Bon,
You don't need to add a second linkage. Here is a possible proposal since the implementation is not our concern. It is the same as this one I posted before.
For this arm, the guide is in the front and is a curve which is an element of Liamcon. The guide can be a magnetic one. The green lines indicate the arm. The arm is a complicated one, however, it is not my concern at this point.
You don't need to add a second linkage. Here is a possible proposal since the implementation is not our concern. It is the same as this one I posted before.
For this arm, the guide is in the front and is a curve which is an element of Liamcon. The guide can be a magnetic one. The green lines indicate the arm. The arm is a complicated one, however, it is not my concern at this point.
The challenge is to follow the circular guide paths without a link to the true pivot, which as you say, is inconveniently located in the platter area. The two circle guides are fixed together by a rigid connection and follow the parallel circular paths, as a train wheelset would negotiate a circular track. They can only adopt the radial position since the distance is exactly the spacing of the circle guide paths."X" is the true pivot point. Do you plan to have a linkage connecting from X to the red part of the parallelogram? X is locaed in the platter area which makes it awkward to implement. If X has a linkage to the paralleogram, it seems, everything should fall into place...
Since the tonearm located guide paths are limacons, if I had easy access to a CNC machine, I would do just this and be done. However I assume that most diyers don't have this conveniently on hand but have circle router jigs available. The tangential circle guides are intended for this purpose. By all means those who have a CNC can construct a compact version with far less complexity and fewer friction points, once they work out the proper limacon path.
For the original single circle guide, consider holding the circle cam at a fixed position on its guide. Then the stylus can be lifted and placed elsewhere than the Thales circle due to the rolling pivot, as you demonstrated.
Now, implement the secondary guide as follows:
Duplicate the first guide and links exactly, but then slide it rearwards in a parallel fashion and attach at its indicated location. Then join the two circle guides by a rigid link. In effect the original single guide has been expanded into a linked 2-guide component. Together with the tonearm, the links form a parallelogram under all conditions. The link joining the two circle guides is always radial.
Now try the same procedure as before. Hold one of the circle cams fixed. Then the other is fixed also (They always lie a fixed distance apart on the same radial line). Now attempt to lift the stylus and reposition it off the Thales circle. It can’t be done without violating parallelism, the fixed length struts or the tonearm rolling pivot location.
The reason I suggested the X pivot, a stationary point, is that it allows the 4 corners of the parallelogram to be 4 pivots and linear bearings will not be needed. Anytime you use linear bearing such as slides, glides, and rollers, you are moving the entire horizontal mass. It's no small task for DIYers to begin with and now you are dealing with FOUR linear bearings?! Once linear bearings are employed in this mannered, you are better off just go back to a parallel tracker and save you from all the complexity and hassles. Allowing the X pivot will turn the arm into a true pivoting tangential tracking tonearm with theoretical perfect tangency. But will 5 pivot points beat out Birch style arms with tiny tiny tracking error a la Reed 5A, Thiele, Doug's, etc that typically uses 3 or 4 pivots? All I am asking is that is the added complexity worthwhile?
Hi everyone,
I haven't participated in this thread lately because my CAD computer crashed a month ago and I have been trying to fix it ever since.
In 1984 or so when I designed and built my first tangentially tracking tone arm I was confronted with machining the special non-circular guide cam for it. Not having access to a CNC milling machine, I designed a tool that allowed me to machine the cam manually with as much precision as a CNC milling machine, I dare say. However, it still required a manually operated vertical milling machine.
This post occurred to me late in the evening, too late to go to the messy and dark shed to retrieve the tool and photograph it. But I'll do it tomorrow.
Out of all my friends, there are three who own CNC vertical milling machines and they kindly agreed to let me use those machines for my tone arm hobbies as long as I promised to learn to operate them properly. So, a few years ago I took a semester of CNC set -up and programming at a local community college (Yavapai). My point is this: look around amongst your acquaintances and friends, there may be someone who has those machines and I am certain that in Australia somewhere near you, there must be a place where you can learn to operate those machines.
I just lost half of this post by pressing some obscure icon. I'll continue in another post before I lose the rest of my post.
There are several newfangled features in this "new" website design that I don't like.
