Bike Frame Building Course: Part 2

Day two of the bike frame course was a very exciting one. Not only was it my birthday, but I finally got to use a TIG welder, and a nice one at that. On the end of Day one I had mitered and prepped tubes to practice welding on. Toby set the amperage on the Miller Dynasty 200DX to 65 and turned on the argon. He then handed me a welding mask to protect my eyes from the bright arc and did a demo weld while describing the steps as he went. I'll do my best to describe the process, but I doubt that I can do it adequately.

First you put the tip of the tungsten up to the spot that you wish to start welding, with a gap between the tip roughly equal to the diameter of the tungsten. In this case the tungsten was 1/16". Next you press the foot pedal approximately 3/4 to full to initiate the weld. This particular TIG welder has a high frequency starting feature that makes it easier to initiate an arc. I've read that this is an important feature for welding CrMo steel because otherwise you have to do what is called a "scratch start" and run the risk of breaking off the tungsten tip into the weld area. This would leave a hard spot that would be prone to cracking.

Once the arc is started you must be sure to apply sufficient power to begin a weld pool. The weld pool is the molten puddle of steel formed when the electric arc heats the tubes being joined. It can be seen as a shiny spot that forms under the arc of the tungsten. The basic method used in TIG welding is to form the weld pool, insert the filler rod into the weld pool until the tip of the filler rod melts into the pool and makes it bigger, then move the pool toward the direction of the filler rod. This is repeated over and over along the length of the weld seem until it is complete. Before we do this though we first need to tack weld the tubes together so that they don't move much when heat is applied. This is done in the same way as described above, only you just get the weld pool started, add filler rod and then stop the weld instead of proceeding down the seam. Whenever you stop welding CrMo steel you should slowly let up on the foot pedal to allow the steel to cool slowly so that cracks don't form. Regardless of the material you should keep the torch in place after the weld until after the post-flow of argon gas shuts off. The post flow ensures that the metal is shielded from impurities in the air until the metal is fully cool. Okay, it's still frigging hot enough to burn the hell out of you, but it won't be hot enough to immediately oxidize.

The tubes used on high quality steel frame bicycles are wicked thin . This means that they are very easy to burn through. It also means that the weld pool is pretty small and can be difficult to see. The most difficult aspect to welding the frame that I found was seeing the weld pool well enough to tell when to add filler rod, when to move the arc forward, and when I burned through. I suppose it might be time to get glasses.

I made a few practice welds on the scrap tubing and I did pretty well. Certainly not as well as Toby did, but pretty darned well for my first time. You can see from my weld that it lacks the "stacked dimes" look that Toby's has. This is because I wasn't able to add the filler rod fast enough to create the ideal weld. Adding filler rod is quite difficult as it is done with the non-dominant hand, in my case the left hand. My left hand is usually used for such complex tasks as keeping papers from blowing away and filling the empty space in my left pant pocket. It should therefore be no surprise that it may take some time to get this action down to a science.

Toby told me that he was surprised by how well I did considering my complete lack of welding experience. I've made some crappy MIG welds before, but these TIG welds came out so much nicer. It certainly helped that I had an instructor telling me what to do every step of the way. It was at this point that Toby said he thought that I was ready to start welding the main triangle of my bike frame together. That's right, it was judgment day.

As the main frame tubes were already prepped for welding and placed in the jig, all we then had to do was to tack them together so that the frame could then be taken out of the jig and welded on the welding table. I tack welded each joint in about four places and Toby verified that the tacks were sufficient. We then removed the frame from the jig and placed it in a drill vise on top of the welding table so that we could orient it in a way that allowed easy access to the weld joints.

The first joint that I welded was the top tube to seat tube junction. I'm not totally sure why we started there. I assume that it was because these two tubes have the most similar thicknesses and were therefore the easiest to weld, thus making it a good place to get my feet wet. I then did the top tube to head tube junction, the head tube to down tube junction the down tube to bottom bracket shell junction and lastly, the bottom bracket shell to seat tube junction.


The Bottom bracket shell was pretty difficult to weld as it was much thicker that the down tube and seat tube, so it was a bit of a balancing act to apply enough heat to melt both tubes, without burning through the thinner ones. This was done partly by pointing the tip of the tungsten such that it was 2/3 on the bottom bracket shell and 1/3 on the thinner tube. This ensured that the bulk of the heat was being applied to the thicker area. There were a few instances where I did create some small holes and had to have Toby come over to fix my mistakes. This is where Toby really showed his skill and experience in filling holes I had just made in such a way as to make it barely noticeable. I was really in awe.

Since it is presently more than a month since I took this frame building course the details are starting to get a bit fuzzy. As memory serves me, I was able to complete welding the entirety of the main triangle on day two. I do remember that I stayed pretty late, but it was likely because Toby and I got along really well and goofed off way more that we should have. Luckily for me I don't think that Toby had planned to leave early that week due to the fact that the North American Handmade Bike Show was coming up at the end of the week and while he wasn't going, he was letting a few of his friends use his shop to finish up some bikes for the show. Tony Maietta was finishing up a road bike with some S&S couplings that came out looking pretty sweet.