DIY Audio General - stuff you're making, tips, advice sought, etc

Pulley looks interesting, one of yours Bob?

…How did you get on with the bushes?

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Yes, one of mine. Some work to do yet on the final design to maximise potential. This will include a new bake disc design.

Top bush replaced, have access to accurate pillar drill next week, so will set about the lower bush. Two copper rivets, Garrard design engineer was having a laugh!

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what-do-we-say-that

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Wait until the reaming starts, only way to ensure a snug fit :ok_hand:

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Today a little progress on my star tracker. My first 3D printed part arrived it was quite exciting.
It fitted on my tracker design without fuss and has eliminated a lot of slop.
I can now stretch to an hours tracking (theoretically) without having to move the camera.
Also I have managed to copy and paste a stepper motor drive program into the microprocessor I have so I have the approx angular rate of movement that I need. Next up to get to grips with PWM to help fine tune the speed. Also quite pleased that after two days effort I have managed to understand how to use the Onshape 3D cad program. It was much easier than I thought and I created an assembly of my tracker in parallel with watching youtube tutorials. I didn’t create the camera and lens in the assembly below but did all the rest from scratch.

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The new Al pulley 33/45 and new eddy brake disc. Managed to shave 20gms (nearly 3/4 Oz for any Fail readers) off the original Garrard component weight, about 40%. Will fit up tonight and check reduction in vibration.

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From what points are you measuring the reduction in vibration Bob?
I can see the reduction is mass may well be a good idea, wondering what frequency the bronze is resonating vs Ally? - The speed disk looks reassuringly substantial

The brake disc is the same thickness as the original, smaller diameter and without the brass insert in the centre. That insert is essentially peined in place, over time that only had to move a hundredth of a mill and it’s out of balance. I’ll get mine dynamically balanced later, shouldn’t need much as it’s a one piece machining.

The aim is to reduce mass above the top bearing of the motor, what changes is the force exerted by the vibrating mass as it oscillates, it reduces. The driving frequency is around 28Hz plus harmonics.

Just a very coarse measurement atm, a comparator. Literally running a rizla around the edge of the disk as well as the pulley, gives a good indication of radial movement.

Once fitted, will short out the motors suspension and measure from the garrard top plate.

Wow, got any smarts I can borrow for a bit ? :slightly_smiling_face:

I should add, the frequency won’t change, that’s dictated by the motor speed and is the driving frequency. Imagine you are viewing this from the side such that you have no indication it’s rotating. What you will see is the pulley moving left to right by a distance dictated by the bearings and at a frequency of some 30hz. In simplistic terms, reduce the mass of the pulley and you have a lighter hammer :grin:

In my parallel universe I know I understand this. In this one, however, my understanding is… mnngghb@@%nnngblahblahblah

I guess measuring vibration of the idler when turning would be informative (being one of the two channels responsible for transference to the platter / record / stylus etc - Perhaps measuring from the idler housing top plate?)

Speed disk does look nice, getting them as flat as possible goes a long way to cutting back on additional stator wobble. Speed disks are often chewed, sof ally (More so with the 301 due to the magnet jaws) People moving decks about without the transit clamp even for cleaning can lead to buckle / scrapes, gouges etc

One day I’ll hook something up to the idler top bearing. I suspect one of the reasons Garrard used a rubber idler disc was to help damp the motor down. I’ll see if the nice lab rats at work will do some measurebating for me, a packet of hobnobs should do the trick.

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Nice to see the side by sides, I’ve not tried a smaller disk before - Have you had it spinning yet?

Not yet, wine stopped play, one for the morning. Looking at those original discs, no machining marks at all, I’d hazard they were pressed. Makes sense given the tens of thousands they would have used across their range.

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All fitted and running, quiet and smooth. Had to take a saw file to the speed control lever cam under the rotary knob just to allow the brake to engage a touch more. Used the adjuster underneath the brake lever boss to set the gap to 0.1mm. Unloaded, speed adjuster is hard left with less than 0.3% overspeed. Loaded with stylus then speed can be adjusted bob on with rotary knob just to left of centre, engaging about half the magnet.

Next month will strip the motor, change bearings and check resistance of coils to make sure they are balanced.

Just finishing off the underside of the plinth with a machined tone arm cable exit.

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Bob’s timeline:

Aug 2022: tinkering
Aug 2023: retired
Aug 2024: dividing time between manufacturing TTs and fighting zombie-apocalypse

image

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