Hi Warrjon,
For the core it is best if you can use end grain balsa. This is where the grain runs vertically between the two skins rather than along the length of the carriage. Used in this way balsa is pretty much the best core material available. I purchased a block and cut my own end grain pieces. The front and rear sections of the arm are also built around balsa cores. The bottom section is solid carbon fibre, this was done to add more mass lower down so the centre of mass is better located.
Niffy
For the core it is best if you can use end grain balsa. This is where the grain runs vertically between the two skins rather than along the length of the carriage. Used in this way balsa is pretty much the best core material available. I purchased a block and cut my own end grain pieces. The front and rear sections of the arm are also built around balsa cores. The bottom section is solid carbon fibre, this was done to add more mass lower down so the centre of mass is better located.
Niffy
Hi ppap64,
I had the carbon fibre I used specially laid up by the supplier. It has woven outer skins and a unidirectional middle layer that is normally aligned along the length of the carriage. Unlike normal preprepared carbon fibre the outer woven layers are orientated at +/-45°. This actually increases the longitudinal, lateral and torsional rigidity of the end structure. The carbon fibre is 0.75mm thick. The end grain balsa core of the top plate is 4mm making the whole thing 5.5mm. The buttresses are again balsa cored with a skin of carbon fibre on either side. The front and rear blocks are both balsa cored. There are internal carbon fibre components, especially in the rear section that supports the counterweight and adjuster, which are not visible. It is definitely preferable to keep any piece of carbon fibre as continuous as possible. I did end up using quite a large number of separate pieces in order to add extra bracing in key locations.
I normally quote the vertical resonant frequency, which is the lowest fundamental of the system, as about 19.4khz. The actual calculated fundamental was 26khz. I quote at only 3/4 of this to allow for deficiencies in manufacture. It does mean that the actual fundamental will definitely be above my ageing audio band ~15khz.
Niffy
I had the carbon fibre I used specially laid up by the supplier. It has woven outer skins and a unidirectional middle layer that is normally aligned along the length of the carriage. Unlike normal preprepared carbon fibre the outer woven layers are orientated at +/-45°. This actually increases the longitudinal, lateral and torsional rigidity of the end structure. The carbon fibre is 0.75mm thick. The end grain balsa core of the top plate is 4mm making the whole thing 5.5mm. The buttresses are again balsa cored with a skin of carbon fibre on either side. The front and rear blocks are both balsa cored. There are internal carbon fibre components, especially in the rear section that supports the counterweight and adjuster, which are not visible. It is definitely preferable to keep any piece of carbon fibre as continuous as possible. I did end up using quite a large number of separate pieces in order to add extra bracing in key locations.
I normally quote the vertical resonant frequency, which is the lowest fundamental of the system, as about 19.4khz. The actual calculated fundamental was 26khz. I quote at only 3/4 of this to allow for deficiencies in manufacture. It does mean that the actual fundamental will definitely be above my ageing audio band ~15khz.
Niffy
Hi Niffy,
The carriage I posted is only the top section. The bottom was not glued on. I did this to test fit the wheels, which was a good thing as this is when I picked up the error in the m3 holes for the VEE screws. I have made a new top section.
I could not get balsa thick enough to use it as you did. I would have had to laminate it from multiple thinner sections. Which I thought would negate the weight advantage.
The top is 0.5mm carbon fibre with 3mm balsa core. The top section of CF I laminated 2 bits at 45deg to increase rigidity, making the top section 4.5mm
The carriage I posted is only the top section. The bottom was not glued on. I did this to test fit the wheels, which was a good thing as this is when I picked up the error in the m3 holes for the VEE screws. I have made a new top section.
I could not get balsa thick enough to use it as you did. I would have had to laminate it from multiple thinner sections. Which I thought would negate the weight advantage.
The top is 0.5mm carbon fibre with 3mm balsa core. The top section of CF I laminated 2 bits at 45deg to increase rigidity, making the top section 4.5mm
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I had to buy a 2by4 plank about 3foot long. I only used about 30mm of the length. Not the most economic use of materials.
Niffy
End grain balsa makes an excellent core material because it has a very high comprehensive rigidity to density ratio. Another materials that are commonly used are plastic or resin foams such as polyurethane and honeycomb aluminium or ceramic such as aerolam. Other wood types can be used but, like balsa, work best end grain.
I've never seen it used in this application but have a suspicion that end grain bamboo would work very well as a core material although I think that it would be better suited to other locations such as the sub-chassis or plinth.
I've never seen it used in this application but have a suspicion that end grain bamboo would work very well as a core material although I think that it would be better suited to other locations such as the sub-chassis or plinth.
A heavier carriage will better control the movement of the cartridge body at audio frequency especially in the bass. A lightweight carriage will load the bearings less and have lower friction and less lateral tracking error. There will also be a maximum weight depending on the type of bearing used. All of these factors have to be balanced. I chose to aim for a carriage weight of 55g. A lower compliance cartridge may prefer a heavier carriage though I would be hesitant to exceed 75g with my current bearings. It's all a balance of compromise.
Niffy
Niffy
Quarter grain balsa is used not only for the wing of the model airplanes, bur even for sailing boats (the real ones, not scale models) to build the in-famous* "sandwich" hulls. They use the balsa of a few cm, but not as we would do by gluing the planks, the fibers are instead arranged perpendicular to the outer composite layers, reaching an incredible stiffness. Difficult to use it with our carriages, but in your hands, why not?
carlo
infamous: magnificent rigid and lightweight boats. Until the water, sooner or later, finds a way to get into the sandwich: no breaks are needed, just the thru-hulls, the propeller or rudder axis etc. At that point the balsa becomes what it was in nature: a sponge. Never buy a used sandwich boat
carlo
infamous: magnificent rigid and lightweight boats. Until the water, sooner or later, finds a way to get into the sandwich: no breaks are needed, just the thru-hulls, the propeller or rudder axis etc. At that point the balsa becomes what it was in nature: a sponge. Never buy a used sandwich boat
When I say "end grain" I mean exactly the perpendicular you mentioned in relationship to sailing boats. End grain balsa has been used in several commercial hifi products most notably the sub-chassis of the pink triangle anniversary turntable and the cabinets of the giya speakers by vivid.
