[TheForge] Bronze Bushings
David E. Smucker
[email protected]
Tue Apr 6 23:10:02 2004
Rick, I think you have gotten good information from Andy but one thing you
might want to do is a google search under "journal bearings" and "oil film
bearings". This may turn up things that are too technical for what you are
looking for but a place to try. Journal bearing today are used "mostly" for
high load applications, large sizes such as very large motors, cheap motors
and special very high speed applications. Over half of the bearins used in
high load applications such as rolling mills are journal bearings -- some
running a surface speeds over 5000 feet per minute.
In you case you want a journal bearing because you want to get as much load
capacity in the limited space you have. You space is limited because you
bearing OD can't be bigger (or at least not much bigger that) diameter of
the rolls you will be using. (assuming you want to be able to roll quite
thin material as well has heavy stock.) You want the ID to also be as
large as possible so that you have a large roll neck. This is the same
problem faced in design of a rolling mill for the rolling of strip. I know
you already know this -- but it is what make the Journal bearing very good
for this type of application. Roller bearings are also used in mill
design -- ball bearings are not at all effective because you can't get the
necessary load capacity. Still even Roller bearings have limitations and as
you noted they are often short lived be cause the bending of the rolls under
load cause very high local loading resulting in roller failure.
Now you also will have a very low speed operation so I would assume that you
could use grease lubrication rather than oil. So where do you look for more
detail information.
Have you looked at the section in Machinery's Handbook on "Plain Bearings"
or "Journal Bearing" -- about 25 pages worth? You should be able to find
information here on the fit between the roll neck and the ID of the bushing
itself. As to the fit of the bushing in the housing I would think you are
looking at a light press fit of a class FN 1 or FN2 which will be in the
range of about 0.003 inch interference. You may want it a little less if
the bushing is quite long.
For this kind of thing besides Machinery Handbook I pull out my very old
machine design text called "Design of Machine Elements" by Virgil Moring
Faires (only a mechanical engineer would have a name like that.) My copy
is the 4th edition that dates from 1965 but the early editions go all of the
way back to 1934. I don't know if it is still in print in any form but it
is a great book and I still use it. I just checked -- Amazon still lists
used copies for sale -- but no later edition than the 4th. It was our
machine design Bible back in the 60's in engineering school.
Hope this helps a little
Dave Smucker
----- Original Message -----
From: "Rick at Rafter Lazy C" <[email protected]>
To: <[email protected]>
Sent: Tuesday, April 06, 2004 8:43 PM
Subject: Re: [TheForge] Bronze Bushings
> Andy -
>
> Intended capacities? Good question. The rolls will be 4in wide if
they
> don't undergo any revisions, but I am still designing and have not done
any
> testing as of yet. Would like to be able to do 1x4 HRFB or maybe even 2x2
> HR bar. Small material should be able to get to a 4 inch ID (3.5 in OD
top
> roll). Will keep you informed as the fab and testing phases come up if
you
> wish.
> I went looking for a roller and what I found on the market wasn't up
to
> my idea of what a dollar is worth. As far as the shafts being perfectly
in
> line with each other, I am letting the bottom roll ASSEMBLY find it's own
> center and thereby align itself. (as long as I get both sides of IT
> straight.)
> This roller should be available to the public within a few months if
all
> goes well. I want to be able to sell it for under a thousand dollars.
This
> should be a serious roller for a small shop. No motor involved, this is
> simply leverage applied in the right places to make the work easier. I
have
> been in metal fabricating for over 30 years and have run rollers of all
> sizes. This should be a good one for the size of it.
>
> Rick
>
> PS - I looked all through the Machinery's handbook and couldn't find
> anything specifying what type of fit should be used for a bronze bearing
of
> any size. I have the 20'th edition here and the 25'th at work, and no
luck
> either place. Went in early today and dug out my boss'es Marks handbook
(25
> years or so old) and couldn't find anything in it either. Just because I
> can't find it doesn't mean it isn't there, but ...
>
>
> ----- Original Message -----
> From: "Andy Vida" <[email protected]>
> To: <[email protected]>
> Sent: Tuesday, April 06, 2004 12:43 PM
> Subject: Re: [TheForge] Bronze Bushings
>
>
> >
> >
> > Rick at Rafter Lazy C wrote:
> > >
> > > OK Andy - Here we go =>
> > > I am designing a Ring Roller.
> >
> > Muy cool.
> >
> > > It will be able to roll much more than the nearest competition,
> > > and wider as well.
> >
> > What are the intended capacities? How large by how large,
> > according to material? You cannot just say 1" x 6", for
> > example. You may do that in mild in the annealed state,
> > but a 1/2 hard stainless steel may not only damage the roller,
> > it may pose a safety hazard. Bending metal like that creates
> > a spring. The larger the spring, the greater the stored
> > energy. The greater the stored energy, the more dangerous
> > a failure becomes. So you need to know about the materials
> > that you intend on designing to. If mild is all you want to
> > account for, then by all menas do so, but if this is a
> > commercial product, you'd better plaster it with stern yellow
> > and red warnings all over the place that mild steel in the
> > annealed state is the ONLY material that is safe to use in this
> > machine. Otherwise you need to calculate worst case for
> > some high alloy steel, for example. All you should need is the
> > worst case, as far as I can see, btu I would consult an industrial
> > engineer on this because you don't want to face the liabilities
> > that go with some dink putting an eye out because be tried to
> > roll the wrong material and the machine disintegrated in his face.
