Chris Schwarz's Blog

Fine -tune a Handplane’s Back Iron

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For me, the goal with my smoothing plane is to set it up so I can ignore the grain direction of a board or a glued-up panel.

There are many valid ways to do this. For most woodworkers I know, there are two ways to accomplish this goal that we all agree upon:

  1. Sharpen the iron. Sharp fixes almost everything.
  2. Take a finer cut. Thin shavings reduce tear-out.

After using those two strategies, woodworkers differ on what else we can do to reduce tearing. We fall into three camps:

  1. Use a high angle of attack. The higher the planing angle, the better – 62° or so being the maximum planing angle before you start delving into scraping.
  2. Reduce the mouth aperture. The finer the mouth, the less likely the cut will shift so it is occurring ahead of the iron’s cutting edge. Reduce the aperture to reduce tearing.
  3. Use a “back iron” or “chipbreaker” that is set about .004” to .008” back from the cutting edge.

I will swear on a stack of Joseph Moxons that all three strategies work. You simply need to pick one that suits you best. Using all three simultaneously, however, will cause your handplane to clog.

During the last few years I have used a back iron with great success after I figured out a few of the details that make it effective. The above video shows the steps I take with a new back iron to make it effective. Though I hate to repeat the points of the video, here are the important points:

  1. Sharpen the iron. Sharp. Sharp. Sharp.
  2. Sharpen the tip of your back iron so it has a 50° bevel at its tip. Some back irons have a small flat at the tip that will cause your plane to clog. Sharpening the tip of the back iron removes this small flat and helps eject shavings. You have to do this once every few years or so – not every time you sharpen.
  3. To prevent shavings from getting between the back iron and iron, turn a hook on the tip of the back iron – much like you would turn a hook on a scraper. This hook will eliminate most gaps between the back iron and iron, reducing clogging. It takes about 10 seconds to add the hook right before you screw the back iron to the iron.
  4. Set the cap iron about .004” to .008” from the cutting edge.

Woodworkers who dislike back irons will tell you that these strategies are difficult or time-consuming. Try them out before you agree or disagree.

Using a back iron can be an interesting experience. When set properly, the back iron will push the shavings out smoothly without making the plane difficult to push. But when set poorly or when the back iron has a flat on its tip, the plane can be quite difficult to push.

The tool will still reduce tearing in this configuration, but I have found that the surface quality will suffer a bit, though not any worse than with a card scraper.

I’ll be honest: I like all three strategies for reducing tear-out and have employed them all successfully during the last 19 years of working with handplanes. I encourage you to try them all, and refuse to let anyone tell you there is only one magic trick to eliminating tear-out.

— Christopher Schwarz

31 thoughts on “Fine -tune a Handplane’s Back Iron

  1. Capie

    Chris man, help! Feeling a bit like an idiot here. Don’t seem to be getting a higher angle than about 45deg out of my vintage Eclipse honing jig. Min protrusion the jig will allow is about 19mm. Nobody else seems to be experiencing this problem(?). Not enough meat either to grind the jig’s shoulder away.

  2. tmpattonmd

    I have always kept a nicely sharpened blade. So I tried sharpening and buffing out the cap iron as well as setting the cap iron with a 0.005 feeler gauge.
    Well, I’ve never had shavinging shoot out of the plane before; but now they do!!! No clogging of the mouth!!
    Thx.

  3. wmickley

    One has to sharpen the cap iron every few years?? Are you talking from experience? I have used the double iron for over forty years and have never touched any of my five cap irons once they were in service.

      1. wmickley

        It was less than three years ago you were denying that the double iron plane was effective. Now you are pretending expertise about long term maintenance. I have worn completely through several plane irons without ever having to do any maintenance on a cap iron.

        1. Christopher SchwarzChristopher Schwarz Post author

          I have been tuning back irons since I met David Charlesworth in 2006 and read his first book, including putting a curve on them. David said it aided chip ejection and reduced clogging. And it does!

          I use a lot of resinous woods, such as yellow pine. The resin builds up on the back iron, even though I try to remove it with a handblock. So I sharpen the back iron every few years to give me a fresh, clean edge.

          Some day I’ll be as awesome as you, Warren.

        2. trollymctroller

          can I buy one of those worn through plane irons from you. that way when people come over I can show it to them and they will think that I sharpen a lot. i defiantly want people to think that i sharpen a lot. then they will know that i am an old tyme craftman. that’s all i care about.

          1. trollymctroller

            i may not have ever made anything, but i think about woodworking so much that i am defiantly better then chris. im on w’s level. Ive worn through like 10 plane irons in my mind. cause im constantly mind sharpening.
            chris if you have any woodworking questions, please let me know. i defiantly don’t have any for you. ok im gonna go think about how i would carve a ball and claw. (My 50th mind foot)

              1. trollymctroller

                wordsmith – you

                woodsmith – me

                if you have any questions let me know

  4. Derrick

    Chris – I assume this is easier with the cap iron on a LN given it has a flat bevel like front similar to a blade. What about with a cap iron on an old Stanley? Would you change the way you sharpen that given the curved front edge?

    1. Derrick

      Also, is that the new prototype jig from LN, or some other eclipse like jig? Looks brand new and similar to the sample I saw at the Charleston, SC hand tool event.

      1. Christopher SchwarzChristopher Schwarz Post author

        Same procedure for every back iron I’ve encountered.

        The type of honing guide doesn’t matter either. Mine is a prototype Lie-Nielsen version. The process works fine with the $15 Eclipse, too.

        1. Derrick

          Yea, I was just curios if that was the prototype. I saw it in Charleston and really liked it. Interested in what you think.

  5. Danpope1

    Chris
    Any advantage or disadvantage to using a tight 50 degree chip breaker with a high angle frog as long as the mouth is open?
    Thanks

  6. red_wilson

    What is a good source for the thin feeler gauges you used in step 4? I am also looking to find one to use for plane sharpening, and I assume they would be similar “shims” but I could be wrong.

    1. Christopher SchwarzChristopher Schwarz Post author

      Oh sure. And I’ve experimented with those steeper angles and have found that 50° is sufficient for my work. Please do try the higher angles for yourself, however.

  7. jlg4880

    Ohhh, the gossamer shavings! Stop it! Are you trying to make all of us fall back on our smoothing plane addiction?!?!

  8. Michael Rogen

    Hi Chris,

    As a free hand sharpener for years the need to go back to the future is upon me. A simple honing guide is what I’m after. Similar to yours. If you have an idea or suggestion, please contact me off line as I’m having some issues here at the home front.

    Thank you,
    michael.rogen@gmail.com

  9. BLZeebub

    The epiphany for me happened while planning some recalcitrant curly maple a few years back. That the mouth needed to open to accomplish the smoothing function went against previous experience/knowledge. Since then, I’ve done the same work on burl walnut and quilted maple with measured success [giving the devil his due here] with satisfactory to extraordinary results.

    I dig the feeler gauge setup and turning a burr on the back iron, that is GENIUS. Thanks again.

  10. hmerkle

    Thank you Chris,
    Once again, advice specifically when I needed it!
    Q: “Why oh why when I do all the things I am supposed to do, does this stupid old plane clog?”
    A: “It’s not the tool – stupid!” ha ha

  11. CharlesHart

    Great idea I’ve never heard this one before. What is the make of the burnisher you used? I have never seen that before. You stuff is always amusing.

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