[TheForge] Bronze Bushings

Tue Apr 6 07:32:00 2004

OK Andy - Here we go =>
     I am designing a Ring Roller.  It will be able to roll much more than
the nearest competition, and wider as well.  I have 2 lower rolls that are
free-wheeling, and a top roll that is attached to a keyed drive shaft.  That
shaft will have a bronze bushing at each end and this is the one I am
talking about.  What I need to know is how to fit the bushing in it's
pocket.  Does it need a press fit of .003in or a clearance of .0002in   I
just don't know where to start looking for this, and the Machinery's
Handbook doesn't seem to have this info.  I don't have a Mark's, though I
have seen the need for one for several years.  I already know what thickness
I need (deduced by what is available).  ID and OD are per the catalog and
readily available, thought I am not sure how to mount them.  Most bearing
catalogs are full of info and engineering data concerning their bearings but
the bronze bearing catalog I have has none of that type of info at all.
    If you look at the tried and true methods of roller design, (look at the
old rolling machines that are still useful, not the one that wore out after
a measely 50 years or so) they all use bronze bushings, (or lead based
poured bushings) rather than bearings.

Thanks again,
Rick
BTW oilite is my first choice also.

----- Original Message ----- 
From: "Andy Vida" <[email protected]>
To: <[email protected]>
Sent: Tuesday, April 06, 2004 1:15 AM
Subject: Re: [TheForge] Bronze Bushings

> Rick at Rafter Lazy C wrote:
> >
> > Hello Guys and Gals -
> >
> > I am finding myself in a (not unfamiliar) quandry.  I am trying to
> > design something and am missing some very needed training.  Never
> > had any engineering training, but I need to size a bronze bushing
> > for a 2 1/4 dia. shaft.  Where on the web can I find info on how
> > large to bore the pocket for the bushing, and etc.?  Can someone
> > help me out here?
>
> Several questions.  First, it would be good to have more
> information on the precise configuration of the mechanism,
> what stresses (ballpark guesstimates) it must endure, and
> what is the shaft attached to?
>
> What do you mean by "pocket"?  Are you referring to the
> housing that holds it in place?  Is your question intended
> to divine what thickness the bushing ought to be?
>
> Rather than a bushing, could you use a self aligning pillow
> block?  They are a cast iron housing with usually two or four
> mounting holes.  The bearings can swivel in the housing so that
> any misalignment in the shaft is compensated for by the degree
> of freedom of motion the bearing has in the housing.  Does that
> make sense?  That way all you have to do is bore and tap the
> mounting holes.
>
> >  This shaft will only be turned by hand, so speed
> > of rotation is not an issue here.  If it were, would the requirements
> > change?
>
> Impossible to say for certain, but the higher the shaft speed,
> the more likely this would in face be the case.  If the shaft
> is slow turning and loaded in one direction only, you may be
> able to get away with sloppier tolerances.  But if the shaft
> will take radial loadings from widely differing directions,
> chances are you will want to bore the bearings to pretty tight
> tolerances... no more than a few thousandths.
>
> You will also want to cut oil grooves and bore a radial
> lubrication gallery in both the bushing and its housing
> to you can keep the bearing from running dry, which is
> the express method of achieving bearing death.
>
> Simpler solution is to make the bushing from oilite, a permanently
> self lubricating porous bronze material.  If you go that route,
> do NOT ream the bore to final dimension.  You must never ream
> oilite because the reamer closes and burnishes over the pores
> causing the bearing to lose all its wonderful self lubricating
> properties.  You must also never use heat to affect an
> interference fit of the bearing into its housing because it will
> degrade or even destroy the lubricant, which as far as I know
> cannot be replaced.
>
> >  Where can I get this kind of info when I need it?
>
> I would recommend Mark's Handbook For Mechanical Engineers.  I
> have my uncle Bengtsson's from 1958.  It's a great resource.
> Machinist's Handbook is another excellent source and in fact
> may be better for these sorts of questions.  There are definite
> guidelines for all these bearing issues and you're probably best
> advised to adhere to them.
>
> Best wishes.
>
> -Andy