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timsch (Mechanical) (OP)
21 Apr 10 16:03
Can someone provide a reference for the diametrical interference for a press fit steel pin into aluminum?  I need to press a .125" diameter pin into an aluminum extrusion roughly 1/4".  All references have an interference of no more than .001 between the hole & pin, but I believe that those values are for materials such as steel into steel.  

I want to use standard drill sizes if possible, but the range between sizes is not that small.  I was able to press this pin into a hole with .005" interference.   
desertfox (Mechanical)
21 Apr 10 18:08
Hi timsch

You need to use an interference that suits your application based on what loads and temperatures your fit might see in service.
You can't just say 0.005" or 0.002" interference without knowing something about the application.

MikeHalloran (Mechanical)
21 Apr 10 19:22
Please red flag one of your duplicate posts.

Mike Halloran
Pembroke Pines, FL, USA

hydtools (Mechanical)
22 Apr 10 7:45
If you are permitted by design, use a spring pin and a drilled hole.


timsch (Mechanical) (OP)
22 Apr 10 9:15
desertfox, what I am looking for is a reference to provide some design guidelines specifically for steel going into aluminum, if one exists.  I realize that I cannot say .002 or .005, just like I cannot say that .001 will be sufficient, which is typically what I am seeing when looking at Machinery Handbook or ISO 286.  I have yet to see any mention of the materials being joined, which seems to me to be a variable.  I may be wrong here.  Please bear with me, as I am still learning.

My application:  These pins are pivots on which lightweight indicators are mounted.  The pins are under no load.  Temperature range is -100F to 1000F
desertfox (Mechanical)
22 Apr 10 15:45
Hi timsch

Well I don't know any standard references for steel pins in aluminium, like I stated the first time, you design them around the service conditions, take for example the temperature range you have quoted for your pins, 100F to 1000F now thats 38 degrees to 538 degrees centigrade, now expansion of steel is about 12*10^-6 and aluminium about 23*10^-6 so a 3.175mm pin of steel would have a free expansion of:-

                   12*10^-6*3.175*(538-38)= 0.01905mm

but the alumium     23*10^-6*3.175*(538-38)= 0.0365125mm

so for your pin not to fall out at 538 degrees centrigrade or a 1000F, I calculate the hole in the aluminium would have to be machined to a diameter of 1.656mm at the point of manufacture and then shrink fit the steel pin of 3.175mm diameter into it. Sadly it doesn't look like its going to work.
What happened to the pins you pressed in with 0.005" interference?


timsch (Mechanical) (OP)
22 Apr 10 16:27
I see what you are saying now.  I do not see how you calculate 1.656mm for the aluminum hole, though.  

The difference in free expansion between the two metals is ~.018mm (.0007") at maximum temp.  If I wanted an interference of at least .001" at all temperatures, why would I not drill the aluminum at least .0017" smaller than the minimum pin diameter of .124" ?

.124-.0017" = .1223" (3.106mm)

MikeHalloran (Mechanical)
22 Apr 10 16:41
Now I'm curious about what aluminum alloy is going to behave elastically at 1000F.


Mike Halloran
Pembroke Pines, FL, USA

desertfox (Mechanical)
22 Apr 10 17:24
Hi timsch

Yes sorry my big mistake, had a senior moment then, I got into equal changes in diameter for a given temperature rise, but my point was you need to design your interference for your needs and that temperature rise shows my point.
timsch (Mechanical) (OP)
22 Apr 10 17:27
Mike, you are right to be curious - I have not given sufficient details.  This aluminum will be attached to a steel pipe that may see maximum 1000F in rare instances.  Heat transfer between the pipe and the aluminum channel will not be sufficient to heat the aluminum fully to that temperature. Other than where the aluminum channel contacts the pipe, it will be exposed to the atmosphere at ambient temperature.
hydtools (Mechanical)
22 Apr 10 22:58
The annealing temperature of aluminum is around 650F to 800F, depending on alloy.  That will relax stresses.  If, as was stated, the pins are under no load they should not fall out.  They will still have light contact.


loafer09 (Mechanical)
23 Apr 10 9:27
The CTE will not be linear for steel over that temperature range.     
ornerynorsk (Industrial)
23 Apr 10 11:18
Given the correct press and installation driver, a 0.005 pre-install press fit on a .125 pin is probably going to swage material, thereby not giving you a true .005 interference fit.  Personal experience, all engineering formulae set aside.  You may see better results with .001 undersize hole.  And by the way, if this is a solid pin, you cannot simply drill the hole, you will need a reaming operation to maintain an acceptable hole geometry.   
gadkinsj (Mechanical)
27 Apr 10 15:50
Can you replace your steel pin with a shoulder bolt?  Or how about a spring pin
unclesyd (Materials)
27 Apr 10 22:34
I think you may have an application for grooved pin from Driv-Lok.

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