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Pepe rolling mills for metal sheet


#1

I own an inexpensive India made rolling mill which works fine for
wire reduction and patterning on silver and gold. However, I cannot
produce a sheet of silver or gold without waves. Even though I’ve
been very careful with my mill, and do not use excessive pressure,
there seems to be no way to produce flat or even sheet.

I am ready to spend some more money, but do not have the $800+ for a
Durston or better. I noticed that many reputable jewelry tool
wholesalers supply the Pepe Mills at a lower price, around $500. I
wonder if any of the Ganoksin readers have used one to produce
sheet. I would like to know whether the quality is as good as the
vendors claim, and if it might do the job for me. Your feedback about
this brand specifically would be greatly appreciated. I have seen
some writers suggest that I wait for a used Durston mil. They are
very rare, and I have never been able to snap one up before someone
else gets it. I am open to other suggestions.

On another topic, some responders to this blog have really been
ruining it for me by their critical responses. That kind of
negativity is such a depressing thing in an otherwise great forum.
Can we keep this precious space positive please?

Joris


#2

Hi Joris,

The ‘wavy’ part has to do with flex in the rollers. Which has to do
with how thick (diameter) they are, in relation to their width
(span).

Production mills that do this industrially look downright weird, by
manual rolling mill standards. The a roll that does 6" wide sheet
may well be nearly 6" in diameter as well. Just massively thick in
relation to their width. That way they don’t flex (much) under the
pressure of rolling sheet. Which keeps things flat.

The answer on a manual mill is to go with the narrowest rolls, with
the thickest diameters you can find, that’ll fit the work you want
to do. Then take small bites as you get closer to your target
thickness.

(assuming all other factors (like quality of build) are the same.)
You can also take multiple passes at the final thickness setting.
(or a smidge above. Try it while measuring with a micrometer, and
you’ll be surprised how much more it comes down on the second pass
on the 'same’setting. That was all from flex in the rollers, and
spring in the frame.) Flip the sheet right-for-left between passes
to even out any unevenness in the roll settings. Annealing between
final pass 1, and final pass 2 will help as well. I’ve not seen a
hand mill that will give perfectly flat sheet of any great width.
Much beyond 2-3 inches wide is where things start to wave, even on
the good mills. Want to be really surprised? Roll some wide sheet,
then measure the thickness of the edges that were closest to the
sides of the mill with a micrometer, and compare that with the
thickness at the center of the sheet. Do it on final pass 1, before
you even it out with the second pass. Should give you some sense of
how much your rolls are flexing. Then measure it again after final
2. You should see a surprising amount of change, especially in the
middle. Do a third pass, and it should come in even closer.
Whether the third pass makes any difference depends on how stiff
your mill is.

I just picked up a used Durston D4, but one of the older ones with
the frame made out of steel bars. It has rollers 158mm wide
(6+inches) but they’re only 60mm thick, which means they can flex a
fair bit if you’re trying to roll a full 6" sheet. (It’s the biggest,
nicest mill Durston makes, and a very good mill, but I still had to
stop and think about it.) The consideration was that my current mill
is an older ‘unknown’ brand, probably American, probably circa 1930.
It only has 3" rolls, but they’re nearly 2" (50mm) thick. So they’re
very thick, in relation to their span. (Half the span of the Durston,
and nearly the same diameter, so roughly 3.5x the resistance to
flex.) Gives great sheet, but only about 2.5" wide. Given as I do a
lot of gold foil, where ultimate compression matters I had to think
hard about whether or not to either keep it, or get the Durston at
all. I finally decided to get the Durston, and sell off the little
one, (already gone, I think.) Frequently the right choice isn’t about
name, or size, or ‘quality’, it’s about understanding why machines
work the way they do, and which one is closest to ideal for the job
you want it to do.

