I got a SNAFU in my project...

I need to mount a 10 tooth .200 pitch timing pulley to a 3/8 shaft on my
servo motor. I bored the pulley yesterday before I noticed there's not
enough meat left for a key, let alone set screws.

Anyway, I'm looking for a way to mount this pulley. Press fit? silver
solder? I've got NO experience with silver solder, which kind? Other ideas?

Karl

"Karl Townsend" wrote in message
anews.com...
I got a SNAFU in my project...

I need to mount a 10 tooth .200 pitch timing pulley to a 3/8 shaft on my
servo motor. I bored the pulley yesterday before I noticed there's not
enough meat left for a key, let alone set screws.

Anyway, I'm looking for a way to mount this pulley. Press fit? silver
solder? I've got NO experience with silver solder, which kind? Other
ideas?

Karl

If you heat it enough to silver-braze, it will wind up dead-soft annealed.
If that isn't OK, then you might consider that the shear strength of
industrial-grade epoxies run upwards of 5,000 psi. It might do the job.

--
Ed Huntress

If you heat it enough to silver-braze, it will wind up dead-soft annealed.
If that isn't OK, then you might consider that the shear strength of
industrial-grade epoxies run upwards of 5,000 psi. It might do the job.

--
Ed Huntress

Now, there's an idea. Any particular product?

I could reinforce it a bit with a custom key that is only 0.025" high into
the pulley.

Karl Townsend wrote:

If you heat it enough to silver-braze, it will wind up dead-soft annealed.
If that isn't OK, then you might consider that the shear strength of
industrial-grade epoxies run upwards of 5,000 psi. It might do the job.

--
Ed Huntress

Now, there's an idea. Any particular product?

I could reinforce it a bit with a custom key that is only 0.025" high into
the pulley.

A tiny key and some good Locktite ought to do it. You could also cross
drill and use a roll pin which would be a lot easier to disassemble when
needed.

On Wed, 22 Jul 2009 08:09:18 -0500, "Karl Townsend"
wrote:


If you heat it enough to silver-braze, it will wind up dead-soft annealed.
If that isn't OK, then you might consider that the shear strength of
industrial-grade epoxies run upwards of 5,000 psi. It might do the job.

--
Ed Huntress

Now, there's an idea. Any particular product?

I could reinforce it a bit with a custom key that is only 0.025" high into
the pulley.


Depending on the hub design and load you might also use a tapered pin
to retain the pulley. They also make a tapered pin with the small end
threaded for a retaining nut.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)

"Karl Townsend" wrote in message
anews.com...

If you heat it enough to silver-braze, it will wind up dead-soft
annealed.
If that isn't OK, then you might consider that the shear strength of
industrial-grade epoxies run upwards of 5,000 psi. It might do the job.

--
Ed Huntress

Now, there's an idea. Any particular product?

No specifics, because I'm not up on the latest.

But here are a few general points. You probably can get away with a
room-temperature-cure product (which generally means amine-type hardeners),
because your application probably doesn't justify the complication of A-B
cures at two different elevated temperatures. I always try to ask an expert,
like someone at 3M, before committing to something like this. You'll want to
make clear to them all the details of your application -- metals being
joined, etc. You need shear strength but not much peel/cleavage strength. To
get the latter you generally sacrifice the former, so a general-purpose
epoxy, which usually is oriented toward a compromise, is not your best
choice. And you want to be wary of anything that has a fast cure time. They
may have that issue solved today, but any cure with epoxy that takes less
than 24 hours usually compromises performance.

Assuming both parts are steel, you may want more than extreme cleanliness.
You may want to use the scratch-in method for getting the best bond.

Anyway, I'd try epoxy first, because if it fails, no harm is done to the
parts.


I could reinforce it a bit with a custom key that is only 0.025" high into
the pulley.

I'd be wary of that because it could interfere with getting a good
scratch-in coating on the parts. But whatever works.

--
Ed Huntress

How much torque is involved? Makes a huge difference.

Really quick & easy, and easy to undo (unlike silver solder): a tack of
weld on the end, bridging the shaft & sprocket. Quick & Dirty (tm).

Roll pin or taper pin. If high torque. Whilst drilling for a pin, I
assure the alignment by doing the tack weld above & drilling both at once.

Bob

Bob Engelhardt wrote:

How much torque is involved? Makes a huge difference.

Really quick & easy, and easy to undo (unlike silver solder): a tack of
weld on the end, bridging the shaft & sprocket. Quick & Dirty (tm).

