Hi Carlo,
The lil casey components are looking very nice. Fingers crossed for a successful build. Good to see some on topic building.
Off topic again. I intentionally made the contact between the center of the platter and the bearing as solid and direct as possible in order to create a mechanical ground path. Quite the opposite of your design.
Niffy
The lil casey components are looking very nice. Fingers crossed for a successful build. Good to see some on topic building.
Off topic again. I intentionally made the contact between the center of the platter and the bearing as solid and direct as possible in order to create a mechanical ground path. Quite the opposite of your design.
Niffy
Hi Ray,
In my books the last thing you want is a recess cut in the centre of the platter for the label. If you do have a recess and then use a central clamp the record will be pressed down into the recess in the middle. The edge of the recess will act as a fulcrum pushing the outer edge of the record upwards and away from the platter. This will also have a habit of excentuating warps. All round a bad idea.
It is much better to do exactly the opposite. In the centre of my platter is a 60mm diameter disk whose edge is flush with the surface of the platter. The cross section of the disk is a smooth sin wave that rises 1.2mm above the surface of the platter at its centre. I use a screw down clamp as much greater force can be applied than with a gravity clamp and it doesn't load the bearing. The clamp has a recess, also 60mm in diameter, on its lower surface. As the clamp is screwed down the outer edge of the record is bowed downwards onto the platter. As the clamp is screwed down further the entire playing surface is forced into intimate contact with the platter. This is an excellent way of getting rid of warps as well. This type of clamp is called a Reflex clamp. It actually works as a vacuum hold-down with most records. After I remove the clamp I have to use my thumb nail to lift the edge of the record to let in a bit of air before I can lift the record off the platter. Only the most warped of records have any gaps between record and platter.
It is true that many vintage record players had thick ridged rubber mats. It is also true that many vintage record players sounded awful. I think there might be a connection. I have heard many a vintage deck sounding fine, but they all had upgraded platters and mats.
Niffy
In my books the last thing you want is a recess cut in the centre of the platter for the label. If you do have a recess and then use a central clamp the record will be pressed down into the recess in the middle. The edge of the recess will act as a fulcrum pushing the outer edge of the record upwards and away from the platter. This will also have a habit of excentuating warps. All round a bad idea.
It is much better to do exactly the opposite. In the centre of my platter is a 60mm diameter disk whose edge is flush with the surface of the platter. The cross section of the disk is a smooth sin wave that rises 1.2mm above the surface of the platter at its centre. I use a screw down clamp as much greater force can be applied than with a gravity clamp and it doesn't load the bearing. The clamp has a recess, also 60mm in diameter, on its lower surface. As the clamp is screwed down the outer edge of the record is bowed downwards onto the platter. As the clamp is screwed down further the entire playing surface is forced into intimate contact with the platter. This is an excellent way of getting rid of warps as well. This type of clamp is called a Reflex clamp. It actually works as a vacuum hold-down with most records. After I remove the clamp I have to use my thumb nail to lift the edge of the record to let in a bit of air before I can lift the record off the platter. Only the most warped of records have any gaps between record and platter.
It is true that many vintage record players had thick ridged rubber mats. It is also true that many vintage record players sounded awful. I think there might be a connection. I have heard many a vintage deck sounding fine, but they all had upgraded platters and mats.
Niffy
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Hi Niffy,
I personally like recessed label area of platter. If the diameter of recess area is slightly larger than label of record, and the diameter of clamp is slightly larger than recess area, it won't introduce warp. If you put a thin piece, donut shape and slightly thick than the height of recessed area, of rubber around spindle, it may even reduce warp.
Jim
I personally like recessed label area of platter. If the diameter of recess area is slightly larger than label of record, and the diameter of clamp is slightly larger than recess area, it won't introduce warp. If you put a thin piece, donut shape and slightly thick than the height of recessed area, of rubber around spindle, it may even reduce warp.
Jim
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Hi Jim,
If you make the recess larger then the label and the clamp larger the recess the cartridge will hit the clamp. The label comes up to a couple of millimetres from the runout groove.
If you are putting the donut of rubber underneath the record you are making the central point where the record contacts higher than the surface of the platter. By using the donut you are converting your central clamp into a Reflex clamp.
