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Thread: Fixing a convex-backed plane blade

  1. #1
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    Fixing a convex-backed plane blade

    I recently got a Stanley 5 1/2 (type 11) which came with a blade which I believe is made of laminated steel. However, the back of the blade is significantly convex, both horizontally and vertically.

    I've already used up an 18-inch strip of sticky-backed 120-grit sandpaper trying to flatten it, and there's a lot more to go before I get it flat all the way out to the corners. My free time is limited and I don't really want to spend the time and effort to keep doing this. I've done it enough times to know that it always takes way longer than one expects.

    I'd be willing to buy a new blade, but I can't find one that will fit -- this is an older 5 1/2, with a 2 1/4" blade. At some point Stanley moved to a 2 3/8" blade, and all the modern derivatives use the same width.

    Has anyone had success with Paul Sellers' method of hitting the middle of the blade with a mallet to flatten it (or even make it concave)? I tried it but it didn't seem to have any effect, though maybe I'm just not hitting it hard enough.

  2. #2
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    yes. Set the iron flat on your bench. Feel for the exact center of that "high" spot. first few whacks, just let the weight of the hammer do the work...

    Do NOT clamp a bent iron in a vise, and try to bend it back to straight by hand....iron will snap and cut the hands. You can, however, use 3 dowels and the vise....to take a curved iron back to straight. Doesn't do a thing for the hump in the middle of an iron, though...

    Same can also be done with bowed in the middle chipbreakers. use a ball peen hammer to flatten the high spots....big flat end for the iron, and the ball end for the chipbreaker..

  3. #3
    Hock makes replacement 2 1/4" plane irons.

  4. #4
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    Dremel grind the hump or buy a replacement. They're available.

  5. #5
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    Have actually DONE the flatten with a hammer routine. Irons do get bent...by stay locked down in place, and sitting on a shelf for a few decades....Have rehabbed many such planes. some even had more than one camber...looked like this..~ and worse.

    Buying a new, thicker iron sometimes causes more problems than they are worth.

    "Grind the hump"? Hmmmm, ah...NOPE. all you will do is create a thin spot. The metal needs to be flattened, not ground away...

  6. #6
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    Forty Two bucks from Ron Hock > http://www.hocktools.com/products/bp.html

    If your old chip breaker is in good shape it will work fine.

    You could also spend a little extra for a new chip breaker and use the old blade & breaker as is if you ever need a large scrub plane.

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

  7. #7
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    Quote Originally Posted by steven c newman View Post
    Have actually DONE the flatten with a hammer routine. Irons do get bent...by stay locked down in place, and sitting on a shelf for a few decades....Have rehabbed many such planes. some even had more than one camber...looked like this..~ and worse.

    Buying a new, thicker iron sometimes causes more problems than they are worth.

    "Grind the hump"? Hmmmm, ah...NOPE. all you will do is create a thin spot. The metal needs to be flattened, not ground away...
    Grinding it is virtually no different than lapping it flat. Not sure what your 'nope' is all about. People lap steel flat all the time - humps or hollows. I bet if I look long enough I could find all sorts of threads of you talking about grinding and lapping chisels and plane irons.

    If you beat it, all you're doing is stretching it and distorting it.

  8. #8
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    If you beat it, all you're doing is stretching it and distorting it.
    And possibly cracking it.

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

  9. #9
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    Thanks - I didn't know that Hock made blades that would fit. Unfortunately, I'm pretty sure I would have to file the mouth of the plane to fit the thicker blade.

    I'm going to try the hammer technique first. I hope that the fact that blade is laminated means that there is a smaller chance of the blade cracking, since much of the metal is softer. If that fails, I may buy the Hock blade and file the mouth of the plane.

  10. #10
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    One 18" strip? For a job like this I'd use 80 grit, but more importantly I'd be changing the paper every 5 minutes of lapping. The paper dulls fast, and a fresh strip removes more material the first minute or two of use than in the next 10.

    Not saying don't try the hammering, but lapping can be done much faster than many think. Coarse paper, changed often, with high pressure is the key.

    Also, the convexity along the length is likely not a problem. As long as there is good contact at the heel of the bevel, that's what matters. The lever cap will pull everything right.

    But convexity across the width must be dealt with.

