Q: Press Fit

[Deviant]

Hello,

If I want to press fit a 3mm dimeter piece of harden/ground drill rod into aluminum.

What is the best way to do this? And what diameter hole would I be drilling/reaming.

How much force would I need to press the part together with.

And would it deform the part?

Aluminum disk is 10mm diameter 6mm thick.

Additionally, is there any concern with the disk being made of teflon.

Thanks.

*side note* I have a 3ton arbor press. I would need to make a tooling/fixture to keep everything aligned prior to the big squeeze.

[marcel beaudry]

i would use locktite instead of press fit

[Deviant]

Does locktite expand? What clearance would you suggest for the locktite choice?


The part will be pushing and pulling. While the force wouldn't be alot. ((Valve))

Do you still suggest locktite?

[marcel beaudry]

if heat is involved loctite will not stand . what i would do if it's a valve , machine a sholder then rivet the shaft to the aluminim disk

[NC Cams]

Whenever you do a press fit, you have to consider the yield points of the materials and the thermal differential that they will undergo - especially when you're mixing ferrous and non-ferrous materials. You also have to consider the heat treat of the materials as well as the cross sectional areas.

Essentially, the answer to ALL your questions posed is "YES", "NO" and "MAYBE".

The attached link should enable you to do a downtown fit calculation for steel shaft into aluminum whatever:

Press fits:
http://www.eng-tips.com/faqs.cfm?fid=1230

The thing you have to be careful of is to NOT yield the weaker material when you press them together. This is why and where the proper use of the link will be invaluable to you.

I've seen cases were guys pressed steel pins into aluminum disks and they got cold and the aluminum yielded as it shrunk over the steel. When it returned to room temp, the pin was now loose. OOPS.

Or, it was tight at room temp but when it got hot, the pin would drop out but be tight again when at room temp.

Or, at room temp, the pin caused the aluminum to yield once it was thermally shrunk fit and then the temps normalized.

Pressing steel into aluminum or vice versa is not a situation where a SWAG can be trusted.

BTW: loctite will NOT absolve you of the thermal growth issues that are endemic to aluminum and steel interference fits.

My strong suggestion: use the link and calc the fit properly. Seek help from a friend if you're uncertain of the math or the values asked for.

Better yet: use steel for both parts and don't mess with the aluminum issue. At least you won't have to worry about thermal expansion.

[Paul_S]

When I estimate a press fit for a pin I use this following formula:

min id = pin dia - pin dia x .002
max id = pin dia - pin dia x .001

I use this for pins in fixtures (aluminum or steel) and locating pins in vise jaws (steel soft jaws.)

[dertsap]

if the aluminum part is small enough to drop into a deep fryer , leave no more than .001" on the ID then heat it up in the deep fryer and it should slide right onto the mating part with no restriction ,do this swiftly as aluminum disipates the heat very fast , nothing will get marked or damaged this way and you will have a good fit , ive done this many times on bearings ,