Machine Video of a healthy (?) Kopp variator

[Birkhoff]

From time to time I hear owners of vintage lathes equipped with the iconic Kopp variator mechanical drive despair at the noise, complexity and cost of the units. I have never seen, however, a video of a working or a defective drive unit to help people with diagnosis. My late series Colchester chipmaster has one that seems to work fine. Here is a video of it running through speeds while I had the drivetrain disconnected to fix an extravagant oil leak coming out the rear of the input shaft in the headstock.

The annoying buzz in the background is my noisy RPC and has nothing to do with the variator.

Hope this is useful to someone.

 

[Tom Kitta]

Well, your RPC is indeed super noisy.

My variator is similar but more noisy by far a lot more high pitch noise. But the main issue is that at high speeds over 1500 rpm it may suddenly loose power if speed dail is moved too fast. Something goes BOOM and power is lost.

It is super noisy above 2000 and I am afraid to run it at max speed.

 

[mjautek]

I've got a Kopp variator in my Holbrook Minor that has given me a bit of grief lately...

long story long, I bought the lathe in mystery condition and used it for 4 years with no issues with the variator other than it being pretty loud above 2000 rpm. then earlier this year I decided to finally do an oil change... bought the proper stuff (morlina S2 BL10) from the UK and now my variator is super loud.

ripped the variator apart twice - once to lap the balls (I thought about grinding/hard turning the drive cones but ultimately did not because I don't know anything about grinding), and the other time I replaced the 6207 bearings on the input and output shafts... neither of these made things better. putting the old oil back in didn't do anything either. the howling noise is coming from the input side - the output side is also loud but kind of normal.
I've been using the lathe as it is but something will have to be done - it works but you really have to wear ear protection to use it, it's really that bad...

here's a couple of video clips if you want some idea of "normal" (before the oil change - this video was for showing lazy accel from the 2 speed gearbox clutches I think) and "bad" (after the oil change - I was too scared to run the lathe much but it's more or less the same minus the slipping/surging) sounds out of my variator

here's some pictures of the insides:

I really do like the idea of the variator - it's a pretty clever device and if you believe Allspeeds who makes them now, they should be quiet... I'd like to repair mine to keep my machine original but if I can't fix it I will probably rip it out

But the main issue is that at high speeds over 1500 rpm it may suddenly loose power if speed dail is moved too fast. Something goes BOOM and power is lost.

sounds like a preload adjustment issue? mine would also do this after reassembly but it's not so bad to dial out
(here's the manual in case you don't have it)

 

[Birkhoff]

TK, you are right, I really do need to get off my butt and sort out that phase converter. I thought it might be bearings in the idler, but replacing those made zero difference. Next step is to look for an electrical imbalance.

I'm cautiously monitoring my variator for oil leaks. Typically, I find the level down after a few months of ignoring it. If I systematically log it and find something significant, my idea was to pull it apart and reseal. Mjautek's experience suggests I should be cautious and not `mess with success' -- topping up a little oil from time to time is not a big deal. Now that the headstock is not puking out oil, I should have a chance to monitor the variator for same.

 

[Tom Kitta]

Ok - here is the noise mine makes -

 

[Birkhoff]

TK,
Ouch, that sounds quite bad.

It might be an idea to pull the two vee-belts and isolate it. On reassembly, I noticed that quite a loud and unusual ticking noise comes from the (new) belts and it can be modulated by varying the belt tension. This is apparently a known issue. I can remove the noise by running the belts rather sloppy for my liking. There is a note in the manual to set them with 3/4 inch slack on gentle pressure. A lot of variables in that statement, but 'on the loose side' seems to be indicated.

That said, it sounds kind of metallic and internal to the drive -- but who knows? There are a lot of other sounds in the video confounding things.

Do you have a supply of oil? I had to buy 19 litres so I have some that I can share. Running it to warm and dumping the oil might reveal something.

 

[Tom Kitta]

TK,
Ouch, that sounds quite bad.

It might be an idea to pull the two vee-belts and isolate it. On reassembly, I noticed that quite a loud and unusual ticking noise comes from the (new) belts and it can be modulated by varying the belt tension. This is apparently a known issue. I can remove the noise by running the belts rather sloppy for my liking. There is a note in the manual to set them with 3/4 inch slack on gentle pressure. A lot of variables in that statement, but 'on the loose side' seems to be indicated.

That said, it sounds kind of metallic and internal to the drive -- but who knows? There are a lot of other sounds in the video confounding things.

