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Experience with large disc cutters


#1

Good morning,

I’m looking at purchasing a set of large disc cutters (up to 2"). I
have been told that they may not work with a hammer, but will require
a press. Does anyone have any experience with these and what guage of
metal will they cut using a hammer?

Thanks in advance
Gerry


#2
I'm looking at purchasing a set of large disc cutters (up to 2").
I have been told that they may not work with a hammer, but will
require a press. Does anyone have any experience with these and
what guage of metal will they cut using a hammer? 

It all depends on how big is your biceps. The problem is that cross
section of disk cutter increase as a square of it’s diameter.
Cross-section of 1 inch cutter is 0.785 square inches, 2 inch cutter
will be 3.14 square inches. That is by doubling diameter, we
increase force requirement by factor of 4.

If you using 5 pound sledge to cut your disks, you would need to go
to 20 pound sledge and been able to swing it as fast as 5 pound
sledge, or stay with 5 pound sledge but swing it with 4 times of
speed.

That puts it outside of most goldsmiths athletic abilities.

Leonid Surpin
www.studioarete.com


#3

Hi Leonid,

[snip]

will be 3.14 square inches. That is by doubling diameter, we
increase force requirement by factor of 4. 
If you using 5 pound sledge to cut your disks, you would need to
go to 20 pound sledge and been able to swing it as fast as 5 pound
sledge, or stay with 5 pound sledge but swing it with 4 times of
speed. 

Errr… Not quite. I=.5(M*V^2)

Translation: Impact Impulse=half of the quantity of the mass times
the square of the velocity. The important bit being that impact is
exponential with velocity.

So to achieve a 400% increase in impact, you don’t need a 400%
increase in speed. I’ve been moving stuff all day, so backing out the
math is more than I’m game for at the moment, but it’s somewhere in
the neighborhood of twice as fast.

(This is the underlying principle behind hypervelocity projectiles,
etc.)

Regards,
Brian.


#4
Errr... Not quite. I=.5(M*V^2) 
Translation: Impact Impulse=half of the quantity of the mass times
the square of the velocity. The important bit being that impact is
exponential with velocity. 

If cross-section increased by factor of 4, the force also should
increase by factor of 4, because cutting ability depends on
generating enough pressure per square inch to overcome metal
resistance to shear.

I take you point that my analysis was an over-simplification, and
actual calc is more involved, but the overall thrust of the argument
remains intact.

Leonid Surpin
www.studioarete.com


#5

Gerry,

I own a set of these cutters (Pepe, purchased from Rio), including
the 2". I have cut thin, annealed or half hard, non-ferrous ( 30-26
ga) metals successfully using a 3 lb plastic ‘dead blow’ hammer. The
larger the cutter the more force required, sometimes a second or
third strike. Try and center your blow. The cutters also work nicely
on leather, card, thin flexible plastics.

I can’t say I’d advise the “get a bigger sledgehammer” approach.

I’ve used a large machinist’s vice in a pinch, although it is a bit
awkward, not ideal. I imagine an arbor press would work as well.

That said, I do all of my cutting/punching over 3/4" dia. (up to 16
ga bronze) using a 12 ton hydraulic press. A lot less drama. Way
easier on the tool, fingers, nerves.

If you are going to try the hammer approach use a thin pad (leather
or gasket rubber) of some sort under the cutter assembly so you
don’t end up slamming the cutter punch and cut piece into your
support surface. Remember that the cutters are hardened steel and
select your hammer accordingly (ideally softer than). The cutter
edges can get chipped if misaligned in the die (it happens) or
dropped on a concrete floor.

Store the two part female die separated (unless you like to swear)
until you are ready to use them.

They are useful tools but not inexpensive to replace if you break
them, hence the hydraulic press recommendations by suppliers.

Charles Wiggins


#6
Remember that the cutters are hardened steel and select your hammer
accordingly (ideally softer than). The cutter edges can get chipped
if misaligned in the die (it happens) 

Just a quick addendum to Charles post, if you use a steel hammer on
a disc cutter (or any other steel tools for that matter), make sure
you use eye protection. That hardened steel can shatter and blow
little chunks in all directions with amazing force. They can also
cause sparks, so keep all flammable liquids (and paper towels, etc)
covered and away from the general area.

