So far I have $25 tied up in Frankenframe not including welding costs and time. I have added more stuff since this photo was taken. After easily stretching it open with that six ton bottle jack,I'll be adding more bracing. The weak spots are the corners and the vertical member. I made a bigger and much stiffer frame, but won't fit in my shop. DUH!
Frank

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Cool name.


No matter how heavy the frame is,by the nature of it's basic shape,it WILL flex under load.
The larger the throat,the more leverage working against the vertical backbone,
so the easier it will flex.

Adding gussets to the corners will help,but the point of maximum leverage is
the center of the vertical backbone.So I think this part wants to be pretty substantial.
Also consider stiffness in torsion.

What is the throat dimension Frank ?

Hi Ian,
The throat depth is 24 1/2" from the mounting plate surfaces. Thanks for the suggestions. I was thinking of adding some pipe to the vertical spine so as to make the truss into two tetrahedrons. We'll see what I can dig up.
Frank

That's about the same size as mine.
I should do a stiffness test on mine to compare to some of Richard's numbers.

It would be an interesting engineering exercise to build the stiffest possible frame,
for a given throat size,using the least amount of material.

Perhaps something like a Geodesic Dome;lots of small,light pieces loaded in tension.




For those of us who don't remember all our Geometry classes:

Main Entry: tet·ra·he·dron
Pronunciation: "te-tr&-'hE-dr&n
Function: noun
Inflected Form(s): plural -drons or tet·ra·he·dra /-dr&/
Etymology: New Latin, from Late Greek tetraedron, neuter of tetraedros having four faces, from Greek tetra- + hedra seat, face —more at SIT
Date: 1570
: a polyhedron that has four faces

We could all imagine fancy designs, but actually the tube may be the optimum design. The maximum stiffness per pound would be thin wall with large box sections. Of course, if you carried thin walls too far, buckling might be possible. The limitation is actually a practical one, how large a tubing can you live with? If the tubing gets too large, then it could interfere with wheeling, especially if that was near the lower anvil. I have seen wheels where the part of the arm going up to the lower wheel was tapered to keep from interfering with wheeling.

Even if you can't buy tubing of the size you want, the people who have welded up wheels from plate or sheet metal have shown that to be a viable design. Those frames look like tubing when they are done, but often tubing that varies in dimension as it goes around the frame. The wheels where the side panels have been cut out of one piece of steel can look great, but the pretty curves mean a lot of time spent bending the inner and outer pieces of the frame. I suspect that it could be more efficient to make the inner and outer pieces thicker than the sides, but I do not have any easy way to determine how far one could go without creating problems. I would probably try sides half the thickness of the inner and outer pieces. I notice that H-beams (wide I-beams) generally have a web thinner than the flange. Tubing is like an H-beam with two flanges, in my view, but with more torsional rigidity, which is good.

Another efficiency consideration is to minimize the distance around the frame. Any height above the upper wheel is wasted, in my view, contributing flex without making the wheel more usable. Some people have frames that go way down below the anvil; do you really need to go down that far when you have all that free space in front of the machine?

As far as material, steel is a good choice, in terms of stiffness vs. weight. Aluminum would actually be a little worse than steel in that regard, while titanium would be slightly better. (The key ratio in choosing material is the modulus of elasticity vs. the density).

It is a nice intellectual exercise, but rectangular steel tubing is very efficient, as well as being easy to fabricate.

Richard

If a wheeling frame can be too flexible or too rigid then a logical evolution of the design would seem to be a frame that actually has adjustability.On a basic frame, utilizing square tubing and triangles, perhaps a device that limits the throat depth could accomplish this. If I recall correctly, this is done on Pullmax machines.
Adaptability seems important too. Interchangable arms for the lower wheel is an example of ingenious design that add utility to the frame.Yadda Yadda .......
So where does a wheeling frame that looks like a '57 Chevy, or has spider web gussets fit in? I'm not sure, but I sure like em!
Frank

Making a frame that is constructed of tetrahedrons and octahedrons(they fit together to form an octet truss)would yield one stiff puppy indeed.Making this type of structure could be easier than one might first imagine. The most tubes joining at one point would be twelve.If a universal hub was used, the fanciest tube miter would be a straight cut.A ball with those twelve holes in the right places could serve as the hub. I have no idea how to make that, perhaps a casting.A deviation from this system would be to change the length of the tubing pieces so a curve could be constructed.A lot less pieces would be needed, but a universal hub wouldn't work.
Another option would be building a traditional appearing frame, but utilizing inner cells that are tetrahedrons and octahedrons.The triangles could have a big hole cut out of center. This could be made using rather thin sheets of steel, maybe 1/8".This would require accuracy, but a CNC might fit the bill there. TOOOO MUCH,
Frank

Frank,

I've been out of town again and, as usual, missed the activity.

Being "egg headed" can be fun and useful in its own right. I too have thought about these same things. I'm also reminded of the industrial revolution and the development of railway bridges in particular. The Victorians evolved the (straight slab) gusseted and riveted plate bridges and they have stood the test of time. They were simple, easy to build (considering the available technologies back then), and withstood great stresses with little movement. I don't know how they compare to the tube frames being discussed, but it's another form of (theoretical) construction to think about.

Sometimes I think I go off on these "mental tangents" too often. So to keep myself in check, when I've finished, I always like to remember a few choice quotes to bring me back to Earth. <smile>

"Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away" - Antoine de Saint-Exupery

"Things should be as simple as possible ... but not simpler" - Albert Einstein

"Striving to better ... oft we mar what's well" - William Shakespeare


Graham

At one point the hearing aid was a funnel, that when stuck in the ear, amplified the sound and made communication possible for those hard of hearing.It was "simple". To the benefit of society, a great Canadian inventor named Alexander GRAHAM Bell, didn't leave well enough alone. Other fields that he experimented with was aviation and architecture. The principal shapes he utilized in both endeavors were the tetrahedron and the octrahedron and their combination.His studies in this area preceded Bucky Fuller.Both men are heros to me, eh?
Frank

Did you make this one too,Frank?



I was thinking something along these lines,as a tapering C-frame.
Larger(therefore stiffer)in the middle,smaller on the ends.

Probably for my next life time.

Hi Ian, My son made the tower out of 2 foot long pieces of 3/4" conduit(the apple doesn't fall far, he's normal though). It is basically icosahedrons with the ends removed and connected(five helixes one way and five going the other)).I made the chime from 1 1/2" copper pipe(scrounged). The longest pipe is eight feet, tuned to F, the sail for the chime is a brass mask that I screwed up and couldn't toss.
I tried to make a curved model using this system and it was too difficult for me. You can easily make a giant cork screw though. I did however make a curved octet-truss quite easily.You leave out the pieces with orange dots on them, all the other pieces are the same length. This will be like a belt. Then you wrap the belt around the desired profile. You then fill in the missing pieces. Visual mathematics, no numbers.
Frank

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Today , I finally purchased the upper and lower wheels for Frankenframe. I know, its about time. I chose Hoosier Pattern as a supplier. When ordering I was asked if I was a member of Metalmeet and replied yes. This got me a 5% discount. I told the person, I was ordering from ,that I saw their ad on the Metalshapers site, and that people in this group recommended their products. I suggested that people from Metalshapers get the same 5% discount. Joe Andrews e-mailed me back and said they would and it was OK to post that decision.Thanks Joe!
Frank