fixture-modular for pickets, rails, & pre-stressing

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This is posted at the request of Bob Warner.The pic's were taken at various times on various work and tosave me some time, at not at the best resolution. This fixture has been usedto build fence panels, gates, railings and general fitup. It's open, underneath which allows for welding and tacking from the bottom, whennecessary. Inside dim's. of the basic frame is 6' x 12'. The 2 center beams slideback and forth and are removable. There's a bunch of other details, modularclamps, etc. that are used, depending on the situation.1.5 square picket bars, hole locations all marked from one datum end of the barare thru drilled to accept 1/2" pins. Drilled on all 4 sides. Pitch spacing for smallpickets is 3.375, for larger is 3.875. Bars are clamped to the tops of the crossbarsof the fixture frame, distance from frame sides is equaled. Standoff washersslide over the pins to center the pickets in the mating beams or frames, which aresquared to each other.http://weldingweb.com/attachment.php...1&d=1249955730http://weldingweb.com/attachment.php...1&d=1249955757http://weldingweb.com/attachment.php...1&d=1249955786http://weldingweb.com/attachment.php...1&d=1249955819At the bottom is an example of pre-stressing to counteract weld bowing of the 114" long panel, which is pictured in full in the fourth picture. Top beam was F-L-A-T. Bottom beam was1/8" convex at the center, so that relegates me to the amateur nook in this forum, not the professional side.     (And yes, the open picket bottoms were sealed with vinyl plugs, as usual.)I've discussed this pre-stressing biz--from a practical, hands-on standpoint,  before on this site and at the moment, can't find the link....but, it's 'out-there'. Attached ImagesBlackbird
Reply:Interésting can You do the same on sheet metal doors??
Reply:The jig in the first picture looks good but there is an easier way. Just buy prepunched bar the same width as your frame. Cut into each hole from the side with a cut off disc. Use the prepunched bar as your jig. It will space your bars as well as center them.
Reply:I used the pre-punched channel idea on a pipe rail.  Awesome way to self center the pickets on round tubing.  Picked up the pre-punched idea from Bob when he first introduced several years ago.