OK for the wifi thing, but first we need to clear out the ground and this can be done better here.
This whole discussion remembered me that someone in the family did a thesis about concrete mixtures and their properties. Going for a little chat after her holiday.
Epoxy/lead shot! Never thought of that. (dispose TT as toxic waste?)
Going for my courses on electrical machines. I had different holiday lecture in mind but....
Self aligning or to be aligned. Because this is diy, we better have something that can be easily machined and then takes a day (or two) to align/adjust, than something that completely depends on precision machining. The latter is better for commercial production no doubt, and the former will benefit if precision made, so it gains whenever possible, but excellent performance should be possible without 0.005mm tolerances.
OK, lets forget the magnetic bearing for now.
This whole discussion remembered me that someone in the family did a thesis about concrete mixtures and their properties. Going for a little chat after her holiday.
Epoxy/lead shot! Never thought of that. (dispose TT as toxic waste?)
Going for my courses on electrical machines. I had different holiday lecture in mind but....
Self aligning or to be aligned. Because this is diy, we better have something that can be easily machined and then takes a day (or two) to align/adjust, than something that completely depends on precision machining. The latter is better for commercial production no doubt, and the former will benefit if precision made, so it gains whenever possible, but excellent performance should be possible without 0.005mm tolerances.
OK, lets forget the magnetic bearing for now.
Pedro,
1st, what are the units in your drawing?
Could we settle on inch or mm? (me would prefer mm, of course, European engineer
)
the platter looks good itself but i see lack of stability for the bearing. It is an industrial bearing with industrial tolerances and shaft and center pin are one piece so diameter is 7.2mm. Not very stiff, not a very tight bearing gap.
If i would be you, i would look for another bearing, more stiff and with tighter gap. Why not have the bearing inside the platter thickness ? and it would not hurt to even increase platter height for that.
We have not yet settled on a technical spec; i loathe to throw in ideas that early, but your drawing pushes me to it. So, idea:
you could use the valve cartridge of a hydraulic valve for your platter bearing. It has just about the platter height. The gap between valve piston and cartridge bore is what needed here: about 5µm and the surfaces are ground to incedible precision. For an inverted bearing, you could mount the piston on a flange and the cartridge inside the platter. The bearing should be accessible from platter top. A trustplate made from POM or PTFE is then mounted from top and a trust ball made from synthetic ruby is put into the piston's conical center hole.
Even if we buy the hydraulic valve at nominal retail price, it will be cheaper than a Scheu bearing. But we do not buy retail. Hydraulic valves have in fact sealing edges acting as sealing lips. Those edges are µminiature precision chamfers. We buy not the whole valve with solenoid and all, we buy the cartridges rejected for flawed sealing chamfers.
I have to inquire if and what is available, but i am quite sure we can buy for cheap what other wise is trashed. Anyone interested?
You could also check if you can mount a platter bigger in diameter but i would not go over 320mm unless you decide to only use 12" pivoted tonearms from then. I wrote 320 mm max platter diameter in the spec of my own linear tracking tonearms, too.
What is perspex? it is like acrylic, plexiglas? If yes, would be well matched impedance-wise.
Well, PVC would be matched even better but black PVC is hard to get and the grey one looks shitty.
i like the idea of having a 3mm center hole instead of a 7.2mm center pin. Your platter design allows that. Purpose: centering excentric records by a platter clamp. If there is interest for that, (some of the linear tracker crowd mayby ) i will elaborate on this.
-------------------------
All,
CAD warning : anyone drawing his parts with help of computer aided design: stick with scale 1 for design by any means. If your parts do not fit on the paper for printing, change the printing scale as your CD allows but stick with design scale 1 !! And never overwrite associative dimensions !!!
And if you think you know better, well then the day will come when you pay better. Promised.
1st, what are the units in your drawing?
Could we settle on inch or mm? (me would prefer mm, of course, European engineer
)the platter looks good itself but i see lack of stability for the bearing. It is an industrial bearing with industrial tolerances and shaft and center pin are one piece so diameter is 7.2mm. Not very stiff, not a very tight bearing gap.
