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Thread: Question on Chipbreakers

  1. #1
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    Question on Chipbreakers

    Greetings to all,

    I picked up a very clean coffin smoother at an antique store a couple of weeks ago. The iron isn't original, but seems to have been around for a good long time. Some etching on the back side shows it's a piece of T-1 Tungston High Speed tool steel (the stuff they make taps, dies, and metalworking cutters out of). It's bedded at 45 degrees and doesn't have a chipbreaker. Based on the flat bed that the iron sits in (no clearance pocket for cap iron screw), I don't believe the original iron was ever equipped with one.

    Following a thorough sharpening, it cuts pretty well if set for a light cut, although the adjustment process is pretty fussy (small hammer). The mouth isn't as tight as I'd like and I may insert a stick of rosewood to remedy that. I'm wondering if I should make provisions for a chipbreaker as well. I have access to a wire EDM so I could slot the blade pretty easily and install a Hock version, but I wonder if it would improve anything.

    Any thoughts from those who have been down this path?

  2. #2
    Haven't been down your path but I know a chipbreaker helps break the shaving away quicker which would be of major benefit in a smoother.

  3. #3

    What's the bed angle of the plane?

    I'm not a big fan of cap irons. All the published information on cap irons make the claim that cap irons were some big advancement. I think they do what's claimed by emulating steeper pitched planes and they need to be set very close to the edge to do that. I don't believe they do the job as well as the York, middle or half pitch planes because the increased angle of deflection of the steeper pitched planes begins right at the cutting edge. When I look at the history of planes, what I see is that the traditional pitches were discontinued in favor of double iron planes at common pitch. I wouldn't trade my York or middle pitch planes for similar common pitch double iron planes but that's the trade-off that was made--a poor choice, I think.

    One issue you don't seem to be aware of is the transition point near the mouth of the abutments, cap iron and the horns of the wedge. I've looked at a lot of old double iron wooden planes and I've never seen a good solution to the problem of creating this transition that won't trap shavings and cause the plane to choke. That transition is easy in a single iron plane and can be made very close to the mouth which results in firm bedding of the iron. It'd probably take writing a major article to explain all the problems double iron planes cause at this transition point and I just don't have time for that right now.

  4. #4
    I have to agree with Larry. Leave it a single iron. With a wooden smoother, you won't be able to have a tight mouth and a cap iron or the throat will jam with shavings unless you eliminate the lower portion of the throat and make it slope toward the toe of the plane right from the mouth (a bad idea). I recently made a coffin smoother with a double iron I got from Garret Wade a few years ago just for the purpose (they no longer sell them). I had to open the mouth up to keep the throat from jamming with shavings right at the high point of the cap iron. The only other option would be to eliminate the slope of the lower throat which would lead to a quickly expanding mouth as the plane wears. If (when ) I to do it again, I would make a single iron from some 3/16-1/4" thick O1 and eliminate the cap iron. The throat would be able to be much tighter without jamming. I'll re-use the double iron in a fore plane where a tight throat doesn't matter as much.

  5. #5
    Join Date
    Mar 2007
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    Many people (I won't call myself and expert, but I include myself) think that chip breakers are mis-named and their importance in getting good results is grossly overstated. I've done some experimenting where I had the chip breaker very close to the edge and then on the same plane/iron backed it up so that the iron extended more then 1/8" beyond the chip breaker. I got identical results either way, except that when the chip breaker was too close to the edge and the mouth was really tight, the shavings got jammed... I can't seem to find the post, but I remember Chris Schwarz had pretty similar findings.

    There are many fine planes that do a wonderful job even on the most difficult grains that don't have chip breakers at all.

    Personally, I think chip breakers do very little except provide a way to control the depth and lateral movement of the iron in the Stanley style bench planes.
    "History is strewn with the wrecks of nations which have gained a little progressiveness at the cost of a great deal of hard manliness, and have thus prepared themselves for destruction as soon as the movements of the world gave a chance for it." -Walter Bagehot

  6. #6
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    Thanks to all for the advice. I'll just leave it a single iron. It's 1/4" thick so I don't need any more mass.

    The throat of this plane is interesting in that it slopes back towards the back of the plane, following the 45 degree bedding angle. I can flatten the sole for about 3/8" of thickness without changing the mouth opening.

    I'll try shimming the iron a bit to emulate a closed up mouth. If it works I may still inlay a hunk of rosewood.

  7. #7
    Rob,

    Are you hollow grinding that iron? HSS can be a bear to get sharp, especially if you're working that much bevel.

    Wiley

  8. #8
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    Quote Originally Posted by Wiley Horne View Post
    Rob,

    Are you hollow grinding that iron? HSS can be a bear to get sharp, especially if you're working that much bevel.

    Wiley
    Tougher than anything I've seen! One of our machine builders ground a new 25 degree primary bevel using a surface grinder. He commented on how tough it was and how long it took just to true up the grind about .020" total. This from a guy that works with A2 and D2 at RC60 all the time. I lapped that and the back mirror smooth then honed a 27 degree secondary bevel. I suspect the edge will be pretty durable.

  9. #9
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    After getting the input of Larry I think no other comments are needed.

    I have a couple of planes with older W. Butcher irons, these are laminated and thicker on the business end, probably around 1/4". I have similar experience as well. I keep the cap iron about 1/4" back from the cutting edge and don't seem to have any issues with the surface of wood or shavings. In fact I prefer keeping the cap iron back on wooden planes, as it allows the the shavings to travel straight out of the mouth instead of starting to curling too soon. On the wooden planes, owing to the front ramp there is limited room for shavings, if I keep the cap iron back it allows shavings to curl more gradually allowing them to clear the front ramp before they curl all the way back. Iron planes don't have a front ramp hence no such issues. I also think the cap iron increases the stiffness of the rather thin Stanley blades, for a 1/4" iron it adds nothing. Just look at how well the Japanese planes work.
    The means by which an end is reached must exemplify the value of the end itself.

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