Why does a glazed or hardened pinch roller cause trouble??

sweetbeats

sweetbeats

Reel deep thoughts...
I've always forwarded the advice that if a pinch roller is shiney/glazed or hard that it is time to replace it, but I must admit I really don't understand why this is a problem.

All the pinch roller does is press the tape against the capstan shaft...the capstan shaft does the gripping and driving of the tape, so why would it matter if the rubber pinch roller has lost its gripiness? It just squeezes...it doesn't drive anything.

I have to get my head around this as I'm having some trouble with my MM-1000 tape tension varying.
 
Yes...the capstan does the "driving"...BUT...it's pressing agains the pinch roller, and so as it grips the tape, the tape presses against the pinch roller too...if the roller is hard-n-slick...the tape slips.

The capstan can't "grip" if there isn't a counter grip action from the roller.
 
I've had a number of them harden. If they harden, they A) don't grip very well , and B) don't track very well, as in the tape will want to wonder and roll off one side or the other.

Now, I want to know what does indeed to all of the work in a deck. I've had a capstan motor blow out on my Pioneer deck and the tape stopped dead bang. Now (not in my most brilliant moment), I fed the tape from the Pioneer through my Akai deck and played a tape. It was awkward, but it worked. The capstan motor from my Akai was doing all of the work. I'm just wondering if all the reel motors do is keep tension and perform ffwd/rewind functions.
 
I recall having major wow & flutter with a hardened, glazed roller, seemed in places that the tape actually glided out from the grip and made it sound faster at times, stop & go sorta thing, like someone driving who didn't know how to do the shift gears / clutch thing and all you got was a rough ride. :D It's amazing how a tiny $30 rubber puck can mean so much in terms of proper functioning of the tape recorder. The guys summed it up nicely and also Muck.. in the other thread: "tape is kinda slippery, both on oxide and back coating. A shiny pinch roller means a pinch roller that is less porous, more hard, more slippery. slippery surfaces on slippery surfaces = issues."
 
Okay, yeah, I get the whole wandering thing, but saying that a hardened or slippery pinch roller doesn't grip the tape is like...is like complaining that you're stuck in the snow because of bald tires on your back wheels in a front wheel drive car with chains on the front...the back tires have nothing to do with making you go.

Is it that an appropriately soft pinch roller is more effective at mating the tape to the capstan? And a shiny roller is just an indicator of hardness and it is the hardness that is the issue and not the fact that it is glazed or shiny?

Do you guys see where hanging up on this?

It's amazing how a tiny $30 rubber puck can mean so much in terms of proper functioning of the tape recorder.
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Heh...yeeeah...unless you have one off an MM-1000 and you just got the quote from Terry Witt to rebuild it...in that case you'd better convince yourself that it means everything and then you'll have an easier time writing out the $75 check... :eek: Not knocking Terry...its just part of the price of admission for big iron. :o

So see below. What do you think, fellas...time for a rebuild??

IMG_6864_1_1.JPG


[pssst! It actually looks shinier than that in real life! :eek::eek::drunk:]
 
sweetbeats said:
Heh...yeeeah...unless you have one off an MM-1000 and you just got the quote from Terry Witt to rebuild it...in that case you'd better convince yourself that it means everything and then you'll have an easier time writing out the $75 check... :eek: Not knocking Terry...its just part of the price of admission for big iron. :o

So see below. What do you think, fellas...time for a rebuild??
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Cory, let me pose this question to you: Would you rather fork out the $75, one time vs. not doing it and having an almost $300 reel of tape(s) (if it's new RMGI or ATR anyway) get crinkled up because of a bad roller? I consider it cheap insurance.:D

That's where I'm at now, looking at the maintenance and repair aspect of a handful of things. I've got a DA88 and MD-801R that need to be fixed and I still have to replace the left side panel on my M-2516, as well as pulling the Studiomaster board apart to clean and lube the pots. The last couple are cheap and easy, just takes a little time. Getting the digital units fixed, not so cheap. I'll trade you: a pinch roller for a repair bill.:p
 
Cory, your analogy about front wheel drive/ bald back tires is all wrong.
If the capstan is doing all the work here, then why do you need a pinch roller at all? Cause the pinch roller is where the friction is, NOT the capstan. One of the two surfaces that contact the tape needs to have grip to move the tape...otherwise THAT is bald tires on ice. Put on chains (grippy pinch roller) and you are good to go. Consider: you would not want a rough capstan as thats the side that contacts the oxide, and it could damage the business side of the tape.

Nuff said.