Sincerely,
Ralf
I haven't participated in this thread lately because my CAD computer crashed a month ago and I have been trying to fix it ever since.
In 1984 or so when I designed and built my first tangentially tracking tone arm I was confronted with machining the special non-circular guide cam for it. Not having access to a CNC milling machine, I designed a tool that allowed me to machine the cam manually with as much precision as a CNC milling machine, I dare say. However, it still required a manually operated vertical milling machine.
This post occurred to me late in the evening, too late to go to the messy and dark shed to retrieve the tool and photograph it. But I'll do it tomorrow.
Out of all my friends, there are three who own CNC vertical milling machines and they kindly agreed to let me use those machines for my tone arm hobbies as long as I promised to learn to operate them properly. So, a few years ago I took a semester of CNC set -up and programming at a local community college (Yavapai). My point is this: look around amongst your acquaintances and friends, there may be someone who has those machines and I am certain that in Australia somewhere near you, there must be a place where you can learn to operate those machines.
I just lost half of this post by pressing some obscure icon. I'll continue in another post before I lose the rest of my post.
There are several newfangled features in this "new" website design that I don't like.
Sincerely,
Ralf
Hi everyone,
Rewriting the lost half of my previous post:
There are two features of your tone arm design that could be troublesome:
1) The fact that your tone arm becomes longer or shorter during operation troubles me. How do you intend to handle the requirement that the tone arm counter weight has to constantly change its weight?
2) The other problem I see is that, it will be difficult to design a sliding bearing that has sufficiently low friction to make the tone arm work properly. A shielded ball bearing for instance, has two precision cylindrical surfaces in contact with the ball complement that are NEVER exposed to the environment outside of the bearing. However, that is not the case for a linear ball bushing. The ball bushing has one precision surface within the bearing that is somewhat sealed from the environment outside of the bearing. The other precision surface however is external to the bearing and there is no way to prevent dust and other particles to coat its surface. In industrial machinery, sliding seals are used to keep the outside ways clean at the expense of increased friction, unacceptable for use in a tone arm. All of this could be solved with the use of an air bearing. But as I understand it, you don't want that.
My suggestion, to avoid the above potential problems, would be this:
Keep the pivot for horizontal motion of the tone arm where it is.
Keep the straight-line motion of the tone arm as is,
Allow the to and fro motion of the pivot for vertical motion of the tone arm to straddle the pivot for horizontal motion of the tone arm.
There is an ingenious mechanism for straight-line motion used in a cross-cut saw manufactured by Bosch. It consists of two hinges spaced at 90 degrees to each other, one in the vertical plane and one in the horizontal plane. I don't know the model number, but you'll be able to find the saw on their website.
Some time ago there was a tone arm featured on this website that utilized the above straight-line mechanism. Maybe Direct Driver remembers it? That mechanism used a lot of ball bearings although it could be done with jeweled bearings.
Sincerely,
Ralf
Rewriting the lost half of my previous post:
There are two features of your tone arm design that could be troublesome:
1) The fact that your tone arm becomes longer or shorter during operation troubles me. How do you intend to handle the requirement that the tone arm counter weight has to constantly change its weight?
2) The other problem I see is that, it will be difficult to design a sliding bearing that has sufficiently low friction to make the tone arm work properly. A shielded ball bearing for instance, has two precision cylindrical surfaces in contact with the ball complement that are NEVER exposed to the environment outside of the bearing. However, that is not the case for a linear ball bushing. The ball bushing has one precision surface within the bearing that is somewhat sealed from the environment outside of the bearing. The other precision surface however is external to the bearing and there is no way to prevent dust and other particles to coat its surface. In industrial machinery, sliding seals are used to keep the outside ways clean at the expense of increased friction, unacceptable for use in a tone arm. All of this could be solved with the use of an air bearing. But as I understand it, you don't want that.
My suggestion, to avoid the above potential problems, would be this:
Keep the pivot for horizontal motion of the tone arm where it is.
Keep the straight-line motion of the tone arm as is,
Allow the to and fro motion of the pivot for vertical motion of the tone arm to straddle the pivot for horizontal motion of the tone arm.