Do you have a supply of oil? I had to buy 19 litres so I have some that I can share. Running it to warm and dumping the oil might reveal something.

I have very little oil left - I just added some.

It does sound bad - I may take off the belts to see whatever it makes a difference. BUT, it seems to work - i.e. I use the lathe almost daily without a problem - I am just afraid to run it at full speed - at max.

I try to make it sloppy and see whatever it removes some of the noise.

With clutch engaged over 2000 rpm it does feel like the thing may explode

 

[Birkhoff]

That's a shame. I find myself taking advantage of the higher speeds available on the chipmaster for carbide; pretty much all negative aspect tooling in my arsenal. After running via seat of the pants for a while, I took the time to work out feeds, speeds and DOC by the book and even my offshore carbide is now producing good results. For the smaller (sub 1 inch) work, this frequently puts me in the upper half of the RPM range for the old chipmaster. I have now adjusted my seat of the pants metric, and I feel lucky to have the rpm headroom, and the power up there to push it.

DM me if you want some oil. Not sure the complexity of shipping oil, but I've heard it is done all the time ;-)

 

[Tom Kitta]

Well, I run out of ISO 18 oil but I am mixing ISO 15 oil (its totally like water) with ISO 22 or ISO 32 oil to get "ISO 18".

By any chance do you have electronic version of the manual?

I worked on 1in just an hour ago - got it precisely at 1in plus minus like a tenth. I run at max 1500 rpm. Soft steel - I think something similar to 1008. One problem I have is a lot of mystery steel and a lot of rather hard to work steel like 4330.

 

[Birkhoff]

This (below) is what I understand is the current equivalent of the recommended variator oil. Conveniently, it is also correct for the headstock on the chipmaster. When I purchased this a few years ago, it was not difficult to source through a local commercial oils outfit.

Mjautek provided a link to Allspeed's 'manual' and parts diagram in his post above. I have that, as well as some photo walkthroughs from the web, but a good start would be to scan through the linked manual which covers disassembly and assembly as well as adjustment.

 

[Tom Kitta]

Damm, just checked - I was under impression what I got in a bottle was ISO 18 and if I add any ISO 15 it would be too water like!

Turns out ISO 15 straight is actually... on the thicker side - the recommended oil is actually ISO 10 (!)

Maybe I should do an oil change? I mean the thing leaks so it sort of was changing oil itself and I was adding 1L of oil I got from someone till I run out few days ago.

 

[slow-poke]

Being an electronics guy, I'm always amazed at the lengths designers of yesteryear jumped through to accomplish something as simple as variable speed.

I replaced (IIRC) 217 custom parts in my lathe with two servo motors mated to a ball screw assembly. All of those parts were to simply control the leadscrews at the desired speed. Software doesn't break, have backlash, leak or require oil changes. Software can emulate a lot of mechanical things and do it for basically free once developed.

I also don't understand why they continue to make lathes with all those parts when that solution is so antiquated. I don't think the "because that's the way we've been doing it for the last 150 years is a good answer.

 

[PeterT]

Turns out ISO 15 straight is actually... on the thicker side - the recommended oil is actually ISO 10 (!)

Wow. I think ISO is a defined kinematic viscosity at 40C, so if your operating temperature is much above that, its not too far off the equivalent viscosity of water ( = 1.0 cS)

 

[Birkhoff]

Damm, just checked - I was under impression what I got in a bottle was ISO 18 and if I add any ISO 15 it would be too water like!

Turns out ISO 15 straight is actually... on the thicker side - the recommended oil is actually ISO 10 (!)

Maybe I should do an oil change? I mean the thing leaks so it sort of was changing oil itself and I was adding 1L of oil I got from someone till I run out few days ago.

The AllSpeed manual that Mjautek linked makes a big deal about using ONLY the Shell BL product. What they seem to be saying is there are other aspects than simply viscosity that are at play in the internals. I have no idea either way.
I do use vector drives on other machines I own, either for straight phase conversion or for that plus speed/direction control, but the ones I have seem to lose torque at the lower end of RPM (like frequency below 10 HZ) and the motors don't like to run there for long under load without supplemental cooling. My experience with the Kopp is that, while the range of speed is perhaps not as wide as the electronic solution (9:1 approx) the torque seems to stay constant down to the very lowest of speeds. And, there is no notchiness or cooling issue as the motor is running at constant speed.
The BL 10 is like baby oil. 19 litres weighs not much.