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Are FOP really progressive depth raker generators?

Discussion in 'Chain Sharpening' started by BobL, Nov 9, 2009.

  1. BobL

    BobL Addicted to ArboristSite

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    All this talk about the cutting angle, admittedly mainly by me, got me thinking. What about a digital angle finder (DAF)?

    A new 3/8 chain has a gullet of ~0.25" and a raker depth of 0.025", the resultant cutting angle should then be 5.7º

    Put short bar in vice and zero DAF, mark position on bar.
    ZeroRef.jpg

    Put chain on bar and locate at same position on bar where DAF was zeroed.
    CHains1.jpg
    This is a new chain that has had the cutters touched up but the rakers have never been touched, hence cutting angle is less than optimum.

    Here is one of my old square ground chains - note the poor profile of the left side raker nevertheless the angle is approaching optimum.
    sqground.jpg

    Here is my well used ripping chain.

    With a 6.2º cutting angle the gullet is around 0.41" so the raker depth is around 0.044"
    Last time I used it this chain was cutting well.

    The DAF body appears to be made of some kind of Zn? alloy so it should be soft enough not to damage the cutter edge but I'm thinking of adding some sort of sacrificial angle in brass to protect the cutter a little more. When the piece of brass angle becomes too mangled I would just replace it.

    The DAF has to be held near vertical along the other axis but that could be achieved using a bubble level. While not perfect it appears to be easier than the caliper method especially as it is a direct measurement.
     

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    Last edited: Dec 13, 2009
  2. Philbert

    Philbert Addicted to ArboristSite

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    So BobL,

    Do you REALLY think that the D.A.F. is a BETTER way, or is this just an excuse to show off a cool new tool that the rest of us now have to ask Santa for?

    Philbert
    (Still using a plastic protractor from eighth grade . . .)
     
  3. BobL

    BobL Addicted to ArboristSite

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    I have 2 DAFs and the newest one is more than one year old . One I keep in my van and take it milling with me to assess "log rail"/"guide board" twist. One I keep in my home shop for all sorts of things like setting table saw angles.
     
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  4. Philbert

    Philbert Addicted to ArboristSite

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  5. BobL

    BobL Addicted to ArboristSite

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  6. tdi-rick

    tdi-rick Addicted to ArboristSite

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    Mine looks the same as your Wixey Bob, but is named something else.
     
  7. willsaw4beer

    willsaw4beer Addicted to ArboristSite

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    So I got some grinding wheels for my 308 finally and have been playing with it a bit. For rakers I set the wheel at 6 degrees and ground them a tad under where the file o plate said was a good depth since it's a brand new chain. The chain seemed to cut very well, at least as well as out of the box.
    What I was thinking is that to be more precise I need to line up the raker angle so that it points directly to the cutter and from there start experimenting with a 5 to 7 degree raker angle for individual saws. Is this plausible or am I over thinking it and should I just keep doing it how it works?
     
  8. BobL

    BobL Addicted to ArboristSite

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    if the wheel has a flat front edge, what you will end up with are rakers that skate flat on the wood so the front of the raker will still need rounding over. Flat skating rakers will also not dig into the wood as much as fully rounded rakers. This means that flat rakers will not generate as great an effective cutting angle as rounded rakers. If you want to stick to this method then you will need a greater cutting angle to make up for the fact that the raker is flat to the wood.

    Just setting the wheel to 6º is no guarantee the cutting angle will be 6º unless as you check with the FOP. The critical factor in determining the cutting angle is the raker depth and the gullet width. Grinding the raker depth a tad under the FOP setting will make the cutting higher than normal. The problem with the FOP is it does not generate a constant cutting angle over the lifetime of the cutter, as the cutter wears the FOP reduces the cutting angle.

    You won't be able to do this with the grinder alone and you cannot accurately check any other angles with the FOP because it is a fixed angle device (well at least for a fixed cutter length).
     
  9. willsaw4beer

    willsaw4beer Addicted to ArboristSite

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    So I need to round the front of the raker 1st of all.
    And the angle on the raker itself makes no difference whatsoever? It's all about the triangle from the top of the raker to across the gullet, up to the leading point, then back down to the raker?

