AVO VCM roller switch - how stiff to rotate?

[woodchips]

I have done some hunting using search to find this information, sure I have seen it, but where?

Just how stiff should the roller switches on the Avo VCM's be?

I bought mine when they turned up in sales other than a Mk2 bought off this forum long ago. So not any of them in years, just looking at them to possibly get sorted and functional. All the switches need a thumb nail to push the castellation to turn the switch. Using the ball of the finger friction wasn't anywhere near enough, need the physical drive by the nail.

Do they free up with use, or get worse?

There are lots of posts about don't use liquid lubricants, possibly dried up grease in the switch, how fragile they are and many more. What I didn't find was a whole thread devoted to repair and restoration of these switches. They are what makes the VCM's so usable, quick to operate and obvious to the position set.

Looking at the photos of their innards, they do not look like something easily made as spares. Can rods of silver solder be used in place of the switch contacts?

The search does a logical OR of the terms, seems why it comes up with so many unwanted hits, can this be changed?

[Electronpusher0]

I am sure others will come in with more experience but my advice would be that if you can rotate them without needing so much force as to risk breaking them then leave well alone.
The roller switches on my 2 panel AVO were too stiff so I stripped them and rebuilt them.
I did not use ANY solvents or solutions on the plastic (bakelite) parts, just wiped them off.
The contacts I cleaned with lead free flux remover (thats remover fluid for use on lead free solder) as I find that is best to remove the black tarnish.
I reassembled using petroleum jelly as lubricant including on the contacts.
I did have to increase the thickness of some of the washers slightly, I guess that someone in the past had used a liquid cleaner and the bakelite had swollen.

I did not refit the zero rod, this was dropped on all AVO valve testers after the 2 panel.

A long and fiddly job, I laid out a large piece of paper and laid each part in order.

Peter

[Dekatron]

I agree with "Electronpusher0" on his advice on how to clean them.

It is usually enough to get rid of the dust that has accumulated over the years between the wheels with a good clean to get them to work nicely.

Do take some photos and notes along the way when you dismantle it, especially when it comes to which wheel and washer goes where. Having one small box for each wheel and washer is good so that you put them back in the right order.

[Station X]

I've never thought about this before, so I got the CT160 out. I can rotate the switches using my thumb, but it's slightly painful and the switch doesn't always move far enough to latch into place. That's probably why I've been using my thumbnail for the last 20 years without realising it, or thinking about it. The switches are 100% reliable in operation.

[Bazz4CQJ]

I think that mine is more difficult when it's cold; if it's kept somewhere warm, it is just that bit easier. The task of dis-assembling the wheels of the 163 looks very off-putting!

B

[Hartley118]

The wheels on my Mk IV have always been pretty stiff, needing help from a thumbnail for easy rotation. However, I remember using a brand new Mk IV at university in the 1960s and ISTR that was much the same, allowing for the extra strength of youthful thumb muscles.

So I've left well alone.

Martin

[Backtoreality]

Some of the rollers on my Two Panel tester were really stiff, others were quite easy to turn. I squirted the stiff ones liberally with switch cleaner while turning them and they slackened off to make them usable. I did read the renovation threads on the forum and Electronpusher0's excellent description of the dismantling and cleaning process but decided it was not something I wanted to do if I could avoid it!
David

[Dekatron]

Some 10 years ago I was very lucky to have access, only for a few hours though, to one AVO VCM Mk IV and one AVO VCM 163 that had just been opened from factory sealed delivery boxes. They were in pristine condition and looked absolutely like new inside and out, this as they had been stored properly in a dry and tempered laboratory environment for all those years since they were bought. They were the spares that had been bought at the same time as the ones that had been used daily, but they hadn't been unpacked. The ones that were used had seen some heavy use and had been in for repairs on several occasions I was told, I am not sure if they had had more spares standing by as the used ones wasn't bought by the person buying the boxed ones.

I was contacted by the buyer (who had bought a lot of boxes from an estate) as he had seen that I was searching for original manuals for AVO testers in a forum and in the VCM 163 box there was a service manual which I was allowed to scan to complete my manuals. I drove across the country with a portable computer and a scanner so I could scan the manual as the buyer didn't have access to a scanner.

