Apologies if this is common knowledge and I've been lost in a desert of ignorance. A previous post about another question I had about my Unisaw restoration (thanks Chris) raised the question of shims and aligning the blade to the table when the blade is at 90 degrees AND 45 degrees. http://www.sawmillcreek.org/showthre...Unisaw-rebuild number 15. I had never heard of that but sure enough there is such a thing and turns out my saw needed it done. We’re not talking about making sure the blade is at 45 degrees from its vertical position but is at the same height relative to table top at the front and back of the blade. It took me a while to figure out the explanation located at the links posted in my earlier thread. I finally figured out it’s nothing more than assuring that the table is parallel to the shaft of the raising mechanism. If it’s not then the blade is either closer or further away from the table top on one end of blade. When wood is passed by the back of the blade after being cut at the front, the blade back will cut it a second time on one side of the blade or the other at the rear of the blade (when angled) depending on the table alignment. If bad enough, it may bind the wood if using a fence or even deflect the blade. In any event it was simple enough to check and I found my blade (actually the table) was .018 inches out of alignment at 45 degrees measuring with a micrometer mounted in the miter slot. It was closer to the table at the rear of the blade meaning my saw’s top was not high enough in the front.
That .018 inches was over the measured length of the blade which in my case was 8.5 inches. That’s where the micrometer measured the blade at the gullet of the same tooth in back and front. That distance is critical to making the table parallel and will vary between setups. Another critical measurement is the distance between the front and rear table mounting bolts. The left and right side are the same on my Unisaw which means that both the left and right shims placed under the front bolts to raise the table will be the same thickness. If the bolt pattern on one side differs in distance apart from the other side the shim thickness will be different on each side. I measured the distance between front and rear mounting bolts to be 20 inches.
Armed with the math instructions in the linked post I calculated that I needed a .06 (almost 1/16) inch shim under the front mounting bolts. Found some washers nearly that thick and mounted them. Rechecking per the procedures instructions it was now .005 inches off from front of the blade to back. Much closer but I ran through the procedure one more time just to see if I could get it closer. I Used some sand paper for additional shim material on top of the washers. Final result was within .001- .002 inches front to back. Before each check at 45 degrees the table miter slot is set to be parallel to the blade at 90 degrees. Easy to do on a cabinet saw.
Oh, instead of the table being shimmed, one could also shim the trunnion. Same difference just easier for me to do the table. Normally, I’m not anal about things like extreme alignment, but found this easy enough to check and was surprised it was so far off. I haven’t used the saw yet as I still have some pending things to do before I can use it but at least, if there are problems I’m confident it won’t be from an alignment issue. Plan on checking the saw I’m replacing just to see if it might explain why I always had accuracy issues with angled cuts. Live and Learn.
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