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Thread: Thin Kerf Saw Blades and Loss of Stiffness

  1. #1
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    Thin Kerf Saw Blades and Loss of Stiffness

    Destroyed thin kerf sm pic.jpg
    I got curious about how much easier it was to damage a thin kerf saw blades than a regular kerf saw blade.

    I worked on it most of the day and finally found the answer on Dr. Bruce Lehmann's website.http://www.thinkerf.com/

    As saw plate gets thinner the stiffness of the saw blade falls off by the cube of the difference. If we take a saw blade that is 20% thinner than it has 80% of the original thickness. To calculate the difference in strength you take the 80% and multiply it by itself three times. Thus .8 x.8 x .8 = .512 or 51.2%.

    Roughly a 20% reduction in saw plate thickness means about a 50% reduction in stiffness.

    I'm a Creeker, yes I m.
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  2. #2
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    Assuming the young's modulus is the same for both blades, you are correct about the cube relationship. This is due to the area moment calculation for the bending stress.

    However, what is the acceptable amount of deflection? The deflection depends on the force applied. Are we applying enough force to deflect a TK blade an unsuitable amount even though it is only 1/32" thinner?

    For example, a 1/4" thick blade is many times stiffer than an 1/8" blade, is it overkill? Are we at the cusp of blades that are too thin? What if the material properties change, which changes the young's modulus, and changes the deflection for the same force applied?

  3. #3
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    I think you also have to take into consideration what your using the blade for, no? For instance, I would hazard a guess that miter cuts and cuts in materials such as mdf, plywood, particle board, plastics and aluminum will have little effect on the side of the blade....where stiffness would matter. I think the only type of cuts where you have to worry about deflection is on solid wood rips?

    Having said that I prefer more horse power and thicker blades

    JeffD

  4. #4
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    Cool site.... Lots of fun math

  5. #5
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    I think the only type of cuts where you have to worry about deflection is on solid wood rips?
    Based only on my own ham handed - stupid - inexperienced - ignorant & hind-sight is always 20/20 - total destruction of a thin kerf blade,,,,,,

    The type of cut isn't anywhere near as crucial as the amount of torque applied to the arbor nut.
    If you tighten that baby down using my fat brother in law's "turn it unti the little veins on your forehead turn purple" method, the blade will deflect and once it heats up any, that deflection will become a permanently warped blade.

    That little lesson cost me an 80T Freud thin kerf blade and the laser on my CMS.
    The warpage was bad enough so that the blade would pick up small pieces of crown cut-offs and throw them at the back of the saw - where one found it's mark on the laser and knocked it right out of it's mount and busted it all up.

    W/any luck others can learn from my mistake and save themselves the cost of a decent blade.

  6. #6
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    Interesting thread.

    I use TK blades. I suspected they flexed somewhat.

    So I got a blade stabilizer from Forrest.

    I wanted to know whether the blade stabilizer did anything, so I performed a test.

    I cross-cut a piece of wood with my sled, and then I colored the cut edge with a black marker. I then ran the already cut wood through the blade a few more times.

    I did this test with, and without, the stabilizer.

    What I discovered was that, without the stabilizer, the blade was removing more of the black marker.

    So the stabilizer does seem to be keeping the blade running flatter.

  7. #7
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    Quote Originally Posted by Rich Engelhardt View Post
    Based only on my own ham handed - stupid - inexperienced - ignorant & hind-sight is always 20/20 - total destruction of a thin kerf blade,,,,,,


    If you tighten that baby down using my fat brother in law's "turn it unti the little veins on your forehead turn purple" method, the blade will deflect and once it heats up any, that deflection will become a permanently warped blade.

    Oh I hate that! I've had a couple other guys work in my shop over the years and it drives me nuts when I go to loosen something and I can't get it to budge b/c they think it needs to be torqued on like a lug nut on a truck wheel I just snug the nut on my table saw and it's good to go. Most things are good to go with just what I'd call hand tight. When you start forcing things nothing good can come of it IMHO. In fact the only thing I really crank down is the shaper heads....and even that I'm careful not to go too over the top.

    JeffD

  8. #8
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    It is fairly common here to see someone recommend a thin kerf blade without mentioning the added dangers.

    There is nothing inherently wrong with thin kerf blades. We make and sell a great number. I just thought someone should mention the additional possible danger.

    Besides stiffening collars many blades have "built in" collars in the form of a thicker center such as "thin rim" "hollow rim" and "stepped rim" blades.

