[TheForge] Bronze Bushings

[Andy Vida]

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. 
	
	There's a sizable difference between rolling 1x4 and 2x2.  The
	bending moments, IRK, will not be the same.  It's been so long
	since I've done any sort of calculation such as this that I do
	not want to give any sizing recommendations.  But if you are not
	going to do the precise calculations of the forces, then you
	have my unequivocal recommendation to grossly over engineer this
	contraption.  Turning 2x2" HRS cold to a tight diameter (in this
	case I would define that as, say, 36") will require large
	bending forces and cranking that upper roll will take some work.

	At the shop in Mesa I did twists on 2" sq. cold using Mongo and
	that kept me uptight because of the high loadings.  Mongo was a
	15 hp custom built bender whose 1750 rpm motor was geared down to
	9 rpm.  It had tremendous torque multiplication, but I digress.
	Point was that moving that much steel cold requires serious force.

	2x2 roller...  I may be crazy... OK I am crazy, but I'd probably
	build using 6" diameter rolls with at least 4" journals.  This
	will not only be stronger, but will distribute the forces over
	a much larger area which translates into longevity for the machine.
	It also necessitates a far larger frame which gives an added
	margin against catastrophic failure.  If you're going to build a
	top drawer machine, then you may as well go all the way.  True,
	your material costs go up, but in the grand scheme of things it
	may not be that significant and if you really have a market for 
	this contraption and you produce a superlative machine, it is well
	worth the added expense to the buyer, most likely.  If you don't
	have a real market, I may suggest you reexamine the wisdom of
	the undertaking.  Again, on the safety issue, you HAVE to assume
	that your user is an inbred imbecile that will do the wrong
	things with the machine such as using stock larger than the
	max. rating and trying to turn a 12" diameter in one pass.  You
	should also develop a set of "safe" operating procedures, e.g.
	how far to deform a given size stock for a pass.  You have to
	exceed the elastic limit of the material, but you should not go
	past x% plastic deformation for a given size as you approach the
	machine's capacity limit.  One, it is a safety hazard and two,
	it wears the machine out.

	Another thing: if you are really going to build this to do 2x2
	your driver roll will almost certainly have to be knurled in
	order to gain purchase of the surface.  Every industrial strength
	ring roller I've ever seen, except for the old Champion tire
	rollers, have knurled drivers.


> 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 can tell you now that a 4x3.5" top roll is going to flex
	significantly turning 2x2.  I think you would need to produce
	two different rollers of varying capacities.  One hydraulic
	roller I knew of, down in Buckeye, could roll 4x1 material the
	hard way, cold, and in fact I watched it do so.  The journals on 
	those bearings were about 5" or 6", the rollers being about 10"
	diameter and about 3" wide and outboard of the bearings.  Very
	slow, but very, very strong.


>     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.)

	A good idea.  How will it deal with inconsistent material, though?
	If you get steel that is not quite perfect in diameter or HT, will
	that cause the assembly to deflect and steer the material into a
	spiral?  Just throwing out questions.

>     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.

	OK, question: will the frame be cast iron or fabbed?  I would
	recommend cast iron over fabrication.

	Another thing: what diameter capacity are you looking for?
	I ask because it effects how you decide to orient the
	rolls, i.e., vertical or horizontal.  You can turn a 30'
	diameter ring a whole lot easier with vertical rolls than
	with horizontal.  If anything goes wrong, a long arc of steel
	standing 15 feet high in the air presents another major safety
	hazard, whereas if the rolls are vertical and the work passing	
	through them horizontally, there is no opportunity for anything
	to fall on one's head and controlling the work is far easier.
	You could design the machine to be flippable 90* and give the
	best of both worlds.  Just a thought.  You can even design and
	market spot rolls that sit on the floor to provide a support
	surface for long material being rolled, thus preventing twisting
	in the rolls under large weight (imagine 2x2x 30'... heavy
	stuff and would definitely cause spiraling due to weight)

	Another way to keep things straight and narrow is the provide
	feed guides.  You really only need one that adjusts to the
	precise width of the stock and serves as an infeed/outfeed
	mechanism to keep the stock properly aligned as it passes through.
	It could be an optional item.

>
> 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 ...

	This can't be the case.  Try "bearing", "plain bearing", "journal
	bearing", "babbit bearing", "bronze bearing", "bronze bushing"...

	Best wishes for success in this.  I would be very interested in
	seeing how this machine shapes up.  Thanks for sharing.