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Care of a Rolling Mill


#1

Hi, a question about the care of a rolling mill: is it possible
to put too much pressure on the rollers when rolling something
tightly through the mill? I’m fairly small and don’t weigh a lot
(and don’t lift weights!), but when I put most of my weight or
strength behind the crank, I worry about damaging the mill. Is
this possible? If so, how much force is too much? Thanks -

Rene
Calif No coast


#2

I am confused… By too much force, do you mean by overtighening
the pressure of the top screw? If so, then remember that you
should be able to pass the work at hand through the mill with
some but not excessive resistance. If the rollers are too tight,
you have to exert lots of force. This could hurt the gears. Rob


#3

Just remembered another dumb thing NOT to do with your mill.
After pickling your metal when you anneal between rolls MAKE SURE
YOU DUNK IT IN BAKING SODA AND WATER. I got some nasty acid
stains on my new rollers when I first got it from not doing
that…Dave

Kickass Websites for the Corporate World http://www.kickassdesign.com
Crystalguy Jewelry http://www.opendoor.com/stephensdesign/crystalguy.html
Recumbent Cyclist’s Advocacy Group
http://www.opendoor.com/stephensdesign/bent/rcag.html


#4

Rene: it sounds like you may be taking too big a “bite” in
rolling your metal. If you have to thrash around and jump on the
handle thats what you’re doing. And yes you can damage a mill, a
friend of mine cranked down too far on the rollers and using
brute strength cracked the frame that holds the rollers. This
seems to be a common mistake for first time users. Dave

Kickass Websites for the Corporate World http://www.kickassdesign.com
Crystalguy Jewelry http://www.opendoor.com/stephensdesign/crystalguy.html
Recumbent Cyclist’s Advocacy Group
http://www.opendoor.com/stephensdesign/bent/rcag.html


#5

Rene, I don’t know personally whether or not it is actually
possible to damage the mill. The advice I would give you would be
to take smaller steps in rolling, By this I mean don’t try to
roll the piece to the desired thickness on the first roll. And
are you annealing the piece before you are rolling it?? this may
help. … So basically, anneal the piece, roll thru 3 or 4 times
turing the roller down just slightly each time, then anneal
again, and repeat… Eventually if you don’t anneal the piece you
may experience cracking from the outer edges of the metal in
towards the center… I hope this helped… Marc Williams


#6

Hi Rene,

Assuming the mill is a good quality mill with well made side
frames, good bearings & heavy shaft for the rolls you probably
won’t put enough strain on these pieces to cause a problem. Just
don’t close the rolls with more than hand pressure & don’t take a
big bite at each pass through the mill. If the metal is annealed
& you can turn the crank you’re O.K.

The biggest source of damage to mills comes from letting the
rolls get rusted/corroded because they were not protected with a
light coat of oil when not used for some time (days/weeks). One
other source of roll damage comes from not cleaning the rolls or
metal before use. If there are any stray dirt particles on the
rolls or metal as it passes through the rolls, it can damage the
rolls or metal. Just be sure to clean the rolls & metal of any
contamination before rolling.

HTH

Dave


#7

Dear Rene, your query reminded me of the time I busted what I
had thought was a good set of rolling mills. I’d bought them
brand-new too and only had them six months.

They were a nice looking Italian product which were geared
down/up (?) - anyway, one wheel and its teeth were much bigger
than the other. They were a big change to my original old rollers
which had equal toothed cogs with big thick ugly teeth. The
Italian Job had really neat little teeth and plenty of 'em. The
only problem was that the gears were made out of cast iron and
one day the big wheel cracked, literally falling off in two
pieces.

I still use my old 100 year-old rollers with their big ugly
strong teeth and their primitive separate winders for draught
adjustment, while the neat little Italian Job sits in the corner
reproachfully waiting for me to visit the engineering shop and
get new gears made out of proper steel.

If it’s possible, check out what the gears are made of, and
avoid neat, pretty, little chrome-plated teeth on the gear train.
I guess that some modern rollers might have case-hardened rollers
in them too, which might present problems at a later date.

Lots of luck in your search. You might do a lot worse than find
an old pair of rollers that might only need a little restoration
to bring them back to another hundred years of faithful duty.

Kind regards, Rex from Oz.


