fork crown seat cutting

[Clockwork]

It was Brett Fleming from Efficient Velo Tool.

Found the pic.

[P K]

Trying understand the need for this fixture. Why not chuck the steerer tube? Wonky lathe?

[Clockwork]

Trying understand the need for this fixture. Why not chuck the steerer tube? Wonky lathe?

You mean chuck an internal mandrel that's in the steerer? That seams awfully unbalanced for thread cutting.

[P K]

Sorry, didn't even bother to notice the threading happening there, somehow spaced it as just cutting the crown race. Duh

[David Tollefson]

Zombie thread resurrection!

I've cut several fork crown seats with a Park unit. Never had an issue, as the headsets I've been using on my rigs (and those of my customers to this point) all use a split ring base closed up by the lower bearing. I called the mechanic who built up my last customer's new frame/fork, and he told me the crown seat was undersize - mic'd to 29.79, and the fsa crown race just slipped on and off with light finger pressure. So I have no idea if the others were undersize (I'd have to year them down and check). Frustrating!

[Andrew R Stewart]

I've had some of the same experience with undersize cutting before and what I've come to believe is that when you cut down a lot of extra seat material the cutter tends to cut more then it's size would lead you to expect. When cutting only a small amount of material (say 27mm to 26.4mm) the cutter cuts down to it's spec size. So new crowns with, maybe, 2mm of seat shoulder thickness need a precut/filing before using the actual cutter. With the 1" stuff I have built most of my forks with I use a 27.0mm cutter first then follow up with a 26.4mm one. For the few 1 1/8" steerers I've filed down the seat shoulder by hand before running the cutter over it.

I've also had some slight oversize head tube reamings happen but my poor combo of not so great heat control and perhaps a too thin head tube choice are the likely causes. Either way a slip on/slide in fit with no real slop is handled by some LockTite retainer compound used. Andy.

[David Tollefson]

Thanks Andy. Hand filing that shoulder makes me nervous as heck, but if it gets the job done then it's worth the anguish. I just measured a road fork I had built up about 6 months ago - 29.8mm.

I'll try the file method on the next one.

[Andrew R Stewart]

David- As you likely have thought of the key to hand filing a crown seat shoulder is consistency. Clamping the steerer in a vice/block and stroke the shoulder following the curve a few strokes, rotate the steerer a bit and repeate. Continue this pattern with the same number of strokes per steerer position, the same pressure on the file as you rotate the steerer about. The strokes should overlap with the other rotational positions. After a few complete steerer rotations the shoulder should look still curved, consistent is it's thickness and even across the height of it. After a bit you caliper the shoulder's diameter and judge how to proceed. Andy.

[Eric Estlund]

It's no longer in my fast recall, but I used to know the number of hand strokes for different files on 5 or so crowns. Good lord.

[David Tollefson]

It took me a good hour of careful and light filing, stopping several times to check OD along the way, but I got it down to 30.3 and consistent within my caliper resolution. Yeah, could have done that in 5 minutes on a lathe (on the list, believe me). Ready for the Park tool to do its work now.

[Tristan]

Keep in mind that if you want to do this on a lathe you'll want a spindle bore larger than 1 1/8" so you can easily chuck the steerer.... Using steadys on a smaller lathe is a real pita and can introduce a lot of chatter

[Paul Jacobs]

DSC01164.jpgThis is one way I do it. My lathe has a 1" bore but 30" between centres.