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'[OT: ] Securing a steel pin in brass'
2004\01\23@104824 by Jack Smith

picon face
>Here's the problem:  how do you join the steel bits to the brass?
>Right now we use super glue, which is okay, but since they really
>need to be sterile, it would be nice to autoclave them, which
>means temperatures up to 150-170 degrees C, and superglue
>doesn't generally like that.

If you are happy with the adhesive approach, why not try a high temperature
retaining compound, such as Loctite 620, which is rated for operation at 230
degrees C. It requires a high temperature cure period, however.
http://www.loctite.com.au/industrial/PRODUCTS/620.htm for more info.

As far as soldering to steel, isn't that mostly a matter of using the right
flux?


Jack Smith

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2004\01\23@162105 by Jinx

face picon face
> As far as soldering to steel, isn't that mostly a matter of using
> the right flux?

Silver solder will join steel to brass. Mike's app is physically small
and it could get fiddly and may need cleaning up afterwards. Also
the metals will have to be heated so hot (around 1200F) to melt the
solder that you may as well use the thermal method as others have
mentioned

BTW, it's a good way of using up scrap metal in an "alternative art"
kind of way. I once made what I thought was a pretty nice-looking
wall piece out of brass plate with captured various diameter ball
bearings and aluminium rod

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2004\01\23@174519 by Mike Hord

picon face
Thanks for all answers!  It sounds like the thermal method is the
best option, but that MAY pose a problem, since we've already
purchased all the bits to be used as well as contracted the
manufacture of the brass components.  If the fit is still tight (as
it has been in the initial batch), I may try it.

As far as heating these things to red hot, that's probably not a
good option, as the parts are ridiculously tiny.  I'm hoping I can
use a heat gun to get it hot enough.

The real bugger is getting the nut to stay in place on the screw,
to affix the upper bit to where it needs to stay.

Anyway, thanks all!  I hadn't even considered it!

Mike H.

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2004\01\23@182249 by Jinx

face picon face
> As far as heating these things to red hot, that's probably not a
> good option, as the parts are ridiculously tiny.  I'm hoping I can
> use a heat gun to get it hot enough.

Look up figures for thermal coefficient of expansion to get an idea
of whether you can work with what you've got. A clockmaker friend
of mine uses a small butane pencil torch to place steel pins and
axles in brass chassis. You need only the minutest difference to
get an exceedingly hard grip on cooling

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2004\01\23@182835 by Roy E. Burrage

picon face
Mike,

Hope you'll excuse me, but I just joined this list so I've probably
missed a bit of what has gone on before.

It is possible to use a standard tin/lead solder on steel and ferrous
alloys, which is what you need to do from what little I've read of this
thread.  The difference is that steel doesn't react well with the
"normal" resin type fluxes we use for electronic soldering.  Several
years ago we had to do something similar and one of our metal suppliers
suggested we look at fluxes with a fluoride component, if memory serves
correctly.  You might try contacting one of the larger solder
manufacturers like Aim Products, Kester, or Alpha Metals to be sure.  If
your steel parts are stainless steel, it's a problem.

You could also try a capacitor discharge type spot weld if you don't
have a lot of these things to do.  This is the kind of spot welder they
use to put tabs on batteries if you've ever seen that done.

REB

Mike Hord wrote:

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2004\01\23@184119 by Dan Devine

picon face
I've done this with large bearings ( larger than 8" shaft dia.) too.
Heat quickly and move quickly before the therms move where you don't
want them to.  Try to keep your heat localized.

Jinx is right, you'll only need something like 0.001" interference fit
to get things locked.  Machinists Handbook has the classes of
"light-press" "med-press" and "interference" type fits.  This depends on
the diameter of the objects you are working with though.

I've seen this done with valve seats in engines too.  Expand the head
with a torch and shrink the seats with dry ice.  Seats drop in easily,
and once everything gets to the same temperature, the seats are locked
in.


On Sat, 2004-01-24 at 04:22, Jinx wrote:
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2004\01\23@194422 by Denny Esterline

picon face
Hmmm.. I didn't know other people had trouble soldering to steel. I've done
it quite a lot with standard plumbing solder and flux. I haven't tried the
new lead free solder and it's flux, but you should still be able to find
zinc chloride flux at most hardware stores.

That said, I'm not sure that soldering is the best idea for these little
gizmos (whatever they're for). A press fit would be the "standard" way to
attach somthing of this nature.

-Denny

{Original Message removed}

2004\01\23@202859 by Jinx

face picon face
> It is possible to use a standard tin/lead solder on steel and ferrous

Absolutely true when you (well I actually ;-) think about - after all,
what are soldering iron tips made of ? And tabs on shielding ?
And pot cases ?

Tin/lead is not something I'd considered, basically because any
work I do with mixed metal is usually on the large size and I don't
rely on ordinary low-temp solder being strong enough (in my
applications at least). However, Mike's small pieces might well be
able to be done with normal solder. Could even get away with
normal flux too if he's lucky

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2004\01\23@211501 by Mike Hord

picon face
>I've seen this done with valve seats in engines too.  Expand the head
>with a torch and shrink the seats with dry ice.  Seats drop in easily,
>and once everything gets to the same temperature, the seats are locked
>in.

Now that's a good idea.  We routinely use dry ice in our lab, and I believe
it would be far easier to use the dry ice to reduce the pin than a heat gun
to expand the work.

Thanks!

Mike H.

