tig questions .7mm bicycle tubing

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Im building a steel bicycle frame from versus chrome moly true temper bicycle tubing. I have an invertec acdc v205. A few questions:1) What would a good filler rod be?2) Are there any pulse settings or gas flow rates that are ideal for that thickness?3) What tungston size would be best?Thanks in advance--
Reply:That small of a material, I would suggest an ER70S2 filler, 1/16". Gas flow around 15-17. Pulse?? I don't use it much. if you are not used to pulse welding, then practice a lot before you try to run with it. Practice on TUBE, not plate. It's a whole different ballgame. Suggestion would be 2 pulse per second.Tungsten 1/16". Amps between 40-65. It wil depend on your speed and how fluid you can move on the tube as you weld. Try to be quick, and don't lag in one place for very long. You will only create a large HAZ, and you can see issues with the metal surrounding the weld.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:Not trying to be a smartazz, but, based on the questions asked, here are my recommendations.1.  Buy a lot of tubing to practice on.2.  Start with thicker tubing to develop tig skill.3.  Buy 5# each of .040 and 1/16" filler.  Use it up before starting on the bike.Rojo's recommendations will "get you started".  The rest is up to you.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Thanks for the replies. I've been practicing on thicker tubes for a while, but no pulse. I'll try that.Since I've chopped up old chrome moly bikes and welded them, I can see the inside of the tubes--What should the "correct" penetration look like from the inside? Shoud it be just a heat ring, or should I have metal penetrating on the other side of the wall?  I will try to take pics.
Reply:My gutt feeling says you should have as close to 100% penetration as possible. This is what the AV guys are required to do on similiar material and in similiar loading applications.
Reply:0.7mm is about 0.025" wall thickness, which is pretty damm thin.  .045 filler would be largest filler size you'd want to use, current set around 20 amps, .045 or 1/16 tungsten, LOTS and LOTS of practice, and PATIENCE!MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:Hi,I have not tigged any bike frames yet but have built a few fillet brazed and lugged. The most common filler is Weldmold 880T at 0.035" or 0.045"small quantity can be purchased from a US builder. PM for details (First post and don't want to spam).Since you are asking these questions I suggest you have a look around here http://forums.mtbr.com/forumdisplay.php?f=142 I would be (and did) building my first bike out of 0.9/0.6/0.9 tubing rather than the 0.7mm stuff, much larger room for error. Also ensure your miters are tight otherwise the frame will not be straight and the bike will pull (don't ask how I know).
Reply:Originally Posted by newlincolnThanks for the replies. I've been practicing on thicker tubes for a while, but no pulse. I'll try that.Since I've chopped up old chrome moly bikes and welded them, I can see the inside of the tubes--What should the "correct" penetration look like from the inside? Shoud it be just a heat ring, or should I have metal penetrating on the other side of the wall?  I will try to take pics.
Reply:Originally Posted by newlincolnIm building a steel bicycle frame from versus chrome moly true temper bicycle tubing. Thanks in advance--
Reply:Here is a pic of 1.0 mm tubing that I was practicing with.Attachment 52475hopefully you can see the penetration here.Attachment 52473Here is a shot of the .7mm tubing from the outside and then another to show penetration.Attachment 52474and the penetration on the .7mmAttachment 52476I don't remember the size of the filler I'm using, but I will check later. Thanks for the input so far--I didn't even expect anyone would reply.Last edited by newlincoln; 05-12-2011 at 07:29 AM.
Reply:here is a pic of the jig I made with the tubing.Attachment 52478and the bottom bracket mitreAttachment 52480Last edited by newlincoln; 05-12-2011 at 07:29 AM.
Reply:I work 99% with automated welding, so my advice may not apply well to this application, but here's what I see.  This is a challenging welding project, even with excellent joint prep and fitup, it will require a very steady hand and keen puddle control to make the beautiful welds that we would all like to see on this frame.Your practice welds are not there yet, they look to have excessive filler that is not properly wet in at the toes, yet they also look overheated and oxidized.  I am picturing that maybe your arc length is too long and/or current it too low, so that you are having to travel too slow which is overheating everything, and you're trying to melt the filler with the arc rather than letting the puddle melt the filler.  Does any of that sound right?A pulsed weld with a very slow pulse frequency like 0.5 or 0.3 pulses per second may help you out.  With the high current set to melt a nice size pool to dip the filler into, and the low current set low enough to let the puddle really cool down, this could help the allow a slow manageble pace without overheating the joint.I don't know practical this is, but if you take the pulse idea to the extreme, you could actually make individual discrete overlapping spot welds, shutting off the arc after each spot and carefully advancing and positioning for the next spot, using the gas nozzle to rest the torch very securely in place.  This could be tedious, but would take far less skill than a contiuous freehand or cup walk weld around the joint.
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Reply:Thanks again for all of the great comments. I will keep practicing and see if I can make use of the advice. I know my welding has a long way to go-- I'm going to keep at the thin tubing until I get it right.I really appreciate the time you folks took to read and write write back to me.I'll post more pics of new practice welds soon.
