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View jamsomito's profile

Table saw blade speed - a photographer's perspective

by jamsomito
posted 11-14-2018 01:49 AM


19 replies so far

View Redoak49's profile

Redoak49

4000 posts in 2382 days


#1 posted 11-14-2018 12:17 PM

That was really interesting.

View jonah's profile

jonah

2075 posts in 3692 days


#2 posted 11-14-2018 02:03 PM

That first guy is lucky he didn’t kill himself handling the material like that. If he’d been using a 3HP+ cabinet saw it might have kicked that 2×4 back into his face and killed him.

View jamsomito's profile

jamsomito

432 posts in 820 days


#3 posted 11-14-2018 02:25 PM


That first guy is lucky he didn t kill himself handling the material like that. If he d been using a 3HP+ cabinet saw it might have kicked that 2×4 back into his face and killed him.

- jonah

I knew that comment was coming. I agree. That old saw even looks like it’s out for blood. But the videos were interesting for the rest of us despite the creators risks.

View 000's profile

000

2859 posts in 1293 days


#4 posted 11-14-2018 02:43 PM

I thought the slo mo’s were pretty good.
Seeing the gussets removing the sawdust was very cool.

Thanks for taking the time.

View Brawler's profile

Brawler

34 posts in 224 days


#5 posted 11-14-2018 02:52 PM

I’m not sure if this would work, but did you ever think about a strobe light?

-- Daniel

View jamsomito's profile

jamsomito

432 posts in 820 days


#6 posted 11-14-2018 03:05 PM


I m not sure if this would work, but did you ever think about a strobe light?

- Brawler

I do have a flash, but it won’t work at fast shutter speeds. It has to do with the way the DSLR’s shutter mechanism works. There are essentially 2 curtains that cover the sensor – one moves down to expose the sensor and the other moves behind it to cover it again, and the time between the two is the exposure time, or shutter speed. The problem is these shutter curtains, being material objects, take time to move across the sensor, and at high speeds, the top curtain is so close behind the bottom one that the whole sensor is not exposed at any one given time. The flash is much faster than that, so all you would see in the final image is a stripe of the image.

Like this: https://northrup.photo/gear-basics/camera-body-features/x-sync-speed/

And another slo-mo video of a DSLR shutter mechanism: https://www.youtube.com/watch?v=usfEGOwamJ8

Because of this, I’m limited to shutter speeds of 1/250th of a second on my camera, which this demonstration showed is way too slow to capture a table saw’s teeth while it’s running. That’s the shutter speed at which the curtains can move completely over the sensor, leaving it fully exposed, prior to the 2nd curtain covering it again.

To fix this, you basically need a high speed video camera at that point ($$$$$$) which has a totally different “shutter” mechanism, or a camera with high-speed sync on the flash, which essentially fires the flash in a strobe-like effect so you get equal “stripes” on your exposure as the shutter curtains move across the sensor to fill out the whole image. This is much more obtainable, but on more expensive professional DSLR’s. But again, you’re limited to the camera’s 1/8000s maximum shutter speed. So you’re back to the crazy expensive high speed video cameras again.

Interesting problems with high speed imaging.

View bondogaposis's profile

bondogaposis

5414 posts in 2745 days


#7 posted 11-14-2018 03:21 PM

Try it with low light and use your flash. You might be able to show more.

-- Bondo Gaposis

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GR8HUNTER

6106 posts in 1106 days


#8 posted 11-14-2018 03:30 PM

VERY NEATO :<))

-- Tony---- Reinholds,Pa.------ REMEMBER TO ALWAYS HAVE FUN

View theart's profile

theart

95 posts in 948 days


#9 posted 11-14-2018 03:38 PM


I m not sure if this would work, but did you ever think about a strobe light?

- Brawler

I do have a flash, but it won t work at fast shutter speeds. It has to do with the way the DSLR s shutter mechanism works. There are essentially 2 curtains that cover the sensor – one moves down to expose the sensor and the other moves behind it to cover it again, and the time between the two is the exposure time, or shutter speed. The problem is these shutter curtains, being material objects, take time to move across the sensor, and at high speeds, the top curtain is so close behind the bottom one that the whole sensor is not exposed at any one given time. The flash is much faster than that, so all you would see in the final image is a stripe of the image.

