I'm hoping someone can help me with a problem I am having. I have a telescope
mounted on a 54 inch tall, 3/16 inch wall, 8x8 square aluminum tube with 1.25
inch plates welded to the top and bottom and bolted to 2/3 of a yard of
concrete. The problem is I am getting a little too much movement out of the
tube and I need to increase the stiffness of the tube. The ideal situation
would be to replace the tube with something larger but that's just not possible
at this point in time. I don't need a radical increase in stiffness either so I
think there is something I could do to for a slight increase in stiffness. I
need to kill low frequency vibrations so please don't suggest sand or concrete,
beside concrete and alumimun don't get along with each other. Any ideas ? Would
putting the tube under tension help ?


Scott Hogsten

Maybe wrap the whole thing in fiber reinforced plastic (fiberglass,
carbon fiber, kevlar)?
Wicks Aircraft Supply www.wicksaircraft.com sells graphite carbon fiber
"tape" that's 5" wide and compatible with all major resin types:
http://www.wicksaircraft.com/gotopage.php?page=20
They also have kevlar cloth (which is difficult to cut) and epoxy tapes
(cheap).
As I believe someone else already mentioned, you would want to determine
whether the tube is bending or twisting before you decided how to apply a
uni-directional tape, or use a bi-directional cloth. Possibly wrap the
uni-directional carbon fiber tape in a "barber-pole" pattern from top to
bottom... once in each direction?
If you scrub the thing down with a scotch-brite pad soaked in an
acetone/resin mixture... it will "prime" the aluminum and prevent oxides
from forming on the surface, so you get a better bond.
David




"qedude" wrote in message
...
I'm hoping someone can help me with a problem I am having. I have a
telescope
mounted on a 54 inch tall, 3/16 inch wall, 8x8 square aluminum tube with
1.25
inch plates welded to the top and bottom and bolted to 2/3 of a yard of
concrete. The problem is I am getting a little too much movement out of
the
tube and I need to increase the stiffness of the tube. The ideal situation
would be to replace the tube with something larger but that's just not
possible
at this point in time. I don't need a radical increase in stiffness either
so I
think there is something I could do to for a slight increase in stiffness.
I
need to kill low frequency vibrations so please don't suggest sand or
concrete,
beside concrete and alumimun don't get along with each other. Any ideas ?
Would
putting the tube under tension help ?


Scott Hogsten

And the problem with sand is? Filling with sand probably won't do
much for the stiffness, but would kill the vibrations. It would also
increase the mass and therefore the deflection caused by a bump.

What causes your problem? Stepper motor?

Putting the aluminum under tension will do nothing as far as I know.

Dan


domain (qedude) wrote in message ...
I'm hoping someone can help me with a problem I am having. I have a telescope
mounted on a 54 inch tall, 3/16 inch wall, 8x8 square aluminum tube with 1.25
inch plates welded to the top and bottom and bolted to 2/3 of a yard of
concrete. The problem is I am getting a little too much movement out of the
tube and I need to increase the stiffness of the tube. The ideal situation
would be to replace the tube with something larger but that's just not possible
at this point in time. I don't need a radical increase in stiffness either so I
think there is something I could do to for a slight increase in stiffness. I
need to kill low frequency vibrations so please don't suggest sand or concrete,
beside concrete and alumimun don't get along with each other. Any ideas ? Would
putting the tube under tension help ?


Scott Hogsten

In article ,
says...

And the problem with sand is? Filling with sand probably won't do
much for the stiffness, but would kill the vibrations. It would also
increase the mass and therefore the deflection caused by a bump.

What causes your problem? Stepper motor?

Putting the aluminum under tension will do nothing as far as I know.

Dan

I'm trying to kill a low frequency vibration (think a slow sway back and
forth). I agree that sand will kill the high frequency stuff but it's not going
to help in this situation. I'm having a hard time determining exactly what is
causing this vibration. It's not the mount as I can kill the power and there is
still a slow sway to the mount and it doesn't seem to die out. Either I have
created a really good pendulum or I may be getting a low frequency harmonic
from a highway about a 1/3 of a mile away.

I was thinking about running a tensioning rod from each corner down to the edge
of the concrete pier to triangulate the top and help add a little resistance to
the mount bending in tension.

If I can't solve the problem simply in the next couple of weeks I'll probably
just replace everything with steel. I have the steel but the aluminum came
available at the right price (scrap price) and I didn't have to spend the time
to sandblast and paint it like I will the steel. The only reason I am spending
time with it is that it is so close to working. If I can cut the size or the
error or move the frequency lower so that I can guide it out I'll be happy.

