I am working on a project using two bronze flange bearings and a 3/4" diameter aluminum shaft of type 6061 - all mounted on a 2" X 4" rectangle steel tube. See the picture attachment.

My question: will this arrangement be acceptable using the aluminum shaft with a downward load of 50 pounds and a sideway load of 25 pounds?

The maximum continuous rotation speed will be 200 RPM.

I wish to keep this low cost as possible.

I think you should use a steel shaft. Preferrably case hardened.

Hello,
You need to look into a surface coating if you want to make this last. NiTuff is a hard coat - Teflon impregnated surface coating I use quite often when dealing with Aluminum. It gives the aluminum a 60 to 70 on Rockwell C scale hardness. They have shops all over the country that do the treatment. It is cheap for the most part and I highly recommend them. I have been using them (Nimet Industries Inc.) and you can find them and the specifics on the internet.

The aluminum on Bronze will not hold up. If this machine setup will not be a production machine you will get some life out of the aluminum. The good thing about Nituff, is the Teflon impregnation, it will wear out the bearing before any wear shows on the aluminum shaft. Trust me on this one, you will thank me!
Good Luck,
Glen

I agree the aluminum will disappear RAPIDLY without some sort of surfacing.
Turn the shaft out of 4142 for decent life.
And mabe to go along with that use composite bearings (Nylon/Teflon). Let the bearings wear out and pop new ones in once a month or whatever.

With 200RPM continuous and 50# thrust I strongly recomend a redesign utilizing thrust capable bearings.

"A job worth doing is a job worth doing well"

I realized using aluminum shaft will wear out quickly with bronze bearings.

So, I redesigned using a different bearing. I plan to use four-hole flange bearing instead.

I'll pose the new drawings soon.

Thanks for your feedback.

This is the different design using flange bearings. The shaft is aluminum 6061.

What do you think?

I think it will outlast your first suggestion by several thousands to one! ;)

Those bearings will last you a very long time. But you really did move your cost up quite a bit too. Unless you can get them at surplus prices of course.

It will still suffer from the axial load if you use simple ball bearings. They should be angular contact or taper bearings. They would cost more, though. Check SKF (http://www.skf.com/) or FAG (http://www.fag.de/NASApp/Access/index.jsp?lang=1) for bearing specs.

HTH, Nikolas

The bearings axial load is rated 1500 pounds.