Using a steel hammer is also a good way to ruin a cutter, especially
the small ones. Most sets require you to buy a whole new set, you
can’t get just the one cutter you broke or bent. Voice of experience
speaking here.

Be mindful of the hazards to you and the tools when whacking steel
with steel. A brass hammer, deadblow mallet, a vise or a press might
be preferable. A press is definitely the way to go with larger
cutters, whenever possible.

Dave Phelps


#7

Leonid,

Your calculations for square inches are correct, however, how you
view this as being applied to disc cutting is incorrect.

Cross-section of 1 inch cutter is 0.785 square inches, 2 inch
cutter will be 3.14 square inches. That is by doubling diameter, we
increase force requirement by factor of 4. 

In plain English.

A disk cutter used as a blanking tool cuts along what is known as a
shear edge or more accurately a cut length.

Therefore on a 1 inch cutter, that cut length is 3.1416 inches and
on a 2 inch cutter, the cut length is 6.2832, therefore the
requirement is doubled and not quadrupled. The Blanking force will
be double that of the required Shearing force in most cases, and the
force is measured in tons of course. Therefore, double the diameter
in blanking and you double the tonnage.

Now striking as in coining, well that’s another matter :slight_smile:

Best regards.
Neil George


#8

A large disc cutter can be manipulated so that the hammer blow does
not have to cut the whole circumference simultaneously.

Depending on how the cutter is constructed it’s possible to strike
the cutter off-centre and cut deeper on one side. Repeat striking
off-centre while moving the off-centre point around the disc. The
cutter must never be allowed to get out of the first cut groove for
this to work. The disc is eventually cut while using lighter and more
controllable blows of the sledge hammer.

I found that a 2" or 50mm length of pipe of suitable diameter,
sharpened and case-hardened at the edge will work using this method
for a small quantity of discs out of annealed 1mm silver. A thick
(5mm+) brass or bronze backing plate sitting on an anvil is best.

Using shears to cut octagonal blanks so that the disc cutter leaves a
3 to 5mm wide offcut makes a big difference. The cutter has more
trouble expanding the surrounding sheet than in the actual cutting.

Alastair


#9

G’day;

In my experience, using hammers to cut metal discs up to 2mm thick
fron sheet is that I soon thought “There must be a better way” A
press is the obvious, but I couldn’t afford that expense. The next
thing is a decent sized machinists vice. Simply use a piece of
whatever diameter piece of steel sharpened and case - hardened iron
tube. Hold it against one jaw of the vice and the piece of silver
sheet or whatever on a small piece flat wood, and close the vise jaws
slowly until they get a grip. Then swiftly close the vise tightly
with a single part turn. And that’s it.

I made dies from 4mm steel plate, pierced with quite complicated
shapes -( fish; cats, leaves etc.) in the plate with a No.8 saw
blade. Yes, a bit laborious, but once you get the hang of it you
don’t break too many blades. For instance when making a die of an
tiny pair of oak leaves with an acorn (used in a necklace) I broke
about 5 blades. It was the first time I had pierced-sawn thick metal
But the male and female dies must have a positive register. OK I
know there is a system to be bought that uses bigger blades (No.4) bu
I didn’t want to pay for it. Al Cheepo they call me.

As well as other names, like,–

Cheers for now,
JohnB of NZ


#10

Alistair,

Enjoyed your post. I would like to just add to one of your points.

The cutter has more trouble expanding the surrounding sheet than
in the actual cutting. 

This is due to the amount of clearance, or allowance between the
punch and the die.

The tool and die maker when designing a blanking tool, will
determine whether it is the outside/skeleton part, or the slug as an
example that will be saved, and therefore design accordingly to stress
the scrap rather than the required saved part.

If you have a square sheet, and you require a doughnut as an
example, this as you know, is a two stage process.

The first stage would be to cut the main doughnut diameter out of
the sheet, and this will be the saved part.

The outside skeleton will be the scrap. In this instance, the gap or
cutting allowance between the tools will be tight, and the stress will
be taken up by the scrap/skeleton, and in essence, cause the edge of
the cut diameter hole in the skeleton, to bulge up, leaving you with
a nice and clean disk/part.

This happens because the metal wants to flow outwards. In fine
blanking, they will use stinger plates to prevent this from
happening. Very important in a progressive / multi stage die.