Scott

You might try clamping some weight on the top of the column. That
will lower the column resonate frequency and may help. If it does,
filling the column with sand will help.

Do you stand on the same concrete as the tube is mounted on?

A rod or cable from the corners of the top plate to the corners of the
base will help a lot if it is the tube flexing. Compression or
tension on the aluminum won't make a difference, but adding to the
structure will.

It would be good to understand what is causing the vibration before
changing to steel. The problem may not be in the column flexing.
Maybe you could clamp a magnet to the column top and figure out a way
to support a coil so you can measure the vibration. We used a
geophone from a surplus store on the BPAA telescope.

Dan


domain (qedude) wrote in message news


I'm trying to kill a low frequency vibration (think a slow sway back and
forth). I agree that sand will kill the high frequency stuff but it's not going
to help in this situation. I'm having a hard time determining exactly what is
causing this vibration. It's not the mount as I can kill the power and there is
still a slow sway to the mount and it doesn't seem to die out. Either I have
created a really good pendulum or I may be getting a low frequency harmonic
from a highway about a 1/3 of a mile away.

I was thinking about running a tensioning rod from each corner down to the edge
of the concrete pier to triangulate the top and help add a little resistance to
the mount bending in tension.

If I can't solve the problem simply in the next couple of weeks I'll probably
just replace everything with steel. I have the steel but the aluminum came
available at the right price (scrap price) and I didn't have to spend the time
to sandblast and paint it like I will the steel. The only reason I am spending
time with it is that it is so close to working. If I can cut the size or the
error or move the frequency lower so that I can guide it out I'll be happy.

Scott

Hey Scott,

Or how about adding the suggested rods/cables, but instead of taking
them to their respective corners in triangulation, take them to the
"next" corner and force the highest torquing action you can? Takes
the aluminum out of it's normal harmonic range and close to it's
elastic limit.

Take care.

Brian Lawson,
Bothwell, Ontario.
XXXXXXXXXXXXXXXXXXXXXXXX
On 4 Nov 2003 19:46:22 -0800, (Dan Caster) wrote:

You might try clamping some weight on the top of the column. That
will lower the column resonate frequency and may help. If it does,
filling the column with sand will help.

Do you stand on the same concrete as the tube is mounted on?

A rod or cable from the corners of the top plate to the corners of the
base will help a lot if it is the tube flexing. Compression or
tension on the aluminum won't make a difference, but adding to the
structure will.

It would be good to understand what is causing the vibration before
changing to steel. The problem may not be in the column flexing.
Maybe you could clamp a magnet to the column top and figure out a way
to support a coil so you can measure the vibration. We used a
geophone from a surplus store on the BPAA telescope.

Dan


(qedude) wrote in message news


I'm trying to kill a low frequency vibration (think a slow sway back and
forth). I agree that sand will kill the high frequency stuff but it's not going
to help in this situation. I'm having a hard time determining exactly what is
causing this vibration. It's not the mount as I can kill the power and there is
still a slow sway to the mount and it doesn't seem to die out. Either I have
created a really good pendulum or I may be getting a low frequency harmonic
from a highway about a 1/3 of a mile away.

I was thinking about running a tensioning rod from each corner down to the edge
of the concrete pier to triangulate the top and help add a little resistance to
the mount bending in tension.

If I can't solve the problem simply in the next couple of weeks I'll probably
just replace everything with steel. I have the steel but the aluminum came
available at the right price (scrap price) and I didn't have to spend the time
to sandblast and paint it like I will the steel. The only reason I am spending
time with it is that it is so close to working. If I can cut the size or the
error or move the frequency lower so that I can guide it out I'll be happy.

Scott

On Tue, 4 Nov 2003 22:54:30 +0000 (UTC), domain
(qedude) wrote something
.......and in reply I say!:

You're not in California are you G??

Sounds as if you may have discovered the ultimate ground vib detector.

I'm trying to kill a low frequency vibration (think a slow sway back and
forth). I agree that sand will kill the high frequency stuff but it's not going
to help in this situation. I'm having a hard time determining exactly what is
causing this vibration. It's not the mount as I can kill the power and there is
still a slow sway to the mount and it doesn't seem to die out. Either I have
created a really good pendulum or I may be getting a low frequency harmonic
from a highway about a 1/3 of a mile away.


