How to measure tape thickness (2024)

A recent discussion surfaced a question about measuring tape thickness. It seemed to me that you could get a rough idea using an inch micrometer which has the .0001 vernier graduations. Since one is in a sense interpolating, and it can be assumed that if the micrometer has been zeroed, while a reading for a particular tape might be good enough to establish a nominal thickness, it might not be good enough to detect thickness variations.

What would you use to get another order of magnitude, which I think is where the thickness variations would live in a particular tape?

For a rough idea it would the easiest way to take maybe 20 layers, measure them and divide by 20.

Thickness variations for quality tape are usually smaller than +-0,5µm... most probably no way to measure that without special equipment and clean room conditions.

I don't. Another poster remarked on tape thickness as a criterion for a bench-mark standard, I asked which thickness he'd settled on. He answered with a thickness and then stated that this number was not the result of a measurement with a "Vernier" instrument. I suggested that a serious micrometer which could measure to tenths of a thousandth of an inch might do. We then learned that tape thickness was divined at his house by measuring the width of the spooled tape in question, which if you think about it, getting a reasonable answer required knowing how many layers. Possible BS?

So I tried measuring a random tape with my Mitutoyo 1", got a number and concluded that this number might be useful for inferring fragility or some other physical quality, but not variation which would be too small a number.

So when someone writes that a C120 tape is too thin, measuring it with a micrometer as described above will give a good idea of "how" thin.

It really doesn't matter how thin it is. In terms of robustness with all but the most perfectly aligned and tensioned mechanisms, ALL C-120 tape is too thin to be reliable. Period.

All we really care about is relative thickness. C-60 and below will be the thickest. C-90 - C-110 will be thinner, and more problematic in marginal mechanisms. C-120 and above will be thinnest of all, and the most prone to damage and malfunction.

We then learned that tape thickness was divined at his house by measuring the width of the spooled tape in question,
which if you think about it, getting a reasonable answer required knowing how many layers. Possible BS?

Click to expand...

No BS.

But obviously you didn't understand. I didn't say measuring the width of the spool.
I said, extracted from the ratio of the spool.

And exactly, it is the change of this ratio that counts. That change is acceleration. We can retrieve total time and tape thickness.
You still don't understand, don't you ?

Ok, let's see an example:
we have a cassette, but the tape is extremely thick. Like 3mm thick. The supply hub is full, take-up is empty (tape at beginning).
Now, press play. What happens ? The take-up spool will grow very quickly and the supply spool will diminish quickly.
That speed is not constant, it's accelerating. Then, it is the acceleration that tells me the thickness. See ?

So, computed with the always changing ratio of the speed of both spool, we can get the total time, remaining time and tape thickness.

Let's say we have a C-90 cassette, the tape is a lot thinner than 3mm. So, the take-up spool will grow at a lot slower rate than a 3mm tape, right ?
A C-60 ? Now the acceleration will be a bit faster than the C-90.

So, for sure tape thickness is retrievable with great accuracy.
Got it ?

There has been a discussion concerning tape thicknesses here:
https://www.tapeheads.net/threads/what-are-the-cassette-tape-thickness-of-various-lengths.82763/
from a german catalogue, it becomes apparent that there are differences even between tape types of ther same brand:

So, computed with the always changing ratio of the speed of both spool, we can get the total time, remaining time and tape thickness. ...So, for sure tape thickness is retrievable with great accuracy.

Click to expand...

No, not really... every tape pack is different more tight, more loose

Quote by Nakamichel
No BS.
But obviously you didn't understand. I didn't say measuring the width of the spool.
I said, extracted from the ratio of the spool.
And exactly, it is the change of this ratio that counts. That change is acceleration. We can retrieve total time and tape thickness.
You still don't understand, don't you ?
Ok, let's see an example:
we have a cassette, but the tape is extremely thick. Like 3mm thick. The supply hub is full, take-up is empty (tape at beginning).
Now, press play. What happens ? The take-up spool will grow very quickly and the supply spool will diminish quickly.
That speed is not constant, it's accelerating. Then, it is the acceleration that tells me the thickness. See ?
So, computed with the always changing ratio of the speed of both spool, we can get the total time, remaining time and tape thickness.
Let's say we have a C-90 cassette, the tape is a lot thinner than 3mm. So, the take-up spool will grow at a lot slower rate than a 3mm tape, right ?
A C-60 ? Now the acceleration will be a bit faster than the C-90.
So, for sure tape thickness is retrievable with great accuracy.
Got it ?

Or you can just measure it like a normal person with a micrometer. But hey if you want to pull a Rube Goldburg , fly at it. Its not accurate at all as already mentioned for obvious reasons. But you keep on with your little fantasy.

"I'll bite, Nakamichel. How do you know what the rpm of each spool is?"

but that's exactly how it does work, in hundreds of cassette deck designs. some of them (the 215 being one) need a little prod- "what size tape is it?" precisely because they can't know the thickness.
but you could work it out on a deck with a simple turns counter, & a stopwatch.... couldn't you?

btw, "C-110 will be thinner, and more problematic in marginal mechanisms. C-120 and above will be thinnest of all, and the most prone to damage and malfunction."

I've got dozens of both & never had an issue. I think the makers would argue that for the cassette to bear the philips "compact cassette" logo, the functionality would have to be demonstrably reliable.

looking at it another way, & given that these lengths were widely available for decades, if the mechanism was 'marginal', then it's the mechanism that's at fault, not the stock.

where these longer tapes are weak is in the depth of the coating, which affects MOL, print-through & so on. I have an EMI C120 from 1975 that has been played hundreds of times & will probably outlive me.