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Rolling Mill Decisions


#1

Hi All, Well I did some hands on comparisons. I had used Durstons in
the past but never Cavallin so I tracked down an tries a Cavallin.
First impressions plastic and stamped/shap edged metal do not impress
me so there was one strike. Now the equivalant sizes ie 120 Cav v.
130 Dur. the Cav. has larger dia. rollers 65mm v. 60 mm… A plus.
Dur. has 6 to 1 gear ratio to 4 to 1 for Cav…

I figured a coin toss and went with the locally available Cavallin.
But not before emailing Durston for a possible local dist. Within 30
inutes of emailing Durston I received a personal reply from sara
Durston with .alas no local dist… But how cool was
that!!

So 4 hours later I’m home from LA with a brand new sparkling
Cavallin 120 mm rolling mill!!.. With scratched rollers!!!
ArrGGGhhh!!! 24 hours later I’m back in LA returning said Cavallin
and ordering a Durston from Rio!

No bad press intended towards Cavallin, they make a nice mill that
many folks just love. I basically went that way judging by specs and
price and learned the lesson I keep teaching myself…a motto I try
to keep front and center while purchasing anything I want to last:

“Buy the best and cry once”

IMHO Durston is the mill I prefer and hopefully I wont have to make
that decsion again.

BTW Los Angeles members… Stay tuned for an update about A-Z Tools
and Supply on 6th st. I have to contact them regarding the return and
so far am not 100% happy with theier service.

Thanks,
Warren Allen


#2

I originally responded privately to the posting about whether
Cavallin or Durston was the preferred mill but feel I should post
publically that I have truly loved my Cavallin mills. 12 or 13 years
ago, when I was first setting up my home workshop my husband
consulted several jewelry making friends and purchased a Cavallin
120cm flat mill for me for Xmas. A couple of years later he
purchased a wire mill - also Cavallin - and also a surprise. I have
loved them both - they have served me well and have withstood the
test of a difficult damp basement workshop for many years. Just my 2
cents. Sherry


#3

Durston vs. Cavallin rolling mills Warren Allen has made a very
logical analyzes of the two rolling mills he compared and I agree
with every point save one. The diameter of the roll is a trade off. A
larger diameter may seem like it is better because it would have less
deflection when stressed and I suppose this is the logic that Mr.
Warren was following and assuming that the material has the same
strength that is a true assumption. The advantage to a smaller
diameter roll is you can roll a thinner gauge metal with it. The
smaller the diameter the thinner you can roll and the larger the roll
diameter gets the greater the minimum thickness you can achieve. The
problem with deflection is the rolled material can come out thicker
in the center and thinner at both edges. There is a way to have your
cake and eat it too. Not all steel has the same yield strength, so by
using stronger material (more costly) a smaller roll can give the
small contact area that allows thinner rolled material and at the
same time not flex anymore than the thicker weaker material. Now
you get the bonus: the stronger steel is also tougher and in my
experience the Durston rolls keep their finish much better than any
rolls anywhere close to the price. Simply put, Durston gives the best
value for your money. I feel confident that Mr. Warren will have a
lifetime of satisfaction and I very much appreciate his business and
the kind words he posted.

Eddie Bell
Technical Director
Rio Grande


#4

Hi Eddie thanks for the informative post, but could you explain just
a little more WHY larger rollers can not roll thin metal as well as
smaller rolls?

I only ask because at one shop I used to use quite a large mill, 6"
diameter by 6" wide rolls, and weighing in about 2000 lbs. Whatever I
rolled came out beautifully finished and flat, and I simply had no
problems rolling out solder sheet to what ever thickness I needed.
You know when you need extremely thin solder for delicate soldering
operations? In other words, I just didn’t notice any difference in my
ability to roll out thin sheet. Perhaps quality of construction has
something to do with it? I could see problems arising if the
tolerances kept during manufacturing are not tight. Not arguing here,
just curious.

thanks
Jeffrey Everett


#5

Dear Jeffrey, You have a really good question. If I remember the
explanation given to me a lot of years ago it has to do with contact
area and approach angle to the roll. I think it has to do with the
force moment getting higher as the contact area gets smaller. You
may have seen rolling mills used for thin material rolling that back
up a small diameter contact roll with larger diameter anti deflection
rolls. The simplest of these is called a four high mill. I have seen
pictures of 30 high mills with very small diameter contact rolls that
are backed up by two larger diameter rolls that are still not large
enough to resist deflection so they are backed up pyramid style by
three and then four and finally five rolls, each set progressively
bigger. This way the large rolls keep the whole set flat and the
small rolls have small approach angle beneficial for making ultra
thin strip. If I add correctly that would be 15 rolls on the top and
15 on the bottom.

I don’t have any text here that I can refer to, but I would start to
look for more on this in The Metals Handbook published by
the American Society for Metals (ASM). I think they have changed
their name to American Society for Materials.

Now for the practical side for us jewelers. First of all I didn’t
think my argument through as carefully as I should have. In my mind I
started with the thought that material strength needed to be
considered when analyzing the rolling mill and one should not
automatically assume that bigger is better. My point, not very
eloquently made, was that smaller and stronger might be better. In
theory the 200 should be able to make thinner strip, but from a
practical standpoint, I don’t know how much thinner a strip can be
rolled from a roll 200 mm vs. 250 mm and both may be able to get the
material thinner than needed.

As for the heavy duty mill you worked with, you are right, there are
other places where a roll can deflect. The bearings and the H frame
must react to every force exerted on them and the stronger the
better. The effect of bearing deflection would be scalloping with
roller bearings (this can also be caused by the face roll not being
concentric with the axle of the roll) and gap opening for bushings.
Frame stretch would open the gap and this could be parallel if both
sides move evenly or wedge if one side moves more than the other.

Eddie Bell
Technical Director
The Bell Group/Rio Grande


#6
Dear Jeffrey, You have a really good question. If I remember the
explanation given to me a lot of years ago it has to do with contact
area and approach angle to the roll. <snip...>

Wow, thanks for a great explanation Eddie. I have seen 4 high
rollers, but it’s been so many years I had forgotten. Your
explanation make perfect sense to me, and I appreciate the time you
took in answering!

By the way, back at the 1985 CA MJSA show you talked me into joining
the MJSA. I haven’t seen you since, but maybe we’ll meet again
someday, and it will be my pleasure.

Jeffrey Everett


#7

The 20 roll cluster mill is a Sendzimir design.

http://www.sendzimir.com/

This is not a precious metal producing mill but is used for
stainless steel ,steel and titanium etc .

more on these BIG mills at:

http://www.dmsbliss.com/himills.shtml

http://www.jfe-21st-cf.or.jp/chapter_4/4c_1.html

jesse