You forgot 7005 alum, and magnesium.

 

those are even more rare to find, I'm just talking about the more easily to buy grades. dont' want to spend a fortune just shipping heavy metals across country because they are so rare they are not available locally.

 

Design also has a lot to do with stiffness. Take a plain piece of paper and try to stand it up on edge, it simply falls over. Now fold it in half, and it stands up. Do multiple corrugations and that sheet can now hold something up.


Thinking about it, you might want to look at that corrugated plastic that they use for lawn signs and so on. It's stiff and light weight, and I believe you can order it in any number of colors and finishes. It's often used for light weight large signs.

 

look at that corrugated plastic that they use for lawn signs and so on. It's stiff and light weight, and I believe you can order it in any number of colors and finishes. It's often used for light weight large signs.

its called "coroplast" , I like the stuff. When the judges, assemblymen, city council, and other crooks run for office in our area, they sometimes don't collect there signs after election. They are a great slip sheet for sliding under autos and equip, to lay on while you work. There light, and can fold them. they will catch fire and burn slowly from hot dinglberrys falling though

 

K@ AluminumWelder - All aluminums have a Young's Modulus (E) of ~ 10x10^6 psi. Irrespective of Grade. Stiffness is related to shape/geometry for a given element, material, or alloy. You could build a shape out of paper mache & bailing wire that would rival the "stiffness" of an ill designed weldment of aluminum sheet.

Recommend you think through your requirements. You say light & stiff. That's a relatiive description. How many translational/ rotational DOFs (degrees of freedom) does your support need to resist? 5lbs tension/compressions or 1k lbf? What you consider light may differ from someone else's interpretation.

People often say that aluminum is good to use over steel because for a given unit weight a product can be made "stiffer" with aluminum. Aah, but here's the rub. The "Figure of Merit", or stiffness per unit $cost of material, is ~ 3.5 times greater for aluminum than steel.

You want strong, light, stiff, extensible, and cheap? Select steel.

 

I have tons of coroplast very flimsy for base plate, but good for other stuff, also have alumalite which is coroplast with aluminum skins too weak as well.

I'm talking about a 50 lb kiosk box on a 4 foot tall torque arm that people press all day long with 5 to 10 lbs of force, that's a lot of torque on the plate and I don't want it wobbling back and forth. see example photo, but box will be twice as big! I'm talking about the base on the floor

I really want something light and strong, but in my google searches have next to zero information on people that use high strength aluminum plate.
, also have tried HAP, or hexagon hollow aluminum 1/2" plate with .040 skins, skin tends to get dinged up so solid is best. Also tried 1/8" aluminum with 1/2x1" aluminum tube welded under it, works well, but a lot of labor.

Honestly steel has been the best so far, but would love to switch to high strength aluminum for weight savings!

as far as design goes, it's a base plate, there are no design tolerances that allow me to fold, bend or otherwise make it stronger through mechanical means, it's either stiff enough or not

 

Skip any aluminum. Portability a key requirement? What a about a heavy duty, circular, base with embedded wheels so when you tip the column 30deg, say, the wheels engage and off you go? Would expand the x-y dimms of thre base. You say ~ 40ft-lb of torque. What about when someone applies 2x in force, or worse, falls into the product by accident?

You def want heft/mass in the base to resist all DOFs. If you are unable to bond the item permanently on site, then consider a smart/strong alternative. What's the floor material the product's base will rest on? What about supplemental support via suction cups?

 

the carbon steel base I'm using now is about 20 lbs so less than that would be great
as far as deflection I think less than 5 degrees would be good, collum is bolted to base from under neat with 4 stainless steel 3/8" bolts
if a person falls on top of it, that's gonna hurt, no way am I gonna make the kiosk so heavy that it can withstand a 200 lbs individual falling over, I want it portable and strong, not tank proof and heavy.

 

I'd go with a heavy steel plate and then just move with a two wheel cart. With camera and stuff on top, you don't want it tipping over.

2nd choice would be a base made out of square tubing, covered with sheet, and big enough that the operator has to stand on it.

 

already have a heavy 20 lb steel plate, just looking for alternatives on a metal alloy that no one seems to have experience with?

