How would you tackle this?

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Im making  a base for a hobby CNC machine, the base is made out of 3X2X0.180 steel tube.Because of it being a CNC machine I need to minimize distortion as much as I can. My plan is to tack everything together, and then weld each piece in increments. Not putting to much heat at any particular point for too long. Il be using TIG on all of this.Is there anything else I should be aware of?The whole thing is 43.375in X 27.5in. Attached Images
Reply:Do the vertical fillet's first, then the horizontal.  Weld verticals opposite corners of the cross bars.  Weld one, move to another, come back & weld the opposite corner, then move on in an X pattern.Horizontal welds figure out which way you want it to shrink to, weld the opposite side first.  All welds will shrink, so choose wisely.MarkI haven't always been a nurse........Craftsman 12"x36" LatheEnco G-30B MillHobart Handler 175Lincoln WeldandPower 225 AC/DC G-7 CV/CCAdd a Foot Pedal to a Harbor Freight Chicago Electric 165A DC TIG PapaLion's Gate Build
Reply:Use of doublers1-Mig will produce less total heat input that TIG. That 3/16" wall tubingradius edges has room for a rather large bead--which you do not wantor need. Tubing isn't necessarily dead on straight, has camber, twistroll and pitch, to begin with, something you might gander at. You don't mention how flat this needs to be.....weldmentsthat require high accuracy are either machined post welding orhave provision for adjustment, shimming, etc.2-use 3" x 5" x .190 doubler plates as shown in the lined drawing.3-the crosstubes can be fully welded around to the doubler plates,but only do the longitudinal welds (BLUE LINES) for the doubler tobeam tube connection.3-The offset nature of the cross tubes (flush on bottom) will createconcave bowing of the frame beam tubes if doublers are not used.4-Tack all in place, first. Short welds, alternating from one cross tubeside to the other, without finish the short welds, go to the far end cross tubeand repeat, then back to the other end crosstube, then to the middle tube.5-The use of doublers is not understood or appreciated--by most (asevidenced in many, many project postings), since they add time and hassle.They are highly effective at reinforcing, distributing and translating loads at right angles,increasing the strength and reliability of the assembly; widely used inlight to heavy structural, aerospace......and in my shop!http://weldingweb.com/attachment.php...1&d=1256003875 Attached ImagesBlackbird
Reply:Thanks for the replies.I completely understand what you mean about the doubler plate, unfortunately I already have all my pieces cut, drilled and tapped. So, adding the doubles will throw off all of my dimensions.
Reply:Originally Posted by tanky321Thanks for the replies.I completely understand what you mean about the doubler plate, unfortunately I already have all my pieces cut, drilled and tapped. So, adding the doubles will throw off all of my dimensions.
Reply:the doubler is there to add mass?intriguing idea..
Reply:This is exciting to come across, I am in the planning stages of making my own CNC plasma table.I imagine that it might be wise to put on some large and thick angle aluminum in the area of the welds where ever you can to help keep things at an ideal temperature, maybe this is completely wrong.I don't know what a doubler plate is and I am very interested.  I did some googling, the contextual definition seems fleeting to this application.As interesting an important as a true table can me, I am very interested in the design you are going with.  I've worried at great length about the true-ness of the X and Y axis.  I don't know if angle steel comes with any sort of distortion, I'd surely hope it was true when I got it, but I have seen many designs  that use V bearings (http://www.linearvguides.com/linearv...uidewheels.htm) and I imagine there are many ways you could utilize those to avoid any kind of warping that may occur in the base frame.I hope I don't go and hijack your thread, but I'd love to hear about your chosen CNC layout.Miller 330 a/bp water cooledI believe in gun control, I hold my gun with two hands.  If you want to know why, click here.Buy American or bye America.
Reply:I wouldn't tackle it, that sounds painful.
Reply:Just tack it to gether and just do the verts, I would think that would be all the weld you would needI always tried to work with the oldest hand on the job to gain knowlege but now I can't find any.
Reply:I have already made the frame for my cnc. Here is the procedure I finally came up with.1. tack the top together and make sure everything is straight.2. make a plan for the order of welding that takes into account the direction of shrinkage based on the direction of welding (see picture). Alternate side to side and make sure to weld in the same direction to offset shrinkage.3. Do not weld across the side of a tube.(see picture) If you feel you need more strength in this direction add a diagonal or a shear panel.4. After you have the top together, weld the legs on.5. You can make small corrections for twist in the table top by tweaking the legs. Proceed like you are trying to make a shelf between the legs near the floor like mine. To work out twists first tack on a perimeter then experiment with pulling two legs together until the twist in the top is gone and then weld in a diagonal. Attached ImagesIan TannerKawasaki KX450 and many other fine tools