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Turning wide silver bezel into C channel strip


#1

Greetings:

OK, here’s a weird one. I’ve got a client who’s wanting me to help
him work out the manufacturing aspects of making custom coin holders.
(No, unfortunately, buying stock ones won’t work, for a variety of
reasons.) To grab the edges of the coins, I need to figure out how to
make (and then bend) silver “C” channel. I’ve got a full machine
shop, so making tooling isn’t a problem. The problem is that we need
about 8 different widths of channel, from Xmm to X +2mm, by.25mm.
Wheeee…

My thought about how to get “C” channel was to take wide fine
siliver bezel strip, and make up something sort of like a mini
rolling mill, except instead of having flat rolls, it has a square
groove turned into the lower roller, with a square (in cross section)
raised ring in the upper roller. In use, the wire gets folded down
into the lower groove by the raised ring on the upper roller. It’d
probably take a pass or two to get it folded down right, and I’m
worried about having to build the mother of all infeed guides to have
a prayer of it tracking straight.

Anybody seen how the commercial outfits do it? I gave some thought to
just using a bonny-doon press as a brake, but the quantities
involved, combined with lining up the strip killed that thought,
unless someone knows a sure-fire way to do it fast and controllably.

The next question is how to take this “C” channel and then bend it
into a circle. I’m thinking of something like a miniature slip
roller, again with the grooved + tongued rollers. Again, a major pain
to machine up from scratch. Anybody got a better idea?

Any help or suggestions would be greatly appreciated.

Regards,
Brian Meek.


#2

Hi Brian,

I have done foot lenghts in a drawplate with a steel wire in it,
like making tube, only you stop short at about 200 deg circumference.

you make the section a little bit too narrow and then when you coil
it up it will open to the right size. This gives you a circular
section, you would have to experiment with thickness and widths, I
don’t know how to do channel with corners.

regards Tim Blades.


#3

Call Stullers tech dept. Go to Italy. Cast em.


#4

Brian

here's a weird one. I've got a client who's wanting me to help him
work out the manufacturing aspects of making custom coin holders. 

I would skip all the other ideas and go straight for the ring
roller. The reason is this, a basic ring roller is a very inexpensive
design, for the dimensions you want it is well within the
capabilities of compression of a ring roller and the advantage is
that all you would have to do is purchase standard strip, or if you
buy enough, they could probably cut custom at a reasonable price.

Now if you don’t mind, lets look at your problem a little deeper;

All measurements are with used coins out of my can and a
non-calibrated electronic caliper and double stacking my glasses to
see contact points, for the sake of completeness, my glasses are a
1.75 and a 2.25 pair of readers.

Quarter
24.19 mm Dia.
22.33 mm inside at bevel
23.33 mm at top of outer bevel
1.69 mm thick at edge

A standard US Quarter has an overall diameter of about 24.19 mm with
a variance of .04mm. The inside dimension edge to edge is about 22.33
mm and bevel to bevel is 23.33 leaving an actual grip surface of
about.93 to.88 mm or a rim variance of about.05mm. The beveled edge
on a quarter is ~ 0.43 mm wide. The thickness of the edge of a
quarter is about 1.69 mm overall.

Dime
17.91 mm Outer diameter
15.81 mm Inner diameter dif/2 = 1.05 mm lip width
17.09 mm inner edge at the bevel/2 = 0.41 bevel width
1.36 mm thickness

Snagging some coins from the wife’s collection, I do not see a whole
lot of difference in construction except ours seem to be the only
ones with the outer bevel, I don’t know what she did with the
Canadian coins.

As you do not say what this will be used for,.25 mm in a static
display with 30 gauge would hold, if it is to worn our used, I would
go with a minimum of.6mm depression and 26 to 22 gauge or more.

I think you may be over estimating the difficulty of holding the
strip as it goes through the roller, I think a simple bracketed slide
guide would be sufficient for the tensions and materials you are
using and more than likely you will be using spooled material to feed
from.

