How to soften harded pinch rollers? (+ worn tape heads)

[C.B. - Boudio]

Turning the heads is only workable when you’ve had the heads lapped by that method from what I understand?

Not really; you start with the worn head as-is, etc; the Marotick Method (as the inventor calls it). The drawing of the lapped head is more to show what it's about, and the differences (or lack thereof in the final product).
Scraping the oxide... In the drawing, it ocurred to me as well, but in pratice, I don't think it will do harm that way. A slightly warped aluminum spool will do a better job of scraping, at least at the edges

I know not to use pure alcohol. I first thought of using alcohol, before starting this thread, but I didn't start because of that very reason. I'll see what's laying around in bathrooms and kitchens and washrooms.

 

[RoadrunnerOZ]

The idea reading the text again looks to be to reduce the surface area presented to the tape which is all very well in theory but
1: for a new head with a radial surface the point contact pressure would remain the same no matter which way you twist it around the vertical axis
2: for a worn head with a transverse flattening the air gap is in the centre of the flat, so a very slight twist (that must keep the flat in full contact with the tape without lifting it away from the tape) will reduce contact area - but only by a small amount thereby increasing point contact pressure against the tape by a small amount. The twist cannot be allowed to lift the tape off the air gap or you get loss of signal.
3: when there is sufficient wear to rotate to the other side of centre the tape will still need to remain in full contact with the flat wear surface
4: the amount you can twist the head is governed by the lead in/lead out angles - the shallower the angles the less you can twist the head.
The net result seems to be an increase in point contact pressure of tape to head.
Can you accurately twist a head and be sure you’re doing it the exact right amount (and if it’s not designed to twist bend the framework without destroying anything).
Does the increase in point contact pressure give any noticeable increase in performance?
One possibility is the mechanical deformation of the tape by running over sharp edges just prior to or just after the pole gap will also change the direction of the oxide particles as they pass over the pole gap and when as the heads wear and then later are turned to the opposite twist the stretch/deformation will be different - meaning tapes recorded with the head twisted one way and played back with the head twisted the other way or centred after the second wear in twist would maybe not sound the same.
As when you reduce the radius of curvature of the tape by having a smaller head area in contact then the particles will be forced together at the curve on the inside, differently to a normal radius head causing higher concentration of particles which would alter the response and linearity. Tapes and heads were designed around each other.

Also the one obvious problem I see that is not really solved here is that wear creates a waver in the vertical line of the head face which is smoothed by relapping the heads, but not by this twisting method. A tape that is old and has been played on the machine as it has worn will have stretched to conform to head shape changes. A new tape however being flat and not bowed will basically have parts of the tape not coming into contact with the heads at all - the valleys in the wear line. The increase in contact pressure would not give the same result as a smooth profile new or relapped head. Okay for a domestic cassette machine if you want to up the output I guess.
Twisting a worn head and increasing the point contact pressure will tend to increase the linear wear and lateral stretching of tapes. Not sure I’m a big fan of the whole idea. I’ve worked with tape in many studios since 1977 and had many technical service oriented and operational discussions with people from Studer, Sony, BASF, Ampex etc and learned a lot about the importance of head alignment and surface integrity to achieve full magnetic saturation on tape without screwing with the frequency response and output. Tape tension also is a factor that is designed into tape machines to present the tape to the heads at the optimum pressure so as not to deform/flatten the magnetic material as it is recording or playing, stretch the tape or cause excessive wear and by doing so to achieve optimum output and linearity. Head surface profile is to optimise tape performance within the designed tape path.

 

[C.B. - Boudio]

@RoadrunnerOZ Thank you for the explanation! Again something new learned. So I'll be looking for the right sanding paper I guess

 

[rh001]

Old hardened pinch roller can't be rejuvenated to any degree .. anyone who says they had success with this or that cleaner or method is kidding themselves...maybe got better, but still kinda sucks.

You can have rubber completely replaced by Terry's Rubber Rollers. Don't delay, Terry's likely to retire any day.

Athan in South San Francisco has many pinch rollers and if you do't see the roller you need on Athan website then inquire cuz they have rollers that aren't on their website.

 

[C.B. - Boudio]

You can have rubber completely replaced by Terry's Rubber Rollers. Don't delay, Terry's likely to retire any day.

