Hi folks. I was hoping that someone here might have an idea that would
send a project a different direction; Basically inspiration to get off
the path that things are stuck in. I believe I've asked this before but
am re-addressing the issue as nothing has been resolved yet.

Here's the situation: We need to take a long 1/2" dia CRS rod, drill
the ends 1-1/2" deep x 5/16 and insert a 3" long hardened and ground
dowel pin in the end. The pin doesn't get much tension but gets some
torque in the form of tens of thousands of cycles over it's life.

Quantity is about 1000 ends a month so it's not enough to get really
fancy or a high investement (IE induction hardening a journal on
hardenable rod instead of using the insert). Cheap and servicable is
the order of the day.

We've tried using a hydraulic compression fit (heavy press in) which
held ok but didn't like the repetative stress cycling for long enough.
We've also tried perimeter welding the joint which draws out some of
the hardness (bad) and takes a little too much time. Currently, the
procedure is to cross drill the 1/2" rod with a small hole about an inch
from the end and plug weld into the hole and to the pin. This works OK
but there is a very small (5% or so) failure rate over time.

Any thoughts on a better procedure to use off the shelf dowel pins (or
whatever) and get the cycle strength we need? Other ideas? I'm just
trying to "break out of the box" here in my thinking. Labor needs to be
in the range of a couple of bucks per end.

Thanks

Koz

"Koz" wrote in message
...
Here's the situation: We need to take a long 1/2" dia CRS rod, drill
the ends 1-1/2" deep x 5/16 and insert a 3" long hardened and ground
dowel pin in the end. The pin doesn't get much tension but gets some
torque in the form of tens of thousands of cycles over it's life.
snip
We've also tried perimeter welding the joint which draws out some of
the hardness (bad) and takes a little too much time.

Could try brazing followed by oil or air quench then tempering? Depending
on what kind of steel the dowel is, of course. You'll want oil or air
hardening to reduce warpage. You may need to grind it afterwards to get a
good finish on it though, and that's extra work...on the plus side they
don't need to be ground to begin with.

Tim

--
"California is the breakfast state: fruits, nuts and flakes."
Website: http://webpages.charter.net/dawill/tmoranwms

Koz wrote:
....
Here's the situation: We need to take a long 1/2" dia CRS rod, drill
the ends 1-1/2" deep x 5/16 and insert a 3" long hardened and ground
dowel pin in the end. The pin doesn't get much tension but gets some
torque in the form of tens of thousands of cycles over it's life.
....

Maybe try longer pins, eg 4" long pins in 2.5" deep hole.

We've tried using a hydraulic compression fit (heavy press in) which
held ok but didn't like the repetative stress cycling for long enough.
We've also tried perimeter welding the joint which
....

Are brazing temps too high? Could try grooved or necked pins wrapped
with brazing wire or sheet, pressed in, then locally heated.

Any thoughts on a better procedure to use off the shelf dowel pins (or
whatever) and get the cycle strength we need?
....

Perhaps modify pins with "hose barb" pattern or a light knurl,
and swage rod end after pressing pin in. I think swaging without
a pattern on the pins won't help.

Have you considered using knurled/splined dowel pins? See

http://www.zycon.com/CompanyDetails_... 1&ccid=52352

http://www.spirol.com/apps/internet/spirol/website.nsf/KnurledPins!OpenForm

http://www.groov-pin.com/pin-knur.htm

http://www.fostermation.com/cap.html

and a bunch more

GmcD


On Wed, 01 Jun 2005 09:23:14 -0700, Koz
wrote:

Hi folks. I was hoping that someone here might have an idea that would
send a project a different direction; Basically inspiration to get off
the path that things are stuck in. I believe I've asked this before but
am re-addressing the issue as nothing has been resolved yet.

Here's the situation: We need to take a long 1/2" dia CRS rod, drill
the ends 1-1/2" deep x 5/16 and insert a 3" long hardened and ground
dowel pin in the end. The pin doesn't get much tension but gets some
torque in the form of tens of thousands of cycles over it's life.