    Edit: When I set the raker angle, I try to grind a bit then line up the fop crossways to see where the raker angle points. I keep grinding down until the angle of the raker points directly to the point on round chisel. I then set the wheel at this height and do the rest of the rakers. Before I do this I do all the cutters so everything is all the same length..
    All this is unnecessary is what you're saying?
     
    Last edited: Dec 30, 2009
  10. kevin j

    kevin j Addicted to ArboristSite

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    Are any of the high speed video of the tooth porpoising action posted on the web somewhere?
     
  11. BobL

    BobL Addicted to ArboristSite

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    You should round after setting the raker height other wise you won't have a smooth edge for the raker to run on.

    The raker angle and rounding are important because they determined the depth to which the raker penetrates into the wood. It's difficult to believe that the raker penetrates at all into the wood, but depending on the surface area of the top of the raker, and shape in contact with the wood and the type of wood, this is what it does. The flatter the rakers are the less the penetration but the greater the surface area the greater raker friction between wood and raker. The pointier the raker the greater the penetration and more power is needed to maintain this penetration.

    There will always be a trade off between minimizing the surface area of a raker in contact with the wood and depth of penetration so some sort of middle ground would appear to be best.

    Really hardwood does not permit much raker penetration so it can use pointier rakers to minimize wood contact, softwood should benefit from flatter rakers.

    Here is a well formed raker - the cutting angle is 6º and it's nicely rounded over. There is a fair balance between flatness and ability to penetrate
    Nicecutter.jpg

    Here is a raker with three areas of flat and two distinct ridges. The raker would work better if these ridges were removed and rounded smooth.
    Ridges.jpg

    Here is a case of flat topped 6º raker such as you describe. The problem here is it will have close to the maximum surface area in contact with wood (hence greater friction) and a ridge on the leading edge which is very likely to catch adding more load to the powerhead.
    flatraker.jpg

    Edit: When I se the raker angle, I try to grind a bit then line up the fop crossways to see where the raker angle points. I keep grinding down until the angle of the raker points directly to the point on round chisel. I then set the wheel at this height and do the rest of the rakers. Before I do this I do all the cutters so everything is all the same length..
    All this is unnecessary is what you're saying?[/QUOTE]
    This is a reasonable way of doing it provided you round the rakers over when you finish. The easiest way to check is with a digital angle finder as in post #41 of this thread

    I haven't see a video but I believe some does exist.
     
  12. willsaw4beer

    willsaw4beer Addicted to ArboristSite

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    Thanks again BobL, that's exactly what I needed to know. Getting an 0-1 od mic and a vernier caliper are probably my next step.
    Just from my personal experience it is definitely worth the extra time sharpening chains. The fixed .030 raker gauge is completely worthless except to clean out bar rails and a fop is a sure step in the right direction but having a properly ground/ sharpened chain saves so much gas, time equipment wear, etc. in the long run I'm sure. Plus it maximizes a saw's potential and makes what would be work more fun.
     
  13. BobL

    BobL Addicted to ArboristSite

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    :rock:
     
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  14. edisto

    edisto Spelling/Reality Check

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    Here's a prototype of a simple gauge. Just a 6 degree angle scribed into black acrylic glued to a piece of clear acrylic that sits on the teeth.

    I need to move the reference mark to the middle and have the angle run down both ways so I can do the teeth on the other side.

    [​IMG]
     
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  15. Philbert

    Philbert Addicted to ArboristSite

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    See, I like this better: 1) Because it does not rely on the preceding tooth, and will work on full comp, skip tooth, low-kickback, etc.; 2) it does not require levels and protractors and feeler gauges or micrometers; and 3), because it agrees with my earlier post (#32)! I want a cut of the proceeds if this goes commercial!

    Philbert
     
  16. edisto

    edisto Spelling/Reality Check

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    It does require that the teeth be the same length, which could be a pain for some.
     
  17. Philbert

    Philbert Addicted to ArboristSite

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    I don't think so. Having your cutters the same length is just good practice. People who don't care about basic details like that are probably not all that concerned about measuring a 6 degree angle all that accurately. They probably just hit the depth gauge with a file until it's 'good enough'.

