Coping chain stay and seat stays by hand

Does anyone have tips for coping chain stays and seat stays evenly? I find it so challenging to keep them the same when filing by hand.

Tips on process, technique, fixtures would be super helpful. Keep in mind I don’t have a mill or lathe.


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I scribe matching lines on the top of mine, grinder/file one to fit how I want. Then make a paper template of my cut and flip it 180* to mark the other stay. Line up the cut on your paper template with the line on your stay, do the same when you flip it over.

I’ll mark the edge of the bench or use a craft mat with measurements on it to figure out where to put the paper template.

Sounds kinda janky but works better than I would have thought. Let me know If that makes any sense, I can take a few pictures if that would help :metal:


Hey. That actually makes a lot of sense. I’ll have to try this next time to see if it makes my life easier.


I also scribe lines across the top, and then use paper templates from bikecad. Even with the templates, I get one side exactly how I want it and slowly file the other side to match, always careful not to go too far.

Also, for the first couple bikes I left a couple extra mm on the chainstays incase I messed up and had to file some more.


Hey Andy -

Agreed, scribe top and bottom and use the paper templates from BikeCAD. Couple other tips:

For any hand mitering, keep your file stroke horizontal to the ground and in line with an edge of your workbench. Always! If you need to adjust the angle of the miter as you go along, don’t angle your filing up or down. Instead, adjust the angle of the tube in the vise or adjust the angle of the vise in relation to the bench (if it swivels). Over time, you’ll get much quicker and more consistent results doing it like that. Even though you don’t have a mill, try to act like one. Use a digital angle finder and protractor to dial in the angles, assuming the file stroke will be level and in line with the bench.

Same thing for a compound miter, like fastback seat stays… You’ll just be adjusting both angles (tube in vise and vise on bench) and then filing level, accounting for any offset from the seat tube center by eye.

For chainstays… Once you get them close individually, install them onto a dummy axle and clamp them together in the vise (soft jaws!). Put a digital angle finder down on the dummy axle, and level the whole assembly to 0. Then take a few strokes across both chainstays at the same time. Going back and forth you’ll chase your tail forever, but take the last few strokes on both at the same time and it’s super easy.

Hope that helps!



Oh! One more thing:

On pairs of tubes like this, do each one of your steps on both individual tubes before moving on to your next step. That is… Scribe A, Scribe B. Rough cut A, rough cut B. Mark miter length on A, mark miter length on B. And so on and so on. Seems minor, but it’s huge. Mitering one fastback seatstay is easy–mitering two exactly the same is the challenge. Treat them as a pair from the start.



Hey Chris. Thanks for taking the time to write that. Makes a lot of sense to act like a mill. Nice tip too about taking the last few strokes across both chainstays at the same time.