Framebuilders - Crown race question
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I have an old Raleigh 531 frame that I had the fork replaced on when it was almost new (misaligned dropouts). The shop I bought the frame from didn't have a seat cutter (the seat was bigger than my campy race), so I took it to a machine shop, who cut the seat too small. I've always used a piece or two of shim stock in with the race and it has worked fine all these years. I would like to fix it correctly however, so am asking if this is something that could be done? Does in involve replacing the crown lug or are there other ways of dealing with this? Thanks.
I googled this since I know what I would do, probably use epoxy on a personal bike, I shower in the stuff just love it. Apparently though you have some choices:
- Go to Chris King, he sells headset baseplates in a wide range of sizes! Nice headset, and you don't have to rebuild a fork, might be the one case where you save money by buying one of his sets.
- This is another one of my approaches, use a punch to dimple the seat so that around the dimples there are little rims that will recenter the part. Then use locktite or epoxy to fill the rest. I do this when making forks to center the tube. Unnecessary, but I like the idea of having the tube dead nuts with good braze clearance.
- Another option is a knurling tool, this raises enough metal that it may need recutting, so back to the machine shop.
- I also think that if the shimming isn't causing you problems that is a very acceptable route. As long as they don't shift out or something. Basic practice is you would single point something like this on a lathe, but once you get to very light passes that remove less than 1 thou, you are in reamer territory. I can't afford the reamer so I single point, however, in this situation, the reamer often doesn't do a better job than the singlepointing. Perhaps the reason is that best practice is to turn and then ream only the half a thou, but people are jamming these down and making essentially rough cuts. Anywho, when all else fails shim stock is the decent thing to do, so if it works be happy. That is what a machinist would do.
08-11-10, 02:33 PM
This works as I have done it many times
If you know some one handy with a lathe and knows how to measure and use it!
they turn the seat down on the fork to almost the steerer, Example 25.6mm
Then turn a mild steel bush with ID of 25.50mm and OD of 26.7 -26.8 and part off about 6mm long
One presses the bush onto the fork (interference fit)
then the fork is returned to the lathe
and one takes very light cuts till you have 26.42 -26.44mm
Fit Camp 26.40m crown race
Nice idea, thanks. I'll have to see if I know anyone who could do that.
I assume that the only way to actually fix the fork without adding a bushing would be to rebuild it with a new crown lug? Or is the race seat a separate part from the lug? The current lug is a Nervex Professional, and those aren't really available anymore (unless you can find someone who has one and will part with it).
08-11-10, 10:20 PM
The race seat is part of the lug. Rebuilding it with a new crown is probably silly. It's so much more work than just building a new fork that you really should just build a new fork instead.
Having said that, I wouldn't do either one. Silverbraze outlines a much simpler method, and in fact I have seen ready-made rings for just such an application.
Personally, I have run into the same troubles as you on several occasions and have had perfect results by dimpling the existing seat with a center punch as outlined by Peterpan. I don't even bother with the Locktite. If that is too low tech for you, Stein makes a knurling tool just for the job (http://www.biketoolsetc.com/index.cgi?id=307097927233&d=single&c=Tools&sc=Headset&tc=Crown-Race-Knurling-Tool&item_id=SN-KT). It's quite expensive for what it is, but it's still less than having a fork made (or remade).
And if you have a lathe or lathe access, the knurling tool for a lathe is like 20 bucks. Lots of other uses.
Thanks for the input. Yeah, replacing the lug might be a bit crazy. If I could do it myself, I might go that route. I use two strips of shim stock, cut to nearly the circumference of the steerer. Race goes on, then I fit the shim stock in one at a time. Pretty tight, but of course not perfect. Bike has always ridden fine, including no hands, but bothers me cuz it isn't right :)
The International frame I had before I had the same fork problem with (fork blades slightly misaligned with the crown lug). The same machine shop milled that one perfectly; why they decided to screw this one up I don't know.
As for dimpling the seat, is this done from the top edge (parallel to the steerer tube), or the face (perpendicular to the steerer tube)? I may start with this approach.
08-12-10, 09:20 AM
I do it at the face. Just a line of dimples, each a dimple-width apart. Have never had any trouble with it and it takes just a minute or two with an automatic punch.
It is done on the part that is loose, which is the part parallel to the head tube, stearing tube. It is amazing how rapidely the thickness can increase. On the one hand you want as many dimples as possible to provide more support, but it can take as few as 3 to jam things up good.
08-13-10, 06:48 AM
I like the dimple idea because its new to me and seems a very simple fix, and it doesn't ruin the paint, but I always just brazed a little silver around the crown, building up the seat and then recut it with a tool. I have run into this a couple of times with my Park crown cutter. The cutter is not self-centering and you can get it off center just a hair, cutting the crown too small, very frustrating. Does anyone have a fix for this problem. I have talked to Calvin at Park Tool and he has basically told me the precautions to take so it doesn't happen much anymore but for a while I thought about making this tool a boat anchor and I don't have a boat.
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