Some literature here in post #7:

https://www.mig-welding.co.uk/forum/threads/how-do-you-open-a-kopp-allspeeds-variator.55125/

Edited By Pete Rimmer on 16/11/2020 18:42:37

It may just need adjusting. If you can adjust the play out and it quietens it down you can fill it with new oil and you should be good for years to come.

The only potential issue with replacing a variator with a VFD is loss of torque and power at lower rpm when retaining the standard motor. Variator speed range is, typically, around 8 to 1. More than a VFD can deliver without significant compromise on either power output, speed range or motor size.

Rule of thumb for home shop guy or gal with a modern VFD is:-

2:1 change – you will almost certainly never notice any power issues

4:1 change – should be fine but you may need to alter gearing or belt drive rations to keep power up at lower revs. Generally high speed means small work which needs less power so gearing down to keep power up at low speeds works fine as any losses at high speed due to fall off in motor efficiency will be immaterial.

Flat out on a Chipmaster is scary anyway!

Over 4:1 change you need to get your engineers hat on and sort out the best compromise for your work.

I've always felt that a two speed intermediate drive sorts all the potential issues with using a VFD to replace either variator or Reeves drive unless the application is very demanding needing full power at all speeds. I'm surprsied that no-one markets a simple drop in unit for this sort of thing at reasonable price. Basically two input pulleys with dog clutch selector and one output. How expensive can that be?

In practice many folk find it perfectly acceptable to set the 4:1 range over which the VFD power variation is acceptably modest to cover most of their work and just cope with the occasional times when a bit more oomph would be nicer.

Clive