    Just my opinion.

    As I said, I would send you rep for posting that, except that the Rep Gods say that you are still in my 'holding pattern'.

    What would you think of a version of the 6 degree gaugethat works more like the Oregon gauge? It would rest on the previous few teeth and let the extra depth gauge poke through a slot to be filed off. That way you would not have to look at the chain from the side and estimate visually.

    Philbert
     
  18. mtngun

    mtngun Addicted to ArboristSite

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    I like the concept. The next step would be to make it out of hardened tool steel and rather than a scribed line, have a ledge for filing.

    On another subtopic, I've been using a 0.325" FOP for a few months now. Yet, despite the FOP, and despite the chains being only lightly used, they are starting to not want to bite unless I apply pressure. That's strange, my experience with the 3/8 FOP has been that it produces an aggressive chain..

    So I did a BobL and measured the raker depth with a straight edge and digital caliper. :laugh: Only about 0.020" - 0.023" after FOPing ? Huh ? I haven't taken the time to sort out why the 0.325" geometry is causing the FOP to produce wimpy rakers. Just wondering if anyone else had seen this, or maybe my chain (Woodland Pro) is just weird ?
     
  19. edisto

    edisto Spelling/Reality Check

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    It is a prototype, but the only change I plan to make to the final version is to get the scribed line going both ways.

    For me, having a filing ledge is not that important, and the thought of laying steel across the teeth to register such a gauge makes me cringe.

    With this gauge, all I need is a Sharpie (or other marker) to mark the portion of the raker that needs to be removed, file away, and recheck.

    I sharpen freehand, but about 3-4 times on a chain, I'll mount the Granberg File-N-Joint to make sure the teeth are the same length, and the angles are correct. Using this, I could do one raker, set the depth on the guide, and then file all the others to that same depth.
     
  20. BobL

    BobL Addicted to ArboristSite

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    I set the rakers on both my full comp 60" milling chains today.

    To read correctly a DAF needs to be held square across the cutter and raker, so freehand holding a DAF leads to an uncertainty in measruing the cutting angle of about +/- 0.3º .

    To get around this I clamped a rebated block of wood onto the bar for the DAF to lean up against and so the chain can still slide past easily onto the bar
    42inbar.jpg

    Wixey3.jpg
    wixey4.jpg
    Measuring the cutting angle is then
    1) Remove chain from bar and zero DAF against a marked position on bar
    2) Replace chain and mount block of wood as shown
    3) Move cutter of interest above marked position on the bar
    5) Place DAF down onto cutter edge,
    6) Lightly push back of DAF flat up against block and rotate DAF down till it makes contact with the top of the raker.
    Care should be exercised to ensure the DAF does not make contact with adjacent rakers and cutters.

    Before filing my ripping chains I had an average raker angle of about 4.5º but the range of angles was between 2.9 and 5.2º - ie all over the place.

    The raker of interest is then slid a little away from the wooden block and filed, then slid back over the marked position and remeasured.
    Repeat until you get 6º
    sixdegreea.jpg
    After while you get good at guessing the number of file strokes needed to reach 6º. I work out that each full rounding file stroke removes about 0.3º

    A few times I got a bit vigorous and a couple reached 6.7º , so all were between 6.0 and 6.7º ie a lot better than before

    Then I bunged a chain onto my mill and . . . . . check out post #24 in this thread.

    Conclusion:
    The DAF is a marked improvement usability wise over a Vernier Caliper because it directly measures angles with a single measurement. Apart from the rebated block of wood and a clamp, no jigs are needed and I will be moving to doing all my chains with the DAF in the future.

    BTW I also tried using a FOP for the first time and found out it does not pivot about the base of the next cutter but the top of the vertical side of the raker being filed. This means it is truly progressive.
    BUT
    The best I could get from it (as measured by my DAF) was a filing angle of only 4.7º on a new chain - so I agree with you mtngun - this is rather wimpy!
     
    Last edited: Jan 20, 2010
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