When I used to own the pink triangle deck I used it with an SME clamp. This clamp gripped the outside of the spindle then pulled down. It was nice as it didn't need a threaded spindle. It's a really solid piece of kit, probably the same as the one you have. The pink triangle had a label recess but I used a penny washer to convert it into a reflex clamp. It didn't work at all well when used without the washer. My current smooth dome is a refinement on the washer idea and does seem to work quite a lot better.
Niffy
If you make the recess larger then the label and the clamp larger the recess the cartridge will hit the clamp. The label comes up to a couple of millimetres from the runout groove.
If you are putting the donut of rubber underneath the record you are making the central point where the record contacts higher than the surface of the platter. By using the donut you are converting your central clamp into a Reflex clamp.
When I used to own the pink triangle deck I used it with an SME clamp. This clamp gripped the outside of the spindle then pulled down. It was nice as it didn't need a threaded spindle. It's a really solid piece of kit, probably the same as the one you have. The pink triangle had a label recess but I used a penny washer to convert it into a reflex clamp. It didn't work at all well when used without the washer. My current smooth dome is a refinement on the washer idea and does seem to work quite a lot better.
Niffy
Niffy,
I am at work now and will measure it tonight to see if my understanding is correct.
Jim
The Michell Orbe uses a similar approach that Niffy alludes too above.
It to has a raised centre section and a screw on clamp so when you tighten the clamp it pushes the record firmly onto the platter (which is also acrylic, although not one platter but 3 Gyro platters bonded together).
I have an Orbe and find it very good from creating a very quiet background when playing my records.
The oil pumping spindle (I swapped the original steel ball bearing for a ceramic bearing) appears to be a good solution to me - very quiet also.
I have changed the 3 springs used for the suspension with something similar to what SME used (elastic o-rings) which also help with noise transmission (reducing) from the environment and the twisting of the chassis due to the motor pulling on the drive belt and platter.
Not totally DIY I know but the original Orbe I find to be very good and the little tweaks have elevated it even higher.
It to has a raised centre section and a screw on clamp so when you tighten the clamp it pushes the record firmly onto the platter (which is also acrylic, although not one platter but 3 Gyro platters bonded together).
I have an Orbe and find it very good from creating a very quiet background when playing my records.
The oil pumping spindle (I swapped the original steel ball bearing for a ceramic bearing) appears to be a good solution to me - very quiet also.
I have changed the 3 springs used for the suspension with something similar to what SME used (elastic o-rings) which also help with noise transmission (reducing) from the environment and the twisting of the chassis due to the motor pulling on the drive belt and platter.
Not totally DIY I know but the original Orbe I find to be very good and the little tweaks have elevated it even higher.
One interesting feature of Michell decks, though not the Orbe, is the brass weights that hang from the underside of the platter. These are often thought to be primarily for adding rotational inertia in order to improve speed stability. The actual main role of the weights is to break up and prevent the formation of the pattern of nodes in the platter. (I think 7 weights would both look and work better, but I nit pick)
Their inverted bearing and the way it interacts with the platter is well though out and implemented.
Niffy
Their inverted bearing and the way it interacts with the platter is well though out and implemented.
Niffy
Hi Niffy,
You are right. I measured my table. The diameter of reassessed area is 11 cm. Actual reassessed area may be smaller because I cover the platter with my DIY mat. Record label is 10 cm. The diameter of SME clamp is 8.8 cm.
Here is a photo of my diy mat. It is brass sheet I bought from Blick Art supply store. Cut in size to glue on top of 1 mm donut shape carbon fiber.
Jim
You are right. I measured my table. The diameter of reassessed area is 11 cm. Actual reassessed area may be smaller because I cover the platter with my DIY mat. Record label is 10 cm. The diameter of SME clamp is 8.8 cm.
Here is a photo of my diy mat. It is brass sheet I bought from Blick Art supply store. Cut in size to glue on top of 1 mm donut shape carbon fiber.
Jim
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Hi Jim,
I wouldn't have thought of using brass. I understand that it is a very thin sheet with the section that sits under the playable portion of the record being carbon fibre. How did you make the label recess? Did you simply press the brass into shape? I have no electoral grounding of my platter and have never noticed a problem with static. I use a carbon fibre brush before each play which should discharge any that there is. It might be one of those problems that I don't realise I have until it goes away. How does the elimination of static effect sound in your opinion?
I see that your spindle is externally threaded so I guess your clamp is not the same as the one I used to own.