Roll pin or taper pin. If high torque. Whilst drilling for a pin, I
assure the alignment by doing the tack weld above & drilling both at once.

Bob

Welding an aluminum sprocket onto a steel shaft would be an interesting
trick...

Pete C. wrote:
Welding an aluminum sprocket onto a steel shaft would be an interesting
trick...

Aluminum?

Bob Engelhardt wrote:

Pete C. wrote:
Welding an aluminum sprocket onto a steel shaft would be an interesting
trick...

Aluminum?

I've not seen any 10T .200 pitch sprockets available in anything but
aluminum or plastic.

On Jul 22, 8:49*am, "Karl Townsend"
wrote:
I got a SNAFU in my project...

I need to mount a 10 tooth .200 pitch timing pulley to a 3/8 shaft on my
servo motor. I bored the pulley yesterday before I noticed there's not
enough meat left for a key, let alone set screws....
Karl

Could you make and attach a separate hub?

"Karl Townsend" wrote in message
anews.com...
I got a SNAFU in my project...

I need to mount a 10 tooth .200 pitch timing pulley to a 3/8 shaft on my
servo motor. I bored the pulley yesterday before I noticed there's not
enough meat left for a key, let alone set screws.

Anyway, I'm looking for a way to mount this pulley. Press fit? silver
solder? I've got NO experience with silver solder, which kind? Other
ideas?

Karl

If there is any hub, split it with a saw blade. Make or buy 2-piece shaft
collar with the ID the same as the OD of the hub and clamp it. Otherwise,
some green loctite.

I'd be wary of that because it could interfere with getting a good
scratch-in coating on the parts. But whatever works.


What do you mean here? Don't know the term scratch in.

If there is any hub, split it with a saw blade. Make or buy 2-piece shaft
collar with the ID the same as the OD of the hub and clamp it. Otherwise,
some green loctite.

I'd have to make a hub, do-able but not easy. I started with a six inch
length of timing pulley stock. green loctite or whatever Ed says will be my
first run.

"Pete C." wrote in message
ster.com...

Bob Engelhardt wrote:

Pete C. wrote:
Welding an aluminum sprocket onto a steel shaft would be an interesting
trick...

Aluminum?

I've not seen any 10T .200 pitch sprockets available in anything but
aluminum or plastic.

material is steel, don't know grade, soft and easy to machine

Karl

"Bob Engelhardt" wrote in message
...
How much torque is involved? Makes a huge difference.

1/2 hp. servo. I think this is at 3000 rpm. Torque*rpm* factor= hp. Don't
remember factor off hand.

Really quick & easy, and easy to undo (unlike silver solder): a tack of
weld on the end, bridging the shaft & sprocket. Quick & Dirty (tm).

Don't like this idea.

Roll pin or taper pin. If high torque. Whilst drilling for a pin, I
assure the alignment by doing the tack weld above & drilling both at once.

Bob

May try a roll pin if adhesive bonding don't work.

"Karl Townsend" wrote in message
anews.com...

I'd be wary of that because it could interfere with getting a good
scratch-in coating on the parts. But whatever works.


What do you mean here? Don't know the term scratch in.

Clean the steel conventionally as well as you can. Then mix up a small
amount of epoxy and apply a glob to a piece of sandpaper. Sand the spot
you're bonding to, "wet" with the epoxy, until you've scratched into the
entire surface. Keep the spot wet with epoxy; don't let air touch the metal
again once you've started.

If you want to be neat about it, apply another glob of mixed epoxy to a
piece of rag, and wipe the spot to wipe away the grit, oxide, etc. Again,
keep it wet; air should never touch metal.

Then do the same to the other piece you're bonding. Apply another small glob
of epoxy to the spot and stick the two pieces together. Let it cure.

This "scratch-in" method produces similar results to the chemical treatments
used in production -- phosphoric-acid anodizing on aluminum, and some acid
etches used on steel. It's used in high-grade repair work and some custom
assembly. Obviously, it's too labor intensive to use in production. It works
on most metals but it's particularly useful on stainless and aluminum. The
mechanical bond you get from the rough surface is secondary. The primary
objective is to produce a clean, high-energy surface to which the epoxy gets
a true adhesive bond. Scratching also produces more surface area for the
adhesive bonding.

The higher the strength of epoxy you're using, the more critical it is to
have an oxide-free surface to bond to. The difference is really large. Also,
keep in mind that you do not want a really tight fit in metal-to-metal
bonding with epoxy. You get the strongest joint with a gap of 0.002" to
0.005", depending on the epoxy. For that reason some people leave the
sanding grit in the epoxy and don't clean it off; it serves as a spacer.
It's easy to starve an epoxy joint and ruin its strength.

