Take a look: http://www.metalworking.com/DropBox/wire_cutter.jpg
This rough drawing shows a cutter to cut 3" pieces of flat steel wire, 3 at
a time, every 0.5 seconds. The wire is advanced through the block between
the two shown 3/4" x 3/4" x 1/4" carbide inserts. Notice the notch in the
lower insert. The arm pivots on a 3/4" shaft in 2 Timken bearings in the
bored hole in the block nearest the step. The other bored hole has bearings
for the 1" shaft that has a cam follower with a 5/16" offset to act as an
actuator cam -not shown. The cutter arm also has a 3/4" x 3/4" x 1/4"
carbide insert. As the cam makes the arm pivot the wire is cut and a spring
returns it to the open position.

The part I need thoughts on are how to pre-load the carbides in such a way
that it is easy to unload to change the carbides...(notice I get 8 cutting
edges on each insert!) The lower carbide should last almost forever as it
is not used in cutting and has the guide notch ground into it. I wonder how
much pre-load is needed on the carbides, they will be sliding on each
other's faces. One thought is to have the carbides backed up with a block
of steel that slides in a cut-out in the main block but can be clamped
tightly and have a differential screw apply the loading pressure then clamp
the sliding block. The goal is to be able to change the carbides in a few
minutes and have a positive, easily adjustable and reproducible pre-load.
Oh, by the way, the assembly is not extremely accessible. I figure if the
carbides are real easy to change, they will last a long time and if it takes
an hour, they will need to be changed often...Right?

"Tom Gardner" wrote in message
m...
Take a look: http://www.metalworking.com/DropBox/wire_cutter.jpg

Tom,

Neat gadget. Have you already decided on the inserts, or are you open to
suggestions? You can buy inserts with holes for a securing screw. The screws
aren't cheap, but they're not crazy and that would be a quick way to index
them.

It would probably be a good idea to have the inserts nested in the block.
When we build our dies with steel punches and trim steels, we go to great
lengths to have solid steel/cast iron support (shoulders or keys) in every
steel in order to keep them from moving. Carbide would be significantly more
susceptable to failure due to a sloppy fit.

I would not have the carbide inserts sliding against each other, if you can
avoid it. This rubbing will cause premature failure, as well as excessive
stress on the arm and base block. While rubbing will give you the advantage
of nearly zero burr, your insert life will be shorter.

I'm not sure what an ideal clearance between your inserts would be.
Typically, 10% of material thickness is used in many punching operations,
but you may find that this much clearance will create a massive burr, deform
the end of your wire, and smear metal on your inserts (causing premature
failure and nasty cuts). Ideally, you could make some shims and try out
different clearances.

As your clearance increases, the required force should decrease, which
should increase the lifetime of the wear components within your tool
(bearings, inserts, wear surface on arm, cam, motor, etc.)

Finally, I would take care to make sure there is no slop in your tool at
all. Again, if things don't fit correctly this will cause premature failure
(which can be fun when it's burried inside some monster machine).

Just my $0.02 worth.

Regards,

Robin

"Robin S." wrote in message
.. .

"Tom Gardner" wrote in message
m...
Take a look: http://www.metalworking.com/DropBox/wire_cutter.jpg

Tom,

Neat gadget. Have you already decided on the inserts, or are you open to
suggestions? You can buy inserts with holes for a securing screw. The
screws aren't cheap, but they're not crazy and that would be a quick way
to index them.

Screws would mean complete dissassembly to change.

It would probably be a good idea to have the inserts nested in the block.
When we build our dies with steel punches and trim steels, we go to great
lengths to have solid steel/cast iron support (shoulders or keys) in every
steel in order to keep them from moving. Carbide would be significantly
more susceptable to failure due to a sloppy fit.

I have the inserts shown floating out of their pockets for clairity, imagine
they are seated and clamped.

I would not have the carbide inserts sliding against each other, if you
can avoid it. This rubbing will cause premature failure, as well as
excessive stress on the arm and base block. While rubbing will give you
the advantage of nearly zero burr, your insert life will be shorter.

I have a similar cutter with the wire passing through a hole in in 1/2"
round carbides. They have to be but-tight to each other or the hard steel
wire forces them apart and destroys the carbides and leaves a bad burr.

I'm not sure what an ideal clearance between your inserts would be.
Typically, 10% of material thickness is used in many punching operations,
but you may find that this much clearance will create a massive burr,
deform the end of your wire, and smear metal on your inserts (causing
premature failure and nasty cuts). Ideally, you could make some shims and
try out different clearances.

As your clearance increases, the required force should decrease, which
should increase the lifetime of the wear components within your tool
(bearings, inserts, wear surface on arm, cam, motor, etc.)

All the wear should be on the carbides. My target is anything better than
125,000 cuts or a week.


Finally, I would take care to make sure there is no slop in your tool at
all. Again, if things don't fit correctly this will cause premature
failure (which can be fun when it's burried inside some monster machine).

Just the flex in the arm is enough to demand a pre-load.

Just my $0.02 worth.

Regards,

Robin

"Tom Gardner" wrote in message
...


Screws would mean complete dissassembly to change.

I can see the upper insert being clamped with some type of over-arm, but it
looks like there's no room for any type of clamping system which sits proud
of the lower insert.

I'll assume there are other components which prevent the arm from swiveling
to a vertical position (which could clear both inserts)?


I have the inserts shown floating out of their pockets for clairity,
imagine they are seated and clamped.

I understand what you drew, but I thought I should emphasize the importance
of a good fit.


I have a similar cutter with the wire passing through a hole in in 1/2"
round carbides. They have to be but-tight to each other or the hard steel
wire forces them apart and destroys the carbides and leaves a bad burr.

I stand corrected. In sheet metal work, trim steels never touch because of
the increased tonnage and reduced life of the cutting edge.


All the wear should be on the carbides. My target is anything better than
125,000 cuts or a week.

In my experience (heavy stamping dies), anything which moves will wear.
While the inserts will no doubt show excessive wear, having a sloppy fit or
soft bearing surfaces (cam and lever arm) will probably cause premature
failure and rework. Of course, I've never worked with wire...

Regards,

Robin

"Robin S." wrote in message
. ..

"Tom Gardner" wrote in message
...


Screws would mean complete dissassembly to change.

I can see the upper insert being clamped with some type of over-arm, but
it looks like there's no room for any type of clamping system which sits
proud of the lower insert.

I haven't done any virtual cuts yet but imaging an end cap, like on the arm,
clamping the inserts into place. I'm thinking of a sliding piece that
backs-up the carbides then clamp the **** out of them.


I'll assume there are other components which prevent the arm from
swiveling to a vertical position (which could clear both inserts)?

But of course! The block is kinda' buried and the block is bolted onto a
flat apron from underneath.


I have the inserts shown floating out of their pockets for clairity,
imagine they are seated and clamped.

I understand what you drew, but I thought I should emphasize the
importance of a good fit.

Oh yea! On the other cutter with the round inserts I had to make hardened
pockets for the carbides. The first iteration was cold-roll and deformed
like wet clay in a few months.


I have a similar cutter with the wire passing through a hole in in 1/2"
round carbides. They have to be but-tight to each other or the hard
steel wire forces them apart and destroys the carbides and leaves a bad
burr.

I stand corrected. In sheet metal work, trim steels never touch because of
the increased tonnage and reduced life of the cutting edge.


All the wear should be on the carbides. My target is anything better
than 125,000 cuts or a week.

In my experience (heavy stamping dies), anything which moves will wear.
While the inserts will no doubt show excessive wear, having a sloppy fit
or soft bearing surfaces (cam and lever arm) will probably cause premature
failure and rework. Of course, I've never worked with wire...

I'll use a McGill follower for the activator and ride it on a Stelite
surface. Nothing lasts forever so I want the wear parts to be off the shelf
rather than make them.


Regards,

Robin

"Tom Gardner" wrote in
m:

Can you preload via pneumatics or a mechanical spring (say belville
springs) with an adjustable solid stop on the backside to prevent over
stressing the components?





--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

http://www.machines-cnc.net:81/

Good thought! Aren't Belvill's cool?

"Anthony" wrote in message
. ..
"Tom Gardner" wrote in
m:

Can you preload via pneumatics or a mechanical spring (say belville
springs) with an adjustable solid stop on the backside to prevent over
stressing the components?





--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

http://www.machines-cnc.net:81/

"Tom Gardner" wrote in news:raPBe.2579
:

Good thought! Aren't Belvill's cool?


I use them in a lot of fixture and automation designs. Very versatile if
you keep the design constraints of belvilles in mind.


--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

http://www.machines-cnc.net:81/

On Thu, 14 Jul 2005 18:50:40 +0000, Tom Gardner wrote:


The part I need thoughts on are how to pre-load the carbides in such a way
that it is easy to unload to change the carbides...(notice I get 8 cutting
edges on each insert!)

