Reply to u/arightler at tk
As one of the few here who may be typing on a regular basis on index cards, I'd generally recommend standard typewriters (which have larger diameter platens and thus handle thicker cardstock better) which also have either card fingers or Perspex card guides. These latter will help hold the card to the platen for a better imprint and make the process much quieter. Any of the Royal standards (all of which have card fingers) here would be great (KHM, KMM, KMG, HH, FP, etc.) or the Olympia SG1 which has Perspex guides.
You can get away with portables, but they're not as great for regular card work (smaller diameter platens). I might recommend one of the Smith-Corona Series 4 or 5 machines as long as they've got adjustable card fingers. (In the late 50's typically only the Silent-Super model had card fingers, but earlier models often had them as well.) Most of the Olympia SM series (2-9) will do relatively well as they all have Perspex card guides.
Ultra-portables, with their miniscule platens and barely extant/broadly useless paper bails, will be the worst possible option. Most don't have fingers or card guides at all. I highly recommend against them for this work. If you insist on using one for it, DON'T every try anything else as you'll discover how bad these are for this work and it will utterly ruin you.
Grippy platens and paper bail rollers with nice tension along with card fingers/Perspex are usually required for being able to type all the way to the bottom of a card or label cleanly.
For quickly doing labels or small cards, some of the advanced typing techniques in this video will help: https://youtu.be/JUJfCfqgsX0?si=li5bPyn8NdAr2F69&t=1649
Create a small zig-zag fold into a piece of paper to create a pocket slot which can be Scotch taped on either side. This template paper can then be inserted so that the pocket is visible above the writing line, but the paper below it is still in the platen. The label or card can be placed into the pocket and the platen reversed to feed the label or card in backwards to the desired typing line. Using a v-groove or hole in the typing line can create a pencil line to serve as a guide for inserting many labels at the same place so that the typing lines up between labels.
Some offices had special platens for holding cards like this.
Pockets like this can also be used to hold the page to add additional lines at the bottom of pages. Deeper pockets may need to be used for doing this with carbon packs whose carbons are longer than the pages.
Alternately one can do something similar by creating a inverted u-shaped set of slits into an index card to hold such labels.
My usual typewriter recommendations and some information on the market:
