Theory behind this accident *GRAPHIC* - Woodworking Talk - Woodworkers Forum
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post #1 of 35 Old 04-22-2019, 10:23 PM Thread Starter
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Theory behind this accident *GRAPHIC*

Hey I hope this is allowed it does contain a tiny bit of blood.

This is the accident I had earlier. It was entirely my fault as I ignored many warning signs and contributed to it.

What happened was, I was using my cross cut sled and it had been getting hard to push. I know it needed waxed but I wanted to push through and get this lumber milled up. In the process I had used the skeletonized table on my saw to grab and pushed the sled forward. This is my contribution to this accident.

Now the mechanics I was pushing forward and it kicked a tiny bit. So i pulled the slide back and pushed forward again making the first cut slightly bigger. This time the second the wood touched the blade it jumped back a ton.

What are your thoughts as to what happened.

My theory is that A. I had clamped both ends to tight (i find this highly unlikely but meh) and the board was cupping on the edge grain. I did put the cup towards the sled fence. So my theory is that when I cut into the board the cup opened up and put pressure outwards closing the cut, then with the clamps it prevented the board from releasing the added tension....

Any other thoughts?


Things I learned. If the sled sticks wax it right away. Don't stick fingers in holes behind the board. Wear gloves (probably wont do this)
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post #2 of 35 Old 04-22-2019, 10:43 PM
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It appears the sled was made out of too thin material for one. This makes it less solid. The main thing was the runners on the sled probably swelled up do to humidity and became stiff. Wax may have helped a little but the runners that fit in the dado slots need to slide freely. I believe when you started pushing harder to get the sled to move it raised up out of the dado slots and caused the kickback. I have a sled that was doing the same thing. I had to take a sharp chisel and scrape wood off the sides of the runners to make it fit correctly.

As a general rule when you are doing something that feels cumbersome is when you are setting yourself up to get hurt.
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post #3 of 35 Old 04-22-2019, 10:46 PM Thread Starter
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This sled is trash so next one is going to be an upgrade. Thicker wood. My runners when first built slide freely but wasn't much play. Your saying I need to have some wiggle room or just when they swell shave a bit off?

Quote:
Originally Posted by Steve Neul View Post
As a general rule when you are doing something that feels cumbersome is when you are setting yourself up to get hurt.
Yea i definitely ignored some safety rules here and learned a painful lesson

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post #4 of 35 Old 04-22-2019, 11:09 PM
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Quote:
Originally Posted by nckheinrich View Post
This sled is trash so next one is going to be an upgrade. Thicker wood. My runners when first built slide freely but wasn't much play. Your saying I need to have some wiggle room or just when they swell shave a bit off?



Yea i definitely ignored some safety rules here and learned a painful lesson
Yes there should be at least as much wiggle room as the miter gauge does.

Just so you know I used my sled probably a half dozen times overly stiff before I took the time to scrape the runners. I knew it was wrong so I kept my hands well away from the blade when I was doing it just in case. My sled is different from yours in that it's made to miter molding and I wasn't using it very often and was too busy to fix it.
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post #5 of 35 Old 04-22-2019, 11:44 PM
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Another approach, not seen very often ......

On a small size portable table saw, which yours appears to be, you can use the outboard edges of the table as the guides for the sled rather than the miter slots. You just make 1 X runners that are located on the right and left sides of the sled and hang down enough to allow the sled to slide without binding, at least 1" . Obviously, the table's edges must be free from any paint or imperfections as they become a sliding surface.


We are also assuming they are machined surfaces and are parallel to the miter slots OR that the blade can be adjusted parallel to the outboard edges. It's a bit of thinking outside the box, but mechanically it will work. It will still require at least a 1/2" thick top for the sled and front and rear rails/fences to prevent squeezing or pinching the blade, and you can't cut though either of the fences/rails!



