Let me continue our discussion of lug thinning and whether disturbing poorl y filed lugs is sacrilegious. My feeling is that crappy work doesn't deserve special protection irregardless of who made it unless it has significant historical value like Confente's first frame or something. There can be a lot of lug shaping preparation before brazing in getting the curves just right and the point to be sharp and centered. We'll ignore that part of building because you are wanting to do after brazing thinning.
I categorize lug filing after brazing into 4 levels of achievement - which can also be used as guidelines to judge other work. The first and most basic level is to make the surface even. For example knocking off any casting ridges or welding seams or overflowing silver. The second is to continue filing until the entire surface has the same flatness. This can b e a challenge to keep the file exactly level (or at the same tilt) with the tube on every file Stroke. The third, if one has the ambition, is to keep filing until the entire socket has the same thickness throughout. And the fourth is to thin everything down to a consistent amount. At the NAHBS, I went around and checked out everyone's lugs using that criteria to measure what I saw. I think every builder can decide at what filing station they want to get off at. Sometimes those steps can get mixed up, for example a builder can really thin the lugs but they don't make the surface quite flat or even. Most students that put real effort into filing do get them thinner but the surface isn't quite even. It seems like the hands can't keep the file rotation (twist) consistent throughout the entire process. It is like looking at a car bumper and the light spot doesn't reflect evenly.
I always use the best brand files like Nicholson or Simonds or, as a 2nd best choice, Grobet. Cheap ³import² files dull quickly and waste effort. I would at least get bastard cut round and half round files in 4, 6 and 8 inc h lengths and also a 10² round. In addition I would also get (if you don¹t mind spending $30) a Grobet Swiss pattern 6² half round file (not the much smaller Swiss pattern needle file) for finish filing. I would buy the Scroo-zon brand file handles that match the file sizes.
Remember to start at the hardest place to file - right on the side of the lug with the flat side of as large a half round file that you can handle. You can only take very small file strokes before the end bumps into the hea d tube portion. The flat of the file should be parallel (or at a slight tilt ) with the top tube. You can tell if it is at the right angle by watching th e results on the lug and adjust accordingly. You keep filing that small 1/8t h of a section until you have reached the desired lug thickness. The top and bottom points can be filed fairly quickly (maybe too quickly if you aren't careful). Just remember to move the file enough so as not to create flat spots during your stroke. We don't want to mimic a diamond's facets. Roun d files work well in downsizing the thickness of the crease between the frame tubes and head tube. When using a round file, you use a twisting or rotating motion and ³slide² the file over a greater area than the width of the diameter of the file. If you don¹t you¹ve created a channel into the lug. You want to slide the file far enough to reach the lug edge but not s o far as to fall off of it. That can be nasty because it is easy to start th e next file stroke on the tube and wipe out a small section of lug edge. Repeating again, the successful clocklike motion is to file a stroke, move just beyond the filed area and stroke again, move incrementally and stroke again (leaving no unfiled space in between strokes) until you need to move the work. Always move the work rather than file in an awkward position. Success is achieved by coming right up to but not over the lug edge. It is that hand control that separates the good from the not good. Beginners hav e a hard time visualizing the desired result and piddle around not taking muc h off and then start getting ride of file marks too soon before the shaping process is complete.
You should take encouragement from the fact that patience and taking your time trumps pure hand coordination. Many times I¹ve seen less talented students turn out nice work because they were determined to do so. It will take you longer but it is possible to get to a high standard with persistence. Don't be surprised that it can take a day of work to get to level 4 on one lug even if you are experienced. In addition it is tedious work that is difficult to stay at for too long of a time and not go nuts. You don't need an excuse to check the CR list but it does help to take breaks like that to keep your sanity.
I'll send some before and after pictures so you can send some gushing prais e in return (well hopefully, I'm not big on receiving ridicule and scorn) as well as my class notes on filing tips. I'm teaching 3 framebuilding classe s before the new year. There is a special one next week for making transportation frames. I have one starting Oct. 22 and another Dec 2. If I remember right, there is still one space open in those 4 student classes.
Doug Fattic Niles, Michigan USA