A Wooden Stick Holding Weight Without Bending?

1200cm... Is this correct? And 1Kg?

How about a wood veneer over whatever structure you may select, in lieu of the plan as stated. Are you (or your client) in love with this stick?

no of course, it should be 120 cm!! and , not in love, but it`s a nice oak stick :)

I figured it was a typo...

Well, how about a nice oak veneer wrap? Is this practical/acceptable?

I might end up doing that if my other plans fail. Originally I want to keep the whole wood as it has a different quality than the veneer. Thanks for the suggestion anyway.

Although wood may be called 'Composite' material (being made of fibers bonded by resin) there are much lighter and stronger alternative to replace it's intended use, especially if you want to be "Environment-Friendly"

A hollow Carbon-Fiber tube for instance

http://www.carbonfibertubeshop.com/

http://www.macqc.com/

As phrased, even with the typo correction, this cannot be done. There will always be some bending that will happen with the added weight. Now stiffer materials will deflect less than the original stick. Possibly stiffer materials can be found that makes the bending virtually imperceptible.

As far as calculating the stress on the stick, you should draw up a free body diagram of the stick, added weight and the support point(s) of the stick to start a stress analysis.

What typo? The OP said 120cm (~ 4 ft) and as far as I can tell that's what he meant. It's a more likely figure than 120mm or 1200cm.

Cheers...........Codey

You didn't give the inside diameter of the stick.

You might try filling it with polyurethane foam, like the kind used for insulation that comes in spray cans with long nozzles. That stuff expands once it is squirted out of the can and becomes very stiff. (It's also very sticky until it cures.)

Of course, it's impossible to get no bending, but with the stick angled 15 degrees off vertical you won't get very much bending. The question is 'how much is too much?' And, can you pre-load the stick during the stiffening process so that it straightens out once the weight is applied?

I am not so sure about the strengthening properties of poly foam, but the pre-load is the only sure way to make it straight with a load.

If you run a rod along the top of the inside section and cap the wood tube then tighten nuts on the end of the rod, it will create tension along that side. The weight applied at the end will have to pull against that tension before any bending can occur.

If it still bends, you could try to put a tube along the bottom that can absorb some of the compression forces that occur. It would be best if you could open the wood tube and affix this tube to the bottom (with good contact adhesive) to keep it from bending during compression.

You could try a truss rod through the center, threaded on one or both ends passing through plates to apply compression and "tune" out the bend as is done with guitar necks.

To calculate deflection, we need to know the moment of inertia of the hollow rod (i.d. and o.d. will do). This is equivalent to an end-anchored cantilever with uniform load of 1 kg per 120 cm, plus concentrated load of 0.6 kg; then the sum times sin 15°.

The more difficult bit is establishing the elastic modulus!

Cheers.........Codey

No sweat--structural wood manual.

inside diameter is 10mm, and outside 28mm. The inside diameter could be adjusted to fit some tube or other reinforcement.

Go to your local hobby store and look and ask for something like the truss below in a scale you need. If you can sandwich it between the halves of your wood, it will add the most strength. You may even be able to reinforce it by adding a thin threaded rod along the top and fixing the ends of the rod to the girder with small tubes that will allow you to apply tension with locking nuts.

Might also try something like this, thanks!

sure it is sin15° ?

I think so, but it might be tan (except that would imply infinite force if the stick were horizontal). (Or, if measuring the angle from horizontal, cos.)

As others have noted, you cannot avoid bending unless you pre-load the tube, so that it becomes straight when loaded. There are many tubes that would not bend perceptibly under such a small load, given how close to vertical the tube is.

Do you really need zero bend?

An aluminum tube .063 wall and 1.5" diameter would not bend appreciably under such a small load. If the tiny bend were objectionable, the largish diameter would allow an internal tensioning member to be strung to pull the tube out of column when unloaded (and, therefore, straight when loaded).

With wood, the ordinary warping from moisture in the air would prevent a truly straight tube shape being maintained.

According to engineering theories, it is impossible to have no bending. Only thing, bending may be negligible. So firstly you need to define, how much bending is acceptable.

Secondly, filling anything in the core will not help. Anything in the core will not contribute to increasing the strength. You need to add material in the plane of bending, and at the extreme distance possible from the neutral axis of bending.

Instead of adding material in the center or over the total length of the stick, better to put is in struss form, forming a triangle with original stick or adding more material near the support point and go on reducing the material towards the hanging weight, will give maximum strength and minimum bending

gsuhas has a good point, locating your reinforcement as far from the center of the tube as possible lends it the most leverage.

You said the wood tube is 2 sections glued together. If you can separate them again by cutting or softening the adhesive you could add a thin sheet of truss material. It only has to be really thin where it acts as a layer between the wood halves. In the center it could be thicker. If you set this truss system inside and remounted the pole with the seam vertical to the load, it should work well, especially if you can pre-load the truss system.

you didn't give us the outer diameter. the bigger the diameter , the stiffer will be the stick, even when the wall is hollow. Maybe that a 6 c.m diameter ,0.5 c.m wall thickness will provide you the best solution.

Hint: That's way overkill.

... unless the OP really means that it must not bend or move, in which case this solution is insufficient.

But how could one know? The OP seems to have disappeared, without giving any indication of how straight he wants this thing to stay.

well as many have said here already if you want to control the deflection of your extended member for whatever length or cross sectional shape it is you can post-tension it with embededed end plates that are drilled to locate your tendons that you can tension to adjust to accomodate the load you have. - as long as the glue joints don't give in and you don't crush the containment you can offset the deflection of a static weight with tension on steel rods acting as tendons and positioned appropriately.

I have replaced my over priced wood stick on my laser sail boat with a hockey stick, lighter and stronger on the correct force axis the stick being rectangular.

if you are emotionnaly "bonded" to your stick, you may want to look at the west-system web site, they have free technical infos and very well illustrated. They send me interesting projects on "epoxy works" mag. Bamboo bike projects among others. There are reinforcing fiberglass rods on the market, google it and you should find it.

Wood is a living thing "originally" it is a fiber oriented material bending will occur anyway but not alot. Even with Viagra or Cialis, it will not help.

Otherwise, in Florida, there is a university that is researching on implementing electrodes into the brain for depression supression, good for Parkinson prevention too. Will help you forget your GREEN stick although you can recycle carbon hockey sticks which is GREEN too. Will reduce demand on electricity too.

Good luck on your "sticky" project.

regards,

Is there a way for you to sandwich a thin piece of aluminum to your glued surfaces?

In the building biz, we can glue and bolt thin steel between wood boards, creating what is called a fletch beam, which allows a greater span to carry heavy loads.

If you can shape the aluminum to the desired curve you are needing you may be able to hold that shape without distortion. And if necessary you could build in flanges on your glue surfaces to allow more gluable surface... Once the alum. is sandwiched between the wood it can't twist thus offering incredable strength. Think of a sheet of plywood and how strong it would be if you tried to bend in laterally.

Without seeing the desired product, this is all i can offer. if you want more suggestions my email is marshal 7002 at yahoo.com

good luck.

thom

Prior to gluing the two halves together, bond a cross shaped insert, balsa wood maybe, into the one half and then apply glue to the top edge of the cross element before gluing on the other half of the "stick".

Thank you for your answers! Opening up the stick is fine, I am gonna make a new one, but veneering a pipe it isn`t quite good enough for me. I will try reinforcing it with either an aluminium tube/extrude or a carbon fibre tube. See how it goes!

Thanks!