Quantity is about 1000 ends a month so it's not enough to get really
fancy or a high investement (IE induction hardening a journal on
hardenable rod instead of using the insert). Cheap and servicable is
the order of the day.

We've tried using a hydraulic compression fit (heavy press in) which
held ok but didn't like the repetative stress cycling for long enough.
We've also tried perimeter welding the joint which draws out some of
the hardness (bad) and takes a little too much time. Currently, the
procedure is to cross drill the 1/2" rod with a small hole about an inch
from the end and plug weld into the hole and to the pin. This works OK
but there is a very small (5% or so) failure rate over time.

Any thoughts on a better procedure to use off the shelf dowel pins (or
whatever) and get the cycle strength we need? Other ideas? I'm just
trying to "break out of the box" here in my thinking. Labor needs to be
in the range of a couple of bucks per end.

Thanks

Koz

Pardon me; I don't mean to insult your intelligence but have you thought
about Locktite or similar stuff. You said there wasn't much tension but
implied there was some "torque", presumably meaning lateral force. It seems
to me if the dowel pin was fully seated and fitted to the hole according to
"instructions", it should work. Locktite is recommended to fix wheels on
railroad axels - your load may be less.

Bob Swinney
"Koz" wrote in message
...
Hi folks. I was hoping that someone here might have an idea that would
send a project a different direction; Basically inspiration to get off
the path that things are stuck in. I believe I've asked this before but
am re-addressing the issue as nothing has been resolved yet.

Here's the situation: We need to take a long 1/2" dia CRS rod, drill the
ends 1-1/2" deep x 5/16 and insert a 3" long hardened and ground dowel pin
in the end. The pin doesn't get much tension but gets some torque in the
form of tens of thousands of cycles over it's life.

Quantity is about 1000 ends a month so it's not enough to get really fancy
or a high investement (IE induction hardening a journal on hardenable rod
instead of using the insert). Cheap and servicable is the order of the
day.

We've tried using a hydraulic compression fit (heavy press in) which held
ok but didn't like the repetative stress cycling for long enough. We've
also tried perimeter welding the joint which draws out some of the
hardness (bad) and takes a little too much time. Currently, the procedure
is to cross drill the 1/2" rod with a small hole about an inch from the
end and plug weld into the hole and to the pin. This works OK but there
is a very small (5% or so) failure rate over time.

Any thoughts on a better procedure to use off the shelf dowel pins (or
whatever) and get the cycle strength we need? Other ideas? I'm just
trying to "break out of the box" here in my thinking. Labor needs to be
in the range of a couple of bucks per end.

Thanks

Koz

Koz wrote:
Hi folks. I was hoping that someone here might have an idea that would
send a project a different direction; Basically inspiration to get off
the path that things are stuck in. I believe I've asked this before but
am re-addressing the issue as nothing has been resolved yet.

Here's the situation: We need to take a long 1/2" dia CRS rod, drill
the ends 1-1/2" deep x 5/16 and insert a 3" long hardened and ground
dowel pin in the end. The pin doesn't get much tension but gets some
torque in the form of tens of thousands of cycles over it's life.

Quantity is about 1000 ends a month so it's not enough to get really
fancy or a high investement (IE induction hardening a journal on
hardenable rod instead of using the insert). Cheap and servicable is
the order of the day.

We've tried using a hydraulic compression fit (heavy press in) which
held ok but didn't like the repetative stress cycling for long enough.
We've also tried perimeter welding the joint which draws out some of the
hardness (bad) and takes a little too much time. Currently, the
procedure is to cross drill the 1/2" rod with a small hole about an inch
from the end and plug weld into the hole and to the pin. This works OK
but there is a very small (5% or so) failure rate over time.

Any thoughts on a better procedure to use off the shelf dowel pins (or
whatever) and get the cycle strength we need? Other ideas? I'm just
trying to "break out of the box" here in my thinking. Labor needs to be
in the range of a couple of bucks per end.

Thanks

Koz


Did you try some killer locktite? What about a touch of powdered
aluminum with a little water in the hole? Seems that would set 'em
pretty good.

