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Thread: Flattening back of plane irons

  1. #1

    Flattening back of plane irons

    I'm new to hand tools and have several old bench and block planes I'm refurbishing. One constant theme for me it trouble flattening the back of the iron all the way to the cutting edge. Unfortunately, none of my irons have had any kind of hollow back so it's taken a long time to get the back flat. I'm currently working on an angled block plane and I got the the first couple of inches flat using sandpaper on a granite block. Then when I got to my diamond stones (300/600/1200), i have a heck of a time getting it flat all the way to the edge. There's about a couple mm of area next to the edge where it's obvious that the diamond stone hasn't touched. I'm using plenty of downward pressure toward the edge of the blade - my fingers are fatiguing.

    I tried Paul Sellers method of wacking the iron with a nylon hammer in an attempt to create a hollow back but that didn't work. I was afraid to hit it too hard, because I did that with a different iron and busted it. Any advice would be appreciate. The diamond stones are brand new and not the cheapo ones. I don't know if the swarf can get under the iron and cause this issue. I think I'm using plenty of glass cleaner.

  2. #2
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    I would like to suggest you just try for the first inch. And make sure your diamond plate is flat and sitting on something very solid and flat.
    I haven’t done a plane blade for a couple years now. The last one blade I bought from?? took lots of elbow grease to add pressure right where it counts hold a piece of a hardwood across the back as you bear down.

    Good Luck
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    Aj

  3. #3
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    It sounds like those old irons might have back bevels. Whoever sharpened them might have either lifted them up at the end of the stroke, or maybe used stones that were dished in the middle. Can you regrind the irons past the back bevels? I’m doing that right now with some used chisels that came to me with very slight back bevels. Once you take off that little strip of metal the problem is solved. If you don’t have a grinder, try looking up a local woodworkers group and ask around. Someone probably has a Tormek.

  4. #4
    The blade only needs to be flattened near the cutting edge, maybe for a half inch or so. Chisel backs get flattened all the way, but plane blades do not need it. In fact, it is common for some woodworkers to slightly raise the blade a half degree or so at later stages of flatting the back (known as the "ruler trick" in some quarters), so the pressure is all put on the edge (alhough you have to be careful about doing that on a bevel up block plane, you might not have enough clearance). Look in the Neanderthal Haven section, you will have lots of info on sharpening in the archives. In fact, the mods will probably move this thread there, which will elicit lots of opinions on the best way to prepare a plane blade

  5. #5
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    Makita makes a water cooled horizontal sharpening wheel with a 100g stone which is perfect for this application. I found it useless for anything else, and it is often available on the Craigslist market very cheap.
    Regards,

    Tom

  6. #6
    Quote Originally Posted by Steve Schnurbusch View Post
    I'm currently working on an angled block plane and I got the the first couple of inches flat using sandpaper on a granite block.
    Sounds to me like you could have spent more time on this stage,
    Using those grits on only a "couple of inches" might be aggressive enough to change geometry and lead to more problems with a belly on your irons.
    That couple of inches principal.... can be used well with finer abrasives, that's not saying I would use a 300 grit on just a few inches if I can help it.
    Nothing bad to be said with having a bit more polished area if you can get it done quickly on a granite plate.
    Its the first thing you would do to get an idea of the flatness, if it had been a rusty ebay purchase.

    Since you started on the plate, you might as well flatten it whilst at this stage of iron preparation.
    If the iron is in a mess then I would ensure as much contact with the iron on the abrasive as possible.
    Skew the iron in both directions to take off an even amount, I prefer to dub the edge rather than the sides of the irons at this stage (on the surface plate which I keep my abrasive tightly clamped down from both sides of the strip)
    and move to finer abrasives and hones and hone to your liking.....

    If you can see that you are not getting full contact at the edge (an incomplete polish from the roughest hone you got)
    then you still have a hump.
    Depending on how close to the edge the hump is, will dictate if you could get away with doing said principal with hones.

    Good luck
    Tom
    Last edited by Tom Trees; 06-09-2020 at 7:47 AM.

  7. #7
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    Before going crazy on getting the perfectly flattened back it should be remembered the results are what is important.

    Set up the blade in a plane and see how it works. If it works well enough, then over time you will remove the back bevel a little bit at a time as the blade is sharpened through use.

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

  8. #8
    You could also try the ruler trick: have the plane blade rest on a thin metal ruler when flattening the back. The slight inclination ensures your work addresses the area at the edge of the blade.

    Eric

  9. #9
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    First, where do you live? I am in the middle of Ohio, if you are also, bring it over and we will sort it out.

