Is Structural Aluminum Alloy the Right Choice?

I'd go for steel.

I'd think Ali' and the others would be likely to gall or chaff whereas steel would probably have a better bearing surface and higher strength.

But hey what do I know? I'm a cat!

Del

Good kitty . Thanks for the advice.

The segments are telescoped under 'no load' conditions after which there is no motion; it simply supports the weight. One test is using a 1/2" square .065 wall stainless tube as the innermost tube but frankly, even if it has the strength, it LOOKS uncomfortably thin / flimsy.

Jim

The way these tubes interface to each other (overlap, clearance, bearing surface) has much to do with the strength of this telescoping devise. I would recommend help from an experienced structural engineer. Depending on safety implications Finite Element Analysis (FEA) may be called for.

Agreed. That was part of my question Dave.

I'm hoping to find someone like that who can help.

Tube interface: 2" over lap for all tubes. Should this change as the OD changes? Maybe 'the smaller the OD the larger the overlap'?

Gap: with 1/16" wall and 1/4" OD increments it leaves aprox 1/16" slop on all sides. When the inner tube is pushed to a corner it leaves almost 1/8" gap on the far side. Without a lot of additional labor to sand 1/8" wall down to telescope this is the best I've been able to accomplish with readily available alum and stainless tubing. There exists the possibility of sanding 1/16" wall stainless in 1/8" increments to tightly telescope if the current 'sloppy' version doesn't measure up.

But since the stress on the telescoped pole is vertical, its strongest dimension, I think maybe the screw that locks two segments together is the 'weakest link' and might stand improvement. It's currently 10-24 zink plated steel. Would a larger diameter improve the joint? How about placement within the 2" overlap; toward the top, bottom or middle of the overlap?

I take it these are the FEA questions an experienced structural engineer would examine?

Thanks for participating.

Jim.

http://www.google.ca/search?hl=en&safe=off&q=%22telescoping+beam%22+%2Bbuild&btnG=Search&meta=

some leads here?

I think the 'Beam' takes it into heavier industry items.

I went through a couple of pages and didn't see anything helpful.

Thanks though.

Jim.

It is not only a material problem but also a stability problem of the structure as a whole. Since the segments are guided with a clearance the axial load will also generate a bending due to excentric position summing from top to bottom. So the structure is under compression and bending. If the load is not perfectly centered the COG's position will give a + bending. It is well known that slim structures under compression can become unstable. Your structure has due to the single point connection a series of weak points playing the role of a kind of "hinge". Preloading could help but requires a controled torque for assembly.

Since the inertia radius r= (J/A)^0.5 is variable the safe compression load to avoid buckling is not easy to compute.

The safety coefficent should be > 3..4 to avoid catastrophics. The high coef. is due to the tolerances in geometry (especially wall thickness), "hinge" effect and excentricities.

Making a simple estimation based on the middle segment with D=1.5" and assuming a circular section only for a more simple estimation the slenderness uf the structure is about 61 (assuming the length over the 1.75" segment only) <120 thus corresponding to plastic buckling. This means that as long as the stress is under the yield limit the strcture will be stable.

Compressive stress 30.3 N/mm² + estimated bending 10.7 N/mm² (each segment generates an excentricity of 1mm at the load) = 41 N/mm².

It seams that the safety is ok.

But let it be computed by a structural engineer not only by a mechanical one.

... yeh...but what material?

Cool! Now we're down to the real problems! Thus the 'Power User' rank?

The 'hinge' would be the overlap? Or, really, the screw connection of two segments? Increasing the overlap (double wall) length should eliminate that. I've used 2" overlap but realize that should probably vary by tube OD increasing inversely.

But what if, in an attempt to lighten the pole for portability, I drop the tube sizes clear down to 1/16" wall 1/2" stainless steel for the center tube, and then Alum (6061) for the ¾, 1, 1 ¼, 1 ½ inch tubes. That cuts the weight almost in half but makes the pole thinner and more susceptible to the forces you discus. With a 2" overlap at both ends where the wall thickness is double that leaves 8" single wall and 10" on the inner most stainless steel ½" tube. There's probably some optimum overlap size or maximum single wall size that can be calculated.

If I do your calculation on each segment separately I should be able to shorten the weakest segment to achieve optimal compressive and bending strength. (Obviously a 1" tall 1/2" square 1/16" wall would support 2000 lbs. But would a 10"? 8"?) Can you tell me those formulas? What do you mean "the slenderness of the structure is about 61"? And where did the 120 come from? It probably changes for each r?

