Bicycle Mechanics - Facing?
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10-18-07, 10:33 AM
Time for an expert opinion.
I am familiar with facing head tubes for headset installation. But of late I have noticed tools for facing bottom brackets, disk brakes, seat tubes, and nearly every other attachment point to frames.
Is this REALLY necessary? Does it matter based upon frame material? Is this a nice thing to do to expensive frames, but you would likely skip it on a Huffy?
10-18-07, 01:46 PM
Why would you face a seat tube? I would say facing a bottom bracket is important if your using new external bearings.
10-18-07, 04:33 PM
I think that the real issue is the paint.
Paint adds a layer onto the bike frame that the other components don't allow for. Sometimes that extra layer isn't nice and even. Powdercoat tends to be thicker than a typical paint job. In this case, thick=bad.
If you have a nice, flat, even paint job, you can get by without faceing anything. If you have a powder coated frame with globs on the headset, bottom bracket, or disc caliper mounting points; you're going to need to face those areas.
10-18-07, 05:12 PM
Cartridge BBs could generally get by without facing because of their continuous design, but external bottom brackets come in two pieces, so their alignment is crucial.
And you're right. Not worth it for Huffys, I don't think anyone really does that. And are you sure you weren't talking about boring out a seat tube? It's a pretty standard operation if you want to switch seatpost sizes or clean out a rusted or chipped, or even bent seat tube. But I haven't heard of facing the top of one.. maybe for a special clamp?
When I built up my C-50 it was necessary to face the fork crown before installing the headset lower race. It would not have gone on otherwise and I could have ruined the fork trying.
Old engineering maxim: "A bearing is only as good as it's installation."
Facing yields parallel bearings to eliminate misalignment.
Older better-quality steel frames usually used sand-cast BB shells (cheapos used stamped steel) and there was no way to guarantee perfect surfaces in the molding process, hence facing.
Newer bikes use various manufacturing processes (CNC machining, investment casting, etc.) so they are usually more precise but there are no guarantees.
I face everything.
10-18-07, 07:17 PM
what do you guys use for facing, when I hear facing I think lathe or mill
10-18-07, 08:04 PM
it's like a mill, but hand-operated, and usually with some sort of guide.
i forget who it is ATM, but someone makes a stem facing tool. for the top and bottom of the steerer tube clamp to make headset installations even more precise, and you can use it on cantilever cable hangers that install on the steerer tubes of threadless forks. those things can be VERY imprecise.
this is quite possibly the nicest head tube facing tool anyone will ever see. and i don't think they make it anymore. http://www.chrisking.com/tools/tls_cutting.html i used to sit at the computer late at night and drool over that thing.
10-18-07, 08:14 PM
Well, to stir the pot a bit, one local LBS proprietor I intrinsically trust, who's been in the business for 30 years, believes facing a BB is really unnecessary, because the cups on an adjustable BB are designed to accommodate 'unparallelism'. I recently had an adjustable cup issue, which most on here suggested indicated a need for facing. He disagreed, but humored me by facing it. It didn't solve the problem.
I asked why he had such a tool, then, to which he responded that every once in a while he'll be presented with a BB shell that is waaay out of square, which the facing tool can at least improve a bit.
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