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Old 27th February 2020, 09:39 PM   #3511
dahlberg is offline dahlberg  Sweden
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Quote:
Originally Posted by niffy View Post
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.

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Old 28th February 2020, 05:17 AM   #3512
nocdplz is offline nocdplz
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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
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Old 28th February 2020, 05:39 AM   #3513
niffy is offline niffy  Europe
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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
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Old 28th February 2020, 06:08 AM   #3514
nocdplz is offline nocdplz
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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.

Last edited by nocdplz; 28th February 2020 at 06:24 AM.
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Old 28th February 2020, 09:16 AM   #3515
dahlberg is offline dahlberg  Sweden
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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.

Click the image to open in full size.

http://www.dahlbergaudiodesign.se/images/linear_18.png
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Last edited by dahlberg; 28th February 2020 at 09:34 AM.
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Old 28th February 2020, 10:46 AM   #3516
niffy is offline niffy  Europe
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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
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Old 28th February 2020, 11:53 AM   #3517
nocdplz is offline nocdplz
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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
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Old 29th February 2020, 10:16 PM   #3518
dahlberg is offline dahlberg  Sweden
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Should the steel/tungsten bearings be lubricated (silicone grease maybe) ?
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Old 1st March 2020, 12:34 AM   #3519
warrjon is offline warrjon  Australia
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Originally Posted by dahlberg View Post
Should the steel/tungsten bearings be lubricated (silicone grease maybe) ?

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.
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Old 1st March 2020, 06:58 AM   #3520
nocdplz is offline nocdplz
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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

Last edited by nocdplz; 1st March 2020 at 07:07 AM.
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