in need of Engineering help (now with PICS)(kinda done)

[vancamp]

I need some engineering help i am building a collapsible cart material is aluminum basically its two aluminum rectangles and four legs that pivot i am trying to come up with a easy way to lock it in the up position doesnt need to lock closed, i have an idea rolling around on how to do it but thought i would get some other ideas. pic kinda shows what it does.

[SFRT]

drill a hole through one of the uprights and the edge of the top and use pin.

[vancamp]

drill a hole through one of the uprights and the edge of the top and use pin.

that would work except its aluminum and gonna be supports a couple hundred pounds, and pinned and unpinned alot, what im going to do is mount an aluminum box on top to hold tools and equipment. i was think of some kind of arm from  the top cross bar to the bottom with some form of release if that makes sense. something kinda like this

[Tilar]

Does it have to be aluminum? If it were made from say 3/4" box tubing, I would think it would better withstand the use you're wanting to put it through.

[vancamp]

Does it have to be aluminum? If it were made from say 3/4" box tubing, I would think it would better withstand the use you're wanting to put it through.

i was using aluminum due to weight and the fact i had some parts and alot of aluminum tube.

[Alaskan_TA]

Single pin at center of bottom rail with two braces. If you do it just right, you may be able to un-pin the tops & fold it all flat.

[vancamp]

heres what it will look like like from the top there are 2 cross bars with cast pivot points that the legs attatch to.

[nvrbdn]

what about using arms that fold in the center like a pop-up camper that had the aluminum arms on the outside with a pin in the knuckle. they could fold toward the inside and the top tray would still come down flat.

[Darkman]

I wouldn't put a lot of weight on that if you are going to fold it flat. It wouldn't be a very stable structure and may twist while you are lifting/lowering it. It will need some cross bracing otherwise it can buckle your uprights.

IMO, if you are building it out of aluminium, the don't make it collapsable

[Domino]

here's a light weight and homemade solution: You can put the lower pivot maybe 6" up each leg, with the lower section of each leg fixed to the base.  Have a piece of tubing (maybe 12") on each leg that slides over the pivot to stiffen it, then slide the tubing up on each leg to allow the table to fold down.

It will add a little thickness to the collapsed package and probably some wobble with loose fitting tubes.

You can also buy locking inversion links like those used on folding tables, "A" frame ladders, etc.  Just install those between the top and each leg.

[twodko]

At first glace Frank's safety pin idea would be easy and inexpensive. If you go that route, use at least 2 pins and thick ones like 3/8 - 1/2" in diameter. Drill holes only large enough to receive the pins. A nice tight fit would go a long way preventing the holes from ovaling. Different folding leg options say "amputated digits" to me and folding one or more "legs" might be a PITA.

[vancamp]

thanks for the suggestion guys i will post a pic in a week or so with what i come up with, if anyone else has any suggestions i'll take em as this is a work in progress and a winter project i have playing with.

[vancamp]

well i started out with a broken and used X frame ambulance stretcher and started eleminating parts and trying to get it to do what i wanted but i really needed a H frame setup so alot of cutting and head scratching.................

[vancamp]

.............I ended up with this, im not done yet i still have to redo the single brace one end its to tall when its folded down, and im gonna add some aluminum cross pieces to the curved braces on the other end and add some brackets to hold tools etc, but i got the main part constructed and a box mounted on top of it.

[bakerhillpins]

I'm a bit late to the party but I would put a cross brace in to form a triangle. Triangles are the backbone of trusses and are inherently very strong. Think of the legs on a folding table. They all have the small pop out locking cross brace that forms a triangle to support the legs. 

[vancamp]

I'm a bit late to the party but I would put a cross brace in to form a triangle. Triangles are the backbone of trusses and are inherently very strong. Think of the legs on a folding table. They all have the small pop out locking cross brace that forms a triangle to support the legs.  

thats kinda what i was going for (see arrows) im not an engineer obviously, if anyone sees a problem let me know.  

[bakerhillpins]

Ok. Looks like those supports are/were on pivots allowing the table to drop. Maybe that's why folks were talking about pins? 

[vancamp]

Ok. Looks like those supports are/were on pivots allowing the table to drop. Maybe that's why folks were talking about pins? 

they are pinned at he top and bottom for removal when it folds i have changed it up a little more today i will post more pics as i am getting closer to done with  it.

[vancamp]

ok i have come up with what i think will work after adding a safety bar that only allows it to collapse in one direction, i added some tool holders on each end and down the front and all my tools pack inside for transport still gonna do a few odd and ends to it but its pretty much done.

[vancamp]

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[vancamp]

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[vancamp]

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[nvrbdn]

how heavy is it to pick the box up and hold it to put the support bar in? and what keeps the wheels from rolling while trying to pick it up? is there wheel locks?  nice looking box.

[vancamp]

how heavy is it to pick the box up and hold it to put the support bar in? and what keeps the wheels from rolling while trying to pick it up? is there wheel locks?  nice looking box.

Thanks, wheel locks are in the works. empty its really light loaded its probaly a 100-125 pounds. the support bar has a knuckle in the middle that allows it to bend and be istalled and as you lift it locks into place.

[nvrbdn]

i like your plan and would like a close-up of the support bar to see just how that works. surely would need wheel locks to make sure it stays put..

[vancamp]

i like your plan and would like a close-up of the support bar to see just how that works. surely would need wheel locks to make sure it stays put..

I will try and get some in the next couple days basically its a pivot with a spring loaded sleeve that slides up and locks it in place

[nvrbdn]

ah-ha, that makes sense. so you can lock it in one handed. great job. where did you find the ambulance stretcher? im assuming it will line up to the pick-up bed for easy in and easy out. sorry for all the q's this is just the perfect thing for the mechanic on the go.

[vancamp]

ah-ha, that makes sense. so you can lock it in one handed. great job. where did you find the ambulance stretcher? im assuming it will line up to the pick-up bed for easy in and easy out. sorry for all the q's this is just the perfect thing for the mechanic on the go.

it started out as an x frame stretcher that i cut apart and made an h frame out of, would be alot simpler if you staart out with an H frame but i couldnt find one anywhere around here, h frame were one man stretchers and everyone has went to the two man x frame, i got mine from an ambulance service that ordered new ones and was supposed to destroy the old ones, so i destroyed it for them the box is an aluminum box designed for flat bottom boats, tool racks used to be bed rail off a ford truck, some hitch pins, all thread, and aluminum flat stock later this is what icame up with.