After seeing a number of setups and procedures on the web that are used to set jointer knives. I thought that the best methods were the one that used a dial indicator. I designed a setup using two precision 1-2-3 blocks and two dial indictors. These precision 1-2-3 blocks are ground and cases hardened and are used in precision machine setup and precision measurements. The blocks are 1” by 2” by 3”. They are parallel within 0.0002”, flat within 0.0002” and square within 0.0002” they are also case hardened. The 1-2-3 blocks that I was looking for were the perforated ones having both tapped and plain holes. These blocks have 23 holes through them, 5 of the holes are threaded with 3/8-16 NC. I was able to get the 1-2-3 blocks at LittleMachinShop.com for $12.95 for a set of two. (http://littlemachineshop.com/products/product_view.php?ProductID=1233&category)
I wanted to use ¼ – 20 Star Jig Fixture Knob to hold a mounting bar to the 1-2-3 blocks so I had to make a threaded insert to go from 3/8-16 thread that are machined in the blocks to ¼ – 20. To do this I modified two brass threaded Insert for hard wood by removing the outer wood thread and turning it down to a 3/8” diameter on a lathe and then re-thread the outside using a 3/8-16 die.
Next I needed a mounting bar for the dial indicator, I used a piece of aluminum ½” x 1 ½” x 4 ½” long, I drilled four holes to act as mounting holes. The two of the holes are ¼” to mount the bar to the 1-2-3 in two different locations. One hole is 3/8” hole that is used to mount the dial indicator which is held in place with 8-32 knurled nut and pan head bolt. The fourth hole is drilled into the end of the aluminum and taped with an 8-32 tap. See drawing for details for the drilling the hole patterns.
I’m using two dial indicators that are fitted with a flat tip. The tips are mounted to the dial indictor rod using 4-40. The tip is 5/8” in diameter which makes it easier to place the dial indicators over the jointer knives at top dead center on the cutter head. I end up making my own flat tip but you can buy a set from Little Machine Shop for $4.95 at http://www.littlemachineshop.com/products/product_view.php?ProductID=1783&category I also purchased the dial indicators were from Harbor Freight for about $14.00.
Note that the photo show I am using two dial indicators setups. The indicators have flat tips installed to more easily determine “top-dead-center”. Although you can set jointer knives with only one indicator, two of them are nice because you can immediately see the movement you are introducing at the opposite end (and there will be some) when you are adjusting the knife. The gauges are zeroed with its flat probe on the outfeed table. Move the dial indicator setup onto the edge of the knife and rock the cutterhead back and forth to find the exact top of its arc. Read the dial and adjust the knife height to bring the pointer back to zero. Do this at both ends of the knife, check it over its full length by simply sliding the gauge across the outfeed table and you are ready to move to the next knife.
The following are the steps that I used to set the jounter knives,
Step 1: With the tool unplugged remove the knives, clean all dust and debris from them, the gibs, and the cutterhead slots. Lightly coat the parts with a light machine oil to help make adjustments easier,If the knives need sharpening, have them reshaped or replace them.
Step 2: Place the knives in the cutterhead, making sure they sit below the outfeed table height. Snug the gib bolts to hold the knives in place. Do not tighten yet.
Step 3: With the dial indicator mounted in the holder (as shown in the top photo) Set the 1-2-3 blocks with dial indicator mounted in the bar on the outfeed table and zero out the dial. Move 1-2-3 blocks with dial indicator mounted so the probe rests on the edge of the knife and rock the cutterhead back and forth to find top dead center. Read the dial and adjust the knife height to bring the pointer back to zero and you are done. If you have only one 1-2-3 block with a dial indicator setup you will check to both ends of the knife, check it over its full length by simply sliding the 1-2-3 block with the dial indicator across the outfeed table and you are ready to move onto the next knife
Step 4: Using an Allen wrench and the jackscrews in the cutterhead, raise the knife until the dial reads zero along the entire length. Tweak each end of the knife to reach the desired height.
Step 5: Gradually tighten the gib bolts in the sequence shown so the knife won’t creep upward and need readjusting. Recheck the knife height, and repeat Steps 5 and 6 on the remaining knives. Check all bolts and guards before turning on the jointer.
-- Jake Brain, Florida