Friday, January 28, 2011

Skewed Rabbet vs. Straight Rabbet

I often get questions regarding skewed irons vs. straight iron. My original set of hollows and rounds have a slight skew to them. The skew is slight and might be 5 degrees. When I started making my own planes I made them with straight irons and have not looked back. I do little across the grain and the few times I do I usually just deal with the deficiencies, which my experience tells me is primarily a mouth that clogs and secondarily a less than perfect surface. 

I am about to send out a skewed rabbet and thought you might like to see the difference. It's obvious.

Skewed Rabbet.
video
Notice that everything is coming out cleanly. The shavings are held together as they are ejected by the structure of the wood. The skewed iron is in contact with a single point of several fibers at any given instant during the cut. (Please forgive the awkward way I'm holding the plane, I wanted to let you see.)

Now on to the straight iron. (Note: I intended to show you a more productive example, but this was just too perfect. Look inside the mouth.)
video
The shaving has no strength to it since there is no shearing action. At any given time during the cut the iron's edge is in contact with a single fiber across the iron's width and fiber's length. Due to this, the shaving always falls apart and it often happens in the mouth. 

So the next question is 'Should I get a skewed rabbet instead of a straight rabbet?' It depends on how you work. Do you do a lot across the grain? I personally won't give up my straight rabbet. Again, I find it much easier to be aggressive with a straight iron and I have much more control...with the grain. 

Is your experience different?

8 comments:

  1. Nope. Same experience. All the straight rabbets I've tried were easier to fence by hand to sink the rabbet. They are hard to find in the wild though. I'm looking but they don't turn up nearly as often as skews, and usually not in good condition.

    Because my skews always want to pull right when trying to sink the rabbet with them, I will use my moving fillester to sink followed by my unfenced skews to clean up to the line, ala Nicholson's description. I'm still looking for a straight rabbet or two though.

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  2. Matt,

    As Bob said, antique rabbets with square irons seem to be very hard to find, and I have always wondered why. Is it because the square ones are used so much that they get used up? Or is it because, historically, craftsman used more skewed rabbets than straight? Would appreciate your thoughts and experiences.

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  3. Matt,

    I am not a tool historian and cannot speak to the history of these planes. I could guess, but that's all.

    I prefer the straight rabbets for the reasons I listed. I can be much more aggressive and accurate with one in my work.

    Matt

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  4. Hi Matt. Thanks for the education. I've really enjoyed your blog in the short time it's been around. And your planes are an inspiration. I have a question about rabbet planes. Lie-Nielsen's iron blank for a 3/4 rabbet plane is .937. Is the plane body still .750 wide? And is that blank symmetrical and centered in the plane so about 3/32" hangs out each side of the plane?
    Thanks again for a great blog and I'm looking forward to seeing the Bickford plow plane. :)

    Jamie Bacon

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  5. Jamie,
    The iron needs to be ground so that it is slightly wider than the plane body. If the body is .75 I shoot for .765. The wider iron gives you the option of fitting the iron to the body, which is much easier than fitting the body to the iron. Additionally, the wide iron allows you to make a skewed rabbet of .75.

    The iron is centered in the plane and in the mortise.

    Thanks for reading. The plow is a long way off, but it will happen.

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  6. Thanks Matt! That makes much more sense. So glad there's another maker of fine wooden planes out there now. This is a great time for tool consumers.

    Jamie Bacon

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