With a tube that size, and thickness, if you are still having trouble,
steel will probably not solve the problem.

If I can't solve the problem simply in the next couple of weeks I'll probably
just replace everything with steel. I have the steel but the aluminum came
available at the right price (scrap price) and I didn't have to spend the time
to sandblast and paint it like I will the steel. The only reason I am spending
time with it is that it is so close to working. If I can cut the size or the
error or move the frequency lower so that I can guide it out I'll be happy.

Scott

************************************************** ****************************************
Until I do the other one,this one means nothing
Nick White --- HEAD:Hertz Music

remove ns from my header address to reply via email

!!
")
_/ )
( )
_//- \__/

On Tue, 4 Nov 2003 22:54:30 +0000 (UTC), domain
(qedude) wrote:

It's not the mount as I can kill the power and there is
still a slow sway to the mount and it doesn't seem to die out. Either I have
created a really good pendulum or I may be getting a low frequency harmonic
from a highway about a 1/3 of a mile away.

If it's really not dying out, then it is VERY likely
to be extremely frequency-dependant. Adding sand
might just do it. Test whether changing the frequency
will help by clamping a large weight near the upper
part of the column with "lossy" pads between weight,
column, and clamps. If the vibration changes in frequency
or amplitude, you may be on track to cure it.

--
--Pete
"Peter W. Meek"
http://www.msen.com/~pwmeek/

Wow so many good ideas ! Some responses below.

The pier is completely isolated from the observing deck. The hole goes down
about 42 inches into fairly dense soil. At the 36 inch mark I hit a layer of
large stones that appears to go in for a while. The shape of the footer is like
a pyramid with the top chopped off. Someone asked about pouring a concrete
pier. While this is a great idea for a pier it creates a problem if you ever
want to move. Someone also mentioned pouring concrete into the pier - This is a
real no no with aluminum. The concrete will corrode aluminum in no time.

Someone asked how am I measuring this ?

Laser pointers :-) Clamp a laser pointer or in my case last pointers to the
pier and aim them at a target some distance away. This is how I can be fairly
sure that the pier itself is flexing. I can't be 100 percent sure since the
laser pointers don't give a really precise dot. I can also see this in the
eyepiece of the scope using a high power cross hair eyepiece.

Someone asked about the pier to concrete mounting.

I imbedded 3/4 inch jbolts 18 inched into the concrete. I leveled the top of
the concrete with a sheet of thick plexiglass so that it was level and smooth.
The bottom of the pier is flat to a very good straight edge. I used large
washers below the nuts and I tightened the nuts to 100 ft lbs.


I did an experiment last night. I took some 1.5 x 1.5 steel tubing and I
roughed it up with a 40 grit sanding disk. I clamped the tubing very tightly to
the pier with some homemade H clamps. This appears to have really helped
perhaps enough to allow me to image. Unfortunately clouds rolled in before I
could try the camera. So I am thinking of welding a rib down sides of the pier
as step one. I still want to try adding the tensioning rods as well to see if
that improves it more. I also started cleaning up the steel pipe last night as
well as I may end up going that way.

Scott Hogsten

On Wed, 5 Nov 2003 16:31:31 +0000 (UTC), domain
(qedude) wrote something
.......and in reply I say!:

Someone asked how am I measuring this ?

Laser pointers :-) Clamp a laser pointer or in my case last pointers to the
pier and aim them at a target some distance away. This is how I can be fairly
sure that the pier itself is flexing. I can't be 100 percent sure since the
laser pointers don't give a really precise dot. I can also see this in the
eyepiece of the scope using a high power cross hair eyepiece.


A question or two. When you say you can see the effect in the
eyepiece, using a cross-hair high mag eyepiece, what are you looking
at? Stars, or the Laser dots?

I ask because I am wondering if you are over-reacting. If the laser
pointer rotates at a radius of say, 3", and the dot is 100 feet away,
you have a 400:1 "magnification". If at that point you are hard-pushed
to see any movement, will the 'scope's view be affected at all?

I know a lot depends on the mounting etc, and the effective radius of
rotation of the laser. But it is a thought.
************************************************** ****************************************
Until I do the other one,this one means nothing
Nick White --- HEAD:Hertz Music

remove ns from my header address to reply via email

!!
")
_/ )
( )
_//- \__/

No I am looking at polaris with the drives off. Also it takes very little
vibration to introduce problems into system. We are talking arc seconds of
movement. With a little luck I will be doing some welding this weekend. Also on
the recommendation of a fellow amateur astronomer I am going to insert a gasket
between the pier and the concrete to see if that helps. BTW for those of you in
the eastern US there us a lunar eclipse tomorrow (Nov 8) starting at 6:30 and
reaching the darkest stages (totality) at about 8:10. Thanks for everyone's
help with this.