Now the opposite comes into play when you want to get a nice hole by
now removing the slug for the center hole of the doughnut. Plastic
deformation is now transferred to the slug which of course becomes
the scrap. We do not want to see the edge of the doughnut hole bulge
like we did on the square sheet, because now the doughnut of course
is the good part. Therefore, the way to control this, is to
essentially have more cutting clearance between the punch and the
die. This causes the slug to dome downwards because the punch is
smaller, and the point of pressure engagement is away from the
cutting or supporting edge of the die. Quite obvious if you think
about it. Instead of pushing metal outwards like in the first Op, this
wants to essentially, push the whole material through the hole but
of course the shearing edge does the job before that happens. Granted
with the thicknesses used in jewellery, this is quite minor, but with
thicker material in industrial applications, it’s a big deal.

Now this of course is using a press with everything aligned on
centre. Manual stuff with a hammer etc where deflection now enters the
mix, is a whole different animal. Theory is the same, but in
practice, another story :slight_smile:

Just thought it may be of interest.

Best regards.
Neil George


#11
A large disc cutter can be manipulated so that the hammer blow
does not have to cut the whole circumference simultaneously.
Depending on how the cutter is constructed it's possible to strike
the cutter off-centre and cut deeper on one side.

This sounds to me like a recipe for the fastest possible way to
wreck your disc cutter! What’s more to the point, the newest Pepe
cutters I’ve seen are machined with the cutting surface at a slight
angle so they aren’t cutting everything simultaneously anyhow. I
thought they were faulty when I first noticed this, then it dawned on
me that it was a good idea.

Happily, there is a press where I teach, so I use that for all but
the smallest discs. But if I did have to use a hammer, this design
should help a lot.

Noel


#12

hey johnb!

do you have photographic “evidence” of this procedure? or pix of your
dies?

this sounds like something that would be…entertaining! …; ^)


#13
Therefore, the way to control this, is to essentially have more
cutting clearance between the punch and the die. This causes the
slug to dome downwards because the punch is smaller, and the point
of pressure engagement is away from the cutting or supporting edge
of the die. 

I think you just explained a mystery which has bugged me. When I cut
a small disc, regardless of which meal, the disc will never fit back
into the hole afterwards. I like to cut a hole in a piece, a
matching one in another metal, then insert the contrasting piece and
solder. I always have to file the little disc down just a bit. In
fact, the disc will not fit back into the hole in the disc punch,
once it is popped out!

Noel


#14

Noel Y and Neil G, your comments are spot-on for a shearing type
cutter. I see in a paper punch (which has a top and bottom die with
the top die passing through the bottom die), the round cutter is
scalloped in order to disperse the shearing force to resemble a
scissors cut, thus reducing the forces.

I’m talking about a wad cutter or leather punch process. The cutter
is forced through the material and there is no shearing as such…the
cutter is done when it has imbedded itself into the backing plate.
The surrounding waste must expand according to the outside bevel on
the cutting edge. This is the most basic and quick’n’nasty method. No
shearing involved; it’s more like hammering a nail through a penny!
(In my youth I hammered a needle through a penny. Couldn’t believe it
was possible, but it is with care and perseverence).

It works. All you need is an iron pipe of suitable diameter bevelled
and case hardened, a backing plate, a big hammer, and an anvil. I
can do the pipe part very quickly, but shearing with a corresponding
bottom die is a whole other story…a machinist process rather than
a crude hand process.

Alastair


#15

I know the Pepe cutters are very nice and each cutter has some sort
of angle on it in relevance to it’s size. They recommend that you
slightly tap the cutter and then turn the top some and repeat. This
is probably the safest way and requires less brute force.

Other options would be using a screw press,hydraulic press, and even
a arbor press with a cheater bar would probably do in a pinch. You
shouldn’t “try” to tilt the cutter top punch. It also seems hard to
do since there is only a few thousandths clearance between the punch
and the die. You also need to realize that commercially made disc
cutters are made to punch a specific thickness range of metal and
also some are designed for ferrous or non ferrous metal. You need to
keep this in mind considering the application you have because a 28
gauge disc will not punch the same as a say 18 gauge disc. Also put
your cutter on a solid surface and wear eye protection at minimum.

