Press Fits and Slip Fits: Machining the Right Tolerance for Your Part

Arbiser Machine achieves a precise fit every time.

Achieving tight tolerances is a critical requirement in machining. It’s also one of the most difficult challenges when machining metal parts because 2D drawings and 3D CAD models don’t always translate seamlessly to the shop floor. 

Trust us, the last thing you want is to end up with a press fit when you really needed a slip fit. So how can you be certain that your parts have the right tolerances to function properly? 

Arbiser Machine is committed to machining the right fit every time. But first, let’s review the difference between a press fit and a slip fit—just to be consistent. It’s always smart for engineers and manufacturers to be on the same page!

Press Fits and Slip Fits

• Press fit tolerance. A press fit tolerance is a very hard fit where parts are forced together under pressure. Manufacturers either tap parts together or use a mechanical or hydraulic press to achieve the fit. The frictional forces involved in pressing the parts together hold the parts without any additional hardware like keys or set screws. Once the parts are fitted, they’re almost impossible to separate. 

Tolerances for press fits are critical because parts can be easily damaged by attempts to press fit them if there is a lot of difference in their mating dimensions. Also, press fitting physically deforms the parts to some extent, so the result can be damage, mechanical binding or the need for a secondary resizing operation such as reaming or honing after the parts are pressed together. Common press fit applications include bushings, bearings, and custom mechanical assemblies. 

• Slip fit tolerance. The opposite of a press fit tolerance. In a slip fit tolerance, a certain amount of clearance exists between mating parts. Because this tolerance is looser, fabricators can secure it by hand. Slip fit tolerances are ideal for when the part needs to functionally slide (e.g. a bolt) or when something else like a keyway will secure it. 

Arbiser Machine Achieves Precise Tolerances Every Time 

Arbiser Machine encourages engineers to provide us with detailed tolerancing specifications in their initial drawings. But we always conduct due diligence to avoid part measurement errors. 

We confirm that your mating parts have matching tolerances 100% of the time. If we notice a discrepancy, we’ll give you a call right away to clarify. We also test-run both mating parts to ensure a proper fit before proceeding to production. 

There are many types of fits for specific situations, like turning fit, running fit, sliding fit, etc. , and all these can be found in the Machinery's Handbook. One chart we use frequently for our typical bore and shaft fits for various tolerance zones that makes life easier for engineers, is from R+W Company. It is in metric, and remembering that 1 micrometer = .00004” makes the conversion process pretty quick.

Need a precise fit for your part? Try our Georgia machine shop for your next project!