Welding Frame - Butt joints vs miter joints

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Welding Frame - Butt joints vs miter joints

Postby justageorgiaguy » Wed Feb 10, 2016 8:32 am

For those of you who welded your frame, did you use butt joints or did you miter to a 45 degree angle? Is there a benefit to one or the other?

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Re: Welding Frame - Butt joints vs miter joints

Postby Dale M. » Wed Feb 10, 2016 10:19 am

I did mitered joints for corners, as it was easier (for me) to make them than to do a butt joint with extended a tab to fill end of tube on tube intersecting at 90 degrees.... I think either way the strength is there so technique is not hyper critical... A lot will depend on your workmanship ( ability to cut and fit good joint) and welding skills and less with strength of actual way joint is made...

All cross bracing and stringers where done in "tee" fashion as the do not have any issue as closing up end of tube for strength and to keep moisture and crud out of open end of tube...

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Re: Welding Frame - Butt joints vs miter joints

Postby Redneck Teepee » Wed Feb 10, 2016 10:59 am

The only advice I will give is to "Tack" your whole frame together (the main square part) before welding it out completely. Doing so will help hold everything square and true during the cooling process. The 90 degree joint on your outside corners will shrink more in the throat than the heel and will pull it out of square slightly if welded individually.

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Re: Welding Frame - Butt joints vs miter joints

Postby justageorgiaguy » Wed Feb 10, 2016 11:24 am

Thanks for the replies! I was thinking to try the 45 degree cuts, and def. tack it all together first. Of course this is a ways off, as I have to play with learning to weld first :)
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Re: Welding Frame - Butt joints vs miter joints

Postby KCStudly » Wed Feb 10, 2016 4:13 pm

I went the other way and did simple corner joints on SQ tube and then capped the open ends. There are a bunch of reasons why I preferred doing it this way.
1. Simple straight 90 degree cuts do not require changes to the cutoff saw settings and are most accurate to layout and make.
2. Welding along a pointy corner, even if ground back for proper penetration is not as easy as welding a seam on a face.
3. Jigging/clamping is easier. The sides and xmbr's can be pulled together w/o sliding past each other.
4. The radius of the long side tube makes a natural weld prep for good penetration with the cross tube, so two sides of the joint require less grinding prep.
5. If you hold the length of the long tube back enough to allow for a flush cap/closure plate, and make the closure plate slightly smaller than the cross section of the tube, it provides a nice "cabinet corner" fillet around three sides (that is easy to weld and comes out looking nice and rounded/chamfered); and leaves a nice weld prep for good penetration on the forth edge (the one against the xmbr).

Another reason I did it this way was because I wanted to round the front vertical edges of my main rails to match the radius on my wall profile. It was easier to cap the radius with a segment of round pipe that way than it would have been with mitered corners; but either way, the above reasons are enough that I would still have used the same joint style.

Don't forget to drill a small vent hole in any tubing that you are trying to weld shut. Otherwise the air inside the tube will expand from the heat of welding and will try to push out thru your molten weld puddle, making a nasty porous blowout like a volcano. With the dedicated vent hole(s) once you are done with all of the structural welds and everything has cooled off, you can do a quick weld, like a tack, to cap the vent hole(s), getting in and out fast before it has a chance to do the same.

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Scan down this post to "Blocked the xmbr up off of the sleeve..." and you can see a little more detail about how I did my end caps on the small swivel coupler xmbr at the front of the tongue. (It happens to be mitered because of the tongue angle, but was still welded as a corner joint, so don't let that confuse you.)
Last edited by KCStudly on Wed Feb 10, 2016 11:02 pm, edited 1 time in total.
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Re: Welding Frame - Butt joints vs miter joints

Postby H.A. » Wed Feb 10, 2016 4:41 pm

H
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Re: Welding Frame - Butt joints vs miter joints

Postby MtnDon » Wed Feb 10, 2016 5:08 pm

Mitered, welded corners can look prettier than butt corners. However, mitered corners are a lot more work IMO. I did them once and called it good experience. For butt corners on some things I weld cap plates in place,sometimes make them overlap the tube being butted against the other. On things That don't need the tube end capped with a welded plate I use plastic plugs... not on a frame. Either corner will be as strong as the weld, the skill of the welder. You can make the corner stronger by welding a triangle of steel plate inside the corner. That can also be used as a place to bolt the floor down.
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Re: Welding Frame - Butt joints vs miter joints

Postby martymcfly » Wed Feb 10, 2016 8:13 pm

I did mitered corners So that I wouldn't have to make a cap for the but joints. I ground the outside point flat before I welded them to make it easier to weld. I cut my pieces at the same time to make sure that all sides were the same length. If you have a HF metal chop saw, cut slow because the wheel will flex causing the cuts to be not straight. Then I welded gussets in all of the corners and drilled them to bolt the floor to.
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Re: Welding Frame - Butt joints vs miter joints

Postby dales133 » Wed Feb 10, 2016 10:36 pm

I but jointed mine as its just far simpler in general.
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