 

As ManoKai already mentioned, all the grades of aluminum you mentioned have the same basic Young's modulus. They're all equally stiff. Their tensile strengths differ somewhat, but they all deform elastically at the same rate. Don't spend any more time or money on trials with other grades of aluminum.

I just re-read all of your posts. Let me see if I can sum up what I heard:

• I've tried commonly available mild steel and aluminum plate
• Steel is too heavy
• Aluminum is too light and too expensive
• I can't change the shape or size of the base plate to a stiffer, more rigid design
• I don't want to spend more money on materials like titanium that I already know are stiffer and lighter than aluminum
• What is a material that is stiffer, cheaper, and lighter than steel?

The short answer is that wood is about the only thing that's stiffer(maybe), cheaper, and lighter than steel. Unfortunately it's also a lot softer, easier to damage, and won't look very good with the rest of your Kiosk.

If you can't change the design to make the base plate a box or some hollow section that has greater resistance to deflection, and you won't spend more money on material that has a greater Young's modulus(like Titanium), and you won't opt for a heavier solution (Concrete is stiffer than steel), you're done. There's no answer to your dilemma.


The best solution I'm aware of is boxing the base plate. Shorten the column an inch or two, and make the base plate into a box 1-2" tall. This keeps the overall height the same, but results in a much more rigid base for the Kiosk. If you're changing the design, I'd go ahead and make the base plate larger as well, since this will make for a more stable base that doesn't rock when a person pushes on the touchscreen at the top.

 

Well, I'm admittedly an idiot :jester: when it comes to this stuff, but...

Were it I, I would go with steel; and if stiffness was an issue I would weld on some reenforcing gussets going from that center post out to the four corners of the plate.

I would do like ManoKai said and also add wheels that only engage when tipped up at an angle. Actually, ditto everything he said.

 

What about putting the base down with thin set? Problem solved. Might be a devil to move/remove....

If it were me I'd bevel a piece of half inch steel plate and put anti-skid on the bottom.

Maybe 3M has something designed to keep kiosks in place that's easy to remove... like their command hangers. Might be worth calling them.
https://www.youtube.com/watch?v=PbD6-A5xB3M

 

All good ideas but honestly i am also just curious how strong these hard to come by aluminum alloys are? Gonna buy some off ebay and find out

 

Steel is three times the density of aluminum. Steel is three times the stiffness of aluminum. High strength steel is over three times the tensile strength of high strength aluminum. In a properly designed part where deflection is the limiting factor, steel and aluminum parts will have very similar weights.

Now before you start jumping on me about steel airplanes, airplane parts are generally designed so strength is the limiting factor. That favors aluminum. But airplane parts are not welded aluminum parts. High strength aluminum parts are fastened together by bolts, screws, rivets, and glue.

It appears to me your biggest concern should be stability of the part. Think of a couple of teenage boys screwing around and one pushes the other. You don't want the whole thing to fall over when somebody is knocked against it. That suggests as heavy of base as practical, favoring steel or iron.

 

so regardless of aluminum alloy 3003 5052, 6061 2024 7075, they will all deflect the same amount because youngs modulus is the same among all alloys?

Unfortunately if I made the base 100 lbs or 5/8" thick steel 24x18" in size it would not sell. People that buy these things I make want them to be easy to move. anything more than 30 lbs is probably not sellable.

 

i guess what I dont' understand is how can the 2000 and 7000 series aluminum be considered stronger alloys, but have the same youngs modulous?
doesn't a stronger metal bend less?
https://books.google.com/books?id=L...oVChMIvuvFhveRxwIViVk-Ch3qMgE0#v=onepage&q=stiffness of aluminum alloys&f=false
started reading this , but it is a bit over my head.

 

When we talk about strength of a material, we most often talk about tensile strength. Young's Modulus is rigidity.

Young's Modulus is a basic material property. Why it is what it is for a given element is something I don't know. But it doesn't change with heat treatment, solution hardening, or any other method to increase strength. Steel is as good as it gets for common materials, almost everything else is less. Tungsten and Beryllium are exceptions and have a higher Young's Modulus than steel.

Young's Modulus will tell you how much a shape will deflect with a specific load. Yield strength will tell you how far it will bend and still return to the original shape. And Ultimate Tensile Strength will tell you how far it will bend before it breaks (assuming it will be a tensile failure).

