A unipivot made from scrap

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IslandPink
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#211 Re: A unipivot made from scrap

Post by IslandPink »

Ant wrote: Mon Apr 05, 2021 7:06 pm
Counterweights with offset holes are a pain in the arse as the azimuth and tracking force adjustments are altered by each other. The mayware counterweight will also eventually creep downwards and cock the azimuth up, even with a replacement bush. Decoupling the counterweight in this way seems to muddy the bass response to me too.

The amount of things to consider isnt trivial.
I did also consider using a cursor weight on the arm tube to allow the effective mass to be altered, im still considering it if i can get away with a small weight, because it will alter the weight distribution and stability.

Further buggering about is required for that, maybe a small piece of stainless tube with a 12mm id and some felt inside to make it stay in place.
Hmmm
Goods point about the Mayware eccentric counterweight.
One of the things I did to get it to work with the Denon 103R is to add a second, brass, counterweight behind the standard one. This one is a concentric cylinder with a grub-screw. Maybe this helps the bass to be tighter.

As regards effective mass, it seems to me that adding weight at the headshell is the best way to do this - then it's a very short distance from the stylus to the inertia against which it works. I used lead plate - might have been something James suggested from Morsiani's work.
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#212 Re: A unipivot made from scrap

Post by Ant »

revision 6.

ImageCx unipivot rev:6 by anthony cresswell, on Flickr

changes as follows
1. counterweight stub is now aluminium instead of acetal
2. cart mount is now aluminium instead of acetal
3. arm tube damping is now 2 pieces, one 10mm long silicone piece right behind the cart mount and one 15mm long piece in the mouth of the arm tube where it meets the bearing housing. this is instead of 1 large 100mm piece in the rear of the tube where it meets the bearing housing
4. wiring now runs inside the arm pillar through a long slot that goes from right under the pivot to the shoulder where the diameter changes. this is soldered to a Cardas din socket, couldn't find an alternative to the Cardas one, which annoyed me because its diameter is 11.5mm, and the smallest hole i could bore on the lathe because of the boring bars i have is 12mm.... so i had to sleeve it with black nasty. which is a bodge.
this is causing even worse azimuth changes than the loop did. so i will have to go back to the loop.
the problem is that the arm tube is higher than the pivot is, so the wiring cant go straight out of the tube and into the pillar like a mayware can, and because it is higher, the weight distribution means it is more sensitive to where the wiring is than the mayware, where all the weight is lower than the pivot. so it doesn't care about the wiring
5. the angle of the outrigger for the bias guide is now sharper so that the pull on the wire is more square to the outrigger on the housing.

the changes to the wand have slightly reduced the effective mass from 8.8 to 8.3g

ImageCx unipivot rev:6 by anthony cresswell, on Flickr

sounds better though.
more thought required
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JamesD
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#213 Re: A unipivot made from scrap

Post by JamesD »

Nicely done - it certainly looks sharper now. Any idea which changes made it sound better?

ciao

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#214 Re: A unipivot made from scrap

Post by Ant »

The change that has made the most difference i think is the much smaller amount of damping in the arm tube.
The reason for the ally cart mount is to get the effective mass back up after removing the damping in the tube, and the ally stub was because the setscrew in the counterweight was gouging the acetal stub.

Ill have to make yet another wand because the bearing housing design needs to be altered so that somehow the wiring can come straight out of the top above the pivot.

I can take the ally cart mount, outriggers and bearing pin from this one, the counterweight and arm pillar from the one before so i dont have to make everything.
Hopefully i can get the ring weight out of this one otherwise ill have to make another....
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#215 Re: A unipivot made from scrap

Post by JamesD »

That all makes perfect sense! Driven by the need to reduce the dampening on the CF tube.... Is the effective mass that critical that the head shell change was necessary or are you ensuring the design parameters are met? Just curious - I think it looks better and if it sounds better or tracks better that's even better :-)

Looking forward to next version now - its inspiring me to complete my design then I just have to build it...
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#216 Re: A unipivot made from scrap

Post by Cressy Snr »

I would try to increase the mass of the outrigger weights first before abandoning the idea of the wires being internal to the arm.
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#217 Re: A unipivot made from scrap

Post by Ant »

I originally wanted the effective mass to be around 9/10g so that it would be fairly universal in terms of the cart compliance, so the 8.8 it was was about right. Without the damping in, the first carbon fibre wand came out about 7g which was abit too low, so the damping was adding a fair bit of mass.

