Robvolz 

Probably the wrong name for the part. the top part of the fork that goes through the head.

I found a 1972 De Rosa fork. Then found it’s for a 54cc frame, not a 56.

is this something a competent Framebuilder can swap out a tube? Or is there an extender system?

what to do?
swedish extender pump?

Cynikal 

Long story short, it can be done but paint and/or chrome will be ruined. I doubt a fork for a 56 cm frame will be that difficult to find.

bulgie 

That's not my bag, man.

Yes the steerer can be grafted to a longer one. The joint is done partway up, below where the stem quill will tighten, but above the point where steerers bend or break, which is just above the crown race seat. Some do it by brazing, with an internal sleeve or doubler inside the joint. Others do it by TIG welding, with or without a sleeve inside. I don't have a strong opinion on which is best, except I think the TIG method with no sleeve demands more perfection, as in any little mistake or lack of perfection may cause it to break there. Even the braze method requires care and skill to do it safely.

Here's Paul Brodie's how-to on the subject:

Either grafting method (TIG or braze) can be done without affecting paint or chrome at all, except on very small frames. A short steerer might not have enough length for the joint to be enough above the crown, but still below the stem. Putting the graft higher to be well away from the crown can work, if TIG welded with no sleeve, but then your weld had better be perfect, to not interfere with the stem quill nor be cracked by the tightening of the cone/wedge.

Replacing the entire steerer has its own problems, and also must be done by someone really good. Plus side is you have an all-new steerer. Minus is a lot of heat on the crown — brazing temperature heat-cycle at least twice, or 3 times if the old one is melted out, which is the most common way I think. Machining the old steerer out cold is possible, but that sort of precision machining can be expensive, and doing it badly can result in an unsafe fork.

I've done both methods and my preference is boring out the old steerer cold, if the fork is getting repainted and it's not chromed. Grafting is OK with me when saving paint and chrome is the goal.

Finding a FB willing to do any of those methods is getting harder. Lots of builders will say no, for various reasons including liability worries. Me, I'm retired. I'd do it on my own fork but not for a customer.

EDIT: as you can tell from my talk of stem quills, I am stuck in the past. (I'm a C&V guy.) Stems don't have quills anymore, except for a few holdouts like myself. I'm not trying to advocate for quill stems, don't worry, I know that ship has sailed. Everything else I wrote is still mostly true though, as far as I know! Just ignore the bit about worrying about where the quill will tighten.

Mark B

Kontact 

Just curious if anyone has ever successfully cut and extended a steel steerer by bonding in a carbon tube for an aheadset? WIth 3-4" of steel steerer to bond the carbon inner sleeve to, you should have more strength than a typical carbon to ti lug assembly, but you would still be dealing with a bit of stress riser where the outer steel and carbon tubes meet. Unless you beveled the the steel tube so carbon could overlap it on the outside. As long as the inner sleeve was quite thick and the steel to carbon bond was clean, it seems like this method would produce a light and strong solution with relatively low technical skill.

Robvolz 

Oh, but I've been looking for years.

It was an odd year for De Rosa. it would have to be repainted anyway, so that isn't a concern.

glad to hear it can be done though.

Thanks!

guy153

Assuming you were going from 1" to 1 1/8" that only gives you room for a 1/16" wall CF tube. I don't think that's thick enough for a steerer with a decent safety margin. You'd want at least 1/8".

Kontact 

The inner diameter of the carbon tube does not have to match the inner diameter of the steel tube. The thick walled insert between them could be stepped to fit in the narrower opening of the thick carbon tube and the larger opening in the steel tube.

The easiest way to create that step would be to add layers to the bottom of the insert after it is bonded to the carbon steerer until it has the correct outer diameter to match the inner diameter of the steel tube.

Smokinapankake

I converted a Kona Project Two threaded fork to threadless using a machined stub made from 4130 tubing sourced from an airplane homebuilders' supply site:





Before welding....

The stub initially had a thick enough wall that I could machine down the insert portion, then bored out the ID of the remainder to shave some weight off. I've also used this same technique to lengthen threadless steer tubes.