Doing the scratch-in thing to a hole or other internal shape is a little
tricky, but it works.

BTW, this is for a high-strength joint. If the torque load is light enough
that green Loctite would do the job, then this is all a waste of time.

--
Ed Huntress

On Wed, 22 Jul 2009 07:49:26 -0500, "Karl Townsend"
wrote:

I got a SNAFU in my project...

I need to mount a 10 tooth .200 pitch timing pulley to a 3/8 shaft on my
servo motor. I bored the pulley yesterday before I noticed there's not
enough meat left for a key, let alone set screws.

Anyway, I'm looking for a way to mount this pulley. Press fit? silver
solder? I've got NO experience with silver solder, which kind? Other ideas?

Karl

For a timing pulley on a 3/8" shaft, I think Loctite would more than
suffice. I'd use Loctite 609 or 680. These are anaerobic one-part
adhesives, not epoxies. I have both, use both and frankly can't tell
any difference between them. Tawm, they're both green.

Parts should fit snugly. They should be reasonably clean but this
isn't terribly fussy. A quick squirt of Brake-Kleen and a wipe or
blow off is quite sufficient. Better bonds are achieved if an
accelerator is used, but they work OK without it. Once assembled with
these compounds, after some cure time you'd probably need heat to get
the parts apart. About 400F would get it done.

Don Foreman writes:


Parts should fit snugly. They should be reasonably clean but this isn't
terribly fussy. A quick squirt of Brake-Kleen and a wipe or blow off is
quite sufficient.

I've always used starting ether for the final cleaning as the
residue from other stuph can bite you back.

Comments?
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

"David Lesher" wrote in message
...
Don Foreman writes:


Parts should fit snugly. They should be reasonably clean but this isn't
terribly fussy. A quick squirt of Brake-Kleen and a wipe or blow off is
quite sufficient.

I've always used starting ether for the final cleaning as the
residue from other stuph can bite you back.

Comments?

I don't know how pure starting ether is, but commercial acetone, for
example, usually is recycled and contains some hydrocarbons. In good
fiberglass shops, they don't use the commercial grade, which is the stuff
you find in paint stores.

--
Ed Huntress

"Don Foreman" wrote in message
...
On Wed, 22 Jul 2009 07:49:26 -0500, "Karl Townsend"
wrote:

I got a SNAFU in my project...

I need to mount a 10 tooth .200 pitch timing pulley to a 3/8 shaft on my
servo motor. I bored the pulley yesterday before I noticed there's not
enough meat left for a key, let alone set screws.

Anyway, I'm looking for a way to mount this pulley. Press fit? silver
solder? I've got NO experience with silver solder, which kind? Other
ideas?

Karl

For a timing pulley on a 3/8" shaft, I think Loctite would more than
suffice. I'd use Loctite 609 or 680. These are anaerobic one-part
adhesives, not epoxies. I have both, use both and frankly can't tell
any difference between them. Tawm, they're both green.

Parts should fit snugly. They should be reasonably clean but this
isn't terribly fussy. A quick squirt of Brake-Kleen and a wipe or
blow off is quite sufficient. Better bonds are achieved if an
accelerator is used, but they work OK without it. Once assembled with
these compounds, after some cure time you'd probably need heat to get
the parts apart. About 400F would get it done.

I like the "booger green" for permanent installations and the "snot green"
if I might have to take it apart.

Ed Huntress wrote:
"Karl Townsend" wrote in message
anews.com...

I'd be wary of that because it could interfere with getting a good
scratch-in coating on the parts. But whatever works.


What do you mean here? Don't know the term scratch in.


Clean the steel conventionally as well as you can. Then mix up a small
amount of epoxy and apply a glob to a piece of sandpaper. Sand the spot
you're bonding to, "wet" with the epoxy, until you've scratched into the
entire surface. Keep the spot wet with epoxy; don't let air touch the metal
again once you've started.

If you want to be neat about it, apply another glob of mixed epoxy to a
piece of rag, and wipe the spot to wipe away the grit, oxide, etc. Again,
keep it wet; air should never touch metal.

Then do the same to the other piece you're bonding. Apply another small glob
of epoxy to the spot and stick the two pieces together. Let it cure.