Thanks for your insight and help.

Jim

Maybe the 120 refers to .120w or 1/8" wall tubing.

I recently rebuilt and improved a commercial 70ft aluminum telescopic mast. The biggest issues were friction. The original mfr used a nylon block on all four sides at the base and top to make it easier to raise and lower. However, the material (nylon) greatly increased the needed size of the tube (8" down to 1 1/2"). I don't know where you will find a source for 1/4" increments but it will probably gall. You will need some sort of friction reducing material between the wall. I don't believe you will have a strength issue. (we have made some support stands out of AL 1 1/2" x 1/8" that routinely support over a ton and are easy to move). Side bending was an issue with the unit we overhauled because of the method of lift but that may not be an issue with your project.

This telescoping pole (support stand) will be extended under no load, positioned and the weight gradually placed on it. So I doubt friction will be a problem. We are considering a thin (3/64"?) Teflon gasket around the bottom of each segment to decrease the 1/8" total slop and 'hinge' effect.

Side bending COULD be a problem because, though I've been describing this like a table leg (COG=0) the weight actually hangs from a bolt that extends 1" from the top of the narrowest tube. So, COG is 1" out of 50" instead of dead center but it's not a horizontal boom like aurizon below mistakenly thought. Still, I'm sure that 1" will greatly increase the 'bend factor' and we're working on decreasing this 'off center hang' condition.

1/4" OD SQUARE Tube increment in alum and stainless are not a problem. www.SpeedyMetals.com is good or MARTIN HESTRIN [mdhestrin-co@msn.com] for personal service and even better prices. 1/8" increments with 1/16" wall IS.

One supplier is trying to extrude them for me at >$100 per segment .

Thank you for all your good points. The 'support stand' info is especially encouraging.

Jim

I have no idea on how to calculate structural strength or stability, but from my experience with plastics and metals, I would vote for carbon fiber reinforced polyester or epoxy tube with a thin bushing or coating of either teflon or Turcite.

Gary,

Aren't the costs of "carbon fiber reinforced polyester or epoxy tube with a thin bushing or coating of either teflon or Turcite" something like 10X? For example, a 1/8" wall, 1.5" square tube, 12" long alum (6063) 1 each cost is between $3.00 and $4.60 from current suppliers. What do you think the carbon fiber, if it is even available in square tubing, might cost? Would this material be commonly available or manufactured by job?

Thanks.

Jim.

Where does 6063 come from? I can't find a reference for that grade. I don't see it under the designations for different countries either.

While researching sources for aluminum tubing the common alloys available are 6061 and 6063. 6061 is stronger and appears more common on smaller OD thinner wall tubing usually below 1 in OD. Above that size 6063 becomes more common.

6063 and 6061 are structural aluminum alloys from the group of aluminum alloys consisting essentially of the Aluminum Association's 2099, 2219, 2519, 6005, 6013, 6063, 6061, 7005, 7050, and 7075.

Try this for more detail: Handbook for Material Selection for Engineering Applications

Jim

Thank you.

I had just went through the process of finding out why we had 2017A on a drawing when an outside fab shop asked me if they could use 6061 because they couldn't get 2017A in the form they needed to do my job, in fact they said they could only find it in round bar form.

I found out that in France they use 2017A as a common grade for most of their applications instead of 6061.

So I did some research and had a hard time finding anything that I wanted to know because I wanted to know what was the difference and what were the applications that each grade was used for.

I finally came across Maryland Metrics and a chart for Aluminum/Aluminium: USA popular grades vs several overseas grades.

http://mdmetric.com/tech/alumcomp.htm

I work for a company that manufactures machinery used in produce packinghouses. We've built sizers for everything from cherries to watermelons. We use aluminum for some of our applications but we primarily use stainless steel and mild steel.

I did notice some variations between our sources.

6061 in your reference has a compound made up of Al-MgSiCu0.05.

6061 in my reference has a compound made up of Al-Mg1SiCu.

Interesting that 6063, which I've found to be the most common in the size/shapes I'm looking for, isn't even on their 'USA popular grades' list.

Jim

I would consider step one to be to find a material that will do the job. Step two would be to find it at the best possible cost without sacrificing the necessary quality to maintain saftey. Some other contributors with more knowledge than I have stated that they don't believe that aluminum will do the job. I am only offering an idea that might work. I did a quick google search for "composite rectangular tube" and saw a huge number of manufacturer's sites with info that might help. It is now up to you to do the follow up research if the idea is of interest to you.

