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Question about finishing lugs and for crowns

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Question about finishing lugs and for crowns

Old 01-14-22, 11:12 AM
  #1  
BTinNYC
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Question about finishing lugs and for crowns

Originally Posted by Doug Fattic View Post
It has long been a tradition that the best of the American builders file lugs thinner. We donít taper the thickness so the edges blend into the tubes but we do thin them so they end up to be about a mm thick. This comes from a couple of influences. The first is that the father of American builders - Albert Eisentraut - did this and got a lot of publicity in American bicycling magazines in the 70ís. It became the defacto standard of judging quality. The second reason was that when we got back from our apprenticeships in Europe, we needed to visually show why our frames were better than our European competition (we didnít compete against other at that time). Our spiel was that we not only took time to make frames look better where you could see it but also with alignment and mitering where you couldnít.

There is plenty of meat on your Peugot lugs to thin them some, just donít get carried away. I would start by evening the thickness all the way around. Pressed lugs are always uneven in thickness. Then you could evaluate whether you wanted to thin them more.

Start on the sides of the lugs first where it is more awkward to get a decent length file stroke. Be careful not to let the file slip off the lug onto the tube. This rounds the edge (the mark of an amateur). The top and bottom lug tips should be done last because it is easy by comparison to motor those down. Use a bastard cut file to hog off the offending bulk. Next go to a fine cut file to remove the file marks left by the bastards and then polish with 80 grit emery cloth to give a final smooth finish.
Thread dredge, I'm currently working/practicing on a Centurion Sport DLX and here's my related question; Do the fork lugs also get filed?

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Old 01-14-22, 12:04 PM
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I decided to split out your question because the other thread was so old and a lot of people no longer participate here.

A production bike probably had at least a little bit of filing. Most people building frames would file every part, they tend to be a bit crude even now that they are investment cast.

But you asked about fork lugs (normally called a crown) and showed a picture of a seat cluster, which part are you asking about? Centurians often were built with a crown that was a Nervex copy. The original nervex crowns were very thick, and they were often filed quite a bit because they were really crude. Lower end production bikes would have them virtually untouched. The Japanese copies weren't quite as crude. Really depends on the factory though.

Last edited by unterhausen; 01-14-22 at 12:08 PM.
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Old 01-14-22, 12:20 PM
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Thanks!
The fork crown is crude, sloppily brazed, and the most banged up piece of the bike. I've made progress on the general cleanup.
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Old 01-14-22, 03:38 PM
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I always questioned how thin I should go on a welded up sheet metal crown like that. Especially after the fork has been built and you can't tell how thick the metal is. Your fork has a lot of extra brazing filler that's really not doing anything. It would have been nice to have the opportunity to clean up the shorelines of the crown before brazing. It would be pretty difficult to clean them up now.
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Old 01-14-22, 08:29 PM
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I might consider smoothing out the general surface removing the many file marks. But not doing any real socket or even edge filing. I'd also consider the crown's underside but would want to feel comfy about how much filler was still about the seam.

I consider the fork crown the second hardest joint to finish file. Only the BB shell is worse.

A not yet asked possible question is who's painting the bike? If not the OP than does the OP have an idea to how the painter wants the bike to be like and what they can do as far as taking care of "spots" Andy
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Old 01-15-22, 05:52 AM
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Originally Posted by Andrew R Stewart View Post

A not yet asked possible question is who's painting the bike? If not the OP than does the OP have an idea to how the painter wants the bike to be like and what they can do as far as taking care of "spots" Andy
Thank you for the good pointers, I'll work on the crown cleanup/smoothing.

I'm rattle can painting, and if you have tips about "spots" or anything, it would be appreciated.

Paint plan: Get the the frame to a uniform brush with 400 grit then scotchbrite red. Spray primer with the 2K epoxy primer. Bondo the dings. Second primer coat. Color with Duplicolor. Clear coat with 2K.
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