John

On Wed, 01 Jun 2005 09:23:14 -0700, Koz
wrote:

Hi folks. I was hoping that someone here might have an idea that would
send a project a different direction; Basically inspiration to get off
the path that things are stuck in. I believe I've asked this before but
am re-addressing the issue as nothing has been resolved yet.

Here's the situation: We need to take a long 1/2" dia CRS rod, drill
the ends 1-1/2" deep x 5/16 and insert a 3" long hardened and ground
dowel pin in the end. The pin doesn't get much tension but gets some
torque in the form of tens of thousands of cycles over it's life.

Quantity is about 1000 ends a month so it's not enough to get really
fancy or a high investement (IE induction hardening a journal on
hardenable rod instead of using the insert). Cheap and servicable is
the order of the day.

We've tried using a hydraulic compression fit (heavy press in) which
held ok but didn't like the repetative stress cycling for long enough.
We've also tried perimeter welding the joint which draws out some of
the hardness (bad) and takes a little too much time. Currently, the
procedure is to cross drill the 1/2" rod with a small hole about an inch
from the end and plug weld into the hole and to the pin. This works OK
but there is a very small (5% or so) failure rate over time.

Any thoughts on a better procedure to use off the shelf dowel pins (or
whatever) and get the cycle strength we need? Other ideas? I'm just
trying to "break out of the box" here in my thinking. Labor needs to be
in the range of a couple of bucks per end.

Thanks

Koz
I would use Loctite 609. Follow the instructions. I've been using it
for years in highly stressed situations. Both tension and torque. Only
one failure in twenty years or so. That was recently and it must be
something I did. Maybe it was past it's shelf life. There are many
shaft assemblies on fishing boats where parts I made and assembled for
transmitting power from big cat engines to and from hydraulic pumps
and motors.
ERS

In the old days we would use a Jarno tapered dowel with thread on other end.
One solid whack would almost blend the hole and dowel and nothing, not even
an elephant, could disloge once set. I still have some Jarno tapered drills
for making the holes. Try McMaster Carr, they still might carry them.

Wayne

Robert Swinney wrote:

Pardon me; I don't mean to insult your intelligence but have you thought
about Locktite or similar stuff. You said there wasn't much tension but
implied there was some "torque", presumably meaning lateral force. It seems
to me if the dowel pin was fully seated and fitted to the hole according to
"instructions", it should work. Locktite is recommended to fix wheels on
railroad axels - your load may be less.

Can't do it. 400 degrees in oil and can't have any contaminants at all.

Koz


Bob Swinney
"Koz" wrote in message
...


Hi folks. I was hoping that someone here might have an idea that would
send a project a different direction; Basically inspiration to get off
the path that things are stuck in. I believe I've asked this before but
am re-addressing the issue as nothing has been resolved yet.

Here's the situation: We need to take a long 1/2" dia CRS rod, drill the
ends 1-1/2" deep x 5/16 and insert a 3" long hardened and ground dowel pin
in the end. The pin doesn't get much tension but gets some torque in the
form of tens of thousands of cycles over it's life.

Quantity is about 1000 ends a month so it's not enough to get really fancy
or a high investement (IE induction hardening a journal on hardenable rod
instead of using the insert). Cheap and servicable is the order of the
day.

We've tried using a hydraulic compression fit (heavy press in) which held
ok but didn't like the repetative stress cycling for long enough. We've
also tried perimeter welding the joint which draws out some of the
hardness (bad) and takes a little too much time. Currently, the procedure
is to cross drill the 1/2" rod with a small hole about an inch from the
end and plug weld into the hole and to the pin. This works OK but there
is a very small (5% or so) failure rate over time.

Any thoughts on a better procedure to use off the shelf dowel pins (or
whatever) and get the cycle strength we need? Other ideas? I'm just
trying to "break out of the box" here in my thinking. Labor needs to be
in the range of a couple of bucks per end.

