Hi all,
Few questions on unipivot geometry:
Tha shaft will be made from SS,any sugestions for cup materials?
Could I go with Delrin?
What would be the best tip geometry: very sharp or should it have a small radius?
Would appreciate any comments.
Attached is a drawing of my initial thoughts
Thanks
I.k.
Few questions on unipivot geometry:
Tha shaft will be made from SS,any sugestions for cup materials?
Could I go with Delrin?
What would be the best tip geometry: very sharp or should it have a small radius?
Would appreciate any comments.
Attached is a drawing of my initial thoughts
Thanks
I.k.
Thanks EC,
While I couldn't find your post with the pic, I did find a thread where you mentioned that the pivot point should be as close as possible to the record plan.
On other posts I've been reading that the pivot point should be in the center line of the arm tube. (that is arm radius + cartrige hight abouve the LP).
Could you elaborate on the best hight for the piivot point ?
Also, did you use any dumping fluid in your design ?
Thanks
Izhak
While I couldn't find your post with the pic, I did find a thread where you mentioned that the pivot point should be as close as possible to the record plan.
On other posts I've been reading that the pivot point should be in the center line of the arm tube. (that is arm radius + cartrige hight abouve the LP).
Could you elaborate on the best hight for the piivot point ?
Also, did you use any dumping fluid in your design ?
Thanks
Izhak
For minimum wow as the arm rides up and down a warp, the pivot should be at record height. Additionally, if the pivot is at record height, any tendency for the arm to yaw merely reduces stereo crosstalk rather than changing the tracking force on either side of the record groove.
For a unipivot to be stable, the centre of gravity must be below the pivot point. That's why all unipivots have underslung counterweights. Some unipivots deliberately raise the pivot height in the mistaken belief that this improves stability. It doesn't, all it does is lengthen the pendulm, which lowers the resonant frequency. Because there are fewer oscillations per second, it is far harder to damp a low frequency oscillation. Thus, the ideal unipivot has its C of G just below the pivot.
Yes, my unipivot uses damping fluid. It's in the annular trough.
The picture is there, you just have to click to download it.
For a unipivot to be stable, the centre of gravity must be below the pivot point. That's why all unipivots have underslung counterweights. Some unipivots deliberately raise the pivot height in the mistaken belief that this improves stability. It doesn't, all it does is lengthen the pendulm, which lowers the resonant frequency. Because there are fewer oscillations per second, it is far harder to damp a low frequency oscillation. Thus, the ideal unipivot has its C of G just below the pivot.
Yes, my unipivot uses damping fluid. It's in the annular trough.
The picture is there, you just have to click to download it.
Glad you like the arm.
I'm afraid I haven't done full drawings. When I did the drawings and explanation for the headshell, I realised that it would be a huge amount of work. Realistically, if you're capable of making it, you're capable of working out most of the details from the photograph.
The damping trough is the big 45mm diameter moat that the tapered pins either side of the bearing housing dip into.
I'm afraid I haven't done full drawings. When I did the drawings and explanation for the headshell, I realised that it would be a huge amount of work. Realistically, if you're capable of making it, you're capable of working out most of the details from the photograph.
The damping trough is the big 45mm diameter moat that the tapered pins either side of the bearing housing dip into.
Hey EC and everyone else,
Any explanation why this arm works so good ?
The pivot is very high (abouve record) and the weight COG is so low.
http://www.enjoythemusic.com/magazine/equipment/0701/rslabs.htm
Thanks
Izhak
Any explanation why this arm works so good ?
The pivot is very high (abouve record) and the weight COG is so low.
http://www.enjoythemusic.com/magazine/equipment/0701/rslabs.htm
Thanks
Izhak
I can't see any reason for that arm to sound good. Call me boring if you like, but I like to see designs based on proven physical laws and engineering. Still, it would be easy enough to copy if you wanted to try it out. If you're not going to use a tube (which is conventional, but handy when you have a lathe), why not use balsa for the arm?
