In this pic, you can see a cam that operates a lever that is part of a wire
cutter. This is an old pic and we now use a roller instead of a cam but the
chain drive is the same. I want to replace this whole drive mechanism with an
air cylinder to move that lever. I roughly figure a 2" bore x 1" stroke will
have enough guts.

http://metalworking.com/Dropbox/_200...ob290-head.JPG

I need the cut timed within one degree of rotation of the same 1" shaft that
drives the chain. I want to be able to easily adjust the timing and have
adjustable dwell. Is there an off-shelf item to do this? I will need two
separate operation switches on the shaft.

I currently use an air limit switch on the other mechanism driven by a cam that
I constructed and we have to replace those switches four times a year due to
failure. Would electrical limit switches and solenoid valves be more reliable?

We are building the third of these machines. The first two are constantly
scheduled for overtime and weekends. The logs show less than 70% up-time due to
all sorts of little issues that we are addressing on the third machine. I'd
like to target 90%+ up-time, that would fall in line with what other machines
log.

(tempest in a teapot---I'm the largest manufacturer of these items in the whole
WORLD)

On Mon, 7 Jul 2008 23:27:43 -0400, "Tom Gardner"
wrote:

In this pic, you can see a cam that operates a lever that is part of a wire
cutter. This is an old pic and we now use a roller instead of a cam but the
chain drive is the same. I want to replace this whole drive mechanism with an
air cylinder to move that lever. I roughly figure a 2" bore x 1" stroke will
have enough guts.

http://metalworking.com/Dropbox/_200...ob290-head.JPG

I need the cut timed within one degree of rotation of the same 1" shaft that
drives the chain. I want to be able to easily adjust the timing and have
adjustable dwell. Is there an off-shelf item to do this? I will need two
separate operation switches on the shaft.

There's this...
http://www.candycontrols.com/Switch/Switch_EMM.htm
and I know I've seen other brands, but can't think of the names right
now.

The traditional way to adjust the timing and dwell of a cam is to use
a pair of plate cams sandwiched together by a clamping hub. Here's a
photo of a camshaft on a spring winding machine I tooled up. Someone
else made the fancy graduated hubs - I doubt anyone ever really looked
at the numbers.
http://www.suscom-maine.net/~nsimmon...leeperCams.jpg

If you can get away with a homing routine at startup, a quadrature
counter or a cheap PLC and an encoder would also work. If you're sure
the shaft will never turn backwards, then the quadrature is
unecessary.

--
Ned Simmons

On Tue, 08 Jul 2008 00:32:34 -0400, Ned Simmons
wrote:



The traditional way to adjust the timing and dwell of a cam is to use
a pair of plate cams sandwiched together by a clamping hub.

I should have mentioned, if it's not obvious, the dwell is adjusted by
changing the overlap of the plate cams. The cams are usually identical
so you get a 2:1 adjustment in dwell.

--
Ned Simmons

Ned Simmons writes:

Someone else made the fancy graduated hubs ...

Those are stock items, or somebody actually engraved them?

Tom Gardner writes:

(tempest in a teapot---I'm the largest manufacturer of these items in
the whole WORLD)

Indeed, some can boast of being the world's largest because they are the
world's only manufacturer of certain niche items. Niches are nice.

"Tom Gardner" wrote:

In this pic, you can see a cam that operates a lever that is part of a wire
cutter. This is an old pic and we now use a roller instead of a cam but the
chain drive is the same. I want to replace this whole drive mechanism with an
air cylinder to move that lever. I roughly figure a 2" bore x 1" stroke will
have enough guts.

http://metalworking.com/Dropbox/_200...ob290-head.JPG

I cant get that picture to load but google programmable limit switches. They use an
rotary encoder connected to a control box which provides the switching.

Wes

Tom,
Switches are a non-starter. You will never get the cycle rates you are
looking for. I suggest you keep it simple and stick to hall effect sensors,
amplifier and a solid state switch. Then drive a mechanical solution like an
electrical clutch and brake or a simple dog clutch and latch or if the lever
forces are not so high, a simple electrical solenoid. Avoid optical sensors
in a contaminated environment, because dirt will get you. Hall effect
sensors work in all conditions. Resolve the problem with simple electronics.
I would not use pneumatics, as response times are poor and leaks are a
pain.. If you use a solid state magnetic solution, be wary of back emf
reverse biasing the solid state switch and use a diode of reverse polarity
across the coil.
Steve

"Tom Gardner" wrote in message
...
In this pic, you can see a cam that operates a lever that is part of a
wire cutter. This is an old pic and we now use a roller instead of a cam
but the chain drive is the same. I want to replace this whole drive
mechanism with an air cylinder to move that lever. I roughly figure a 2"
bore x 1" stroke will have enough guts.

http://metalworking.com/Dropbox/_200...ob290-head.JPG

I need the cut timed within one degree of rotation of the same 1" shaft
that drives the chain. I want to be able to easily adjust the timing and
have adjustable dwell. Is there an off-shelf item to do this? I will
need two separate operation switches on the shaft.