Have fun and make Jewelry!
Daniel Wade
IJS


#16

Noel,

I think you just explained a mystery which has bugged me. When I
cut a small disc, regardless of which meal, the disc will never fit
back into the hole afterwards. I like to cut a hole in a piece, a
matching one in another metal, then insert the contrasting piece
and solder. I always have to file the little disc down just a bit.
In fact, the disc will not fit back into the hole in the disc
punch, once it is popped out! 

A progressive die will take advantage of this. They will have 2
stinger plates that secure the material top and bottom. Once the slug
has been cut, an ejector ram from below, will match the retraction of
the ram punch so that the slug remains flat, and pushes the slug back
into the skeleton.

Two fold scenario here depending on the requirements.

  1. The skeleton now, will carry the good part slug on location to
    the next stage in the operation.

  2. The skeleton is the good part, and the slug will re-inforce the
    skeleton and prevent already cut profiles from being distorted during
    further stages of interaction.

Now in your case :-

If you look at the edge of the slug you will notice a few things. The
top edge will have a slight roll over. This comes from the initial
engagement pressure, and it’s approximately the clearance value
between the punch and the die diameters.

Below that, a certain amount of the side wall will have a nice
burnished look to it as it starts to shear. This will vary by how
used the tool is (Sharpness).

As the force continues, the metal will fail and fracture. Now the
interesting thing is that the fractured edge is not a vertical wall
like the burnished section, but actually becomes an angle.

On thicker material, it is more visible to the naked eye, but on
thinner sections not quite so apparent. Here you will have a fracture
depth as well as a fracture angle.

The angle comes again from the clearance values between the tools.
Therefore no wonder they won’t fit :slight_smile:

Next time, remember which is top and bottom, and flip one of them
before re-inserting. This may be easier for you. At the indistrial
level, they have the tonnage to force it back in location regardless
of flipping.

Hope it helps.
Best regards.
Neil George


#17
It also seems hard to do since there is only a few thousandths
clearance between the punch 

Interesting thread - just a reminder that there comes a point where
the best way is a compass or template and a jeweler’s saw… Even
shears, sometimes…


#18

Alistair,

Noel Y and Neil G, your comments are spot-on for a shearing type
cutter. 

Thank you.

I see in a paper punch (which has a top and bottom die with the top
die passing through the bottom die), the round cutter is scalloped
in order to disperse the shearing force to resemble a scissors cut,
thus reducing the forces. 

Add to your points

I would say that the scallop is more to obtain a sharper cutting
edge primerily, and secondly, to allow a recess for material to move
into. Thin paper wouldn’t require much of a scallop as an individual
sheet, but stacked or using thicker sheet would. Material thickeness
would be goverened by the depth of the scallop. What happens with
thicker material, is that before the cutting edge comes into effect,
there is some compression of the material and this needs somewhere to
go, which is why, on production hang tag hole punching machines, the
punches are completely hollow. The Slug, or Chad in this case gets
sucked through the tool and clear of the process. On stacked material,
the scalloped edge or fully hollowed punch, technically allows the
cutter to cut the first sheet and get things started and as you
pointed out nice and easy with sufficient clearance. The last thing
you need is to start dragging the material and causing it to tear
rather than cut.

I'm talking about a wad cutter or leather punch process. The
cutter is forced through the material and there is no shearing as
such...the cutter is done when it has imbedded itself into the
backing plate. The surrounding waste must expand according to the
outside bevel on the cutting edge. This is the most basic and
quick'n'nasty method. No shearing involved; it's more like
hammering a nail through a penny! 

Well I guess that trully was a penny for your thoughts :slight_smile: Wadcutters
and leather hole punches are both soft material processes and remind
me of Dinking Dies in application.

Although they do pierce the material, they are more of a forming
strategy than an actual cutting one for the sake of argument.
Interesting read just the same. Well for me anyway :slight_smile:

Best Regards.
Neil George


#19
    A progressive die will take advantage of this. They will have
    2 stinger plates that secure the material top and bottom. 
I have no idea what a stinger plate is... and I'm sure I'm not
the only one. 

Noel


#20

Noel,

I have no idea what a stinger plate is... and I'm sure I'm not the
only one. 

Think of this as a plate with a V protrussion. ----^ This will
have the same profile as the punch (meaning follow the hole contour
100%), except offset from the hole by a value of approximately 50% of
material thickness. Maintains flatness and restricts lateral movement
in the material.

Used in Fine Blanking, and not really a requirement for what you do.

Best Regards.
Neil George