Thanks

Koz

F. George McDuffee wrote:

Have you considered using knurled/splined dowel pins? See

http://www.zycon.com/CompanyDetails_... 1&ccid=52352

http://www.spirol.com/apps/internet/spirol/website.nsf/KnurledPins!OpenForm

http://www.groov-pin.com/pin-knur.htm

http://www.fostermation.com/cap.html

and a bunch more

GmcD


I'll look into this. Maybe press fitting with the right knurl pattern
will do the trick. However, I seem to remember the costs for the
knurled pins got a little steep. At the very least, it'd be an
improvement.

As to Other's comments about Locktite, Aluminum powder, brazing,
etc...this is a food grade application and can have NO presence of AL,
CU, or glue type items such as locktite. Temp is 400 degrees running in
an oil bath, followed by a caustic bath at 200 and an acid
neutralization of the caustic.

Koz


On Wed, 01 Jun 2005 09:23:14 -0700, Koz
wrote:





Hi folks. I was hoping that someone here might have an idea that would
send a project a different direction; Basically inspiration to get off
the path that things are stuck in. I believe I've asked this before but
am re-addressing the issue as nothing has been resolved yet.

Here's the situation: We need to take a long 1/2" dia CRS rod, drill
the ends 1-1/2" deep x 5/16 and insert a 3" long hardened and ground
dowel pin in the end. The pin doesn't get much tension but gets some
torque in the form of tens of thousands of cycles over it's life.

Quantity is about 1000 ends a month so it's not enough to get really
fancy or a high investement (IE induction hardening a journal on
hardenable rod instead of using the insert). Cheap and servicable is
the order of the day.

We've tried using a hydraulic compression fit (heavy press in) which
held ok but didn't like the repetative stress cycling for long enough.
We've also tried perimeter welding the joint which draws out some of
the hardness (bad) and takes a little too much time. Currently, the
procedure is to cross drill the 1/2" rod with a small hole about an inch


from the end and plug weld into the hole and to the pin. This works OK


but there is a very small (5% or so) failure rate over time.

Any thoughts on a better procedure to use off the shelf dowel pins (or
whatever) and get the cycle strength we need? Other ideas? I'm just
trying to "break out of the box" here in my thinking. Labor needs to be
in the range of a couple of bucks per end.

Thanks

Koz

"Koz" wrote in message
...
Other ideas? I'm just trying to "break out of the box" here in my
thinking. Labor needs to be in the range of a couple of bucks per end.

I don't think you specified exactly how the assemblies are failing - tension
or torque?

Out of the box... Friction welding. Perhaps a fixture on the lathe carriage
for the dowel and the CRS rod in the chuck. May be difficult to control the
strength of the weld, but that may not be much of an issue in your case.

Or... What about some kind of forming tool? You may be able to grind a
groove into the dowels (some simple fixturing on the surface grinder would
allow you to quickly place a crosswise slot using a cutoff wheel in multiple
pieces in a single setup). Then, a simple die to press the CRS into the slot
in the dowel. This would require some care during assembly as the orentation
of the dowel would be important.

Now that I think about it, dowels with a slight flat ground into them (and a
threaded hole in the end, for a dowel puller) may provide enough room to
deform the CRS such that the dowel is able to resist the torque loads. These
pins are called "flat-vent pull-out" as per McMaster-Carr.

HTH.

Regards,

Robin

Two ideas come to mind.

Stainless steel roll pin in a cross hole.

A cross hole filled with that plastic that GM puts on the U joints
instead of E clips. Lasts forever, takes a lot of torch to blow
them out on purpose.

(top posted for your convenience)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Keep the whole world singing . . . .
DanG (remove the sevens)




"Koz" wrote in message
...
Hi folks. I was hoping that someone here might have an idea
that would send a project a different direction; Basically
inspiration to get off the path that things are stuck in. I
believe I've asked this before but am re-addressing the issue as
nothing has been resolved yet.

Here's the situation: We need to take a long 1/2" dia CRS rod,
drill the ends 1-1/2" deep x 5/16 and insert a 3" long hardened
and ground dowel pin in the end. The pin doesn't get much
tension but gets some torque in the form of tens of thousands of
cycles over it's life.

Quantity is about 1000 ends a month so it's not enough to get
really fancy or a high investement (IE induction hardening a
journal on hardenable rod instead of using the insert). Cheap
and servicable is the order of the day.

