PDA

View Full Version : Bearings, Bushings or Steel on Steel



gkman11
06-16-2005, 07:04 AM
Making a ring roller with a capacity of 3/8 X 2 Flat with 3 1/2" rollers. Hand cranked through gearing. How much do bearings or bronze bushings reduce friction (torque) on a highly loaded, slow turning shaft?

.RC.
06-16-2005, 07:16 AM
http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm

down the bottom there is a table of coefficient of friction for all sorts of materials...

J Tiers
06-16-2005, 08:12 AM
Does it matter?

The friction of various solid materials assumes "full contact" between them, i.e. no ball bearings, oil, etc. Metal-to-metal contact, in your case.

Any bearing which is expected to last some real amount of time should NOT have metal-to-metal contact.

Grease etc is intended to provide a film to prevent metal-to-metal contact. When that doesn't happen, it is called a lubrication failure, and the bearing is galled or worn into uselessness.



[This message has been edited by J Tiers (edited 06-16-2005).]

wierdscience
06-16-2005, 09:05 AM
Bronze sleeves and grease cups aren't expensive or difficult to install and needle bearing inner rings pressed on the shafts make for a good surface that will last nearly forever.

Avoid oilite bushings though,932 cast bronze sleeves are a few bucks more,but much more durable.

Considering the load you will have(3-15tons depending on radius)handcranking may be very stressful.

CCWKen
06-17-2005, 12:32 AM
Wow, I think the near 10+ tons needed to roll form 3/8x2 is going to be beyond bronze bearing capacity. Full complement needle bearings should do it though. Your shaft will need to be around 2 to 3" in diameter, depending on material used.