Re: [CR]Re: Singer geometry


Example: Framebuilding:Norris Lockley
Date: Thu, 19 Jun 2003 14:51:19 -0700
From: "Chuck Schmidt" <chuckschmidt@earthlink.net>
To: classicrendezvous@bikelist.org
Subject: Re: [CR]Re: Singer geometry
References: <000001c3368b$8b540800$59af4943@computer> <a0501040ebb17a80f5ca4@[66.167.252.211]>


Jan Heine wrote:
>
> (cut) Head angle: I measured the head angle using one of those
> adjustable triangles engineers use to draw lines at angles. I put the
> bike on a level surface (measured with a carpenter's level), I placed
> a plumb (line with heavy nut on bottom) on the head tube, and
> adjusted the triangle until one side was parallel to the head tube,
> the other to the string. Obviously, this means I had to eyeball it.
> What is a bevel protractor?

The easiest, most accurate way is to use an adjustable triangle (either a metal machinest or plastic draftsman version will do). This will eliminate the bubble levels and plumb line errors. Take a long (3') straightedge and aline along the top of the top tube, extending past the head tube. Place the adjustable triangle on the lower edge of the straightedge and adjust the angle till you see an equal (top to bottom) sliver of light between the front edge of the headtube and the triangle. Tighten the set screw on the adjustable triangle and read out the resulting angle on the scale.
> 3. The fork offset is another problem. I didn't remove the fork from
> the frame. I held a very long metal ruler in the center of the head
> tube, as best I could, and then measured the distance from the
> dropouts. But it is easy to see that an error of 1 degree in getting
> the level parallel to the head tube will result in a significant
> error of the measurement.

There is a german-made clear plastic gauge that has a channel to aline with the fork blade (or a rod to aline with stem quill to fork crown center) and a scale that measures the axle offset of a bike without wheel or fork removal. But of course the best way is to remove the fork, block the steerer tube above a surface table (parallel to it), measure with fork blades up and then down and split the difference.

Chuck Schmidt L.A.

.