If i would be you, i would look for another bearing, more stiff and with tighter gap. Why not have the bearing inside the platter thickness ? and it would not hurt to even increase platter height for that.
We have not yet settled on a technical spec; i loathe to throw in ideas that early, but your drawing pushes me to it. So, idea:
you could use the valve cartridge of a hydraulic valve for your platter bearing. It has just about the platter height. The gap between valve piston and cartridge bore is what needed here: about 5µm and the surfaces are ground to incedible precision. For an inverted bearing, you could mount the piston on a flange and the cartridge inside the platter. The bearing should be accessible from platter top. A trustplate made from POM or PTFE is then mounted from top and a trust ball made from synthetic ruby is put into the piston's conical center hole.
Even if we buy the hydraulic valve at nominal retail price, it will be cheaper than a Scheu bearing. But we do not buy retail. Hydraulic valves have in fact sealing edges acting as sealing lips. Those edges are µminiature precision chamfers. We buy not the whole valve with solenoid and all, we buy the cartridges rejected for flawed sealing chamfers.
I have to inquire if and what is available, but i am quite sure we can buy for cheap what other wise is trashed. Anyone interested?
You could also check if you can mount a platter bigger in diameter but i would not go over 320mm unless you decide to only use 12" pivoted tonearms from then. I wrote 320 mm max platter diameter in the spec of my own linear tracking tonearms, too.
What is perspex? it is like acrylic, plexiglas? If yes, would be well matched impedance-wise.
Well, PVC would be matched even better but black PVC is hard to get and the grey one looks shitty.
i like the idea of having a 3mm center hole instead of a 7.2mm center pin. Your platter design allows that. Purpose: centering excentric records by a platter clamp. If there is interest for that, (some of the linear tracker crowd mayby
) i will elaborate on this.-------------------------
All,
CAD warning : anyone drawing his parts with help of computer aided design: stick with scale 1 for design by any means. If your parts do not fit on the paper for printing, change the printing scale as your CD allows but stick with design scale 1 !! And never overwrite associative dimensions !!!
And if you think you know better, well then the day will come when you pay better. Promised.
Bernhard
I agree with drawing unit to be mm, and the autocad units 1mm=1 drawing unit.
(in fact, my drawing was in meters 1m=1drawing unit, sorry about that. I'm used to draw bridges, not mechanical stuff...).
What kind os hydraulc piston are U talking about? it should be a very small one. what is the comercial aplication?
I agree with drawing unit to be mm, and the autocad units 1mm=1 drawing unit.
(in fact, my drawing was in meters 1m=1drawing unit, sorry about that. I'm used to draw bridges, not mechanical stuff...).
What kind os hydraulc piston are U talking about? it should be a very small one. what is the comercial aplication?
Havoc,
You cannot make all that adjustable. Moreover, you cannot compensate with your manpower and time and diligence for all those errors. Complexity eats up benefits and smoe benefits are theoretical ones.
So what does an airbering designer do to achieve his goal of an ultra precise rotational air bearing? He strives to reduce the count of relevant dimension AFAP. HE will not be happy with two plane-ground trustplates with a precision-ground spacer in between Because each surface, even the centering surfaces of the space have to be plane-parallel, not tilted. And without plane deviaton. Each rotational surface has to be centered and free from roundness deviation. If all relevant dimensions are added up, he arrives at more than 10 dimensions to be kept ultra precise and worse, related to dimensions of another component.
He will be happy however if the beaqring has two spherical bearing surfaces. Two spheres have to be ground to precision diameter, easy. the spherical bearing cups have a radius bigger by the intended bearing gap. And the sphere center distance of the cups is already irrelelvant if the spacer keeping the rotor's spheres apart can be ground to fit. This spacer mustn't even be plane-parallel, it just must be keep the rotor spheres. Try differnt spacers until you have it.
So we have cup radius (2x) sphere radius, (2x) , spacer thickness. As the spacer is adjusted by grinding, we are at 4 and a half dimension to be kept ultra precise.
I am not suggesting we use such a bearing. I want to demonstrate the way of thinking.