I would suggest that you not make the roller square, if you do the
metal will want to stick to the form, and at higher speeds this can
be a real disaster. I do not know what the modulus of elasticity for
silver is, so you will have to experiment a little for that value.
This will affect how deep the channel will have to be in forming for
a given depth of the final channel. It should be easy to calculate
the displacement of the groove into the channel width you are looking
to make, again, do not use square corners or sides, it ‘will’ stick,
I think 3 degrees was what was used, a over should not be a problem.

Hope this helps
Terry


#5

I made C channle by scoring my bend lines down the bezel srip and
then starting th bend with Miland plyers. This gave me a shallow U
shaped strip with the scorde lines down the center with the proper
width between the lines that I needed to end up with. I then put the
piece which was curled up in the proper diameter from the plyers and
squished the whole thing in my Bonny doon so that the sides flattened
down to the scored lines. That was a C channel finished. I soldered
the ends together prior to squishing so the whole thing was the
perfect size I needed. I could then cut the piece at the seems to act
as a coin bezel but I think it could be squished with out being
soldered so that you end up with a length of C channel that could be
cut to length.

Sam Patania, Tucson
www.bahti.com


#6

That sounds complicated. My only suggestion is to run a square wire
inside of your channel if you use a draw plate.

M’lou


#7
The next question is how to take this "C" channel and then bend it
into a circle. 

I’m not a machinist, so please forgive if this is all wet, but…

How about using the hydraulic press to make, in essence, bezel cups,
punch a hole out of the bottom, then fold the upper edge over like a
typical bezel? Good for any thiichness, though just one diameter.

Noel


#8

Brian, I’ll say very respectfully that you’re nuts ;} I’m a bit of
machinist, but not a bona-fide one, but just from general knowledge
I’d say this: Making a “C” channel is not going to be that difficult
in some way as you describe. Bending it into a circle might very well
be near impossible, though I could be 100% wrong, too. You will have
two flats of metal trying to compress inwards as you bend, and even
if it can be done they will need tough support inside and outside all
the way around or they’ll just crimp on themselves. To do that you’re
talking about a die for each size that will hold the stock with
precision, or tool and die to begin with - punch press stuff. If the
OD of the frame is 1", and the ID is 3/4", which is a 1/8" rim, then
you have to pack the silver on the id into 3/4" without distortion.
Almost impossible without hand forging, which I know you don’t want
to do, or heavy steel all around it, plus lots of force. The other
way would be pieces - a circular bezel and two washer shapes, which
would be assembled. Not what you’re looking for, I’m sure, but far
easier to do…We happen to have a coin money clip right now -
definitely die struck…

http://www.donivanandmaggiora.com


#9

Hey Alberic

Have you tried pulling the bezel thru a drawplate? That’s what I do,
however, my bezel is quite wide and I make sure it is very soft. I’ve
been setting treasure coins since 1977 (ack!!). Let me know if I can
help in any way.

Lainie


#10

Hello Brian,

You want make (and then bend) silver “C” channel.

OK. This is really out of the box, but it might stimulate ideas.
Think how grooves are routed in woodworking. Recognizing that there
would be a lot of high dollar scrap produced, one could “rout” a
groove in square wire. The result would be a U-shapped channel.

Well, it was a thought anyway,
Judy in Kansas


#11

Brian

This may not give you exactly what you need but it may steer you
toward a process that will.

If you have a ring sizer with compressing dies you can use those
dies for lots of things. Take some fairly heavy bezel material and
make a soldered ring way oversize for your coin. If you start to
compress that bezel ring as if it was a real ring, gradually on both
sides, it will curve in gently on the edges if the metal is the
right thickness giving you a gentle c cross section and the circular
shape at once and really quick. You could probably even insert the
coin and continue compressing or plan to cut the ring open at the
solder joint and insert the coin. I think you will need to flatten
the bezel at the edges more to completely secure the coin, perhaps
with some slightly concave dies or by hammering.

I discovered this method when making some domed inlay material for a
ring, it is a really efficient way to make perfect hollow forms for
rings and earrings.

Celeste


#12

I just made a silver coin bezel yesterday. Why don’t you just put
some wax on a lathe and turn it? Takes about 10 minutes to turn one
and then all you have to do is cast it. Turn eight, slightly
oversized, then cast, then mold each and you’re done.


#13

I think a drawbench is a good tool to form the strip into a 'C’
channel. It will produce long lengths of uniform section.

