I'm involved with a repair project to restore an old
sickle bar hay mower that may be about 50 years
old. The manufacturer is unknown and there is no
parts manual either. The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.
The drive lugs are gone and someone in the past
welded the two parts of the clutch together! Not
good! So I made a replacement unit but I don't know
what the angles of the drive lugs should be. The two
halves are held in engagement by a heavy spring.
I can't find any info on the web about this unit so
I'm guessing for a start that the angle of contact is
45 deg simply because I had a cutter to do that.
Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas

On Jul 11, 6:57*pm, "Phil Kangas" wrote:
The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.

The two
halves are held in engagement by a heavy spring.

Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas

I think I understand what you are talking about. A torque limiter so
if something get stuck between the teeth of the mower, the " clutch "
will slip.
I think one could calculate the angle if one knew the spring rate of
the spring and the torque it should slip at. But you probably do not
know either of those things.

Do you think it would be good if it took 70 % more force before it
ratchets?
If so then use 30 degrees. If it were me, I would change the angle of
the parts you made. Would not be as strong and would have a lot of
backlash, but would give you another data point, and if if breaks then
you can make another.

If you think 70 % more is not the right amount, let me know and I will
make another back of an envelop calculation.


Dan

"Phil Kangas" wrote in message
...
I'm involved with a repair project to restore an old
sickle bar hay mower that may be about 50 years
old. The manufacturer is unknown and there is no
parts manual either. The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.
The drive lugs are gone and someone in the past
welded the two parts of the clutch together! Not
good! So I made a replacement unit but I don't know
what the angles of the drive lugs should be. The two
halves are held in engagement by a heavy spring.
I can't find any info on the web about this unit so
I'm guessing for a start that the angle of contact is
45 deg simply because I had a cutter to do that.
Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas

I've seen one of those before and was told it was a torque
limiting clutch. Googling gives a bunch of hits but I didn't
see exactly what you are describing. Maybe you could
update it with something more readily available?
Art

"Phil Kangas" wrote:

I'm involved with a repair project to restore an old
sickle bar hay mower that may be about 50 years
old. The manufacturer is unknown and there is no
parts manual either. The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.
The drive lugs are gone and someone in the past
welded the two parts of the clutch together! Not
good! So I made a replacement unit but I don't know
what the angles of the drive lugs should be. The two
halves are held in engagement by a heavy spring.
I can't find any info on the web about this unit so
I'm guessing for a start that the angle of contact is
45 deg simply because I had a cutter to do that.
Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas




Not sure if this will help you but on chip conveyors for CNC's, there is often a couple
disks with steel balls held captive in less than 1/2 diameter deep holes forced together
by a strong spring. If all goes well, torque is applied, we get a chip jam, the balls and
spring cause the plates to move away from each other protecting the drive system. Too
late for me to draw you a picture.

Night,

Wes
--
"Additionally as a security officer, I carry a gun to protect
government officials but my life isn't worth protecting at home
in their eyes." Dick Anthony Heller

Dan Caster
wrote in message
On Jul 11, 6:57 pm, "Phil Kangas" wrote:
The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.

The two
halves are held in engagement by a heavy spring.

Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas

I think I understand what you are talking about. A torque
limiter so
if something get stuck between the teeth of the mower, the "
clutch "
will slip.
I think one could calculate the angle if one knew the spring
rate of
the spring and the torque it should slip at. But you
probably do not
know either of those things.

Do you think it would be good if it took 70 % more force
before it
ratchets?
If so then use 30 degrees. If it were me, I would change
the angle of
the parts you made. Would not be as strong and would have a
lot of
backlash, but would give you another data point, and if if
breaks then
you can make another.

If you think 70 % more is not the right amount, let me know
and I will
make another back of an envelop calculation.


Dan


This part may be coming back in a day or two and if it does
then I'll
try 30 deg. Art is probably right that it is called a torque
limiting
clutch but the web is useless on finding details on it. New
parts are
out of the question, gotta stay cheap you know..;)) It's
good to hear
your feedback so I can get on the right track here. Thanks.
phil

On 07/11/2010 04:45 PM, wrote:
On Jul 11, 6:57 pm, "Phil wrote:
The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.

The two
halves are held in engagement by a heavy spring.

Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas

I think I understand what you are talking about. A torque limiter so
if something get stuck between the teeth of the mower, the " clutch "
will slip.
I think one could calculate the angle if one knew the spring rate of
the spring and the torque it should slip at. But you probably do not
know either of those things.

Do you think it would be good if it took 70 % more force before it
ratchets?
If so then use 30 degrees. If it were me, I would change the angle of
the parts you made. Would not be as strong and would have a lot of
backlash, but would give you another data point, and if if breaks then
you can make another.

If you think 70 % more is not the right amount, let me know and I will
make another back of an envelop calculation.


Dan

Stronger spring?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

On 07/11/2010 03:57 PM, Phil Kangas wrote:
I'm involved with a repair project to restore an old
sickle bar hay mower that may be about 50 years
old. The manufacturer is unknown and there is no
parts manual either. The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.
The drive lugs are gone and someone in the past
welded the two parts of the clutch together! Not
good! So I made a replacement unit but I don't know
what the angles of the drive lugs should be. The two
halves are held in engagement by a heavy spring.
I can't find any info on the web about this unit so
I'm guessing for a start that the angle of contact is
45 deg simply because I had a cutter to do that.
Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas

You can't tell by inspecting the old part, or by sawing the old part
apart to see?

I agree with the rest of the responders that this is probably a torque
limiting clutch. It sounds like someone was being very aggressive with
the mower to wear it out -- then to put a penny behind the mechanical
fuse, as it were. I'd check the rest of the mower for subsequent
breakage, or for worn parts that are absorbing way too much power.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

"Wes" wrote in message "Phil Kangas" wrote:

I'm involved with a repair project to restore an old
sickle bar hay mower that may be about 50 years
old. The manufacturer is unknown and there is no
parts manual either. The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.
The drive lugs are gone and someone in the past
welded the two parts of the clutch together! Not
good! So I made a replacement unit but I don't know
what the angles of the drive lugs should be. The two
halves are held in engagement by a heavy spring.
I can't find any info on the web about this unit so
I'm guessing for a start that the angle of contact is
45 deg simply because I had a cutter to do that.
Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas




Not sure if this will help you but on chip conveyors for
CNC's, there is often a couple
disks with steel balls held captive in less than 1/2
diameter deep holes forced together
by a strong spring. If all goes well, torque is applied,
we get a chip jam, the balls and
spring cause the plates to move away from each other
protecting the drive system. Too
late for me to draw you a picture.

Night,

Wes

I know what you're talking about here, Wes. The lead screw
on my
turnpro 13x40 is set up like that. Might be too light for
this mower
though. One thought comes to mind and that is maybe the
owner
was curious about what I did and took it apart and might
have lost the anchor key behind the adjusting nut. He did
say the
nut came off twice! That would relieve the spring, eih?
Something
is not right here. I'll let you know what happens....
phil

Phil Kangas wrote:
Dan Caster
wrote in message
On Jul 11, 6:57 pm, "Phil Kangas" wrote:
The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.

The two
halves are held in engagement by a heavy spring.

Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas

This is usually called a slip clutch. most clutches like this have the
same angle on the used side of the tooth as on the unused side, so can
you tell the angle on the unused side. Is the spring setup so you can
compress it more or add washers behind it?

On Jul 11, 3:57*pm, "Phil Kangas" wrote:
I'm involved with a repair project to restore an old
sickle bar hay mower that may be about 50 years
old. The manufacturer is unknown and there is no
parts manual either. The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.
The drive lugs are gone and someone in the past
welded the two parts of the clutch together! Not
good! So I made a replacement unit but I don't know
what the angles of the drive lugs should be. The two
halves are held in engagement by a heavy spring.
I can't find any info on the web about this unit so
I'm guessing for a start that the angle of contact is
45 deg simply because I had a cutter to do that.
Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas

Phil, is the wooden pitman arm still on the mower? This is the
secondary safety point on old mowers. It will break if the slip clutch
doesn't slip. On old mowers, the wooden arm is usually rotten after
being outside in the weather for a few years. It may also have been
replaced by a steel arm.

Probably someone was mowing brush with the mower and jammed the cycle
bar one too many times and decided to fix it good and for ever!

I loved watching the cut grass fall behind the cycle bar until I ran
through a phesant's nest and cut the legs off the hen. Cats also were
a problem.

