dowel pin (press fit) design question - Page 1
Forum section: electronics / general

author: engineheat
author_rank: Frequent Contributor
timestamp: January 30, 2020, 09:49:10 pm
content: Hi,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.Thanks

author: ConKbot
author_rank: Super Contributor
timestamp: January 30, 2020, 10:55:00 pm
content: Step 1) buy the Machinery HandbookThere is no step 2.Alternatively, pick a fit from the chart herehttps://amesweb.info/fits-tolerances/preferred-tolerances-table.aspxPlug said fit and your nominal size into here.https://amesweb.info/fits-tolerances/tolerance-calculator.aspx

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: January 31, 2020, 05:56:38 am
content: I sometimes watch ABOM79 make something. He's a machinist with quit a bit of experience.https://www.youtube.com/user/Abom79Whenever 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.

author: Szumi
author_rank: Contributor
timestamp: February 02, 2020, 08:42:59 pm
content: 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.

author: coppercone2
author_rank: Super Contributor
timestamp: February 06, 2020, 04:58:20 am
content: 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

author: Ian.M
author_rank: Super Contributor
timestamp: February 06, 2020, 07:46:48 am
content: @coppercone,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@All,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!

author: Benta
author_rank: Super Contributor
timestamp: February 06, 2020, 07:50:07 pm
content: @engineheatBlending out the irrelevant "aluminium/steel" fit discussion here, you'll need to check "ISO limits and fits":https://en.wikipedia.org/wiki/Engineering_fitThis 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).https://www.elesa-ganter.com.cn/static/technicaldata/files/DIN_ISO_286_ISO_Fundamental_Tolerances_EN.pdfDone.

author: tooki
author_rank: Super Contributor
timestamp: February 06, 2020, 09:23:26 pm
content: @benta: FYI, German “ausblenden” translates to “hide” or “ignore”. (The English “blend” means only “mix”.)