Lets cover this first
That is pretty much it followed by adjusting the Tensioning Knob.are there any tricks to mounting the blade, or is it release the cam, insert blade, tighten screws, engage cam
There is not anything on the left side of the blocks as shown in the picture below. The flip handle screw on the right side locks the blade in place. The top assembly is the upper block with the cam and elongated slot and the bottom assembly is the lower block.
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The ends of the arms on the older Gray Model 555220 Scroll Saw are different because the original blade mounting blocks were removed from the arms for mounting the blades. This was done by pulling the spring loaded pin out to remove or insert the blocks on the end of the arm as seen in the picture below. The original pair of Mounting Block Assemblies included 3 parts, the Blade Holder, Blade Clamp and Socket Head Cap Screw which is shown in the drawing below.
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In the picture below is the upper arm of the Model 555220 Scroll Saw and the lower arm end is similar.
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Using the Scroll Saw Blade Block Upgrade Kit eliminates the need to use the original removable pair of Blade Blocks and the Blade Mounting Fixture. The upgraded Blade Blocks are no longer removed when mounting the blades. Because there is no change to the arm you can switch back and forth between the original blocks and the upgrade blocks if desired.
The clear plastic cover was part of the Blade Change Upgrade that Shopsmith made available in the past. That is the main difference between it and the Scroll Saw Blade Block Upgrade Kit that is still available.
Neither the original Model 555220 Blade Blocks or the upgraded Blade Blocks use any set screws.