Back to Ganoksin | FAQ | Contact

Rolling mill hints


#1

I have a rolling mill which is rubbish. It’s a cheap one, don’t even
know the brand and it warps anything I pass through it, despite
calibrating the rollers all the time. So I’d like to think about
stretching to a nice one. Durston.

No, I will not use it all the time but there is a lot I’d like to be
able to pass through it.

Any hints?


#2
it warps anything I pass through it, despite calibrating the
rollers all the time. 

There are two (or more) flavors of the way metal warps in a rolling
mill. If the rolls are not flat, usually where the center of one or
both rolls is worn, so the centerline of the metal isn’t rolled as
thin as closer to the edges, then you’re right. It’s messed up, or at
least, could benefit from having the rolls trued by a machine shop.
Or save that mill for roll printing. Metal put through that sort of
mill will warp in multiple directions as the edges get stretched
more than the middle. can almost look like frilled edges.

However, another type of warping happens with even good mills. There
are often slight differences in an ingot from one spot to another,
plus, while rolling, the surfaces tend to stretch more than the
interior of the ingot, at least initially until it’s been rolled down
far enough for internal stresses to equalize. Before that happens,
the metal will often leave the mill curved in the same directions the
rolls curve, or may wave up and down. The key here is that side to
side the metal remains at least mostly flat and unform. The waves are
in one plane only.

if you keep rolling that thinner, eventually internal stress evens
out and the sheet will again become mostly flat. Prior to that, you
can anneal and flatten with a mallet. This type of warping/curving is
related mostly to uneven ingots, or to very slight but normal
variances in roll parallelism, as well as being more pronounced with
smaller diameter rolls. Buying a better rolling mill will help all
this, but will not eliminate all of the wavyness. If you expect to
take annealed sheet or an ingot and roll it down and have it come out
of the mill dead flat, just like it went in, every time, you’re going
to be very disappointed.

Mills that come close to that are going to be more in the range of
industrial sized rolling mills, with much larger diameter rolls than
seen on jewelers mills.


#3

Your really can’t go wrong on a Durston mill. They are a real
pleasure to work with.

My favorite mill is Durston 130mm Combination Rolling Mill. It is
wide enough to do sheet and roller imprinting and it can also create
square, half round, rectangle and triangle wire.

I can even make my own bezel wire from my scrap. I recycle all my
scrap so it saves me a ton of money.

Hope this helps.
Phillip Scott
Graduate Gemologist
Technical Support Specialist
Rio Grande, A Berkshire Hathaway Company
1.800.545.6566


#4

Thanks Peter for this sound advice! I will give my mill another go.
however the warped also refers to the fact that everything I pass
through the mill comes out looking like a metal banana! The bumps I
can deal with but the curved is a different story as then I have to
spend time hammering it back into a relatively straight shape before
I can do anything with my new piece of sheet.

Silly question perhaps, but where would I go to have the rollers
trued?

Emma Tallack


#5

Rolling mill hints

All Peter’s points are spot-on. There are two more I would like to
add:

  1. Metal down the centerline of the strip you are rolling can be
    reduced in thickness by squeezing forward, where it exits the pinch
    area of the rolls.

At that point it can now spread sideways.

Until it exits the pinch area, it is constrained by its neighboring
metal against sideways spread, so it can only spread at exit. But
metal on the left and right edges of the strip you are rolling has no
outboard neighboring metal to stop it spreading sideways WITHIN the
pinch area. For that reason, the unconstrained edges can go forward
AND sideways while being pinched. This effect means that un-annealed
strip will behave very differently AT THE EDGES, compared to annealed
strip. ALL strip will be unpredictable at the edges and the
unpredictability reduces as you get closer to the centerline.

  1. There will be spring-back on thickness, too, and that will be
    different depending on the elastic modulus of the metal, on its
    location across the strip width, on its rolling history and on its
    degree of annealing (freedom from prior stresses).

So you can get rolled results that are all over the shop, even with
an excellent mill. Look to generous roll diameter, adequate annealing
between passes, repeatable rolling velocity, carefully recorded
stages of reduction and complete absence of lubrication on the roll
surfaces. It actually helps to have a roll surface finish whose very
fine “grain” is parallel to the path of the strip - NOT a perfect
mirror finish. Why? To minimize the “escape” of metal at the extreme
edges.

Mark Bingham
Relativity PL


#6
Your really can't go wrong on a Durston mill. They are a real
pleasure to work with. 

That’s the one I have on my Rio wishlist :-))

Emma Tallack


#7
Your really can't go wrong on a Durston mill. They are a real
pleasure to work with. 