    Yes, Mr. Clark, I believe there are occasions when the blades are overflexed. However the saw blade industry very badly needs a better material than steel for saw bodies.
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  9. #9
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    Interesting topic, I only use my full kerf saws unless I need to save wood then put on one of my TKs. I think most of the time recommendations for a TK are for a sub 2hp machine where a full kerf may limit the saw and maybe a strong enough caveat isn't issued.

    Tom, is there anything on the horizon as a replacement for steel on the saw body, I know you guys have a replacement for "carbide". I have been trying to come up with a reason to get you and the Snook's to set me up with one of your "space age blades" but with close to 30 Freud Industrial and Forrest blades in just about ever grind imaginable and being just a hobbyist it always seems a long time before I need another saw for my table saw! I guess I could get a bizarre special grind but I wouldn't use it enough to realize the longevity benefits!
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    Guess I want to chime in here, and ask for a little SawBlade 101 info:

    My understanding is that there are two basic reasons to go TK:

    1) Easier spin/cutting, where HP or torque are in short supply;
    2) Less loss, when cutting expensive wood species.

    Are there other reasons ??

    TIA....
    He's no fun. He fell right over !

  11. #11
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    Dear Mr. Huskey,

    Thank you for the kind words.

    The truth of the matter is that there are a lot of people making good saw blades anymore. Part of that is due to people such as you. If someone does produce poor quality, it is exposed on the Internet.

    Another factor is a more rigorous definition of what good quality means. You used to see saw blades on store shelves that would have runout of 0.008 or 0.010. This is rare anymore. Now a retail blade should have a total runout of no more than 0.004 and many are down around 0.002.

    The blades Mr. Snook makes for us typically have a runout well under 0.001 inches but this is a pretty small difference for a lot of users.

    Mr. Snook uses our advanced materials saw tips which cut cleaner and longer with less energy but, again, this is not a benefit that most users will see or appreciate.

    Fortunately Mr. Snook and I are doing well in the industrial market. This is an area where wood cut is measured in miles instead of feet.

    There really isn't anything to replace steel in sawblades. You can alloy steel with nickel, chrome, vanadium and similar to make better saw plate. Warren Bird of California Knife and Saw make stainless steel saw plate that is considerably superior to ordinary saw plate but which is much more expensive.

    One of the big problems with building better saws is that almost no one runs the saw it until it is used up. Weyerhaeuser once retipped one of their mill saws 50 times as an experiment. This doesn't happen in real life. Much more commonly, in real life, the saw gets damaged or the steel loses its ability to hold tension.

    Another consideration with saw steel is the cost of getting alloy steel that is homogenous enough and flat enough for saw plate. They don't make any steel like that on the North American continent so it all has to be imported.

    It is extremely difficult to try new steels on any sort of our production basis because the minimum order is 20 tons. So a significant test of a new steel means ordering 40,000 pounds. Plus it has to be shipped in sheets instead of rolled which adds to the cost.

    As far as your Freud blades go, I've always been very impressed by their R&D department. It is pretty exciting to get a call from the head of Freud R&D saying he wants to buy one of my new sawblades. They are very competitive and do stay on top of the advances in the market.

    Mr. Snook and I do well because we're very small and we can afford to address a much smaller market than Freud can. So I invent saw tips that are little more expensive than carbide tips. Both Mr. Snooks are very, very good in every saw blade that leaves or shop has been individually made by a true master of the art. This is not something a major manufacture, such as Freud, can do so we have our own little niche and we are pretty happy there.

    Tom
    I'm a Creeker, yes I m.
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  12. #12
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    Lower energy use in commercial operations. However that is a pretty low priority and probably covered under your #1.

    99% commercially is material utilization. Think of window blind plants or flooring companies. In even an ordinary sawmill the cost of logs is maybe 80% of the cost of finished material.

    Maybe the best source of thin kerf application is John Schultz of Super Thin Saws. http://www.superthinsaws.com/

    Tom
    I'm a Creeker, yes I m.
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  13. #13
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    Good link.

    Thanks, Tom !
    He's no fun. He fell right over !

  14. #14
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    Tom,
    Interesting about the new materials for the bodies. I had no idea that you had to buy that large of a quantity. We buy special alloys where I work, didn't know about the quantity required, but lead times can be a real pain. However, we are not buying custom alloys, but more exotic alloys.
    Mike

  15. #15

    Can compensate somewhat with smaller diameter

    If you don't need the depth of cut, you can run small (5.5" and up) circular saw blades on a tablesaw. These are also available in ultra-thin kerf--1.3mm (0.051").

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