Why does a glazed or hardened pinch roller cause trouble??
- Thread starter sweetbeats
- Start date
sweetbeats
Reel deep thoughts...
What part is confusing?
SteveM
New member
It appears the recorded side is on the side the pinch roller is on. But I'm not sure if I'm looking at it backwards. I've never seen a set up like that. (I don't think)
Wait. Does this pinch roller not make contact with the tape?
Wicked confused.
sweetbeats
Reel deep thoughts...
I'm not sure I'm able to "see" what you are "seeing", but maybe it would help to know that the tape is not in its normal position. I pulled it out from in between the capstan and pinch roller to get a better view of the pinch roller.
cjacek
Analogue Enthusiast
I have to be honest that when I first saw that photo, I had trouble identifying the roller 'cause it looked like the other chrome metal parts. Yes, it's that hardened, glazed and shiny! 
I've never seen one this bad, looks like it's morphing into one of the metal roller guides. 
I'm not gonna attempt to answer the "whys" but rather say that it's def gonna impede performance significantly. On the other hand, I'm amazed how new and clean the surrounding components are. Wow!!
Terry aside, do you think careful fine sanding the roller and treating it with the Rubber Renue would help?
Probably but if you then decide to send it to Terry, the dimensions might be slightly different to the untouched roller and thus might get re-rubbered slightly off spec or..... am I just splitting hairs?
I've never seen one this bad, looks like it's morphing into one of the metal roller guides. I'm not gonna attempt to answer the "whys" but rather say that it's def gonna impede performance significantly. On the other hand, I'm amazed how new and clean the surrounding components are. Wow!!Terry aside, do you think careful fine sanding the roller and treating it with the Rubber Renue would help?
Probably but if you then decide to send it to Terry, the dimensions might be slightly different to the untouched roller and thus might get re-rubbered slightly off spec or..... am I just splitting hairs?toddbailey
New member
Meanwhile,
I did some experimentation and found when I invert the roller no change in curling issues, but when I swap sides the problem stops.
There isn't much one can do for adjusting reel torques on this particular deck (teac x10r)
I bounced a few ideas off Sam as far as making a few circuit mods but with him being quite busy, I'm sure he hasn't had time to give the ideas any thought.
My measurements put reel torque levels with-in factory specified ranges, abeit on the low side, again I'd like to alter the circuitry to make torque levels adjustable.
BTW:
The curling only happens on certain tapes. Not sure why this is, and if I provide increased drag on the supply reel, the problem also stops.
The rollers are in good condition with no issues, the rubber is solid but pliable, no defects.
The bearings on the other hand appear to be fairly worn. I took some measurements and the roller shaft is .190 in diameter, the bronze bushing, however has a diameter of.205 inch.
The net result is radial play of .015 and is clearly too loose and probably accounts for poor wow/flutter and potentially the tape tracking issues.
I did a bit of research on retro fitting precision bearing into the rollers and it appears that a 5x13x4 mm could be utilized, however the bronze sleeve would have to be removed, easy to do and the aluminum collar would have to be reamed to allow for the bearings larger size, do-able but easy to screw up. Going with a bearing solution reduces the play to apx .006 so a big improvement in play but no guarantees it will fix the problem.
Play could be further reduced to .0005 by the use of loctite, basically gluing the bearing to the shaft
I've sent an email to Terry's rubber rollers describing my project for his review, but no reply as of yet.
I also found a posting on a forum at homerecording.com where others were having the same problems and one poster suggested that having a mirror smooth capstan could be a possible cause. The X10 has this style of capstan
I had to post a response to the effect that maybe one could use 600 + grit sandpaper to remove the mirror finish. again no response.
well, never a dull moment around here...
I did some experimentation and found when I invert the roller no change in curling issues, but when I swap sides the problem stops.
There isn't much one can do for adjusting reel torques on this particular deck (teac x10r)
I bounced a few ideas off Sam as far as making a few circuit mods but with him being quite busy, I'm sure he hasn't had time to give the ideas any thought.
My measurements put reel torque levels with-in factory specified ranges, abeit on the low side, again I'd like to alter the circuitry to make torque levels adjustable.
BTW:
The curling only happens on certain tapes. Not sure why this is, and if I provide increased drag on the supply reel, the problem also stops.
The rollers are in good condition with no issues, the rubber is solid but pliable, no defects.
