Garrard AT-6 autochanger, idler wheel dia?

[Al (astral highway)]

Hi,

I'm restoring this AT-6 autho-changer (as well as the Dansette Hi-Fi amplifier MKI that helps it realise its ambitions, for someone else.

I've removed and de-greased the idler wheel, which was covered in machine oil.

I'm just checking, what's the diameter of a new wheel (ie not worn), before I replace it an circlip it back.

Also...

Has anyone found slippage of the wheel on the spindle? What's the remedy?

[Station X]

The diameter of an idler wheel is immaterial unless it's worn so small that it does not grip the motor shaft and turntable rim.

[BRASSBITS]

Garrard wheels are 40mm but as Graham says the diameter plays no part in speed accuracy

[Al (astral highway)]

Thanks Graham and brassbits...

What about the wheel slipping on the spindle? It’s only push-fit, so why wouldn’t it slip?

[Station X]

Sorry, but I don't understand the question. Is the (idler) wheel required to drive the spindle it's mounted on?

[Herald1360]

Spindle = motor shaft?

[Station X]

Possibly, but that would be fitted with a pulley, not an (idler) wheel.

[leslie5555]

Originally Posted by Herald1360

Spindle = motor shaft?

I think what Chris means is that the o/p is referring to the motor pulley but calling it a spindle? (maybe)

[BRASSBITS]

Originally Posted by astral highway

thanks graham and brassbits...

What about the wheel slipping on the spindle? It’s only push-fit, so why wouldn’t it slip?

post a picture to show what you mean re spindle

[Edward Huggins]

The AT6 idler wheel should rotate freely on its own spindle mount.

[AC/HL]

Originally Posted by astral highway

Has anyone found slippage of the wheel on the spindle? What's the remedy?

The turntable is immaterial. All rim drives, auto or manual, rely on friction to drive them. Astral has cleaned and de-greased the idler. The turntable rim, and the motor spindle will also require cleaning and de-greasing of course, due to cross contamination, and all must be free running. The idler shouldn't be excessively hardened, possibly the most common problem with half century old turntables. That's all that's needed to work as designed.
Other problems relate to drag in the auto mechanism or excessive pickup tracking weight.

[ms660]

Originally Posted by astral highway

Has anyone found slippage of the wheel on the spindle? What's the remedy?

Check spring tension.
Check clean enough.
Check lubed enough.
Rough up rubber.
New idler.
Rebuilt idler.
Replace idler with a homebrew DIY job....that's been covered on this forum somewhere, basically a stock plastic or metal wheel with a stock O ring or square section ring glued to it or the old one machined down a bit to take a square section ring glued to it.

Lawrence.

[terrykc]

I think the OP is getting confused between the rubber idler wheel and the stepped motor drive wheel.

The stepped wheel slipping is a common fault and for the best long term method of fixing it, copy the way that tyres are fitted on railway wheels.

What happens is that the motor is somewhat inefficient and runs very hot. In manufacture, everything is assembled at room temperature and relies on a pointed grub screw being tightened so much that the point makes a slight indentation in the motor spindle.

In use, the motor spindle and drive wheel get very hot, which loosens the screws grip but, for some time, the small indentation and the point remain engaged and all is well.

I assume that the repeated expansion and contraction eventually blunts the screw point slight;y until one day, when everything gets nice and hot, it is able to escape from the indentation and the turntable stops.

Switch off, wait for it to cool, and it will work normally - for a time ...

For a permanent cure (I fixed no end of these and never had one bounce) my method is as follows.

Use the transit screws to clamp the changer so that it doesn't wobble around.

Check, whilst cold, that the drive wheel height is correct by checking that the idler sits in the middle of each step as the speed is changed, then set the speed selector mid-way between two speeds so that the idler is retracted away from the drive wheel.

Switch the motor on and leave running for at least half an hour.

In the meantime, modify a pair of pliers by wrapping something insulating, such as a strip of cloth round the jaws. This serves two purposes: it avoids damage to the wheel and stops the wheel being cooled down while it is fastened in place - it is vital that it stays hot.

Don't touch the hot drive wheel with bare fingers!!

Switch off the motor and, with a bit of cloth round a finger, rotate the drive wheel - if necessary - so that the grub screw is in a suitable position. To help avoid moving the vertical position of the wheel, keep the finger in place whilst starting to tighten the grub screw. However, don't apply any undue pressure, as you are certain to end up with the blade embedded in your finger! Use the insulated pliers now to hold the wheel firmly in place while you finish tightening the screw as tight as you possibly can.

You can, of course, tighten the screw without heating the motor/drive wheel combination but it won't be such a permanent fix.

[Edward Huggins]

Originally Posted by terrykc

I think the OP is getting confused between the rubber idler wheel and the stepped motor drive wheel.

This now confuses me, surely on a Garrard AT6, they are the same thing?

[BRASSBITS]

Originally Posted by Edward Huggins

This now confuses me, surely on a Garrard AT6, they are the same thing?

I think / assume he is calling the stepped pulley on the motor shaft a motor drive wheel

[Herald1360]

Isn't a pulley a wheel with a rim profile suitable for driving a belt? Otherwise it's just a wheel.

Whatever..... there's a motor with a shaft, axle or spindle which may itself be stepped or it may have a stepped wheel attached. This drives the idler wheel which spins freely on its spindle or axle which in turn drives the platter either directly or via a secondary rim attached to the platter.

A decent annotated picture showing all the bits in question would save all the confusion over terms and probably another thousand words discussing them. Unfortunately, I don't have one to attach!

[Station X]

I'd always assumed that a pulley was something which drove, or was driven by, a belt. The belt itself could take many forms. However, as far as turntable drives are concerned, the term pulley is also used to refer to the stepped portion of the motor shaft. Whether this is correct terminolgy I don't know, but it's certainly in common use.

We need an update from the OP which will hopefully put an end to our speculating.

[BRASSBITS]

Originally Posted by Herald1360

Isn't a pulley a wheel with a rim profile suitable for driving a belt? Otherwise it's just a wheel.

Whatever..... there's a motor with a shaft, axle or spindle which may itself be stepped or it may have a stepped wheel attached. This drives the idler wheel which spins freely on its spindle or axle which in turn drives the platter either directly or via a secondary rim attached to the platter.

A decent annotated picture showing all the bits in question would save all the confusion over terms and probably another thousand words discussing them. Unfortunately, I don't have one to attach!

Fresh out of a Garrard exploded view, part number 58646 motor pulley 50hz

[Herald1360]

Errrr........ where?

Missing attachment?

[BRASSBITS]

Originally Posted by Herald1360

Errrr........ where?

in any Garrard service manual exploded view
vinyl engine list most models