On both of these testers all switches including the roller selectors turned very smoothly with distinct positions, even after all those years in storage, only after cleaning and relubrication have I felt similarly smooth switches on used units.

So, on at least some factory "new" units everything turns very smooth.

[Electronpusher0]

Originally Posted by Backtoreality

Some of the rollers on my Two Panel tester were really stiff, others were quite easy to turn. I squirted the stiff ones liberally with switch cleaner while turning them and they slackened off to make them usable.
David

Sorry David but switch cleaner should be kept well away from Bakelite, it tends to absorb it and swell.
If the switches really are too stiff the only cure is a strip down, clean and rebuild.

Peter

[woodchips]

Thank you everyone for your feedback and comments.

Simplest solution seems to be to find some new sealed factory fresh ones, somewhere.

I also do not want to dismantle the switches. But, something seems to be needed. Can the switch be released from the panel and then the end nuts removed so it is possible to slightly separate each switch. It can then be brushed out, or is some liquid cleaner ok so it can dry? With the end nuts loosened it should also be possible to feel if the slackening makes them easier to rotate. What if the nuts are left slightly loose?

Is Vaseline a good choice of lubricant, it is conductive, well it seems to be on the car battery terminals. Silicone grease seems pretty inert.

Perhaps what is needed is the VCM switch torque gauge. If the indentation in your thumb lasts for more than 15 minutes then they need repair, less than 2 minutes then ok, sort of thing?

One other thing was that twiddling the rotary switches there was a definite jerk as each switch was first moved off the position it was on. After that they moved just like a rotary switch does.

[Electronpusher0]

Originally Posted by woodchips

Can the switch be released from the panel and then the end nuts removed so it is possible to slightly separate each switch. It can then be brushed out, or is some liquid cleaner ok so it can dry? With the end nuts loosened it should also be possible to feel if the slackening makes them easier to rotate. What if the nuts are left slightly loose?

Is Vaseline a good choice of lubricant, it is conductive, well it seems to be on the car battery terminals. Silicone grease seems pretty inert.

Please do not use any liquid cleaner on these switches, as stated the Bakelite tends to absorb this and swell.
Vaseline is not conductive but can be displaced by compression (car battery terminals) or wiping under slight pressure (rotating contacts) so is ideal for this application. I have seen on another thread about these switches that silicone grease is not suitable, I can't remember the reason but it might be worth a search.

Slackening the nuts slightly can ease the switch rotation, there is no harm in leaving them slightly loose, they can be locked with nail varnish. Just don't slacken them too much.

Peter

[Bazz4CQJ]

A few years ago, Dekatron (Martin) kindly sent me a roller wheel which had some dried out deposits of "lubricant" on its sides. Investigating these, it became clear that it had dried to the extent of just being a deposit of particles, and I seem to recall they quickly dispersed and completely washed away in just a tiny amount of IPA.

The thought occurred to me that this stuff had never been a lubricant, but perhaps some sort of tacky paste used to help assemble the switch and which subsequently dried out. If you talk to the market-leading makers of lubricants for this sort of application, the reply comes back that a lithium grease would be their recommendation.

I'm not sure whether any one has ever reported trying a modern Li grease on VCM rollers. I think it could be a better approach than most other options.

B

[Oldmadham]

Originally Posted by Station X

I've never thought about this before, so I got the CT160 out. I can rotate the switches using my thumb, but it's slightly painful and the switch doesn't always move far enough to latch into place. That's probably why I've been using my thumbnail for the last 20 years without realising it, or thinking about it. The switches are 100% reliable in operation.

I think that's how they always were!
Using the AVO valve tester at a TV site on & off between 1969 & 1988, it didn't seem to change, (though it was probably already a decade old in '69).

[Dekatron]

Originally Posted by Bazz4CQJ

A few years ago, Dekatron (Martin) kindly sent me a roller wheel which had some dried out deposits of "lubricant" on it's sides. Investigating these, it became clear that it had dried to the extent of just being a deposit of particles, and I seem to recall they quickly dispersed and completely washed away in just a tiny amount of IPA.

