On Thu, 28 Aug 2008 14:46:23 -0700, Roy Lewallen
wrote:

Jeff Liebermann wrote:
. . .
You don't want to heat the outside. That will cause the outer tube to
expand, which will increase its compression on the inner tube. You
want to cool both tubes causing both to contract. If you can remove
an end cap, pour in some ice water.
. . .

If you heat a ring of material, both the OD and ID increase in
proportion. This loosens, not tightens, its hold on an inner object.

I did this with an aluminum torus way back in college daze. You're
mostly correct. The O.D. does most of the radial expanding, but there
may be a small amount of expansion in the I.D. depending on the
compressibility of the material. If the material is soft, the I.D.
will shrink slightly. If the material is hard and incompressible,
then the I.D. will expand slightly. This illustrates it fairly well
(for incompressible materials):
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thexp2.html

What I'm counting on is NOT the change in radius cause by a change in
temperature. I'm looking for a slight change in length, which with a
taper, has a somewhat similar effect on releasing the jam than a
radial change. In that case, the inner taper shrinks, while the outer
taper lengthens.

I recall from freshman physics that if you heat two concentric rings
made of the same material (having a positive coefficient of expansion),
all dimensions increase by exactly the same proportion. A little
geometry shows that any gap, even microscopic, between them will
therefore also increase proportionally. Cooling both objects of course
has the opposite effect, reducing the size of any gap and tightening the
fit.

Apparently, I'm not the only one having problems with the concept.
See:
http://www.eng-tips.com/viewthread.cfm?qid=99646

Heating the outer one and cooling the inner one, as Ed did, gives
you the best of both, increasing the ID of the outer tube and decreasing
the OD of the inner tube.

Maybe. If the ID of the outer tube does not change with temperature,
then heating the outer tube is a waste of effort. If the material is
sufficiently incompressible, then it will expand slightly as you
suggest. I'm not sure how fiberglass reacts as it depends heavily on
the glass weave pattern and composition. If the pole bends, it may
have some compressibility.

Drivel: If the surface roughness is more than the heated or cooled
radial expansion of the tubing, it may still remain stuck.

Roy Lewallen, W7EL
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 28 Aug 2008 17:40:08 GMT, Ed
wrote:

This mast is smooth all the way, no cams, locks, etc. The tubes must
be "slightly" tapered such that as you pull one out of the other it locks
in place by sheer friction.

After stuffing myself with a near-terminally fattening ice cream, I
realized that we may be talking about two different types of masts.
I'm thinking of a telescoping mast, where each smaller section fits
inside a somewhat larger diameter section. Kinda like a telescoping
metal whip antenna (i.e. rabbit ears). However, there are also masts
made of equal diameter tubing, with some sort of coupler at the ends.
Your initial posting clearly said "telescoping" but I'm wondering how
one makes a self supporting telescoping mast without an internal or
external locking mechanism.

Which type to you have?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:
On Thu, 28 Aug 2008 12:07:01 +0100, Ian White GM3SEK
wrote:

On the other hand,
I've never damaged one by end-on impact.

I have. It split the tubing just below the locking area. The problem
is that there are many types of locking mechanisms. You need to know
what's inside and how it works before applying the traditional brute
force.

That's a fair point. From what Ed did (and did not) say, I was assuming
his pole had a simplest kind of tapered friction lock... which turns out
to be so. These often can be freed by end-on impact when twisting
doesn't work and squeezing might crush the thin walls.


For example, some poles use external compression or cam type locking
mechanisms:
http://www.telescopingpoles.com/specs.html
http://www.briarwoodproducts.com/newtools.htm
These do not jam and will respond properly to the inertial hammer
(brute force) disconnect method. However, they add width which is
often undesireable.

Internal locks, with expanding cores, cams, or wedges are a different
story. To prevent collapse, most become tighter when loaded in
compression, especiallyl those that take advantage of a slight conical
taper in the tubing:
http://www.google.com/patents?id=78duAAAAEBAJ
http://www.google.com/patents?id=fvc5AAAAEBAJ
http://www.google.com/patents?id=i2ZMAAAAEBAJ
http://www.google.com/patents?id=_hMBAAAAEBAJ
(Look at the drawings). Banging on these internal locks will jam them
only worse.

I couldn't find a picture of the inside of the common window washer
fiberglass pole. It has partial threads molded into the fiberglass.
1/4 turn to lock. Bang on that design, and you'll split the tubing
(like I did).



But even so... hitting something with a hammer shouldn't always be
condemned as "brute" force. Sometimes it *is* the most intelligent thing
to do.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

This mast is smooth all the way, no cams, locks, etc. The tubes
must
be "slightly" tapered such that as you pull one out of the other it
locks in place by sheer friction.

After stuffing myself with a near-terminally fattening ice cream, I
realized that we may be talking about two different types of masts.
I'm thinking of a telescoping mast, where each smaller section fits
inside a somewhat larger diameter section. Kinda like a telescoping
metal whip antenna (i.e. rabbit ears). However, there are also masts
made of equal diameter tubing, with some sort of coupler at the ends.
Your initial posting clearly said "telescoping" but I'm wondering how
one makes a self supporting telescoping mast without an internal or
external locking mechanism.

Which type to you have?


Very cheap plain fiberglass tubes, slightly tapered so that as an
inner tube is pulled up in its outer tube, the taper reaches a point of
great friction. Incidently, the tubes on the outside are all coated
glossy smooth except for a couple inches at the bottom where the inner
and outer tubes meet.... raw fiberglass has great friction coeficient,
apparently.

Also, I suspect my problem is that the extended mast was left out in
the rain a week when it rained a bit and water got in the joints causing
swelling?

There is no make / model number on this. Its a cheap generic made-in-
China flag banner pole for RVers, etc.

I managed to loosen one of the frozen connections, but the two
others, one of which I tried the lubricant are yet to be unfrozen.

I have a strong feeling that the use of those rubber type wrenchs
would simply apply enough torque to the tubes to fracture them.

I am letting the stuck sections sit in my garage in hopes that
eventually they will dry out on the inside and then perhaps I can get
them unstuck with further application of hand pressure.

I may stuff myself with terminally fattening ice cream, too, while
waiting..... :^)

My thanks to all who have provided suggestions, etc.

Ed K7AAT

That's a fair point. From what Ed did (and did not) say, I was assuming
his pole had a simplest kind of tapered friction lock... which turns out
to be so. These often can be freed by end-on impact when twisting
doesn't work and squeezing might crush the thin walls.



I guess if I use a somewhat soft wood as a backstop, I may resort to
that. I'm going to give the tubes another week to dry out before resorting
to further violence! :^)

Ed