PAPER HORN "BALMAIN"

Discussions on Talking Machines of British or European Manufacture
old country chemist
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Re: PAPER HORN "BALMAIN"

Post by old country chemist »

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.

old country chemist
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Re: PAPER HORN "BALMAIN"

Post by old country chemist »

View of angled wheels ON steel rod.
6979 (1).JPG

old country chemist
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Re: PAPER HORN "BALMAIN"

Post by old country chemist »

Large view of WATT LINKAGE attached to bottom of horn with a bracket.
6978.JPG

old country chemist
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Re: PAPER HORN "BALMAIN"

Post by old country chemist »

SIDE VIEW of STEEL ROD with SUPPORTING BRACKET FOR HORN within the two hoops supports, and bracing rods (removable)
6982 (1).JPG

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Inigo
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Re: PAPER HORN "BALMAIN"

Post by Inigo »

Nice arrangement! What a fine work!
I never heard before of that Watt linkage... It's like a kind of pantographic device!
Inigo

old country chemist
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Re: PAPER HORN "BALMAIN"

Post by old country chemist »

Here is some technical details about the machine.
The track is supported on two hoops made of 9mm. diameter steel bar. (concrete reinforcing bar), which was shaped by jamming it between the bars of a metal gate and carefully pulling to to bend a small section at a time. It was frequently checked against the curvature of an "Allen Scythe" tyre which happens to approximate the right radius. The front hoop is larger than the back one because it has to have enough clearance to allow the horn to pass through it.
when the hoops were set up they were loaded with 7 kg. to represent the weight of the horn and their deflection was measured with a clock gauge. It was found to be excessive and would result in the track tilting significantly when the wheels ran from one end to the other. To stiffen up the hoops, extra bars were welded onto the inside of the curved section at three points to form curved triangles. the vertical portions did not require stiffening and the triangles prevented the "arch" from pushing the verticals outwards.
The final deflections were measured as 2mm on the front hoop and 0,75mm on the back hoop with a load of 7kg. The front deflection does not matter too much because the soundbox won't be on the record in this position, but the back deflection will give a side force of 17.5gms inwards on the needle at the end of the record, this is tolerable in view of the tracking weights of the soundboxes it is designed to be used with.
The bar which forms the track has reduced diameter extensions which rest in curved "V" grooves in trunnions above the tops of the arches. The "V" shape automatically centres them and the curvature allows for a range of adjustments or misalignments without rocking or looseness. Because the track is self-aligning, it can easily be slipped into place with one hand whilst supporting the horn with the other hand.
To permit the track to be levelled, the support at one end includes a tentering screw with a pitch of 1mm per turn, the trunnion is mounted on this with a ball bearing swivel, so the trunnion does not have to turn with the screw. Over a 13 inch length of track. a deviation from the level of 0.5mm,(corresponding to half a turn of the tentering screw), is easily detectable by observing the tendency of the horn to run in one direction.
The hoops did not need to be very stiff in the fore and aft direction as long as they both move together, but it was found that a hefty accidental shove against one of the hoops could move them far enough apart to allow the track to drop out of the trunnions with the potential for disastrous consequences to the horn, soundbox and record. A fixed strut between the hoops would have prevented dismantling and the track could not be fixed because it needed to be threaded through the wheeled carriage during assembly. A pair of struts were made with "Terry" clips at their ends to fit over the hoop bars, these are snapped into place after the track has been installed.

old country chemist
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Re: PAPER HORN "BALMAIN"

Post by old country chemist »

6982R (2).JPG
Here is a slightly larger picture of the right hand side of the machine.
There is still more to be done. the point from the centreline of the horn at the soundbox end to the top of table is 13.4inches. The Watt Linkage at the soundbox end has yet to be added, and how to attach any relevant brackets to the motor cabinet to allow this to happen. There may be a requirement for levelling screws to be incorporated in the base of the motor cabinet, but that has yet to be decided whether it is necessary or not. A small spirit level can be used on the turntable prior to records being played to assure at least that the turntable is correct for playing records.
A special table, approximately 30inches wide by 5 feet in length has yet to be designed with sturdy legs that can fold up inside it for storage. The motor cabinet will be located in a section on the table on a pre-determined place. After using, the whole machine will be able to dismantled into it's individual pieces for storage

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emgcr
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Re: PAPER HORN "BALMAIN"

Post by emgcr »

What a wonderful, well-made creation Alastair and many congratulations to Adrian and yourself. Great thought and expertise has been given to the design which I am sure will work well and must have been an immense joy to develop and construct. I am certain James Watt would be thrilled to see his eighteenth-century thoughts still flourishing in gramophones as well as motor cars and many other areas of engineering nearly three hundred years later !

Levelling screws under the motor casing would seem eminently sensible to allow for uneven floors and general alignment. Very much looking forward to the advent of "the other end" and successful completion of this great and worthwhile project.

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mrrgstuff
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Re: PAPER HORN "BALMAIN"

Post by mrrgstuff »

Lucius1958 wrote: Mon Mar 29, 2021 9:05 pm
I think there may be some issues with using a feed screw on 78s:

One is the inconsistency of thread pitches (especially on early discs). Systems like the early Sonoras had to provide some "play" in the soundbox, in order to overcome those differences - hence the infringement suit.
If you don't mind straying into more modern technology then its quite possible to use a leadscrew where the speed of advance is actually controlled by the pitch of the record grooves - so (within certain limitations) the pitch can vary across the record without causing a problem

Here is one I made like this for a DIY cylinder phonograph:

https://youtu.be/EE-sP0BRzvQ

The principle works fine for disc records also. Here is a rather different design I made which works on the same basic principle:

https://youtu.be/fI880kTJ5b0
Lucius1958 wrote: Mon Mar 29, 2021 9:05 pm Another is the problem of run-out grooves: what happens when the needle hits those?

- Bill
This is indeed a problem - though its possible to detect that and then trigger the stop mechanism (or remove power from the electric motor)

mrrgstuff

old country chemist
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Re: PAPER HORN "BALMAIN"

Post by old country chemist »

Hello there mrrgstuff (interesting forum name), Adrian is still waiting to see about joining the forum, but has viewed your suggestions. He can understand it much much more than I can, myself being more into the basic mechanical style of reproductions. I did look on youtube, and your entries are impressive-clever chap!
It is good that the forum has, like yourself, members who contribute ideas and have put them into practice for us all to see and enjoy, and perhaps marvel at in their ingenuity!

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