I have a Durston 130mm combo mill with the half round extension
rollers and love it.

I do have to say, my previous mill was a 40 year old Italian
Cavallin combo mill and I was somewhat disappointed with the Durston
at first - I expected more of it from all the hype I’d read. I did
not have the reduction gears on the Cavallin and I didn’t find the
reduction gears that much more helpful. As the gears and the width
of the rollers were the main reason for the upgrade it was
disappointing in that regard. When I made the decision to upgrade I
thought I’d be able to purchase patterned rollers to use in it. I
near choked on my coffee when I found out each roller was $800!
Scrap that idea! Cheaper to get one of the

One of the issues with the Durston that upset me was I read here
after someone posted photo’s here of badly marked rollers that one
shouldn’t roll wire through on the flat section of the mill or it
would leave marks because the rollers are not solid all the way
through, they have an outer casing over a somewhat softer core. I
had rolled many a heavy wire through the flat part of my Cavallin
with nary a hint of trouble. None the less, the Durston is a lovely
machine and will last many years with proper care.

Aurora


#8
Thanks Peter for this sound advice! I will give my mill another
go. 
however the warped also refers to the fact that everything I pass
through the mill comes out looking like a metal banana! The bumps
I can deal with but the curved is a different story as then I have
to spend time hammering it back into a relatively straight shape
before I can do anything with my new piece of sheet. 

If the banana curving is in the vertical plane, then it’s just flat
sheet that’s been bent. Easily straightened. That, you’ll get with
almost any mill, with smaller diameter rolls doing it more. If the
curve is side to side, then your rolls are not adjusted paralell.
This is the adjustment often talked about, to get the rolls paralell,
so it doesn’t roll thinner on one side from the other.

The catch to this is that the parallel rolls needs to refer to how
the rolls are working when actually rolling the metal, under
pressure. Not how they meet each other when at rest. The reason is
that the bearings are what need to be adjusted right, not the visual
impression of the rolls, which may not be pressed tight into their
bearings when not in use. So you make the adjustments to the rolls
based on what they do to the metal. If the metal bends to the right,
you tighten the screw on the right to thin the metal slightly more on
that side. If the metal bends to the left, same thing, tighten the
screw on the left. Each adjustment should be only one gear tooth at a
time (you can’t get it adjusted more precisely that that, so there
may be limits on what you can do. Finer than that might be possible
with thin shims, but that’s harder to do or describe.

Also, note that to a certain degree, this side to side bending may
vary with the hardness/annealed state of the metal and the thickness.
Thinner generally will bend more, so that’s what you based the
adjustments on.


#9

Hi Emma,

To restore rolling mill rollers, you will need a machine shop which
does precision grinding on centers. Not all machine shops do this.
You need to tell them that you want the rollers trued to 0.001" and
that they must match in diameter when finished. So they’ll need to
take down the smallest roller, or the one with the most faults
first, and then match the dimension of that with the second one. but
they will know this, no need to tell them. Getting both rollers the
same diameter eliminates one cause of bowing.

The rollers are case hardened and should have a layer of about
thirty or so thousandths of an inch of hardening. The shop should
only be removing a few thousandths of an inch, so unless the rollers
are very pitted or have been resurfaced numerous times, they should
still be hard after the work. If you cut through the casehardening,
the rollers would have to be rehardened, but I’ve never heard of
that happening.

I think last time I asked a shop about this, truing a pair of
rollers was about $100, but it might be more, depending on your
geographical area and the particular shop, so you may want to ask
around. You can probably find a list of machine shops in your area by
googling. Possibly more than you wanted to know…


#10
One of the issues with the Durston that upset me was I read here
after someone posted photo's here of badly marked rollers that one
shouldn't roll wire through on the flat section of the mill or it
would leave marks because the rollers are not solid all the way
through, they have an outer casing over a somewhat softer core. I
had rolled many a heavy wire through the flat part of my Cavallin
with nary a hint of trouble. 

I also have my Cavallin for about 40 years and regularly flatten
wire with it—one of its main purposes for me! Could it possibly be
true that flattening wire on a Durston damages the rollerse? Aurora.
were the heavy wires you rolled on your Cav precious metals or
iron/steel?

Janet in Jerusalem


#11

I have a durston mill it is very old as I am very old…35 years old
is the mill. I am much older. have run thousands of feet of wire
thru it and with proper care is still rolling away!!!

Vernon Wilson
Panama Bay Jewelers


#12

To prevent the curving of my plate and wire I built a steel shelf on
the back side of my rollers that has a edge ground to fit the
curvature of the lower roller it is mounted so it is a fraction of a
mm lower then the top of that roller. It is very sturdy. When sheet
or wire comes out it is pressed against the top of the shelf. and it
comes out straight every time.