I made this large sled for my Craftsman table saw which does use the miter slots and Maple runners:

https://www.woodworkingtalk.com/f27/...d-build-49218/



The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #6 of 35 Old 04-23-2019, 01:52 AM
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If I had a table saw, I would buy a metal mesh butchers glove.
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post #7 of 35 Old 04-23-2019, 02:20 AM
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That sled itself was an accident waiting to happen.
Clamping the board on both sides of the blade was also inviting trouble.
I also think the saw table was too small to hold that board safely.
Also, if the saw was on the floor, were u bending or sitting or otherwise positioned where you were not balanced to have complete control of the sled?

You are very lucky to still have your fingers.

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post #8 of 35 Old 04-23-2019, 09:33 AM
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you made 2 mistakes.


one by placing the concave edge against the fence, as you said, as it cut though you pushed the board against the fence closing the kerf up against the blade. seen this many times on miter and radial arm saws. best to place the convex edge against the fence, or place a small wedge behind the bow so th board can't pull in.


second, you had what we call a "near miss" in the safety industry, and you chose to ignore it. many accidents are preceded by a near miss!


smaller job site saws require more attention to safety in my opinion.


I hope you injury heals fast and well for you!
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post #9 of 35 Old 04-23-2019, 10:39 AM
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One more thing to add I didn't think of before is if that saw is like the Ryobi saw I have the dado slot is only about 1/4" deep. You shouldn't be using a sled on a saw like that. The slot isn't deep enough for the sled to stay on the saw no matter how good it is made.
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post #10 of 35 Old 04-23-2019, 10:53 AM
where's my table saw?
 
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That's why I suggested .....

Quote:
Originally Posted by Steve Neul View Post
One more thing to add I didn't think of before is if that saw is like the Ryobi saw I have the dado slot is only about 1/4" deep. You shouldn't be using a sled on a saw like that. The slot isn't deep enough for the sled to stay on the saw no matter how good it is made.

I suggested using the outboard edges of the table itself as guides for a sled on the smaller type saws. It would give you more control and eliminate any possibility of "lift off" during a cut.

Sometimes on a jobsite, the construction crew will clamp or screw a guide rail to the bottom of a sheet of plywood and run that rail against the outboard edge of the table. There are a zillion DIY tablesaw fences you can buy or build to improve the fence on your small jobsite tablesaw:
https://www.youtube.com/results?sear...able+saw+fence

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #11 of 35 Old 04-23-2019, 10:59 AM
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A small saw is made for small work. You were asking too much of it. Just because the motor is able to cut thicker boards doesn't mean it should.

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post #12 of 35 Old 04-23-2019, 12:52 PM
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You were really lucky!
You ignored the warning! Lesson learned?
Wrong tool for the job.
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post #13 of 35 Old 04-23-2019, 06:12 PM
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clamping both sides of a cut ensures that if anything goes wonky, you'll get a serious binding / kickback / splintering / pieces flying / bad scene.
had that clamp flipped off and engaged the saw blade . . .

that said, your initial instinct was absolutely correct - when it doesn't feel right, it isn't.
listen to yourself - you are a lot smarter than the internet.

you need to stop right there and figure out why things are not going to plan.
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post #14 of 35 Old 04-23-2019, 06:21 PM
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Im very glad you escaped with such minor injuries and I guess all the folks above have covered what you did right or wrong so Ill just mention some thing about runners. They dont have to be made out of wood. You can purchase metal ones of course but theres lots of materials you can use that dont swell. I had some HDPE sheet stock left over from a project and I cut two runners out of it. The HDPE slides very nicely in the slots and it does not expand/contract with humidity changes. Im sure like anything else it changes a bit with temp changes but not enough that I have ever noticed. Just a FYI and good luck with your next sled.
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post #15 of 35 Old 04-23-2019, 06:39 PM
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smart VS experienced

I have a lot of experience using powered saws, tablesaws, circular saws and chain saws. My experience with sawing down trees and bucking logs also can be used in working with the woodworking saws.
When you cut a long log that is supported only on either end, it compresses the wood at the top of the cut. That's why your blade with get stuck before you can saw all the way through it. You have to make a "V" cut rather than a straight down vertical cut OR push up underneath the cut with a support log.