One way is to pull the strip through a round hole in combination
with a round rod, the rod can be brass and the strip will form itself
around the rod when both are pulled through successive holes in the
drawplate together. The ‘C’ section produced in this way will have
thinner edges and a thicker centre.

Another way is to make a custom die for the drawbench; a two-piece
die where the top half can be screwed down against the bottom half.
Each half of the die can have it’s own separate profile. For a
uniform ‘C’ section the top and bottom halves will match each other.
Any kind of embellishment can be added when making the dies, eg to
form a linear pattern on the outside of the ‘C’ channel, or to modify
the inside of the channel to fit a coin better.

To form the channel into rings, wind the annealed channel on a
cylindrical mandrel. Two things happen when doing this: a) the 'C’
section will spread out or widen slightly, and b) the diameter of the
mandrel will need to be smaller than the required coin size to allow
for the coil to spring open after winding. In my experience a) is
negligible and not a problem, and b) just needs a little trial and
error with different sized mandrels.

Now you have a coil of ‘C’ section. Cut the coil as you do for jump
rings and you have the frames for the coin mounts. The next problem
is how to close the frames around the coins. A method I use is to
solder a large heavy jump ring to the frame so that the cut in the
frame and the cut in the jump ring line up, but the cuts themselves
are not soldered. It looks like a fig 8 with a small top and big
bottom, and the center bit split with a vertical gap. You could
solder the whole lot together and then make a vertical cut through
the center of the ‘8’ afterwards. Add a bale to the jump ring part.

To mount the coin, the vertical gap is spread open, coin insertd,
then the gap is pinched closed. If the jump ring is heavy enough it
can be relied on to keep the frame closed on it’s own, but for
long-term security I pinch a second jump ring around the waist of the
’8’ to keep the gap firmly closed. The second jump ring is cold
fitted without solder.

I have seen something like the method described above, but with the
addition of a tube between the jump ring and the frame, with the
tube cut in half on the same vertical plane as the gap. A screw or
rivet pinch the waist closed (>8<) and keep it locked securely.

Alastair


#14

There are sheet metal hand benders which are 2 flat plates of steel
welded together with a slit running the length. You insert the edge
of your sheet metal and, keeping it in tight, lift up. That gives
one of the 90 degree sides. Then you repeat for the second side.
These tools are available from Heating suppliers and sheet metal
suppliers. You may be able to make your own with your own dimensions
by clamping 2 flat steel plates etc. together, sandwiching your
bezel between. the greatest difficulty I can see would be the small
size of your dimensions. Alternately could you wrap a bezel around 3
sides of a square wire and run it through a draw plate?

Just some thoughts on possible approachs to the problem. I’m sure
there are many ways to do the same thing.

Dan Wellman


#15

Brian,

On a lathe, machine a rod and add the thickness of a slitting saw to
the diameter/circumference that will fit a particular size of coin
frame on the ID. Machine a thread that resembles the C or U channel
form and as deep and as wide as the walls need to be to support the
material as it curves. Make a stand that will hold this threaded rod
on one end only, but will allow it to rotate freely, and then mount
directly in front of the rolling mill. Additionally, a piece of
polished rod or a bushing that could be height adjustable for
different metal thickness to push the material onto the threaded rod
as it rotates.

For the rolling mill, make a guide plate/forming die to start the
process in the right direction, feed it through using your roller
idea to get the C or U shape. As it comes off the rolling it will
feed onto the threaded rod. Bend the material around the threaded rod
a little and by hand should be fine to get it started. Once the
threaded rod has material on it, and one rotation should do it, will
now rotate at the same speed as your rolling mill. Eventually,
material will come spiraling off the loose or open end. The threaded
rod doesn’t need to be long, maybe 6 full turns. Or Keep the rod to
say 12 inches and when full of spirals, mount it on your Mill and
slit saw them off

Just an Idea.