The bearings on the other hand appear to be fairly worn. I took some measurements and the roller shaft is .190 in diameter, the bronze bushing, however has a diameter of.205 inch.
The net result is radial play of .015 and is clearly too loose and probably accounts for poor wow/flutter and potentially the tape tracking issues.
I did a bit of research on retro fitting precision bearing into the rollers and it appears that a 5x13x4 mm could be utilized, however the bronze sleeve would have to be removed, easy to do and the aluminum collar would have to be reamed to allow for the bearings larger size, do-able but easy to screw up. Going with a bearing solution reduces the play to apx .006 so a big improvement in play but no guarantees it will fix the problem.
Play could be further reduced to .0005 by the use of loctite, basically gluing the bearing to the shaft
I've sent an email to Terry's rubber rollers describing my project for his review, but no reply as of yet.
I also found a posting on a forum at homerecording.com where others were having the same problems and one poster suggested that having a mirror smooth capstan could be a possible cause. The X10 has this style of capstan
I had to post a response to the effect that maybe one could use 600 + grit sandpaper to remove the mirror finish. again no response.
well, never a dull moment around here...
technoplayer
Recovering Gear-aholic
Todd...I have an X20R with the same problem apparently you are having.
The tape will ride up on the infeed capstan pinch roller. I too tried inverting it (no difference) but did not try swapping rollers. Irritating
The tape will ride up on the infeed capstan pinch roller. I too tried inverting it (no difference) but did not try swapping rollers. Irritating
toddbailey
New member
I have a thread on this topic on a tapeheads.net forum.
aside from keeping the roller and capstan clean the only other thing to evaluate is tension arm and reel table height, easy to do with a 8-10 mm socket wrench and a philips screw driver.
I suspect that bearing slop, allowing the roller to not perfectly mate with the capstan shaft might be a issue as well.
I'll be retro fitting my rollers with precision bearings in a few days and hopefully forcing the roller to run true (er) to the capstan may help.
aside from keeping the roller and capstan clean the only other thing to evaluate is tension arm and reel table height, easy to do with a 8-10 mm socket wrench and a philips screw driver.
I suspect that bearing slop, allowing the roller to not perfectly mate with the capstan shaft might be a issue as well.
I'll be retro fitting my rollers with precision bearings in a few days and hopefully forcing the roller to run true (er) to the capstan may help.
toddbailey
New member
don't forget to marinade for at least an hour before cooking.
Personally I like to use a honey glaze with a dab of sweet mustard
Personally I like to use a honey glaze with a dab of sweet mustard
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Analog_tapeworm
New member
Sorry for reviving this old thread but I just have to dispel some of the tripe that's been uttered here.
The claim that the pinch roller (i.e the free-spinning rubber wheel) does NOT drive the tape forward is absolutely preposterous. The capstan (metal spindle) cannot drive the tape forward by itself, with or without the pinch roller acting as a counterforce against the tape.
If you've noticed, the pinch roller is slightly wider than the tape itself. If it wasn't, tape transport would not occur. The capstan does not interact with the tape in any considerable way, it drives the pinch roller which in turn pulls the tape forward. The slight contact surface between metal and rubber on each side of the tape is what provides the friction and thus force from the motor. If this surface is non-grippy, this process fails.
So in summary, the pinch roller does indeed drive the tape. The capstan is "just" a preceding mechanism (and counterforce). As an analogue, google image search "robson drive", where the driving axle would represent the capstan, the intermediary metal spindle the pinch roller, and the tape the support axle.
The claim that the pinch roller (i.e the free-spinning rubber wheel) does NOT drive the tape forward is absolutely preposterous. The capstan (metal spindle) cannot drive the tape forward by itself, with or without the pinch roller acting as a counterforce against the tape.
If you've noticed, the pinch roller is slightly wider than the tape itself. If it wasn't, tape transport would not occur. The capstan does not interact with the tape in any considerable way, it drives the pinch roller which in turn pulls the tape forward. The slight contact surface between metal and rubber on each side of the tape is what provides the friction and thus force from the motor. If this surface is non-grippy, this process fails.
So in summary, the pinch roller does indeed drive the tape. The capstan is "just" a preceding mechanism (and counterforce). As an analogue, google image search "robson drive", where the driving axle would represent the capstan, the intermediary metal spindle the pinch roller, and the tape the support axle.
sweetbeats
Reel deep thoughts...