If you are going to have 2000lbs of something in the air and it comes down and kills someone, are you going to explain to OSHA that it is ok because you got the materials at a great price?

Very wise. And I agree.

This is part of an existing product that works but it weighs 4 lbs.

I'm trying to get it down to half that and exploring what's available. The weight is so important because it will simply not be used, carried, purchased, exit if, for example, it is heavier than will willingly be carried by a hiker.

I really like the idea of carbon fiber because of its weight and strength but if the cost is too high there is no market. Using aluminum a 1 each cost is around $50. Maybe $35 in quantity. End users would buy it at $200 but not $2000.

Your help with "composite rectangular tube" is greatly appreciated but don't you agree, given the above data, that it is likely outside of, by a large margin, the cost parameters?

Thanks,

Jim

Yes, I understand. Composites are not cheap. Have you looked, there may be off the shelf composite tubes that would telescope per your needs and may not cost 10 times as much as aluminum.

Just curious, why does a hiker want to carry a frame that wil support a 2000lb. load?

I see you are close to Magic Mountain. I just moved away from Ventura County after over 40 years there. Great place to live. I am in NE Pennsylvania now where there are real seasons, clean air, and drinkable water, but not much in the way of good restaurants, especially Mexican.

(The hiker thing is just an example of the kind of effect weight has on product viability. I'm thinking of a move but it will more likely be TO Ventura or Ojai or Big Bear.)

My understanding is that plastics (is that the proper/best generic name to use?) are between aluminum and steel in strength but lighter than (by half?) aluminum.

I've started to look but very quickly ran into my ignorance and so was very easily distracted.

For example: @ http://carbonfibretubes.co.uk/ they say:

• All of the general purpose tubes are constructed using 2 layers of 224 gm/m glass at 90° and 3 layers of 300 gm/m carbon at 0°.

Looking at this I don't know the value or optimum for:

• how many layers
• at what angles
• of what thickness
• of what material
• angle between layers
• is .96 KNm2 stiffness good?
• what other parameters are critical for my use
  
• et al

Product, I.D., O.D., Wall, Stiffness, Weight, Maximum

Code, (mm), (mm), (mm), (KNm²), (Kg/m), Length (m)

CG29.3/26.5, 26.5, 29.3, 1.4, 0.96, 0.21, 4.0

I think I'll post the following question in the 'Chemical & Material Science' category and see what comes up. What do you think?

--------------------------------------

This is my first excursion into plastic and I'm ignorant of the technology and terms so I apologize in advance.

I'm using 'plastic' as generic for composite materials, fiberglass, carbon fiber, Kevlar, and any others that might reasonably be so categorized.

I'm hoping that you will advise me about the materials and terms I should be using for these products.

My understanding is that plastics are between aluminum and steel in strength but lighter than aluminum.

I'm investigating replacing with plastic, two existing aluminum/stainless 50" telescoping support poles made up of 5 - 12" telescoping segments of 1/8" wall and the other of 1/16" wall.

The ODs increment in 1/4" steps from 3/4" to 1 3/4" in the 1/8" wall and 1/2" to 1 1/2" in the 1/16" wall (the 1/2" is stainless steel).

The weight these support poles are subjected to is planed at an outside weight of 2000 lbs static typically for less than a minute.

These aluminum/stainless support poles weigh between 2 3/4 to 4 lbs. I'm trying to cut this weight in half without sacrificing strength. (We have to sand the 1/8" wall to telescope but not the 1/16" wall.)

Are there standard plastic square tube sizes that would telescope like this?

Would round tubes be stronger than square?

Is the resulting plastic pole likely to require a larger set of tubes and wind up not reducing the weight of the pole? Is plastic so much stronger that the ODs can be reduced even beyond the current alum/stainless poles?

The other CRITICAL factor is cost.

The current product is made from commonly available aluminum square tubing that is relatively inexpensive. For example, a 1/8" wall, 1.5" square tube, 12" long alum (6063) 1 each cost is between $3.00 and $4.60 from current suppliers (including freight).

Can you give me an estimate for the same piece in plastic (even if it is only a ball park guess)?

---------------------------------------------

Thanks for your help.

Jim

I just happen to be Saugus High graduate class of '81. I live up here in Tulare now, that's 60 miles north of Bakersfield.

Cool!

My "baby" graduated from Saugus a couple of years ago.

Jim

I doubt that a solid piece of 2" aluminum could hold 2000 pounds cantilevered at 50 inches?