This "scratch-in" method produces similar results to the chemical treatments
used in production -- phosphoric-acid anodizing on aluminum, and some acid
etches used on steel. It's used in high-grade repair work and some custom
assembly. Obviously, it's too labor intensive to use in production. It works
on most metals but it's particularly useful on stainless and aluminum. The
mechanical bond you get from the rough surface is secondary. The primary
objective is to produce a clean, high-energy surface to which the epoxy gets
a true adhesive bond. Scratching also produces more surface area for the
adhesive bonding.

The higher the strength of epoxy you're using, the more critical it is to
have an oxide-free surface to bond to. The difference is really large. Also,
keep in mind that you do not want a really tight fit in metal-to-metal
bonding with epoxy. You get the strongest joint with a gap of 0.002" to
0.005", depending on the epoxy. For that reason some people leave the
sanding grit in the epoxy and don't clean it off; it serves as a spacer.
It's easy to starve an epoxy joint and ruin its strength.

Doing the scratch-in thing to a hole or other internal shape is a little
tricky, but it works.

BTW, this is for a high-strength joint. If the torque load is light enough
that green Loctite would do the job, then this is all a waste of time.

--
Ed Huntress



I don't know about loctite these days but I was told by a race engineer
that years ago they used a loctite product that seemed to be exactly
what they wanted to hold hubs on a race car so would result in a lighter
hub assembly. They failed with regularity, it turned out that on
examination the loctite, while it had the tensile and compressive
properties, had **** poor fatigue properties, so failed due to the
cyclical nature of the drive shaft.

"Karl Townsend" wrote in message
anews.com...
I got a SNAFU in my project...

I need to mount a 10 tooth .200 pitch timing pulley to a 3/8 shaft on my
servo motor. I bored the pulley yesterday before I noticed there's not
enough meat left for a key, let alone set screws.

Anyway, I'm looking for a way to mount this pulley. Press fit? silver
solder? I've got NO experience with silver solder, which kind? Other
ideas?

roll pin?

"Karl Townsend" wrote in message
anews.com...
I got a SNAFU in my project...

I need to mount a 10 tooth .200 pitch timing pulley to a 3/8 shaft on my
servo motor. I bored the pulley yesterday before I noticed there's not
enough meat left for a key, let alone set screws.

Anyway, I'm looking for a way to mount this pulley. Press fit? silver
solder? I've got NO experience with silver solder, which kind? Other
ideas?

Karl

Press fit and green Loctite

or

Drill and roll pin

or

BOTH!

Ed Huntress wrote:
"Karl Townsend" wrote in message
anews.com...

I'd be wary of that because it could interfere with getting a good
scratch-in coating on the parts. But whatever works.


What do you mean here? Don't know the term scratch in.

Clean the steel conventionally as well as you can. Then mix up a small
amount of epoxy and apply a glob to a piece of sandpaper. Sand the
spot you're bonding to, "wet" with the epoxy, until you've scratched
into the entire surface. Keep the spot wet with epoxy; don't let air
touch the metal again once you've started.

If you want to be neat about it, apply another glob of mixed epoxy to
a piece of rag, and wipe the spot to wipe away the grit, oxide, etc.
Again, keep it wet; air should never touch metal.

Then do the same to the other piece you're bonding. Apply another
small glob of epoxy to the spot and stick the two pieces together.
Let it cure.
This "scratch-in" method produces similar results to the chemical
treatments used in production -- phosphoric-acid anodizing on
aluminum, and some acid etches used on steel. It's used in high-grade
repair work and some custom assembly. Obviously, it's too labor
intensive to use in production. It works on most metals but it's
particularly useful on stainless and aluminum. The mechanical bond
you get from the rough surface is secondary. The primary objective is
to produce a clean, high-energy surface to which the epoxy gets a
true adhesive bond. Scratching also produces more surface area for
the adhesive bonding.
The higher the strength of epoxy you're using, the more critical it
is to have an oxide-free surface to bond to. The difference is really
large. Also, keep in mind that you do not want a really tight fit in
metal-to-metal bonding with epoxy. You get the strongest joint with a
gap of 0.002" to 0.005", depending on the epoxy. For that reason some
people leave the
sanding grit in the epoxy and don't clean it off; it serves as a
spacer. It's easy to starve an epoxy joint and ruin its strength.

Doing the scratch-in thing to a hole or other internal shape is a
little tricky, but it works.

BTW, this is for a high-strength joint. If the torque load is light
enough that green Loctite would do the job, then this is all a waste
of time.

I thought I knew all there is to know about epoxy. How wrong can one be?
This is another one for the library. Thanks, Ed!

