Wednesday, August 24, 2011

A homemade riving knife

Recently I heard my table saw making a funny noise when it was winding down. That's never a good sign. I have a delta-rockwell 34-350 with a 3 hp motor in it, if your not familiar with the saw this saw takes a 12" or 14" blade, and the motor is a real 3 horse, it weighs in at about 150 lbs, and needs a 220V 20 amp circuit.

So when this saw makes funny noises I respect it and try to find out why.

After a little searching this is what I found. This picture is looking down through the insert hole at the arbor. In the middle you'll see the threaded thing. That piece is a retaining ring and threads in to the yolk to hold the arbor bearing in place. Now I'm not a mechanical engineer, but I am certain that loose bearings holding a 12" blade spinning at 3400rpm is a bad thing.

So although I had other projects going on at the time (don't we all) I decided I needed to put the ring back. So after a few checks I wasn't convinced that I could just grab a spanner and tighten up the retaining ring, I was afraid sawdust had gotten around and in the threads and in any space left from the bearing moving. So I decided to pull the arbor, clean it up, and re-assemble.

And of course in order to pull the arbor I have to remove the table, remove the motor, and pop the whole thing out. And when growing up on a farm you learn that any time you pull something from a bearing, you replace the bearings. And since I was tearing it down, and this tablesaw is at least 50 years old, I would have the motor rebuilt at the same time. So this will include a bearing job, and motor rebuild as well. And if you're wondering about rebuilding a motor, it's a really easy job. Just take it to a motor rebuilder and pick it up a week or two later.

At this point your probably wondering why this post is titled a homemade riving knife, since I haven't mentioned a riving knife yet. It's because I decided that since I will have the entire saw stripped down I will add a riving knife. I had a close call a few weeks ago with a piece of wood pinching the blade. Fortunatly this piece was only about 18" long so I was able to finish the cut, but it made me pause. A pause that made me consider going out and buying a sawstop, and if it was in the budget I would have. But anyway over the next few weeks I will post my trials, and try to detail the design process I go through to make the riving knife.

I won't claim that what I'm doing will be successful, or that it's even smart, but I'm hoping that some of you will help in this effort and offer some suggestions on improving my design, and in the end I'll end up with something that's safe and works reliably and well.

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