We've tried using a hydraulic compression fit (heavy press in)
which held ok but didn't like the repetative stress cycling for
long enough. We've also tried perimeter welding the joint which
draws out some of the hardness (bad) and takes a little too much
time. Currently, the procedure is to cross drill the 1/2" rod
with a small hole about an inch from the end and plug weld into
the hole and to the pin. This works OK but there is a very
small (5% or so) failure rate over time.

Any thoughts on a better procedure to use off the shelf dowel
pins (or whatever) and get the cycle strength we need? Other
ideas? I'm just trying to "break out of the box" here in my
thinking. Labor needs to be in the range of a couple of bucks
per end.

Thanks

Koz

In article ,
Koz wrote:

Any thoughts on a better procedure to use off the shelf dowel pins (or
whatever) and get the cycle strength we need? Other ideas? I'm just
trying to "break out of the box" here in my thinking. Labor needs to be
in the range of a couple of bucks per end.

Sticking with your "no foreign metals, glue, etc." foodservice
requirement:

Try a slightly different press fit to see if that solves your stress
problem?

If the cracks (on the press-fits) are coming at the bottom of the hole,
a hole with rounder bottom corners might not crack? (I don't think you
described the failure in enough detail for this to be anything but a
WAG). Think finishing the bottom of the hole with a ball-end mill to
reduce stress concentration, if that's what's happening. Presumably a
drill could be ground to do something like that directly.

Grind divots or a tapered flat on the dowel pin (part that will be
inside the CRS) and squish the CRS into them/it with a hydraulic press.
If using a tapered flat, be sure that the end of it is radiused to
reduce stress concentrations. Hemispherical divots might be better for
that reason. This assumes that the CRS need not be perfectly round near
the end. I'm guessing that the outer part of the pin needs to be round,
so the fully-flatted pins that are available off the shelf probably
would not work?

I am curious just where the failures occurred when you used a heavy
press in.
Would it help if you made the hole for a heavy press fit at the bottom
of the hole and a lighter press fit toward the top of the hole.

Or how about grinding a very shallow groove about half a inch from the
end of the pin. Medium press fit with the groove inside the crs. Then
use a knurling tool with smooth knurls to press the crs into the
shallow groove.


Dan

wrote:

I am curious just where the failures occurred when you used a heavy
press in.
Would it help if you made the hole for a heavy press fit at the bottom
of the hole and a lighter press fit toward the top of the hole.

Or how about grinding a very shallow groove about half a inch from the
end of the pin. Medium press fit with the groove inside the crs. Then
use a knurling tool with smooth knurls to press the crs into the
shallow groove.


Dan



Sorry...phone kept ringing and I was trying not to give so much
information as to limit responses..sometimes wild guesses can spark
inspiration. I also apologize if any of my responses have seemed abrupt
but It's been busy here the last couple of days.

The protruding pin has slight torque on it (impossible to calculate as
it's caused by spontaneous miss-alignments) and little tension (50
pounds worst case tension) if things are aligned properly. There is
also slight flexing. Every once in a while, the torque on the pin might
be higher but not so high that would count as high enough to pull things
apart on their own. What seems to be happening is related to the number
of cycles. Eventually, either the plug weld breaks off or in the case
of the press fits, things just eventually work to loosen the hole in the
rod so the pin eventually works itself out. Typical life is about 2
years and in that time, they see about 2 million cycles (quick calculation)

Unfortunately, even a very low failure rate can cause downtime on the
order of $ 10 grand an hour. It's clearly worth it to go high tech and
expensive to do it right but customers don't want to actually pay for
what they would be getting. This puts us in the corner of needing a
cheap solution about the equivalent of the plug-weld method on costs
while trying to get the results of finish ground induction hardened ends.

I believe that the better way to do it would be a heavy press fit with a
knurled pin AND mechanical fastening of some kind. I have to see if the
costs would work out though. .

Sooo...basically I was hoping that someone might have a novel solution
to send it in a different direction. The 1/2" rod does need to be cheap
mild steel and the pin needs one hell of a hard surface to reduce wear
and galling without becomming brittle at all.