Paul

Artemus wrote:
"Phil Kangas" wrote in message
...
I'm involved with a repair project to restore an old
sickle bar hay mower that may be about 50 years
old. The manufacturer is unknown and there is no
parts manual either. The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.
The drive lugs are gone and someone in the past
welded the two parts of the clutch together! Not
good! So I made a replacement unit but I don't know
what the angles of the drive lugs should be. The two
halves are held in engagement by a heavy spring.
I can't find any info on the web about this unit so
I'm guessing for a start that the angle of contact is
45 deg simply because I had a cutter to do that.
Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas

I've seen one of those before and was told it was a torque
limiting clutch. Googling gives a bunch of hits but I didn't
see exactly what you are describing. Maybe you could
update it with something more readily available?
Art




Sprag clutch?

http://hrsbstaff.ednet.ns.ca/bvogel/...tarter_clutch/



In searching for the above, I also turned up this little gem!
Automatic Transmission/Transaxle Flash Animations

http://www.jameshalderman.com/data/flash/a2.htm

I thought it was interesting enough to present here.

--

Richard Lamb

Dan Caster
wrote in message On Jul 11, 6:57 pm,
"Phil Kangas" wrote:
The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.

The two
halves are held in engagement by a heavy spring.

Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas

I think I understand what you are talking about. A torque
limiter so
if something get stuck between the teeth of the mower, the "
clutch "
will slip.
I think one could calculate the angle if one knew the spring
rate of
the spring and the torque it should slip at. But you
probably do not
know either of those things.

Do you think it would be good if it took 70 % more force
before it
ratchets?
If so then use 30 degrees. If it were me, I would change
the angle of
the parts you made. Would not be as strong and would have a
lot of
backlash, but would give you another data point, and if if
breaks then
you can make another.

If you think 70 % more is not the right amount, let me know
and I will
make another back of an envelop calculation.


Dan

So far it looks like the 30 deg angle is the way to go.
Don't know
if that is the most efficient angle but but....I may not see
another.
The original angle appears to be 45 deg judging by what is
left of
the lugs and that may be the original problem. This mower
does
have a wooden pitman arm and a v-belt that could slip if
bound up
hard. Anyway, the guys mowing for the year is done and he's
happy! phil

wrote:
On Jul 11, 3:57 pm, "Phil Kangas" wrote:
I'm involved with a repair project to restore an old
sickle bar hay mower that may be about 50 years
old. The manufacturer is unknown and there is no
parts manual either. The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.
The drive lugs are gone and someone in the past
welded the two parts of the clutch together! Not
good! So I made a replacement unit but I don't know
what the angles of the drive lugs should be. The two
halves are held in engagement by a heavy spring.
I can't find any info on the web about this unit so
I'm guessing for a start that the angle of contact is
45 deg simply because I had a cutter to do that.
Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas

Phil, is the wooden pitman arm still on the mower? This is the
secondary safety point on old mowers. It will break if the slip clutch
doesn't slip. On old mowers, the wooden arm is usually rotten after
being outside in the weather for a few years. It may also have been
replaced by a steel arm.

Probably someone was mowing brush with the mower and jammed the cycle
bar one too many times and decided to fix it good and for ever!

I loved watching the cut grass fall behind the cycle bar until I ran
through a phesant's nest and cut the legs off the hen. Cats also were
a problem.

Paul

Yeah sickle bars are nice and quiet compared to most modern cutting
methods. The quiet part is what caused a lot of the problems. The
animals didn't hear you coming and didn't run. Of course I would rather
not hit a 'chuck hole while on a horse drawn unit though. Not much in
the way of suspension or comfort with steel wheels and a steel seat!!!

--
Steve W.
(\___/)
(='.'=)
(")_(")

Phil Kangas wrote:
I'm involved with a repair project to restore an old
sickle bar hay mower that may be about 50 years
old. The manufacturer is unknown and there is no
parts manual either. The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.
The drive lugs are gone and someone in the past
welded the two parts of the clutch together! Not
good! So I made a replacement unit but I don't know
what the angles of the drive lugs should be. The two
halves are held in engagement by a heavy spring.
I can't find any info on the web about this unit so
I'm guessing for a start that the angle of contact is
45 deg simply because I had a cutter to do that.
Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas




Sounds like an old McCormick-Deering type sickle. They used a ramp type
limiter like that on a couple of the old horse drawn units. Basically
two ramped sections held together by spring. Seem to remember that the
angle was steeper than 45 degrees. The one we had was a LONG LONG time ago.

