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I'm looking to manufacture some steel pins and plates, with a view to large scale production in the future. One of the pins of the design has a constant diameter. This pin passes through holes in two different plates. One of the plates has an interference fit with the pin and the other has a clearance fit with it.

To me, this sounds like it should use a shaft-based system, where the shaft diameter is constant and the hole sizes vary. Given, however, that the difference between hole diameters is only a matter of tens of microns and I've heard that it is typically harder to make non-standard holes than non-standard shafts, I am wondering whether I should use a hole base system, where the hole sizes in both plates are the same and the pin has a small step (tens of microns) to accommodate the different fits.

I think the hole-base system could work but the question really comes down to whether it is easier to accommodate the tiny difference in fit through the manufacture of the shaft or the hole.

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  • $\begingroup$ Are there any other features on the shaft? Is it a custom item or 'off the shelf'? How will you ensure it's always installed in the correct orientation? $\endgroup$
    – Jonathan R Swift
    Apr 25, 2019 at 17:37
  • $\begingroup$ In addition, we need to know more about the application in order to recommend the fit. Is the shaft rotating? What’s the function? $\endgroup$
    – GisMofx
    Oct 23, 2019 at 12:21

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I guess it depends on the respective materials of each part. Normally for an interference fit, you'd the shaft to be a lot stiffer than the plate in which the hole is, to ensure a good interference. Also, some materials are a lot easier to machine than others.

Having said that, and given that the difference in diameter is very small (0.01-0.02m), I would have thought that it easier/more reliable to drill/ream a hole in a plate of the right size with the right tolerance, than to turn down a shaft to the right diameter, even if this means buying a specialised reamer. So my vote is for the hole-based system.

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In a common workshop you will probably find H6/H7 reamers for different hole diameters. If you are not going to fabricate special tools for your project, you will be limited to standard hole sizes - meaning you will easily find a 8 mm H7 reamer but would never find a 7.38 mm H7 reamer on the shelves. enter image description here The manufacturing capability of a standard lath machine (turning machine) should provide you a greater flexibility, since it offers a great accuracy for a wide range of shaft sizes. If, for instance, the machine gives you a +/- 0.001 mm tolerance up to a 15mm shaft diameter, you will get the same accuracy for both 8 mm and 7.38 mm shafts.

enter image description here

Hope It helps...

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