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I am looking for calculator or chart for slip fit and press fit for non standard size parts.

For example, I have oversized dowel pin 10mm +0.03/+0.01 diameter. I need to create a slip fit hole for that oversize dowel pin. What the size and the tolerance of the hole should be?

Another example is I have an undersized plastic bushing which diameter is 20mm -0.05/-0.02 diameter. I need to create press fit hole for that bushing. What the size and the tolerance of the hole should be?

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  • $\begingroup$ Slip fit is heavenly dependant of you application and its friction values. When the CoF is really important here, i would recommend testing. If you know how tight or how much clearance you require, you can calculate your fit. Hence I/you need a bit more context to answer you question. For (ISO)fit size determination i frequently use fit calculator & info. $\endgroup$
    – SimpelenLeuk
    Commented Oct 29, 2016 at 17:52
  • $\begingroup$ You have to measure your dowel pin with a micrometer first, whatever the micrometer reads just add .0005 inches to .001 inch to that reading and that is the size reamer you need to ream your hole for a slip fit. Press fits are a little trickier because it is material dependent to determine how much interference you want ( and how much force you want to apply to force the pin into the hole). $\endgroup$
    – William Hird
    Commented Nov 28, 2016 at 15:50
  • $\begingroup$ Before you start specifying hole/shaft tolerances, you need to define the function of the fit. Do you need a running clearance? Asliding fit where the parts can move, but are not free running? Is the fit definging location? How precise does the controlled location need to be? How much slop in the joint is acceptable? How tight does the press need to be? Do you need a shrink fit? A light press? There are a good 25 pages in Machinery's Handbook on designing fits, not including fastener clearances, with the information you've provided, all I can suggest is to read those pages or use Google. $\endgroup$
    – DLS3141
    Commented Feb 27, 2017 at 16:40
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    $\begingroup$ I've seen people set the micrometer to a specific size and wiggle the pin in it around to get a feel for what the fit would be. You're going to need to ream anyways and reamers come oversized and undersized so you only have so many choices to reasonably choose from much of the time. $\endgroup$
    – DKNguyen
    Commented Apr 1, 2022 at 21:24

3 Answers 3

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You will need to decide what standard you want to base your estimates off of and the level of tolerance. There is also the expense and manufacturability to consider. Here is a calculator I found. The site has others as well. I am sure an internet search will lead to other calculators and guidelines:

https://www.engineersedge.com/calculators/mechanical-tolerances/ansi-fit-tolerances.htm

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I think, unless you are planning for mass production, you need not search for any standards.you can experiment and decide the values yourself.(Iam not sure about this suggestion.But from what I learnt IT grades are used in mass production of hole shaft assemblies because machining cannot be done precisely and identically for all the parts.In case of single components, I think its not needed)

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Another aspect is usage. You want it to be tight so it doesn't fall out I assume, as it's not specified what material it is it can be anything from wood/plastic/steel or bronze or whatever with very different expansion/retraction coefficients depending on temperature. Shall it be used in the cold,in an oven, does it need to not fall out if the temperature changes several hundred degrees? The simplest answer is already given test...you can manufacture it to perfection at 1 atm air pressure and 20° Celsius just to fail where it should be used...

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