#8

Tight rollers can make the edges of your metal crack open… then
you have a another mess…If you roll fraction by fraction you go
faster and safer then using brute strenght But everyone always
seem to think that brute strength is the only way to go… Not
so…Also annealing more often keeps the metal pliable…
think of it like when one rolls out dough… The gently touch
does it all faster and better …no cracked edges or thin edges
etc… calgang


#9

Hi all, thanks for your comments so far. Let me clarify a couple
of things. I have a Durston 120mm flat mill with a reduction gear
(got it from Rio a few years ago). As far as I can tell, the
rollers are in alignment. I use the mill largely to do
roll-printing. You get one crack at this; if it doesn’t make a
decent impression on the first roll, you can’t go back and try it
again. Of course, I always start with thoroughly annealed metal.
I’m using deep-etched 17ga nickel silver for my pattern plates,
and I’m cushioning the back of the sheet I’m printing with paper
towels or a heavy stiff fabric like denim. (This is necessary to
counter the effect of the steel roller flattening the metal out
from the backside, as I’m trying to print it on the front.) I’m
not rolling very large pieces, 2" wide max. The resistance I’ve
been looking for is “stiff and a little difficult, but do-able
with two hands” (remember, I’m small and don’t have a lot of arm
strength). I’ve usually printed on 24 guage metal. Recently I’ve
needed 20 guage, and it has been very difficult to get a good
impression unless I really bear on the handle. So far I’ve only
done 20 ga copper, but I need to do some sterling too, and this
is going to be much stiffer, prompting my question here before I
try it.

Dave, you said <don’t close the rolls with more than hand
pressure>. I’m not sure I know what you mean. When I roll the
sandwich, I first put it in the mill and tighten the rollers down
to see where it comes up on the dial. Then I take the metal out
and tighten the rollers another few numbers past that; otherwise
it wouldn’t print at all. There has to be quite a bit of
resistance. Could you explain your comment a little more?

I appreciate all of your advice.

Rene


#10

Hi Dave,

Excellent advice on Rolling Mill care. I would add also that
the #1 reason we get mills in for repair at Gesswein is because
the maximum sheet tolerance of the mill was not observed. For
example, if the mill specifies a 3mm sheet tolerance and you
routinely try to roll 4mm sheet, sooner or later, the gear teeth
will break.

Elaine Corwin
GESSWEIN CO INC USA


#11

Rex, I use one of those 100+ year old rollers, and will never
get tired of it. I can remove the handle (approx. 10lbs!) and
place it on either side of the mill, making the handle above or
below the rollers. Mine is a square wire roller, and I wish my
father had purchased the flat one that was available, when he got
this one about 30 years ago. Curtis


#12
      is it possible to put too much pressure on the rollers
when rolling 

Hi Rene, We had, many years ago at school, some copy of Cavalin
rolling mills. A student put so much pressure on it that the
bottom steel roller split in two parts. There was surely a
weakness in this steel part but it can happen with any parts of a
cheap rolling mill like any other tools. Anyhow you never need to
put so much pressure on a rolling mill. A good rolling mill
should last a lifelong if it is use and well-kept correctly.

Vincent Guy Audette
in Quebec city


#13

I have a Cavallin combination rolling mill. I bought it new
about … hmmm … twenty? years ago. Back then I weighed 130
lbs. I started jumping on the thing to get metal to pass thru
when I got it. Where I trained, I was never told not to jump on
the mill. Never broke one either. Today, I weigh a little closer
to 180. I still ocasionally jump on it. I’ve gotten pickle pickle
and a wide assortment of dirt on the rollers as well. I still
serves me well. I expect that someone will be using this thing a
hundred years from now. My only regret as to the abuse that I
have given this thing is the time I rolled a small piece of
spring steel. That wasn’t too bad, but a larger piece of steel
might have called for a new mill.

By subscribing to this list, I’ve learned of others that have
broken their mills. I guess that you’ve gotta do what you’ve just
gotta do.

That;'s my story and I’m sticking to it.


#14

Rene, I’ve only recently aquired a rolling mill, so my
experience is very limited. However, I did have a need recently
to rollerprint onto 20ga. sterling from an etching. So, I used
the old Native American trick of annealing the metal dead-soft
when you don’t have a kiln, and it worked beautifully.

Use a self-pickling or Pripp’s flux to prevent firescale and
bring your silver up to heat. Instead of plunging it into a water
bath, lay it in a plaster bed and cover it over on all sides. The
plaster bed can be made with plaster-of-Paris or casting
investment which is too old to use for casting. After the metal
is covered on all sides with the plaster powder, allow it to cool
to room temperature without hastening the cooling. Remove the
metal and scrub off the flux. Polish if you need a mirror surface
for rollerprinting.

What happens in this process, from my understanding, is that you
allow more cooling time, so molecules have more time to align
themselves loosely. If the metal needs to be even softer, you can
do this process several times, each time getting the metal a
little softer. This method also works well for repousse’ work.

