Over at Tools of the Trade, they found a video that shows table saw cutting action captured using a Phantom ultra high speed camera.
The video shows the sawing action at 44,000, 75,000 and then 150,000 frames per second (fps). It’s neat to see how the individual teeth on the blade just nibble away at the wood.
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If you look carefully, you might also notice that the blade height is a little too tall. It shouldn’t be that much higher than the thickness of the material that’s being cut.
http://youtu.be/QPR3xNNMdl0
It would be neat to see high speed videos of other woodworking tools and power tools. This is something we looked into in the past, but the cameras that can do this are incredibly expensive, even just to rent for a week.
Daniel Reetz
Seems like they’re feeding that wood pretty slowly.
Here’s one on chip formation in metals: chip formation: https://www.youtube.com/watch?v=mRuSYQ5Npek
Here’s one showing the Built Up Edge forming on a tool:
https://www.youtube.com/watch?v=-TfNouJbJrg
Absolutely fascinating stuff!
Jim
“If you look carefully, you might also notice that the blade height is a little too tall. It shouldn’t be that much higher than the thickness of the material that’s being cut.”
What is your basis for this comment?
Stuart
Every table saw and circular saw user manual and manufacturers’ recommendations I have ever read.
Why, have you ever seen anything contrary to this?
mikeh
i agree with you stuart, the blade appears to be set very high and would normally be just above the material – my guess is that they did that on purpose to catch the cut action, but who knows
Jim
Interesting, one of my best friends, co-owner of a large commercial shop in Switzerland and Woodworking teacher at Basel Technical Institute for over 25 years, instructs raising the blade height h higher with respect to the material (maximum height for solid materials, +1”/2cm for panels) . In Germany and Switzerland, most woodworkers have formal training and apprentice before become full-time woodworkers. This is the best practice approach in Europe.
Several points, from and ‘engineering and science’ perspective.
Background: My home workshop saws are a Knapp Profit 410 and Robland X-31.
Blade design. Blades are designed to cut at a certain angle with respect to the material. With a blade in a higher position (maximum height for solid materials, +1”/2cm for panels), the blade angle with respect to the material remains constant and with the design parameters of the blade. Cutting with the design parameters of the blade will result in the best finish cut. I challenge anyone who states setting a blade to a lower blade height results in a better finish. Probably using the incorrect blade, dull blade or improper feedrate. (Note: for panel cutting, a height 1” above the material is often more than 1x and often 2x the thickness of the material being cut and proportional exposing more blade than when cutting 2by material, since many common saws have maximum cutting heights less than 4”)
Ease of cut. The shortest distance through the material is a cutting edge path 90 degrees to the table. Using a shallower cutting height puts more distance and teeth into the material, creating more friction, taking more effort and reducing feedrate. Slower feed rate in tougher materials increases the chance of burning.
Safety. With blade guards in place, the blade height is not an issue since the blade is not exposed. With anti-kickback devices in place, kickback should not be a problem either. But, with a high blade height, the blade path pulls the material downward, onto the table. Reducing the blade height begins to exert forces parallel to the cutting table, wanting to pull the material forward. No safety device, with the exception of a power feeder, will prevent this. Should this occur, the material will ride up the blade, compromising the cut and potentially launching the material. Anyone with frequent experience cutting shallow dadoes was likely encountered this situation.
Further Reference: Felder Video (See approximate time 9:50) https://www.youtube.com/watch?v=Dj7H7oVWe6s
Stuart
Those are interesting points to consider, thank you for sharing!
I haven’t done my own analysis of optimal blade height, but wouldn’t be surprised if manufacturer’s guidelines were based on safety considerations.
Ross
There are numerous reasons for matching the blade height to the thickness of material. One major reason is for safety. The less the blade is exposed, the lesser the chance that it will come into contact with the operator. Yes, all the guards should be in place and that shouldn’t be an issue, but the reality is that they often get removed.
Otherwise, it helps make a cleaner cut, especially with cross-cuts and when cutting plywood or other materials with a face veneer. As the blade is raised higher, the angle that teeth contacts the wood increases. This tends to increase tear-out.
fred
As Ross says: “it helps make a cleaner cut” -Hence the use of first doing a shallow scoring cut on veneered materials followed by the through cut. Our big sliding table saw could do this all in on motion since it had both a small (4.75 inch) scoring blade and a follow-up main cutting ( 14 inch ) blade to produce better cuts on veneered plywood.
Jim
Fred, Regarding your reference to a secondary scoring blade, this result is acheived with the scoring blade turning in the opposite direction of the main blade. You want to cut ‘Up’ into the material, not ‘down’ thru the material (resulting in tearout). The same results are not achieved if turning in the same direction. So, making a shallow cut, followed by a thru-cut with the same balde at different heights will not achieve the same results. In addition, the tooth configuration of the scoring blade is unique. In some materials, modern professional blade grinds all but eliminate the need for a scoring blade.
fred
Thanks – I learned something again – guess I never paid attention to how the scoring blade was turning.
Bob S
High speed cameras are tremendously useful tools in many industries. I worked in a multi-location printing operation. We had one high speed camera that we used to ship to different locations to solve feeding, folding and trimming operations. The information you gain from seeing the operation in slow speed is invaluable to a process improvement initiative.
As a woodworker I vary blade height depending on the material being cut and the type of cut I want. Showing how a blade cuts wood in slow motion is interesting. In this case, blade height really doesn’t matter much unless you know what the research was trying to show.
Stuart
I know, and figure that the blade was raised to get more interesting angles on camera. But in watching it, my mind drifted towards “hmm, that blade is raised too high” thoughts.
Jeremy
I’ve always heard and been told to raise the blade so the bottom of the gullet sits just above the top of the work piece. That way the gullets can clear the dust effectively. I have however seen articles where authors mention that they’ve “raised the blades for clarity and demonstration purposes, so maybe that’s it.