Box Section Joints

[Richard.]

If your welding is good enough there's no difference between leaving the weld on a cap or the weld on a joint. Knock the wire feed and power down to an appropriate level and you're fine. The type of joint makes no difference if the welding is cack.

Even with the welds nice and flat the end plates don't look good unfinished. Mitres look tidier if the joint is to be left as welded in think so any way.

 

[Kent]

This isn't strictly appropriate as the end cap on this is 20mm thick and protrudes from the end, not flush with the cross member. As far as the discussion goes though - the end of the long member and end of the cross member join at the same point though so could be mitred. This would be a no-brainer though to mitre the frame and assemble then add the tapped endcaps. Much easier to cap off the long bearers to size and square, then assemble the frame as square cut joints. The end caps are always ground and once painted you can't tell if it's capped and square joint or mitred.

When it's called for I do exactly as shown here, but for a frame to be flush on the ends? Never unless it's asked for, the exception being a flush in the corners with an open end and just three welds which saves time, electric and consumables.
Of course there are times were an open end has a purpose

 

[Kent]

Even with the welds nice and flat the end plates don't look good unfinished. Mitres look tidier if the joint is to be left as welded in think so any way.

Even ground it's a faff getting radius correct. I think it's easy to fall into a run but I cannot see a reason why a flush closed corner could be quicker or easier or even better looking capped
So I am with you on this

 

[outofthefire]

At work i'd use either joint depending on what I was making, for a workbench it would definitely be an uncapped butt joint because i'd use the length of the box for storing long lengths of bar in. At home it would just be a butt joint because I hate cutting mitre's with a grinder.

I have two of them corner clamps and I can't remember ever using them. I use c grips to clamp pieces of scrap to the corners, check that the four sides measure parallel then tack the inside corners, then check for square across the diagonals and then tack or clamp some long lengths of scrap diagonally across the frame to hold it in square then tack the outside edges then weld it up.

 

[Bede]

Even with the welds nice and flat the end plates don't look good unfinished. Mitres look tidier if the joint is to be left as welded in think so any way.

If the joint weld is to be left, what is the difference between tidiness of a mitred joint or capped and butted - the outside corner is exactly the same, be it mitred or capped. A **** weld is a **** weld. If it's good enough to leave as mitred it's good enough capped? Not that I would leave capped ends as is. Mitred or capped, I'd generally flush off anyway as a matter of course.

This isn't a cap, but same principle - about the only time it's acceptable to weld vertical down. Corner-corner joint, same as an end cap. Quick tickl;e with a 36 grit sanding pad at the corners where the weld starts and it's as good as any comparable mitred joint.

MOD: Edited for language

 

[Bede]

Even ground it's a faff getting radius correct. I think it's easy to fall into a run but I cannot see a reason why a flush closed corner could be quicker or easier or even better looking capped
So I am with you on this

You can't tell the difference between a mitred joint or a capped joint when flushed off. Finishing capped welds to match the radius of the corners of the box takes literally seconds. Flush end, flush edge, 45 degree chamfer, two tangent chamfers then finish with quick graduated passes to round off. No slower than flushing off a mitred weld.

 

[Richard.]

If the joint weld is to be left, what is the difference between tidiness of a mitred joint or capped and butted

General appearance of a joint left "as welded" IMO looks a lot better if its mitred. If it's finished And linished then yes they look as good as one another. Like said above its a matter of preference.

 

[Bede]

To me, that's a bit like the difference between being stabbed in the leg or stabbed in the arm. Neither are particularly desirable! If the welding is neat then there's no difference really. But that's moving away from my original point of capping as opposed to mitring. There are less parts to faff about getting right. The length of one side of the frame is taken care of by capping. That's my main advantage of capping over mitring - ease of final assembly. That's the overriding focus of me explaining all of this on a forum aimed at the novice welder. Easier to worry about lining two members up correctly than all four.

 

[fixerupper]

I spent many years working in theatre , we used to build loads of rostra for stages of all shapes sizes and hights out of 50x50 box .
I think the only time I would mitre a joint is when a it's an angle greater or less than 90 degrees .....jeff

 

[Bill Edwards]

For all those who prefer to use a mitre:

What are you using to cut the metal?

I do what I can to avoid using a mitre as I don't find it great to do with a grinder - and I use a 9", I'm sure plenty on here will only have a little 4 1/2" and would probably struggle.

 

[Bede]

Evolution Raptor Chop Saw.

 

[Richard.]

Doesn't matter really as we all do things in our own way. The photos of your work show nice quality fabricated structures as does the fab work I've seen from Kents shop. There are differences in the methods but it's the product at the end that counts.

 

[Richard.]

I use a small chop saw at home and a ban saw at work. Both capable of cutting straight and angles. From what I can remember the chop saw was not much more than £150 and it's at least 5 years old so it's done well considering it's not an industrial hd job.

 

[ukracer]

Here's a decent sequence of building structures from RHS. Not a mitre in sight - apart from the diagonal bracers.

Nice but what the hell is it?? lol

 

[ukracer]

To me, that's a bit like the difference between being stabbed in the leg or stabbed in the arm. Neither are particularly desirable! If the welding is neat then there's no difference really. But that's moving away from my original point of capping as opposed to mitring. There are less parts to faff about getting right. The length of one side of the frame is taken care of by capping. That's my main advantage of capping over mitring - ease of final assembly. That's the overriding focus of me explaining all of this on a forum aimed at the novice welder. Easier to worry about lining two members up correctly than all four.

Apart from upsetting you by suggesting you might be a hobbyist I think you are saying the same thing I feel but so much has been written my head is spinning. I only had 3 hours sleep last night and now I have a cold on top of that so I will read and digest all your pics and stuff at a later date

 

[ukracer]

For all those who prefer to use a mitre:

What are you using to cut the metal?

I do what I can to avoid using a mitre as I don't find it great to do with a grinder - and I use a 9", I'm sure plenty on here will only have a little 4 1/2" and would probably struggle.

I have a cold saw but I can see exactly how long a piece of steel is when cutting 90 degrees. IF I try a Mitre I find it hard to get the correct length.. I can cut it fine as the saw turns through 45 degrees... but its measuring I find awkward.

 

[Kent]

The saw and the accuracy of the cut makes a LOT of difference. With an angle grinder no way should I even try a mitre (in fact I hardly ever cut free -hand if it can be avoided) . With a great shop saw I have always double cut first straight then mitred to leave a perfect corner to corner joint on the outside, on a less than great site or chop saw its pointy outside corners all the way in one cut always set up with an angle finder never the markings or just chopped square with an open end if it don't matter.

I cant ever remember being asked to cap flush with metal plates only with plastic and that was nearly all on box too thin to get nice mitres or metal caps with very easy (meaning quick without fancy polishing like catering equipment in s/s etc)

 

[Bede]

Nice but what the hell is it?? lol

It was a custom built extension door to a bespoke precast concrete shunt stillage trailer.

The trailer drops to the floor, leaving the whole stillage / trailer floor behind. Without the stillage the only thing holding the two sides of the trailer together is the rear gate. The client needed modified longer stillages to accommodate longer precast concrete panels and thus required a gate that gave an extra metre of internal load space whilst maintaining structural integrity to the trailer.

 

[Bede]

Here it is in use....