[TheForge] Bronze Bushings
Ries Niemi
[email protected]
Wed Apr 7 00:12:00 2004
I will be interested to see how your roller turns out. From what I know
about rolls, you are talking impossibilities, but I am eager to be
proved wrong, as if you can really build a hand roll that will do what
you are talking about, a lot of people will want it.
A few points- to get a 3.5" roll to bend a 4" ID, you will need to run
the centerlines of the two bottom rolls up past the centerline of the
center roll. All commercial rolls I have seen that are capable of
rolling the kinds of stock you are talking about use a pair of larger
diameter outer rolls to keep the material from deforming. This, of
course, increases the minimum ID you can roll. For instance, if you
want a 4" ID on 2" material, you need a roll which has an outer
diameter of 8". This is usually done by adding up smaller diameter
spacer rolls, sandwiched between two larger diameter outer rolls. This
kind of a setup is absolutely essential to bend flat bar the hard way.
But it is also much better for keeping distortion in plain old round
and square bar to a minimum.
Of course, this means your rolls need to have a threaded end, be
machined to a precise OD, and have some kind of keyway on them to keep
the donut shaped spacers and outer rolls from turning. More money,
more complexity.
And if you want your rolls to be able to bend square tube, or pipe, you
need some kind of removable rolls that are sized to each size of pipe
or tube.
In terms of capacity- are you talking hot, or cold?
Because the biggest hand rolled machine I have ever seen tops out at
about 1/4" thick by 2" wide flat bar, the easy way, cold. There are a
couple of reasons for this- first, to get a big piece like say 1"
square solid HR to bend, you need to push the center roll down pretty
hard- most small hand rolls use a hydraulic jack for this. But of
course, jacking it between those 3 rolls with 10 tons or so of force
increases the friction between the stock and the rolls, making it a lot
harder to crank. Motorised commercial machines use lots of horsepower
to overcome this friction. My guess would be your 1" by 4" HR, the easy
way, would take about 10hp, geared down to say 15RPM or so. I dont know
about you, but my arms aint that strong. It would take a pretty decent
set of gears to gear that load down enough so you could turn it
manually. And that would mean an awful lot of turns of the crank to
crank a very big piece thru.
And even if you did have the strength to turn the crank, the metal
wants to just slide in there. So commercial machines use knurled rolls,
to get a grip on the stock. And they usually will use a sprocket and
chain system to link the two bottom rolls together, and drive them-
twice the turning power, because you have twice the driven surface area
to overcome friction.
To bend big stock without knurls, which of course leave knurl marks on
your steel, they use all three rolls driven. And lots of HP.
This is why machines that can really bend 1" x 4" HR cold cost about
10grand, and need 40 amps of 3phase power. 2" square- I am thinking
more like 15hp. And the machine would have to be awful darn sturdy- I
have a piece of 2" square on my rack right now- 20 feet long. And it
takes a forklift to move it. The weight of the steel alone would bend
any hand machine I have ever seen.
I bend a lot of stuff on my power rolls, but for smaller jobs, I use a
hossfeld- securely bolted to the floor, with fixed radius dies, I can
pull circles in any material from 1/8" round up to 2" pipe. I did bend
some 1" x 4" flat bar a while ago, for a driveline loop for my
minitractor. I did it hot on the hossfeld, and got a quite decent 4" ID
bend. And my hossfeld only cost me $775 used.
But hey- if you really can build a roll that will do even a quarter of
what you say, you will be able to sell a bunch of them. People are
always looking for rolls like that, here, on keenjunk, and on
anvilfire. There is definitely a market, so good luck!
ries
On Tuesday, April 6, 2004, at 05:43 PM, Rick at Rafter Lazy C wrote:
> 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. :)
>
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