I have used some products for conditioning/ re-stickying pinch rollers, and have had reasonable success. You could even mechanicaly resurface a roller , assuming it is not so dry that it would crack. Unlike the capstan, the diameter of the pinch roller has a bit of tolerance. Round is critical tho..:)
 
technoplayer said:
Cory, your analogy about front wheel drive/ bald back tires is all wrong.
If the capstan is doing all the work here, then why do you need a pinch roller at all? Cause the pinch roller is where the friction is, NOT the capstan. One of the two surfaces that contact the tape needs to have grip to move the tape...otherwise THAT is bald tires on ice. Put on chains (grippy pinch roller) and you are good to go. Consider: you would not want a rough capstan as thats the side that contacts the oxide, and it could damage the business side of the tape.

Nuff said.
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I disagree completely.

Why do you need a pinch roller at all? Just like miroslav said, because the capstan is a hard slick surface and needs something to "pinch" the tape to it so it can drive the tape. And of course the capstan has to be a hard slick surface or it wouldn't last and would also wreak havoc with wow and flutter.

Ampex asked the question why do you need it and *poof* gave us the ATR-100 which has no pinch roller, just a big capstan. Stephens asked the bigger question and *poof* gave us a capstanless transport, but I digress...

Techno, how can you say the pinch roller is doing any "drive" work when it is a passive roller? Unless one of your tape machines has a powered pinch roller?? The traditional name for a pinch roller is the "capstan idler"...Webster's definition for idler says "not working or active...doing nothing." I can say that the capstan is doing all the work (the driving force) because it is the only thing powered in the relationship!

I've got another analogy: you ever had a car stuck in the snow and the wheels are just spinning, but then you get some buddies to bounce on the bumper and when they push the car down the tires grip better? The ground is the tape, the tire is the capstan, and your buddies are the pinch roller improving the frictional coefficient between the tires and the ground.

I bet the contact area onto the tape of a hardened pinch roller is smaller than a new pinch roller as the rubber can deform and shape itself to the contour of the capstan with properly soft rubber, but it cannot with hardened rubber. If a proper pinch roller can conform itself somewhat to the contour of the capstan shaft and the tape is in between that also means the tape will be somewhat more contoured to the capstan increasing the contact area and the frictional coefficient.

THAT's how it works...who cares if it is slick, the pinch roller is doing no driving but if it can't effectively pinch (i.e. shape itself to the capstan) because it is hardened then that's the problem.

And BTW, right, you don't want a "rough" capstan but you don't want it polished like a mirror either. You would think that a mirror-smooth surface would have a higher friction coefficient but in this case there is an issue with air getting in between the capstan and the tape, and the smoother the capstan the greater the possibility of air to be in between and reduce the grip of the capstan. Aaaaand while the backing side of the tape is indeed smooth it is also a matte surface and two matte surfaces together will grip better than shiny and matte.

A proper capstan has a matte finish, at least that's the case with decks I have except for the BR-20T, but that is pulling 1/4" tape and has a wonderfully harmonius transport with the servo system. You are right to be concerned about the capstan rubbing on the "business side" of the tape, and that's why it is desirable to have a tape path with the capstan on the backing side of the tape. I've never had a deck with the capstan on the oxide side of the tape, though I know that's one way it is done, but of the decks I have or have had (Ampex MM-1000 and 440, Tascam BR-20T, 48, 58, and 388) they all have the capstan mate with the backing side of the tape.

Now, I want to know what does indeed to all of the work in a deck...I'm just wondering if all the reel motors do is keep tension and perform ffwd/rewind functions.
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You've got it. Reel motors provide holdback and takeup tension in PLAY mode to keep the tape from getting slack and more importantly to ensure positive tape-to-head contact, and then they provide for fast shuttling in FFWD or REW. The capstan is what drives the tape in a capstan drive transport in PLAY or REC. As I mentioned above, Stephens and others (though IIRC correctly Stephens was the first...Otto?) developed capstanless systems in which the servo mechanism was sophisticated enough to place tape drive responsibility on the reel motors.
 
Actually, a slick capstan causes wow and flutter. It has to have some texture to it.

When the pinch roller is functioning properly, it deforms around the tape and contacts the capstan. You then effectively have two moving surfaces pulling the tape through.
 
LDS said:
Actually, a slick capstan causes wow and flutter. It has to have some texture to it.

When the pinch roller is functioning properly, it deforms around the tape and contacts the capstan. You then effectively have two moving surfaces pulling the tape through.
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I didn't say a slick capstan didn't cause wow and flutter...we were talking about tape drive problems.