    I have seen a lot of good advice, so let me see if I can pull some of that together:


    1. You said it is there except for the last few mm, and someone suggested that it was back-beveled. Then it was mentioned that you too could do a back bevel (the ruler trick). If you do not know the ruler trick, say so, but, I did this once with an otherwise great plane that was just not going to be fine without removing a bunch of steel.
    2. Related to above, if I had just a few mm because it was back-beveled, I would simply throw it onto my Tormek and grind that blade down a few mm so that you took the edge to the flat.
    3. For serious flattening, I usually use sand paper (and I own a lot of diamonds and similar). I then hold onto the blade with a strong magnet, which then causes the removed steel to stick to the blade; good and bad.


    And now my mind went blank!

  10. #10
    Thanks for all the advice and unfortunately I live in Oregon - so quite the long trip to Ohio! But airfares are really cheap right now...

    I finally just kept at it this afternoon and got it flat to the edge up to 1200. It just seemed weird that using 220 grit sandpaper I got a consistent sanding pattern all the way to the edge and then switching to the 300 grit diamond stone it was clearly not getting to the edge. I guess it's hard to comprehend the miniscule thicknesses were talking about when sharpening. I had better luck pushing the iron back and forth into the stone as opposed to laterally across the stone - if that makes sense.

    I still didn't get it ultra sharp - couldn't cut hair on my arm. I got decent shavings but it seemed like I had to push harder than I should have. This is where it's hard when you're new to this stuff and don't have a way to determine if you got it sharp enough. But I'll just keep at it and learn as I go along. Thank goodness for youtube and forums like this.

  11. #11
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    Sometimes, especially with sandpaper, the flattening process can can also be causing the problem; for example, when the paper curls up or similar. Have also had problems related to how I was holding the blade. May not be it off course...

    Sounds like you have it until control, however.

  12. #12
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    Thanks for all the advice and unfortunately I live in Oregon
    What part of Oregon?

    My place isn't terribly far from Portland.

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

  13. #13
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    I only flatten the back edge just enough for chip breaker to sit on. Flattening an inch or so took forever and I get the same results with my shavings. Only a 1/4 to 1/2 an inch at the most is on the stone.

  14. #14
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    Come up to Bellefontaine, OH.....just flattened a 2" wide plane iron ( to be shipped out) in about..8 minutes....total time to get the iron to shave arm hair? 15 minutes....

    Bring an old plane iron along with you....and see how it works...

  15. #15
    Steve - We seem to be struggling with the same task but with a different approach. See the thread I started titled "Twisted Handplane Blade" in this forum section. Using the Charlesworth ruler trick to flatten only the leading edge with a back bevel I'm finding that twists in the blade to be troublesome. All steel when heat treated will move. If you're lucky or if the process is possibly more refined the movement will be limited to a slight twist or cupping on the side you're trying to flatten. Cupping is easy to deal with as the reference position for the ruler trick involves only 2 contact points. The resulting grind would bring the 2 contact points on the corners of the blade together near or at the middle. A twist in the blade would result in a grind that tapers from one side to the other. All is well if a flat grind is accomplished with either condition but I'm thinking all that good work becomes wasted when the chip breaker is installed and the cup or twist is altered again by the tension it creates. In other words the chip breaker will somewhat make the cup or warp conform to its shape. While communicating with Lie Nielsen about all of this they suggested checking the diamond plates I was using. To my surprise the Trend plate I was using was severely warped on the 1000 grit side, not so much on the 300 grit side. The DMT plates I have, all 3 of them fared much better. So what is my current thinking on a solution ....

    At least for the new Lie-Nielsen blades I just purchased I'm finding that all of them have a uniform thickness and were probably flat before heat treating. Since I was able to remove all of the cupping, twists, etc. on the blades by placing them on a magnetic chuck (it springs back when removed) I'm thinking the backs will be flat when the chip breaker is installed. So I don't intend to do anything to the backs. That leaves the bevel side of the blade and what to do with it while sharpening. How will that edge mate with the edge on the back side that will be flat while under tension of the chip breaker. It seems to me the bevel side should be sharpened under the same tension.

    I agree with the comments above about sandpaper having a tendency to curl and dulling the edge trying to be sharpened. I see no problem in using sandpaper for flattening but the edges need to be addressed differently. That's been my experience anyway.

    And probably the best bit of information that my anal brain is slow to process is from those practical minded folks that suggest use the tool and see how it performs. If it has a problem like chips getting under chip breaker, then look for a solution. If the tool performs well and to your liking then ignore all of what is above and enjoy.

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