Athan in South San Francisco has many pinch rollers and if you do't see the roller you need on Athan website then inquire cuz they have rollers that aren't on their website.

Those seem fine adresses! But the catch is, it will be a drag getting them back and forth since I'm located in Belgium - if they don't get lost in postage...

 

[RoadrunnerOZ]

Old hardened pinch roller can't be rejuvenated to any degree .. anyone who says they had success with this or that cleaner or method is kidding themselves...maybe got better, but still kinda sucks.

You can have rubber completely replaced by Terry's Rubber Rollers. Don't delay, Terry's likely to retire any day.

Athan in South San Francisco has many pinch rollers and if you do't see the roller you need on Athan website then inquire cuz they have rollers that aren't on their website.

These resurfacing of a pinch roller will work to bring the rubber back to a smooth matt finish as long as the rubber internally has not perished. The surface material glazes, perishes and hardens over time and the removal of the outer surface gets rid of the layer of material that is embedded with contaminants and has perished. This has been done for decades and there are solvents specifically designed for this cleaning process. It will not fix fully hardened rubber, synthetic rubber or eurethane. The Revox rollers in question are IIRC some sort of polyurethane and may not respond well to solvents that are harmless to EPDM rubber - they can go sticky and stay that way. EPDM doesn’t like mineral oils and solvents and will swell, but lasts longer than urethane and is widely used for rollers. There are a lot of reports about replacement translucent rollers breaking down after not a long time. Revox online don’t use urethane for their rollers.
The re-rubbering of your original roller may be an issue if the bearing is worn.
These guys are in Italy
https://www.sofh.it/products/revox/g36/g36-pinch-roller-black/

 

[Brian Roth]

In his first post, the OP mentioned the rollers are greenish-gray which indicates they are the synthetic rubber Revox used on many models. Typically that rubber turns into a goo...or something like the consistency of modelling clay. I seem to recall one (or more?) where the "rubber" had become essentially petrified.....as in rock-hard.

The OP has nothing to lose by experimenting with various procedures, but I believe it will be a lost cause. I never found a "renewing" method that worked for those greenish Revox rollers. The answer was replacement or sending it to a vendor that could actually replace the aged/defective "rubber".

Back when tape recorders were a mainstay, pinch rollers were considered an "expendable" item requiring replacement at some point....like tires on an automobile.

Bri

 

[RoadrunnerOZ]

That’s why a lot of replacements are EPDM rubber. It doesn’t cost a lot more than re-rubbering to buy a new replacement which will also have new bearings. The G36 rollers readily available will also apparently fit the A-F as well

 

[Brian Roth]

That’s why a lot of replacements are EPDM rubber. It doesn’t cost a lot more than re-rubbering to buy a new replacement which will also have new bearings. The G36 rollers readily available will also apparently fit the A-F as well

My Revox experience only goes back to A-77/A700/PR99 machines. Now you're "making" me look up those older models to have a clue about what they are....lol! Off to Google.....

Bri

/EDIT: Hmmmm.....those are cool looking machines from the early 1960's!

 

[C.B. - Boudio]

/EDIT: Hmmmm.....those are cool looking machines from the early 1960's!

They sure are! And if you look carefully, they are not too hard to find, at least over here. The all-valve amplifiers sound terrific, and they are also very good 6-7W mono amplifiers (from D onwards; two ECL82 in PP).

So, now I have written to some sellers or redoers you all proposed me (which I am very grateful for!), and I'll see if there comes something out.

 

[sodderboy]

It reads like a loss, so nothing to lose with solvents, but they will dillute the surface if anything rather than soften it. And hard rollers will not grip tape properly glossy or matte and apply too much pressure. emory? only if I had to play a tape to stop the aliens from blowing up the world. All roller vendors mentioned are great, buy new! I need to get from Athan for my Nakamichi. Thanks for the reminder.
On a good roller I would not use window cleaner, with ammonia or not. Any dillution of isopropyl. TEAC or Radio Shack "rubber cleaner". I realized early on that they are all more harsh than needed.
I used Athan cleaner for decades, and now dillute clear DAWN in distilled water, 40:1 by weight. This would do bupkis for a hard old roller except de-grease it. It also works great for finger cheese when detailing vintage gear.
Mike

 

[RoadrunnerOZ]

Might be worth reading this:
https://www.tapeheads.net/threads/new-athan-pinch-roller-rotting.105574/

 

[Dennis F.]