Thanks to all those who answered


Koz

Not a stupid question at all. Drilling the soft 1/2" rod is easy..it's
drilling into the hardend surface of the dowel pin that will cause
problems. You aren't missing anything except trying to get the hardened
pin drilled and getting alignment right to cross pin things. Again, it
might be a good way to go if I can simplify the drilling part down to
idiot-proof in the shop.

Thanks,

Koz

Ignoramus12247 wrote:

I am sorry for a stupid question, but why can't you just cross drill
it and put in a "cross pin" or even a screw that would hold the axial
pin in place. That should not fail much. Should not require a lot of
equipment beyond a drill press and a grinder. What am I missing?

i

On Thu, 02 Jun 2005 10:01:23 -0700, Koz wrote:


wrote:



I am curious just where the failures occurred when you used a heavy
press in.
Would it help if you made the hole for a heavy press fit at the bottom
of the hole and a lighter press fit toward the top of the hole.

Or how about grinding a very shallow groove about half a inch from the
end of the pin. Medium press fit with the groove inside the crs. Then
use a knurling tool with smooth knurls to press the crs into the
shallow groove.


Dan





Sorry...phone kept ringing and I was trying not to give so much
information as to limit responses..sometimes wild guesses can spark
inspiration. I also apologize if any of my responses have seemed abrupt
but It's been busy here the last couple of days.

The protruding pin has slight torque on it (impossible to calculate as
it's caused by spontaneous miss-alignments) and little tension (50
pounds worst case tension) if things are aligned properly. There is
also slight flexing. Every once in a while, the torque on the pin might
be higher but not so high that would count as high enough to pull things
apart on their own. What seems to be happening is related to the number
of cycles. Eventually, either the plug weld breaks off or in the case
of the press fits, things just eventually work to loosen the hole in the
rod so the pin eventually works itself out. Typical life is about 2
years and in that time, they see about 2 million cycles (quick calculation)

Unfortunately, even a very low failure rate can cause downtime on the
order of $ 10 grand an hour. It's clearly worth it to go high tech and
expensive to do it right but customers don't want to actually pay for
what they would be getting. This puts us in the corner of needing a
cheap solution about the equivalent of the plug-weld method on costs
while trying to get the results of finish ground induction hardened ends.

I believe that the better way to do it would be a heavy press fit with a
knurled pin AND mechanical fastening of some kind. I have to see if the
costs would work out though. .

Sooo...basically I was hoping that someone might have a novel solution
to send it in a different direction. The 1/2" rod does need to be cheap
mild steel and the pin needs one hell of a hard surface to reduce wear
and galling without becomming brittle at all.

Thanks to all those who answered


Koz

What about using a shoulder screw and then cutting the head off?

If you are willing to foot the cost, material can be hardened with very
little distortion, etc. using controlled
environment ovens, special vacuum packs, and so on.

In other words, a threaded part could be made (dimensions adjusted for
growth/shrinkage) and heat treated afterwards.

Good luck!


"Koz" wrote in message
...
Not a stupid question at all. Drilling the soft 1/2" rod is easy..it's
drilling into the hardend surface of the dowel pin that will cause
problems. You aren't missing anything except trying to get the hardened
pin drilled and getting alignment right to cross pin things. Again, it
might be a good way to go if I can simplify the drilling part down to
idiot-proof in the shop.
Thanks,

Koz

Ignoramus12247 wrote:

I am sorry for a stupid question, but why can't you just cross drill
it and put in a "cross pin" or even a screw that would hold the axial
pin in place. That should not fail much. Should not require a lot of
equipment beyond a drill press and a grinder. What am I missing?

i

On Thu, 02 Jun 2005 10:01:23 -0700, Koz
wrote:

wrote:


I am curious just where the failures occurred when you used a heavy
press in.
Would it help if you made the hole for a heavy press fit at the bottom
of the hole and a lighter press fit toward the top of the hole.

