I Put Blade Depth To The Test. We’re Getting It WRONG!

Exactly how much of your circular saw blade should stick out past the material you're cutting? I went on a journey to find the perfect answer and.. I did just that. Learn about what produces the least tear out and how safety factors in as well. #diy #circularsaw #woodworking

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[treka]

Do you think a neighbouring cut affects a cut? It seemed like the first cut had the full solid support of a solid board, whereas after the first cut, the board had less support to the cut, possibly causing more vibration, which might mean not a fair comparison across cuts due to uneven conditions for the cuts. Maybe try the same experiment but start with a different cut first and see what you get. Or have a large separation, maybe even seperate boards... You have lots of boards to spare right? 😁

[colinweir]

My late brother was a wood machinist for about 50 years and always said saw teeth should just clear under the board being cut. I don't use a power saw very often, so I follow his advise and keep the blade about 1/8 inch. 🐯

[seanhorton]

Way back when taking wood shop in Jr. high, our instructor taught us the projection should be the thickness of the saw blade. As most blades were about 1/8" thick back then, it would hold true to your results.

[GoodlyEarth]

This video is great. I have always set my blade depth at the minimum to get the cut done. Your video shows that is the way to go.

[Lord_zeel]

Consider the geometry of the cut. When cutting at minimal depth, only a small cross section of the blade is engaged at a time, and the kerf will have a gradual slope at the front following the blade curve. That means the angle at which the teeth engage the material is shallow, with the teeth cutting more forward than upward. On the other hand, at full depth a larger section of blade is engaged, the end of the kerf is nearly vertical, and the teeth engage in an almost entirely upward direction. From the geometry alone, it's clear that greater depth will result in more upward force which would result in more tear out. Additionally, the lower depth cut with its low angle of attack should mean the teeth spend more time engaged and the next tooth should enter the cut before the previous tooth leaves it which should reduce the chance of a tooth getting caught causing kickback or additional tear out. The disadvantage though, is that when you make an incomplete cut you have a really long ramp out of the kerf, where a deep cut can get closer to flush.

[Locane]

I admire your effort and intent, but there's a reason your first and last cuts look clean. The cuts you made in your tests are too close together - the wood is waggling while your blade goes through it - if you got a shot of an end-on view and had slow motion, you'd see the sliver of wood you're cutting near jumping up and down, likely causing the tearouts you're seeing in the middle.

[BigBopper]

I was taught in my Wood Technics course in trade school that just past the bottom (or about 1/8") is best. The reasons given is that puts the most teeth in the cut and for safety.

[HammerNQuill]

I always set to about a 1/4" - so this is a welcomed tip! Thanks for doing the extensive testing.

[dakkon]

What order did you make your cuts? Those resulting wooden fingers are unsupported. That could allow part of each subsequent cut to flex and could partly account for some of the differences.

[seanfeeney]

Was taught that gullet depth was the way to go & never really tested it. Some new things to think about & test. Thanks for doing this!

[longleaf]

excellent video my dude! I never gave much thought to cutting depth before now but have usually always stuck to about 1/8th inch simply cause it seems like the safest way to do it. its really nice to see that it also gives the best cut. 10/10 great video!

[kaffirfromgod]

10:01 Look at your slow motion. By test cutting so close together causes narley vibration. Which it's now moving crazy like. So your tests are null and void your going to have to do each cut at least 4" away from the next actually put shims in-between each cut like WTF dood....

[handycrowd]

I've always done the 'just though' method. Better for the 'bench' you're working on and makes less mess. Nowadays I usually cut on a piece of rigid insulation foam, instead of on sacrificial boards, but I still keep to just a tad through the bottom. Nice to see the results though 🙂

[Poindexters-Obsession]

Hard to judge because cut quality is too dependent on feed rate/force and keeping the saw straight. Both can make good cuts if youre careful. A shallow blade at the same rate is taking a shallower but longer bite. Full depth is more dangerous for exposed blade, but less dangerous for kickback when the wood pinches. I use both methods depending on what I'm working on.

[OlTrailDog]

Wonderful to learn the overall best results is also the safest.

[The_Ubatron]

I was taught to reduce the depth to the minimum required to make the cut, mostly for safety reasons. The 'full-depth theory', however, was once explained to me as being safer because the blade, despite the turning force, would be acting on the material in a more vertical action, rather than horizontal, thereby mitigated kickback. I've never been convinced, and I've always stuck to what I was taught. As for quality of cut, well, this video is very helpful! 🙏🏽

[timfarry]

You only need logic to tell what works best. What cuts cleanest? Slowly cutting a board or pushing it through as hard and fast as you can? The slow cut has more "cuts per second" due to the slow moving push, so it is clean. The fast cut must take out more material per tooth cut, so it "tears" through to keep up with the push. By that reasoning alone, setting the blade just below the other side is best because MORE teeth are contacting and cutting per revolution than if set deeper. To achieve the same results at a deep cut you would have to push about 5 times slower, but even then, the angle of attack is almost perpendicular compared to angled, so it will tear more. But another reason to show as little blade as possible is that it is far easier to "adjust" if your line is not perfectly straight going in. A full blade has more surface and you cannot "twist" it out to straighten it like you can with minimal show (mostly for skill saw use since guides are used for table saws.) Safety is an added bonus with less showing. I always adjust for every cut, especially if changing thickness regularly.

[Handleyman]

Thanks. I’ve always wondered about that. And now I know! 👍

[forresthouser]

There is one thing you DON"T mention i n this video, and I have never heard mentioned in any video, but have proven to myself and my co-workers time and again. If you set the depth shallower (i.e. 1/8th to 1/4 inch through) the lower blade guard works WAY better, and is less likely to make the cut go off line as you enter the board. Just a personal observation I wanted to share.

[jimspc]

Nice simple test and all the results next to each other. Also shows that a guide fir the saw is needed where possible as there is a clear sign of blade cut wander with just the slightest movement of the saw. And. Cut veneers upside down with a guide.