--
Michael Koblic
Campbell River, BC

On Wed, 22 Jul 2009 18:51:42 +0000 (UTC), David Lesher
wrote:

Don Foreman writes:


Parts should fit snugly. They should be reasonably clean but this isn't
terribly fussy. A quick squirt of Brake-Kleen and a wipe or blow off is
quite sufficient.

I've always used starting ether for the final cleaning as the
residue from other stuph can bite you back.

Comments?

Brake-Kleen isn't supposed to leave a residue. I use it for final
cleaning of bearings after gross cleaning with varsol and acetone,
which do leave residues.

Karl Townsend writes:

Anyway, I'm looking for a way to mount this pulley.

Finely thread the pulley ID and the shaft OD. Might require disassembling
the motor.

"Michael Koblic" wrote in message
...
Ed Huntress wrote:
"Karl Townsend" wrote in message
anews.com...

I'd be wary of that because it could interfere with getting a good
scratch-in coating on the parts. But whatever works.


What do you mean here? Don't know the term scratch in.

Clean the steel conventionally as well as you can. Then mix up a small
amount of epoxy and apply a glob to a piece of sandpaper.

snip


I thought I knew all there is to know about epoxy. How wrong can one be?
This is another one for the library. Thanks, Ed!

--
Michael Koblic
Campbell River, BC

It hope it will be useful to you sometime, Michael. Epoxy can be fairly
complicated, especially when you get into the elevated-temperature-cure
industrial products that we never see on the regular markets. They can have
tensile and sheer strength running 2.5X stronger than anything we can buy in
small quantities. Epoxy is great stuff but you really have to understand its
properties when you use it for hefty loads. For example, the stronger it is
in shear, the weaker it *may* be in peel.

I don't know where this scratch-in idea started, but I think I know where it
first appeared in print: in the Gougeon Brothers' first book, published in
the early '70s. (The Gougeons were the originators of the WEST epoxy
system.) They used it to fasten stainless deck hardware to their boats.

Since those guys are highly respected empiricists -- they actually test and
try their ideas before talking about them -- it caught on in the boating
community. Then it started to show up in metalworking, with some of my
writing in the late '70s a possible contributor. d8-)

Anyway, I've used it many times, and I've done some of my own testing (with
pry bars and hammers g), and I'm sold on it. FWIW, I've gotten mixed
results with copper alloys, so I don't know about using it on them.
Sometimes yes, sometimes no.

--
Ed Huntress

"David Billington" wrote in message
...
Ed Huntress wrote:

snip


BTW, this is for a high-strength joint. If the torque load is light
enough that green Loctite would do the job, then this is all a waste of
time.

--
Ed Huntress


I don't know about loctite these days but I was told by a race engineer
that years ago they used a loctite product that seemed to be exactly what
they wanted to hold hubs on a race car so would result in a lighter hub
assembly. They failed with regularity, it turned out that on examination
the loctite, while it had the tensile and compressive properties, had ****
poor fatigue properties, so failed due to the cyclical nature of the drive
shaft.

That's interesting. The thread-locking Loctite products are mostly anaerobic
acrylic adhesives. I wouldn't know if that's a characteristic of acrylics in
general or not.

Epoxies usually have pretty good fatigue properties, which is evidenced by
the fact that they glue a lot of aluminum aircraft skins with them. Those
rivet-bonded wings do NOT derive any significant strength from the rivets.
That's not why the rivets are there. The strength comes from the epoxy, and
aircraft wings are always a potential fatigue site.

--
Ed Huntress

On Jul 22, 10:39*am, "Buerste" wrote:
"Karl Townsend" wrote in message

I need to mount a 10 tooth .200 pitch timing pulley to a 3/8 shaft on my
servo motor. I bored the pulley yesterday before I noticed there's not
enough meat left for a key, let alone set screws.

If there is any hub, split it with a saw blade. *Make or buy 2-piece shaft
collar with the ID the same as the OD of the hub and clamp it.

This gets my vote, too. If (unlikely) the hub has enough
extension, one can also pipe-thread it with a die, and cinch
with a pipe-threaded nut (to make a kind of collet). The taper
on pipe threads makes a lot of circular wedging operations
do-able.

On Jul 23, 11:16*am, whit3rd wrote:


This gets my vote, too. *If (unlikely) the hub has enough
extension, one can also pipe-thread it with a die, and cinch
with a pipe-threaded nut (to make a kind of collet). * The taper
on pipe threads makes a lot of circular wedging operations
do-able.

