Butt or Mitre on SHS?

[londonsean69]

OK, yet another question

When joining 2 pieces of RHS or SHS together at right angles, do you generally just do a butt weld, or do you cut the pieces and do a mitre joint, thus sealing the end at the same time?

The part will be taking a fair bit of load, but not sustained (jacking point on a motorcycle table lift)

Grey one is what I see most of the time

Orange looks like it would be stronger (more weld area).

Piece will be 50x50x3 mild steel

Cheers

Sean

 

[English Steve]

Mitre is by far the structurally stronger joint as the load is being transferred into all faces of the vertical box section. If you use the grey joint, all of the load is going into one face only. If forced to use the grey joint, I would use a full face gusset on at least one side.
Personally, I also think a well formed mitre looks better and results in a closed section so you don't need to cap it.

 

[londonsean69]

Thanks very much for the answer.

It's what I had assumed, as the load will be trying to pull the joint apart (the load is perpendicular to one of the inner faces)

 

[rtbcomp]

On the grey one it would be better if you could arrange for the horizontal to sit on top of the vertical.

 

[londonsean69]

On the grey one it would be better if you could arrange for the horizontal to sit on top of the vertical.

Fair enough.

I just chucked these together in CAD to get across my point.

Is there any particular reason? I would assume so the force is going perpendicular through the weld, rather than in shear force (sideways through weld).

I have to say, I prefer the look of the mitred joint.

Cheers

Sean

 

[rtbcomp]

Fair enough.

I just chucked these together in CAD to get across my point.

Is there any particular reason? I would assume so the force is going perpendicular through the weld, rather than in shear force (sideways through weld).

I have to say, I prefer the look of the mitred joint.

Cheers

Sean

Yes (and yes)

 

[TechnicAl]

The strongest would be to cut one side square. Cut the other piece so that you remove 3 sides the same size as the section (you are left with something like a finger nail). Then weld the sections together along 6 equal lengths
Difficult to describe and even harder to draw with my IT skills.

Sure someone can visualise what I mean. Basically the same as the grey but filling in the end by extending the top of the top piece.

 

[londonsean69]

Like this you mean? Sorry about the size, just a screen grab

 

[Hitch]

I think thats what he meant yes.

Certainly a lot more time consuming to do than either a but or mitre.

It very much depends on the application normally. In a strength critical peice, go for the mitre, prep it nicely on both faces, take the point off the long edge of the mitre so you can get a nice 3mm corner weld...

 

[londonsean69]

I think thats what he meant yes.

Certainly a lot more time consuming to do than either a but or mitre.

It very much depends on the application normally. In a strength critical peice, go for the mitre, prep it nicely on both faces, take the point off the long edge of the mitre so you can get a nice 3mm corner weld...

Excellent, thank you.

I never though about taking off the corner, but I can see why, then you will have a decent flat(ish) area to elde, rather than a long, thin edge.

That's what I like about this forum, if people can help, they do. Beers all round if we ever meet

 

[English Steve]

Beers all round if we ever meet

Carefull Sean! Hitch does quite a bit of work in London

 

[londonsean69]

Carefull Sean! Hitch does quite a bit of work in London

Not a problem, the offer stands

 

[TechnicAl]

Like this you mean? Sorry about the size, just a screen grab

Thats it

As Hitch says it will be more time consuming but it will be stronger.

 

[hareng]

Recently done all my 9 work benches mitred, had to cut with hack saw
Bandsaw packed up years ago. To get a nice joint i milled it to exact length at 45 degrees, dead easy with a DRO.
Nice metal cutting chop saw and away you go.