So: for our platter bearing we could use components that already come with desired precision. Weird idea: we use a small sintered bronze bushing and a dowel pin for the radial bearing. And for the axial air bearing we take two precision-ground granite slabs like used in mechanical workshops for
measuring. They can had for $100 each cut to size. Ok, not rround, only square. But if we can live with that, we can put one slab on the other with with their precision surfaces facing. We glue our platter on top of that..And then we pump air in the gap. Ready is the air bearing.
So, and if we know a stone mason who just bought a new plane grinding machine, we get the stone plates even cheaper 'cos his machine alread provides the precision.
Folks, which product do you know that come already machined to precision, maybe surplus available? like my hydraulic valve cartridge?
You get the concept?
Hmmh, i am not sure about that. Platter bearings require what all bearing's require: precision. Surfaces can be excentric, tilted, rough, at wrong distance or taper angle.
You cannot make all that adjustable. Moreover, you cannot compensate with your manpower and time and diligence for all those errors. Complexity eats up benefits and smoe benefits are theoretical ones.
So what does an airbering designer do to achieve his goal of an ultra precise rotational air bearing? He strives to reduce the count of relevant dimension AFAP. HE will not be happy with two plane-ground trustplates with a precision-ground spacer in between Because each surface, even the centering surfaces of the space have to be plane-parallel, not tilted. And without plane deviaton. Each rotational surface has to be centered and free from roundness deviation. If all relevant dimensions are added up, he arrives at more than 10 dimensions to be kept ultra precise and worse, related to dimensions of another component.
He will be happy however if the beaqring has two spherical bearing surfaces. Two spheres have to be ground to precision diameter, easy. the spherical bearing cups have a radius bigger by the intended bearing gap. And the sphere center distance of the cups is already irrelelvant if the spacer keeping the rotor's spheres apart can be ground to fit. This spacer mustn't even be plane-parallel, it just must be keep the rotor spheres. Try differnt spacers until you have it.
So we have cup radius (2x) sphere radius, (2x) , spacer thickness. As the spacer is adjusted by grinding, we are at 4 and a half
dimension to be kept ultra precise. I am not suggesting we use such a bearing. I want to demonstrate the way of thinking.
So: for our platter bearing we could use components that already come with desired precision. Weird idea: we use a small sintered bronze bushing and a dowel pin for the radial bearing. And for the axial air bearing we take two precision-ground granite slabs like used in mechanical workshops for
measuring. They can had for $100 each cut to size. Ok, not rround, only square. But if we can live with that, we can put one slab on the other with with their precision surfaces facing. We glue our platter on top of that..And then we pump air in the gap. Ready is the air bearing.
So, and if we know a stone mason who just bought a new plane grinding machine, we get the stone plates even cheaper 'cos his machine alread provides the precision.
Folks, which product do you know that come already machined to precision, maybe surplus available? like my hydraulic valve cartridge?
You get the concept?
OK, some ideas, probably not all usable but here it goes:
1: glass ... (the thing doctors use to inject stuff in you when you stick a needle on it), these were (are) very tight tolerance.
2: same for the air bearing instead of the measuring slabs. Float glass is very flat, so is ground glass for mirror making. Should be easy to find everywhere. If you do not object the price then 1/20 wavelenght optical flats can be used
3: axial bearing instead of air: the ruby balls someone mentioned in the diy arm thread. Can be had in optical quality for laser focusing.
4: rad bearing: injectors for gasoil engine, these must be well fitting regarding the pressure involved. Auto scrap yard?
5: rad bearing: bearing of a hard disk. Should be easy to find and high tolerance but meant for high speed.
6: rad bearing: turbocompressor of a motor? This is an oil bearing if I remember.
7: I will try to look into guides for molds. If I remember these are obtainable in different tolerances, even negative. These are meant for linear movement along the axis, but might be usable as a radial bearing as a TT turn quite slow. Very strong! Think of something like a stacked ball bearing, that has linear motion. Might be expensive.
For the specs:
1: must have a removable center pin.
2: must be able to carry the laadegard arm.
1: glass ... (the thing doctors use to inject stuff in you when you stick a needle on it), these were (are) very tight tolerance.