Niffy
Niffy
Back to my teen memories: we called "quarter grain" (in english, not knowing how to traslate the term of those imported items ) the stiffer planks, cut radially, and "tavole piane" (in italian) those softer and lighter, cut parallel from the outer layers. Someone sells "end grain" balsa of few mm thickness? interesting.
c
sorry, never heard before the term "end grain" in italian that cut is called "di testa" literally: from the head
sandwich boats were made with the excuse of lightness, but the real reason is that balsa is much cheaper than good glass fiber.
c
sorry, never heard before the term "end grain" in italian that cut is called "di testa" literally: from the head
sandwich boats were made with the excuse of lightness, but the real reason is that balsa is much cheaper than good glass fiber.
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Prototyping looks like this at this moment. Titanium armtube (100x6x4mm),
aluminum carriage and cartridge mounting plate (70/75 alloy, 8mm thick).
Carriage should weigh in at 50-60g incl cartridge and counter weight.
Rods will be polished 6mm H6.
The arm will rotate at the base and there will be some additional functions
added as well.
http://www.dahlbergaudiodesign.se/images/linear_18.png
aluminum carriage and cartridge mounting plate (70/75 alloy, 8mm thick).
Carriage should weigh in at 50-60g incl cartridge and counter weight.
Rods will be polished 6mm H6.
The arm will rotate at the base and there will be some additional functions
added as well.
http://www.dahlbergaudiodesign.se/images/linear_18.png
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Hi Carlo,
I've never seen end grain balsa sold in 3mm thickness. If I recall correctly I've only ever seen it in about 20mm thickness and then it was only sold as a full sheet, 2.4x1.2m.
Making your own is easy enough. You do what to start with wood with a reasonable cross section. Stick bits together with wood glue then cut with a saw to almost the right thickness then sand to the final dimension. I placed my balsa between two metal plates of the desired thickness so that when I sanded the balsa came out with a consistent thickness.
In this application the use of a core is to maximise the rigidity to weight ratio and not to save money.
A 5.5mm sandwich with 0.75mm skins and a 4mm core will only weigh 28% the weight of a solid section of the same thickness but retains 62% of its rigidity. The rigidity to weight ratio in this case is over twice that of the solid section. A major part of composite engineering is the use of cores, the cores are in many ways as important as the material and layup of the skins.
Niffy
I've never seen end grain balsa sold in 3mm thickness. If I recall correctly I've only ever seen it in about 20mm thickness and then it was only sold as a full sheet, 2.4x1.2m.
Making your own is easy enough. You do what to start with wood with a reasonable cross section. Stick bits together with wood glue then cut with a saw to almost the right thickness then sand to the final dimension. I placed my balsa between two metal plates of the desired thickness so that when I sanded the balsa came out with a consistent thickness.
In this application the use of a core is to maximise the rigidity to weight ratio and not to save money.
A 5.5mm sandwich with 0.75mm skins and a 4mm core will only weigh 28% the weight of a solid section of the same thickness but retains 62% of its rigidity. The rigidity to weight ratio in this case is over twice that of the solid section. A major part of composite engineering is the use of cores, the cores are in many ways as important as the material and layup of the skins.
Niffy
Surely you have a lot of patience, Niffy, and the talent to bring your realizations to the maximum level.
On boats that way they save tons of fiberglass (and a lot of cash); of course on our TAs it would be something less.
Once I had in my hands a carbon+aluminum honeycomb sheet for aeronatic use: impressive stiffness vs weight.
carlo
On boats that way they save tons of fiberglass (and a lot of cash); of course on our TAs it would be something less.
Once I had in my hands a carbon+aluminum honeycomb sheet for aeronatic use: impressive stiffness vs weight.
carlo
I would say no - because the bearings are open and any lubricant will trap dirt, as well as increase stiction. There is about 2 revolutions of the wheels per LP side so not even a lot of wear.
Should the steel/tungsten bearings be lubricated (silicone grease maybe) ?
just my point of view
direct experience: on ball bearings (rolling friction) oil increases the rolling stiction-friction of each ball (from some to many)
indirect web knowledge: on sliding friction (pin bearings - 0,1 π contact in your case) an oil film separates the two surfaces from scraping on each other. On watches the pivot has some play, and "swims" in a oil drop inside the jewel. 3-4 types of special oil are used, so the matter seems not simple.
direct experience : in pen tips their greasy ink works fine (better than silicone, no use to substitute). No oil instead between ball and vee cup: motion must happen just inside the pen tip, that's the reason to use them.
carlo
just my point of view
direct experience: on ball bearings (rolling friction) oil increases the rolling stiction-friction of each ball (from some to many)
indirect web knowledge: on sliding friction (pin bearings - 0,1 π contact in your case) an oil film separates the two surfaces from scraping on each other. On watches the pivot has some play, and "swims" in a oil drop inside the jewel. 3-4 types of special oil are used, so the matter seems not simple.
direct experience : in pen tips their greasy ink works fine (better than silicone, no use to substitute). No oil instead between ball and vee cup: motion must happen just inside the pen tip, that's the reason to use them.
carlo
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