Or run the pipe tap into the hub and bore out a reducer bushing to fit
the shaft, then slit the threaded end to allow it to compress. Iron
pipe fittings aren't always threaded very accurately, so I center a
machined brass one in the lathe and use it to center the threads of
iron pipe and fittings. Steel hydraulic fittings turned from bar stock
may be concentric enough inside and out.

jsw

On Wed, 22 Jul 2009 07:49:26 -0500, "Karl Townsend"
wrote:

I got a SNAFU in my project...

I need to mount a 10 tooth .200 pitch timing pulley to a 3/8 shaft on my
servo motor. I bored the pulley yesterday before I noticed there's not
enough meat left for a key, let alone set screws.

Anyway, I'm looking for a way to mount this pulley. Press fit? silver
solder? I've got NO experience with silver solder, which kind? Other ideas?

Karl



Just clean pulley and shaft and then use Loctite 603 or a close relative. I
use it with no problems both on pulleys and to drive 5" dia 4340 blanks on
1/2" drill rod arbour. Works well enough to take .050" cuts with nice blue
chips :-)


Mark Rand
RTFM

"Ed Huntress" wrote in message
...

snip

It hope it will be useful to you sometime, Michael. Epoxy can be fairly
complicated, especially when you get into the elevated-temperature-cure
industrial products that we never see on the regular markets. They can
have tensile and sheer strength running 2.5X stronger than anything we can
buy in small quantities. Epoxy is great stuff but you really have to
understand its properties when you use it for hefty loads. For example,
the stronger it is in shear, the weaker it *may* be in peel.

I don't know where this scratch-in idea started, but I think I know where
it first appeared in print: in the Gougeon Brothers' first book, published
in the early '70s. (The Gougeons were the originators of the WEST epoxy
system.) They used it to fasten stainless deck hardware to their boats.

Since those guys are highly respected empiricists -- they actually test
and try their ideas before talking about them -- it caught on in the
boating community. Then it started to show up in metalworking, with some
of my writing in the late '70s a possible contributor. d8-)

Anyway, I've used it many times, and I've done some of my own testing
(with pry bars and hammers g), and I'm sold on it. FWIW, I've gotten
mixed results with copper alloys, so I don't know about using it on them.
Sometimes yes, sometimes no.


I did a lot of reading and experimentation with epoxy a couple of years back
when I was trying to glue stones to one another. I got pretty decent
results - until you put the stone structure outside in the sun. Epoxy does
not like that!

Now I am experimenting with gluing the sundial faces to the armature. The
obvious way to attach the two is either welding or brazing, but any heat
application to a finished face can play havoc with it. I tried screwing the
two together, but there is only so many 10-32 threads you can get into a
blind hole drilled at the back of a 5 mm face, let alone the sweaty feeling
when drilling the blind hole into a finished face hoping that you do not
break through.

I had a fairly decent result with JBWeld but he key was the area of
adhesion which I made purposely quite large. That is something I would like
to change. I did a few experiments with different shapes of the bonded
surfaces (milling little pockets etc.) but the strength has been inferior so
far.

What I noticed almost without exception is that when the bond breaks the
epoxy separates almost totally from one of the surfaces whilst still
adhering to the other. There is almost never a break "through the middle" of
the bond. I make it a rule to prepare both surfaces the same way but this
suggests to me that I am failing on one of them (both are steel, BTW). The
scratch-in method may be the answer.

--
Michael Koblic
Campbell River, BC

"Michael Koblic" wrote in message
...

"Ed Huntress" wrote in message
...

snip

It hope it will be useful to you sometime, Michael. Epoxy can be fairly
complicated, especially when you get into the elevated-temperature-cure
industrial products that we never see on the regular markets. They can
have tensile and sheer strength running 2.5X stronger than anything we
can buy in small quantities. Epoxy is great stuff but you really have to
understand its properties when you use it for hefty loads. For example,
the stronger it is in shear, the weaker it *may* be in peel.

I don't know where this scratch-in idea started, but I think I know where
it first appeared in print: in the Gougeon Brothers' first book,
published in the early '70s. (The Gougeons were the originators of the
WEST epoxy system.) They used it to fasten stainless deck hardware to
their boats.

Since those guys are highly respected empiricists -- they actually test
and try their ideas before talking about them -- it caught on in the
boating community. Then it started to show up in metalworking, with some
of my writing in the late '70s a possible contributor. d8-)

Anyway, I've used it many times, and I've done some of my own testing
(with pry bars and hammers g), and I'm sold on it. FWIW, I've gotten
mixed results with copper alloys, so I don't know about using it on them.
Sometimes yes, sometimes no.