Tom, this might be a crazy idea, but I wonder if it'd be too complicated
to incorporate a mechanism to rotate the cutter 90 degrees on each return
stroke, thereby presenting a "new" cutting edge to the work on each cutting
stroke. This would make the cutter last 4 times as long between changes,
requiring the cutter only to be flipped over when dulled. I'm imagining some
sort of a ratchet/indexing mechanism.

In article ,
says...
On Thu, 14 Jul 2005 18:50:40 +0000, Tom Gardner wrote:


The part I need thoughts on are how to pre-load the carbides in such a way
that it is easy to unload to change the carbides...(notice I get 8 cutting
edges on each insert!)

Tom, this might be a crazy idea, but I wonder if it'd be too complicated
to incorporate a mechanism to rotate the cutter 90 degrees on each return
stroke, thereby presenting a "new" cutting edge to the work on each cutting
stroke. This would make the cutter last 4 times as long between changes,
requiring the cutter only to be flipped over when dulled. I'm imagining some
sort of a ratchet/indexing mechanism.



With the right details it's possible to do this passively.
The rotating tools need to have a circular form and the
force that drives the rotation is usually a result of
placing the cut point somewhat off center. I've built
cutters for tungsten wire (tungsten is horribly abrasive)
that operate up to 1800 pieces per minute with auto-
rotating tools.

Ned Simmons

On Fri, 15 Jul 2005 12:52:32 -0400, Ned Simmons wrote:

In article ,
says...
On Thu, 14 Jul 2005 18:50:40 +0000, Tom Gardner wrote:


The part I need thoughts on are how to pre-load the carbides in such a way
that it is easy to unload to change the carbides...(notice I get 8 cutting
edges on each insert!)

Tom, this might be a crazy idea, but I wonder if it'd be too complicated
to incorporate a mechanism to rotate the cutter 90 degrees on each return
stroke, thereby presenting a "new" cutting edge to the work on each cutting
stroke. This would make the cutter last 4 times as long between changes,
requiring the cutter only to be flipped over when dulled. I'm imagining some
sort of a ratchet/indexing mechanism.



With the right details it's possible to do this passively.
The rotating tools need to have a circular form and the
force that drives the rotation is usually a result of
placing the cut point somewhat off center. I've built
cutters for tungsten wire (tungsten is horribly abrasive)
that operate up to 1800 pieces per minute with auto-
rotating tools.

Yes, that's much better for a number of reasons. When I was writing up
my description I was thinking what a waste it was to not be able to
use up all of the cutting edge on each face of the square cutter. With a
passively rotating circular cutter, much more of the total cutting surface
can be exploited. I would think that another advantage to an offset
circular cutter would be in its cutting action; more of a slicing
action than a chopping action (think of the angle on a guillotine
blade), potentially reducing burrs and reducing the power needed
to make the cut (and that saved power can be translated
into increased speed).

In article ,
says...
On Fri, 15 Jul 2005 12:52:32 -0400, Ned Simmons wrote:

In article ,
says...
On Thu, 14 Jul 2005 18:50:40 +0000, Tom Gardner wrote:


The part I need thoughts on are how to pre-load the carbides in such a way
that it is easy to unload to change the carbides...(notice I get 8 cutting
edges on each insert!)

Tom, this might be a crazy idea, but I wonder if it'd be too complicated
to incorporate a mechanism to rotate the cutter 90 degrees on each return
stroke, thereby presenting a "new" cutting edge to the work on each cutting
stroke. This would make the cutter last 4 times as long between changes,
requiring the cutter only to be flipped over when dulled. I'm imagining some
sort of a ratchet/indexing mechanism.



With the right details it's possible to do this passively.
The rotating tools need to have a circular form and the
force that drives the rotation is usually a result of
placing the cut point somewhat off center. I've built
cutters for tungsten wire (tungsten is horribly abrasive)
that operate up to 1800 pieces per minute with auto-
rotating tools.

Yes, that's much better for a number of reasons. When I was writing up
my description I was thinking what a waste it was to not be able to
use up all of the cutting edge on each face of the square cutter. With a
passively rotating circular cutter, much more of the total cutting surface
can be exploited. I would think that another advantage to an offset
circular cutter would be in its cutting action; more of a slicing
action than a chopping action (think of the angle on a guillotine
blade), potentially reducing burrs and reducing the power needed
to make the cut (and that saved power can be translated
into increased speed).


Exactly, but you have to be careful how far off center you
go or you can have problems with the wire slipping out of
the desired nip point as the shearing angle between the
blades gets too large.

Ned Simmons

"Artemia Salina" wrote in message
news
On Thu, 14 Jul 2005 18:50:40 +0000, Tom Gardner wrote:


The part I need thoughts on are how to pre-load the carbides in such a
way
that it is easy to unload to change the carbides...(notice I get 8
cutting
edges on each insert!)

