Monday, October 10, 2011

Well it's finally done. Actually it was done a week ago, but I've been so busy I haven't had a chance to post. So I am going to do the update now. I have been using it for the past week, quite a bit actually, and it's been working great!

After completing all of the parts, and before installing them I painted them.

The picture doesn't show a lot but if you look close you'll notice the knife itself is missing from here. Because once I got home I checked the width of the knife against the width of the blade. The knife was .135" wide and the saw blade teeth are .120". This was not good, so in order to flatten it I tried running it though my drum sander. That didn't work to well, because after 2 hours of sanding it was down to .130". But fortunately we have a surface grinder at work. So the next day I stayed late and ground down the blade to .110". I planned to paint the knife and figured a little thinner is better than thicker. And with the paint on it's .115.

Now that that was taken care of, the first thing I had to do was to mount the pivot ring. In order to get it centered I turned a stepped cylinder on my lathe.

The smaller end fit's in the arbor hole, and the larger end is the same size as the pivot ring. I slipped this into place and marked the holes on the yoke (I turned it a touch to small hence the tape).

I then drilled the holes for the screws and tapped them for a 10-24 screw.

With the screw holes in place I mounted the ring, and fortunately it came out to be in the center (It looks like the entire ring is painted in this shot, but only the face where the screws are mounted is painted. The parts of the ring and mating flange that touch were masked off and left unpainted.

I then quickly found out that I had to remove the ring to get the retainer behind it. Then I mounted the flange and the retainer. I spun the whole thing a few times to check for interference from other parts and happily it cleared everything.

Then I installed the adjustable arm mounting bracket.

And then the arm.

This is actually an after picture. with the arm installed I found first that I had drill the pivot hole in the wrong location. I must have moved the table on the mill in the wrong direction from my marked point, since the hole was 1/8" above the line when it needed to be 1/8" below the line. So I flipped the piece and re-drilled the hole on my drill press. The arm also hit the letters that were cast into the yoke (visible just below the arm in the above pic) and the yoke casting also flared out a lot from the pivot point and I had to grind some of the arm away to clear these two obstacles. But after that everything moved freely and apparently level.

So the I installed the arbor assembly.

And the next part was probable the hardest part of the entire installation. Putting on the belts. I used a car jack to lift the motor after the retaining bolts were loosened. When installing the belts and lowering the motor I found that the motor had to be perfectly level to the arbor or 1 of the 4 belts would be slack. I had always intended to put the original belts back on, since I remembered them being in good shape when I took them off. But after looking at them when the time came, they were in pretty rough shape. So after calling every place nearby that carries belts, I found that no one had 4 in stock. Actually no one had more than 1 in stock. So I drove to Woodcraft and picked up some link belt. I like link belts since they do a great job of eliminating vibration and they are always the correct size. but they are overkill on this saw since it never vibrated anyway. but here's the arbor in place with the belts on.

I gotta admit it does look pretty cool with those belts on though (of course you can't see them with the top on).

Next was the knife arm.

At this point I pulled out my Wixey angle gauge, zeroed it with one of the cross members and put it on the far end of the arm. I then adjusted the pivot point of the arm up and down and forward and back until I had it pivoting (almost) perfectly. Whenever I would tighten the bolts it would go out just a hair, but when all was done it was only off .8 degrees through it entire rotation, and this is most likely due to the pivot ring not being perfectly centered. but that only translates to .018" of a difference in height of the knife which is about 1/64" so I can live with that.

At this point I put the blade on the arbor and knife on the saw. I had to do a little grinding for clearance from the blade, and shorten it's height just a tad. I also ground a bevel on the front to have a knife edge so the wood would not hit an abrupt edge. So when when I was done it was about 1/8" from the blade, and about 1/16 lower than the top. The split in the arm worked really well, I had to fuss with back of the arm a little to get the knife perfectly aligned with the blade. And the oversized hole design allowed me to do that easily. The knife holding mechanism works great as well. 1/4 turn and the knife comes out. But since this works the way a riving knife should, I will only be removing it when I put my dado stack in.