Best Regards.
Neil George
954-572-5829


#16

I had a bit of a brainstorm last night about this, though it could be
Rube Goldberg, too. It’s easy to make a channel - swage blocks will
do it nicely, plus the question requires precision, which swage
blocks would do reasonably well. It’s bending a channel into a circle
that’s a bear. Try it - the two upright legs will just bend all over
without being tightly controlled. A person could make a device that
would take in strip, bend it into a C, and roll it around a disk. I’m
thinking a lever that rotates around a disk on a common center with
the lever having a gradual shaping surface similar to a swage block
that would shape the strip into a C as it went around the disk.
That’s pretty complicated, though it could likely be done. I still
think it’s punch press work, though, for any kind of production…

http://www.donivanandmaggiora.com


#17

What you might look at and maybe able to duplicate is something like
the “gutter makers” use but on a miniature size. They run a flat
strip of material through a machine that shapes it to the common "c"
gutter shape.

Larry E. Whittington
http://www.jewelrycabs.com


#18

Hi Gang.

Thanks for all the many interesting replies. I was getting brain
lock, and needed a fresh set of concepts. Many thanks. I think a
little more explanation is in order, just so you understand the
nature of the beast.

The short form is that the client is looking to do coin mounts for
ancient, detector-find type coins. No two will ever be the same, and
they mostly aren’t even round, nevermind a common circumference or
thickness. Thus the need for strip that can be cut to size. Oh, and
it’d be nice if the mounts wholesale for under $30, in silver. So
it’s got to be fast.

[sigh] fun, no?

I think I’ve worked out the beginnings of a concept on how to get
the grab rings (the ‘C’ channel) made. Now comes the decoration. (I
forgot to mention that? There’s a decorative bail too…)

Again, many thanks,
Brian Meek.


#19

Depending upon how much volume the customer wants, you might take a
look at having a draw plate made by the edm process. You would have a
series of forms that would start out with just a gradual lift of the
outer edges of the strip. The next hole would increase the angle
slightly, and so on, and so on, until the edges are vertical. I would
imagine that this would require a series of 4 or possibly 5 draws.

If the quantity is fairly small, you could do this by sawing the
shapes in the same way as you would saw out a blanking die. Use 1/16"
thick 0-1 tool steel, tilt the bench pin to the same angle as on a
standard draw plate, and very carefully saw out the pattern. It can
be done! It certainly helps to have good sawing equipment (and
skills). Either one of the new saws that I have developed can do it
fairly easily. I just got an email from Daniel Brush commenting on
the knew concepts electric saw saying “I just spent the last nine
hours sawing filagree in 1/8” stainless." The website (with hdtv
quality videos of the saws in action) are at knewconcepts.com

Lee


#20
I've got a full machine shop, so making tooling isn't a problem.
The problem is that we need about 8 different widths of channel,
from Xmm to X +2mm, by.25mm. 

Since you have a machine shop, the easiest way to make C channel
will be to make male/female dies and press the strip into the the
shape you need. The dies will need to be long enough to create a
strip that will at least equal the circumfrence of the coin. Since
your working in silver, this can all be one rather easily since the
metal will move nicely.

Example, cut a channel into some tool steel that is the width of the
channel (coin) + 2x the material thickness, make this a bit deeper
than the channel needs to be. Then figure out how wide the strip
needs to be, once you have this, cut a second channel the exact width
of the strip, going down the thickness of the strip (gage). This will
give you a guide to rest the material in. Now round off the corners
where the material will get forced into. Then make a male die equal
to the thickness of coin, to press the offending material into the
channel.

I did a simple drawing of the contraption here. Its obviously not to
scale, but you get the point. This is an end view, and youll need
some sort of press to use this in.

Now to bend the channel circular, this is going to take a bit more
work, but create a mandrel out of round stock, cut two grooves into
the round stock the same thickness as the strip your working with,
cut deeper than the channel is, then simply put the legs of the
channel into the grooves and hammer away, this keeps the legs of the
channel straight and lets you bend the channel appropriately.

Now the real issue is keeping the material from getting stuck in all
these mandrels/dies, so tweak the dimensions so you get what you
want.

Alternatively, you can make these dies in multiple parts, so that
when the material is forced into them, you can unbolt the pieces to
drop out the material that might get stuck in there.

In the long run, these dies should allow some moderate production
capacibilities for you. Good luck, and if you need further help,
please feel free to contact me off list.

P@
www.patpruitt.com