1/2/14 10:59 PM

I've noticed on many occasions that threadless stems aren't machined accurately square at the top and bottom of where they clamp around the steerer tube. On most of them, if you clamp them on a steerer tube and then slide a long (eg 40mm) spacer up against the stem, there can be anything up to half a millimetre gap at some point between the faces of the stem and spacer. I had a brainwave today and realised that I could use my old 1" fork reamer to face these surfaces accurately square. The photo below is pretty self-explanatory - besides the reamer you just need a 1" fork or a piece of 1" OD tubing, and a shim intended for fitting a 1-1/8" stem on a 1" steerer. slide the shim onto the steerer, clamp the stem on the shim so that the top of the shim is slightly below the top of the stem, and use the reamer.

After reaming all my stems using this method, I no longer have any bikes where the headset can't be adjusted so that it turns smoothly with no play or binding from lock to lock.

If for some reason you can't see the image below, I put this image and a couple of others up on Picasaweb at https://picasaweb.google.com/100520469917381690611/ImpromptuThreadlessStemFacer

1/3/14 6:42 AM

Now, if I only had a fork reamer kicking around... ;-)

1/3/14 7:10 AM

...for a Rivendell fork!

1/3/14 8:23 AM

Maybe I've just been lucky but I've never had a threadless stem that wasn't adequately square with no noticeable gaps and I've always been able to adjust headsets for simultaneous zero play plus free turning. I have 40 mm of spacers under the stems on three of my bikes and have Nashbar/Performance house brand stems on two of them and an FSA on the third.

1/3/14 9:33 AM

http://www.steintool.com/Html/StemFacingTool.html

Why use an existing tool when you can buy a new one?

1/3/14 11:23 AM

I just hand file a small carbon spacer for under the top cap when I get into this situation. Or the last spacer under as well. But have not seen and issues with the Thompsons, Oval Concepts, Specialized, Easton Stems I have been using in the builds since I got here. But one or two MTN bike clearance stems I have done the top spacer mods on..
Kalloy and another, forget brand...

1/3/14 1:23 PM

quote:

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Theres also a tool for that

http://www.steintool.com/Html/StemFacingTool.html

Why use an existing tool when you can buy a new one?

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1/3/14 2:50 PM

Is this a problem that causes a problem?

Other than possibly wanting to better exclude water, any gaps shouldn't effect the bearings, since a slight tilt in the bottom surface of the stem ultimately presses against the wedging washer, which can somewhat tilt-correct itself within the top bearing cup.

I.e., I don't think that these threadless headsets require the squareness of contact as was the case when threaded headsets needed true parallel support from the locknut on down in order to allow the bearings to turn freely.
And, as the top bearings are so lightly loaded (although sometimes damaged from water intrusion), a tilted surface on the bottom of the stem wouldn't seem likely to affect either bearing's service life.

I have noticed minor gaps before, but which always seem to close up as the spacers and wedging washer are compressed by the top bolt's tension, due to each element's inherent slight flexibility.

1/3/14 10:09 PM

Drill press + sanding wheel + DIY fixture

1/4/14 12:08 AM

I'm just very reluctant to d anything approaching a "modification" to the clamping portions of a stem.

Whatever testing data is used to allow a mfg to decide that a part is safe becomes useless when any dimensional modification is done.

But, today's parts are designed to hold up to strong, heavy riders, which affords a margin of safety for most of us.

And I'm assuming here that only a few thou needed to be removed.

Also I could swear that I've seen someone do this, on this forum, once before.

1/7/14 9:48 AM

Interesting. Next challenge: a solution to get the wheels perfectly true, that is the section where the two ends of the rim meet.

1/7/14 2:41 PM

" ...Next challenge: a solution to get the wheels perfectly true, that is the section where the two ends of the rim meet."

Ok, I'm down with having smooth braking tracks!

But don't machine, grind or sand anything. You really don't want to remove any metal there, as an overall "variation of thickness" will likely result in your brake rotor (i.e., your rim), giving a pulsating braking feel, either from the change in surface finish or from the rim's resulting actual variation in thickness.

Pinned rims (those not welded) can be so easily re-aligned, you don't even have to remove the tire unless it's much wider than the rim.
Just slap the side of the rim with the narrow edge of a 2x4 to realign as needed.
In rare instances, a rim joint sleeve will have somewhat bulged out an area of the rim next to the rim seam, but here I take a jumbo set of plumber's pliers, cushion the rim with a 1/4"-thick piece of leather or tow webbing, and pinch the sidewalls back down to the needed thickness. Even damaged rims can be tuned up during truing using this latter method, such that he rim slips between the tightened pointers of your truing stand smoothly as the rim is turned.
On rims with canted sidewalls, the latter method is done in concert with adjustments to the roundness of the rim, with smooth braking again being the primary goal.

My biggest peeve WRT bicycle machining tolerances might have to do with seatpost fit, and not only have I select-fitted posts from a pile of nominally same-sized posts, but have in several instances found a different (printed)-sized post to take up slack or make removal easier.
I've found 27.2 posts that fit better in a 27.0mm GT LTS frame, a 27.2mm post that fit better in a 27.4mm Richard Moon frame, and a 25.6mm post that took the place of a 25.4mm post for a smoother fit and better clamping.

I also have little "tolerance" of frame/forks where the bike pulls even slightly to one side, nor for any headset that binds in the slightest with the wheel pointed in the more-or-less straight-ahead pos'n.
Luckily, it's very simple to loosen a headset or to move/bend a steel fork's dropouts/legs a mm or two to the left or right to restore proper steerin'.
If the bars pull to the right, then the tire's contact patch needs to be moved to the right, and vice-versa.
In some cases, the filing of dropout-slot depth is the better approach, when tire centering at the fork crown can be achieved simultaneously, but many mechanics don't take all these considerations into account before filing or bending, and of course any filing is irreversible. A centered (dished) front wheel, properly seated, is another first step before proceding.