It is with fear and trembling that I bring this up because I don’t want to lead anyone astray. In the 1980s I successfully lapped heads on an Ampex 351 and a Sculley 265 that had Nortronics heads. Get flat sheet of plate glass. Start with 2000 grit lapping compound, making figure 8 patterns on the glass, all the whil

 

[RoadrunnerOZ]

It is with fear and trembling that I bring this up because I don’t want to lead anyone astray. In the 1980s I successfully lapped heads on an Ampex 351 and a Sculley 265 that had Nortronics heads. Get flat sheet of plate glass. Start with 2000 grit lapping compound, making figure 8 patterns on the glass, all the whil

Some heads that are badly worn with a deep flat spot need a lower grit paper, wet and dry on glass with water to do the cutback shaping and progression from 1500 to 2500 wet and dry, then lapping film on the same glass from 9 micron down to 1. It’s a long process and you need to be sure to maintain an even turn keeping the head flat to the surface as the head is passed over the paper or film and rinsing the head and the glass with each grit transition. You need a microscope to inspect each stage. You also need to be very careful not to rip out the terminal leads/pins or it’s new head time.

 

[Dennis F.]

You’re right about it being a slow process. It’s been 40 +yrs but now that I think about it, I played a reel of old tape for a day or two and let that do the final polishing. I didn’t have anything as fine as 1 micron lapping compound. Not sure what that is in inches….. I did recording as a hobby back then, and eventually went into digital recording but don’t do audio any more due to bad hearing. Used to repair and build audio equipment as a hobby back then. I always liked the old Ampex…

 

[RoadrunnerOZ]

We had a few specialist places here where heads were sent to for relapping. I started on tape machines in recording studios in the late ‘70s and for 15 and 30ips machines tape head wear was common in busy studios. Not a DIY project for 16 and 24 track machines. If a studio had or bought a second hand machine with worn heads you’d send them off for treatment (before ever recording or playing back client tapes on a second hand one). You sent the whole headblock and got them all done together- 3 heads.

 

[RoadrunnerOZ]

This might be of interest to those who need vintage Neumann mic parts new and vintage German preamp parts as well. The guys name is Gunter Wagner.
He does head relapping for 1/4” to 2” machines:
https://www.wagner-microphones.com/forsale/prices.htm

 

[RoadrunnerOZ]

I didn’t have anything as fine as 1 micron lapping compound. Not sure what that is in inches…..

0.00003937008”
In grit terms you need about 14,000 grit for 1 micron
9 microns is 1800 so if you go to 2000 paper you save on lapping film costs, you only need the 5 and 1 microns - 5 microns is about 4500 But you can get specialist papers for car detailing spot finishing at 5000 grit - lapping films are expensive and don’t handle wear like sandpaper. Best I’ve seen in wet and dry is 10,000 grit

 

[sodderboy]

This is what happened to a A820 pinch roller sitting in my Studer drawer for 20+ years

Dried and cracked with little green crystals on the shards. Taken out of service circa 2000 after 6 or so years of pinching. I remember that the 'thane would harden/darken at about the same time of the bearings going jiggly, so I never replaced bearings on the pucks, just the whole assembly. A beautiful piece of engineering/machining, I kept it.
Mike

 

[Brian Roth]

Not a pinch roller failure tale, but quite similar....

In the 1990's, our studio bought a new Otari MTR-90 Mk III 2" 24 track. For those unfamiliar, those were pinch-roller-less. Instead, the capstan motor attached to a "rubber" coated aluminum drum.

After a couple of years, we noted that the "rubber" was becoming sticky. You could also press on it with fingertips and it would leave a dimple.

I called Otari service in Cali, and the tech admitted there were problems with those capstan drums. He told me not to buy an Otari replacement, but rather an Athan part.

Fair enough, an Athan went on the machine and lasted for at least two decades before the machine was sold.

Here is the punchline. We sat the OEM capstan drum on a piece of paper on a shelf in the shop area. Over the period of a year (?) the "rubber" SLOOOOOWLY oozed down the drum and created a puddle of slime on the paper. Eventually all that was left was a shiny aluminum drum sitting in a gooey puddle.

Wish we had taken pictures, but in the 90's no one had phones with cameras. Conventional snapshots were taken on a roll of 36 images and required photo finishing.

Bri