2: same for the air bearing instead of the measuring slabs. Float glass is very flat, so is ground glass for mirror making. Should be easy to find everywhere. If you do not object the price then 1/20 wavelenght optical flats can be used
3: axial bearing instead of air: the ruby balls someone mentioned in the diy arm thread. Can be had in optical quality for laser focusing.
4: rad bearing: injectors for gasoil engine, these must be well fitting regarding the pressure involved. Auto scrap yard?
5: rad bearing: bearing of a hard disk. Should be easy to find and high tolerance but meant for high speed.
6: rad bearing: turbocompressor of a motor? This is an oil bearing if I remember.
7: I will try to look into guides for molds. If I remember these are obtainable in different tolerances, even negative. These are meant for linear movement along the axis, but might be usable as a radial bearing as a TT turn quite slow. Very strong! Think of something like a stacked ball bearing, that has linear motion. Might be expensive.
For the specs:
1: must have a removable center pin.
2: must be able to carry the laadegard arm.
Havoc,
1) glass syringe: though myself over it, too much gap, not precise enough, but i havent't thought over it for radial bearin alone, maybe useable if a huuge axial airbearing surface kills platter tilt. Could be worth a try.
2) great idea! Glass slabs! Can be drilled with tungsten carbide drill bits. Plugs made from brass and carrying the nozzles.
Bingo!
3) yes, possible. My TT uses such. Have a trustplate from POM or PTFE and it is lifetime stable. Sounds terrific.But .. the beauty of an air bearing lies in the huge load it can carry.
I vote for axial air bearing. But one thing: if we use an axial "hovercraft" air bearing (platter weight adjusting the air gap, no second bearing surface preventing the platter from lifting), no plinth suspension, please! Two masses (platter and plinth) separated by two springs (plinth suspension and the air gap) : a chaotic system. both masses will dance a rubber skeleton's tango with each other.
So if we use a supension for the plinth (no linn style, but veryvery heavy plinth and air/rubber suspension), we could combine ball/trustplate and air for the axial bearing and let the air carry 80% of the platter load. Which is similar to what the Verdier of today does, just the weight carrier is the magnetic bearing.
4) very good idea, similar to my hydraulic valve, similar reason for the precision. Seconded.
5) if the harddisk bearing is a ball bearing: a firm NO: stay away from ball race bearings. Think of a bunch of roughly spherical thundering down a small river's bed valleywards: this is a ball race bearing, considered under record groove dimensions.
6) Dig deeper, not a bad idea!
7) ball races. Stay away!
Your spec contributions: seconded.
All,
i did not hear fervent objections so i will start to fill the wiki with our spec as soon as i have some time left. Spec is a living document, wiki is exactly meant for such.
Anyone of you can delete or overwrite what i write there but i will take care to get a condensed version of what you wrote and what i remember from my diploma thesis and see fit into DIY scale and possibilities.
Pedro and all,
find attached a pix from the hydraulic valve cartridge.
You find me sitting with a big grin!
Have a good night, all!
1) glass syringe: though myself over it, too much gap, not precise enough, but i havent't thought over it for radial bearin alone, maybe useable if a huuge axial airbearing surface kills platter tilt. Could be worth a try.
2) great idea! Glass slabs! Can be drilled with tungsten carbide drill bits. Plugs made from brass and carrying the nozzles.
Bingo!
3) yes, possible. My TT uses such. Have a trustplate from POM or PTFE and it is lifetime stable. Sounds terrific.But .. the beauty of an air bearing lies in the huge load it can carry.
I vote for axial air bearing. But one thing: if we use an axial "hovercraft" air bearing (platter weight adjusting the air gap, no second bearing surface preventing the platter from lifting), no plinth suspension, please! Two masses (platter and plinth) separated by two springs (plinth suspension and the air gap) : a chaotic system. both masses will dance a rubber skeleton's tango with each other.
So if we use a supension for the plinth (no linn style, but veryvery heavy plinth and air/rubber suspension), we could combine ball/trustplate and air for the axial bearing and let the air carry 80% of the platter load. Which is similar to what the Verdier of today does, just the weight carrier is the magnetic bearing.
4) very good idea, similar to my hydraulic valve, similar reason for the precision. Seconded.