> >
> > Mi capisce?
> >
> > > 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.
> >
> > Why are the other shafts not bushed? They will be under equal
> > stresses, so you will probably want equal load bearing capacity
> > and a good bearing makes for long machine life. Cast iron against
> > steel is, in fact, a rather good bearing material (graphite is a
> > good lube) but the surface is not readily replaced. Think of
> > long term machine maintainability. That is the consideration that
> > the designers of yore made and those of today generally do not.
> > I doubt there is a CNC machine out there today that will be in
> > any decent operating condition in 100 years. A will further bet
> > that at that time there will still be South Bend machines and their
> > ilk that will in fact stilll be up and running as the day they
> > came off the assembly line.
> >
> > Anything worth doing is worth doing right. Just my worthless
> > plugged kopek's worth.
> >
> > > 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.
> >
> > Machinery's Handbook doesn't have this? Are you certain? That
> > seems very strange to me.
> >
> > Well, given what I've seen on machinery, I would think that a
> > light interference fit would be OK, but I'm not sure about this.
> > You don't want the bushing slapping around in it's mounting, but
> > OTOH, the bearing will be loaded in one direction at a time with
> > only slight variations as the radius is progressively tightened,
> > so I would imagine that a super tight fit is not necessary. But
> > you don't want to give the machine much opportunity for
> > misalignment of the shafts. I don't know how far they can be
> > out of line before the rolls start tracking in a spiral, but
> > I'm sure it isn't very much. 0.003" is probably OK as long as
> > the shafts are all perfectly parallel. What would concern me
> > more is the bedding in which the bearing rides. It should be
> > a precise hole such that the bearing doesn't ride on any high
> > spot and rock, which would be disastrous for the longevity and
> > precision of the machine and may again pose a potential safety
> > hazard should it give rise to a structural failure. The best
> > way to minimize this is to use a very beefy bushing and to
> > anchor it solidly against the shoulder with screws and a flange
> > as so in not quite so properly rendered cross section:
> >
> >
> > ______________ ______________
> > Flange -->___|______________|_ _|______________|___
> > | | | | | |
> > | | | | | |
> > Frame -> | | | | | |
> > | | Bearing | | Bearing | |
> > | | | | | |
> > | | | | | |
> > | | | | | |
> > | |____________| |____________| |
> > | | | ^ |
> > | | | | Shoulder |
> > | | | |
> > | | | |
> > |___________________| |__________________|
> >
> >
> > The larger the bushing OD, within limits, the less the effect
> > of slight rocking will have, but my recommendation is to have
> > none. Holding a 0.001" tolerance on the bore should be child's
> > play if you have decent machinery. That should be plenty good
> > enough to provide the necessary stability. What I might do is
> > go to your local automotive machine shop and see if they can
> > bore the holes on a Sunnen align boring machine (bores the
> > main bearing seats on engine blocks. Probably not a viable
> > idea... just tossing it out to you. But I would see that the
> > the shafts were not out more than 0.001" in parallelism over
> > their lengths. It doesn't take a lot to cause spiraling, and
> > therefore you'r rolls should be ground true as well.
> >
> > > I don't have a Mark's, though I
> > > have seen the need for one for several years.
> >
> > Get one. I got mine for free when uncle Bengtsson died. He
> > was this big tall Swedish d00d that wore a monocle... a real
> > Victorian era person. He was so cool... and an ME to boot. :)
> >
> > I think they run about $150 new. If you're going to use it,
> > then they are worth every penny, but do a search at alibris.com
> > or similar and I'm sure you can find one less costly than that.
> > An older one might be your bet. Same for Machinery's Handbook.
> > Mine is from 1935 and the wealth of information there is
> > impressive.
> >
> > > 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.
> >
> > I agree. One way is to look at a well designed and built
> > machine that is close to your capacity requriements and
> > double everything. Overkill in such machinery is almost
> > never a bad thing. Will the frame be cast or fabbed?
> > >
> > > Thanks again,
> > > Rick
> > > BTW oilite is my first choice also.
> >
> > If you're going to use very beefy bearings, you may want to
> > use a regular bronze only because oilite isn't cheap and I
> > am not certain what sizes it is available in. A regular
> > bronze bushing with grooves, galleries, and oil cups works
> > really well and I'm so very partial to the aesthetic of
> > glass oilers. :)
>
> _______________________________________________
> http://mailman.qth.net/mailman/listinfo/theforge
> theforge mail list group photo site is
> http://www.photoaccess.com
> Login: [email protected]
> password: anvil
> ___________
>
>
>