The Importance of Tolerances in Precision Machining

Using tolerances effectively is crucial to ensuring your parts function the way they’re intended to. And strategic tolerancing can save you time and money during the manufacturing process. 

But determining the right tolerance for a feature can be challenging. Many engineers end up going with the default settings on design programs like SOLIDWORKS without realizing that they are creating more work for themselves down the road. 

Quick Tolerance Overview for Precision Manufacturing

Let’s take a minute to get on the same page about tolerances. Essentially, the indicated tolerances let us know how much room for error exists in a part’s dimensions. When two parts need to fit seamlessly together, there’s far less room for error and, therefore, a tighter tolerance is required. Tolerances may be less precise when a tight fit isn’t critical to the part’s end-use function. 

Tolerances are depicted as “+/-.XXX.” The more spaces after the decimal, the tighter the tolerance. This table shows some standard tolerances we use at our precision machine shop:

How Do Tolerances Factor Into Precision Machining? 

Here’s a closer look at how tolerancing factors into part functionality, cost, and lead time: 

Functionality

If your part is out of tolerance, it won’t function as intended. Want an example? 

A customer sent us a fluid connector that needed to be dimensioned to fit into a .750” port. Their “guarantee” that the connector would fit into the port was to dimension it at .740” with no tolerance. The parts were sealed with an o-ring. Per design standards the .740” dimension would have allowed a gap large enough so the o-ring connection would leak.

Instead, we recommended that the customer label both components as .75,” making the hole’s tolerance +.002”/+.004” and the male part’s tolerance -.002”/-.004.” That way, the part was guaranteed to turn out smaller than the hole. 

Cost and lead time

Proper tolerancing can also save you time and money during precision machining. The tighter the tolerance, the higher the cost and lead time, generally speaking. Why? Because more precise machining takes longer, and ensuring that a part is accurate within three decimal places is more challenging than ensuring accuracy to one decimal place. 

A loose or fractional tolerance will suffice when a part only requires a crude assembly and doesn’t need to fit seamlessly with other components, so there’s no need to request tighter tolerances if they aren’t actually necessary. Knowing minimum tolerances—and calling them out correctly—prevents high costs and long lead times for simple parts.

Arbiser Machine encourages engineers to send detailed tolerancing information with every part. We’re always happy to help in this process by contacting you when a tolerance seems off and by testing all parts in your assembly to ensure a proper fit before proceeding to production. 

Want to work together on your next precision machining project? Request a quote today!