5) if the harddisk bearing is a ball bearing: a firm NO: stay away from ball race bearings. Think of a bunch of roughly spherical thundering down a small river's bed valleywards: this is a ball race bearing, considered under record groove dimensions.
6) Dig deeper, not a bad idea!
7) ball races. Stay away!
Your spec contributions: seconded.
All,
i did not hear fervent objections so i will start to fill the wiki with our spec as soon as i have some time left. Spec is a living document, wiki is exactly meant for such.
Anyone of you can delete or overwrite what i write there but i will take care to get a condensed version of what you wrote and what i remember from my diploma thesis and see fit into DIY scale and possibilities.
Pedro and all,
find attached a pix from the hydraulic valve cartridge.
You find me sitting with a big grin!
Have a good night, all!
Attachments
Most modern HD bearings use hydrodynamic bearings. I'm dismantling one at the moment, when I can find the right tools. None of the metrics or imperial I have fits.
The turbocompressors use oil bearings, but presurised. So out of the question probably.
Only problem I see with the combined air/ball bearing for axial is what hapens when the air pressure stops? Does the ball get to carry all load? Other possible setback: If we re-use something like the valve you have, how on earth will people from all around the world be able to get the same if they do not want to redesign some parts of the TT?
Read somewhere there are 3.5 coutries using inches. UK should be using mm but not completely, Birma, US and another I don't remember. So mm it is.
The turbocompressors use oil bearings, but presurised. So out of the question probably.
Only problem I see with the combined air/ball bearing for axial is what hapens when the air pressure stops? Does the ball get to carry all load? Other possible setback: If we re-use something like the valve you have, how on earth will people from all around the world be able to get the same if they do not want to redesign some parts of the TT?
Read somewhere there are 3.5 coutries using inches. UK should be using mm but not completely, Birma, US and another I don't remember. So mm it is.
For Planet 10
Sadly, I have yet to ever see a Linn distributor walk away shaking their head with their belief structure shattered.
Normal response seems to be to walk away shaking their head telling you that imaging doesn't matter and you just don't know how to listen. The head shaking seems to be because they feel sorry for you and know how much you are missing by not achieving correct replay of "tunes".
Poor me. I know how much they're missing (of my pay packet) by not convincing me that a pretty normal sounding amplifier should cost over 3 months of my salary.
Oh well. Back to my DIY unipivot...
Drew
Sadly, I have yet to ever see a Linn distributor walk away shaking their head with their belief structure shattered.
Normal response seems to be to walk away shaking their head telling you that imaging doesn't matter and you just don't know how to listen. The head shaking seems to be because they feel sorry for you and know how much you are missing by not achieving correct replay of "tunes".
Poor me. I know how much they're missing (of my pay packet) by not convincing me that a pretty normal sounding amplifier should cost over 3 months of my salary.
Oh well. Back to my DIY unipivot...
Drew
Havoc and Dave,
that was naugty me : http://www.diyaudio.com/forums/showthread.php?s=&postid=23650&highlight=birma#post23650
HD bearing: if they use hydrodynamic bearing, then those need a minimum speed. If the HD is meant to run at 3000, 7000, 10000 rpm, then speeds between 33 and 78 are certainly not enough to create a stable oil film.
I see your problem with the ball and the air off. Agreed, we have to take this into consideration. However, you would nt believe what a load. ball/trustplate can carry. my own TT has a 4kg platter and the ball has 3mm diameter, the trustplate is PTFE, virgin Teflon. Soft.
The ball sinks in by 1/4 of its diameter. If i consider testing of surface hardness is also done with a ball and the force to make a dent is proportional to the material volume it pushes aside to create the sperical indent, then the ball's ability to carry load (limited by sinking in by a given percentage of its radius) is proportional to the square of its radius.
So: a 10mm ball could theoretically carry a 44kg platter.
Another idea: we could let a ball/spherical surface pull the platter down so that it cannot lift. The air bearing could easily carry that downforce, too. Just prevent the platter from bouncing on the air film.
Methinks, we find a ball size able to carry the platter alone if the air is off.
