Author Topic: dowel pin (press fit) design question  (Read 628 times)

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Offline engineheat

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dowel pin (press fit) design question
« on: January 30, 2020, 09:49:10 pm »
I'm designing a part (part A) that has to be press fit into another existing part (part B) like a dowel pin. On Solidworks, the diameter of the hole on part B shows 2mm (the theoretical value), but the PDF drawing shows tolerance of 1.985mm to 1.997mm.

So for part A, what tolerance should I specify for the diameter of the shaft that gets press fit into part B? I don't want the fit to be too loose but I don't want it to be too tight that makes installation impossible.

Both parts are stainless steel.


Offline ConKbot

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Re: dowel pin (press fit) design question
« Reply #1 on: January 30, 2020, 10:55:00 pm »
Step 1) buy the Machinery Handbook
There is no step 2.

Alternatively, pick a fit from the chart here

Plug said fit and your nominal size into here.

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Offline basinstreetdesign

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Re: dowel pin (press fit) design question
« Reply #2 on: January 31, 2020, 05:56:38 am »
I sometimes watch ABOM79 make something.  He's a machinist with quit a bit of experience.
Whenever he has to make a "press-fit" or "interference fit" part it seems he makes the inner part about 0.001 inch to 0.002 inch bigger than the outer part.
STAND BACK!  I'm going to try SCIENCE!

Offline Szumi

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Re: dowel pin (press fit) design question
« Reply #3 on: February 02, 2020, 08:42:59 pm »
For a press fit I use the rule of 0.001" of interference per inch of diameter.  You can move up or down a bit for light or heavy fits.

Online coppercone2

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Re: dowel pin (press fit) design question
« Reply #4 on: February 06, 2020, 04:58:20 am »
I notice old stuff I find involving dowel pins in non-anodized aluminum are often corroded (i.e. physics lab jigs)

Something to keep in mind when designing with dowel pins I think. Kind of sad since the parts are otherwise primo
« Last Edit: February 06, 2020, 05:00:34 am by coppercone2 »

Online Ian.M

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Re: dowel pin (press fit) design question
« Reply #5 on: February 06, 2020, 07:46:48 am »
That's what happens if you use ordinary steel pins (or other fasteners) in aluminum.  It only takes occasional condensing humidity for the interface to suffer from significant electrochemical corrosion, and the corrosion products of both aluminum and steel take up significantly more volume than the parent metal, so close fitting fasteners will seize in place.  Aluminum + stainless steel is somewhat better as then only the aluminum corrodes, but if you want trouble-free reassembly in the future, if dissimilar metals are involved and one is a light alloy, you need to use an electrochemical corrosion inhibiting and passivating jointing compound, e.g. Duralac

I suspect the O.P's project is FUBARed and the hole tolerance is too coarse for any guaranteed press fit.  If you play around a bit with the calculator ConKbot linked, the hole specs out at 1.985 H8 and there are *NO* H8 hole press fits in the associated tables. 

You might be able to bodge it with a knurled pin and the right grade of Loctite!
« Last Edit: February 06, 2020, 09:58:13 pm by Ian.M »

Online Benta

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Re: dowel pin (press fit) design question
« Reply #6 on: February 06, 2020, 07:50:07 pm »

Blending out the irrelevant "aluminium/steel" fit discussion here, you'll need to check "ISO limits and fits":

This ISO standard defines the hole/shaft tolerances for different types of fits. You select the type of fit needed, in your case probably light or medium cold interference fit (H7/p6 or H7/s6).
Using these tolerances (H7, p6 and s6), you look up the hole and shaft tolerance tables for your desired diameter in the ISO tables (ISO 286).


« Last Edit: February 06, 2020, 08:05:53 pm by Benta »

Offline tooki

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Re: dowel pin (press fit) design question
« Reply #7 on: February 06, 2020, 09:23:26 pm »
@benta: FYI, German “ausblenden” translates to “hide” or “ignore”. (The English “blend” means only “mix”.)

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