K8 rebuild. Motor trouble.

[TThomson]

Hey y'all!
So me and a friend started a rebuild of a K8 and now we're stuck on the motor. What we are doing is taking everything and making it its own separate unit.We removed the amp, motor and cutter and put them into their own external cases so we could get rid of the rim drive turntable to eliminate any motor noise and so we can easily hookup/fix any amp problem without having to go into the machine.
What we have here is the same motor, with a 1/4" pulley attached to the turntable. Now we just need to get the turntable to spin at 78rpm. We thought we had all the math right but somewhere we were off and The turntable spins too fast.
I attached so pics so you can see what we've done.
If ya have any ideas pleas let me know! Until then, back to the drawing board.
Thanks!

[Gus]

Hi,
if the motor is synchronus you can drive it electronically via motor inverter at any speed you want

http://www.ebay.com/itm/SIEMENS-MICROMASTER-420-AC-DRIVE-0-75kW-1HP-6SE6420-2UD17-5AA1-/252720590590?hash=item3ad7522efe:g:1Z0AAOSw241Ydr1D

more infos here

http://www.lencoheaven.net/forum/index.php?topic=11817.0

and here
http://lathetrolls.com/viewtopic.php?f=1&t=2505

http://www.floka.com/lofi/portable_lathe.html

http://lathetrolls.com/viewtopic.php?f=1&t=2308&p=12244&hilit=premotec#p12244

poor man's inverter is a car inverter 12volt to 110V or 220V through dc transformer 110v or 220v to 12v with Mark's Rob modification

[markrob]

Hi,

How far off are you?

Mark

[TThomson]

Hi,

How far off are you?

Mark

Pretty far. The platter is really spinning. We had the motor set up to a dimmer to try and slow it down some but that idea didn't work out that we'll.

[TThomson]

Hi,
if the motor is synchronus you can drive it electronically via motor inverter at any speed you want

http://www.ebay.com/itm/SIEMENS-MICROMASTER-420-AC-DRIVE-0-75kW-1HP-6SE6420-2UD17-5AA1-/252720590590?hash=item3ad7522efe:g:1Z0AAOSw241Ydr1D

more infos here

http://www.lencoheaven.net/forum/index.php?topic=11817.0

and here
https://lathetrolls.com/viewtopic.php?f=1&t=2505


https://lathetrolls.com/viewtopic.php?f=1&t=2308&p=12244&hilit=premotec#p12244

poor man's inverter is a car inverter 12volt to 110V or 220V through dc transformer 110v or 220v to 12v with Mark's Rob modification

Our motor is the stock motor from a K8

[Jccc]

Have you tried the original spindle adapter that goes on the k8 motor that makes it spin on 78?

From the looks of it that spindle adaptor you have on the motor might be too big?

[markrob]

Have you tried the original spindle adapter that goes on the k8 motor that makes it spin on 78?

From the looks of it that spindle adaptor you have on the motor might be too big?

Hi,

That's an excellent point! That pulley looks way too big in diameter. Can you run by your calculations that gave you that dimension?


BTW, you can't adjust the speed of an AC induction or synchronous motor by varying the voltage. You need to use an VFD (variable frequency drive) or inverter. They vary the motor speed by changing both frequency and voltage applied to the motor.

Mark

[Gus]

If i'm not mistaken the pulley works right at inner side of platter that means if you attach it at the outside it will run a little faster.
Cheap solution is to machine a new pulley
Gus

[TThomson]

Well I put the K8 spindle on it and it works perfectly. I was really surprised.

[Prestofan]

The pulley on the motor for the K8 is meant to run against a rubber rim on the outside of the turntable. Do you still have it, or did it not come with the K8. The rubber rim is about 1/2 inch thick, so your belt is a little more to the center than the outside of the rubber rim would be, so your speed is not as it should be, but a little off Possibly it won't make enough difference to bother you. You will know when you put a recording on another turntable.

Alan