Valve: my idea was to get in contact with the manufacturer and ask him what help he can offer, maybe he has 100 pieces of a fitting size as reject and just wanted to trash them and is happy now to make some money on it. Another hope would be that we have him manufacture a very simple cylindrical bushing and piston for us at an affordable price, i will inquire for that (would be my preferred solution.) Another means to get price down is to accept a vague delivery time so that he can use time when his machines would else be idle. After i got his response, you folks can decide.
that was naugty me
: http://www.diyaudio.com/forums/showthread.php?s=&postid=23650&highlight=birma#post23650HD bearing: if they use hydrodynamic bearing, then those need a minimum speed. If the HD is meant to run at 3000, 7000, 10000 rpm, then speeds between 33 and 78 are certainly not enough to create a stable oil film.
I see your problem with the ball and the air off. Agreed, we have to take this into consideration. However, you would nt believe what a load. ball/trustplate can carry. my own TT has a 4kg platter and the ball has 3mm diameter, the trustplate is PTFE, virgin Teflon. Soft.
The ball sinks in by 1/4 of its diameter. If i consider testing of surface hardness is also done with a ball and the force to make a dent is proportional to the material volume it pushes aside to create the sperical indent, then the ball's ability to carry load (limited by sinking in by a given percentage of its radius) is proportional to the square of its radius.
So: a 10mm ball could theoretically carry a 44kg platter.
Another idea: we could let a ball/spherical surface pull the platter down so that it cannot lift. The air bearing could easily carry that downforce, too. Just prevent the platter from bouncing on the air film.
Methinks, we find a ball size able to carry the platter alone if the air is off.
Valve: my idea was to get in contact with the manufacturer and ask him what help he can offer, maybe he has 100 pieces of a fitting size as reject and just wanted to trash them and is happy now to make some money on it. Another hope would be that we have him manufacture a very simple cylindrical bushing and piston for us at an affordable price, i will inquire for that (would be my preferred solution.) Another means to get price down is to accept a vague delivery time so that he can use time when his machines would else be idle. After i got his response, you folks can decide.
Pedro,
i guess it is a pressure limiting valve but i am not sure. I also have other valve cartridges but they do not have the dimension i would like to have. This one just fits. BTW, purpose in unimportant , the mechanical properties count.
All i can tell is that it is hard if not impossible to put the piston into the bore, but when the piston is in place, it runs smoooooth. And without noticeable play.
And i have seen the drawing, so i know the gap and the tolerances.
i guess it is a pressure limiting valve but i am not sure. I also have other valve cartridges but they do not have the dimension i would like to have. This one just fits. BTW, purpose in unimportant , the mechanical properties count.
All i can tell is that it is hard if not impossible to put the piston into the bore, but when the piston is in place, it runs smoooooth. And without noticeable play.
And i have seen the drawing, so i know the gap and the tolerances.
Wel, it is holiday season, so lets attribute it to that. I'll be off soon also.
As for the HD bearing. Did some searching and took 2 specimen apart. It is impossible to separate the bearing from the platters, both are crimped together, so I do not see much hope to separate them easily. So for the time being, the air/ball combination seems the best bet.
Though about some other non resonant material, but it will be messy! There is some kind of bitumen that comes in great lumps and is intended to be melted and then poured into gaps in roofs or roads etc. So if we use that instead of the plaster, it will stick to more materials and crimp will be less an issue. But it will be messy and smelly.
As for the HD bearing. Did some searching and took 2 specimen apart. It is impossible to separate the bearing from the platters, both are crimped together, so I do not see much hope to separate them easily. So for the time being, the air/ball combination seems the best bet.
Though about some other non resonant material, but it will be messy! There is some kind of bitumen that comes in great lumps and is intended to be melted and then poured into gaps in roofs or roads etc. So if we use that instead of the plaster, it will stick to more materials and crimp will be less an issue. But it will be messy and smelly.
Big bad bearing
OK I'm wayy overmy head here, but when I was thinking of making a turntable years ago, a device I had seen years before kept popping into my mind.
