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Please note, I am not asking or suggesting Aluminum for the horizontal rods/ dowels here. I am asking about the Vertical frame.

Since suggested "Extruded Aluminum Section":

To balance strength, stiffness & weight, I was wanting to make the Vertical FRAME out of Extruded Aluminium Section as there are many kinds out there.

Reference to DIY Woodworking Project for Home Fitness & Rehab:

https://woodworking.stackexchange.com/questions/3032/lightest-woods-that-would-be-strong-stable-for-2-components-of-diy-wall-stall

  • Horizontal: Wooden parallel bars/ rods/ dowels

    • Less thick than frame & probably need greater strength, rigidity & less flex
    • Looking at certain wood types
  • The Vertical Frame holding them

    • Will need to be made of thicker, wider & bigger pieces of wood, adding more to the weight, so a lighter wood would be better, maybe plywood?

http://www.roymech.co.uk/Useful_Tables/Timber/Timber_Strength_Calcs.html

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  • It's not clear what you're asking. Are you building something like this from scratch? Repairing something? – isherwood Mar 31 '16 at 21:02
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    And I think the term you're after is "aluminum extrusion". – isherwood Mar 31 '16 at 21:03
  • @isherwood - Thanks for that term. Plan to build this new, and it needs to be light - So steel and heavy wood is out. – Alex S Mar 31 '16 at 21:35
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    I don't think she'd have any problem moving that one herself. If you do, you need to start with some more basic calisthenics ;) "I think you're over thinking this." – Mazura Apr 1 '16 at 2:32
  • @Mazura - It's not just about moving it myself, but due to Urban Metro city space constraints it'll be mountable/ removeable; maybe even disassemble-able. This will be built only once - So I'd like to do it without any "I wish I'd researched/ though of that" :) And I appreciate all the wisdom of people here. – Alex S Apr 2 '16 at 6:23
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Edit: You are looking for a 2x6 aluminum tube. This should be pretty much have the same physical properties as a pine 2x6 (which looks like what you have in the lower picture). In the upper picture, it looks like two 2x2s that are sandwiched together. I would think that a single 2x4 tube would be fine to replace that, unless it needs that sandwich arrangement. enter image description here

Edit2: I bars are much more commonly used in metal working (for providing load bearing support). So, I found some load calculations for I beams, and did a little physics (maybe I should have pursued a physics career). It looks like the beams need to support about 425 lbs. See the pic below. enter image description here

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Edit- After some debate, I have added the calculation for torque, using 80kgs (only 176.4 lbs) for the weight. The torque is most simply and accurately found by adding the two forces (pulling hands and pushing feet) which would be separated by about 1 ft from a hypothetical pivot point (necessary for torque calculations). The formula for torque (mentioned in comments/discussion below) is T=FxLxSinA. The image below provides a clear description of the calculation. Please note that rounding errors involved with multiple calculations are never better than an elegant approach. The elegant approach is to realize that the hands and feet are 2 ft apart, so the length to the pivot is 1 ft, and the total torque (force) is (120kg+120kg)∙ft. Torque is (pretty much always) expressed in either english (529.2ft∙lb) or metric (717N∙M)... not met-lish (240kg∙ft); but it really doesn't matter, because it's the same number. Nobody can disagree with math. Whether or not torque is relevant to your search for aluminum beams is more of an opinion... but I'm pretty sure that most engineers would agree that the load bearing specifications for aluminum beams are the most suitable criterion for your project because the torque-force will necessarly be converted to the push and pull (the perpendicular, load bearing) force. So the force on the beams (for a 200 lb person) would be about 300 lbs through the narrowest part (the most important consideration for beam failure)... but the force on the bars (important, in my humbe opinion) could be a bit more (like 424 lbs). enter image description here

  • Typical build of Stall Bars is wood frame based, and few steel builds out there, but both are heavy. I'd like to know if I have to go Aluminium to make it lighter, what kind/ size/ thickness would I need to go to replace the wood. – Alex S Mar 31 '16 at 21:18
  • I am not considering for the rods to be Aluminium. Only the vertical main frame to decrease weight. – Alex S Mar 31 '16 at 21:20
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    @AlexS - One 8' piece costs ~$150 and weighs ~35 pounds, which weighs more than a pressure treated 2x6: 26lbs (kiln dried: 16lbs). Plus one however, for answering the question as asked. – Mazura Apr 1 '16 at 2:10
  • @Mazura - Wouldn't a hollow/ extruded Al section be lighter than that wood you pointed out? PS: Variety of cross sectional designs if there's something with better structural strength than border rectangular jindalaluminium.com/jindal-ecatalogue.php – Alex S Apr 2 '16 at 6:08
  • @Ben - Thanks for the changed, enhanced & improved answer. I love the physics you've added and will read through it more carefully and update my question with some more loading info - Unless there's a better SE to address that? PS: I will pull out my physicas/ engg. old books/ notes so I better absorb what you've written - You Rock sir :) – Alex S Apr 2 '16 at 6:15
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outside of any opinion i have on the idea, my two cents would be:

vertical members out of solid 3/4" 6061-t6 drilled to take the transverse tubes or rods. less costly than going to a rectangular tube due to the loads you look like you are applying and thus the need for heavy wall and tig welding of the tranverse tubes to the uprights. if solid, you can drill and tap a single retention bold per horizontal connetion.

horizontal members (i assume approximately 1.5" od) from solid 6061-t4 or 7075-t6 heavy wall tubing. the latter is very costly and hard to find, so i would just go solid - cheaper and much more available. do not underestimate the loads you will be applying on a 36" span. wood has a very high flexural memory that aluminum doesn't. aluminum doesnt like to bend, and once it does, it likes going back even less - it will fatigue over time if you allow flex in it. wood doesn't have the same problem. you could a much better result if you did in fiberglass tubing with far less mass required.

or

just do it in steel - far less cost, way stronger, but more weight

  • Typical build of Stall Bars is wood frame based, and few steel builds out there, but both are heavy. I'd like to know if I have to go Aluminium to make it lighter, what kind/ size/ thickness would I need to go to replace the wood. – Alex S Mar 31 '16 at 21:19
  • I am not considering for the rods to be Aluminium. Only the vertical main frame to decrease weight. I was wanting to make the vertical FRAME out of Extruded Aluminium Section - There are many kinds out there – Alex S Mar 31 '16 at 21:23
  • PS: Looked up FG - ebay.com/bhp/fiberglass-tube - Wondering what kind.. for the Vertical Frame? – Alex S Mar 31 '16 at 21:25
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    check mcmaster.com first. they have all types, shapes and sizes. if you go extrusion for the aluminum, you will have to figure out how to mount the wood into it without having the extrusions walls saw through the wood over time. maybe surface mount socket flanges? why is weight so important? the differences in weight between wood, alumimum and steel are going to be wood heaviest, aluminum second (because of the rods section thickness) and then steel (thinner parts for the same strength). hybrid systems will be different – personal privacy advocate Mar 31 '16 at 21:54
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    ...their qualities enormously. the real secret behind being an engineer is not just being able to build something strong enough to do the job. its the ability to do it elegantly, with the least amount of cost vs. weight vs. complexity. anyone can russian engineer stuff. just make everything twice as big as necessary. the real art is in minimizing all inputs to get the same resultant fulfillment of application parameters. that is why all of those extrusion profiles exist - to solve someone's problem for some application as elegantly and as minimally as possible with the best cost vs mass – personal privacy advocate Apr 2 '16 at 15:03

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