# Foo - Adding stiffness to this parallelogram

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phantomcow2
03-01-06, 06:02 PM
Imagine a parallelogram. It is made from aluminum extrusion for the longer legs of it, and aluminum plate for the sides.

__________
|_________|

I believe with the loads this will see, this parallelogram will try to make more of a rhombus

________
/______/

That is not acceptable. I was thinking just get a plate to mount in the back of this parallelogram, that would add excellent resistance to twisting. But, though my stock pile is pretty good, its not that good!

So my thoughts were to add angle supports, like this

===========
||/\/\/\/\/\/\/\/\||
===========

Except these angle supports would actually be touching the other material!

So my question is, what would be the angle of these angle supports to maximize resistance to deforming?

THis all has to be much more overbuilt than I had expected, for all I know I might have a 4HP motor in the middle of this...

blonduathlongrl
03-01-06, 06:05 PM
Just went I thought I was logging into foo to unwind from a busy day, you throw this at me? :p

Taerom
03-01-06, 06:10 PM
Oh man, I'm not even gonna try to help you on this one...no clue :(

phantomcow2
03-01-06, 06:19 PM
There must be some mathematical way to figure this out. I've not taken physics or statics and dynamics yet :(

free_pizza
03-01-06, 06:24 PM
I've not taken physics or statics and dynamics yet :(
wanna buy my statics/dynamics book? its barely used! (my transcripts will back me up on that)

slvoid
03-01-06, 06:53 PM
Use a thin matrix of honey combs. It's the strongest structure for the most volume inside (meaning the least amount of material for the walls).
Or stick a couple of arches in there, also one of nature's strongest forms.
Why use your brain when you have 2 billion years of evolution behind you?

slvoid
03-01-06, 06:53 PM
I'm beginning to think this guy's the Merton of engineering..

Just went I thought I was logging into foo to unwind from a busy day, you throw this at me? :p

mcoine
03-01-06, 06:55 PM
45 degrees

jyossarian
03-01-06, 06:57 PM
Jeez, what good is cereal gonna do?

phantomcow2
03-01-06, 07:02 PM
Use a thin matrix of honey combs. It's the strongest structure for the most volume inside (meaning the least amount of material for the walls).
Or stick a couple of arches in there, also one of nature's strongest forms.
Why use your brain when you have 2 billion years of evolution behind you?

Thanks, I was hoping for a reply from you.
By Honeycomb, do you mean something like this?
http://www.midcoast.com/~bo/CloseFromTop.jpg

As for the arch, I see that more as a resistance for loads as if a person was pushing from ontop. The extrusion is very solid, plenty to resist this. I dont see much how the arch would help this thing from turning into a Rhombus.
THe honeycomb idea is great, might be a little complicated to make, but I think it could be done...

mcoine
03-01-06, 07:06 PM
estimate the loads in both directions, one load going straight down, one load going to the right. Lets say the load is 4 down, 3 to the right, so the hypotenuse would be 5. The angles here would be 36.87 and 53.13.
That should work. Just don't put a 5hp engine in.

jyossarian
03-01-06, 07:08 PM
Make sure it doesn't go past 400 watts or it'll drop you like a poser and you'll never catch it.

phantomcow2
03-01-06, 07:10 PM
Well it wont be an engine really, it would be a wood router. I have a 4HP servo motor that I might try to use for a spindle, I am overbuilding everything just incase I use that someday

hi565
03-01-06, 07:11 PM
I'm beginning to think this guy's the Merton of engineering..

Difference: PC has an idea what he is talking about ;)

blonduathlongrl
03-01-06, 07:15 PM
I'm beginning to think this guy's the Merton of engineering..
whoa!!! that was a little harsh..

slvoid
03-01-06, 07:17 PM
Difference: PC has an idea what he is talking about ;)

Then he'd be the one giving answers. :-p

phantomcow2
03-01-06, 07:27 PM
Well, like i've said, I have not taken a physics course yet or anything like it (signed up for next year). I want to build this thing right the first time, so this project has dragged and dragged on as I gather parts, knowledge, all of that. The frame of this SHOULD be done in 2 weeks.
ALl .5" anodized black aluminum, except .75" in some places. Should be rock solid...

Bike Lover
03-01-06, 07:30 PM
45 degrees

Agreed. You'd essentially be creating a truss- very strong. That's why you see them in all the large buildings...

Oh, and it'd be statics you'd want for the question...