Tom, this might be a crazy idea, but I wonder if it'd be too complicated
to incorporate a mechanism to rotate the cutter 90 degrees on each return
stroke, thereby presenting a "new" cutting edge to the work on each
cutting
stroke. This would make the cutter last 4 times as long between changes,
requiring the cutter only to be flipped over when dulled. I'm imagining
some
sort of a ratchet/indexing mechanism.


Good thinking but it would be difficult to get the rigidity. I'd be happy
to just flip the carbides once a week in 5 minutes or so.

Tom Gardner wrote:
"Robin S." wrote in message
. ..

"Tom Gardner" wrote in message
om...


Screws would mean complete dissassembly to change.

I can see the upper insert being clamped with some type of over-arm, but
it looks like there's no room for any type of clamping system which sits
proud of the lower insert.

Any chance of brazing the cutter to a holder that has a recess that will
support the carbide?

John

Tom Gardner wrote:

Take a look: http://www.metalworking.com/DropBox/wire_cutter.jpg
This rough drawing shows a cutter to cut 3" pieces of flat steel
wire, 3 at a time, every 0.5 seconds. The wire is advanced
through the block between the two shown 3/4" x 3/4" x 1/4"
carbide inserts. [...]

You also wrote "The block is kinda' buried and the block is
bolted onto a flat apron from underneath" but if perchance
you have access to the back side adjacent to the white end
(of the upper-right block in diagram), maybe the following
would work: Instead of just a recess, cut all the way through;
braze the square carbide inserts on to a length of square key
stock. Use clamp bolts through the block top like on a lathe
tool holder. To change cutting edge, loosen bolts, slide
stock out the back, rotate 90, slide back in, tighten bolts.

Alternately, leave the recess as shown; cut the block
between the insert end and the bushing bore; bolt that
part to the apron from above rather than underneath; to
change the inserts, unbolt the block part, pull it out,
change the inserts, and bolt back in.

Re the moving arm, preload, and clearance -- if you
tilt the axle forward 1 degree and mount the guide
carbide at matching angle, you could have 0 clearance
when the moving carbide hits the wire, and a few
thousandths of clearance at end of cut. Or negative
clearance at start of cut, and 0 clearance at end.

You wrote somewhere that cutters "have to be but-tight
to each other or the hard steel wire forces them apart
and destroys the carbides and leaves a bad burr." Would
it decrease wear if the center of the carbide face were
relieved? Also, how much difference in cutter life and
burring does rake angle make?

-jiw

"James Waldby" wrote in message
...
Tom Gardner wrote:

Take a look: http://www.metalworking.com/DropBox/wire_cutter.jpg
This rough drawing shows a cutter to cut 3" pieces of flat steel
wire, 3 at a time, every 0.5 seconds. The wire is advanced
through the block between the two shown 3/4" x 3/4" x 1/4"
carbide inserts. [...]

You also wrote "The block is kinda' buried and the block is
bolted onto a flat apron from underneath" but if perchance
you have access to the back side adjacent to the white end
(of the upper-right block in diagram), maybe the following
would work: Instead of just a recess, cut all the way through;
braze the square carbide inserts on to a length of square key
stock. Use clamp bolts through the block top like on a lathe
tool holder. To change cutting edge, loosen bolts, slide
stock out the back, rotate 90, slide back in, tighten bolts.

Alternately, leave the recess as shown; cut the block
between the insert end and the bushing bore; bolt that
part to the apron from above rather than underneath; to
change the inserts, unbolt the block part, pull it out,
change the inserts, and bolt back in.

Re the moving arm, preload, and clearance -- if you
tilt the axle forward 1 degree and mount the guide
carbide at matching angle, you could have 0 clearance
when the moving carbide hits the wire, and a few
thousandths of clearance at end of cut. Or negative
clearance at start of cut, and 0 clearance at end.

You wrote somewhere that cutters "have to be but-tight
to each other or the hard steel wire forces them apart
and destroys the carbides and leaves a bad burr." Would
it decrease wear if the center of the carbide face were
relieved? Also, how much difference in cutter life and
burring does rake angle make?

-jiw

A burr causes problems after the cut. The wire then gets bent 180 deg.,
like a Bobby pin, then gets a 1/2" long 16 ga. staple and jammed into a hole
in a block of wood. 98 of these tufts make a grill cleaning brush. A burr
will cause the cut wire to drag a little on one side or the other and the
bend won't be in the center.