# Calculating strength??

• posted

Not sure if anyone here can help, so please suggest better sites for this question if I do have it wrong.

I have decided to build a stand from steel box section. The dimensions were in Imperial measurements. Not a problem, I thought, just use the other side of my rule, but no. I can only get a metric size.

The plan asks for 1 1/4" square box with a wall thickness of 1/82.

My steel is 30mm square, with a wall thickness of 3mm.

Now the exact metric conversion is

1 1/4" = 31.75mm ,so I'm .25mm down here

1/8" = 3.175mm, again down by 0.175mm.

There is quite a wait to go on this so I am worried about the strength lost, but the next size up is just far too over the top.

Can anyone help here? Have I lost a huge amount of strength or not?

The dimension lost looks very small but when you calculate this as a strength will it become a far greater problem, I just don't know?

Yours Hopefully

RV

• posted

The lightest of aircraft structures allow for a 1.5 times normal load before failure. Hopefully you are building something more conventional where design failure is five to ten times normal load. If you building something like a work bench then no worries. Your dimensions are only changing around 6 percent... Not a concern.

Randy

I have decided to build a stand from steel box section. The dimensions were in Imperial measurements. Not a problem, I thought, just use the other side of my rule, but no. I can only get a metric size.

The plan asks for 1 1/4" square box with a wall thickness of 1/82.

My steel is 30mm square, with a wall thickness of 3mm.

Now the exact metric conversion is

1 1/4" = 31.75mm ,so I'm .25mm down here

1/8" = 3.175mm, again down by 0.175mm.

There is quite a wait to go on this so I am worried about the strength lost, but the next size up is just far too over the top.

Can anyone help here? Have I lost a huge amount of strength or not?

The dimension lost looks very small but when you calculate this as a strength will it become a far greater problem, I just don't know?

Yours Hopefully

RV

• posted

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