2lbs telescopic pole extended to 50inch lifting 2000lbs. Good luck.

How ever you should try contacting "MACHINE BUILDING SYSTEMS" . http://www.item.info/en/. I'm sure there is a US site also.

These guys make alimimum extrusion and can build very neat stuff.

IF you give these guys a drawing of what you what, they should be able to help you will the concept and do the calculations for you. However, 2lbs, I don't think so.

Thanks Jonny5, that DOES look like a good place to start.

How does "2lbs telescopic pole extended to 50inch SUPPORTING 2000lbs" sound? Like a table leg?

Remember, this is not LIFTING, it is SUPPORTING.

Jim

Where do you find 6063 aluminum?

The only references I find are:

6005A

6012

6060

6061

6082

And that's it for the 6xxx series. 6061 is most commonly used in the USA.

Go into the 7xxx series and you get into aluminum with higher strength values becuause 6xxx series is considered to be a medium strength alloy. I don't know about all of Europe but in France they use 2017A in place of 6061, they believe that the Mg1Si content to 6061 is hard on tooling but from what I've heard from my outside fabrication suppliers it's not a problem at all.

From what I gather in your post you are making a telescopic device consisting of five segments using square tubing with the base starting at 2"x2" square tube, am I right?

We have telescoping applications using square tubes and one things that is prevelent is that the next size smaller doesn't exactly fit inside the larger size. There is always some play. This will cause your device to lean when weight is placed on it and the leverage from the leaning will cause undue stress that could cause your device to fail.

I would consider that a major safety issue.

How are you going to raise this weight? Using jacks then using the telescoping device like a jackstand? If that is the case, I would go with something with a larger size square tubing. Why not go with a round tubing? You have more options in sizes with round tubing and can possibly get a tighter fit. Square tubing tends to bind up easier when slipping inside one another. When going from one size of square tubing to another the corners tend to go from a rounded corner to a more square corner and this causes the binding. The square corners tend to dig in.

Let's say you are using this devise as a jackstand, what are you going to use to lock the tubes in place? If you use a pin it will tend to wall out the holes because the aluminum is still a soft metal even if it is the harder variety.

Where do you find 6063 aluminum?

From earlier in this discussion: 1/4" OD SQUARE Tube increment in alum and stainless are not a problem. www.SpeedyMetals.com is good or MARTIN HESTRIN [mdhestrin-co@msn.com] for personal service and even better prices. 1/8" increments with 1/16" wall IS.

Go into the 7xxx series and you get into aluminum with higher strength values

I haven't seen it readily available so considered it would be too expensive (see above). I'll look into it.

This will cause your device to lean...

discussed in earlier responses.

Why not go with a round tubing?

Is round stronger than square? I thought, for the same wall and OD that round would be weaker than square. Not true?

what are you going to use to lock the tubes in place?

Zinc plated steel screws 10-24 x varying lengths. I guess a larger diameter would decrease the 'wall out' although we haven't seen any of it yet.

Many good points

Thanks,

Jim

telescoping rods are almost universally round if used in simple compression.

Round will turn, so if you need to prevent rotation non round is better.

Round tubes that nest fit closely into each other are far easier to make at low cost than square.

Can you tolerate independant lengths that fit into each other with a swaged end? No pins/screws needed as compression keeps them together. Tent poles like this with a central cord are commonly used.

You want strong and stiff. The best strength to weigh ratio comes with carbon fiber/epoxy and titanium. Aluminium for aircraft is somewhat less stiff/strong, but is much cheaper. Stress concentrations at join points are the enemy of all strong stiff composites, especially bolted. That is why slide fits are stronger.

some ideas here...

http://www.google.ca/search?hl=en&safe=off&q=telescoping+%2B%22tent+pole%22&btnG=Search&meta=

You make some VERY good points.

Beyond doing the job, cost and ease of deployment are major factors. Round tubes are a good idea. They present other problems but these are solvable.

Brilliant! Going to same OD, 12" swaged poles greatly simplifies things and, compared to telescoping and pinning the segment, greatly speeds up deployment. Further, with only 3 or 4 hours spent Googling I found existing tube sets on the market meaning we may be able to cut costs further by using these. A tube connector insert instead of swaging is also a possibility:

This 'same size' suggestions opens the way to multiple size solutions too!

Very helpful. Thank you arizion.

Jim

aurizon,

See the thread Swaged-support-tube-dimensions from Ralph

Do you know swaging rules for this?

Jim