How did this kickback happen?

[dasgud]

this is an interesting thread. I think if you don't know why it was kicked back, it could happen again. good problem to solve.

I'd like to see the piece that was kicked back if you can post a pic. Seeing that could help explain what happened.

Keep safe everyone.

[Ed in Tampa]

A splitter helps keep the cut off running parallel to the blade and even if the wood does twist the piviot point is on splitter which should prevent any part of the wood encroaching on the blade.

The fact your blade guard exploded says it did it's work. However having two major kickback within a rather short time period says to me you are either cutting a lot of wood or something could be wrong with the initial setup of you machine.

On my Shopsmith the splitter to blade gap is less than 1/8 of an inch so for the wood to piviot into the blade after running along the splitter would require an awful lot of movement of the waste cut. It would have to piviot nearly 45 degrees from parallel of the saw blade to have a corner be able to touch the blade and to accomplish that is would also have to move opposite the feed rate.

I agree the according to the picture you were doing everything right except you didn't have blade guard or splitter in place. However I don't agree totally with the picture, any time you have something that can cause damage flopping around a blade turniing 3400 rpm I want to be able to control it. Any vibration could cause the wood to vibrate into the blade and be fling around the shop.

[JPG]

"Normal" kickback is when the workpiece is pinched between the blade and something else. Your 'incident' was not kickback as described above since no 'pinching' took place.

It was picked up and thrown by the blade due to the piece making contact with the blade.

How to avoid:

Always control both parts of the workpiece and always remove workpieces from the table as soon as possible. If you are not moving it, it doesn't belong on the table.

Control of the workpiece is compromised by the use of devices which do not actually grip the workpiece. IMHO a push stick is an accident waiting to happen(better the stick than a finger, but waiting nonetheless).

Bottom line: If something is not preventing the workpiece from contacting the blade as/after the cut is complete, the blade can toss the workpiece.

[pennview]

If while crosscuting the off-cut drifts into the sawblade, it will be thrown somewhere by the blade, especially when the off-cut is small or lightweight. This is pretty much a given. If the saw vibrates to any degree, the off-cut can drift back into the blade and go flying. If the blade is not much higher than the wood being cut, it's quite easy for a 1/4" piece to drift back over the blade and take off.

Regarding possible vibration causing the wood to drift back into the blade, try the nickle test. Stand a nickle on edge on the saw table while it's running. If it falls over , you've got a vibration problem and off'-cuts will be a problem if they're allowed to lie on the table while the saw is running.

Back to the original problem, did the shoe you were using straddled both sides of the blade. If yes, it possibly contributed to the incident, somehow dragging the wood into the blade.

[dusty]

If while crosscuting the off-cut drifts into the sawblade, it will be thrown somewhere by the blade, especially when the off-cut is small or lightweight. This is pretty much a given. If the saw vibrates to any degree, the off-cut can drift back into the blade and go flying. If the blade is not much higher than the wood being cut, it's quite easy for a 1/4" piece to drift back over the blade and take off.

Regarding possible vibration causing the wood to drift back into the blade, try the nickle test. Stand a nickle on edge on the saw table while it's running. If it falls over , you've got a vibration problem and off'-cuts will be a problem if they're allowed to lie on the table while the saw is running.

Back to the original problem, did the shoe you were using straddled both sides of the blade. If yes, it possibly contributed to the incident, somehow dragging the wood into the blade.

Does anyone have a Mark V that passes the nickel test?

[pennview]

Originally post by Dusty:
Does anyone have a Mark V that passes the nickel test?

I gave my 510 the test and it passed.

I had my doubts, so I started the test at slow speed with the saw table in place, but no blade. It worked fine.

I then installed the saw blade, ran up the speed and then put the nickle on the lower left corner of the table. It fell over after a bit, but then I noticed I had the blade turning at router/shaper speed. After slowing it down to sawing speed, it passed the test as well but the nickle rotated about a quarter of a turn and shook a bit, but remained upright. I moved the nickle around to other spots on the table and it rotated and remained upright. When placed behind the blade, it fell over from the breeze created by the rotation of the blade.

The nickle also remained upright when turning the Shopsmith on and off, but that was at slow speed as my 510 seems to struggle a bit when starting at sawing speed.

[heathicus]

"Normal" kickback is when the workpiece is pinched between the blade and something else. Your 'incident' was not kickback as described above since no 'pinching' took place.

It was picked up and thrown by the blade due to the piece making contact with the blade.

That explanation makes a lot of sense. Simple and obvious, but my brain has been focused on "kickback" caused by the workpiece being pinched/wedged against the blade.

Back to the original problem, did the shoe you were using straddled both sides of the blade. If yes, it possibly contributed to the incident, somehow dragging the wood into the blade.

No, the shoe was only one one side of the blade.

[charlese]

Does anyone have a Mark V that passes the nickel test?

Yes!!! Here is a post from the past (July 2008). See the third Paragraph, first sentence.
https://forum.shopsmith.com/viewtopic.php?p=19445&postcount=9

[dusty]

Yes!!! Here is a post from the past (July 2008). See the third Paragraph, first sentence.
https://forum.shopsmith.com/viewtopic.php?p=19445&postcount=9

How about that sports fans. The old faithful Mark V does pass the nickel test. I placed the nickel (which I carefully selected from a small handful of nickels in my mad money can out in the shop) on the table with the rip fence between it and the saw blade. It turned 90&#176]BTW That was an interesting post, charlese. However interesting, I'll not jump on it at this time. I agree with almost everything stated therein. I love my Shopsmith. It does everything that it is advertised to do and then some.
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[Ed in Tampa]

"Normal" kickback is when the workpiece is pinched between the blade and something else. Your 'incident' was not kickback as described above since no 'pinching' took place.

It was picked up and thrown by the blade due to the piece making contact with the blade.

How to avoid:

Always control both parts of the workpiece and always remove workpieces from the table as soon as possible. If you are not moving it, it doesn't belong on the table.

Control of the workpiece is compromised by the use of devices which do not actually grip the workpiece. IMHO a push stick is an accident waiting to happen(better the stick than a finger, but waiting nonetheless).

Bottom line: If something is not preventing the workpiece from contacting the blade as/after the cut is complete, the blade can toss the workpiece.

JPG40504
I think you have definition and usual cause mixed here.
The definition of Kickback from Webster is 1 : a sharp violent reaction

I think what you are saying is the kickback you are most familar with is when a piece of wood is wedged or caught between the rotating blade and something else.

I have heard war stories from different wood workers telling of kickback incidents where a sharp violent reaction occurred and there was nothing wedged.

I guess I could say I saw an example of kick back when a piece of wood that was being cut literally exploded. Evidently there were tensions within the wood that when one of them got cut it make the wood reaction as if there was a bomb in it.

On a tablesaw kickback can occur any time the blade tries to push or throw the wood instead cutting through it.