Or how about grinding a very shallow groove about half a inch from the
end of the pin. Medium press fit with the groove inside the crs. Then
use a knurling tool with smooth knurls to press the crs into the
shallow groove.


Dan



Sorry...phone kept ringing and I was trying not to give so much
information as to limit responses..sometimes wild guesses can spark
inspiration. I also apologize if any of my responses have seemed abrupt
but It's been busy here the last couple of days.

The protruding pin has slight torque on it (impossible to calculate as
it's caused by spontaneous miss-alignments) and little tension (50 pounds
worst case tension) if things are aligned properly. There is also slight
flexing. Every once in a while, the torque on the pin might be higher
but not so high that would count as high enough to pull things apart on
their own. What seems to be happening is related to the number of
cycles. Eventually, either the plug weld breaks off or in the case of
the press fits, things just eventually work to loosen the hole in the rod
so the pin eventually works itself out. Typical life is about 2 years
and in that time, they see about 2 million cycles (quick calculation)

Unfortunately, even a very low failure rate can cause downtime on the
order of $ 10 grand an hour. It's clearly worth it to go high tech and
expensive to do it right but customers don't want to actually pay for
what they would be getting. This puts us in the corner of needing a
cheap solution about the equivalent of the plug-weld method on costs
while trying to get the results of finish ground induction hardened ends.
I believe that the better way to do it would be a heavy press fit with a
knurled pin AND mechanical fastening of some kind. I have to see if the
costs would work out though. .

Sooo...basically I was hoping that someone might have a novel solution to
send it in a different direction. The 1/2" rod does need to be cheap
mild steel and the pin needs one hell of a hard surface to reduce wear
and galling without becomming brittle at all.

Thanks to all those who answered


Koz

Koz wrote:
What seems to be happening is related to the number
of cycles. Eventually, either the plug weld breaks off or in the case
of the press fits, things just eventually work to loosen the hole in the
rod so the pin eventually works itself out. Typical life is about 2
years and in that time, they see about 2 million cycles (quick calculation)


On the fatigue failure of the welds, I'm thinking of two causes:
- Excess Martensite in the weld since the dowel has a high carbon
surface. The carbon enriches the molten weld, cools quick, martensite
forms. Add high cycles and the brittle martensite fails easily.
- Thermal stresses in the weld, since the cold CRS rod is a heat sink.


Both of these would be helped by a pre-heat. Need to have the
surrounding metal just after welding to be above the Martensite Start
temp to prevent M formation. This is pretty hard to estimate since the
molten pool has unknown % carbon. And it will depend on how much of
the dowel is melted in the pool. If the pool is ~1050 steel, M-start
is about 600F. I'd talk to a welding expert for a rec on preheat temp.
1/2" dia wouldn't take long to get to temp, and that is good since the
exposed pin will lose some carbon and hardness if it is preheated too
long. (May need to protect the exposed pin during preheat with a high
carbon cover). Perhaps a post-weld stress relief as well, though that
is probably more cost than you want.

Make sure both parts and the filler rod have lowest possible alloy
content (Cr, Mo, Mn...) for lowest hardenability. Oh!-- if you are
currently using an alloy steel dowel, changing to a case-hardened
carbon steel dowel would result in much less M w/o any preheat. And
have nearly the same surface hardness. And save $.

Yet another idea: Make everything w/ low carbon steel, then carburize
the welded ass'y in large batches. No martensite in the weld
guaranteed. $ per part depends on how big your parts and oven are.

Good, simple, explanation of Martensite in welds:
http://www.esabna.com/EUWeb/SA_handbook/585sa3_1.htm

Also are you plug welding on one or both sides of the CRS? Two welds
would lower the stresses, perhaps double the life, slow the cool, too.


David Malicky
www.malicky.com/davidm

Koz wrote:

... in the case
of the press fits, things just eventually work to loosen the hole in the
rod so the pin eventually works itself out. ...

A 5/16 hole in a 1/2" rod leaves a 3/32 "wall". That's not much in CRS.
Depending upon the radial loads, the CRS could be stretching enough to
loosen the pin. If so, a longer pin would improve things.

But, what do I know,
Bob