It sounds backwards, but the key to shooting faster than the max shutter speed is using a longer exposure so the whole sensor is open at once. The strobe is then used to produce a a very short pulse of light mid-exposure. This does, however, require low ambient light and a very bright strobe, so it’s not something I would try with a table saw.

View jamsomito's profile

jamsomito

432 posts in 820 days


#10 posted 11-14-2018 03:43 PM



Try it with less natural light and use your flash. You might be able to show more.

- bondogaposis

Hmm now that I think about it I might be able to do a longer exposure with a single flash. That would give a blur for the blade but possibly superimpose the teeth. I don’t know my flash fire time, I’ll have to look it up. Could be a cool effect.

I also have some concerns blasting myself with a flash while I’m trying to make a cut on the table saw. I might need to leave that to someone else to try.

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jamsomito

432 posts in 820 days


#11 posted 11-14-2018 03:44 PM


It sounds backwards, but the key to shooting faster than the max shutter speed is using a longer exposure so the whole sensor is open at once. The strobe is then used to produce a a very short pulse of light mid-exposure. This does, however, require low ambient light and a very bright strobe, so it s not something I would try with a table saw.

- theart

Yup, my thoughts exactly.

View Andybb's profile

Andybb

1920 posts in 997 days


#12 posted 11-14-2018 05:29 PM

Kool! Just curious what blade was used in the 2nd video. Wondering if the teeth are offset as it looks like every other tooth is shaving wood and it is alternating to the inside and outside of the center of the blade.

-- Andy - Seattle USA

View jamsomito's profile

jamsomito

432 posts in 820 days


#13 posted 11-14-2018 05:33 PM

Yeah, it looked like ATB rip blade to me… on cross cuts. It’s really hacking those fibers on the last clip and leaving a rough cut.

View oldnovice's profile

oldnovice

7485 posts in 3762 days


#14 posted 11-14-2018 06:25 PM

High speed photography makes the real world very interesting.
The videos also show that the sides of the saw blade teeth are as important as the tips!

While I was an intern in the lab of a very large business machine company, the engineers did high speed potography on computer card reader mechanism with a film camera (before digital as this was over 50 years ago) at somewhere around 4000 frames per second. An 24 inch diameter film feed reel was depleted of film in a matter of seconds and the results of the card reader moving mechanism, made of stainless steel, looked as if it was made of rubber. Of course we had to wait until the film was developed, not an instantaneous view for feedback of the test._

-- "I never met a board I didn't like!"

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Andybb

1920 posts in 997 days


#15 posted 11-16-2018 12:01 AM


The videos also show that the sides of the saw blade teeth are as important as the tips!
- oldnovice

Yeah. I saw that. Interesting tidbit.

-- Andy - Seattle USA

View knotscott's profile

knotscott

8290 posts in 3769 days


#16 posted 11-16-2018 05:14 PM

Very cool.

-- Happiness is like wetting your pants...everyone can see it, but only you can feel the warmth....

View Andre's profile

Andre

2626 posts in 2200 days


#17 posted 11-16-2018 07:11 PM

Why not just use an I phone? :)

-- Lifting one end of the plank.

View RogR's profile

RogR

113 posts in 1259 days


#18 posted 11-19-2018 12:42 AM



Hmm now that I think about it I might be able to do a longer exposure with a single flash. That would give a blur for the blade but possibly superimpose the teeth. I don t know my flash fire time, I ll have to look it up. Could be a cool effect.

A typical speedlite flashes down to about 1/20,000. Have you considered high speed sync and a dedicated flash?

View jamsomito's profile

jamsomito

432 posts in 820 days


#19 posted 11-19-2018 01:25 AM

Ah, that might be just enough to freeze the blade. My setup isn’t compatible with HSS though, unfortunately.

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