Originally Posted by
ham_sandwich
Hi all,
This isn't strictly related to my framebuilding, but thought I'd ask here as there's probably more expertise than on most other forums..
I've acquired a brand new frame (not mentioning manufacturer for now) and I'm not sure whether to be concerned by the headtube (standard 1 1/8ths) being slightly out of round / ovalised.
Along the plane of the frame (so along top tube), the ID of the top of the headtube is 34.1mm. At right angles to this, it's 33.6. So it's a bit off. Am I right in thinking this is unacceptable..? Headtubes are usually reamed to more like 33.8mm, right? So with a headtube that's 34.1 in one direction, the headset is always going to be a loose fit here, no matter what I do?
Measured at the bottom of the headtube, it's more like 33.90 and 33.65mm.
Thanks!
The decision to ream or not is based on the average of those two measurements because once you start pressing the cup in it will make it a bit rounder.
The average of your two measurements is 33.85 at the top and 33.78 at the bottom which should be about right, maybe a little bit tight at the bottom.
I would try pressing in the cups but carefully. If it's taking excessive force back up and reconsider.
If you did ream it first you might end up with the cups too loose because your dimensions would be about 33.8/34.1 which averages to 33.95.
Not sure how unusual a variation of 0.5mm is between the two dimensions but all the frames I've built have ended up slightly ovalised there after welding.