A friend of mine helped with the instructional equipment in an intro physics course and while talking to him I saw an interesting air bearing:
They had taken a 2" diameter ball bearing, wiped it with silicone for a release agent, and pressed about halfway into into an epoxy substance like JB Weld. The epoxy was in a container, so when it hardened it made a base with a socket that perfectly fit the high presision ball. They removed the ball and drilled a small hole in the socket in the center (bottom) . Then connected the hole on the outside to an air pump. When the air was turned on, and the ball put in the socket, you could spin the ball, and wait just about forever for it to stop spinning.
So, heres my scheme:
Cast a large base for the turntable out of concrete composite
leaving a recess in the middle for filling with epoxy.
Make the bearing as above. After removing the release agent, epoxy the ball to a platter. The platter would have to have a heavy rim that would hang below the center of the ball to make it nominally stable, and the drive belt would have to be aligned with the "equator" of the ball to keep the torque from tipping the platter. Aquarium pump for the bearing.
So far, anyone could make this in their flat. The platter would be the biggest problem, but could be a disk laminated to a bunch of rings to produce the rim. Use acrylic sheet. Making the platter is a problem for any design. Glass is available in circles- I'll bet a glass company can order float glas cut in a circle- alot ceaper I'll bet than a custom machined acrylic. Rings of some other material could be added to form the overhung rim.
How to machine it? Maybe chucked in a drill press and turned by hand with a sanding drum chucked in a hand drill clamped against the edge. Turn the drill press spindle by hand!!???
I'm sure Planet 10 would agree that a reasonably priced high endturntable for the masses would be a great contribution
Any hope or interest?
OK I'm wayy overmy head here, but when I was thinking of making a turntable years ago, a device I had seen years before kept popping into my mind.
A friend of mine helped with the instructional equipment in an intro physics course and while talking to him I saw an interesting air bearing:
They had taken a 2" diameter ball bearing, wiped it with silicone for a release agent, and pressed about halfway into into an epoxy substance like JB Weld. The epoxy was in a container, so when it hardened it made a base with a socket that perfectly fit the high presision ball. They removed the ball and drilled a small hole in the socket in the center (bottom) . Then connected the hole on the outside to an air pump. When the air was turned on, and the ball put in the socket, you could spin the ball, and wait just about forever for it to stop spinning.
So, heres my scheme:
Cast a large base for the turntable out of concrete composite
leaving a recess in the middle for filling with epoxy.
Make the bearing as above. After removing the release agent, epoxy the ball to a platter. The platter would have to have a heavy rim that would hang below the center of the ball to make it nominally stable, and the drive belt would have to be aligned with the "equator" of the ball to keep the torque from tipping the platter. Aquarium pump for the bearing.
So far, anyone could make this in their flat. The platter would be the biggest problem, but could be a disk laminated to a bunch of rings to produce the rim. Use acrylic sheet. Making the platter is a problem for any design. Glass is available in circles- I'll bet a glass company can order float glas cut in a circle- alot ceaper I'll bet than a custom machined acrylic. Rings of some other material could be added to form the overhung rim.
How to machine it? Maybe chucked in a drill press and turned by hand with a sanding drum chucked in a hand drill clamped against the edge. Turn the drill press spindle by hand!!???
I'm sure Planet 10 would agree that a reasonably priced high endturntable for the masses would be a great contribution
Any hope or interest?
Looks like a good idea. If we combine it with a flat air bearing we would not even need the overhanging rim. The rest of the construction would get a bit more difficult but not prohibitive.
We would then have a flat glass bottom with a hole for the ball/air bearing as described by Variac. The platter would be a large glass affair (I like that one) with the same hole in a flat bottom, but the ball would be glued to that one. Pump air in the bottom, and the ball is the radial bearing, the flat part the axial one.
This looks easy enough to make on a kitchen table with fairly common materials that could be found anywhere.
Comments?
We would then have a flat glass bottom with a hole for the ball/air bearing as described by Variac. The platter would be a large glass affair (I like that one) with the same hole in a flat bottom, but the ball would be glued to that one. Pump air in the bottom, and the ball is the radial bearing, the flat part the axial one.
This looks easy enough to make on a kitchen table with fairly common materials that could be found anywhere.
Comments?
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