Scott Hogsten

In article ,
says...

On Wed, 5 Nov 2003 16:31:31 +0000 (UTC), domain
(qedude) wrote something
......and in reply I say!:

Someone asked how am I measuring this ?

Laser pointers :-) Clamp a laser pointer or in my case last pointers to the
pier and aim them at a target some distance away. This is how I can be fairly
sure that the pier itself is flexing. I can't be 100 percent sure since the
laser pointers don't give a really precise dot. I can also see this in the
eyepiece of the scope using a high power cross hair eyepiece.


A question or two. When you say you can see the effect in the
eyepiece, using a cross-hair high mag eyepiece, what are you looking
at? Stars, or the Laser dots?

I ask because I am wondering if you are over-reacting. If the laser
pointer rotates at a radius of say, 3", and the dot is 100 feet away,
you have a 400:1 "magnification". If at that point you are hard-pushed
to see any movement, will the 'scope's view be affected at all?

I know a lot depends on the mounting etc, and the effective radius of
rotation of the laser. But it is a thought.
************************************************* *****************************
************
Until I do the other one,this one means nothing
Nick White --- HEAD:Hertz Music

remove ns from my header address to reply via email

!!
")
_/ )
( )
_//- \__/

qedude wrote:

If I can't solve the problem simply in the next couple of weeks I'll probably
just replace everything with steel.

Probably won't help. Steel has three times the elastic modulus so will
raise the frequency. Steel has three times the mass so that will lower
the frequency. Haven't calculated it but the net result may well be
little or no change.

Ted

Before calculating the steel is 10 inch 3/8ths inch wall. So larger, thicker,
and much much heavier.

Scott Hogsten

In article , says...

qedude wrote:

If I can't solve the problem simply in the next couple of weeks I'll
probably
just replace everything with steel.

Probably won't help. Steel has three times the elastic modulus so will
raise the frequency. Steel has three times the mass so that will lower
the frequency. Haven't calculated it but the net result may well be
little or no change.

Ted

"qedude" wrote in message
...
I'm hoping someone can help me with a problem I am having. I have a
telescope
mounted on a 54 inch tall, 3/16 inch wall, 8x8 square aluminum tube with
1.25
inch plates welded to the top and bottom and bolted to 2/3 of a yard of
concrete. The problem is I am getting a little too much movement out of
the
tube and I need to increase the stiffness of the tube

Why not get rid of the aluminum tube and get a piece of cardboard sonotube
and fill it with concrete, maybe put a couple of lengths or rebar in it for
good measure. (Obligatory Metalworking Content!!)

John

"John Holbrook" wrote in message
...

"qedude" wrote in message
...
I'm hoping someone can help me with a problem I am having. I have a
telescope
mounted on a 54 inch tall, 3/16 inch wall, 8x8 square aluminum tube with
1.25
inch plates welded to the top and bottom and bolted to 2/3 of a yard of
concrete. The problem is I am getting a little too much movement out of
the
tube and I need to increase the stiffness of the tube

Why not get rid of the aluminum tube and get a piece of cardboard sonotube
and fill it with concrete, maybe put a couple of lengths or rebar in it
for
good measure. (Obligatory Metalworking Content!!)

John



Or fill the aluminum tube with concrete! Simple, cheap and I'd bet would
take care of the problem.
Lane

In article , qedude
wrote:

I'm hoping someone can help me with a problem I am having. I have a telescope
mounted on a 54 inch tall, 3/16 inch wall, 8x8 square aluminum tube with 1.25
inch plates welded to the top and bottom and bolted to 2/3 of a yard of
concrete. The problem is I am getting a little too much movement out of the
tube and I need to increase the stiffness of the tube. The ideal situation
would be to replace the tube with something larger but that's just not
possible
at this point in time. I don't need a radical increase in stiffness either so
I
think there is something I could do to for a slight increase in stiffness. I
need to kill low frequency vibrations so please don't suggest sand or
concrete,
beside concrete and alumimun don't get along with each other. Any ideas ?
Would
putting the tube under tension help ?


