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Thread: Blades and Frogs

  1. #1

    Lightbulb Blades and Frogs

    As I'm tuning up a couple of planes, I noticed something.One of the first mentioned tune-ups is flattening the frog face . I use a file, but I've done a fair bit of filing in my work. OK,fine. But what about the blade. Nobody seems to mention the flatness of the blade. I'm using the word blade, but cutter or iron, depending apon country or manufacturer usage. That is the other half of the mating. On the old blades I'm working on, the word flat can't be used in the same room as them. One is a laminated Stanley and the other a Anchor brand, so both were worth the effort.After some careful hammering, I resorted to using to using a dial indicator mag base and a 6x48 sander. Tricky but doable. Thanks Derick Cohen (sp). It's just something else to think about.

  2. #2
    I would think the cap iron lever will take out any minor discrepancy in blade flatness.

  3. #3
    I don't think so, Robert. If you fully tighten the screw on the cap iron, the blade will arch,even that 99 cent rule you picked up at the store counter will show the gap. My expertise isn't planes, rather it's setting up machinery. The Stay-Set lever cap of the Record/Clifford or the hinged one of MillersFall would help.My usual answer would be the thicker Vertas blade and cap iron but at $100 for a $12 planes, Canadian $,it's pricey. I'm not sure if there is an answer here.

  4. #4
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    The dirty little secret here is that most planes (including premium ones from people like LN and LV) have gaps between the iron and the frog when tightened, and work perfectly well. As you say, the fact that the lever cap only applies pressure at two points along the blade makes gaps in between nearly inevitable. As you also point out the manner in which the cap-iron attaches to the blade adds to this, because preload that holds the cap iron in place also bends the middle of the blade (along the lengthwise axis) away from the frog. In the absence of any lever cap load in the middle that basically guarantees a gap even if everything starts out perfectly flat.

    Basically every plane I own has a gap, though most are quite small and only detectable with effort. I suspect the same is true of many people who claim to have flattened everything for "perfect registration". They just aren't using the right methods to detect small gaps.

    This is one of those things where you can drive yourself nuts trying to flatten everything in sight, and not get any real improvement in performance. What really matters is that the blade is bedded well directly behind the edge, where the leading edge of the lever cap applies pressure. Are you seeing a specific problem that leads you to suspect inadequate bedding? If not I'd suggest not worrying about it.

    One other remark: LV actually manufactures the datum surface on the adjuster (the round pad that the blade rests upon, directly below the tightening screw) very slightly slightly proud of the flog. Even if the blade/cap-iron assembly were perfectly flat when assembled (it isn't, see above) the blade would still contact at the base of the frog and at the adjuster. All of the precisely machined "registration surface" in between is for show.
    Last edited by Patrick Chase; 10-22-2016 at 3:24 PM.

  5. #5
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    I just wonder how exactly we NEED to be.
    Is there an "excessive" factor that is used?
    I just keep my planes tuned to work, and don't bother about .002 shavings.
    Not tryin' to be a bummer, just a realist.
    Bill
    On the other hand, I still have five fingers.

  6. #6
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    Quote Originally Posted by Robert Engel View Post
    I would think the cap iron lever will take out any minor discrepancy in blade flatness.
    As Ray points out, the opposite is true. The Cap iron is effectively a spring that "pushes down" on the iron at its ends and "pulls up" at the attachment screw (where "up" and "down" are as installed in the plane). The attachment screw is smack in the middle of the frog, in between the lever cap's two interface points, so the cap iron pulls the middle of the blade away from the frog.

    As Ray says, all you need to do to disprove the "large mating area myth" is to actually take a straightedge to an assembled double iron.
    Last edited by Patrick Chase; 10-22-2016 at 3:41 PM.

  7. #7
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    Quote Originally Posted by Bill White View Post
    I just wonder how exactly we NEED to be.
    In my experience you need to have good mating at the base of the frog, close to the edge. If you don't have that then you will be susceptible to chatter.

    I suspect that the reason LV machines the rear mating surface (at the adjuster) very slightly proud of the frog is to add some tolerance, such that even if the iron is slightly concave-up most of the lever cap's pressure will still be applied at the base of the frog. It's a simple matter of optimizing functional importance over mythology.

    Quote Originally Posted by Bill White View Post
    Is there an "excessive" factor that is used?
    I just keep my planes tuned to work, and don't bother about .002 shavings.
    Yes, there is an "excessive" factor.

    As I said previously almost all of my bench planes have at least some gap over middle/upper part of the frog. I can get 1/2 mil shavings out of any of them with a well-prepared iron, and I don't experience chatter.
    Last edited by Patrick Chase; 10-22-2016 at 4:48 PM.

  8. #8
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    One other thought: The lever cap can only apply so much normal force before Bad Things (tm) happen, for example you lose the ability to adjust the plane or you strip the screw.

    That being the case, registration of blade<->frog becomes a zero-sum game. If the blade is pressed against the frog in the middle then there will be less pressure at both ends ("both" because the overall pressure distribution must be centered about the screw).

    Given that reality, I question whether it's even desirable to have the blade in contact with the frog along its full length, as opposed to having the normal forces distributed more towards the cutting edge. LV's design choice looks increasingly sensible as I think about this more deeply.
    Last edited by Patrick Chase; 10-22-2016 at 7:22 PM.

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    Didn't Millers Falls have a lever cap with three point contact?

    Not sure if it improved performance or just sounded good in advertising.

    I have adjusted many a cap iron to do less warping of the blades. The cap iron being softer than the blade will give a little more and still supply good contact at the chip breaker's edge.

    jtk
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  10. #10
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    Maybe just need a Millers Falls type lever cap?

    IF the blade is bowed a bit so that when installed, the bow flattens out. Seen way too many "curved" irons come through the shop. The "bow" would flatten out, when the lever cap is installed.

    Just food for thought......

    BTW: what IS this "gap" you be talking about? Haven't seen any around here......

  11. #11
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    Quote Originally Posted by Jim Koepke View Post
    Didn't Millers Falls have a lever cap with three point contact?
    Not sure if it improved performance or just sounded good in advertising.
    I'm going to go out on a limb and guess that the fact that nobody bothered to copy that design when the patent ran out (c. 1946) is telling us something. It seems to me that it's just wasting normal force where it's not needed, except for marketing purposes of course.

    Quote Originally Posted by Jim Koepke View Post
    I have adjusted many a cap iron to do less warping of the blades. The cap iron being softer than the blade will give a little more and still supply good contact at the chip breaker's edge.
    You can make a blade bend further away from the middle of the frog that way by increasing the cap-iron's preload, though only to a point as the cap iron is quite weak relative to the blade. You can't go the other way without decreasing the cap iron's preload, and that causes other problems such as jammed shavings at the blade to cap-iron interface.

  12. #12
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    Have quite a few Millers Falls planes. Never had an issue. Why nobody copied it? Cost, pure and simple. Stanley was too busy cutting costs then.
    IMAG0135.jpg
    Then again....YMMV

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    Quote Originally Posted by steven c newman View Post
    Have quite a few Millers Falls planes. Never had an issue. Why nobody copied it? Cost, pure and simple. Stanley was too busy cutting costs then.
    What about the modern makers?

  14. #14
    It was copied. Pope in Australia post-war (definitely) and I believe Record as well, but don't quote me on that.

    As far as why no one in the US copied it, well...

  15. #15
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    They are too busy making Stanley knock-offs.....unless you count Clifton. Might cost too much to make one out of Bronze?

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