I did a lot of reading and experimentation with epoxy a couple of years
back when I was trying to glue stones to one another. I got pretty decent
results - until you put the stone structure outside in the sun. Epoxy does
not like that!

Now I am experimenting with gluing the sundial faces to the armature. The
obvious way to attach the two is either welding or brazing, but any heat
application to a finished face can play havoc with it. I tried screwing
the two together, but there is only so many 10-32 threads you can get into
a blind hole drilled at the back of a 5 mm face, let alone the sweaty
feeling when drilling the blind hole into a finished face hoping that you
do not break through.

I had a fairly decent result with JBWeld but he key was the area of
adhesion which I made purposely quite large. That is something I would
like to change. I did a few experiments with different shapes of the
bonded surfaces (milling little pockets etc.) but the strength has been
inferior so far.

What I noticed almost without exception is that when the bond breaks the
epoxy separates almost totally from one of the surfaces whilst still
adhering to the other. There is almost never a break "through the middle"
of the bond. I make it a rule to prepare both surfaces the same way but
this suggests to me that I am failing on one of them (both are steel,
BTW). The scratch-in method may be the answer.

--
Michael Koblic
Campbell River, BC

It may be. The failure mode you're describing sounds like a basic adhesion
problem, due either to tying to bond to an oxide layer or to contamination
of the surface.

It's not unusual for epoxy to let go like that, and the stronger the epoxy,
the more likely it is. When there is a peel or cleavage load on the joint
and a tiny spot at an edge has poor adhesion, the peel will start there.
Then it peels catastrophically. That's the exact type of failure that
rivet-bonding is intended to prevent in aircraft skins. The rivets prevent
the initial lifting of an edge.

Epoxies modified with elastomers are intended to reduce that peel weakness.
Most epoxy products sold at retail have some degree of resistance to it (and
a somewhat lower shear and tensile strength as a result), but most epoxies
are more vulnerable to peel failure than some other adhesives.

So it's important to have a really clean surface to eliminate the weak spots
near the edges of the bond. On many metals, the degree of cleanliness needed
to get the best performance disappears within seconds of the metal's
exposure to air. Preventing that contact with air is what scratching-in is
all about.

Good luck.

--
Ed Huntress

On Jul 23, 10:26*pm, "Michael Koblic" wrote:
[attach thin plate?]
Michael Koblic

http://www.midwestfasteners.com/prod...ess/whatis.php

Ed Huntress wrote:

It may be. The failure mode you're describing sounds like a basic
adhesion problem, due either to tying to bond to an oxide layer or to
contamination of the surface.

It's not unusual for epoxy to let go like that, and the stronger the
epoxy, the more likely it is. When there is a peel or cleavage load
on the joint and a tiny spot at an edge has poor adhesion, the peel
will start there. Then it peels catastrophically. That's the exact
type of failure that rivet-bonding is intended to prevent in aircraft
skins. The rivets prevent the initial lifting of an edge.

So when I intuitively applied a layer of epoxy to a flat armature base and
then also screwed it down with 10-32 screws (each with about 1.5 threads) I
seem to have followed a sound principle! Great minds and all that...

Another way (again, intuition!) I tried to prevent a peel was to embed a
stud into a shallow milled cup at the back of the face. That did not work
but I wonder if that was partly because there was a lot of play around the
0.495" diamter stud in the 1/2" (nominal) milled hole.

I have got a 1/2" reamer on order. I wonder if a tighter fit in a hole will
restrict the tendency to peel better (the hole is only about 0.1" deep).

Epoxies modified with elastomers are intended to reduce that peel
weakness. Most epoxy products sold at retail have some degree of
resistance to it (and a somewhat lower shear and tensile strength as
a result), but most epoxies are more vulnerable to peel failure than
some other adhesives.

I have another trial under way right now - same hole pocket as above (the
reamer has not arrived yet) but tried the scratch-in method (difficult to do
in a 1/2" hole) and instead of JBWeld using a West System epoxy. Note to
self: Even the minimum amount mixed up in a 30 degree weather can produce
impressive amount of smoke and bubbling very quickly.

That is the main knock against the West: You have to mix up a minimum amount
which for me is usually many times what I need. I have taken to using the
rest up in making knobs for my Taig etc. but today the speed of the reaction
rather overtook me.

