Welding Flush End Caps To Square Tube 1

[valmeidan]

I know this is a kind of no brainer question for a welder, however I was wondering the best and most economical and possibly cleanest way to put an endcap on a square tube. I have included a link for a pic of the tube assembly. I know I could weld the cap in the pic onto the square tube, but you would see a weld joint around the part. I have seen 3d images of endcaps that are flush with all sides, but not sure how they could weld this without seeing a beed around the edges. The part in question is a 1.5" square tube, so could I just use a 1.5" square cap? what kind of weld joint would this be, and how would you make it look like there is no weld after....sand it?? or could you just insert a smaller cap into the hole through the tube to sit flush with the end of the tube and solder??

 

[Duwe6]

The flush endcap you saw was probably;
Cap fit flush to tube end, with some small gaps in the corners due to the inside radii of the tube. This flush fit usually requires ID grinding of the longitudinal seam of the tubesteel to allow the cap to slip in.
Then the flush seam is welded on the face, getting fairly good penetration and strength in the corner gap areas only. Remainder will have a small ammount of penetration [below the surface of the parts], being a 'face weld' only.
Then the weld bead is ground almost flush, taking care not to dish out the cap or excessively round over the end of the tubesteel.
Finally, the cap area is sanded to remove the grinding marks and smooth out the end, again taking care not to excessively round over the end of the tubesteel.

Slow, onerous, requires a Master Fabricator, not just a common welder, and thus expensive. But that's how it gets done.

 

[valmeidan]

wouldnt it be easier to just get a cap smaller than the 1.5" tube...say 1.25"x 1.25" square cap then do a fillet weld around? your saying the cap slips into the tube? what i was talking about was a 1.5x1.5 cap welded to a 1.5x1.5 tube like pic if thats possible?

 

[SnTMan]

Four ways, varing degree of difficulty

Regards,

Mike

 

[moltenmetal]

That depends on the function of the end cap. If it's just to keep water and debris out, the cap is set in flush with a small gap all around the ID of the box tube (gap of perhaps 1/3 the wall thickness or so), then a seal weld is deposited over the gap, with very little useful penetration being achieved. The weld is then ground flush for a neat appearance. We have these end plates microplasma cut to size, including the ID radii and a little bump-in to accommodate the scarf of the seam weld on the ID.

Structural strength required? Then you pick one of the details shown by SnTMan, and suffer.

 

[SnTMan]

Well, shown as full-pen, need not be, it depends on the function.

Regards,

Mike

 

[MintJulep]

If you're just trying to keep crud out and make it look pretty.

http://www.mocap.com/tube-plugs.html

 

[kingnero]

do you really need to have no weldment visible?
like you showed in your first post, a fillet weld all around requires almost no prep and takes less than a minute all-in.

The other options cost a whole lot more and require special tooling (band grinder, mill, perhaps a plasma or laser cutting machine if you have to do a whole lot of bevelling). depends on your application off course.

 

[SnTMan]

Depends on quantity as well.

 

[valmeidan]

About making the cap smaller than the tube ID then welding a seem around it...just curious how they would actually weld something like that. I would imagine the cap would fall into the tube. How do you secure the cap to weld around it when it cannot even rest on anything?

 

[kingnero]

Either you hold it by hand and tack it on the corners before welding, or you make it slightly oversized so that the inner seam prevents it from falling. A hammer is then required to position the end cap.
Both methods are used daily, and depending on the size either one method is actually being used.

Also, if you cut the end caps with a shear, it rests on the four corners (on the inner radii of the HSS), and you can weld it all around without problems.

 

[Duwe6]

To fit the cap as an insert, you use a fitup magnet:

http://www.mscdirect.com/product/80..._sJXegN7a0_PLA__15557577904_c_S&026=-99&025=c

This gives an accurate flush fit. Please refer to "Master Fabricator". There is no 'cheap' way to make the weld disappear. Any way you have it build, there will be a LOT of grinding and sanding. And if you turn the finishing work over a laborer, plan on having to reweld about 10-20% of the items due to overgrinding. Archetectural finishes are difficult and expensive.

 

[SnTMan]

You tack a "handle" on it and cut and grind later.

 

[moltenmetal]

We use the fitup magnet method, do a couple tacks, then burn away. A TIG wire is used as a spacer during fit-upto ensure that there's a gap so you at least get some penetration.

 

[SceneryDriver]

I use the fit-up magnet method all the time when capping box tube. If it's thick wall, plan on beveling the edges of the "plug" piece to get some penetration. MIG it up, and grind with a flapper wheel until smooth. As others have said, don't over grind; you'll have a dish shaped depression. How many of these do you have to do?


SceneryDriver

 

[tbuelna]

I would describe the examples shown as "plugs" rather than "caps". A cap would fit over the outside of the tube, while a plug would fit inside of the tube. If the design intent is to provide a fully-welded closure of the tube end, that can also be easily finish machined or ground to provide a "seamless" cosmetic appearance, then I would propose the no.3 example shown in SnTMan's sketch. All four bevel groove welds can be done without rotating the tube, and all of the welds can be finish machined flush using a single operation.