guy153

Purists look away now, but this actually works.

Head-tube reaming does not actually have to be all that precise. So long as the diameter averages out to somewhere around 33.8 or 33.9mm the headset will squash in there nicely without splitting the tube or being loose. It's not the cylinder bore of a Formula 1 engine. You probably do want to face it properly though.

Like anything there is a proper tool for the job but it costs $$$.




The drum in the drill is a piece of Al turned down to 31mm with a slot cut in it at angle. The drum is threaded for the M8 bolt which is then all clamped up with a nylock nut (as it happens because that was what I had). This leaves just enough room to wrap a bit of emery tape (80 grit or 120 grit is a good choice) but have it fit fairly tightly inside the HT. A close fit means you have no choice but to sand in something approximating a circle of about the right size.

Measure the HT twice at 90 degrees and average the measurements. If it's a little oval you can concentrate the sanding where you need it. Otherwise sort of precess the tool around evenly inside the joint while running the drill on its high speed setting. The other bit of Al there has been turned down to 33.7mm. If that fits in the HT reasonably comfortably by hand it's about the right size and you're done. This should take about the length of time it takes for the drill battery to run out.

This actually seems to work pretty well.

dsaul

That would take about a week with a Paragon 44mm head tube.

unterhausen

Are the Paragons way undersize? Would you feel bad about borrowing someone's reamer? I may eventually build the mountain bike that has been sitting in a box for years.

guy153

I don't have any friends in RL who own a reamer 😢 But I would feel a bit bad about borrowing one in case I chowdered it up. Also they presumably do go blunt at some point.

Actually for most projects now I'm just getting Reynolds HTs which are supplied with a 34mm ID and don't need reaming.

Idk why the paragon one is so huge, perhaps it's for tapered steerers? Would probably be best to get it to within a mm or so on the lathe before building the frame and then just finish it with a reamer.

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unterhausen

Yes, for tapered steerers. I think if I didn't already have it, I would go with a tapered head tube. I just hate the fosters can look.

I have had the idea of thinning the Paragon, but I'm afraid of distortion and it's a lot of $ for a tube.

I'm sure the bike shop would let me use their reamer. The main thing is not to ever go backwards, no matter how tempting it might be.

guy153

Yes never go backwards. I do have the ST reamer and my seatposts fit much better than on any mass produced bike I've owned where they slipped down if you weren't within about 1Nm of the maximum torque the bolt would take. With a proper fit you don't need to do it up that tight. I'm not sure this sanding hack would work so well on an ST.

​​​​​​The Columbus tapered HT has a system of sleeves you braze in and then drop bearings into. No reaming required and no press fit. Seems to work pretty well but difficult to face. I'm also not a fan of those beer can HTs.

unterhausen

I was a bit worried about the ones you have to face, but my lbs has the facer for that too. I was thinking about getting an external cup tapered head tube for a gravel bike frame.

guy153

The Columbus MTB tapered HT is 56mm at the fat end. Do you get hand facers that big? Even if you assume the fat end is square from the factory (which it did seem to be) the cut end is 46mm.

It's a dilly of a pickle because it's also too fat and thin-walled to hold in a lathe to attempt to face it before making the bike.

I took mine to a place that makes custom motorbikes and he got it really flat with a belt sander and checking the squareness on a machined table. He said that the only way to lathe it would be to machine a bit of aluminium to go inside it to support it so you could grip it properly.

I don't think any of the LBSes near me have any of these tools or would even know what they were.

unterhausen

Most bike shops don't know much about facing. When I was a mechanic in the '70s, I don't think we even had a bb tap, and definitely no facers. The LBS has been named one of the top 25 shops in the U.S. a number of times. They face every new bike they sell. And they sell a lot of internal cup mtb's nowadays.

I might possibly have a collet setup I can use to shorten tapered ht. Have to check it for that

Andrew R Stewart 

Back when headsets were loose ball angular contact things some cup/cone missalignment could be tolerated. These days what with cartridge bearings (and the tiny balls found in them) facing alignment is more vital. That said I sometimes do an initial facing with a hand file and a square. (But this is with a constant diameter HT). When I reface with the proper cutter the hand jobs have shown to be pretty close, minimal high spots being initially cut. Andy

dsaul

The original Paragon's were way undersized and reaming them was a chore. The current ones are not as undersized, but the reamer still takes a good amount out.

I recently built 2 frames with tapered 34/44 head tubes and cutting the tube to length was a challenge. I tried cutting the first one on the lathe by chucking it and parting off the excess, but the parting tool jammed and ripped the tube out of the chuck jaws. It mangled the 44mm end of the tube, but I was able to metal work it back into the proper shape and get the dents out well enough to fill them with silver. It was for my wife's bike that will probably never get ridden anyway, so it wasn't a big issue. I turned an aluminum plug to fit in the second one, so that I could tighten the chuck properly, and the second one went much better.

From an aesthetic view point, the tapered ones look better, but I still prefer the Paragon ones for their versatility, strength and ease of mitering the down tube.

unterhausen

I have had my Paragon head tube long enough, it's probably one of the old ones. It would be a little difficult to chuck it up in the lathe. I made an O-ring collet once to hold some headset parts that were too long for the reaming in a bike, Wouldn't be too hard to make one for a tapered head tube.