I have a Craftsman 10" Radial arm saw. It’s probably at least 30 years old, and looks like it was made to last. Unfortunately, the motor’s power seems to have diminished - it takes a long time to start up, and if I don’t cut very slowly, it stalls. It’s not a lubrication issue, as the blade turns fairly freely when the power is off.
Any ideas? I’m hoping it’s something simple like the brushes…
When did you last change the brushes?
Motors act funny when their carbons get down to the last few mm, and the springs/clips have to push extra far to force contact with the rotor.
That’s where I’d look first. Change the brushes and clean the commutator.
If it’s 30 years old, it could benefit from disassembly, thorough cleaning, lubrication of bearings, and such. Do that, and you’ll get another 30 out of it.
Unless it’s a fractional horsepower motor, which is unlikely for a radial arm saw, it most likely is an AC induction motor, and doesn’t have brushes and a commutator. Check and see if it is a capacitor start motor, it will most often have an external capacitor. Check and see if you can replace the capacitor, that will most likely eliminate the slow starting problem. The other thing thas happens is that some motors have an internal centrifugal switch that switches from the start winding to the run winding once the motor gets up to speed. This switch can get gummed up, a thorough cleaning as suggested by danceswithcats would help this also.
Oh, and if you do replace the capacitor, make sure it is the correct type – a motor-starting capacitor (non-polarized). A polarized electrolytic capacitor will blow immediately, even if it is the same capacitance and voltage.
be sure and use the right value as well… just because it looks just like the other cap, doesn’t mean its the right value. Caps are rated in microfarads, the symbol looks like a lower case “u” with a twisty little tail. Also they are rated in volts… typically 250-500 V for your type of motor, but go by what is written on the capacitor.
Check your yellow pages for electric motor repairs. Be prepared to disconnect your capacitor and bring it in, to get the best replacement. Cost should be under $15 or so…
How to disconnect your cap:
If the cap is leaking an oily/sooty fluid, it is most certainly shot.
try not to get this fluid on your skin. Some caps of that vintage contained PCB’s, ((Polychlorinated bi-phenols) which are toxic. If you do get it on your skin, wash it off.
Installation is the reverse of removal, with the exception of shorting the cap.
Good luck
FML
Thanks for the great responses so far. What cleaners and lubricants do you recommend? Would any motor oil work for the latter?
What I’d use to clean things out *if * you can find it is 1,1,1,-TCE, the TCE standing for trichloroethane. It’s a great degreaser, and works well to flush old lubricants from bearings. Once the old stuff is cleaned out, see if you can determine what the manufacturer recommends regarding replacement lubricant. If Sears has a spec, you can then use it to match a proper replacement lubricant from an industrial source such as Grainger or MSC. If you’re a consumer, find a friend who has an account. 
I came in also to suggest checking the capacitor, but I want to add a question. Does the motor quickly get very hot? If it does that would also indicate the need for a new capacitor.
A radial arm saw would most likely have a series (universal) motor. Due to high rpm operation, they are much lighter for the same power. Thus all the gantry mechanism can be lighter for a given stiffness and precision.
So try cleaning the commutator and replacing the brushes. The other possibility is a shorted winding. Most larger citys will have at least one shop that specializes in rewinding electric motors…though they often don’t want to mess with anything that small.
Really now TCE !! And all those tax payer dollars that are used to clean it up.
TCE is really bad for the environment
I wasn’t advising anyone to pour it on the ground.
So where were you planning to dispose it at the end ?
I have an older radial arm saw of the same vintage. It was given to me as none working. You must remove the brushes prior to any other disassembly, you can damage them if you don’t. To check the brushes, you will notice 2 caps on the sides of the motor on the opposite end of the blade. Remove the caps and there will be a couple brass covers. On some the brass covers are part of the outside cover. Removing the covers will allow you access to the brushes. You will see the spring end. Gently remove the spring and carbon part. The original brush would be about 1 inch long. You will likely find a lot less. Now comes the problem. Sears has become terrible in recent years in supporting older equipment. To fix my saw, I had to buy a couple of brushes for a Makita saw and file them down to fit the Craftsman saw. There are a couple sites on the internet that still sell parts for older tools, the one I used is no longer online. I found the site by Googling the saw part number.
Do not used motor oil in the saw. It will run out when heated. Used a good bearing grease at the bearing assemblies and white grease everywhere else lubrication is required. To clean the parts I used isopropyl alcohol and a stiff stencil brush, it got everything clean enough without the worries of dealing with hazmat. I redid everything about 5 years ago and the saw works okay, I prefer to use my much newer Delta miter saw for most of my cuts.