If your explanation is true, then how do the pinch rollers on the Ampex MM series 2" machines work? They are 1.5" wide for the 2" tape.
I agree with you completely the capstan by itself cannot drive the tape. The tape has to be "pinched" to the capstan, which is what the pinch roller does, and when it does, the friction coefficient between tape and capstan shaft is increased and the tape is driven.
I agree with you completely the capstan by itself cannot drive the tape. The tape has to be "pinched" to the capstan, which is what the pinch roller does, and when it does, the friction coefficient between tape and capstan shaft is increased and the tape is driven.
Analog_tapeworm
New member
I'm not familiar with those units. The friction coefficient does not change. Well, it does when the rubber hardens and that's the problem, but not according to your theory. The pinch roller could equally have been made of metal if all it had to do was to provide the counterforce against the capstan.
sweetbeats
Reel deep thoughts...
Well the Ampex MM-1000 in 2" format uses a 1.5" height pinch roller for the 2" tape...when tape is loaded and PLAY mode is engaged the pinch roller on the machine does not touch the capstan shaft. The MM-1000 is a derivative of the Ampex VR-1000 series 2" quad video machines. Ampex Quad machines were one of the most popular in the television industry throughout the 50s, 60s, 70s and into the 80s...uses the same 1.5" tall pinch roller. When the MM-1100 2" audio machine was introduced it had a pinch roller taller than 2". There were problems as a result with skewing, so rollers were turned down at the top and bottom of the cylinder so the rubber contact area was less than 2"...no contact between the roller and the capstan when tape is loaded and PLAY is engaged. The contact surface is the preferred replacement pinch roller for the MM-1100 and the very popular MM-1200 2" audio machines is less than 2".
The friction coefficient between the capstan shaft and the tape *does* change depending on the hardness/age of the rubber roller and/or the pinch roller pressure against the capstan shaft because when the rubber is at its proper hardness it deforms where it contacts the capstan shaft creating some wrap of the tape around the capstan shaft...a very small wrap yes, but the amount of wrap changes depending on the ability of the rubber roller to deform against the capstan shaft, and the degree of force applied between the roller and the capstan.
Your theory applies too...yes, if the roller is taller than the tape is wide the roller will be in direct contact with the capstan shaft, which will then drive both the tape and the roller and the roller assist the capstan in driving the tape, but that's not the absolute in all cases, as above...and my point is the the capstan shaft, whether the pinch roller is over or under size as compared to the tape width, is the primary driver of the tape.
Pinch rollers become ineffective in their primary role of increasing the friction coefficient between the capstan shaft and the tape when they become hardened and no longer deform when pressed against the capstan shaft, and fail to cause the tape to wrap around a small portion of the capstan shaft increasing the friction coefficient between the capstan shaft and the tape in order to overcome the static and active resistance in the tape path upstream of the capstan shaft. If you think I'm saying the pinch roller could be made of metal and work, then you haven't actually read and comprehended what I've been saying. The pinch roller must be able to deform when pressed against the capstan shaft to increase the surface area area between the tape and the capstan shaft.
Another point that reinforces the capstan shaft drives the tape is bead blasting...bead blasting the capstan shaft is a relatively common service on capstan assemblies of high mileage professional tape machines. The driving surface of the the capstan shaft becomes polished over time from driving the tape, decreasing the friction potential of the shaft as compared to a new matte-finish shaft. So operators pull the capstan assembly and have the shaft bead blasted to restore the original matte finish. If the capstan shaft wasn't driving the tape it wouldn't wear, and the finish of the shaft wouldn't be a significant factor.
The friction coefficient between the capstan shaft and the tape *does* change depending on the hardness/age of the rubber roller and/or the pinch roller pressure against the capstan shaft because when the rubber is at its proper hardness it deforms where it contacts the capstan shaft creating some wrap of the tape around the capstan shaft...a very small wrap yes, but the amount of wrap changes depending on the ability of the rubber roller to deform against the capstan shaft, and the degree of force applied between the roller and the capstan.
Your theory applies too...yes, if the roller is taller than the tape is wide the roller will be in direct contact with the capstan shaft, which will then drive both the tape and the roller and the roller assist the capstan in driving the tape, but that's not the absolute in all cases, as above...and my point is the the capstan shaft, whether the pinch roller is over or under size as compared to the tape width, is the primary driver of the tape.