K.P. in Wyoming


#15
Tight rollers can make the edges of your metal crack open..
then you have a another mess..If you roll fraction by fraction
you go faster and safer then using brute strenght But everyone
always seem to think that brute strength is the only way to
go... Not so.....Also annealing more often keeps the metal
pliable... think of it like when one rolls out dough... The
gently touch does it all faster and better ...no cracked edges 
or thin edges etc. 

I’ll second the need to anneal and that several passes through
the mill are a bit gentler than one brute force one. But it
should also be pointed out that too frequent annealing isn’t good
either. When you roll the metal, especially with smaller step
downs in size, you get more deformation of the metal at the
surface than you get at the center of the sheet. You want to
roll far enough between annealings so that the crystal
deformation of the metal has extended all the way through, and
stresses at the surface have equalized with those at the center.
That way you’ll get a tighter, smaller, and more uniform crystal
structure after annealing, and resulting better sheet metal.
One easy way to tell this point is to watch the wavey deformation
that often forms. As you initially roll the metal, it often
curls or waves a bit. As you continue to roll, it will tend to
then straighten out again. Sometimes you’ll go from a flat ingot
to a peice that is porpoising up and down like a windy day on
the lake, only to have it then straighten out again as you
continue to roll. That point where it is reversing the tendancy
to curl or wave is where the stresses are equalizing out again in
the sheet, and you should then anneal when it seems to have
pretty much equalized out as much as it is going to. The degree
of reduction this will occur at depends on the metal. With white
golds, especially the harder 18K alloys, this may be as little as
a 30 or 40 percent reduction (which will be the sheet being a bit
less than twice as long as when you started). With sterling
silver or yellow golds, it may be as much as a 90 percent
reduction. You should watch the edges of the sheet as you roll.
They will, as you roll, initially form a pebbled texture which
flattens as you roll, showing you the flattening crystal
structure. When the sharp edges start to look a bit raggad, just
suggesting that in a moment they will start to form micro cracks,
stop rolling, no matter what else you are seeing in the sheet’s
behavior. Practice will show you how to judge this, as will
intentionally rolling a bit of the metal too far, to demonstrate
what that edge looks like before it fails. With high karat
yellow golds or platinum, you can sorta ignore those rules. The
stuff is so malleable you can almost take a rough ingot and roll
to a foil without failure. The metal will still be better if
you anneal once or twice along the way, but it’s pretty much your
choice as to when to do so. When you find you’re having to work
harder than you like to move the metal through the rolls,
perhaps, or if it is distorting more than you want…

With white golds, which can be especially tricky, sometimes, it
may help to also, after you’re initial few passes through the
mill to even out the ingot, take a file and knock off the sharp
side edges and any rough spots. These concentrate stresses, and
keeping them smoothed will help to prevent failure of the sheet.
Once it’s been evened out in thinckness, reduced a bit, and
annealed, it becomes more forgiving (due to the smaller crystal
size produced by rolling and annealing) and will need less
coddling along. One other thing to watch out for, especially
with white golds, is a marking along the edge as you roll
consisting of lots of diagonal, almost triangular lines forming,
which will quickly crack if you roll even a trace beyond their
initial formation. Alloys which are doing this when you try to
roll are often contaminated with something, such as bits of
solder in the melt. Metal which is doing this may prove almost
impossible to successfully roll all the way down, and will be
cracky and stiff to work even if you do succeed. You can
sometimes still use it, but in other cases it may be better to
simply refine the stuff and be more careful next time of what you
include in the melt to produce your ingot.

Hope this helps.

Peter Rowe


#16

Hi Rene,

The way you’re closing the rolls is a very good way to adjust
the pressure. I once saw a guy place his package (metal, pattern,
backing plate) into an open mill, then close the rolls as far as
he could by hand. He then added a bar to the wheel to give him
extra leverage & tightened the rolls about another 1/4 turn. He
was a big gorilla sort of a guy & even he had trouble turning the
mill. I was waiting to hear one of the side frames or the crank
break.

That’s 1st & only time I’ve ever seen a mill used as a press.

Dave


#17
   My only regret as to the abuse that I have given this thing
is the time I rolled a small piece of spring steel. That wasn't
too bad, but a larger piece of steel might have called for a
new mill. 