  11. #11
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    I decided to try the hammer technique, but a little different from how Paul Sellers recommends.

    Here's how the blade started out. The gaps look somewhat larger than they actually are, due to backlight bleed, but even so, they're pretty big.

    First, across the width (with a Woodpeckers mini-square resting on top, acting as a straightedge):
    flatten-1.jpg

    And along the length:
    flatten-2.jpg

    You can tell with the naked eye that this blade is a banana.


    I put the blade on a piece of 2x4 and shimmed up a corner, then used a scrap piece of wood as a soft punch and hit it with a hammer. I did a few hits at a time, checked for gaps, and repeated. I did this many dozens of times, hitting with varying amounts of force, trying to get the gaps to get smaller. (You can also see in this photo where my previous attempt on sandpaper scratched the blade, in the middle.)

    flatten-3.jpg


    This is the result, across the width:
    flatten-4.jpg

    And along the length:
    flatten-5.jpg

    Better, but still with a lot of room for improvement.

    I decided to try bending the blade with pliers -- specifically, two Knipex pliers wrenches, which have flat faces so they don't dig too deep into the surface. This is risky. I know from experience that it's easy to accidentally snap off a piece of a blade by doing this. Once in the past, I tried this with a Stanley blade, bending with increasing force in an attempt to straighten it. I made no progress because the blade wouldn't keep the bend that I was imparting -- and then finally it just snapped. The corner I was bending broke right off.

    I hoped that this one would be easier to bend, since it's laminated, whereas the one I broke was a single layer of hardened steel. It turns out that this blade did bend VERY easily. Way easier than I expected. I kept overshooting my target and had to bend it back. I took this photo after bending the right corner up, a little bit too far.

    flatten-6.jpg

    I did a bit of adjusting after this photo and got it reasonably flat, with a slight concavity along the width and length. I got excited and forgot to take pictures after doing that, though.

    Finally, I flattened it on the 120 grit adhesive-backed sandpaper on granite. Here's what it looked like at this point:
    flatten-7.jpg

    Nice and flat near the edge. After that, it was just a matter of going through the grits to get the back polished, and then sharpening the bevel side. Now it works great.


    I think the reason that the blade was originally so bent is because the metal is so soft, and therefore more easily damaged by abuse.

    At any rate, I'm glad this worked. The hammering was only a little effective, and the pliers were very effective. As I said earlier, though, I had a bad previous experience using pliers on a non-laminated blade, and I think they worked well on this one only because the blade is laminated.
    Last edited by Winston Chang; 03-31-2020 at 12:46 AM.

  12. #12
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    When I was hammering on one of the bent irons....laid the iron right on the bench top,,,,nothing between the iron and the broad face of my 32 oz ball peen hammer....but, I wasn't playing a Blacksmith about it.
    Last edited by steven c newman; 03-31-2020 at 1:38 AM.

  13. #13
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    Winston, you seem to have corrected your blade before my afternoon in the shop to take photos of one method to work on the back of a plane blade.

    Your blade looks to have been beyond repair via abrasive sheets. Here is another method for times in the future a blade may need some light adjustment of the back.

    This set up uses abrasive material with pressure sensitive adhesive backing mounted on a scrap piece of granite counter top:

    Blade, Abrasive, Guiding Block.jpg

    This is actually a shop made circle template. For flattening blades a block of wood will work fine. This just has a comfortable handle:

    Working Blade Back.jpg

    Moving the blade in the direction of its length may be better than side to side. If a blade has a high spot in the center side to side may allow the blade to rock, causing the high spot to remain.

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

  14. #14
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    Winston, don't use the hammer trick, I've broken two blades trying it out, including a 2 1/4" blade, like yours. How are you holding the blade while sanding? Check this video out, at minute 8 he brings up a blade holder made of a piece of wood and two bolts to hold the blade flat against the sand paper (https://youtu.be/N_aN2jr5l5w?t=475). That's how I flatten my new blades. You only need about 1/4" of flatness at the edge of the blade. Give it a try.

  15. #15
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    Funny..I just tried that "Hammer Trick" the "anvil" was the top of the leg on my bench,,,end grain pine....hammer was a 32oz ball peen hammer, using the non-ball end..

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