Interference fit sizing

[buzzedge]

Hello everyone,

I'm looking to do an interference fit of a aluminum hub onto a steel shaft. They are very small, the steel shaft is approximately 7.5mm

I'm not sure what alloy the shaft is but the aluminum hub is 7075. Currently the aluminum hub is large enough to slide onto the shaft tightly, I want to change this to an interference fit using heat. When I heated up the hub with a heat gun, I measured an increase of 0.03mm in inner diameter.

With this info, what would be safe sizing for the inner diameter of the hub vs the shaft. I did some searching and saw some say 0.001" per 1" of shaft but I'm dealing with much smaller parts.


Thank you

 

[TugboatEng]

Normally I go off the ISO 286 standard. You will need to ensure you have sufficient interference over the full range of temperatures you expect your assembly to be exposed to. Aluminum has a substantially higher coefficient of thermal expansion than steel and at elevated temperatures the interference fit may be lost.

 

[buzzedge]

Yes, the shaft increases in diameter by 0.01mm compared to the aluminum hub at 0.03mm

 

[BrianE22]

Are you transferring a load (axial or torsional) through the fit?

 

[3DDave]

How do you feel about shaft-locking compound with an accelerator?

 

[buzzedge]

It's a high RPM rotating assembly. There is a retaining nut on the shaft but I don't believe it puts enough pressure to keep the aluminum piece from spinning on the shaft. The interference fit would act as a failsafe to be sure there is no unwanted rotation.

 

[TugboatEng]

Turbochargers with similar shaft and bore dimensions spin at 100,000+ rpm and are clearance fit with a single nut holding everything together. If you are having problems with it slipping it's due to forces.

Yes, an interference fit will improve strength. You could alternatively use a diamond faced washer between the component and the shoulder on the shaft. Retaining compounds work great but you need some clearance for best performance.

 

[buzzedge]

Does 0.02mm sound like a reasonable interference for this if tests show 0.03 expansion after heating above what normal operation will experience? Smaller than this might be hard to replicate over a small production run.

 

[Tmoose]

"It's a high RPM rotating assembly..."

"high" can sometime result in expansion of the spinning component.
Reference precision spindle bearing inner ring fit calculations that ensure slight interference is maintained in operation.
Additional interference at assembly is required.
check out page 30 here -

https://www.schaeffler.com/remoteme...ffler_2/catalogue_1/downloads_6/sp1_de_en.pdf

What does this aluminum hub do?
Is the loading one directional radial, like a pulley/sheave?

What symptoms do you see that make you suspect "spinning" ?

 

[DAVIDSTECKER]

In my "Scrap" book of engineering articles, I have one from Machine Design magazine, dated July 26, 1990, for shrink fits that take in to account different materials.
"Saving weight with shrink fits"
I'd scan it, but I'm not sure about Copy Rights.