Scott Hogsten



Anchor forged eye-bolts to the 4 corners of your concrete pad and
connect steel cables from the eye-bolts to the top flange of your tube.
Use turnbuckles to adjust tension.

qedude wrote:

I'm hoping someone can help me with a problem I am having. I have a telescope
mounted on a 54 inch tall, 3/16 inch wall, 8x8 square aluminum tube with 1.25
inch plates welded to the top and bottom and bolted to 2/3 of a yard of
concrete. The problem is I am getting a little too much movement out of the
tube and I need to increase the stiffness of the tube. The ideal situation
would be to replace the tube with something larger but that's just not possible
at this point in time. I don't need a radical increase in stiffness either so I
think there is something I could do to for a slight increase in stiffness. I
need to kill low frequency vibrations so please don't suggest sand or concrete,
beside concrete and alumimun don't get along with each other. Any ideas ? Would
putting the tube under tension help ?


Scott Hogsten



Why not fill it with sand, as others have suggested, but in order to add
stiffness to the sand's damping qualities, mix it with a resin, so that
as well as having added mass, you have added considerable
stiffness/rigidity to it at the same time. The increased mass will damp
the high frequency vibration while the rigidity of it will damp the
lower frequencies.

Dave, UK

domain (qedude) wrote in
:

I'm hoping someone can help me with a problem I am having. I
have a telescope mounted on a 54 inch tall, 3/16 inch wall, 8x8
square aluminum tube with 1.25 inch plates welded to the top and
bottom and bolted to 2/3 of a yard of concrete. The problem is I
am getting a little too much movement out of the tube and I need
to increase the stiffness of the tube. The ideal situation would
be to replace the tube with something larger but that's just not
possible at this point in time. I don't need a radical increase
in stiffness either so I think there is something I could do to
for a slight increase in stiffness. I need to kill low frequency
vibrations so please don't suggest sand or concrete, beside
concrete and alumimun don't get along with each other. Any ideas
? Would putting the tube under tension help ?


Scott Hogsten


Fill it with urethane foam. Insert through small hole to create
force when foam expands inside.

Greetings and Salutations...

On Tue, 4 Nov 2003 18:24:39 +0000 (UTC), domain
(qedude) wrote:

I'm hoping someone can help me with a problem I am having. I have a telescope
mounted on a 54 inch tall, 3/16 inch wall, 8x8 square aluminum tube with 1.25
inch plates welded to the top and bottom and bolted to 2/3 of a yard of
concrete. The problem is I am getting a little too much movement out of the
tube and I need to increase the stiffness of the tube. The ideal situation
would be to replace the tube with something larger but that's just not possible
at this point in time. I don't need a radical increase in stiffness either so I
think there is something I could do to for a slight increase in stiffness. I
need to kill low frequency vibrations so please don't suggest sand or concrete,
beside concrete and alumimun don't get along with each other. Any ideas ? Would
putting the tube under tension help ?


Scott Hogsten

good suggestions in the other posts to this question.
How "low" is the vibration you are seeing and how close
is the highway?
It may be that the only way to fix this problem is to
decouple the telescope from the ground movement. For example,
you could pull the support shaft loose, & cast a large weight of
concrete around it (say...300 lbs). Be sure to put four lifting
rings on the upper surface of the concrete block, near the
corners. Then...build a heavy frame mounted on the original
pad. Make it a few inches larger than the block on the
shaft...say..maybe 3-5" per side. USe some heavy springs to
support the block base for the telescope inside the frame, so
it is free-floating. If necessary, you can get some cheap
Lawn Tractor inner tubes from Northern Tool, or some other
place, and, put them between the block and the frame, to
add some additional damping. It is best that they only
be inflated to a couple of PSI, though.
If your problem is low frequency vibrations from
the highway, this should do it. Oh...it occurs to me
it should be pretty easy to see if this is the problem,
though, as it should vary depending on traffic...
Regards
Dave Mundt

I think Dave is on the right track here with local vibrations creeping
in thru the foundation.

What kind of soil is your 2/3 of a yard of concrete poured into? Sand,
muck, clay, rocky?

The other issue also to consider is how are you determining movement?
Are you doing a long exposure camera shot and catching a star squiggle
or are you visually seeing a movement with your eye at the viewing piece?

Consider building a deck around the base of your scope to isolate you
the viewer from the foundation that the scope is connected to.



Had to give up looking up due to increased local light pollution.

Regards

Jim Vrzal
Holiday,FL



Dave Mundt wrote:
Greetings and Salutations...

