As John said, in horology, the curve of a fusee has to exactly match the force of the mainspring if it is to do its job properly. The idea is that the force of a wound up spring is much greater than that of a spring which is mostly unwound and the fusee is there as a continually variable pulley to ensure that the gearing of the clock or watch gets a constant force over the whole period of the spring run. When the spring is fully wound it pulls on a small diameter of the fusee whilst, when it is running down, it pulls on a larger diameter. Every mainspring is different in its characteristics, even in our modern technological age, due to slight differences in the structure and composition of the metal and its hardening and tempering. Consequently, a fusee has to be matched to each new spring it encounters. If one is just making a pendulum clock, this exact matching is less important than if one were making a chronometer but, nevertheless, it does have some effect.
The traditional way in which fusees were made and adjusted is as follows... The fusee blank was cast to a shape which experience had shown was about the right profile for the type and size of mainspring being used. It was then put in a very simple, hand powered, screwcutting 'lathe'. This usually had a simple headstock through which was mounted a coarse screw of the same pitch as was desired on the fusee ( this was calculated by knowing how many times the fusee was required to turn to give the desired length of run of the clock - also knowing the cross section of the chain or cord which would be necessary to safely transmit the force fo the fully wound mainspring, the height of the fusee and therefore the pitch of its thread could then be worked out. ). The outer end of this screw had a handle while the fusee blank was fixed to the other end with the other end of this fusee blank being fixed to a plain rod which ran through the tailstock to provide support. The cutting tool was a simple length of steel with the cutting end like a parting tool and it slid in a square hole in the tool rest at right angles to the fusee blank. The initial cuts might be made by pressing a pin on this tool against a metal template of the curve initially calculated for the fusee but correcting cuts were done freehand by just pressing the tool into the work as it was rotated by means of the handle. The final correction of the fusee was done by fitting the fusee and mainspring up in the clock frame and fitting a long rod with an adjustable weight at its end onto the winding square on the shaft of the fusee and at right angles to it. The mainspring was then wound and the weight on the rod adjusted until the force of the mainspring would just lift the rod against the force of gravity. Now the fusee was allowed to turn a little more, unwinding the mainspring, and the effect on the 'adjusting rod' was noted. This was done repeatedly until the fusee was fully unwound and the shape of the fusee was then corrected, thread by thread, until the rod would neither lift nor fall at any point of the fusee's several rotations. It is a long, tedious but ultimately simple and low-tech process and, to get it right, this is the only way to do it. Fortunately, modern clocks and watches have removed the need for a fusee by using escapements which are, largely, not affected by the difference in force provided by the mainspring as it runs down but I still have to do this whole procedure whenever I replace the mainspring of a chronometer or verge watch or clock. I hope that this info is helpful to some.. Ian On 25/01/2012 12:05, John Prentice wrote: > ----- Original Message ----- > From: "John Thornton"<bjt...@gmail.com> > > >> IIRC Jeff Eppler cut a fusee for a mousetrap powered car... >> >> John > Sadly a fusee for clock work needs a curved profile to match spring forces > rather than straight line. > > I think they are hard to cut on a CNC lathe although reasonably easy to mill > with a 4th axis - apart from the required overhang on a small diameter mill. > > Ian Wright may have thoughts. > > John Prentice > > > ------------------------------------------------------------------------------ > Keep Your Developer Skills Current with LearnDevNow! > The most comprehensive online learning library for Microsoft developers > is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, > Metro Style Apps, more. Free future releases when you subscribe now! > http://p.sf.net/sfu/learndevnow-d2d > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > > > ----- > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2012.0.1901 / Virus Database: 2109/4764 - Release Date: 01/24/12 > > ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-d2d _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
