Tape profiling phenomenon- source?

[Glenn Chan]

Originally Posted by Alister Chapman

FACT: Tape heads wear to slightly different shapes depending on the tension, abrasion, lubrication and width of the tape passing over them, this is called profiling. Tape to head contact is not optimum until profiling has occurred.

FACT: Once the head has worn to the profile that a particular type of tape creates it will stay that approximate shape.

FACT: Changing the tape formulation/tension will cause the head to wear to a new profile.

FACT: Repeatedly changing tape formulations/tension will lead to increased head wear due to repeated head re-profiling.

FACT: Head to tape contact will not be optimum until profiling is completed each time.

FACT: During the profiling process more oxide is stripped from the tape and tiny amounts of head material are worn from the heads.

This is a well documented phenomenon, research by the IEEE, Sony, Maxel and I am sure others, so you choose, stick with one type of tape or chop and change.

My question is, where can I read about this phenomenon?

2- If this is true, are multi-format VTRs a good idea? (i.e. sony VTRs that can play back betaSP and/or digibeta and/or HDCAM).

3- What about tape cleaning cassettes? Wouldn't they cause a very very different pattern of head wear?

[Alister Chapman]

This came from a technical bulletin about head cleaning and head wear from Sony. There is also information on the IEEE web site, but you need to be a member to read it.

It is the same whenever you put any different surfaces that are in uniform motion together, for example car wheel or engine bearings. If you make a repair you must put the bearings back the same way around or they will wear.

My guess is with a multi format deck that if you keep swapping and changing tapes that the heads will wear out quicker. As for how much quicker? I don't know.

When I worked in a Digibeta edit suite we had 3 decks, all of which could take both BetaSP and Digibeta. The source decks would be fed with a mix of BetaSP and Digibeta tapes depending on the job, the heads on these decks lasted around 1,500 hours. The record deck only ever got used with Digibeta tapes and the heads on that deck lasted around 2,000 hours, so make your own assumptions from that.

The Sony bulletin recommended the use of head cleaning tapes at periodic intervals because it re-profiles the head back to the factory default profile. This prevents excessive un-even wear and was recommended as part of the regular head maintainance to maximise head life.

[Bob Grant]

Hm,
there's some element of truth in what's said but you'd need to qualify it to some extent.
Oxide based tapes are very abrasive and the article does seem to mention only oxide tapes. DigiBetacam, DV and DVCAM tapes are not oxide based, BetacamSP is. That would account for the wear on the feeder decks more so than anything else. I know from my mates in broadcast that their multiformat decks heads don't last too long when they play oxide tapes in them.

Conversely I'm told by the local Sony repair centre that DV and DVCAM decks rarely needs heads replaced, over 6,000 hours and still going strong.

Also with DV anything and ME tapes head contact wouldn't be as much of an issue as with analogue formats and oxide tapes.

[Mike Teutsch]

Originally Posted by Bob Grant

Hm,
there's some element of truth in what's said but you'd need to qualify it to some extent.
Oxide based tapes are very abrasive and the article does seem to mention only oxide tapes. DigiBetacam, DV and DVCAM tapes are not oxide based, BetacamSP is. That would account for the wear on the feeder decks more so than anything else. I know from my mates in broadcast that their multiformat decks heads don't last too long when they play oxide tapes in them.

Conversely I'm told by the local Sony repair centre that DV and DVCAM decks rarely needs heads replaced, over 6,000 hours and still going strong.

Also with DV anything and ME tapes head contact wouldn't be as much of an issue as with analogue formats and oxide tapes.

First of all, I would respectfully dispute the statement, "Oxide based tapes are very abrasive!" Define "very." Any and all substances are abrasive when put into contact with another. Water and air are abrasive to surfaces too. If the tape had no coating at all it would still be abrasive.

What the contact areas depend on for wear is surface textures and friction. The particulate size of the oxide on the tape is miniscule, but any two surfaces rubbed together will cause wear, and this is why they use lubricants on the tapes in the first place. Best not to mix lubricants! Think of it this way, if you have a sticky hinge or lock, oil it or use graphite powder, but don’t mix the two or you will have a less effective lubricating paste that can clog and clump.

Another factor in wear is the amount of pressure used to hold the tapes against the heads. The more pressure the better the contact and the best chance of data transfer without errors, but it will also cause increased wear, tape stretch and heat build-up. Thus two machines of different manufacture, format, tape size and formula and head pressure can have very different wear factors.

All of Alister Chapman’s list facts or conclusions make perfect sense from an engineering stand point. I think if we just accept them at this point and take of our expensive machines with the proper care and cleaning, we will all be fine.

Clean as necessary, buy sufficient tapes of the same brand so that you don’t run out at a bad time, and keep the tape transport area clean. As abrasive as you might think that an oxide coated tape is, dust is even more abrasive. And of course sand would be a killer!

Let’s go shoot something.

Mike

[John Huling]

Would it make any difference if I used JVC ProHD tapes or Canons (the one that came with the XHA1? As long as I stay with the same JVC tape that is.

[Mike Teutsch]

Originally Posted by John Huling

Would it make any difference if I used JVC ProHD tapes or Canons (the one that came with the XHA1? As long as I stay with the same JVC tape that is.

Use any tape you wish, but try to stick with the same one and clean as necessary.

[Bob Grant]

Originally Posted by John Huling

Would it make any difference if I used JVC ProHD tapes or Canons (the one that came with the XHA1? As long as I stay with the same JVC tape that is.

My own spin on this. If possible use tape made by the same people as made the camera, unless it's genuinely horrible stuff. Reason is totally non technical, just so that when you have an issue and you take the kit in for service you can look them straight in the eye and say "No, it's not because I used cheap tape, I only use Canon tapes in my Canon camera"

[Mike Teutsch]

Originally Posted by Bob Grant

My own spin on this. If possible use tape made by the same people as made the camera, unless it's genuinely horrible stuff. Reason is totally non technical, just so that when you have an issue and you take the kit in for service you can look them straight in the eye and say "No, it's not because I used cheap tape, I only use Canon tapes in my Canon camera"

OK, use the cheap tapes then keep one Canon tape handy for shipping with the camera!!!!!!!!!!!!!!!!!!!!!!!! :)

[John Huling]

Thanks Mike and Bob. You are so funny:) I was going to keep a DAT tape for that purpose!