Vernon Wilson
Panama Bay Jewelers


#13

I am one of those rare people who never even thought about wire
hurting my rolling millS. I yearly roll down thousands of feet of 6
ga. wire. Never had a problem on my carlin, old electric duration,
and a cheap one that my son bought me. I make sure that I do like
people in lapidary. I use the whole roll not just one track. If I
roll one length down in one spot, the next pass would be in a
different spot. I sort of work my way across the rollers until I
start back at the beginning. That does not mean I move it while Im
rolling, just each wire length gets a net track through. BTW i roll
the wire flat not down to a different size wire.

Aggie, hoping the colder weather coming tonight will kill off the
bugs for a while


#14

Hi Janet (and whoever it was with the marked rolls)

The ‘don’t roll wire in the flat rolls’ advice is pretty standard to
all rolling mills, not just Durstons. I’ve seen at least a dozen
different rolls, from half a dozen different manufacturers take a
mark after someone rolled hard wire through them. It’s not such a
problem if you just forge on it to flatten the top and bottom first.
What’s going on is that the roll puts out X number of pounds per
square inch of pressure, and the rolls are set up to be tough enough
to roll material that’s some noticeable fraction of an inch wide.
Round wire isn’t. You get point contact the first time thru, which
concentrates all that pressure right on the contact point. Which can
leave a dent in the roll if the wire’s hard enough. Steel will do it
every time, brass and silver depending on temper, and copper
probably not.

Forge on the wire a bit to flatten it out, and you don’t have such
extreme point contact. Which means the PSI at contact will be lower,
which means you can probably get away with it.

But even with that in mind, I always roll wire over on the edge of
my rolls, just in case it does leave a mark.

Most mills have rolls that are case hardened. In fact, I don’t know
of any that are thru-hardened. (anybody know of any?)

Regards,
Brian


#15

Hi

I am part of a lapidary group on the East Coast of Australia. We have
two mill that are used for flattening and for patterning more that
for roiling wire. My problem I’d like to put out there is we have had
some members who it is suspected not to have made sure the item to be
flattened was dry let alone, annealed before using the roller. The
mill now has marks on it that won’t come off. The marks are on the
surface of the drum. It would be nice to remove them. As we are a
self supporting club funds to replace the mill are not readily
available. Can anyone offer me any hints? Oh and I’ll be able to get
to the mill on the 09.01.2016 but not before.

It’s very hot here, it was about 33 degrees centigrade today and is
forecast to be a hot Christmas.

Thank Suzanne


#16
were the heavy wires you rolled on your Cav precious metals or
iron/steel?

Hi Janet, I only use precious metals in my mills, however I did
flatten miles of 6 and 8 gauge copper and silver with my old
Cavallin.

I wish I’d kept it as I’m afraid of marking the Durston.

Aurora


#17
I only use precious metals in my mills, however I did flatten
miles of 6 and 8 gauge copper and silver with my old Cavallin. I
wish I'd kept it as I'm afraid of marking the Durston.

I am concerned here because I was considering getting a Durston for
sheet only. What sayest Orchidians with Durstons. can 6 or 8 ga.
copper or silver wire damage the rollse?

Janet in Jerusalem


#18

I have both a low cost mill with flat, profiled and textured rolls
and a Durston 130 combo. I regularly roll up to 4 gauge copper and
silver on both. Make sure it’s annealed first and maybe a slight tap
to make it flat.

The biggest problem is copper marking the rollers. Have some
simichrome ready to remove it. Rob


#19

We have had a Durston in our studio at the Boca Museum of Art School
for the past 15 years or so and it has gone through some tough
handling by students.

It remains almost as good as new. These mills are made tough for
tough work. As long as they are not subjected to stupid things like
trying to roll stainless steel etc, they will hold up for many years.
Stick to noble metals, anneal according to the old rule of 1/2
reduction (even iron wire is OK as it is soft as well), take small
bites rather than trying to go from 8 ga to 20 ga in one felt leap,
be sure metal is dry and free of all pickle, patina, acids, etc and
they will be around long after we are gone!!! Oh, and a light
application of Baliistol now and then is a good idea. Cheers from Don
at the Charles Belle Studio in SOFL.


#20

Janet - those wires won’t hurt a good mill. Have them annealed, and
reduce them gradually. The only problems I’ve ever had with mills is
when the school bought cheap and the students forced reductions way
past the capability of the cheap mill. I have two Durstons, probably
misuse them, but have no trouble - ever. (one is a power mill for
milling mokume)

Judy Hoch