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JOINTER KNIVES INSTALATION USING DIAL INDICATORS

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Blog entry by Jake Brain posted 03-05-2012 12:34 AM 5239 reads 0 times favorited 4 comments Add to Favorites Watch

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



4 comments so far

View ShipWreck's profile

ShipWreck

536 posts in 2409 days


#1 posted 03-05-2012 01:23 AM

Why not just square the blades up to a well squared piece of stock? Been doing it all my life with great results…...... it is simple and gets the same results without all the technical stuff.

View chrisstef's profile

chrisstef

10847 posts in 1662 days


#2 posted 03-05-2012 01:29 AM

Certainly looks like youre gonna get sopt on results with that rig, thanks for the great write up too. What would be the acceptable tolerance between either end of the knife?

-- "there aren’t many hand tools as awe-inspiring as the #8 jointer. I mean, it just reeks of cast iron heft and hubris" - Smitty

View canadianchips's profile

canadianchips

1831 posts in 1653 days


#3 posted 03-05-2012 01:53 AM

The tolerances at each end of knife should be zero. BUT the proper height should be slightly higher than outfeed table !
I’m with ShipWreck I use steel straight edge along outfeed table over the knife,if knives carry it back 1/4-3/8” inch the height is right.
http://www.woodcentral.com/bparticles/knife_adjustment.shtml

-- "My mission in life - make everyone smile !"

View Jake Brain's profile

Jake Brain

50 posts in 1426 days


#4 posted 03-07-2012 01:23 AM

I have done a little research on this, and have found that there is a lot of conflicting information.

In theory, the knives should be set to be even with the out-feed table and setting them a few thousandths higher doesn’t make that much difference. Setting them a few thousandths lower will result in a taper, so it’s often recommended to set them a few thousandths higher, which will account for wear as the knives dull.

The use of a dial indicator, is not required, you can use other techniques however the dial indicator(s) will tell you more and will allow for a little more control of the process.

Going through all the trouble to set the knives to ± 0.001” or so pays off, the knives stay sharp longer and the finish is noticeably better.

-- Jake Brain, Florida

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