I have a 10” Craftsman radial arm saw that serves most of my shop cutting needs. However, occasionally I need to cut through material that is just a bit thicker than what can fit under the blade. While in most cases rotating the material and making multiple cuts works, there are some cases where this isn’t possible (say, the material is only flat on one side). In these cases, could I mount a 12” blade on the saw to get a deeper cut depth? Obviously the existing blade guard wouldn’t cover the larger blade and a naked rotating blade would be extremely dangerous, but assuming I made a special guard specifically for the oversized blade, are there other considerations (safety or otherwise) that would prevent this arrangement from working?
The bigger blade will have more mass than the motor is designed to spin. This could cause issues for the motor, potentially burning it out. This is part of the reason that dado blade sets come in 8" size designed for use in a 10" table saw - you're adding multiple blades where only one normally goes, so by making the blade smaller, you're reducing mass, making it easier for the motor to spin.
If you're cutting a softwood like pine, you'd might be OK, but harder woods that the saw may struggle to cut in the first place would definitely be out.
Note: I say might be OK, because I don't know for certain. I would use extreme caution* if I were to attempt this.
*Note that "extreme caution" means I'd mention it to my wife and she would beat me senseless if I attempted it. ;)
Obviously this is questionably safe, even if you can actually fit a 12" blade to your 10" radial-arm saw.
While in most cases rotating the material and making multiple cuts works, there are some cases where this isn’t possible (say, the material is only flat on one side).
There's a very simple and safe solution that should work for any situation you might face: complete the cut using a hand saw.
Any situation in which you can cut through a decent portion of the thickness, or better yet cut around an item one side at a time leaving just a central stub of wood, you're well positioned to finish the cut by hand as the kerf formed by a circular blade makes a very good channel for the panel saw to follow without error.
If you don't currently own a panel saw, modern ones are very inexpensive and because of the impulse-hardened teeth they stay sharp for a very long time so they're great value. Additionally such a saw has numerous other potential uses in a modern woodworking shop.
Really no, it's a deadly proposition.
When these blades turn, the centrifugal force tries to tear them apart, so they have a maximum RPM rating which is usually written on the side. Larger diameter means lower RPM. However if you mount the larger blade on your saw, it will spin at the rpm of the motor designed for the smaller one, which means it will spin faster than intended. Best case, the carbide teeth hit the wood at a faster speed than intended, so they could get damaged. Worst case, the blade splits from centrifugal force, and since you removed the guard, you end up with a chunk of circular saw blade embedded in your face.
It would be a good excuse to get a bandsaw though.