On Tue, 4 Nov 2003 18:24:39 +0000 (UTC), domain
(qedude) wrote:


I'm hoping someone can help me with a problem I am having. I have a telescope
mounted on a 54 inch tall, 3/16 inch wall, 8x8 square aluminum tube with 1.25
inch plates welded to the top and bottom and bolted to 2/3 of a yard of
concrete. The problem is I am getting a little too much movement out of the
tube and I need to increase the stiffness of the tube. The ideal situation
would be to replace the tube with something larger but that's just not possible
at this point in time. I don't need a radical increase in stiffness either so I
think there is something I could do to for a slight increase in stiffness. I
need to kill low frequency vibrations so please don't suggest sand or concrete,
beside concrete and alumimun don't get along with each other. Any ideas ? Would
putting the tube under tension help ?


Scott Hogsten


good suggestions in the other posts to this question.
How "low" is the vibration you are seeing and how close
is the highway?
It may be that the only way to fix this problem is to
decouple the telescope from the ground movement. For example,
you could pull the support shaft loose, & cast a large weight of
concrete around it (say...300 lbs). Be sure to put four lifting
rings on the upper surface of the concrete block, near the
corners. Then...build a heavy frame mounted on the original
pad. Make it a few inches larger than the block on the
shaft...say..maybe 3-5" per side. USe some heavy springs to
support the block base for the telescope inside the frame, so
it is free-floating. If necessary, you can get some cheap
Lawn Tractor inner tubes from Northern Tool, or some other
place, and, put them between the block and the frame, to
add some additional damping. It is best that they only
be inflated to a couple of PSI, though.
If your problem is low frequency vibrations from
the highway, this should do it. Oh...it occurs to me
it should be pretty easy to see if this is the problem,
though, as it should vary depending on traffic...
Regards
Dave Mundt




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Hey Scott,

If the problem IS torsional, when does it occur? Assuming that the
undesirable motion is torsional, does it occur during traverse, or
when the telescope is "touched". If it occurs during traverse at the
start of swing and then again during stopping of swing, is it possible
to put a reverse force collar under the existing, so that the head is
"counter-balanced"? IE an equal mass counter-rotating?

Take care.

Brian Lawson,
Bothwell, Ontario.
XXXXXXXXXXXXXXXXXXXXXXXXXX

On Tue, 4 Nov 2003 18:24:39 +0000 (UTC), domain
(qedude) wrote:

I'm hoping someone can help me with a problem I am having. I have a telescope
mounted on a 54 inch tall, 3/16 inch wall, 8x8 square aluminum tube with 1.25
inch plates welded to the top and bottom and bolted to 2/3 of a yard of
concrete. The problem is I am getting a little too much movement out of the
tube and I need to increase the stiffness of the tube. The ideal situation
would be to replace the tube with something larger but that's just not possible
at this point in time. I don't need a radical increase in stiffness either so I
think there is something I could do to for a slight increase in stiffness. I
need to kill low frequency vibrations so please don't suggest sand or concrete,
beside concrete and alumimun don't get along with each other. Any ideas ? Would
putting the tube under tension help ?


Scott Hogsten

domain (qedude) wrote in message ...
I'm hoping someone can help me with a problem I am having. I have a telescope
mounted on a 54 inch tall, 3/16 inch wall, 8x8 square aluminum tube with 1.25
inch plates welded to the top and bottom and bolted to 2/3 of a yard of
concrete. The problem is I am getting a little too much movement out of the
tube and I need to increase the stiffness of the tube. The ideal situation
would be to replace the tube with something larger but that's just not possible
at this point in time. I don't need a radical increase in stiffness either so I
think there is something I could do to for a slight increase in stiffness. I
need to kill low frequency vibrations so please don't suggest sand or concrete,
beside concrete and alumimun don't get along with each other. Any ideas ? Would
putting the tube under tension help ?


Scott Hogsten

How about some lead shot? Might take a few bags to fill up the column,
though, runs $13-15/25 lb. bag around here. If you're cheap and have
a big enough hole for access, you could scout up some buckets of
wheelweights from tire shops and chuck those in there. Adding weight
isn't going to stiffen up things, but it may change the vibrational
characteristics enough to live with it. You'd have to determine
exactly what sort of vibration you're getting, torsional, bending,
vertical, horizontal, etc. before you can really stiffen the column
up. Welding on a few gussets might make a difference, welding some
plates onto the column faces might help, too, just depends on in what
plane(s) your movement is occuring.

Stan