The thought occurred to me that this stuff had never been a lubricant, but perhaps some sort of tacky paste used to help assemble the switch and which subsequently dried out. If you talk to the market-leading makers of lubricants for this sort of application, the reply comes back that a lithium grease would be their recommendation.

I'm not sure whether any one has ever reported trying a modern Li grease on VCM rollers. I think it could be a better approach than most other options.

B

I do have a few different Li-greases nowadays that are manufactured by Dow-Corning of the brand name Molykote. Those samples I got were made for greasing plastic and rubber materials, especially for plastic cogwheels and for soft and hard rubber used as slide/glide areas. I use one of the samples I got when I repair "sticky keys" on Yamaha electric pianos (originally Yamaha used the same kind of grease I was told by a service technician with Yamaha Sweden).

I could try it on one of my partially broken roller selector wheels and see how it affects the plastic if at all, I have a few with very visible cracks that are still holding together which I can use. I'll try to wipe them clean of the previous grease before applying the new Li-grease so a mix of two greases doesn't make it worse.

However I can't quite say when I can do this, might be next year as Covid-19 and stalled renovations of my apartment means that 99% of my AVo stuff is in external storage and not accessible in a long time. So if anyone else wnats to try this out right now you are wlecome to report back here how it fares. Maybe someone can ask Dow-Corning if they have any good grease for Bakelite too, or maybe someone here knows if Li-grease will work there too?

[Bazz4CQJ]

Just one question Martin; the reference to Bakelite presumably applies to the older instruments, but do they also apply to the VCM163, where (on some instruments) the rollers are colored grey? Are those Bakelite too, or are they something else?

B

[Dekatron]

The VCM163 uses different kinds of plastic, the grey type uses two plastic types, one for the inner part that is stationary on the pins (it has a more shiny look, almost glittering if held up to the light) and another plastic for the rotating piece which is more uniform grey. I have never had to replace a wheel on the black plastic model of the roller selector so I don't have any parts from those so I can't say what the type of plastic looks like in those models.

I've included a scan of the grey type of roller selectors where I have marked some of the cracks with green arrows, others can be seen more easily (unless the forum software compresses the image), you can see the two different plastic types used easily by their difference in color/texture and you can also see some of the stress lines from the moulding in the innermost part.

All of the other earlier models use Bakelite (I wish they had continued with Bakelite in the VCM 163 too).

[David Simpson]

Best bet - follow Martin's advice about greasing. Back in the day, in the RAF we used a tube of grease compound - possiblly Dow Corning - on CT160's thumbwheel switches, during servicing.
Never use hydro-carbon based oils or greases(even vaseline) on bakelite(or Paxolin) switchgear. Just on the metal shafts or bearings etc.
To answer the original question - should be as firm but easily movable as the thumbwheel adjustment on a camera lens assembly.

Regards, David

[Bazz4CQJ]

Originally Posted by Dekatron

The VCM163 uses different kinds of plastic, the grey type uses two plastic types, one for the inner part that is stationary on the pins (it has a more shiny look, almost glittering if held up to the light) and another plastic for the rotating piece which is more uniform grey. I have never had to replace a wheel on the black plastic model of the roller selector so I don't have any parts from those so I can't say what the type of plastic looks like in those models.

Thanks for that - it's really quite an important dividing line in the discussion, realising the possibility that what's best for the Bakelite wheels is not necessarily true for the 163 wheels, and vice versa. I'd make a tentative guess that the grey 163 wheels were injection moulded; somebody with more experience in that area might be able to confirm by looking at the pictures.

B

[Backtoreality]

Originally Posted by Electronpusher0

Sorry David but switch cleaner should be kept well away from Bakelite, it tends to absorb it and swell.
If the switches really are too stiff the only cure is a strip down, clean and rebuild.

Peter

Thanks Peter, I won't do it again!
Having said that the wheels are still turning freely a year or so later.
David