May 01 2012

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Making My Own Riving Knife

In February Tom Hintz of NewWoodworker.com posted an article with a video about kickback that got the woodworking community talking. In the video he pushed a board through his table saw without a riving knife and twisted it at the end of the cut. The board and push block flew out of his hands and his hand almost kissed the saw blade.

This really got my attention, I’ve been using my table saw without the factory guard since I got it because the guard is cumbersome and wasn’t designed to be removed and replaced easily. I perform many different operations on my table saw and I really don’t want to spend 10 minutes monkeying with the poorly designed guard. After seeing this video though, I started looking for a way to retrofit my DeWalt 744 with a riving knife.

After searching, I only found one company that makes custom riving knives, splitters, and guards for my table saw: Leeway Workshop LLC. makers of the Shark Guard blade guard and dust collection system. They also sold just the riving knife for my saw. There was one problem, right on the home page it said lead times were 8 to 10 weeks. After reading the entire site, I found PDF of the riving knife pattern. After looking at that pattern and examining my factory guard, I thought I could make my own, using this pattern. I could have just copied the factory guard and cut off the top, but since I had a simple pattern to follow it wasn’t worth the effort to duplicate it.

I decided to make my riving knife out of 12ga steel because I only use full kerf blades, I could have gone thinner, but I’m glad I didn’t. None of the local hardware stores carried steel this thick, so I ended up ordering a 12″ square piece on Amazon for $15. I know this was a little expensive for a piece of hot rolled steel, but it beat driving to a steel yard in Minneapolis and trying to find a small piece that wasn’t rusted to hell.

Once I got the steel in the mail a few days later, I printed out the pattern, verified that the dimensions were correct, then glued the pattern onto the steel. This was probably a mistake, I should have traced the pattern with a Sharpe instead. As I cut around the outline with my jigsaw, I shredded the pattern, but somehow I still managed to cut out the right shape. For the mounting slots, I drilled a hole at the top and cut the rest of the slot with the jig saw. I messed this part up pretty badly, still I got the riving knife to work. I decided not to cut the guard mounting slots on top of the knife, because I did such a poor job on the simpler slots.

The jig saw left a really ragged cut line, so I tried using my bench grinder to shape the metal. When that didn’t work to my satisfaction, I discovered that my oscillating sander was the best tool for the job. I spent a lot of time going between the sander and my table saw checking the fit of the knife. I didn’t want it to get to close to the blade at any one point even if one of the two bolts that hold the knife loosen and allow it to rock towards the blade.

Once I was satisfied with the fit of the riving knife, I removed it once more and gave it a coat of paste wax to protect the metal and make the knife slippery. Then I concentrated on getting the knife aligned with the blade. The knife is held in place by a plate with two bolts. Between the plate and the trunnion arbor assembly are a series of thin shims. By varying the number of shims between the trunnion arbor assembly and the knife it centers the knife on the blade. Since the knife is slightly narrower than the blade, rather than trying to center the knife, I decided to bias the knife position towards the fence side. This made it easier to position and I figured I would get a cleaner cut on the keeper side (for me usually the piece between the blade and the fence) on the work piece.

When I finally fired the saw up and cut a test piece, it was like I was using a new saw. First I no longer had to try to push the piece forward and against the fence, once the piece hits the riving knife, the knife keeps it against the fence — one less thing to distract you from the spinning blade. Second the cut I got was as clean as if it had been made on a jointer. Usually I’ll have at least one section of the cut with kerf marks and depending on the wood, some burning, but the cut edge on the test piece was as smooth as a baby’s bottom. Above you can see a piece cut with the riving knife on the right and without on the left.

The take away from this article is that if you aren’t using a riving knife you should be. At the very least you’re increasing the safety of your table saw. In my case it gave me much cleaner cuts. There’s really no excuse, even if you saw didn’t come with one. You can either purchase one from someplace like Leeway Workshop LLC, which makes safety equipment for just about every saw I’ve ever seen, or it’s fairly simple to make one to replace your crappy stock guard. Given the amount of time I futzed around trying to build mine, if I had to do it over again, I think I’d wait and order a Shark Guard riving knife.

*note: I contacted Lee at Leeway Workshop LLC after I made my guard and asked him if he was OK with me posting a guard made with his pattern. He told me that sometimes he actually has the parts in stock, but they tend to sell out pretty fast, so before you get scared away by the lead time, drop him a note and see if he has your part in stock.

Permanent link to this article: http://workshop.electronsmith.com/content/making-my-own-riving-knife/

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