The place I worked for in Detroit, before moving to Seattle a
year and a half ago, was a small business with just me and the
owner, most of the time. Her mill was a nice cavalin mill that
she’d scraped and scrimped for when she was just starting out.
The building the business was in is one of those offices where
most of the business are small jewelers, and in this case, many
of them were middle eastern origin. Nice folks, some of them
great jewelers. but also in the habit of bringing their kids to
work. Sometimes quite young. My boss, being a friendly lady who
enjoyed the kids, often let them sit in her back room with her to
watch her work, and sometimes fool around a little at a bench.
She showed one young fellow how to roll pennies down in the mill,
and he was hooked. Next time he came in, he tried several other
items. She got distracted with a phone call, and didn’t notice
that in his curiosity he’d graduated to a few other things.
Seems he was a bit dissapointed with the results, and asked her
why these things didn’t turn into neat stretched out fun shapes.
She says she had to seriously restrain herself from ripping his
head off when she realized what he’d done to her pristine new
flat rollers, which to this day, have an area where your sheet
metal comes out with this clear raised image of a #12 scalpel
blade and a couple oddly jagged raised lines created by a couple
2/0 saw blades…

Peter Rowe


#18
   ...allow it to cool to room temperature without hastening
the cooling. ... 
   What happens in this process, from my understanding, is
that you allow more cooling time, so molecules have more time
to align themselves loosely. If the metal needs to be even
softer, you can do this process several times, each time
getting the metal a little softer. This method also works well
for repousse' work. 

Um. Not quite. this is true for steels, which harden due to a
phase shift on heating that you “trap” with quick cooling. but
with silver, something else occurs. Copper is not completely
soluable in silver, especially at room temp. When you heat to
annealing temps, the copper goes completely into solution. The
annealing temperature cause distored crystals from cold working,
or other stresses, to be relived. Distorted crystals actually
reform into more but smaller crystals. This smaller, more even
crystal structure is not only softer, but better working from a
strength standpoint as well. If you prolong heating to much, or
heat too hot, the recrystalization proceeds to actual crystal
growth, with the new crystals growing together again to form
fewer and larger crystals. The metal will still be soft, but not
as strong. And, if you cool it too slowly, or hold it at an
elevated temp below the annealing temperature, then the copper
which dissolved uniformly in the silver when you annealed it can
differentiate into two distinct compositions: Pure silver
crystals, and crystals which are the eutectic composition of 28.1
percent copper. With extended somewhat eleveated temperatures,
Some of the copper will come out of this solution with the
silver, forming seperate copper crystals at the boundaries
between silver crystals. These differentiations cause a
considerable INCREASE in hardness. The phenomenon is called age
hardening, or precipitation hardening. You can take annealed
sterling silver and more than double the hardness with this heat
treating, to about a “half hard” state. All without any working
of the metal.

When you anneal sterling silver, you want to bring it to a
sufficient temperature to effect the recrystalization that gives
that uniform dense small crystal size, and then you want to
quench cool it quickly enough so the copper does not have a
chance to differentiate. This will give you maximum softness, as
well as the best working metal.

In normal shop practice, we anneal sterling silver by torch
heating just till we see some “glow”, and then waiting just till
the glow is gone, and quenching in water. For maximum softness,
use a kiln set at 1375-1400 F (745-760C). Hold at that temp for
15 minutes, and then quench in cold water. (allow to air cool
in cool air till the bright glow is almost gone, to avoid
cracking the metal) This results in a hardness of about 56
(vickers). cold worked, such as rolling to a 60 percent
reduction, will produce a hardness of 140-180 V. If you take
the annealed metal, and hold it at a temp of 600 F (316 C), and
holding it there from 30-50 minutes, then allowing it to air cool
(no quench), you’ll raise the hardness back up to about 110-120V,
the same as about a 50 percent reduction in the mill, (half hard,
which is defined as reducing the thickness by two B&S guages).

Hope this helps.

Peter Rowe


#19
I'll second the need to anneal and that several passes through
the mill are a bit gentler than one brute force one.  But it
should also be pointed out that too frequent annealing isn't good
either.

Thanks, Peter, for elucidating. I always say the success of
annealing depends on the righ degree of 3 things; heat, time, and
degree of work-hardening. Now I’ll be able to quote your words!

Brian
B r i a n =A0 A d a m R u t h B a i r d J e w e l l e r y
http://www.adam.co.nz ph/fx +64 9 817 6816 NEW ZEALAND


#20

OK, so now I need to clean the rolls on my mill. They are
slightly damaged and I want to repolish them. I’m thinking that
I could sand them with a fine grit (600 or 1000) paper by just
turning the rolls against a stationary object that I faced with
the sand paper. Then put some gold bob or tripoli on rag and do
somew more turning and polishing to take out the scratches from
the sand paper.

Does this sound like a good idea?

thanks

Virginia Lyons
Metalsmith