There is an ingenious mechanism for straight-line motion used in a cross-cut saw manufactured by Bosch. It consists of two hinges spaced at 90 degrees to each other, one in the vertical plane and one in the horizontal plane. I don't know the model number, but you'll be able to find the saw on their website.
Some time ago there was a tone arm featured on this website that utilized the above straight-line mechanism. Maybe Direct Driver remembers it? That mechanism used a lot of ball bearings although it could be done with jeweled bearings.
Sincerely,
Ralf
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Hi Bon, it's a great thread that you have started, thanks for that. Whilst it's always easy to think one sees shortcomings in others work (there's some good geometry studies there), I must agree with concerns voiced by others regarding friction, smoothness of movement and overall inertia. It does seem to be possibly orders of magnitude higher than that normally exerted on a cartridge's cantilever, I would have thought.
Would a possible option be to consider the scheme as used on the Garrard Zero 100SB arm? (https://www.tnt-audio.com/sorgenti/garrarde.html), (there were other designs as well I think). This uses simple pivots, which are a low friction simple location method. Having checked one could make the side rod from small diameter carbon fibre tube, and the main arm tube larger diameter, (https://www.easycomposites.co.uk/2mm-pultruded-carbon-fibre-tube). If 250mm long the small tube would be about 9gms. 1mm dia pivot pins would seem OK. The pivoting head shell is fairly simple too I would have thought, could be 3D printed and then bonded onto the main tube.
PS.
As I understand our nations have a new trade agreement, could you please export some sunshine, we have a terrible shortage at the moment. Many thanks.
Would a possible option be to consider the scheme as used on the Garrard Zero 100SB arm? (https://www.tnt-audio.com/sorgenti/garrarde.html), (there were other designs as well I think). This uses simple pivots, which are a low friction simple location method. Having checked one could make the side rod from small diameter carbon fibre tube, and the main arm tube larger diameter, (https://www.easycomposites.co.uk/2mm-pultruded-carbon-fibre-tube). If 250mm long the small tube would be about 9gms. 1mm dia pivot pins would seem OK. The pivoting head shell is fairly simple too I would have thought, could be 3D printed and then bonded onto the main tube.
PS.
As I understand our nations have a new trade agreement, could you please export some sunshine, we have a terrible shortage at the moment. Many thanks.
Thanks for the illustrations, Jim. To constrain further, I see the other stationary point besides X is the Pink dot, which can be used as a guide point similar to your other drawings. A pivoting V-groove bearing guiding a low mass carbon fiber rod protruding from the tail of the main arm can be done with low friction and high accuracy.
Hi directdriver.A pivoting V-groove bearing guiding a low mass carbon fiber rod protruding from the tail of the main arm can be done with low friction and high accuracy.
This is precisely my plan. Nice to see someone come up with the same conclusion. I have machinable ptfe ready for the grooved guide way and I am waiting on nitride balls.
Hi jotom.
I owned 2 Garrard Zero 100's from new back in the '70's. They do not bring back fond memories. I have a suspicion of pivots at the headshell, which seems the very worst place to locate them. Anyway, I started this thread to investigate whether true tangential geometry is possible passively. I think I have demonstrated that it is. Possible yes, achievable yet to be demonstrated.
BTW, we will sadly soon have more in common with the UK with our covid cases numbers going through the roof. I am an ex-Londoner with lots of family still there.
Cheers
Bon
Hi Ralf.
Thanks for your input. It is really appreciated.
My plan is for the tangential geometry structure to end just in front of the foremost horizontal pivot. Then a sub-tonearm carrying the cartridge, connected by a vertical bearing (possibly knife edge) in the Dynavector style. The rear tangential geometry structure will have 3 vertical supports, so in theory is capable of a level horizontal attitude, provided the mass is arranged to maintain balance.
My plan is to use a nitride ball rolling in a ptfe v-groove. See my response to directdriver above. My first concern is low friction. Issues of environmental pollution will have to be deferred till Iater. This will be a personal diy curiosity driven project, not a product development, so reliability concerns will come later, after feasibility.
I actually own the Bosch drop-saw that I think you are referring to. I have used it for many years. To replicate the mechanism requires machining skills way beyond mine.