I currently use an air limit switch on the other mechanism driven by a cam
that I constructed and we have to replace those switches four times a year
due to failure. Would electrical limit switches and solenoid valves be
more reliable?

We are building the third of these machines. The first two are constantly
scheduled for overtime and weekends. The logs show less than 70% up-time
due to all sorts of little issues that we are addressing on the third
machine. I'd like to target 90%+ up-time, that would fall in line with
what other machines log.

(tempest in a teapot---I'm the largest manufacturer of these items in the
whole WORLD)

"Steve Lusardi" fired this volley in
:

Tom,
Switches are a non-starter. You will never get the cycle rates you are
looking for. I suggest you keep it simple and stick to hall effect
sensors, amplifier and a solid state switch.

I'd like to suggest an alternative. Hall Effect sensors work reliably,
but they're difficult to use in a mechanism requiring as tight an off-to-
on angle of rotation as he requires. They're better for things like
sensing rotation speed, or locating a position that's not so critical as
Tom requires.

The alternative, and one that works well in millions (yes millions) of
consumer machines, that works in hostile, hot, dirty environments; that
can sense angles as small as 1/10th degree easily, and can easily be made
to have adjustable dwell is: A controlled-reluctance sensor.

Pole width determines positional accuracy. Dwell can be established by
distance to the sensed cam or by electronic means.

The cost is a bit more than Hall Effect types, because you'll require
more electronics to sense and condition the signal. But it's minimal
compared to the advantages they offer.

Just because you have a dirty environment doesn't rule out the use of
optical choppers. Proper positioning can keep them clean in most
applications. And they're the simplest of all types, providing all the
features Tom wants without any complex 'tronix.

LLoyd

"Richard J Kinch" wrote in message
. ..
Tom Gardner writes:

(tempest in a teapot---I'm the largest manufacturer of these items in
the whole WORLD)

Indeed, some can boast of being the world's largest because they are the
world's only manufacturer of certain niche items. Niches are nice.

I only have two more manufacturers domestically in the market and they have
very small capacity. When I bring the next machine on line, I'll offer them
pricing that would make it a no-brainer make/buy decision.

These brushes are made with .115" x .017" flat wire and it's a royal bitch to
work with. We've been lucky to find ways to handle it and do it fast. The
Chinese aren't interested in such a small niche but they sure ate my lunch on
most of the "standard" high volume items.

On Jul 7, 11:27*pm, "Tom Gardner" wrote:
In this pic, you can see a cam that operates a lever that is part of a wire
cutter. *This is an old pic and we now use a roller instead of a cam but the
chain drive is the same. *I want to replace this whole drive mechanism with an
air cylinder to move that lever. *I roughly figure a 2" bore x 1" stroke will
have enough guts.

http://metalworking.com/Dropbox/_200...ob290-head.JPG

I need the cut timed within one degree of rotation of the same 1" shaft that
drives the chain. *I want to be able to easily adjust the timing and have
adjustable dwell. *Is there an off-shelf item to do this? *I will need two
separate operation switches on the shaft.

I currently use an air limit switch on the other mechanism driven by a cam that
I constructed and we have to replace those switches four times a year due to
failure. *Would electrical limit switches and solenoid valves be more reliable?

We are building the third of these machines. *The first two are constantly
scheduled for overtime and weekends. *The logs show less than 70% up-time due to
all sorts of little issues that we are addressing on the third machine. *I'd
like to target 90%+ up-time, that would fall in line with what other machines
log.

The most reliable and accurate way would be to replace the cams with
an rotary optical
encoder and electronic cam switch. One unit will do both switch
operations. Adjustments
are all done in software so changing timing is quite simple.



(tempest in a teapot---I'm the largest manufacturer of these items in the whole
WORLD)

On Tue, 08 Jul 2008 01:06:29 -0500, Richard J Kinch
wrote:

Ned Simmons writes:

Someone else made the fancy graduated hubs ...

Those are stock items, or somebody actually engraved them?

I'm pretty sure they were shop-made. My customer bought the machine to
produce a family of parts for a competitor who needed a second source
as they transitioned to offshore production. The competitor
reconditioned the machine for my customer and made some improvements
to it, several of which had the character of those graduated hubs.
They had a beautiful toolroom turning out all sorts of lovely
overcomplicated little gadgets. It was so pervasive, I came to believe
that culture of overcomplication was likely a contributing factor to
the plant being closed.

--
Ned Simmons