I wouldn't have thought of using brass. I understand that it is a very thin sheet with the section that sits under the playable portion of the record being carbon fibre. How did you make the label recess? Did you simply press the brass into shape? I have no electoral grounding of my platter and have never noticed a problem with static. I use a carbon fibre brush before each play which should discharge any that there is. It might be one of those problems that I don't realise I have until it goes away. How does the elimination of static effect sound in your opinion?
I see that your spindle is externally threaded so I guess your clamp is not the same as the one I used to own.
Thanks Niffy: finger crossing.
Being used to work on metals, the carbon fiber (and bakelite) needed much more attention than expected. From the first Casey I knew the points that require maximum precision, but here everything is much smaller and lighter. The weights now are halved and the Vert. mass should be near to the Hor. mass (I love the pivoted ones, you know). We'll see if pen tips bearings will work better than the previous ball bearings: certainly need even more alignment accuracy.
I hope to be able to do the first tests in 2 - 3 weekends.
TT bearing: you complained about your ears, me of the eyes that are no more those of the past, so my doubts for making your system decently. Dealing instead with a "traditional" bearing and making it directly connected to the platter-spindle I would find all the noise into the cartridge. Experience already done.
The current idea is to do something dimensionally rigid, but capable to absorb separately the different resonances (disc tracing and bearing). The interface of the two system is just that thin red disk in the middle. Maybe a silicone mat (those used for oven), or sorbothane, or whatever fascinating brands the devil suggests...
carlo
mat - no mat (attachments) Difficult task, even with a good clamp; if you put a strong light in the back, you'll see it appearing somewhere under the disc. Trying something like # 2817 needs just a 1 mm cardboard donut and your clamp. Then trow it away, or make it better
Being used to work on metals, the carbon fiber (and bakelite) needed much more attention than expected. From the first Casey I knew the points that require maximum precision, but here everything is much smaller and lighter. The weights now are halved and the Vert. mass should be near to the Hor. mass (I love the pivoted ones, you know). We'll see if pen tips bearings will work better than the previous ball bearings: certainly need even more alignment accuracy.
I hope to be able to do the first tests in 2 - 3 weekends.
TT bearing: you complained about your ears, me of the eyes that are no more those of the past, so my doubts for making your system decently. Dealing instead with a "traditional" bearing and making it directly connected to the platter-spindle I would find all the noise into the cartridge. Experience already done.
The current idea is to do something dimensionally rigid, but capable to absorb separately the different resonances (disc tracing and bearing). The interface of the two system is just that thin red disk in the middle. Maybe a silicone mat (those used for oven), or sorbothane, or whatever fascinating brands the devil suggests...
carlo
mat - no mat (attachments) Difficult task, even with a good clamp; if you put a strong light in the back, you'll see it appearing somewhere under the disc. Trying something like # 2817 needs just a 1 mm cardboard donut and your clamp. Then trow it away, or make it better
Attachments
Hmm
On the blanks for a platter:
Checked out a record presser- he can supply me with 50 blanks for 250 euro
They would make them after a normal run, so same material spec- reflection minimized
Further on the platter material discussion: how do mats figure in the equation, as it would change the materials etc etc
Best,
Coolerooney
On the blanks for a platter:
Checked out a record presser- he can supply me with 50 blanks for 250 euro
They would make them after a normal run, so same material spec- reflection minimized
Further on the platter material discussion: how do mats figure in the equation, as it would change the materials etc etc
Best,
Coolerooney
Hi Carlo,
The mat-no mat issue. My recent work to reduce runout was sparked off by two things. First off is that the top of my platter is exactly at eye level from my listening position. The slight wobble of the platter was more noticeable from this viewing angle. The second thing was discussing bearings with you. I also have a window right behind the turntable. The light from the window combined with my viewing angle makes any gaps readily apparent. On occasional records I can see a slim sliver of light between the platter and record that extends about a centimetres at most from the edge. On the vast majority of records there is no light visible at all. As I mentioned before the clamp flattens most records so well it makes an air tight seal that keeps them pressed to the platter even after the clamp is removed.
When I was making the platter and before I had broken the surface it was transparent. I clamped a damp record to the platter and viewed it from beneath. The moisture on the record made it clear where the record was in contact with the platter. The record made good solid contact all the way from the edge to about a centimetre from the run out groove. This means that the entire playing surface of most records is in contact with the platter. The record only breaks contact for the last bit of the run out groove where it slopes up towards the spindle. The only way to improve this would be to add a peripheral clamp.
