A Question about "Box section steel -V- L section steel for fabricating.

[Rob]

A question for anyone in the know really when it comes to engineering in steel etc.
I am about to start fabricating the final part for my backhoe, its a new subframe.
The original subframe was not supplied but i did have the end of it still bolted to the backhoe main chassis.
Basically 2 parallel steel sections with some extra bracing on the underside along each lenght.
The oringinal spec sections were made from "L" section steel and sizes are 50mm x 75mm x10mm thick approx 4-5ft long each side.
My local steel merchant doesnt stock this size anylonger and if he has to buy it in, its going to be a 6M lenght and really expensive.
I was thinking on fabricating the new subframe from box section steel as an altenrative.
If I was to go this route what size box section would i need if it was 5mm thick material and also being able to be as strong as the original "L" spec parts.

any help would be a great help on this guys.

rob

 

[lsmurphy]

I don't have a specific answer for you but box tubing is the way to go.

 

[North Idaho Wolfman]

If you want to make sure it's as strong or stonger then just use smaller box tubing and double it up. that will create a strong center for the beam.

 

[lsmurphy]

He should be able to get 1x3" or 1x4 or 2x? 1/4 wall.........but then he's on the other side of the pond, so who knows?

 

[Russell King]

Rob,

The properties you need to compare are the I values. These are tabled values available in books and on the web. Here are some from a UK site.

The first is the lead in table, the second is for angles and the third is for hot formed rectangular tubes.

http://www.roymech.co.uk/Useful_Tables/Sections/steel_section_index.htm

http://www.roymech.co.uk/Useful_Tables/Sections/U_Angle_prop.htm

http://www.roymech.co.uk/Useful_Tables/Sections/RHS_hf.html

If you compare the properties of the angle to the tube and select a tube that has the same or greater numbers you will be fine. The only thing to look at is the pictures to see the "axis" that is being referenced. Think about a rectangular board (2x4 in USA) it is much stronger in one direction than the other.

If you have more questions let me know.