Stormy Weathers
Wood is a fine material to use, Nature's own fiber-reinforced composite. And it can be cut to shape with pretty inexpensive tools (e.g., jigsaws). I've owned a couple of wooden arms and was quite impressed at how well they worked. Given where most of the mass is (away from the highest moment arm points), there's not too much disadvantage in using a stiffer wood than balsa- IIRC, the Rek-O-Cut was walnut as was the Weathers.
Ebony would look really cool.
Wood is a fine material to use, Nature's own fiber-reinforced composite. And it can be cut to shape with pretty inexpensive tools (e.g., jigsaws). I've owned a couple of wooden arms and was quite impressed at how well they worked. Given where most of the mass is (away from the highest moment arm points), there's not too much disadvantage in using a stiffer wood than balsa- IIRC, the Rek-O-Cut was walnut as was the Weathers.
Ebony would look really cool.
As you say, the mass of the arm itself isn't that important - it's mass at or near the headshell that's important. I suggested balsa for its damping properties (the lunar lander used balsa in its shock absorbers!). Another possibility would be to build up a balsa/hardwood plywood and bury the arm wires inside it. That way, the wires wouldn't be able to rattle, and the wood could be cut with a knife, then clamped in a Workmate or similar. Very much kitchen table stuff.
Well, as you recall, the lunar lander didn't have to be reused. Balsa is wonderfully crushable. "You can successfully play the Telarc 1812. Once."
It would be an interesting exercise to use sheets of wood, cut and built up layer by layer, to give a final structure that is optimized by FEA. This is analogous to some of the oddly shaped speaker cabinets that have been posted here recently, built up from stacked laminations. Kitchen table stuff, ahhhh!
It would be an interesting exercise to use sheets of wood, cut and built up layer by layer, to give a final structure that is optimized by FEA. This is analogous to some of the oddly shaped speaker cabinets that have been posted here recently, built up from stacked laminations. Kitchen table stuff, ahhhh!
Rolled wooden tubes
It is possible to roll up balsa sheet and glue the edge together to form a tube. Model aeroplane modellers have being doing this for years, indoor free-filght planes in the 1 gram class have rolled tube fuselages on 10 mm diameter that resist the force of a fully wound rubber motor and can fly for 30 to 60 + mins.
These are made by soaking the balsa, rolling it around a cylinderical former (tapered ones are also used) then when the wood has dried gluing the seam together to get a tube made from a single layer of balsa wood.
This can also be done with conventional wood veener by soaking it in water applying glue and rolling it arround a former to get a multiply construction. I made one of these from cherry veneer a few months ago and it worked well. I finished up with a 12 mm outside diameter tube 260 mm long with 2 ply thick walls, very light and stiff.
It is possible to roll up balsa sheet and glue the edge together to form a tube. Model aeroplane modellers have being doing this for years, indoor free-filght planes in the 1 gram class have rolled tube fuselages on 10 mm diameter that resist the force of a fully wound rubber motor and can fly for 30 to 60 + mins.
These are made by soaking the balsa, rolling it around a cylinderical former (tapered ones are also used) then when the wood has dried gluing the seam together to get a tube made from a single layer of balsa wood.
This can also be done with conventional wood veener by soaking it in water applying glue and rolling it arround a former to get a multiply construction. I made one of these from cherry veneer a few months ago and it worked well. I finished up with a 12 mm outside diameter tube 260 mm long with 2 ply thick walls, very light and stiff.
Well, the tricky part of that particular design is the pivoting headshell. It appears to be free to pivot 6 degress in either direction, and has a bearing to assist this. Is it constrained at all in this arc? or is it free?
Maybe it sets itself to the perfect geometry relative to the groove this way.... Can it resonate laterally?
Maybe it sets itself to the perfect geometry relative to the groove this way.... Can it resonate laterally?
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