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Thread: Tips on lapping plane blade back?

  1. #16
    Quote Originally Posted by Evan Van Dyke View Post
    You mean put a back-bevel on it? Suppose I could, but I am ultimately trying to solve some faulty chip-breaker mating issues, so I don't want to confuse things while I'm still learning to sharpen & maintain plane blades.

    Good news is that a few more hours on the DMT plates has finished the work on 3 of my plane irons, and the 4th is almost done (#7 iron on the right)
    Attachment 456222
    It isn't a back bevel; that is steeper and is intended to change the cutting angle of the plane.

    For what gets called the "ruler trick" (supposedly invented by about a dozen woodworkers, but probably as old as the hills) you just raise the blade a smidge so that the pressure is concentrated on the end of the blade where the blade cuts. There is no need to polish and flatten the whole back, just the end 1/4" - 1/2" or so needs to be polished flat. Only the very edge of the blade cuts, and only about 1/8" of the blade max is exposed in front of the chip breaker. As long as the chip breaker seats well, you are good.

    I usually do it by putting most of my finger pressure near the cutting end of the blade. That is often enough to just raise the back of the blade a bit to even out the edge faster.

  2. #17
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    Only the very edge of the blade cuts, and only about 1/8" of the blade max is exposed in front of the chip breaker.
    That may be good for a jack plane set up to be used as a scrub plane.

    There are folks here who would be screaming about their chip breakers being more than 1/64" back from the blade. By some folks figuring, that is even too far.

    Search > setting a cap iron < to find an article on Wood Central by David Weaver. The link to the Kato and Kawai video no longer works. It may be available on the web somewhere.

    My suggestion is to keep it simple. If a flat back and a decent bevel isn't working, ruler tricks, secondary bevels and cambers are not likely to make things any better.

    jtk
    "A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
    - Sir Winston Churchill (1874-1965)

  3. #18
    Great! I've been down the same road. Glad you finally made it to the end.

  4. #19
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    Do you like making easy hard?
    Japanese planes work. Look and learn.
    Take a grinder to it, have it done in ten minutes, or spend three days lapping it, your choice.
    Japanese handplane blades are hollow ground.
    Japanese supersurfacer blades are hollow ground.
    Western style plane blades are "Flat" ......and never are! Why? Because even though they don't work, you keep buying them!
    People that don't know how planes work, manufacture handplanes.
    They manufacture hanplanes because the sell, not because they work.
    Think about it, why does it need to be flat for 8"?
    If you can answer that then by all means flatten it, but if you cant answer that then do what needs to be done.

  5. #20
    Mark are you replying to my post? Not sure what you're on about.

  6. #21
    At what point was anyone talking about flattening 8" of the Iron?

  7. #22
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    Quote Originally Posted by Eric Rathhaus View Post
    Mark are you replying to my post? Not sure what you're on about.
    You're not the first to be baffled.

  8. #23
    I have no problem with a hollow ground iron - but the edge needs to be flat for a properly fitted cap iron. I tried striking the plate to pop my bellied iron into a hollow one, but didn’t work for me. My inexperience may very well be part of that. Not sure why you associate the hollow iron with Japanese planes, when they work anywhere?

    Japanese planes are - obviously- quite good. But i have some different ones, that i would much rather put in the time to fix than to throw them out and buy even more.
    Last edited by Evan Van Dyke; 04-20-2021 at 10:07 AM.

  9. #24
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    To get the back of your plane blade flat, you need to remove metal from the high spots. You can try lapping it on sandpaper, on a sheet of glass, granite or MDF if you want, that is difficult and time consuming, or you can grind it away, or tap it out with a ballpein hammer on a junk of endgrain hardwood. I tap them them out on a large ash tree stump, It makes for a great anvil. I also grind them out to hollow them a bit, not deep, easy enough to lap out on a 1000 grit stone If you wanted to.
    To grind it you can use a tiny pencil grinder with a carbide burr or small grinding wheel, just gently run the burr over the high spots, All of the middle area, the check it by a few laps on your waterstone occasionally.
    So you just remove some metal in the middle of your blade, with the grinder. You don't have to remove much, just enough so that when you lap it on your stone it touches around the front for 1/4" or so, and 1/8 on the sides and as far back as you need. You can use any grinder, pencil, die or small disk or even the bench grinder. All you need is to remove a 0.001" in the middle of the blade, so that you have a good flat reference around the sides and front edge. Why try to polish out the middle on sandpaper? Hollow grind it a bit, like the Japanese planes. When you lap one of those blades you are only polishing a tiny bit of metal around the edge, not the whole blade. When your blade is lightly hollow ground it polishes up on the perimeter very fast and right up to the edges for a perfect fit for your chipbreaker. Hollow grinding your blade just removes a tiny bit of metal in the middle of the blade, so you have low spots on the front edge where you have it now.

    I do it on my planes and chisels, but then i modify just about everything to make it work better and more efficiently, lots of people have a problem with changing stuff, I don't. I don't buy tools to look at, I want my tools to work, so whatever gets results, I will do.
    So what i am saying is look at what you are trying to achieve, look at what you need to do to get there, Throw out the "normal" way. Take a few risks, try something, see if it works.

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  10. #25
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    8" 4" 2" how much do you need for the plane to function? Anything more than you need is a waste of time.

    Quote Originally Posted by Russell Nugent View Post
    At what point was anyone talking about flattening 8" of the Iron?

  11. #26
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    Sorry if I didn't make myself clear.

    Quote Originally Posted by Jim Matthews View Post
    You're not the first to be baffled.

  12. #27
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    Diamond plates are not the best to use for this job. They aren't as fast as fresh sandpaper in 80 -120 grit range, and they will get worn out in the process. I'd save them for jobs like flattening/conditioning other stones, where they are very convenient, or random jobs like sharpening carbide or odd shaped tools that would gouge normal stones.

    Get something flat and some PSA sandpaper (or adhere normal sandpaper with spray adhesive) and go to town. Change out the paper every few minutes, it dulls fast. Shouldn't take more than 10 minutes this way to get a #4 size iron flat.

    A 1 meter long surface plate would be great, especially for flattening a plane sole, but for an iron or chisel back something much smaller works fine.

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