RT Kickback-what did I do wrong?

[Michael Colip]

Hi All, trying to understand where I went wrong so that it doesn't happen again.

I have a Jessem RT, lift and fence system with a 3 1/2 HP motor. I was using a 3/8" sharp straight bit to do a .7" x 3/8" dado on 1x2 Maple stock (3/4x1 3/4). The dado is on the 1 3/4 side, about 1/4" from the edge. The .7" dado is for undersized Maple ply. Because I'm using a 3/8 bit I cut to full depth on all stock by taking multiple passes. Once the correct depth was achieved I then moved the fence back incrementally until I got the exact width I needed (~.7"). On the last pass, the bit immediately pulled the stock past the bit and shot out the other side. The last pass was set up to remove a bit more than 1/16", really no more or less that cuts up to this point. Also, I use Jessem stock guides to keep the stock held down and against the fence.

My first obvious thought was that because I moved the fence back, thereby creating a void between the back of the bit and the stock but that shouldn't be the cause as the front of the bit hit the stock in the correct direction...right to left.

Where did I go wrong?

Thanks,
Mike

[Michael Burnside]

Hard to say for sure, but I haven't used a straight bit in years. IMHO, throw them away and get a set of upcut and downcut spiral bits. Not only are straight bits prone to tear out, they're directional and want to pull the stock linearly. I'm guessing at full depth you had some tight grain in the maple that was perfect for catapulting the workpiece along the table.

[Jim Becker]

Did you have a feather board or equivalent holding the stock to the fence?

[Michael Colip]

No, just the Jessem stock guides

[Doug Garson]

Just to make sure we understand what happened. For the last pass you moved the fence back meaning away from the bit so you are cutting on the side of the bit away from the fence ie on the side nearest the front of the table. You moved the stock from right to left with the stock guides pushing the stock toward the fence and the bit grabbed and threw the stock. Which way, to the right or left? The stock guides should have prevented the stock from moving left to right and the bit should have tried to push the stock from left to right. Where the stock guides set too high so they did not apply adequate pressure to the workpiece or are the wheels on the stock guides worn smooth ? Did you momentarily stop pushing the stock against the resistance of the bit?

[Jim Becker]

With nothing to positively keep it to the fence, the workpiece likely moved away just enough for the tooling to catch the existing edge and fling it. The stock guides are great but didn't do the job here.

[Doug Garson]

With nothing to positively keep it to the fence, the workpiece likely moved away just enough for the tooling to catch the existing edge and fling it. The stock guides are great but didn't do the job here.

Don't they push the stock down and against the fence?

[Michael Colip]

Thanks Doug, to answer your questions, yes, to moving the fence back, yes to the feed direction. the stock flew to the left, the same direction as the feed. It actually put a dent in the wall, about ten feet away. The stock guides were fairly tight. I'll ensure they are tighter in the future.

Also, the Maple was quite clear with no crazy grain. Could have been a fluke but if this has ever happened to you it's a bit scary.

Thanks

[Doug Garson]

Sounds like the stock moved away from the fence and the bit engaged the edge of the dado nearest the fence and threw it. The stock guides didn't do their job either not set tight enough or they are defective or worn. Might be worth contacting Jessem and hear what they say.

[mike calabrese]

Not sure I completely understand but I will have a guess as to what happened. You made a climb cut the most dangerous cut on a router / router table.
have a look here and never make a climb cut(if that is what you did) again. PLEASE
calabrese55
https://www.youtube.com/watch?v=KPx3cptC4WI&t=474s
https://www.youtube.com/watch?v=mrE4HyXiwqs
https://www.youtube.com/watch?v=IX-fqmwSSl0

[Jim Becker]

Don't they push the stock down and against the fence?

They do, but it may not have been enough

[Mark Hennebury]

photos of the setup please.

[Andrew Hughes]

I don’t know for sure what happened. I do know if the piece that flew across the room put a dent in the wall that dent would be called a apprentice mark.
Good Luck

[Michael Burnside]

Not sure I completely understand but I will have a guess as to what happened. You made a climb cut the most dangerous cut on a router / router table.
have a look here and never make a climb cut(if that is what you did) again. PLEASE
calabrese55
https://www.youtube.com/watch?v=KPx3cptC4WI&t=474s
https://www.youtube.com/watch?v=mrE4HyXiwqs
https://www.youtube.com/watch?v=IX-fqmwSSl0

The OP said they "moved the fence back incrementally", so it wouldn't have been a climb cut, unless I'm not understanding the comment. If I'm misinterpreting their meaning of "moved the fence back incrementally" then I agree, this is a recipe for some fast moving stock with a straight bit.

[Christopher Charles]

glad you weren’t hurt! My guess is the bit grabbed and the guides kept enough pressure toward the fence to allow the bit to hold onto the work piece and keep accelerating it rather than cutting (as with feather boards) or just kicking it away. Are there marks on the inside of the dado?