In the photo you see an original blade with 1 1/4 inch hole (satin finish). It is resting on top of a new 9 inch 40 tooth carbide tipped blade with a 5/8 inch arbor hole (chrome finish). You can also see the special mount that requires a 1 1/4 inch arbor hole. The blade fits onto the shoulder on the left piece. The nut on the right screws onto the fitting at the left to lock the blade between the two pieces.
I used a marking pen to outline the size of the new hole on the carbide tipped blade.
Step 1: Mount the blade for enlarging the hole
I glued a scrap piece of fiberboard at the center of the plywood disc and marked the center while the lathe was running. I scribed a 5/8 inch circle on the scrap of fiberboard.
Step 2: Turn the scrap to make a center for mounting the saw blade
Step 3: Mount the saw blade
Step 4: Begin cutting out the center to enlarge it
When I thought I had cut about half of the way through the blade blank, I turned the blade over and began cutting from the other side. You can do this while the fiberboard center is in place, but after it no longer supports the blade you will not want to disturb the blade's position in any way.
If the blade did somehow move off center while you are working on enlarging the hole, you could always glue a larger piece of fiberboard to the center of the plywood disc and turn a centering piece the exact size of the hole at that point. That process would center the blade exactly again. Then fasten the blade firmly to the plywood disc and remove the fiberboard centering disc so you can continue to grind the size of the hole to the size needed.
I tried to keep the blade from getting hot. It did not seem to be a problem, anyway.
Step 5: Grind to size and finish the arbor hole
I used a draftsman's divider to compare the size of the shoulder on the Sawsmith blade mount with the size of the hole. When I was sure the size of the new hole was very close to fitting, I removed the blade from the lathe's faceplate. The shoulder of the blade mount almost fit into the hole. I very lightly went around the inside edge of the new hole twice with the grinding stone while holding the Dremel by hand. That was just enough so that the Sawsmith blade mount fit into the hole easily, but without any looseness.
Step 6: The final product
The blade runs true and on center without any vibration. This blade will make my friend's Sawsmith radial arm saw more useful for many, many more years.
Update--May 16, 2009: My friend was laid up with a badly broken leg at the time I fitted this blade for his saw. He has also been traveling since his leg is out of its cast. He just got his first opportunity to use the saw with the new blade. He cut some birch veneer plywood for a project. He said the blade works perfectly.
Update--January 26, 2010: I recently considered buying a corded 5 1/2 inch Skil circular saw (sidewinder with left-hand blade). That saw uses a 1/2 inch arbor. Blades are not widely available. People are usually told to buy 5 1/2 inch blades with 5/8 inch arbor holes and add to that a special bushing to make up the difference. But, 5 1/2 inch blades for battery powered circular saws are widely available. The only problem is that blades for these battery saws use a 10 mm arbor (2.7 mm smaller than 1/2 inch). The process described in this Instructable could be used to enlarge a 10 mm hole to 1/2 inch, but not step 4. Make a wooden center 10 mm in diameter. Mount the blade to a faceplate as in step 3. Remove the wooden center and grind the hole size to 1/2 inch.