 

E is inversely proportional to ambient temperature a given element/alloy is subjected to. QED. E -vs- Temperature

 

Why not build the post and yoke from alum, and bolt a base made from steel to keep bottom heavy? I see they are bolted in your image.

Alum is not really more expensive than steel, because you get 3 times the amount per pound. Alum could be potentially cheaper in the long run. Get alum extruded tube and weld threaded plated inside.

 

Thats what im doing now all aluminum with steel base
Steel is about half the price per equivalent need
However by the time i factor in cleaning by hand and prime and paint the labor makes it more expensive

 

Good point. The weight of the steel base does help keep it from tipping over. I have parking signs that I put out every day that are light alum tube with steel rods in the legs. I can tip them to 45 degrees and they still right themselves.

 

^ Ashby Plot. Perfect context! :cool

 

I took a training class many many years ago on how to use these plots. They are very cool. I have books with plots in small print at home somewhere. But the computer software version that's available now looks even more useful.

 

so these high strength aluminum allows will bend just as easy as the cheap alloys
The only benefit is if you are building somethign that will have pull streteching forces on it and then it won't break as easily?

Kind of useless to me, most things I build dont' get pulled apart, they have side loads that cause bending. and if they do get pulled apart it is typically at a joint that is riveted or bolted together since these high stregth alloys can't be welded. , even if you could weld them the temper is near zero at a welding joint.

Love to know what applicaitons this aluminum is needed in? I know in aerospace, but where? on a plane wing? ON a rudder?

my guess is they are nich product and therefore expensive due to low manufacturing volumes.

 

so these high strength aluminum allows will bend just as easy as the cheap alloys

The high strength alloys will bend further and return to the original configuration than a low strength alloy. They may have other desirable properties as well, such as corrosion resistance and fatigue resistance, among others.

 

tha'ts a cool graph, gotta look for a higher resolution link, becuase it's hard to read.

 

tha'ts a cool graph, gotta look for a higher resolution link, because it's hard to read.

https://en.wikipedia.org/wiki/Material_selection

Looks like the paper charts I'm familiar with have been digitized and built into a computer software package

http://www.grantadesign.com/products/ces/

Look up materials information by a British guy named Ashby. About 30 years ago he compiled a whole textbook of these type of plots or graphs. strength vs density, strength vs modulus(stiffness), melting temp vs density, etc. They are used to help with materials selection when designing or re-designing something to strict engineering requirements. E.g. a company needs their widget to be 10% stronger but no heavier.

 

IF you needed exceptional strength-to-weight & high cyclic fatigue resistance, THEN 2024 would be ideal. Main alloying element is Cu.

IF you desired excellent strength, stress/strain resistance, and anti-corrosion properties, THEN 7075 would be a solid candidate. Main alloying ingredient is Zn.

Your application/design needs none of those properties.

Aerospace Aluminum Alloy Development

 

Commercially available, Kiosk Stands. Note the dimensions and tare WEIGHT of these stands. The carrying handle is convenient.

 

"IF you needed exceptional strength-to-weight & high cyclic fatigue resistance, THEN 2024 would be ideal. Main alloying element is Cu.
IF you desired excellent strength, stress/strain resistance,................. then 7075....."

When I read this those two sentences mean the EXACT same thing to me.
looked up fatigue is the weakening of a material caused by repeatedly applied loads
stress strain is applying a load and measuring the deformation.

Not trying to be dense, but obviously there are reasons to choose one over the other that can be explained more simply? 7075 springs back to it's orginal shape better? is that the main difference you are trying to convey?

 

The difference lies in how the loads are applied. That is how the fatigue resistance differs from stress/strain loading. you even said it yourself: repeatedly applied loads. But then what does "repeatedly" mean in the time domain? Everything has an exact definition that sometimes differ from our natural intuitive definition. keep looking up information and you will eventually be able to internalize the differences.

 

I got a headache from this thread :laugh: here you go !

http://www.ebay.com/itm/New-PSPADLK...splay-Case-Tamper-Proof-/350914164288?pt=LH_DefaultDomain_0&hash=item51b41d3640