Stacey
03-01-06, 07:39 PM
Plate gusset the corners or truss your parallelogram with tube

phantomcow2
03-01-06, 07:40 PM
Yea 45 degrees was my plan, I wanted to see if anybody else would agree. I've also heard 30 degrees suggested, but for 30" unsupported length with two parallel bars that are 9" apart, i think 45 is better.
Maybe one of my teachers has taken statics and can help

phantomcow2
03-01-06, 07:42 PM
Plate gusset the corners or truss your parallelogram with tube

FXjohn
03-01-06, 07:43 PM
simply connect the corners diagonally. Make an "X"

mcoine
03-01-06, 07:43 PM
Honestly its not going to matter, aluminum is stiff as hell and either 30 or 45 will work for that application.

ChAnMaN
03-01-06, 08:01 PM
wrap in in duct tape, the strongest material in the universe

Taerom
03-01-06, 08:10 PM
wrap in in duct tape, the strongest material in the universe

+1

duct tape for the win!

phantomcow2
03-01-06, 08:39 PM
MDF is the 21st century duct tape :)

slvoid
03-01-06, 09:24 PM
I'd use a cable tie. There's nothing you can't do with cable ties if you create a stressed structure.

jyossarian
03-01-06, 09:50 PM
What happened to this idea?
http://theimaginaryworld.com/box466.jpg

slvoid
03-01-06, 09:54 PM
How about you fill it with solid diamond...

iamlucky13
03-01-06, 11:54 PM
simply connect the corners diagonally. Make an "X"

I gotta run to Mass in a few minutes, so no time to do any math, but I'm pretty sure this going to get you the most strength for your effort. Any attempt to deform trapezoidally will change the relative length of the two diagonals, loading your x-support in compression across one diagonal and tension across the other...no bending.

If it's relatively short (say less than 10 times as long as the wider side or so), endplates can help a lot.

DannoXYZ
03-02-06, 03:20 AM
How about giving us some dimensions overall? And the directions and force of the loads?

phantomcow2
03-02-06, 05:38 AM
Dimensions, the two legs will be about 28" unsupported length, these are made from 2x2" extrusion with a .25" thick will.

The sides are aluminum plate, .75" think, 8.5" wide. The sides are going to be 10", which is also the spacing of the extrusion.

As for loads, just a moving 2.5HP spindle in the middle is the best I can say

Stacey
03-02-06, 06:00 AM
Sheesh, just give it some Viagra and be done with it! :D

DannoXYZ
03-02-06, 02:13 PM
Dimensions, the two legs will be about 28" unsupported length, these are made from 2x2" extrusion with a .25" thick will.

The sides are aluminum plate, .75" think, 8.5" wide. The sides are going to be 10", which is also the spacing of the extrusion.

As for loads, just a moving 2.5HP spindle in the middle is the best I can sayWell, depending upon the gearing and thread-pitch of your spindle, it can create quite a lot of load. The progression of stiffening it up would look like this:

http://i42.photobucket.com/albums/e346/DannoXYZ/Artwork/WeinmannTruss.gif

About as important as design is the actual construction methods. I'd recommend having it all welded together for the strongest structure possible. The diagonals can be 2x2" L-beam extrusions for rigidity, 0.125" thickness should do..

dragracer
03-02-06, 02:52 PM
I used to build/fly radio controlled planes and the best way to stiffen/strengthen wings was to add "shear webs" in between every single wing "rib". Basically what it did was to tie the whole structure together. There's a good explanation and pictures HERE. (http://www.airfieldmodels.com/information_source/math_and_science_of_model_aircraft/rc_aircraft_design/shear_webs_in_model_aircraft_wings.htm) This seems to be similar to the structure you are building with aluminum...if I'm looking at it right. I'm no engineer, but this sure made a wing structure a LOT stronger.

phantomcow2
03-02-06, 06:05 PM
Well I think a possible thing to do would be to use just a piece of sheet metal. Even .050" should do it.
This way, if the gantry wants to rock around like I dont want, the sheet metal will have to compress in one area and stretch in another. This is something metal does not like to do...

eubi
03-04-06, 12:16 PM
Using anything as a cross brace between the corners will likely help out.

Place the cross brace so it will be in tension (or the long diagonal in the parallelogram). Shoot, you could even use cable in this case.

If you were building a member that had to be super light, you could get into the optimization loop, with the math that goes with it.

Since this structure is sitting on the ground, weight isn't a issue.