Pinch rollers become ineffective in their primary role of increasing the friction coefficient between the capstan shaft and the tape when they become hardened and no longer deform when pressed against the capstan shaft, and fail to cause the tape to wrap around a small portion of the capstan shaft increasing the friction coefficient between the capstan shaft and the tape in order to overcome the static and active resistance in the tape path upstream of the capstan shaft. If you think I'm saying the pinch roller could be made of metal and work, then you haven't actually read and comprehended what I've been saying. The pinch roller must be able to deform when pressed against the capstan shaft to increase the surface area area between the tape and the capstan shaft.
Another point that reinforces the capstan shaft drives the tape is bead blasting...bead blasting the capstan shaft is a relatively common service on capstan assemblies of high mileage professional tape machines. The driving surface of the the capstan shaft becomes polished over time from driving the tape, decreasing the friction potential of the shaft as compared to a new matte-finish shaft. So operators pull the capstan assembly and have the shaft bead blasted to restore the original matte finish. If the capstan shaft wasn't driving the tape it wouldn't wear, and the finish of the shaft wouldn't be a significant factor.
Analog_tapeworm
New member
The deformation does not matter. The friction will be constant regardless of surface area, the tension from the spring which pushes the roller onto the tape does not magically disappear just because the rubber hardens. C'mon guy, this is basic physics. And stop conflating friction with friction coefficient 
sweetbeats
Reel deep thoughts...
Well this is all confusing, because I have at least a dozen pictures showing different 2" MM-1000s that have the same pinch roller as mine, which is 1.5" tall for the 2" tape. And the 2" 1000-series quad video machines used the same pinch roller assembly as well.
And here is a replacement pinch roller made by Athan Corp. for the Ampex MM-1100 and MM-1200 2" machines:
NEW PINCH ROLLER 2" AMPEX MM-1200 & MM-1100 TAPE MACHINES WITH BEARINGS (ATHAN) | eBay
This is probably the best pinch roller you can get for the MM-1100 and MM-1200 2" machines. I reached out to the folks at Athan and asked what the height of the polyurethane portion of the roller assembly is and George replied:
The height of the polyurethane is 1.90"
Is it possible we are both right?
And here is a replacement pinch roller made by Athan Corp. for the Ampex MM-1100 and MM-1200 2" machines:
NEW PINCH ROLLER 2" AMPEX MM-1200 & MM-1100 TAPE MACHINES WITH BEARINGS (ATHAN) | eBay
This is probably the best pinch roller you can get for the MM-1100 and MM-1200 2" machines. I reached out to the folks at Athan and asked what the height of the polyurethane portion of the roller assembly is and George replied:
The height of the polyurethane is 1.90"
Is it possible we are both right?
sweetbeats
Reel deep thoughts...
The 1" roller is the only roller for the MM-1000. And yes I see and am aware the original MM-1100 and 1200 rollers for 2" were wider than 2" tape.
But the MM-1000 2" roller is less than 2"
The upgrade Athan roller for 2" tape for the MM-1100 and MM-1200 is less than 2"
You cite a third example Studer machines often have a roller that is the same height as the tape width
So in those cases how is the pinch roller driving the tape at all if it doesn't even directly contact the capstan shaft when tape is loaded?
I agree that's definitely not the case at all times. I've got two tape machines, a 1/4" and a 1/2" that have pinch rollers that are taller than the tape width. And I've got a 3M iso-loop machine that doesn't exactly follow either of our scenarios.
My point is that it is not accurate to say the pinch roller drives the tape if the tape is wider than the roller's height...and we have several cases of popular production machines where that is the case. And in those cases I believe my theory is accurate.
But the MM-1000 2" roller is less than 2"
The upgrade Athan roller for 2" tape for the MM-1100 and MM-1200 is less than 2"
You cite a third example Studer machines often have a roller that is the same height as the tape width
So in those cases how is the pinch roller driving the tape at all if it doesn't even directly contact the capstan shaft when tape is loaded?
I agree that's definitely not the case at all times. I've got two tape machines, a 1/4" and a 1/2" that have pinch rollers that are taller than the tape width. And I've got a 3M iso-loop machine that doesn't exactly follow either of our scenarios.
My point is that it is not accurate to say the pinch roller drives the tape if the tape is wider than the roller's height...and we have several cases of popular production machines where that is the case. And in those cases I believe my theory is accurate.