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: Optimal Shrink Fit Clearance for a Press Fit.
: Optimal Shrink Fit Clearance for a Press Fit. -- GatesAJ	Post Reply	Top of thread	Engineering Forum

Posted by: RWOLFEJR ® 02/19/2009, 15:16:11 Author Profile eMail author Edit

Depends on the materials being used... hollow or solid shaft... how it will be used... and if you will shrink or press. Any subsequent machining to take into consideration... Are one or both parts thin wall? If materials are the same then the temperatures this will see assembled won't matter since they'll both expand and contract at the same rate. If this isn't critical and simply to locate and fix... The rule of thumb is about .0010-.0020 INCH per inch of diameter until you get up into bigger diameters.

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: : Optimal Shrink Fit Clearance for a Press Fit.
: : Optimal Shrink Fit Clearance for a Press Fit. -- RWOLFEJR	Post Reply	Top of thread	Engineering Forum

Posted by: GatesAJ ® 02/19/2009, 15:31:54 Author Profile eMail author Edit

The materials are being assumed to be the same or have close enough thermal expansion coefficients to be able to neglect the difference. The application of this is to press a solid pin into a differential to support the spider gears. They are having assembly issues right now so I am trying to determine if it is because they left out any room for clearance to get the parts actually together.

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: : : Optimal Shrink Fit Clearance for a Press Fit.
: : : Optimal Shrink Fit Clearance for a Press Fit. -- GatesAJ	Post Reply	Top of thread	Engineering Forum

Posted by: RWOLFEJR ® 02/20/2009, 10:12:18 Author Profile eMail author Edit

Assuming the parts are within tolerance....Your interference in your fit will range from .0008" and .0023". (Sorry but I just have never been able to talk myself into using the metric system. I'd rather spend the time converting because I feel more comfortable with the numbers and can see if they "look" right.) So with tightest scenario your tonnage requirements to press the pin into the cast housing will be roughly 2 tons (breath under) if total engagement is an inch. I'm Going to guess that each side of the spider pin into the casting will engage at most maybe 3/4" so let's bump the contact area to 1-1/2". At 1-1/2" engagement you'll be looking at almost 3 tons. Again this is at tightest scenario with given tolerances. First thing if there are issues getting these together is to check dimensions of pins and bores. You should whip up a go / no-go gage to your tolerances with allowance for encroachment with enough length that both the go and no-go could be passed through the entire length. You could be having alignment issues hole to hole in the bores the pin spans. Then if your press has a gage you could estimate fit with reading. If this is a production assembly you should install pressure switches to detect under and over pressure conditions in assembly to notify the operator with a buzz or light etc. so that assembly can be inspected and check your past and future parts for size etc. If this is a one timer in your garage etc. the rules change. There are old school ways to cheat the fit without issues.

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