Niffy
The mat-no mat issue. My recent work to reduce runout was sparked off by two things. First off is that the top of my platter is exactly at eye level from my listening position. The slight wobble of the platter was more noticeable from this viewing angle. The second thing was discussing bearings with you. I also have a window right behind the turntable. The light from the window combined with my viewing angle makes any gaps readily apparent. On occasional records I can see a slim sliver of light between the platter and record that extends about a centimetres at most from the edge. On the vast majority of records there is no light visible at all. As I mentioned before the clamp flattens most records so well it makes an air tight seal that keeps them pressed to the platter even after the clamp is removed.
When I was making the platter and before I had broken the surface it was transparent. I clamped a damp record to the platter and viewed it from beneath. The moisture on the record made it clear where the record was in contact with the platter. The record made good solid contact all the way from the edge to about a centimetre from the run out groove. This means that the entire playing surface of most records is in contact with the platter. The record only breaks contact for the last bit of the run out groove where it slopes up towards the spindle. The only way to improve this would be to add a peripheral clamp.
Niffy
Hi Coolerooney,
If the blanks are entirely flat and have a smooth shiny surface they could be made to work. If a stack of the blanks are pressed firmly together so all the air is forced from between them they will tend to stick together. This could be the basis of a laminated platter. The impedance of each lamina will be the same and they will be in intimate contact with each other. There will be a very small reflection of a compression wave at each interface. As the wave passes through the stack there will be multiple small reflections, each being partially reflected again and again. This could act to soften the intensity of reflection by defusing it. A laminate of this type will also likely have a higher level of damping than a single layer of the same thickness though it will have lower overall rigidity. It is possible that a laminated platter of this type could actually have advantages.
A layer of pvc glue of some variety spread of sprayed over the outside edge would help to keep the stack together and prevent air from getting between the lamina. 50 blank records could make a single platter 80 to 100mm thick or several more manageable ones. My brain is still leaning towards a solid platter but a laminated one is intriguing.
I would guess that your bullet proof glass is probably polycarbonate. It should be possible to cut this with a router using standard bits. It could make a good base section to go under a laminated vinyl top platter.
Niffy
If the blanks are entirely flat and have a smooth shiny surface they could be made to work. If a stack of the blanks are pressed firmly together so all the air is forced from between them they will tend to stick together. This could be the basis of a laminated platter. The impedance of each lamina will be the same and they will be in intimate contact with each other. There will be a very small reflection of a compression wave at each interface. As the wave passes through the stack there will be multiple small reflections, each being partially reflected again and again. This could act to soften the intensity of reflection by defusing it. A laminate of this type will also likely have a higher level of damping than a single layer of the same thickness though it will have lower overall rigidity. It is possible that a laminated platter of this type could actually have advantages.
A layer of pvc glue of some variety spread of sprayed over the outside edge would help to keep the stack together and prevent air from getting between the lamina. 50 blank records could make a single platter 80 to 100mm thick or several more manageable ones. My brain is still leaning towards a solid platter but a laminated one is intriguing.
I would guess that your bullet proof glass is probably polycarbonate. It should be possible to cut this with a router using standard bits. It could make a good base section to go under a laminated vinyl top platter.
Niffy
Niffy,
I used a small hammer to hit the middle of brass sheet to make reassessed area.
The bearing of SME 20 is grounded and the spindle sits on a steel ball. I got the inspiration from Benz LPs cartridge. The motor of Benz LPs sits on solid brass. In the process of building my linear arms, I tried many shims made with different material to see how it affected sound. Brass is one of my favorites. My other favorites are carbon fiber, 2024 aluminum, magnesium. Brass mat is natural extension of my knowledge for material.
Does the brass mat reduce static? It is a tricky question to answer. I used have a lot of statics in my room under certain weather conditions sometimes. I could hear low pops noise while I was taking records off the platter and thought to get an anti-static fan to reduce statics. But it never happens since I installed the brass mat. So, I assume it works. At beginning, I used copper conduct tapes to cover the carbon fiber mat. It did reduce static as well. However, I prefer brass for its sound.
Jim
I used a small hammer to hit the middle of brass sheet to make reassessed area.
The bearing of SME 20 is grounded and the spindle sits on a steel ball. I got the inspiration from Benz LPs cartridge. The motor of Benz LPs sits on solid brass. In the process of building my linear arms, I tried many shims made with different material to see how it affected sound. Brass is one of my favorites. My other favorites are carbon fiber, 2024 aluminum, magnesium. Brass mat is natural extension of my knowledge for material.
