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Thread: weld sequence
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26th Sep 2009, 02:43 AM #1
weld sequence
Hi fellas,
Just a query on the best weld sequnce for a light lace truss out of 32x32x2mm and 2850 long
Top and btm chord will be 120mm apart with vertical ends and then at 45° for the rest (forgotten what these pieces r called)
I would think the the best sequence would be start at the center point weld, flip it over do the other side, move then to the next weld (left or right) flip over weld then, move opposite to the previous (left or right) and continue weld flip alternating left or right until the ends.
I will see if I can set it up on a jig so I can flip it each time
If I don't flip it each time but still on a jig how do u think it will turn out if I weld the whole thing on one side only then release it from the jig, flip it, put back in jig, then weld other side. Will it come out like a banana
Peter
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26th Sep 2009, 12:19 PM #2
If it was me I wouldnt weld it all on one side first, with or without a jig. When I weld liteweight retangular frames together I have some heavy items on hand (cause I dont have a jig) and turn over a few times as I am going. Try not to weld the whole lot straight up, usually have other quick jobs to do in between to let it cool a bit before finishing. But thats no good if u are trying to do the job as a production line thing.
As for a weld sequence dunno, but piece as much of the truss together first as practical and tack well before getting serious. Move around heaps to help even out the heat stresses.
But thats only my opinion.Frisky wife, happy life. Then I woke up. Oh well it was fun while it lasted.From an early age my father taught me to wear welding gloves . "Its not to protect your hands son, its to put out the fire when u set yourself alight".
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26th Sep 2009, 02:15 PM #3
Hi.
I would certainly advocate welding opposite sides in progression. Start one end then go oppostite side then back to other side in linear progression
No need to fully weld unless you are driving bulldozers across them.
Small lengths of single fillet weld section keep the weld volume down to minimise further distortion. Weld to parallel to long axis first.If lacework need to be fully seal welded -KEEP BEADS SMALL
You could tack weld bolts at centre points either end of your end plates for a pivot. Attach earth to frame.
Note I said bolts -use the head end to tack to the end plates. Make vee (out of some angle section and tack to legs high enough to allow a swing.
Grahame
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26th Sep 2009, 08:36 PM #4
Thanks Jatt and Grahame,
Just a couple of points I would like to clarify Grahame, you said to start at one end...you wouldn't start in the middle and work out both sides from the center
and.... Weld to parallel to long axis first.... umm not sure what u mean there?
Peter.
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27th Sep 2009, 08:59 PM #5
Long axis = long axis of the truss.
I'd refer to Blodgett's text on welded structures, if I could find my copy, but I reckon you'll get best results (least distortion) by keeping the sequence as symmetric as possible. So, until contradicted by better suggestions, I'd start at mid-span - easier said than done, of course.
I'm having difficulty with your arithmetic. The web diagonals will have a contact length of 45mm (32/0.707), for a panel length of 165mm. Deducting 64mm for the end posts leaves 2786 for panels, and thus 17 panels needed - an odd number, and therefore unsymmetric from the start. Might be OK then, depending on the truss's function, and starting at the end might also be OK. For sequence, alternate side-to-side and top-to-bottom in cycles.
Cheers,
Joe (Structural Engineer, BTW)Of course truth is stranger than fiction.
Fiction has to make sense. - Mark Twain
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27th Sep 2009, 09:59 PM #6
Thanks for that Joe, the length is not a fixed thing at this point, I am using the 2850 length from some existing shelving so to make it symetrical, length will be adjusted accordingly.
Your suggestion of starting in the middle is where I thought would have been the best place to start then proceed as symetrically as possible
I will most likely use a smaller section for the struts.
Peter
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