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2004\01\23@212052 by Josh Koffman

flavicon
face
This is an ok idea, but I believe part of the reason heating the brass
works so well is because it will expand more than the steel will.
Cooling steel might not make it contract enough to get a tight fit. I'm
not an engineer though, so you might want to check out the physical
properties of the metals.

Josh
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Mike Hord wrote:
> Now that's a good idea.  We routinely use dry ice in our lab, and I believe
> it would be far easier to use the dry ice to reduce the pin than a heat gun
> to expand the work.

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2004\01\23@212713 by Mike Hord

picon face
>That said, I'm not sure that soldering is the best idea for these little
>gizmos (whatever they're for). A press fit would be the "standard" way to
>attach somthing of this nature.
>
>-Denny

I think I agree with the "no-solder" assessment.  There is on the order of
<.010" between the pin hole and the head of the screw for adjustment.

Sorry, I don't know the metric equivalent right off.  ;-)

For those interested, and please don't let this become a PETA thing, these
gizmos are "installed" in the skull of a rabbit and then used to raise and
lower
a cannula in the brain, which is then used to inject drugs into precisely
specified locations, activating and deactivating parts of the brain to study
learning.

Mike H.

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2004\01\24@031739 by Robert Rolf

picon face
Dry ice is what, -40C? We get those kind of winters up here so your
pins would fall out <G>. Better to use liquid nitrogen.
Heating the work with a pinpoint flame is
pretty easy to do, and you get much larger diameter change for a
given temperature change when you have a ring, rather than a pin.
IOW, heating the hole works better than trying to cool the pin.
And the lower thermal mass of the pin means you'd better be darned fast.

Robert

Josh Koffman wrote:
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2004\01\24@134326 by Peter L. Peres

picon face
> For those interested, and please don't let this become a PETA thing,
> these gizmos are "installed" in the skull of a rabbit and then used to
> raise and lower a cannula in the brain, which is then used to inject
> drugs into precisely specified locations, activating and deactivating
> parts of the brain to study learning.

Oh, great. I remember vaguely that one of the reasons for which brass is
not ok for in vivo is the fact that it has to be used necessarily with
steel tools (like blades). The resulting battery (when steel touches brass
directly or through a solution with a different conductivity) and its
electro-chemical products, and the corrosion that should ensue, are
undesirable, to put it mildly. Maybe your rabbits will behave like that
battery manufacturer's ones in the tv ads, i.e. run forever. I would test
the assemblies in physiological solution for a week or so before using
them.

glad not to be a rabbit,

Peter the not rabbit

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2004\01\24@220225 by Mike Hord

picon face
>Dry ice is what, -40C? We get those kind of winters up here so your
>pins would fall out <G>. Better to use liquid nitrogen.
>Heating the work with a pinpoint flame is
>pretty easy to do, and you get much larger diameter change for a
>given temperature change when you have a ring, rather than a pin.
>IOW, heating the hole works better than trying to cool the pin.
>And the lower thermal mass of the pin means you'd better be darned fast.
>
>Robert

If these animals are ever exposed to that kind of cold, we'll have bigger
things to worry about.

Mike H.

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2004\01\24@220641 by Mike Hord

picon face
>Oh, great. I remember vaguely that one of the reasons for which brass is
>not ok for in vivo is the fact that it has to be used necessarily with
>steel tools (like blades). The resulting battery (when steel touches brass
>directly or through a solution with a different conductivity) and its
>electro-chemical products, and the corrosion that should ensue, are
>undesirable, to put it mildly. Maybe your rabbits will behave like that
>battery manufacturer's ones in the tv ads, i.e. run forever. I would test
>the assemblies in physiological solution for a week or so before using
>them.
>
>glad not to be a rabbit,
>
>Peter the not rabbit

They actually get embedded in a layer of dental acrylic, and never actually
contact the skull or any tissue.  We have already implanted a few early
generations of these, and they are not so different that a design that
has been in use for years.

The joining problem hasn't ever been solved, though.  I'm going to try
the heating/cooling trick, and possibly some JB Weld, and see if either
of those work.

Mike H.

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2004\01\24@225249 by Dan Devine

picon face
I just did a quick search on Google for stuff relating to this.

Here's a good description of the expansion formula for the brass plate.
The formula for the pin should be similar, shrinking in diameter
according to temperature.  Brass has almost double the expansion ratio,
so you will get more "bang for your buck" by heating the brass than you
will from cooling the pin.  Doing both would be best, depending on
diameter, you may get a really great lock.

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thexp2.html

This also has a table for the expansion coefficients.


>From my machinist's background, I have the following suggestions.

1) When drilling the hole, drill smaller than required and follow-up
with a "straight reamer" to get the hole size accurate.  Drills are
notorious for making slightly oversize holes from indicated size.  This
could be caused by chips, the flutes, whatever.  Use a reamer to get the
size exact, try for 0.003" undersize of the pin to start (depending on
diameter).

2) Slightly countersink the back side of the plate before insertion of
the pin, then after insertion, peen a little mushroom to keep the pin
locked.

3) Use no oil or lubricant!!  Without this, you may get an excellent
friction weld on the metals as the co-mingle during the transition back
to room temperature.

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2004\01\25@120454 by John Ferrell

face picon face
You can heat the brass and cool the pin. As small as the parts are a
soldering iron or a butane mini torch will likely be enough. Salt on chipped
ice will get about -16 degrees F as I recall.

John Ferrell
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