After lots of experience with both, I think the rigid-adjustable 3- or 4-stone hones do a better job than flex-hones, but they are more difficult to use, take a bigger chuck and more torque and more skill. Flex-hones are very fast, easy and cheap.
One caution: a flex hone can beat up the paint right at the top of the seatpost hole.
Since the balls get smaller in use as their abrasive wears down, the
hone has to be a bit oversized at first, e.g. 1-1/8, which is the
_outside_ diameter of the seat tube (i.e. they are oversized by about
the wall thickness of the tube x 2). So as the balls come up above the
top of the lug, they spring outward a bit, and many classic lightweights
don't have a plain circular-cut top to the seat tube, they are shaped in
an aesthetically pleasing contour. On these frames the balls whack
against the contoured edges. If you don't know what I mean by that,
look at an old Cinelli or Bianchi for an example of a straight,
circular-cut top -- then look at oh, say any frame with Nervex lugs for
an example of contoured. Or a Bruce Gordon lugged, or Baylis for extreme
cases of contoured seat tube top - check out
http://www.asahi-net.or.jp/
Imagine spinning abrasive balls beating against those delicate edges. Yikes!
To prevent this you have to insert the new oversized hone below the contour edges while stationary, then start it spinning, keeping it below the edges until you bring it to a stop, then carefully extract. Unfortunately this means the top cut edge is not getting honed, and that can be a location of the very burrs you're trying to smooth.
Once the abrasive balls have worn down to the seat post diameter, you can hone right to the top, if you're careful. You won't wear a new hone down that much on one frame though. So, if your hone is new and oversized, de-burr the top edge if necessary by hand with a fine half-round file. In any case, large burrs (like along the slit for the pinch bolt) should be filed, or ground off with a die-grinder or dremel-type tool, before honing.
Another caveat: as the abrasive wears down, it leaves a deposit of abrasive dust inside the frame, which could migrate down to the bottom bracket bearings on most bikes. The preferred method of honing is with oil, which taps the dust and makes a slurry. My trick is to push a rag down the seattube first, below the extent of where you're going to hone. Then after honing, pull the rag out by hooking it with a spoke head. Typical loose-weave shop rags hook into a spoke head easily, but some rags might not - T-shirt? Test first, you don't want to leave that rag in there! Two spokes threaded into one nipple to double the length is my preferred tool for extraction - bend the upper spoke into a comfy handle shape. If the one pass with the rag doesn't get all the slurry out you can repeat the process, but I find it doesn't have to be perfect, and you get most of it by just extracting the rag.
You have to use a variable-speed drill motor - the single-speed ones go way too fast. Honing should be done at fairly low RPM. Variable-speed drills are usually reversible, and honing in both directions is a good idea.
Finally, don't expect to be able to go up to the next size of seatpost by flex-honing, nor will you be able to correct macro-scale ovalization or other deformation of the seat tube. A flex-hone is not a substitute for a reamer.
Mark Bulgier
Seattle WA USA
>
> The magical mystical Flex-Hone http://www.newmantools.com/
> no shop should be without a couple.
> best,
> Brandon"monkeyman"Ives
> Vancouver, B.C.