When the workpiece compresses against the rotation of the blade it will attempt to stall, OR kickback. The Laws of Physics never stop working to allow for human mishaps. Compression and Tension are forces well known to physics and should always be considered when working with wood. When ripping some woods there are hidden "tension" forces holding the wood together and they only appear during the cutting process, and are often unexpected. Learning some of these causes and effects sometimes comes from experience, unfortunately.


Crosscutting rarely produces kickbacks when properly supported by the miter gauge with an extended wood fence on either side of the blade. It's very easy to bolt on a 1" X 4" about 30" long rather than using a sled, which is large and cumbersome. I have several miter gauges fitting in this way and use them all the time:



The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 04-23-2019 at 06:43 PM.
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post #16 of 35 Old 04-24-2019, 12:01 AM Thread Starter
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Thanks guys for the info and ideas. I'll look into the undersaw for next sled. Yea, I don't think I could have lost my fingers but am damn lucky I didn't break any.
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post #17 of 35 Old 04-24-2019, 07:35 AM
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You dont think you could have lost any fingers?
Accidents like that happen in a flash. According to a few woodworkers I have met that lost fingers or has serious surgery to reattach, all said the same thing..
"I didnt know I lost my fingers until I saw them laying on the table saw"

I'm sure we have more than a few on here that lost at least partial fingers. Maybe they can chime in.

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post #18 of 35 Old 04-24-2019, 07:48 AM
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There were many things wrong about this cut. I am most bothered by the way that the board was clamped laterally against the sled fence with the two bar clamps, one on each side of the blade.

If I were to design a clamping method most likely to result in a kickback, that "lateral squeeze" would be it, even with only one clamp. Once the wood starts to lift, the tension in the clamp would actually help lift the back of the wood and contribute to the kickback.

The second clamp makes it MUCH worse. The two-clamp arrangement with a concave bend against the fence seems almost designed to pinch around the back of the blade.

A clamp on the waste side is a very bad idea, too. There is a basic principle of table saw use that the wood on one side of the blade must always be free to move. That's why you don't use two fences, one on each side of the blade. That's why featherboards and thin rip guides are placed before the wood reaches the front of the blade. That's why you keep the rip fence away from the side of the wood when you make crosscuts with the miter gauge.

Clamping laterally against a sled fence? Bad idea. Anchoring both sides of the wood to be cut? Also a bad idea. In addition, I would have tested the empty sled on the non-running saw to make sure it slides smoothly. If it doesn't, fix it before making cuts.
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post #19 of 35 Old 04-24-2019, 07:58 AM
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Were you using the saw on the ground as pictured? Yikes.


There is no way the clamping as pictured actually straightened the bow in the stock. It may have looked like it, but only because the sled warped to matched.


My approach would have been to first cut the board in half either free hand on the table saw or used a regular mitre gauge, then make a second cut with the sled to make a trim cut at the correct angle.


I make lots of cuts free hand on the table saw, including long rips, and still have all nine fingers, though one is attached with only a bit of skin. It gets in the way sometimes. On days when it is not bleeding, I'll sometimes I wear gloves to keep it more in line. When it is bleeding, the bandaging is too fat to get the glove on. My doc says what doesn't kill you makes you stronger, and will also bolster my immune system in this case. I trust him. For what it is worth, Malcom Gladwell is writing a book about people that have this approach to life/healthcare. He's the guy that wrote "Blink: the power of doing without thinking". He's titled this new work, "Doing the Double Take it With a Grain of Salt". It's in collaboration with Trump, so it's due out the day impeachment hearings commence. That aside, I do in truth make lots of freehand cuts on the tablesaw.

Kerouac, J.
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post #20 of 35 Old 04-24-2019, 08:04 AM
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I just now noticed that I have 10 fingers again. Cool! Maybe I'm part frog.

Kerouac, J.
"to the joyful chaos of uncontrolled appetites ..." Claire Armistad, writing on the late Judith Kerr's The Tiger Who Came to Tea
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