Why do cassettes have the tape go around a solid plastic post next to the roller - Page 1
Forum section: electronics / general

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: June 30, 2023, 03:34:28 am
content: Why are those plastic posts there, next to the rollers, why not just use the rollers which are already there?

author: floobydust
author_rank: Super Contributor
timestamp: June 30, 2023, 03:45:02 am
content: What plastic posts where? Are you talking about the cassette or the transport?Capstan? Pinch roller?

author: bdunham7
author_rank: Super Contributor
timestamp: June 30, 2023, 04:12:35 am
content: It reduces the need for pencils.

author: floobydust
author_rank: Super Contributor
timestamp: June 30, 2023, 04:53:03 am
content: It's mentioned in theWikipedia page."In order to wind up the tape more reliably.... The competition responded by inserting additional deflector pins closer to the coils in the lower plastic case half."Note that reel to reel tape machine transports, most of them have those same pins but on a tensioner lever/spring. I can ask an expert in mag tape about it.

author: Dundarave
author_rank: Regular Contributor
timestamp: June 30, 2023, 05:56:54 am
content: I don’t know the design purpose, but I do know that they can add a certain amount of drag to the tape movement.Back in the ‘80s I had to modify over a hundred cassette tapes used in a hospital dictation system in order to get to a decent level of reliability.Never knew if it was static electricity, a flaw in the cassette case moulding, a transport design issue, or what, but slipping the tape to the inside of those pins did the trick. For what it’s worth…

author: AndyBeez
author_rank: Frequent Contributor
timestamp: July 01, 2023, 12:06:50 pm
content: The posts, which rub on the non-coated back side of the tape, maintain the same angle of the tape against the guide roller, regardless of how much tape is on the spool. They keep the geometry and thus, the correct tension - theory.If you remove the posts, or loop the tape behind them, the tape will hunch up, giving you that dreaded mangled mix tape in a car radio thing.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: July 01, 2023, 12:16:00 pm
content: When the cassette was invented (1960s), my understanding is that at the time, tape thickness, breakage and tradeoffs were very much a thing.Japanese companies like TDK deserve credit for making the tape formulations in the '80s so thin and robust. So much so that that the average consumer didn't have to worry about tape snappage anymore. Now, car tape-eating decks.. that's another story. Nom nom nom.Low and behold today Techmoan put out a vid which vaguely touches on the problem the engineers had with early cassettes.

author: Haenk
author_rank: Super Contributor
timestamp: July 01, 2023, 03:27:09 pm
content: I assume it's for "peeling" off the tape a bit earlier, when there is a bit of static charge holding it to the spool a bit stronger than usual.

author: dmills
author_rank: Super Contributor
timestamp: July 01, 2023, 08:18:03 pm
content: Pretty sure it is a tension thing, the diameter of the reel varies by probably 2.5:1 or so, which means that with a simple minded torque drive on the takeup spool, the tape tension would vary by about 2.5:1.When the tape reel is at minimum diameter (=maximum tension given a constant torque take up) the tape is wrapped further around that peg then it is when the reel is at maximum diameter, increasing the friction and making the tape tension around the rollers and across the front of the doings more nearly constant.This friction also damps the tendency for the thing to overshoot and spew tape when hitting the stop button after fast forward or rewind (Something that requires annoyingly complex brakes on a pro reel to reel machine).For a consumer product, a pair of plastic pegs that work well enough in the injection moulded cassette trumps a rather complicated variable tension set of brake bands and mechanical servo loop (and solenoid) in the player, especially as the brake in the player would need frequent servicing.