Putting new blade on 1940's table saw

To define the lingo:

• Arbor is the threaded shaft that comes out of the motor onto which the saw blade is mounted.
• Arbor Washer goes around the arbor, just like the saw blade does, but is much smaller in diameter than the blade and doesn't have any teeth. Some saws have a washer on each side of the blade, some only have one on the "outside" of the blade (away from the motor).
• Arbor Nut goes onto the arbor after the blade and washer have gone on. This gets tightened down (often is a reverse, or left-hand thread) to hold the blade in place. Do note: It's been a while since I've changed a table saw blade, so I may be confusing that with my miter saw arbor nut threading.
  • Since you seem to have a good view of the threads, look to see if they if they're regular or reverse thread. If they're reverse, you'll drive yourself nuts trying to loosen with "righty-tighty, lefty-loosey" since it would be "lefty-tighty, righty-loosey.
• Blade that's the sharp, round, spinny thing that separates fingers from hands. (Said tongue-in-cheek - but if you didn't know that, please step away from the saw, now.)

At the link you provided, it looks like the major issue is that this saw has a 1/2" arbor and most modern 7 1/4" circular saw blades (which is probably what you'd need to use - you'd probably have to search long and hard to find 7 1/2" blades, if that is actually the measurement) are designed for a 5/8" arbor. If you put a modern blade on there, it'll be a sloppy fit with that extra 1/8" of play. Sure, you could crank the arbor nut down in an attempt to hold the blade in place, but with the torque applied to the blade when it hits wood, I wouldn't count on it holding safely. Even if it did, I wouldn't count on a nice, true cut from it. And, when you put the blade on, all the extra 1/8" of room would be at the bottom since gravity will be on and it will pull the blade down so the arbor hole sits on the arbor itself. Once you've got it tightened down, you fire up the saw and the blade bounces as it spins out of round - not exactly a safe situation, either.

Therefore, you'll need an adapter to accommodate a modern blade with a 5/8" arbor. I hit up my favorite internet search engine with

saw arbor adapter 1/2 5/8

and came up with a variety of options.

There was this post at the Bob Vila forum (from 2005) that has several on-line references and a recommendation to cut a thin piece of copper tubing to use as a bushing. (I'm not sure I'd go with that one, see cautions above).

There were a wide variety of arbor adapters to allow blades with a 1" arbor to work on a 5/8" arbor - make sure you avoid those, that's not the adaptation you're after.

Many of the adapters I found seem to be for hole saws and angle grinders, so without making any recommendation (and at the risk of being down-voted for providing shopping info) I'll list a couple of options, just to ensure you're on the right track:

• McMaster-Carr
  • this one is a ring that fits within the saw blade itself (makes the copper pipe adapter seem more reasonable, though this one is steel).
  • you'd need a handful for different blades, or to carefully transfer this one to each different blade you're going to use.
• Amazon
  • This one threads onto the arbor and gives you a new arbor diameter with new threads for a different arbor nut.
  • A new arbor nut should be fairly easy to find as that seems to be the modern standard. I'd suggest taking your adapter in to your local hardware store and ask to borrow the arbor nut off of one or two of their table saws to ensure the threading is correct, then purchase a replacement arbor nut from them.
  • Keep the old one off your Craftsman as a souvenir/for authenticity (you never know when it'll become a collector's item).
  • If I went with an adapter like this, I'd put some thread locker on between the old arbor and the adapter, just to help keep it in place while tightening and loosening the arbor nut. Essentially, it becomes part of the tool.