FWIW,
Brian

PS. > As far as the PEPE mills, I don’t recall that I’ve ever used
one. I’ve seen them at shows, and they look OK as $500 units. The
’special hardening’ thing is just a deep case hardening, but RC60 at
the surface, and.120" deep is a pretty serious case. I made a set of
rollers for one of my mills (when I was young and dumb) and I only
had mine cased.050" deep, at ?RC55? or so. So that’s an indication
that they’re not fooling around. (I wasn’t fooling around either,
and they’ve gone more than twice as deep as I though was enough, if
that gives you any clue.) I have heard of issues with the gears on
the old ones, but maybe they’ve gotten that sorted? I’d certainly
look at that before I’d start looking at the Indian or Chinese ones.
They also do have a manufacturing facility here in the states.
(Oklahoma City) So it’s not all offshored. I don’t know what all
they make there, but they do make at least some things in the US
now. Surprisingly. I also know, from talking to them at shows, that
they really are trying to make the best tools they can, within the
limits of the pricepoint they’re aiming at. Take that for what it’s
worth.


#3

Hi Joris,

Generally, this problem is caused by one roll advancing a little
faster than the other, then retarding. So what can one do about it? 1.
you need 2 pieces of measuring kit, a micrometer, and a vernier. The
former is to check along the wavy sheet whether the thickness is the
same, if it is, then the rolls are ground concentric. If they are
not, then they can be reground.

  1. you need the vernier to measure the roll diameter. Then multiply
    this measurement by 3.14. What dimension this gives should correspond
    to the distance between the tops of 2 waves.

Now If your mill is geared, you need to mark one roll with a felt
tip, and rotate the handle till the mark returns to the same 0"clock.
Count the no of revolutions because you need the handle and mark in
the same place before you do the following.

Feed the sheet in from the same direction as the previous pass, with
the same thickness setting BUT turn it over. Roll it through. you may
need to turn down the thickness a thou or 2, or maybe even more., I
find what Ive described above straightens out the waves. As Ive said,
if the rolls are concentric then its poorly machined gears that
interlock the 2 rolls.

Try it with some annealed copper to establish the settings. you will
find this will work.

Ted.


#4

I have a Pepe mill, with combo rollers. I use it regularly, and have
had no problems. I take small bites on the reduction, and do not
overload the capacity of the machine by trying to reduce things too
quickly. I would have preferred to have had a better mill, but for
the price I am not complaining. I believe they have improved over
older models.

Melissa Veres, engraver and goldsmith


#5

Hi Joris

I have been using a Durstan, which I truly love, in my main studio
for about 15 years. I had purchased an inexpensive Indian mill,
which broke within a few weeks of use - the roller was poor quality
steel and cracked in half. The vendor kindly allowed me to trade-in
the defective mill for a good one, just paying the difference in
price. My opinion is, if you can find the money, go for the best.
However, I also have a Pepe mill in my other studio, and find I can
do everything I need to with it, including producing satisfactory
sheet (I work in high carat gold, very seldom in silver). Not of the
same quality as the Durstan, but sturdy and serviceable.

Leslie Chapman
Fortymile Gold


#6

I recently purchased a Durston 130 combination mill with external
rollers. It is a wonderful machine to use. I also have an old and
well used made in India machine that I bought about five years ago to
see if, after 35 years working metal, I needed one. I discovered that
I did. I used the excuse of a crack in one of the roller key ways to
justify the Durston. They are expensive. If you buy one, make sure
that you also have a snap ring removal tool. I still use the India
mill, but can leave it set up with the half round and triangular
rolls as I need them often. The Durston does the bulk of my work. I
had the same problem that you describe with wavy sheet in the India
mill. I found that if I could put it under some tension on the input
side, the waviness would go away. I am sure that there is some
metallurgical explanation for this. You can also play with the level
of annealing and, if it isn’t too wide, pass it thru at an angle. In
the end, if I need something really straight, I anneal it well,
secure it in my drawing bench, and give it a tug. You need a little
bit to waste on both ends where it is secured and the tongs grab
ahold. Good luck. Rob

Rob Meixner


#7
Even though I've been very careful with my mill, and do not use
excessive pressure, there seems to be no way to produce flat or
even sheet. 

The cost of the mill isn’t the issue. Jewelers small rolling mills
(all of our hand mills) have roll diameters small enough that simple
uneven stresses in the metal as we roll sheet tends to cause some
curling and waving. You’ll get that with even the most expensive
mills, simply because the mill itself is not the only source of those
stresses. It’s inconsistancies in the metal itself, the ingot, etc.
But try something. Rolling very gently means that in general, the
deformation of the metal as you roll is mostly near the surface,
with less deformation at the center. You can confirm this by looking
at the leading or trailing edge of an ingot you roll, and notice the
surface tends to stretch more, leaving the center core often slightly
depressed or hollow. This stretching of the metal more at the surface
is a large source of your waves and curves. The fix is to keep
rolling. As the metal stretches, it work hardens. As it work hardens
and you keep rolling, the force of the rolling is transmitted by the
now harder surface metal to the still softer metal at the center.

In practice, it looks like this. As you start to roll annealed
metal, it often will curl or wave a bit. Keep rolling, and as you
proceed, stresses are evened out. Eventually, the degree of
deformation in the center will be roughly the same as at the surface.
You’ll know this because at that point, the waves and curves will
have mostly evened out again, and the metal will again be mostly
flat. That’s your signal that it’s now time to anneal.

If you’re in the habit or rolling just a little and annealing as
soon as it seems any work hardening is happeneing, then what you’re
doing is locking in the deformation caused by those uneven stresses,
and you’ll never get flat sheet.

Anneal less often, and you may find the problem mostly goes away.
Try it.

Now, if your rolls aren’t actually concentric, so your mill is
producing metal that actually varies in thickness, then of course the
waves are something else, but even the cheap Indian mills seem to be
decently concentric (lathes kind of do that when the rolls are
made… :-)) Their smaller diameter rolls make it a bit more
difficult to get really good sheet, but not impossible, unless
you’re trying to make sheet wider and thicker and heavier than your
mill can manage.

Then you’d need a heavier mill.

Peter


#8

I studied the math of this (continuum mechanics - second scariest
math I ever did after magnetism) ~20 years ago but never used it in
practice. I can confirm however that Peter Rowe is correct.

One of the things that fascinate me is that at a certain point you
can’t roll the sheet any thinner - and it’s surprisingly thick. The
answer is to roll several thicknesses at once - I believe (with out
confirmation) that Al foil is produced this way…

it does make me wonder though if it would be possible to do this
with silver or gold foil on an appropriate backing…


#9

I tend to get flat metal from my old manual, reduction gear Cavallin
half-wire half-sheet mill. The reason may be that the sheet I make
is usually not very wide, and I am talking about thicknesses under 1
mm. But I do think it may actually be more difficult to get flat
sheet on a half-and-half machine, as you are using only one side of
the roller, thereby having one side of your sheet at the very edge
of the rollers and one side in the center…

My habits are:

  1. Always put the same end in first. Change direction only after
    annealing.

  2. Always do at least one additional pass at the same setting after
    flipping right-left. If you get waves, continue right-left flipping
    at the same bite.

  3. When taking a new bite, make sure the right-left orientation is
    the opposite of what it was on the previous bite.

I anneal often and usually have at least one 90 degree pass (after
annealing, of course). I do get flat sheet, but as mentioned
earlier, it’s only 2 1/2" wide. Also, it’s much easier if the
proportions allow you to do 90 degree passes.

Janet in Jerusalem


#10
it does make me wonder though if it would be possible to do this
with silver or gold foil on an appropriate backing... 

That’s how Sheffield plate and gold fill are made. Though you don’t
start with foil but with a thin sheet soldered to the base metal
backing.

Elliot Nesterman


#11

Greetings,

One of the things that fascinate me is that at a certain point you
can't roll the sheet any thinner - and it's surprisingly thick.
The answer is to roll several thicknesses at once - I believe (with
out confirmation) that Al foil is produced this way... it does make
me wonder though if it would be possible to do this with silver or
gold foil on an appropriate backing... 

Yes. That’s exactly how you do gold foil (without beating it out
between sheets of lambskin…)

Jacket the gold between two sheets of copper, roll the whole thing
as a sandwich, and away you go.

Replace the copper periodically, if you need to, and you can get
pretty fine. The thinnest I’ve ever gotten was about.0003". Probably
could have gone thinner, but I wanted to use the foil for something
that needed it to be at least as thick as it was. Also works for
silver, but you have to anneal more often.

FWIW,
Brian