Re: PAPER HORN "BALMAIN"
Posted: Wed Jun 16, 2021 10:58 am
Now here is some information regarding the machine that Adrian has devised, and almost finished constructing-Here are his words-
For parallel tracking it is impossible to use more than one guidance track without excessive friction. Two or more tracks can never be made to stay exactly parallel and they will "fight" each other and bind up. If two tracks are necessary to support the horn from below the centre of gravity, one of them will have to be fitted with unflanged wheels so that it only acts as a support and does not take part in the guidance process.
By putting the guidance and support system above the cebtre of gravity of the horn, only one track is necessary because the weight of the horn will tend to make it hang with it's centre of gravity directly below the supporst point. This then means that a single grooved wheel could be used and there would be no need for additional bearings to allow "nodding" motion of the horn when the needle is lowered onto the record surface or when a warped record is played.
The problem with ant wheeled system is that dirt or dust settling on the track will cause uneven running, which becomes a problem when a small force is being used to drive a large weight. If the contact point of the wheels is on a horizontal surface the dirt will be ground in and the track will require frequent cleaning. If the contact faces can be angled, dirt will tend to be dislodged and the track becomes partially self-cleaning.
All the above requirements can be met with a pair of flat-treaded wheels angles at 45 degrees to the vertical, straddling a round bar. The weight of the horn will make the system centre itself accurately, the contact angles will allow dust to fall away and the horn will hang freely but move in a perfectly straight line.
Tp prevent the horn from oscillating like a pendulum, the movement of the bottom front edge has to be constrained to an approximately straight line path. This could be done with several different variations of a wheel running on a vertical plane surface, or even a peg in a slot, but they would all involve a compromise between sloppiness and the risk of binding. Any spring-loaded device would increase the friction. A Watt Linkage,(invented by Janes Watt), overcomes the objections and can be made to produce a sufficiently straight line movement over a long enough path for this purpose without needing excessively large link dimensions.
The only movement still requiring restraint is at the soundbox end of the horn, where the frictional drag of the record has to be resisted without interfering with the fore-and-aft motion or the rise and fall of a warped record. Again, a Watt Linkage with ball jointed arms will suffice for this and will give sufficiently accurate approximation to a straight line if care is taken in it's design,(a cardboard and drawing pin model was used to check this because mathematical modelling of a Watt Linkage is extremely difficult). Luckily ball-jointed linkage components are available off the shelf, as they are used for control rods in motorcycles and vintage cars.
Part Two of this description to follow soon.
For parallel tracking it is impossible to use more than one guidance track without excessive friction. Two or more tracks can never be made to stay exactly parallel and they will "fight" each other and bind up. If two tracks are necessary to support the horn from below the centre of gravity, one of them will have to be fitted with unflanged wheels so that it only acts as a support and does not take part in the guidance process.
By putting the guidance and support system above the cebtre of gravity of the horn, only one track is necessary because the weight of the horn will tend to make it hang with it's centre of gravity directly below the supporst point. This then means that a single grooved wheel could be used and there would be no need for additional bearings to allow "nodding" motion of the horn when the needle is lowered onto the record surface or when a warped record is played.
The problem with ant wheeled system is that dirt or dust settling on the track will cause uneven running, which becomes a problem when a small force is being used to drive a large weight. If the contact point of the wheels is on a horizontal surface the dirt will be ground in and the track will require frequent cleaning. If the contact faces can be angled, dirt will tend to be dislodged and the track becomes partially self-cleaning.
All the above requirements can be met with a pair of flat-treaded wheels angles at 45 degrees to the vertical, straddling a round bar. The weight of the horn will make the system centre itself accurately, the contact angles will allow dust to fall away and the horn will hang freely but move in a perfectly straight line.
Tp prevent the horn from oscillating like a pendulum, the movement of the bottom front edge has to be constrained to an approximately straight line path. This could be done with several different variations of a wheel running on a vertical plane surface, or even a peg in a slot, but they would all involve a compromise between sloppiness and the risk of binding. Any spring-loaded device would increase the friction. A Watt Linkage,(invented by Janes Watt), overcomes the objections and can be made to produce a sufficiently straight line movement over a long enough path for this purpose without needing excessively large link dimensions.
The only movement still requiring restraint is at the soundbox end of the horn, where the frictional drag of the record has to be resisted without interfering with the fore-and-aft motion or the rise and fall of a warped record. Again, a Watt Linkage with ball jointed arms will suffice for this and will give sufficiently accurate approximation to a straight line if care is taken in it's design,(a cardboard and drawing pin model was used to check this because mathematical modelling of a Watt Linkage is extremely difficult). Luckily ball-jointed linkage components are available off the shelf, as they are used for control rods in motorcycles and vintage cars.
Part Two of this description to follow soon.