and the variation introduced by the press brake.  A tolerance of +/-.015” hole-to-bend is functionally reasonable for most applications.  Resort to +/-.010” only when absolutely
necessary.

 

Bend to Bend Tolerances

Considering the variables that affect hole-to-bend tolerances, now multiple material surfaces and thickness are introduced. Whenever possible, engineers should allow +/-.020” bend-to-bend.  Resort to +/.010” only when absolutely necessary.  Increased tolerances need to be applied if going
across multiple bends.

 

Amtex Precision Fabrication

At Amtex, we have dedicated staff performing first article, second article, and final inspections on every job.  This ensures our clients receive the highest quality part that meet or exceed their expectations.  If you need precision metal fabrication services, contact Amtex online or call our team at (281) 489-7042 today!