Does the brass mat reduce static? It is a tricky question to answer. I used have a lot of statics in my room under certain weather conditions sometimes. I could hear low pops noise while I was taking records off the platter and thought to get an anti-static fan to reduce statics. But it never happens since I installed the brass mat. So, I assume it works. At beginning, I used copper conduct tapes to cover the carbon fiber mat. It did reduce static as well. However, I prefer brass for its sound.
Jim
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Hi Niffy, i'm trying to better understand your clamp system (drawing according to your description, hopefully), because the idea of avoiding the machining of the acrylic platter attracts me a lot: everything is possible in this world, but to make the recess without a big lathe seems rather complex.
As you said, pushing the disk against the recess can raise the outer edge (bad idea, quote) but, considering that the clamp pushes to the center perhaps it is enough to give a small raised support on the outside and let it do his job, with much less force. Currently my cardboard gadget works fine on my old Lux TT, but maybe diying a new TT it can be improved quite simply.
Of course using a linear TA we have to consider that small tapering when leveling.
carlo
As you said, pushing the disk against the recess can raise the outer edge (bad idea, quote) but, considering that the clamp pushes to the center perhaps it is enough to give a small raised support on the outside and let it do his job, with much less force. Currently my cardboard gadget works fine on my old Lux TT, but maybe diying a new TT it can be improved quite simply.
Of course using a linear TA we have to consider that small tapering when leveling.
carlo
Attachments
My Oracle Delphi Mk2 turntable has a unique clamping system using a screw down clamp and a small convex "button" along with a semi sticky, sorbothane type mat. The clamp would force the outer edge of the label and outward down to make contact with the mat. The only problem is you could cause small cracks around the spindle hole buy using too much force on the clamp. I threaded my spindle to use a similar method but more precisely made. Unfortunately, vinyl records are not perfect in any dimension so we have to figure out how to deal with the minor variations.
Hi Carlo,
Your picture of my clamping system is close to what I actually have. The raised section in the centre of the platter is more of a smooth dome than the cone that you show. Your picture shows the clamp contacting the record outside of the label area. This would cause the cartridge to hit the clamp on the runout groove. The label section is about 100mm diameter and the clamp only 75mm. The clamp is entirely within the label area. The idea of the reflex clamp is that it bows the record downwards onto the platter, your diagram shows the record remaining flat. The cross section or the record that you are using appears exaggerated. Get out an actual record and look at the changes in thickness, they are quite subtle. The downwards bow of the record will be mainly in the thicker label area. The thinner playing area bows back upwards to keep the entire playing area in contact with the platter.
Tapering the surface of the platter will have a similar effect, the surface of the platter will be a concave cone. (I mentioned exploiting this as part of my record centering idea) The down sides of tapering the platter are that in order to adequately flatten the record the tapper would have to be quite severe. This would result in a noticeable variation in VTA across the record and an azimuth misalignment. The azimuth can be corrected easily enough if the arm has this adjustment. Creating the taper accurately would require the use of a lathe if using a bare platter or a profiled mat. A less severe taper can be used if combined with a Reflex clamp or peripheral clamp.
I used a router to cut the recess for the lower part of the Reflex clamp. This was one of the easier parts of making the platter.
Hi Joe,
I used quite a lot of force with my clamp and have never seen any damage to the vinyl itself, definitely not any cracks. With some records with particularly shiny labels the clamp can leave slight marks. The dome in the centre of my platter is very gentle with no edges as you would get using something like a washer. It starts horizontal and flush with the platter and curves smoothly up to the spindle where it is again horizontal. The dome rises 1.2mm. This is designed to stress the vinyl as little as possible whilst giving the maximum flattening. Designing the clamp was one of the first things I did when starting on my tonearm design. I wanted to know what level of warps the arm was going to have to deal with before I started designing it.
Hi Jim,
The reflex clamp will eliminate all the warps on most records and force the vinyl into intimate contact with the platter across its entire playing surface. The addition of a peripheral clamp or vacuum hold down would have little or no effect on these records. Most of the records that a reflex clamp cannot completely flatten will be by the addition of a peripheral clamp. A vacuum hold down system will not have any real advantage on all but a very tiny number of records but is probably the ultimate record flattening system.