--
Steve W.
(\___/)
(='.'=)
(")_(")

"Steve W." wrote in message
Phil Kangas wrote:
I'm involved with a repair project to restore an old
sickle bar hay mower that may be about 50 years
old. The manufacturer is unknown and there is no
parts manual either. The input shaft that connects
to the pto shaft has a 'dog clutch' (that's what I'm
calling it for lack of a better term) that is worn out.
The drive lugs are gone and someone in the past
welded the two parts of the clutch together! Not
good! So I made a replacement unit but I don't know
what the angles of the drive lugs should be. The two
halves are held in engagement by a heavy spring.
I can't find any info on the web about this unit so
I'm guessing for a start that the angle of contact is
45 deg simply because I had a cutter to do that.
Now it's back in service but it ratchets too easily
so maybe the contact angle is wrong? Anyone out
there in RCM know what I'm talking about? Perhaps
the angle should be only 30 deg.? This unit is 3 inches
in dia. with a 1.25" bore....
phil kangas




Sounds like an old McCormick-Deering type sickle. They
used a ramp type
limiter like that on a couple of the old horse drawn
units. Basically
two ramped sections held together by spring. Seem to
remember that the
angle was steeper than 45 degrees. The one we had was a
LONG LONG time ago.

--
Steve W.

It sure would be nice to know this angle just for curiousity
sake. I have a
shipfitters wedge and it's angle is 11 deg. It will not slip
out when driven
in with a hammer. So this angle may be too steep for this
application, eih?
This angle seems to be a rare bit of info....
phil

Phil Kangas wrote:
Sounds like an old McCormick-Deering type sickle. They
used a ramp type
limiter like that on a couple of the old horse drawn
units. Basically
two ramped sections held together by spring. Seem to
remember that the
angle was steeper than 45 degrees. The one we had was a
LONG LONG time ago.

--
Steve W.

It sure would be nice to know this angle just for curiousity
sake. I have a
shipfitters wedge and it's angle is 11 deg. It will not slip
out when driven
in with a hammer. So this angle may be too steep for this
application, eih?
This angle seems to be a rare bit of info....
phil


I visited one of the local Amish earlier. His friend uses an OLD New
Idea that had this style clutch on it so I drove over and took a closer
look. His has some wear but it measured at just a touch under 32
degrees. I would say new they were probably 30 even and have worn in a bit.


--
Steve W.

On Jul 13, 11:49*pm, "Steve W." wrote:

It sure would be nice to know this angle just for curiousity
sake. I have a
shipfitters wedge and it's angle is 11 deg. It will not slip
out when driven
in with a hammer. So this angle may be too steep for this
application, eih?
This angle seems to be a rare bit of info....
phil

I visited one of the local Amish earlier. His friend uses an OLD New
Idea that had this style clutch on it so I drove over and took a closer
look. His has some wear but it measured at just a touch under 32
degrees. I would say new they were probably 30 even and have worn in a bit.

Dan Caster
wrote in message On Jul 13, 11:49 pm,
"Steve W." wrote:

It sure would be nice to know this angle just for
curiousity
sake. I have a
shipfitters wedge and it's angle is 11 deg. It will not
slip
out when driven
in with a hammer. So this angle may be too steep for
this
application, eih?
This angle seems to be a rare bit of info....
phil

I visited one of the local Amish earlier. His friend uses
an OLD New
Idea that had this style clutch on it so I drove over and
took a closer
look. His has some wear but it measured at just a touch
under 32
degrees. I would say new they were probably 30 even and
have worn in a bit.

--
Steve W.

My guess is that the original angle was 30 degrees. For any
amount of
torque , any angle will work as long as the spring rate is
right for
that angle. If you had two flat disks, that would work with
enough
force pushing them together. So the designer probably
choose an easy
angle to cut with tools that are easily bought.

Dan

Great news guys! Thanks for looking into it, eih? So it is
30 deg then.
phil