The cart will be 28" wide and nearly 15’ long. Below is my first draft at how I might use 3" x 3" square aluminum tube, 1/8" thickness, to build a cart with a roughly 800 lb load capacity. All angles are 45 or 90 degrees.
I would appreciate advice on how to connect the aluminum tube, possible changing the 45 degree angle, caster placement, etc…
You are only talking about 24 lbs per sq ft weight capacity, given the size. That shouldn’t require extensive supports. You could probably get way with building the cart with pine 2x4s and be fine. The key will be how many casters you need, I’d suggest keeping the spans between casters to 5 foot. I would use 6 casters, 4 omni directional caster for the corners and 2 non-rotating casters for the middle. The non-rotating casters will make it easier to push the cart in a straight line when needed.
Excellent advice, Nick. I will use your caster strategy for sure.
One more thing-- since I already have the aluminum I’ll go ahead and use it for the cart in case we want to increase the load limit.
I’d weld it. We have a TIG welder in the metal shop.
-Jim
Jim,
I like your welding idea but I have “welded” exactly one time. Is there a way to get nice welds using some sort of mechanical assistance?
I can control linear actuators via a stepper driver I have and G-Code, so I could build a rig that would give us constant welding speed and distance. I have a 400 mm actuator handy.
Bruce
Bruce, May I ask what you intend on using the cart for?
Based on your responses,
I, like @TBJK am wondering what you use for the cart is as well?
If it is a general cart the looks of the welds shouldn’t really matter as you can grind them to make them look better. The key is that the welds are solid in connecting the parts. Welding really is easier than finding special hardware to connect everything like an erector set. I’m not a welder by any means as well, but it isn’t a skill that requires extreme talent given the scale of your project if your just making one of these carts for use in a warehouse, given the parameters.
TBJK,
The cart will be used to hold Big Susie, who will be a generic long CNC machine. I will own her but keep her at Dallas Makerspace for general use
Susie’s first use will be artistic only-- to drill holes in 144" x 2" aluminum poles with 1/4" thickness. The holes will be drilled in mathematically-generated spiral patterns. This version of Susie will have a rotational Y-axis.
Next I will make a long skinny version of our PlasmaCam (Edit: I meant MultiCam) CNC router and the Y-axis will be linear. It will also be aluminum-capable.
I will encourage people to get creative with it.
Bruce
Oops, I meant MultiCam, but it could do plasma later on.
How accurate do you want it to be? You will have to reinforce it more to keep flex down if you want accuracy.
What committee is taking this? I can’t even think of where we have space currently.
Not to be a spoiler: Which committee knows they are going to get this and agreed to store it?
TBJK,
I would like to make it roughly the accuracy of our MultiCam, whatever that is.
I would also like advice on how to reinforce it more, and for all three axes-- not just the two shown.
Later we can build an insane steel version with HAAS-level accuracy, but one step at a time…
Bruce
Jim,
Kris said I could keep the materials in the space we’ll be moving to.
She also suggested I ask the Plastics committee, so I should figure out how to do that…
Bruce
Kris recommended I ask the Plastics committee. I’ll do that next.
I don’t see a Plastics Committee on TALK. How should I proceed?
Plastics is under Machine Shop.
Bit of a reality check here of design goals vs design as proposed. This going to sound harsh.
If you are looking for accuracy like the MultiCam your structure will be no where close to being able to achieve this. There is a reason CNC’s, Lathes, Mills, etc. have massive cast iron beds: to eliminate deflection.
Something as long as you are talking about, I would expect as a very minimum to deflection under it’s own weight somewhere between two orders of magnitude from the accuracy a MultiCam holds: ±.001" . 0.100" of an inch deflection over a 12 foot span isn’t a lot for a lightweight structure. Strongly suggest you get some structural analysis done before starting this.
Also, after completed, you’ll need to align hard points where attachments are going to go. How will you machine these and then inspect for accuracy. .005" over 120" is .0024 degrees or about 8.6 seconds of an arc. Of course these will be meaningless unless deflection is negated.
I did tooling inspection when working, I have never seen anything as light as proposed to hold anywhere near what is proposed.
Photomancer,
Your reality check is greatly appreciated!
You didn’t sound harsh at all, and you just saved me a few hundred bucks’ aluminum.
I will
I suspect I will be Googling “DIY electric golf cart” in parallel since I won’t be strong enough to hand-push the resulting beast.
Bruce
For achieving your goal, drilling holes in a tube.
I would look a CNC tube cutting machines:
As well as Swiss lathes:
You will notice that the defection of the tail end of the stock does not really matter much to the machine as the stock is supported right next to the cutter. taking this approach would also allow you to make a much more compact machine.
