CNC Machining History: Punch tapes EXPLAINED

Ever wondered how punch tapes could deliver so much information to machines? In this video, @GCodeTutor Marc Cronin explains to us how they work.

Punch tapes used to be the only way to store programming information back in the days. When "fed" to the machines, these strings of paper would deliver the information necessary to operate the program.
The name "punch tape" comes from the holes punched on the tape that will be used to convert programming information into binary data.
Punch tapes typically look like strings of paper with multiple lines of holes. Each line will feature either 5 or 8 holes. Each of these holes represents a bit and each line represents a byte.
Once fed, the machine will use a light system to convert the holes pattern into information.

There are two standards of tapes engineers used to work with: EIA, also known as BCD, and the ASCII, which is known as ISO.
Although identical in the looks, the two tape standards there's one main characteristic that differentiates them: EIA system tapes will feature an odd number of holes on each line while ASCII system tapes will feature an even number of holes on each line.
The reason this is done this way is to help the tape reader to identify an error and alert the operator.

Although machinists nowadays don't have to deal with punch tapes, knowing how they work can help understand the difference between high-level programming and low-level programming. G-Code is considered high-level programming language because it converts into 0s and 1s that the machine's CPU can read.

Have you ever worked with punch tapes or seen them in your machine shop? Share your experience in the comments!

Stay tuned for more machining videos!

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Recommended CNC programming books:

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[stevehayward]

My career spanned from manually operated machines, to cam operated autos, to plug board autos, tape NC machines to full CNC machines.
In my lifetime I have seen a revolution of machining happening, machines today can do more than I ever dreamt possible when I was a young apprentice in the 60's.

[spud]

found this video while having a nostalgic lookfor the Laser cutter i programmed back in 1981here in Brisbane Australia. we had an ASR 43 teletype with a punch tape. I remember all the little bottles we kept the programs in. all programs were written out by hand and then typed in. I also remember the hassle of re typing a tape you made too many mistakes in. sometime in late 81 or early 82 my boss bought an Apple 2E with mono green monitor. he also hired a couple of uni students to write a program on the Apple to let us write the programs in a text file then "print" them to tape. they were also able to write a program to read all of our existing tapes and store them on floppy disc! we were a sheet metal factory and the laser was an Everlase 650W CO2 laser with a 1500 mm by 3000 mm bed. we could cut up to 8mm thick mild steel. i remember cprogramming the stainless for elevator doors and button consoles..cut with the plastic still on of course. hard to believe that was over 40 years ago..

[mikes]

Oh the good old days of running the Cincinnati 5v100 with 220 control and depth cams.
Point to point control, hydraulic motors with servo valves. did not have encoders, Used position analog units.
Had this big hydraulic unit sat right next to the machine. its only job was to pump out heat and noise.
Used a flexowriter for punching tape.
Later we had a setup on a pc. With this setup you could edit your program. Then when you are happy with it, send it to the tape punch.

[johnmorack]

i got PTSD watching this! from taping up the cards and other voodoo tricks we used to have to do to get the cards to work. How easy it is now.

[justcurious]

I always wondered how is it converted to voltage.

[johncollins]

So the character set that could be represented was (essentially) cut in half due to the parity bit? Odd that they didn't add a separate column for parity.. Interesting, thanks.

[hwrdmltn]

Your video is very interesting, but it's important to note that the sprocket hole MUST be aligned with the data byte (holes) so the reader knows when a valid byte/code should be read. Your diagrams have too many sprocket holes that are NOT aligned with the data holes. 🙂

[ortuluna]

Is this were the 32, 64, 82 bit things came from?

[sekudha]

ASCII is actually pronounced as ASKEE .just informing you, , good luck

[marksmith]

I was wondering if you would know how to solve this problem. i have an old lottery ticket that used a 4 X 12 binary bits but the serial number was 17 number long like 027-00237087-175804. Any idea how this would be encoded?