Reply:Arc length, arc length, arc length!, personally i reckon you'd progress faster if you step back to flat sheet and concentrate on arc length and puddle control for a while before working with tube- with puddle control being more natural it'll be easier/faster to adapt to  the changing torch/filler angles as you work around tube. As said joint fit up very important, i would consider this sort of fit as the min (can see what looks a fair bit of a gap on the BB cluster)...Did a quick and dirty demo on some 15mm OD, 0.71mm (0.028") wall as it's been a while...Pretty ropey really, didn't help myself with the rough fitup (note the daylight showing in the above pic) and chasing a silly little coupon round the table didn't help but no excuses- it's under filled, a bit hot and there's a touch of undercut..FWIW was done with an invertec v205t, 1.6mm tungsten, 0.8mm wire (er70 something, can't remember exact flavour) and 31A (was using torch button not the pedal, 1.5secs slope out time) with no pulse and around 1mm arc lengthFor pulsed welding you really need to develop your own parameters as each one has an influence on others. As Pulser said a low frequency pulse can help in that you're effectively making a series of spot welds without breaking the arc however personally i think you'll end up a better welder if you learn to do without and then you'll be in a better position to set up and develop pulse parameters to gain the full benefits. Something to watch out for with low frequency/slow pulse is creating a good looking weld that has a bunch of voids at the root because the pulses didn't overlap enough. Need to play around and cut up some coupons to get the full picturePersonally when i use pulse for this sort of work (fillets in thin wall stuff) i always use a high frequency pulse as it 'stiffens' and focuses the arc better resulting a more stable arc and better pudle control. For a given amperage higher frequencies tend to gradually narrow the weld pool as frequency increases (has a small influence on weld width). I'd run around 175Hz with around a 3:1 peak to background ratio i.e. 31A would become approx 50A peak, 17A background and around 35-40% peak time/pulse width as a starting point
Reply:Hi again--I had a chance to do a few more practice welds. Thanks again for the help-- I will post more when I have the chance.Last edited by newlincoln; 05-20-2011 at 06:50 PM.
Reply:I tried a much shorter arc--that seemed to be the issue.Last edited by newlincoln; 05-20-2011 at 06:50 PM.
Reply:still need to work on it, but it is better.Last edited by newlincoln; 05-12-2011 at 07:30 AM.
Reply:Looks like Weld Mold 880 is a stainless steel filler but with a really high tinsel strength.  The thing about welding chrommoly is you typically want to undermatch the parent material.  The problem is the heat affected zone can become brittle if it isn't allowed to cool very very slowly, by using a more ductile filler you get a little bit of flex in there.For race car roll cages ER70S-2 or ER80S-D2 seems to be the prefered choice.  If your going to make a big fillet, use the ER70, if you are going to grind it down flat (not recommended) use the ER80S.The test I've seen is shows the filler rod actually mixing with the base material and resulting in a weld that has higher tinsel than the base filler.  People who have butt welded plates together fine that when they ground the Er80 bead flat and do bend tests, the weld bends right along with the base material.  IE, the bend test passes.  Tinsel strength will be about 95K which is about what normalize chromemoly is.  With ER70, the joint will be a bit weaker, which you compensate for by making the bead a bit larger.Remember, that for 4130 tubing work, the joint itself never fails - it fails right next to the joint.  So putting in super strong filler does nothing for you.  Welding technique is what makes a good weld.I suspect the reality is that a professional welded bicycle frame will rarely outright fail - which means there is very little research done on the failures.  Even with race cars, crashes are thankfully rare and many racing organization insist on mild steel frames (NHRA notably insists on 4130).   I will note the John Force's funny car broke in half even after being built by arguably the most researched chassis builder in NHRA.  Even the best screw up 4130.As for settings.  I would recommend not using pulse.  I'd run just a bit on the low side on amps and form the puddle a bit slower.  The theory is slow heating will actually heat more of the metal.  I would have the tubing wrapped in a blanket to try to keep the heat in as long as possible.   Slow cooling is the only way to go.  Consider a bit of pre-heat just to get the whole frame to 75C or so.  The focus being let the tubing cool as slow as possible - still air or under hot blanket.Con Fuse!Miller Dynasty 350Millermatic 350P-Spoolmatic 30AMiller Multimatic 200Hypertherm PowerMax 1000G3Miller Maxstar 200DX
Reply:Originally Posted by con_fuse9Looks like Weld Mold 880 is a stainless steel filler but with a really high tinsel strength. ...The test I've seen is shows the filler rod actually mixing with the base material and resulting in a weld that has higher tinsel than the base filler. ... Tinsel strength will be about 95K which is about what normalize chromemoly is.  With ER70, the joint will be a bit weaker, which you compensate for by making the bead a bit larger.
Reply:Originally Posted by con_fuse9Looks like Weld Mold 880 is a stainless steel filler but with a really high tinsel strength.
Reply:Newlincoln, it's great to see your welds improving. Good job, keep it up!And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.