Planing Thick-Wall Aluminum

[JesseK]

Weight (specifically, c.g.) is a major consideration this year. In order to minimize impact on c.g., we're looking to shave some weight off of the upper portions of our lift. There are various methods to do so, each with its own associated time and strength tradeoffs, including trussing and cheese-holes.

The two rails are 2x1", 0.125" thick walls for the lift. For a 6 foot lift, that's roughly 10 pounds of rails alone. The it should be noted that the bearings for the lift have their own bearing blocks, spreading out their stresses across a 3" length of rail.

Could we safely plane the outer-facing and inner-facing wall of each rail (leaving the front-facing and rear-facing walls alone)? This would effectively take down the thickness from a 2x1x0.125 to 2x0.75x0.0625 (0.125" on the 1" legs).

Planing would save approximately 4lbs overall, but I'm curious what the tradeoffs of strength are. I'm not a ME and constantly misinterpret/misrepresent stresses in Inventor. Planing would also prevent us from the potential pitfalls of a errant CNC/mill cutting through one of our already-integrated holes. It would be a relatively simple manual operation since we have the right mill tool and would happen just before powder coating that occurs early next week.

Thoughts? Is it a good idea, bad idea, etc?

[MrForbes]

you could, and it would not affect the strength much in the front-back direction, which is where it needs to be strong. What about cutting a bunch of 1.25ish diameter holes in the web instead?

And you probably could get away with more reduction at the top, than at the bottom, which coincidentally would help with the CG location

[AdamHeard]

Why not use 1/16" wall and skip this whole rodeo?

[JesseK]

Originally Posted by MrForbes

you could, and it would not affect the strength much in the front-back direction, which is where it needs to be strong. What about cutting a bunch of 1.25ish diameter holes in the web instead?

We'd have to do 0.75" cheese holes due to the positioning of a few cross rails, guide rails and other items on the lift. We could do it since we have the right drill bit already, but it'd take a bit of time since there's not a set pattern we could do all the way down the rail.

[JesseK]

Originally Posted by AdamHeard

Why not use 1/16" wall and skip this whole rodeo?

2x1"x1/16" 606x doesn't exist locally within a 2 hour drive. We buy our aluminum in bulk each year for all of the teams we support, with specialty aluminum as-needed for FRC (like a 1x1" angle rail of 7075 recently), so online ordering isn't sustainable for everything we do.

The VEX rail costs would have been fine in hindsight (we wound up having to cut our 74" rails in half this weekend so they'd fit in a crate), but at this point they're a 5-day lead time plus we'd rather not re-make them. At first it didn't seem like they'd work since they're only 60" segments, but yea... about that hindsight...

[Jared]

If you weaken the outer facing wall too much, your elevator will be able to bow in and out in the middle so that the width between the two uprights can change, which, depending on how you lift your carriage, may allow it to twist sideways and pry apart the elevator uprights. We're seeing this on our 1" x 2" x .125" elevator right now, but the elevator uprights are 75.5" tall and are only supported on the very bottom.

[s_forbes]

Originally Posted by JesseK

Planing would save approximately 4lbs overall, but I'm curious what the tradeoffs of strength are.

If you need to cut out weight, the planing method will likely leave you with the strongest and stiffest structure. If you have access to a large milling machine and a fly cutter, it's just a matter of manual labor.

The 3" spacing on the bearings is a big factor in how strong your rails have to be. A wider spacing means that the elevator rails see less stress and don't need to be so bulky, which can save a lot of weight with the tall single-stage elevator approach.

[GeeTwo]

Originally Posted by JesseK

Weight (specifically, c.g.) is a major consideration this year. In order to minimize impact on c.g., we're looking to shave some weight off of the upper portions of our lift.

It makes me wonder if we're doing something wrong. Our robot looks like it's going to come in at about 85-90# including electronics but before ballasting and battery. Granted, it's definitely front-heavy as built, but we're more worried about getting the other 60-65# into as small a package as we can than about ending up with a too-forward COG, even carrying four totes, or two totes and an RC (oops; I gave away our stacking strategy ).

[JesseK]

I don't know that you're doing anything wrong - our drive train, electronics, pneumatics and lift come in at 80-85lbs. We're trying to shave a few off of the lift itself since it's very far forward on the robot, and overall c.g. is about 16" from the floor with only those items.

We've built a rear specialty mechanism that will slightly balance the c.g. out, but it's still pretty high and forward.

[Cory]

Originally Posted by JesseK

2x1"x1/16" 606x doesn't exist locally within a 2 hour drive. We buy our aluminum in bulk each year for all of the teams we support, with specialty aluminum as-needed for FRC (like a 1x1" angle rail of 7075 recently), so online ordering isn't sustainable for everything we do.

Obviously you've looked into this more than I have, but it's hard to believe that you can't find someone who either has it, or can get it next day.

We have a reasonably large, but not enormous metal supplier near us we buy from. They have almost anything in stock for next day delivery.

Anything that's not completely oddball they can get within 24-48 hrs from Southern California or AZ.

Does there really not exist any supplier like that in VA? 1x2x.063 is not at all a niche product.

[AdamHeard]

Originally Posted by Cory

Obviously you've looked into this more than I have, but it's hard to believe that you can't find someone who either has it, or can get it next day.

We have a reasonably large, but not enormous metal supplier near us we buy from. They have almost anything in stock for next day delivery.

Anything that's not completely oddball they can get within 24-48 hrs from Southern California or AZ.

Does there really not exist any supplier like that in VA? 1x2x.063 is not at all a niche product.

This same supplier has got items for us from the East coast on a few days notice as well. So I imagine it goes both ways.

[JesseK]

Originally Posted by Cory

Obviously you've looked into this more than I have, but it's hard to believe that you can't find someone who either has it, or can get it next day.

...

Does there really not exist any supplier like that in VA? 1x2x.063 is not at all a niche product.

Potomac Metals, Winchester Metals & BMG all have massive warehouses, each with 6063-T5, 2x1"x0.125 as their 2x1 tubing. I never thought to ask if they would get something specific in for us, so I just called BMG and Potomac Metals. They said for anything outside of their normal stock would require a minimum order size.

I'll talk to my non-profit and a couple of other teams in the area; we may front a bulk-buy for next year depending on interest.

(edit - just noticed post # 3,000 )

[AllenGregoryIV]

Originally Posted by GeeTwo

It makes me wonder if we're doing something wrong. Our robot looks like it's going to come in at about 85-90# including electronics but before ballasting and battery. Granted, it's definitely front-heavy as built, but we're more worried about getting the other 60-65# into as small a package as we can than about ending up with a too-forward COG, even carrying four totes, or two totes and an RC (oops; I gave away our stacking strategy ).

Am I missing something or does that add up to 150lbs? The weight limit is 120lbs.

[Rick]

MetalsDepot.com got us 1x2x.063 6063 overnight with no issues. They charged $22.50 per 6 foot piece plus shipping. They have it in stock right now. Ships from Kentucky.

[Andrew Schreiber]

Originally Posted by AllenGregoryIV

Am I missing something or does that add up to 150lbs? The weight limit is 120lbs.

Battery?