So it's important to have a really clean surface to eliminate the
weak spots near the edges of the bond. On many metals, the degree of
cleanliness needed to get the best performance disappears within
seconds of the metal's exposure to air. Preventing that contact with
air is what scratching-in is all about.

Acetone and Windex usually does it for me. I have used a more aggressive
degreaser on occasions instead of Windex but the rust would form in front of
my eyes.

I shall report tomorrow.

--
Michael Koblic
Campbell River, BC

Jim Wilkins wrote:
On Jul 23, 10:26 pm, "Michael Koblic" wrote:
[attach thin plate?]
Michael Koblic

http://www.midwestfasteners.com/prod...ess/whatis.php

That is cool!

--
Michael Koblic
Campbell River, BC

On Jul 24, 9:27*pm, "Michael Koblic" wrote:
Jim Wilkins wrote:
On Jul 23, 10:26 pm, "Michael Koblic" wrote:
[attach thin plate?]
Michael Koblic

http://www.midwestfasteners.com/prod...ess/whatis.php

That is cool!

Michael Koblic

http://www.harborfreight.com/cpi/cta...temnumber=3223

Don't have one, don't know how well they work, studs aren't rustproof,
but it's a start. Has anyone tried them with other hardware such as
stainless steel flathead screws?

jsw

The stud welders that I'm familiar with utilized studs that are a fairly
standard design in industry. I never saw any applications where studs were
attached for any structural loads, instead, just added to cabinets for cover
panel attachment, mostly (cover panels up to about .250" x 3' x 4').
The welders were considerably larger in size and capacity than the
referenced HF model.

The studs all had a small nib/tit (similar to facing on a lathe, and missing
the center or parting off). It's the small nib that creates the weld bond,
as it melts and spreads.
Being a very small cross-sectional area, the nib gets hottest.

It's likely that many models of spot welders (resistance or capacitor
discharge) could be adapted to weld commercially manufactured studs intended
for welding.
Practice and making notes of different materials, and welder settings could
lead to relatively predictable results, but there would probably be quite a
few that wouldn't achieve proper bond/fusing when starting out.

FWIW, in some methods of attaching straps with spot welders, the straps are
prepared by making a similar nib by punching the strap end with a fine prick
punch to deform the weld area so that the actual welding contact area is
smaller than the end of the strap.
This method is claimed to be more efficient, IIRC, than trying to get the
welding tips to cause the equivalent bond strength and penetration.

I'm still a couple of projects away from playing with the resistance spot
welder I bought a couple of months ago, but one of the ideas I want to try,
is placing a nugget of silver solder between two parts and activating the
welder to make the bond.
I think the nugget will act as the nib does in the above examples.
There is an existing application for this method, IIRC, I seem to remember
reading about it some time ago.

--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html


"Jim Wilkins" wrote in message
...
On Jul 24, 9:27 pm, "Michael Koblic" wrote:
Jim Wilkins wrote:
On Jul 23, 10:26 pm, "Michael Koblic" wrote:
[attach thin plate?]
Michael Koblic

http://www.midwestfasteners.com/prod...ess/whatis.php

That is cool!

Michael Koblic

http://www.harborfreight.com/cpi/cta...temnumber=3223

Don't have one, don't know how well they work, studs aren't rustproof,
but it's a start. Has anyone tried them with other hardware such as
stainless steel flathead screws?

jsw

On Sat, 25 Jul 2009 04:58:09 -0700 (PDT), Jim Wilkins
wrote:

On Jul 24, 9:27*pm, "Michael Koblic" wrote:
Jim Wilkins wrote:
On Jul 23, 10:26 pm, "Michael Koblic" wrote:
[attach thin plate?]
Michael Koblic

http://www.midwestfasteners.com/prod...ess/whatis.php

That is cool!

That one could be used for structural purposes.


http://www.harborfreight.com/cpi/cta...temnumber=3223

Don't have one, don't know how well they work, studs aren't rustproof,
but it's a start. Has anyone tried them with other hardware such as
stainless steel flathead screws?

Wouldn't waste the effort if this is structural - Those studs are
meant to be a short-term weld to grab onto a chunk of fender and pull
out the dent with a slap-hammer. (Which is included, even!) Then
when you have the dent pulled out the stud welds are supposed to
release fairly easily by bending so you can clean up the fender and do
your prep and paint.

And I wouldn't count on the tool to live long - most Harbor Freight
stuff is Light Duty and will live okay for an occasional home project.
If you plan to use it all day, every day, for pay - buy two, and carry
them both. So when one dies, you have the other one to finish out the
day, long enough to go buy a new spare.

-- Bruce --