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?

[Thomas McCurnin]

A full 3/4" is a lot of stock to remove, even for a 16th. Yeah, a feather board to hold the stock against the fence horizontally and another on top to keep the stock against the table. I'm not sure what "Jessem stock guides" are, but if they are these: https://www.amazon.com/JESSEM-Clear-Cut-Precision-Guides-JessEm/dp/B00EZDWLSM?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&smid=A19VW1BL9ZXZVA&th=1 then the guides seem to do a great job at holding the work against the table, but not against the fence. You would need to add something horizontally.

[Patty Hann]

A full 3/4" is a lot of stock to remove, even for a 16th. Yeah, a feather board to hold the stock against the fence horizontally and another on top to keep the stock against the table. I'm not sure what "Jessem stock guides" are, but if they are these: https://www.amazon.com/JESSEM-Clear-Cut-Precision-Guides-JessEm/dp/B00EZDWLSM?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&smid=A19VW1BL9ZXZVA&th=1 then the guides seem to do a great job at holding the work against the table, but not against the fence. You would need to add something horizontally.

But it says it holds it down against the table and against the fence: Unique roller system holds down workpiece and pushes into fence for precision stock feed

[Tom Levy]

Too large a cut, no featherboard so the piece wobbled under the pressure and tiny piece with little mass to resist the cutting force. Little pieces tend to fly easier. How about putting the dado into the full width board before ripping and doing that iteratively. More mass and easier to hold and control. When board starts getting too narrow towards the size you just tried, switch to a new full size board.

[Jim Becker]

But it says it holds it down against the table and against the fence: Unique roller system holds down workpiece and pushes into fence for precision stock feed

Yea, but the lateral push to the fence is just friction from the wheels being turned slightly to the fence. It’s not enough to cope with a catch in some cases. The primary benefit is to help with consistent hand feeding.

[Patty Hann]

Yea, but the lateral push to the fence is just friction from the wheels being turned slightly to the fence. It’s not enough to cope with a catch in some cases. The primary benefit is to help with consistent hand feeding.
Oh. ...................

[John Kananis]

I can only see this happening if you initially moved the fence backwards to make the cut deeper and then moved it forward to clean up the 'back of the groove. In which case you're engaging the cutter in the direction its spinning and that is a climb cut. I've seen people do them with power feeders but I would never consider trying by hand.

[Thomas McCurnin]

Yep, from the picture I do not see how it pushes the stock against the fence. It might do so ever so slightly but not like a feather board would.

P.S. I generally do dados with a table saw. Much safer. You can take full width cuts, and if you're paranoid about safety like me, raise the blade up incrementally without moving the fence.

[Bill Space]

From what I can understand from the previous posts, the OP was cutting a dado length wise in a board.

What could cause the board to suddenly be projected away from the operator? There must have been more force imparted in the forward direction than the reverse.

If the stock moved away from the fence, the reverse force would be less than the forward force, all things considered. So the stock would tend to be forced forward.

I think it gets down to the stock not being held securely against the fence.

Seems like there are two worst case options. The stock goes forward or backwards. But the fence prevents excessive cutting that would result in a backward projectile.

Just my uneducated view of what may have happened....

[Warren Lake]

bunch of people guessing at poor info on what was done, Makes no sense at least to me. Ive climb cut hand held from the start and will continue. It always depends on what you are doing and your feel and understanding.

OP feeding material into a cutter and it goes shooting? The gizmo shown says it has 5 degree tilt to the fence so its keeping pressure that way. There is person feeding material that is all that is needed the person pushes the material to the fence as they feed forward. A few scrap feather boards that keep the material down tight help even an experienced person. I decide if I use feather boards more by how many pieces.

[mike calabrese]

The key to this mystery is going to be solved when a picture of the actual work piece is posted and bite marks can be reviewed.
There is no real evidence of which direction the OP made the last cut attempt
There is no real evidence there was any energy holding the work against the fence
There is no real evidence indicating where the bit grabbed. Was it on the side of the work that was intended to be the cut or was it on the side of the original cut and the work piece was able to move forward toward the operator
Here may be the key statement by the OP On the last pass, the bit immediately pulled the stock past the bit and shot out the other side.
The other side to me this means the side opposite to the side the OP was attempting to feed the work.
That then is most likely a climb cut as the 12:00 of the bit grabbed the previously cut dado BECAUSE the work piece came off the fence toward the front of the table grabbing the earlier cut dado wall and the bit immediately pulled the stock past the bit and shot out the other side.
Need a picture of the actual board with indications of the feed direction. It should all come pretty clear from there.
calabrese55

[Doug Garson]

I think if you read all the posts including the ones by the OP answering questions, it is pretty clear what happened. On the last pass the workpiece moved away from the fence and the bit engaged with the side of the dado closest to the fence making it a climb cut. The stock guides are designed to hold the stock down and against the fence but it appears they did not do their job. Nothing was restraining the stock from moving right to left so when the climb cut happened the workpiece was thrown right to left. It is perhaps not the right application for stock guides, they are intended more for sheet goods where featherboards are not practical, in this case with a narrow workpiece, featherboards would have been a better choice.

[Bill Dufour]

RT?
Bill D.

[Michael Burnside]

RT?
Bill D.

Router Table

[Doug Garson]

Oh, I thought it was Russian TV, maybe in the spirit of good communication we should use less SF's . :confused:

[Warren Lake]

whats an SF? Why dont we just switch to Emojis then ill understand even less :)

Do they have an emojie for Kickback, a hand handing money to someone else?

[Doug Garson]

whats an SF? Why dont we just switch to Emojis then ill understand even less :)

Do they have an emojie for Kickback, a hand handing money to someone else?
I think this is the emogie for kickback :eek:

[Michael Burnside]

Oh, I thought it was Russian TV, maybe in the spirit of good communication we should use less SF's . :confused:

I thought the OP’s (original poster) context was obvious. Notwithstanding the fact I wouldn’t have used such an abbreviation.

[Doug Garson]

Really getting off the original topic here but I've always thought the longest path from start to finish in a project was to take shortcuts. Maybe the same can be said of communication, the more short forms you use, the less likely everyone reading will understand what you are trying to say. I really hate it when someone posts a problem with a machine, looking for help and only describes it by a model number only. Many may recognize which manufacturer and machine he is referring to but many, including myself may be left wondering. Assuming everyone will immediately recognize a Grizzly, Festool or Sawstop model number is lazy, in my humble opinion :rolleyes: again apologies to the OP (original poster) hope you understand what probably happened and how to avoid it in the future.

[Matt Schroeder]

Could it have been a build up of chips/dust in the dado that allowed the off side of the bit to get enough friction on "wrong" side of the dado to pull it forward (to the left)? Maybe once it got going a little bit the board pulled away and the "wrong" side directly engaged the bit to accelerate it even more? Would a straight bit be more prone to this than a spiral bit--straight cutting edge acting as a scoop to collect and concentrate the debris? Were you using dust collection, and was there debris shooting out either end of the dado while cutting?

Matt

[Matthew Hills]

Glad you are okay.

The suggestion to review the workpiece is a good one.

The piece coming off the fence sounds most likely.
Any chance a rising bit working its way out of the collet could cause this, too?

Matt