Awesome! So at this point I put the top back on adjusted everything and here it is:

I repainted the knife after taking the picture and forgot to take one after that. But the knife works perfectly! it goes through the entire range of motion of the saw, tilting and up and down.

And after using it a little, I actually had a piece of wood close up and pinch the knife! The blade spun like the wood wasn't there, and I was able to safely shut down the saw and remove the wood. This wasn't something I was trying to do, but not only does the knife work going up and down while hugging the blade but it also works as the safety device it's supposed to be!

So all in all this was a huge success! I have about 40 hours in the design, and another 40 hours in the building of the pieces. I am a much better machinist that when I started (I'm still not that good but better than when I started).

I'm very happy with all of this in every way, and now I'm happy to get back to real woodworking. The next thing I plan to make is an overhead guard that hangs from the ceiling with dust collection built in. I also have to work on the dust collection in the saw, but I was anxious to get back up and running so that will be sometime in the future.

If you decide to build one of these and have any questions let me know.


  1. Tim,
    I own a 10" Unisaws and would like to add a riving blade also. Could you please email me a copy of your design.

    My email address

    Nice work

    Thank you

    Eric Kipker

  2. Thanks for sharing this wonderful idea, with the helps of the wooden screws you easily to establish your work and make it faster and easier.

  3. Hi Tim,

    Great job on this. I have been looking for something like this for over a year. Your idea is by far the best that I have seen.

    I have a left tilt Unisaw that I would love to adapt to a riving knife saw. I hope that it is not asking to much but could you please send me any information that you may have that would help me with this project.

    My e-mail is

    Thanks so much,


  4. Hi Tim, great work, I intend to copy this concept.

    I have read most of it but can't find info about one thing; the front flange and the retention ring is screwed together and rotates around the pivot ring. How big axial gap do you have in this interface? If all parts were zeroed I guess the would have problems rotating.

    To add to this, assuming a small amount of axial gap; when tilting the blade, does the knife stay in line with the blade?

    Would be very thankful I you have time to answer these questions.

    Best Regards Ola

  5. the pieces were made from the same piece of sheet steel. In order to allow them to rotate. The piece was turned to fit, and has about .0001 clearance which is the accuracy of the lathe. For the Axial clearance I polished the faces of the part. This removed enough material for it to spin freely. I polished it with sandpaper on a granite block. I started with 600 grit, and went to honing compound. It had a mirror finish when I was done. When in place you can't see or hear movement, but it must be there as is spins great. This is not to much work for a 1 off part, but to get those tolerances in a production environment would drive costs though the roof.

  6. Many thanks for your answer. Due to size constraints I hade to make a slightly different solution, ended up with a kind of home made sliding bearing where I can fine tune the freeplay. Anyway, I will finish my work this weekend, everything looks great so far.

  7. Once again, many thanks for your help and thorough description. I finished my work today, quick movie here it works great.

  8. Great R&D, I bet you saved many countless hours of developing their own.
    Any chance of getting your final design emailed to me so I can create my own? I have just bought an old unisaw and it is going to be restored starting tomorrow and I would really like a proper riving knife fitted.

    If you choose to share your design, it would be greatly appreciated.


  9. Tim, it’s been a while since you built this &put it into service. Are you still happy with it? Has any play developed over time? I’m really impressed with how you visualized the design, then built one that works so well. I too have an older unisaw & would really like to attempt to build one. If you would be so kind to send me more information at I would really appreciate it! Thank you!

  10. Hi Tim,

    If you're sending plans out I would appreciate a copy HUGELY. Almost all my tools in the shop are vintage Delta with the exception of the table saw, due to the lack of a riving knife. I've wanted one for a long time and am so excited about the prospect of adding a Unisaw to the shop. I restored a Clausing lathe last year and am finishing up my Clausing mill restoration this week. If you wouldn't mind forwarding me plans/drawings I'd be forever grateful.

    My email is ""

    Thank you!