On my deck a peripheral clamp would have to be exceptionally well balanced or any advantage in reducing warps would be lost to increased runout. The addition of a vacuum system would compromise the whole way my deck works and would almost certainly lower its sound quality.
My clamp and low level of runout results in records that run so flat that I doubt that additional clamping would offer any advantages except for that occasional record.
As I believe that the clamp is more a part of the arm than of the deck at least we are getting a bit more back on topic.
Niffy
Your picture of my clamping system is close to what I actually have. The raised section in the centre of the platter is more of a smooth dome than the cone that you show. Your picture shows the clamp contacting the record outside of the label area. This would cause the cartridge to hit the clamp on the runout groove. The label section is about 100mm diameter and the clamp only 75mm. The clamp is entirely within the label area. The idea of the reflex clamp is that it bows the record downwards onto the platter, your diagram shows the record remaining flat. The cross section or the record that you are using appears exaggerated. Get out an actual record and look at the changes in thickness, they are quite subtle. The downwards bow of the record will be mainly in the thicker label area. The thinner playing area bows back upwards to keep the entire playing area in contact with the platter.
Tapering the surface of the platter will have a similar effect, the surface of the platter will be a concave cone. (I mentioned exploiting this as part of my record centering idea) The down sides of tapering the platter are that in order to adequately flatten the record the tapper would have to be quite severe. This would result in a noticeable variation in VTA across the record and an azimuth misalignment. The azimuth can be corrected easily enough if the arm has this adjustment. Creating the taper accurately would require the use of a lathe if using a bare platter or a profiled mat. A less severe taper can be used if combined with a Reflex clamp or peripheral clamp.
I used a router to cut the recess for the lower part of the Reflex clamp. This was one of the easier parts of making the platter.
Hi Joe,
I used quite a lot of force with my clamp and have never seen any damage to the vinyl itself, definitely not any cracks. With some records with particularly shiny labels the clamp can leave slight marks. The dome in the centre of my platter is very gentle with no edges as you would get using something like a washer. It starts horizontal and flush with the platter and curves smoothly up to the spindle where it is again horizontal. The dome rises 1.2mm. This is designed to stress the vinyl as little as possible whilst giving the maximum flattening. Designing the clamp was one of the first things I did when starting on my tonearm design. I wanted to know what level of warps the arm was going to have to deal with before I started designing it.
Hi Jim,
The reflex clamp will eliminate all the warps on most records and force the vinyl into intimate contact with the platter across its entire playing surface. The addition of a peripheral clamp or vacuum hold down would have little or no effect on these records. Most of the records that a reflex clamp cannot completely flatten will be by the addition of a peripheral clamp. A vacuum hold down system will not have any real advantage on all but a very tiny number of records but is probably the ultimate record flattening system.
On my deck a peripheral clamp would have to be exceptionally well balanced or any advantage in reducing warps would be lost to increased runout. The addition of a vacuum system would compromise the whole way my deck works and would almost certainly lower its sound quality.
My clamp and low level of runout results in records that run so flat that I doubt that additional clamping would offer any advantages except for that occasional record.
As I believe that the clamp is more a part of the arm than of the deck at least we are getting a bit more back on topic.
Niffy
Niffy, thanks for the useful clarifications; that sketch was just a scheme, made using the Riia section which exaggerates the proportions to highlight that disks are not flat, and normally without a recess may remain floating. Even the edge is important and uses a tapering to slide the stylus into the first groove.
The 1mm tapering generates just an angle of 0.35 °, but it is more than enough to flatten the warps of my disks (I try to keep them well): the idea was of making a 0.5mm aluminum disk resting on an 1mm outer ring, and then glue it by pushing at the center. But your system is much easier, and I think I'll try to copy it.
I have a router used only to make the hole (only one, I love Full-range) in my speakers: I think I'll have to do a lot of practice to be able to do a precision work on plexy ...
carlo
I read that cast plexiglass often has no uniform thickness: did you have to level it?
The 1mm tapering generates just an angle of 0.35 °, but it is more than enough to flatten the warps of my disks (I try to keep them well): the idea was of making a 0.5mm aluminum disk resting on an 1mm outer ring, and then glue it by pushing at the center. But your system is much easier, and I think I'll try to copy it.
I have a router used only to make the hole (only one, I love Full-range) in my speakers: I think I'll have to do a lot of practice to be able to do a precision work on plexy ...
carlo
I read that cast plexiglass often has no uniform thickness: did you have to level it?