However, being over damped it had the oddness to it i couldnt put my finger on. I reckon it had pulled the resonance of the assembly too far down.
This one immediately sounded more like it.

So the ally cart mount was driven more by the design goals that i set than by what i thought it would do to the sound.

I did add the small silicone damping part right behind it to try to offset the ringing i expected from the aluminium part though after considering what it might do.

I could add a small steel weight into the space behind the cart mount if i wanted some more effective mass, the cart mount goes 10mm into the tube and there is 20mm of space from the front of the tube to the exit hole for the wiring.
That hole can go wherever, so i could move it back by say 5mm so there is space for the mount, the silicone tube damping and an additional mass weight. Id rather do that than changing the delrin cart mounting plate for something heavier as i think that that initial interface between the cart and the arm kills a little bit of the hf resonance in the assembly so i want to keep that
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#218 Re: A unipivot made from scrap

Post by IslandPink »

Ant wrote: Tue Apr 27, 2021 9:37 pm I originally wanted the effective mass to be around 9/10g so that it would be fairly universal in terms of the cart compliance,
Oy !
Some of us out here use Denons !
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#219 Re: A unipivot made from scrap

Post by Ant »

Just attempted to turn up some heavier lateral weights to try, abandoned it because this lathe steadfastly refuses to part steel. Its just not rigid enough.
Tried everything, cutting fluid, perfectly centred tool edge, various speeds, hss and carbide, and locking the gibs down tight.
It starts to pull the top slide down alarmingly as soon as any real pressure is applied
Fine with brass or aluminium, steel, it just doesnt want to know.
Bugger.
Cant even cut it then face it because its too short for the chuck to grab it and keep it square
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#220 Re: A unipivot made from scrap

Post by JamesD »

Oy !
Some of us out here use Denons !
That's what 50p pieces and AAA batteries are for :-)
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#221 Re: A unipivot made from scrap

Post by Paul Barker »

Ant wrote: Wed Apr 28, 2021 12:44 pm Just attempted to turn up some heavier lateral weights to try, abandoned it because this lathe steadfastly refuses to part steel. Its just not rigid enough.
Tried everything, cutting fluid, perfectly centred tool edge, various speeds, hss and carbide, and locking the gibs down tight.
It starts to pull the top slide down alarmingly as soon as any real pressure is applied
Fine with brass or aluminium, steel, it just doesnt want to know.
Bugger.
Cant even cut it then face it because its too short for the chuck to grab it and keep it square
I have same issue
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#222 Re: A unipivot made from scrap

Post by Ant »

Yep that the issue with most if not all lathes this size, they will face and turn steel perfectly well, but this arent big enough to part it.
Only other thing i could try would be to get hold of one of those thin hss parting tools that have a holder, but they look too fragile for steel to me. Id rather not get a face full of shattered hss if it went, and it wouldnt solve the inherent rigidity issue.
Perhaps mine is abit too old and worn out and a new one would do better....
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#223 Re: A unipivot made from scrap

Post by vinylnvalves »

If steel is an issue use brass it is denser any way so you can get away with a smaller size (it’s only 10% denser). It won’t corode/tarnish as quickly either - cosmetic stainless is easy to machine too. BTW Those thin parting off tool do break - even when machining soft materials. I have issues parting off with my S&B 1024 big items. I generally saw off and true up the face.
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#224 Re: A unipivot made from scrap

Post by Ant »

Yep sawing off and facing is my usual way of doing it, just the small size prevented that this time.

I need to get some more brass in, and also to stop using black bar. Ok for prototyping but no idea what grade it is. I should really get some decent free cutting steel in

I could do with a new parting tool, the hss one and the brazed one arent the best, the hss one has been reground a couple of times now. Ill not bother with the thin hss bladed ones.

I found some brass standoffs on ebay that will do the job as weights, 16mm diameter by 10mm length with an m4 threaded hole in the centre so ive bought them to use as weights. Should be around 15g each, 3 times the weight of the current ones. Adding around 30g 10mm lower than the pivot should hopefully brute force around the wiring problem.
We shall see
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#225 Re: A unipivot made from scrap

Post by Ant »

No the heavy lateral weights dont brute force around the azimuth problem.
There would need to be a fundamental design change to get it to work.
Balls
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