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The blade on my Skilsaw model 5150 wobbles quite a bit. I can tell the wobble is coming from the shaft itself. (I can grab the shaft and wiggle it around quite a bit --- the result of the "looseness" in the shaft is about a 3/16" wobble on the rim of a 7-1/4" blade.)
I found this diagram: http://www.ereplacementparts.com/skil-5150-type-f012515000-714-circular-saw-parts-c-130_160_831.html, but I can't tell what part is supposed to keep the shaft from wobbling.
Any suggestions are appreciated.
If you're sure it's the shaft that's loose, and not a misalignment in the blade attachment, then it's most likely one of the bearings supporting the shaft that's bad. Check for play in the bearing flange (Component 36). If that's solid, then check the bearing sleeve (component 13). Unfortunately if it's the armature that's damaged (component 3), then you're better off buying a new saw.
You will need to open up the saw to find out for sure.
The most common cause of wobble like this is that the bearings or bushings are worn out. These are the things that hold the main shaft in place. They should be a close fit to the shaft, and the shaft rotates within them. When they are worn out, there is too much room and the shaft flops around or wobbles.
In the linked parts diagram, these would be items 13, 814 or 818, and possibly 39. I notice that two bearing sleeves are listed on the side of the page under "popular parts"; no surprise there.
When you open it up, you will likely find that one or both of the bearing sleeves is not fitting nice and smooth on the shaft. It will probably look like an oval or egg-shaped hole in the bearing instead of a perfect circle.
I recently did this replacement on an electric hand drill. Same situation-- bushing was worn, drill chuck wobbled too much, replaced the bushing, now it runs smoothly.
(As to the name bearing versus bushing: if it has an inner and outer ring with balls or rollers in between, it's usually called a bearing. If it is a single part where the shaft just rotates directly in it, it's usually called a bushing. But both are doing the job of holding a rotating shaft. If they want to call it a bearing sleeve when someone else might call it a bushing... well, it's still doing the same job so no big deal)
If it is the bearings,as in the shaft has lateral play in it, the saw is junk. This saw retails for under $50 and if it has an internal problems, it is not worth fixing in my opinion. This saw is typically sold in box stores for light duty occasional homeowner use and is not designed to be tough enough for strenuous use. Rather than spend a bunch of money and time trying to fix a cheap saw, buy a new one or invest in a good grade contractor model.
I disassembled the parts and found the bushing worn in my saw. Because the bushing was worn, ( the saw is is a Mastercraft and over 20 years old) I did not anticipate that I would get replacement parts. I took the bushing to a machine shop and got one made by the machinist. The cost was about 20 USD. However, he made the replacement from Brass and it quickly became also worn. I went and complained and I am expecting to get another replacement made from steel to collect tomorrow.
