# Weight Calculation

1. Mar 1, 2008

### OutCell

Hi,

How do i calculate the weight of a roll cage tubing, solid or hollow, by knowing the material density?

I am trying to estimate the cost of the cage by calculating the weight. Is that possible? Or should i look at estimating the roll cage from a different point?

Would really appreciate any ideas

Thanks

2. Mar 1, 2008

### FredGarvin

Well, volume*density will give you the overall mass. So if you know the volume of all of the tubing used and you know the price per pound of the material, then all you have to do is account for time for labor and other materials required for construction.

3. Mar 1, 2008

### stewartcs

For a hollow tube:

$$V = (d_o^2 - d_i^2) \frac{\pi}{4} \cdot L$$

where,

do = outside diameter (ft)
di = inside diameter (ft)
L = length (ft)

Then multiply by the density in pounds per cubic foot to find the weight in pounds. Multiply by the cost per pound for the total cost of the tube.

If it is solid, then di is zero. Everything else is the same. Of course you'll need to sum all of the tube segments.

Plus like Fred mentioned, there is a labor cost and a cost for any other componets to the cage.

Hope this helps.

CS

4. Mar 2, 2008

### OutCell

Thanks for your time and answer i really appreciate it. This is exactly what i was trying to confirm :)

5. Mar 2, 2008

### OutCell

Excellent. Thanks a million, this is what i was looking for exactly. Does a bent tube act as something other than a segment or should i just consider it as a segment and add it up?
Any good sites where i can find a good estimate of steel materials cost? In English pounds if any :)

Last edited: Mar 2, 2008
6. Mar 2, 2008

### stewartcs

Just add it in as an equivalent length segment.

CS

7. Mar 2, 2008

Thanks CS

8. Mar 4, 2008

### engineroom

Google search the name of your local steel tube merchant. They more than likeley have tables on the net that give kG per meter or pound/foot for all the different sizes and grades. We have several catalouges in the office here with all that infomation and more.

The merchant may also have posted their RETAIL rates for purchase although these are far higher than if you send them a nice material schedule and ask for a quote. If you make sure your schedule lists how many of each size and grade you require and also purchase in standard lengths so the mechant doesn't have to do your leg work then they are also more likly to offer a better price. My general rule "The more you nag the more it costs" and this applies to anything.

9. Mar 4, 2008

### OutCell

Thanks. I will send them an email and explain why i need the costs. I am actually not buying the material, i only need the cost so i can calculate an estimate for my report/project in university.

Appreciate your help and time, thanks :)

10. Mar 4, 2008

### OutCell

How would you calculate the volume of a square and hexagonal tube (hollow/solid)?? Would it be a complicated method?

11. Mar 4, 2008

### stewartcs

The same concept is used.

For example the area of a square is just Length times Width (since it is square it is L times L). Hence...

$$V = (d_o^2 - d_i^2) \cdot L$$

For a hexagon the volume is,

$$V = \frac{3 \sqrt{3}}{2} \cdot (t_o^2 - t_i^2) \cdot L$$

where,

to = the edge length of the outer hexagon
ti = the edge length of the inner hexagon

Everything else is the same.

CS

12. Mar 6, 2008

### OutCell

Waw, i guessed the square right but your way of the hexagon is easier than what i found :) i greatly appreciate your help
V= 〖[((3 √3)/2 x l^2)〗_out- 〖((3 √3)/2 x l^2)〗_in] x L , this was my hexagon way :P

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