I will work through your suggestions. I may have a few questions. I welcome your thoughts on my vertical bearing proposal.
Cheers
Bon
Bon, DD,
Even the arm is constrained at the pink dot, which is exactly on the Thales circle. It still doesn't work. Please the model.
Let's examine Bon's original proposal. The arm has very sophisticated movements. This is why I said before I don't know what it will be. In the diagram, I did below, one side of the guide moves following the Thales circle. I marked the movements with a red arrow. The other side of the guide moves following a curve, which is a part of Liamecons. I marked the movements with an orange arrow. Both sides have to move simultaneously in opposite directions to satisfy the stylus tangential to the groove. I learned a lot from Bon's geometry, but I highly doubt that the geometry can be effectively implemented.
Even the arm is constrained at the pink dot, which is exactly on the Thales circle. It still doesn't work. Please the model.
Let's examine Bon's original proposal. The arm has very sophisticated movements. This is why I said before I don't know what it will be. In the diagram, I did below, one side of the guide moves following the Thales circle. I marked the movements with a red arrow. The other side of the guide moves following a curve, which is a part of Liamecons. I marked the movements with an orange arrow. Both sides have to move simultaneously in opposite directions to satisfy the stylus tangential to the groove. I learned a lot from Bon's geometry, but I highly doubt that the geometry can be effectively implemented.
This is not my proposal. See my previous explanation below. When the secondary circle guide link is created as I described, the links form a parallelogram, the geometry is tangential and determinate.
When a rigid body like the circle guide link moves in a plane, it has an instantaneous centre (IC) of rotation, about which every point rotates i.e. moves at right angles to the line joining the point to the IC. The IC moves with the motion and can occur at non-intuitive positions. The animation shows that the IC (green dot intersection of dashed lines) occurs pretty much where it is expected from your diagram. The path of the IC is called the centrode. I have not shown it but I can plot it if you want.
I have moved the secondary circle guide to the tonearm rear. It has no bearing on the discussion.
It is clear that some of the followers of this thread are more comfortable with a mechanistic approach to the subject rather than the geometric one I have presented. Maybe there is a way to bring the mechanistic viewpoint to the fore. I think this is possible by showcasing the connection of the geometry with rolling circles. To be clear, these rolling circles will not be a part of the physical mechanism because they obviously impinge on the platter area and would not allow use of an actual LP disc. Nevertheless, if someone were to fabricate the circles and links, it would provide a clear mechanical demonstration of the tonearm alignment.
Suppose the guide links are at the mid-point and rear of the tonearm. The tonearm length is equal to the Thales diameter and the three links are 1/2 this value. The guide mechanism and tonearm form a rhombus.
There are 3 circles involved in the rolling action:
1. The green 1/2 Thales diameter fixed circle.
2. The mauve 1/2 Thales diameter rolling circle that rolls on the outside of the fixed green circle.
3. The red 3x Thales diameter red circle that rolls on the outside of the fixed green circle.
The mid link is a radial line fixed to circle 2 (mauve outside) and the mid path is the limacon described by the mid pivot as circle 2 rolls along circle 1.
The rear link is a radial line fixed to circle 3 (red inside) and the rear path is the limacon described by the rear pivot as circle 3 rolls along circle 1.
Although the contact point of both rolling circles is identical, circle 2 is rotating at 3x the speed of circle 3.
Suppose the guide links are at the mid-point and rear of the tonearm. The tonearm length is equal to the Thales diameter and the three links are 1/2 this value. The guide mechanism and tonearm form a rhombus.
There are 3 circles involved in the rolling action:
1. The green 1/2 Thales diameter fixed circle.
2. The mauve 1/2 Thales diameter rolling circle that rolls on the outside of the fixed green circle.
3. The red 3x Thales diameter red circle that rolls on the outside of the fixed green circle.
The mid link is a radial line fixed to circle 2 (mauve outside) and the mid path is the limacon described by the mid pivot as circle 2 rolls along circle 1.
The rear link is a radial line fixed to circle 3 (red inside) and the rear path is the limacon described by the rear pivot as circle 3 rolls along circle 1.
Although the contact point of both rolling circles is identical, circle 2 is rotating at 3x the speed of circle 3.