Talking About Tolerances

A major consideration on most parts we work on is tolerances, IE. how far can our fabrication work deviate from the dimensions on the drawing. Several issues keep coming up with tolerances and it’s something you need to actively think about for your application. The first major issue we get is unreasonable tolerance requests. This can be anything from a customer accepting zero deviation from the drawing, which is impossible, to passively leaving metal tolerance requirements on a drawing that simply cannot be held with a plastic.

There’s another issue that does not get considered enough which is when customers tell us to hold “best possible tolerances” because they don’t know what they actually need. This tolerance, often (+/-) 0.005″, results in a higher cost for the part as it’s more difficult to make with less margin for error. The fact that there are actual costs to “best tolerances” is something the customer should know.

The other issue with tolerances is that the difficulty of holding them depends on the material. For example, it is much easier to hold a (+/-) 0.01″ tolerance on acetal than it is on a rubber product. Absolutely the rule “one size fits all” does not apply. You also really need to think about the application: a bushing which is press fit into a housing and has a shaft going through it with a running clearance needs more precise tolerances than a polyurethane bumper.

For more information on tolerances or a quote on your requirements, please contact us today.