I agree completely with what you say in your second paragraph and that is exactly what I said EXCEPT for your phrase in the second sentence "You then effectively have two moving surfaces pulling the tape through."...I realize I may be battling a semantical issue here but in a tape transport that uses a capstan and pinch roller to drive tape, there is only ONE driving mechanism and that is the capstan...you have one surface driving tape, and the other helping it drive tape...the pinch roller rotates so that it doesn't impede the tape drive, but it is passive and DOES NOT do any "driving" of the tape.
 
Yes, the capstan does the work and in many decks the tape tension is set equal so that lifting the pinch roller away during play will cause the reels to stop. The take-up reel must be able to stay ahead of the capstan that feeds it, but not too much tension. The capstan/pinch roller determines how fast and how smooth the tape runs, so it is very critical that the rubber be in good condition. Same goes for the capstan. It can become too slick over time because the oxide on the tape acts as super fine grain sandpaper.
 
The capstan needs the pinch roller to push against...just like a car tire pushes against the road. The road doesn't "drive" the car..but the tire is useless without the road.

AFA the decks that don't use pinch rollers or capstans...that's just a different technology that uses the other parts of the transport to regulate the tape speed.

It's all about the transport design..and those that use a capstan/roller need the roller to be tacky, not hard-n-slick.
 
Cory, I did not say the pinch roller drives the tape. I said it provides friction and grip to move the tape.
Constant friction is what makes the tape move at a constant speed.
Yes, there are machines that do not have pinch rollers. That is not relevant, since the MM1000 in question does, and needs one.

I agree with the notion that he pinch roller needs to deform somewhat to provide force (friction) of the tape against the capstan (the thingee that moves the tape). If the pinchroller was steel (ie. non deforming at reasonable pressures) I would imagine tape speed stability would be non-extant.

So, back the the original issue in the first post.

You comment that the tape TENSION is varying. Is the tape SPEED varying?
It seems that these two are related, but only indirectly as the reel motors provide the tension, while the capstan motor sets the tape speed.
 
You comment that the tape TENSION is varying. Is the tape SPEED varying?
It seems that these two are related, but only indirectly as the reel motors provide the tension, while the capstan motor sets the tape speed.
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I don't know that yet. My cal tape needs to be baked before I can use it but that would be a nice way to do a quick check on that (to reproduce tone and see if the frquency changes using a frequency counter in concert with the variation I'm hearing in tape tension).

My first step is to get the pinch roller rebuilt and THEN dig further. The issue may be resolved at that point, and if its not then no loss as the pinch roller is past its useful life at this point.

Hey, thanks everybody...though I may have seemed a bit exasperated I was mostly just excited because the dialog has answered the question in the original post.
 
So if I may inject a couple of questions here,

My Teac X10R has dual capstans, both are mirror smooth and highly reflective.

Would it be a good idea to take some 600 grit wet and dry sand paper to reduce or remove the glossiness?

I'm having occasional tracking problems, but so far only in the fwd direction.
Usually cleaning the pressure rollers helps. I use a product from US Recording Media called Laser Media RC-5

The rollers are pliable but still hard, with out any deformations


Next question is regarding pressure roller bearing tolerances, in my case oiled bronze sleeves.

I can rock the roller back and forth a bit and I think it might be the cause of my tracking issues,
I've already added shims to minimise most of the top to bottom sloppiness to be with in specs, but I still get axial play.

can someone educate me on how much slop is too much and maybe worth having it modified with roller bearings or simply replaced?

Using a dial indicator I can get a reading of something like .002 to .004 inch. in trying to measure the bottom to top (of shaft) play

thanks all.
 
toddbailey said:
Is your post in response to my couple of questions?

Do I need to start a new thread ?
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hi. if you're referring to my deleted post above, i only deleted it cuz i think the ops question had already been answered.
my answer would have just been redundant. hence, my being 'late to the party'.

edit-whilst we're here, i've used very fine grit sandpaper on at least one of my r2rs p-roller, the teac a-6300.
don't remember the # tho. worked quite well but eventually i'll probably have to get the roller rebuilt or replaced.
 
Beck said:
The take-up reel must be able to stay ahead of the capstan that feeds it, but not too much tension. The capstan/pinch roller determines how fast and how smooth the tape runs, so it is very critical that the rubber be in good condition.
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This here. .... and everything else too. :D

The two need to work in unison. In order for that to happen the pinch needs to stay stuck in time with the capstan or the take up will pull it ahead. If you were to somehow stop the capstan with the pinch and take up still engaged it probably shouldn't move.

I don't know if this is obvious. :confused:
 
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