Re: [CR]Oversize top-tube v. oversize down tube

(Example: Framebuilding:Norris Lockley)

From: <hersefan@comcast.net>
To: "Norris Lockley" <norris@norrislockley.wanadoo.co.uk>, <classicrendezvous@bikelist.org>
Subject: Re: [CR]Oversize top-tube v. oversize down tube
Date: Fri, 16 Jun 2006 13:13:25 +0000


Just a comment on the last part of the post. The last suggestion for testing (the cold setting) only finds where the yield limit is - this limit I believe is not relevant to issues such as frame stiffness. Cheap tubes and overheated tubes yield with lower force, but until they fail stiffness is the same as I understand it.

Maybe the engineering folks can chime in if I'm wrong.

Mike Kone in Boulder CO


-------------- Original message --------------
From: Norris Lockley

> I refer to the various contris that have been sent to the List in recent

\r?\n> days on this subject and would point the interested parties to the

\r?\n> extended discussion of very similar matters of only two or three weeks

\r?\n> ago.

\r?\n>

\r?\n> However.. in a more positive frame of mind, and in response to the

\r?\n> suggestions of building three frames for testing, I would just suggest

\r?\n> that if three builders were to each build three identical frames, that

\r?\n> none of the frames would be similar to any other except for dimensions,

\r?\n> materials, etc due the variables introduced into the equation such as

\r?\n> the skill of the builder, the heat source used, the size of nozzle

\r?\n> chosen, the manner of brazing/bronze-welding, the choice of dia. of rod,

\r?\n> the number of passes made over th joint assuming that the joints were

\r?\n> bronze-welded/fillet brazed etc etc. All of these factors have more than

\r?\n> a little bearing on the integrity and mechanical qualities of the joints

\r?\n> and hence of the frame.

\r?\n>

\r?\n> Three frames built by the same builder would be interesting, but the

\r?\n> results could not be taken as empirical facts, because another builder

\r?\n> using different methods, heat sources etc would probably not have

\r?\n> identical reults. Arguably finite analysis is a valuable tool when all

\r?\n> variables can be controlled...but in frame-building they cannot be..and

\r?\n> equally arguably no frame-builder coulod ever produce two "identical"

\r?\n> frames ie materials, sizes etc that turned out to be identical in their

\r?\n> ride qualities and response. in the cyclists' tea-rooms of Yorkshire, a

\r?\n> region where you are likely, or were likely some years ago, to find an

\r?\n> abundance of Bob Jackson frames, a regular topic of conversation was

\r?\n> whether one had a "good Jackson " or one of the "poor Jacksons". These

\r?\n> discussions had nothing to do with appearance or even external signs of

\r?\n> build-quality...just about how the frames rode. I have heard similar

\r?\n> discussions about Mercians too.

\r?\n>

\r?\n> I think that it was just inside the time frame of the List that I

\r?\n> visited Kirk...the maker of the blast-moulded magnesium girder section

\r?\n> frames of the early..possibly mid-80s, at the time that he had just set

\r?\n> up his own very small factory, after having developed the concept frames

\r?\n> by using sub-contracted foundries.and it is possibly a little known fact

\r?\n> that the Kirks that were ridden by Pro riders and were used by some

\r?\n> Dutch riders in the T-d_F were pressure cast in aluminium alloy , not

\r?\n> magnesium.

\r?\n>

\r?\n> However on the day in question a very very enthusiastic Mr Kirk talked

\r?\n> me through his design , told me about the one-metric cube of sea water

\r?\n> that provided enough magnesium for each frame, and waxed eloquent about

\r?\n> the .8 of a second that it took to blast the molten "atomised" magnesium

\r?\n> under tremendous pressure up a tube and into the waiting

\r?\n> mould..Bingo!...just a blink of the eye and another Kirk was blasted

\r?\n> into life.

\r?\n>

\r?\n> All this was fascinating stuff..bujt Mr Kirk then went on to make the

\r?\n> claim that only his frame and his frame alone could provide the proof of

\r?\n> just who, in the peloton, was the best rider. Claiming that no two

\r?\n> brazed frames however well and carefully constructed possessed the

\r?\n> identical mechanical and ride qualities but that each and every Kirk was

\r?\n> 100% homogeneous in its construction and that each frame was identical

\r?\n> in every respect. I think that this was his amketing justification for

\r?\n> insisting that every rider in the "Grand Bucle" should ride one of his

\r?\n> frames...the only true test of the champion.

\r?\n>

\r?\n> Trying to be of some assisitance in resolving the query about the choice

\r?\n> of oversize down or top tubes..I venture to suggest that some indication

\r?\n> could be obtained by a much easier experiment. It would be a simple

\r?\n> matter for a frame builder to build two partial "main triangles"..of

\r?\n> identical dimensions, one with an oversized top-tube but no down tube,

\r?\n> and the other woth an oversized down tube but no top tube..only the head

\r?\n> tube and seat tube being constant factors. the construction would be

\r?\n> bronze-welded/fillet brazed becuse the integrity of the joint would be

\r?\n> more visibly obvious than would that of lugged joints ie penetration of

\r?\n> braze material etc etc.

\r?\n>

\r?\n> The structures coulod be clamped in some way to insure absolute

\r?\n> rigidity..with only the "front ends " being able to move. An accurately

\r?\n> machined bar, in terms of diameter to ensure a snug play-free

\r?\n> interference fit with the head tube, would be inserted, with the same

\r?\n> length protruding..and a torsional "force" applied to the bar..and the

\r?\n> deflection and resistance to the applied force measured in some way. I

\r?\n> am not an engineer, only a frame-builder, so I leave the data collecting

\r?\n> bit to the experts.

\r?\n>

\r?\n> To make this experiment even easier, I suggest that the mitres of the

\r?\n> tubes at the point where they are to be welded to the seat tube, be

\r?\n> accurately cut a few degrees off true alignment..a milling machine or

\r?\n> lathe could be used for this degree of accuracy..so that the tubes when

\r?\n> bronze=welded into position would be out of track with the seat tube

\r?\n> by the same amount. It would then be a simple matter of "elbow power"

\r?\n> for someone, pulling and twisting the bar inserted through the

\r?\n> head-tubes to attempt to "cold set" the tubes back into alignment... the

\r?\n> number of beads of sweat forming on his brow as he attempts to do so

\r?\n> during an accurately timed period, being the determining measurement as

\r?\n> to which oversized tube provided the greater resistance to whatever it

\r?\n> was hoped to measure. Or words to that effect...

\r?\n>

\r?\n> Norris Lockley..my legs tell me more about a frame than any dial gauge

\r?\n> can...Settle UK