JimboMartin

Hello All:
I have a Nitto Technomic for 25.4 bars but I happen to need to length same stem for 26.0. A new 26.0 stem is $37 but a 26mm drill bit is only $11. Running that bit through the opening would (obviously) only remove 0.6mm. Plus I imagine that the 25.4s and the 26.0s are the same forging. Any reason not to ream out the 25.4?
Cheers,
Jim

Homebrew01

Because it will be a mess. How will you clamp both parts of the stem to drill it out ?
If you have a milling machine, with a 26 mm endmill, and can clamp each piece on center, then maybe.

Or if it's a quill stem, you will still have a mess as the tip of the drill bit catches on the slot and either breaks, or chatters like mad, scratching the heck out of the stem.

Sell-swap-trade your current stem, and get the proper size.

Cross Creek

I've never heard of anyone successfully drilling out a quill stem, probably for the reasons Homebrew stated. I've heard of people wrapping sandpaper/emery cloth over a dowel and doing it by hand, but removing .3mm by hand sounds like a miserable way to spend an hour or two, and you'd first have to figure out the right size dowel that would make a 26mm reamer with paper attached. If you try your drilling idea, be prepared to end up with a trashed stem, and possibly a trip to the hospital if you're not careful. It would take at least a substantial drill press or a milling machine to do this right. If I had to do it, I'd take it to a machine shop and have them ream it out. Before you start, make sure the stem is securely clamped and perfectly aligned with the drill shaft. Also, make a flat shim that fits into the clamp opening such that when you tighten the bolt, the internal diameter of the clamp is 25.4mm. Otherwise, the bit will tear the clamp apart or you'll end up with a larger than 26mm clamp. I'm curious what kind of bit you found that only costs $11. The proper bit for this job would be a core bit, so far as I know, and that's a machine shop tool that costs $50-150 and is designed to be used in an end mill, not a typical home shop device.

fietsbob

Whats your Time worth , and what kind of Jigs and fixtures for your lathe or drill press do you have
to insure the cut will be precisely as aligned as the Nitto factory used to manufacture them?


Nitto manufactures the Technomic stem to take a 26.0" bar why not just get one?

FBinNY 

There is no issue with reaming the stem, but it has to be done properly and using the tight tool. A drill bit makes no sense at many levels, starting with how would you chuck and power a drill that size.

The right tool is an adjustable blade reamer like this one



Preferably one with helical blades so they don't snag in the slot. A straight blade is also OK because there's a work around for the slot issue (if it arises). The good news is that most decent shops own adjustable blade reamers for seat tubes, and 26mm is within their working range, so odds are you can do the job for cheap or free at the local bike co-op, or the price of a few beers at a bike shop.

Doing it right entails shimming and securing the stem at the neutral slot width, so there's room to close it the same way as it is now. One way to do that is by removing the bolt and improvising a shim using a stack of washers filed down so they don't extend close to the bar space. Then replacing the bolt and clamping down through the stack, so the open slot width is locked in securely. Then you ream (5% oil (any) in kerosene is the cutting fluid of choice, and will float chips from the cutting edges and leave a perfect finish on the cut).

If using a straight blade reamer you have an extra step of using a rat tail file to break the corners of the slot slightly deeper than the .3mm you intend to remove, so the blade catches a ramp rather an edge as it passes over the slot.

fietsbob

Last time I searched , a low cost adjustable reamer was $80, so unless the OP already owned one .

buying a new stem is cheaper .

FBinNY 

As I wrote, there's absolutely no reason to buy a reamer since just about every bike shop owns one in the right size.

fietsbob

There may be a reluctance due to liability issues .. that decision is up to the owner of the (unknown) shop.

FBinNY 

There are always 1,000,000 reasons why something can't be done. The OP can deal with that IF it arises. But there's no reason to look for flies in the soup before the soup has even been made.

I try to deal in ways things can be done, and reaming is the right way to do this job. If the OP has a bike co-op nearby and they have an adjustable blade reamer, which is highly likely, I'll bet a dozen beers that they'll let him do the job under supervision. There's no liability question since they are only lending a tool, and the OP is working on his own bike.

With a regular bike shop it might be harder because most mechanics are fussy about lending tools, but I'll venture that most would do the job for a nominal fee, the liability issue notwithstanding.

Worst case, he can make the shims, and send it to me properly bolted up, and I'll do the job for $8.00 plus the postage both ways.

ddeand 

I did it. It took me awhile to find the right size piece of pipe or dowel or tubing (trial and error). I wrapped some coarse automotive sandpaper around the tube, slid the stem over it, slightly tightened the bolt, and started twisting the tube/sandpaper to sand out the inner surface of the stem. I eventually was able to twirl the stem on the tube to speed things up. It took some time, but it worked. I finished by using successively fine grit sandpaper until the interior was smooth and free of burrs or sharp edges. The stem has worked well all season.

I'd do this for a bike that is going to be a rider, but if it's a garage queen or vintage-correct restoration, I wouldn't touch it. Reaming might have been the best way to attack the problem, but I really didn't want to leave my workshop and spend time looking for someone to pay to do the work - I just used what I could find in my shop. Lazy, I guess.

ThermionicScott 

I've done it. I wanted to keep the stock stem on my Diamondback MTB when switching to a set of 26.0mm Velo-Orange handlebars, and there was plenty of extra beef around the clamp area, so I "bored" it out. I used a 1" grinding wheel on a drill, removing material very gradually as I passed the drill back and forth through the clamp area, and tightening the clamp a little as I progressed until it would accept the 26.0mm bars. I used a 6" machinist's rule along the way to check that I wasn't removing too much material from one side or causing the "bore" to get crooked.

That said, @FBinNY's method sounds better than mine, and I think the OP ought to go for it. My method worked, and it was good for the experience, but it was tedious most of the time, and alarming at other times when the bit would seize in the stem and cause it to flip in my hands.