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Linear tracking turntables, whatever happened?

Curious as to the demise and downfall of the seemingly short lived linear tracking TT.
Just from a geometry point of view I would have thought a linear arm should be superior to one with a fixed pivot that sweeps through an arc.
Obviously there is much more to it than that, sort of the reason for this thread.
I am genuinely interested in trying one out for myself as well.
128x128uberwaltz
ct0517's avatar
ct0517
2,041 posts
 
@whart 
I doubt the arm design has changed. See what Franc says. Myself, I would be tempted to remove your counterweight and bring into a machinist. He can make up new counterweights for you using the thread pattern the rod uses and in whatever material you like to match your arm. i can't see the cost been alot and the reason I mention it. You could start by having him make something that will work. Then if the difference is dramatic, have counterweights made in the material you prefer.   

From the looks and angle of the picture it looks you are giving up 15 -20 % leverage (physics)
If its a cartridge you are going to keep on there for the long term its worth pursuing. With vinyl rigs I have always found that it is the attention to the small details that make big differences.
whart's avatar
whart
3,050 posts
 
@ct0517 - thank you. The FAQ on Franc’s site talks about an optional lighter counterweight. The Airtight Supreme is going to get rebuilt very soon, and I may also try a couple other cartridges, but I guess what you are suggesting is what- smaller lighter weight to go further back on that rod further away from the headshell? My bet is Franc could probably supply those without much trouble, but yeah, there are a couple of pretty good people here who rebuild vintage bikes, do basic mechanical work, so getting it done isn’t a problem, knowing exactly what to ask for is my challenge.
Or, re-reading, it is a materials issue, not just a weight/balance issue?
ct0517's avatar
ct0517
2,041 posts
 
@whart
you can take your counterweight as is into a Home Depot right now and go to the bolts section. they have a rack with bolts sticking out. See which of the bolts it threads into. Coming from Europe it will be metric. That gives you the thread pattern information. Then you can pick up a few nuts fatter and skinnier with that thread pattern and use those to test with. Use as many as needed to get it to the end of the rod. Once the number of bolts required is known - take them into the machinists/bike people and see if they can make you up one nut in that weight and thread pattern.
DIY
whart's avatar
whart
3,050 posts
 
10-4, @ct0517 - very helpful. Thanks. 
bdp24's avatar
bdp24
9,865 posts
 

My knowledge of physics is rather limited, so let me ask those of you who finished high school (;-) if the following is correct:

To achieve higher moment-of-inertia (same as mass?) in the vertical plane, the mass of a counterweight should be located as near as possible to the line described by the arm tube running through the arm’s bearings. In other words, extending left and right of that line in the lateral (horizontal) plane as little as possible, i.e. as close as possible to the arm's bearings laterally. The opposite of that is the Groovetracer counterweight made for Rega arms, which is in the "longhorn" style---extending a couple of inches to the left and right of the rear stub onto which it is installed.

If the above is true, I can envision, say, lead weights being attached to a counterweight above and below the hole running through it for the arm tube’s rear stub, but not to either side of that hole. Correct?

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