Learning to Fill Gaps

admin

Ok, I was trying to lay out a learning task progression for me and my new TIGmachine, I have the following:1. Lead beads on a single piece of sheet2. Butt weld two sheets with no filler3. Butt weld sections of tubing4. Join two sheets positioned with gap using filler rodFor #4, what gap should I use for my first learning attempt?  My initialguess was set the gap to the sheet thickness.  So if I'm using 18gasheet steel, I should try to set up a .047 (or whatever 18ga is) gap.Is this true, or is there some scaling factor leading to a larger/smallerpreferred gap.  Obviously, at some point it will become ridiculous(unfillable) for a single pass.
Reply:Lap joints.  Practice those before butt joints.  That joint configuration makes it a bit easier to learn and practice compared to a butt joint, especially from a 'blowing-right-through' aspect.    The best laid schemes ... Gang oft agley ...
Reply:Originally Posted by ericmOk, I was trying to lay out a learning task progression for me and my new TIGmachine, I have the following:1. Lead beads on a single piece of sheet2. Butt weld two sheets with no filler3. Butt weld sections of tubing4. Join two sheets positioned with gap using filler rodFor #4, what gap should I use for my first learning attempt?  My initialguess was set the gap to the sheet thickness.  So if I'm using 18gasheet steel, I should try to set up a .047 (or whatever 18ga is) gap.Is this true, or is there some scaling factor leading to a larger/smallerpreferred gap.  Obviously, at some point it will become ridiculous(unfillable) for a single pass.
Reply:Historically when joining two sheets as thin as you're decribing, I've butted the two sheets together tightly with no gap with a copper backing plate underneath. The backing plate was typically a 1/4" thick by 4 inches wide by however long I needed it to be. I've never have gone under 12 gauge (0.105") only because the jobs we were doing didn't call for something that thin.Tack your sheets together. Usually every three or so inches is good. The tacks don't need to be anything large. Then proceed to weld your seam. Don't worry about your tacks, you'll consume them as you're welding.  If you stop along the way, make sure you wire brush the seam at the point where you stopped before proceeding with rest of your weld.As MoonRise has suggested, do practice with Lap Joints first.  This will allow you to learn to fine tune your control of the current if you're using a pedal. Continuos flat welding can be done without the pedal with a set current.  Preferable if you're in a position that doesn't allow for the pedal to be used. This happens a lot if you're welding very large sheets together and they're laid out on the shop floor.
Reply:As far as blow through with the 18ga sheet, won't turning the amps down to theproper settings (48amps?) avoid that?With the backing bar, is there not a problem with the copper mixing with the steel?With proper heat, the steel right up against the copper will be molten, right?I bought 1/4 copper strips for heat sinks, but I didn't plan to put them rightin the weld area.  I'd think the copper would melt.No one addressed the gap issue.  Suppose it's impossible to get a perfectalignment between the pieces.  Are people saying I can't use filler on 18 ga?I believe I saw somewhere .040 filler rod (which came in my kit) would work.
Reply:Contol your heat and you won't have a problem with melting into the copper. I've done it too many times to even track. Also make sure you're using the right sized tungsten for this sort of welding. You want a thinner tungsten for better arc control.  As far a alignment goes this is what you could do....make a tack and lightly hammer the tack and this will align the sheets so that theyr'e even. Keep doing that for all of your tacks. Alignment with thin sheets is always a problem and this is a good way of dealing with that. You can use filler on your material.  1/16" filler would work, but I wouldn't go thicker than that.  Your heat input requirements would be too high and thus result in blow through.
Reply:So if I put a backing bar underneath the weld line, obviously I would need to supportthe two pieces of sheet with several other backing bar bits to keep them level, right?Can I just by a huge sheet of copper instead to put on top of my welding table???
Reply:Copper is used as a backing bar/strip because it conducts the heat away PDQ and you don't end up really melting into the copper.The copper has to have enough width AND thickness for the job at hand, putting a strip of copper foil behind a butt joint really isn't the right thickness of copper.  And getting enough copper to have a copper-top for the welding table?  $$$$$  But yes, if you are working on top of a welding table and laying the workpieces out flat to be welded you may have to block-up the rest of the sheet if you have a backing bar underneath a joint.  Depending on the layout and alignment and so forth.You use filler or not depending on the joint requirements.  BTW, you can also use thin MIG wire as a filler instead of cut length TIG filler rods.  Steel MIG wire comes down to 0.025 diameter and the cut-length TIG wire only goes down to 1/16 inch diameter, ER70S-6 spec is the same whether on a spool or in cut lengths.    Same thing with aluminum 4043, etc, etc.  The best laid schemes ... Gang oft agley ...
Reply:You can buy a square foot of 1/4 inch thick copper for about $100 online, soit's not too bad.  It would probably retain its value better than your 401(k).
Reply:OK, I was processing this thread some more and now have a question.  What if I'mwelding pieces of a tube together (to form a longer tube) and don't have access to theinside?  Assume it's still a thin gauge like before.  I can't get the copper behind the weld.I could clamp pieces on the outside near the weld but obviously not on it.Am I overanalyzing?  Seems like you guys were saying the backing bar is required.
Reply:The advantage of TIG is its versatility. So, with a little practice, you can weld tubing end to end without backing. Since tubing isn't flat, you don't have the distortion problems of sheet metal. Remember that all welds shrink, so no matter how hard you try, there will be some movement from where you were clamped.Do you have a pedal? Over analyzing? Maybe some, but it shows you're thinking. Do some welding, post pics.TIG rod must be used, ER70, because it contains the deoxidizers necessary for the TIG process.TIG doesn't like mill scale. Use a flap disk or hard wheel, a wire brush isn't aggressive enough. If you don't, you'll get porosity in your welds.TIG likes a short arc length, try for 1/8" or less.TIG is hard at first, don't let it beat you.Good luckGo up to User CP and fill in your location, someone may be near enough to offer hands on help. 9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:Craig,ER70S-6 is the same wire, whether it's in sticks for GTAW or on a spool for GMAW.Other than that, yup on what you said.  Eric,Practice first on the 'basics'.  If you are just starting out, don't be worrying about gaps and pipe/tube welds just yet.But yes, you (usually) can't put a backing plate/sheet inside pipe/tube welds.  But the pipe/tube -may- have to be back-purged.  Practice, practice, practice.    The best laid schemes ... Gang oft agley ...
Reply:Originally Posted by Craig in DenverTIG rod must be used, ER70, because it contains the deoxidizers necessary for the TIG process.