Switch too stiff for Marconi knob

[abeLovesDIY]

I'm trying to finish this PM1000 dual channel rehousing. Channel 2 went pretty good. I added shaft adapters with a bit of glue to the original 1000 pot shafts in order to use Marconi knobs. But the Preamp switch for channel 1 is very stiff, and the marconi knob just slides on the shaft adapter instead of catching hold. I have used a screw drive to turn the switch and can confirm that the shaft adapter is staying in place. As a test I put a bit of heavy dusty masking tape around it, and the marconi's set screws tore a neat line through the tape. Any ideas that don't involve replacing the switch? I'd really prefer to not go that route...
Deoxit doesn't seem to have made a great change.

 

[ubxf]

Would it help to file the side of the shaft to create a flat surface so the set screw doesn't rotate around ?

 

[cardboard]

Hello Abe,

1. Gunky grease? Switch may need a bit of lubricant on where the shaft rotates.
2. For the 'denting' ation, your switch has a ball that is being pushed onto a bumpy rail by a leaf spring. Your spring pushes too hard. Most of them do. Loosen the spring slightly by sticking a modest-sized screwdriver between spring and the metal structure it rests on, and turn the screwdriver. Stay a bit away from the ball.



Gentle and careful but deliberate and firm at the same time. You're unstiffening the leaf spring now. Do it on the other side of the ball as well, to stay symmetric. Rotate the switch and judge the result every time you've turned the screwdriver, since too far cannot be corrected easily. See picture.

Good luck,

M

ps: great project!

 

[Whoops]

As a test I put a bit of heavy dusty masking tape around it, and the marconi's set screws tore a neat line through the tape.

Can you drill some small holes in the shaft in order for the set screws to have an excursion into the shaft?

I think that would work well

 

[Tubetec]

Normally large multiway rotaries come with D shafts made of steel ,
A splined alloy shaft with a brass insert your going to have wear problems sooner or later ,
Good idea to loosen out the leaf springs a bit and maybe lubricate the shaft in its housing . For long term reliabillity maybe a dial with a splines is best if you can find one in the Neve Style .
The other thing I sometimes do with splined shafts is cut a small piece of metal and super glue it into the shaft slot ,makes it much stronger ,especially if theres a set screw digging into it .

 

[abeLovesDIY]

Hello Abe,

1. Gunky grease? Switch may need a bit of lubricant on where the shaft rotates.
2. For the 'denting' ation, your switch has a ball that is being pushed onto a bumpy rail by a leaf spring. Your spring pushes too hard. Most of them do. Loosen the spring slightly by sticking a modest-sized screwdriver between spring and the metal structure it rests on, and turn the screwdriver. Stay a bit away from the ball.

View attachment 99621

Gentle and careful but deliberate and firm at the same time. You're unstiffening the leaf spring now. Do it on the other side of the ball as well, to stay symmetric. Rotate the switch and judge the result every time you've turned the screwdriver, since too far cannot be corrected easily. See picture.

Good luck,

M

ps: great project!

This worked for me! Thank you!