Est. 1998 — 27 years of woodworking knowledge
Skewing the iron
Robin Frierson
>Does skewing the cut of a plane reduce the actual cutting angle of an iron. So if you are using a high cutting angle, say 60deg for tearout prone wood, and you skew the iron do you lose the benefit of the higher angle.
I was reading the instuctions that came with my LV 62 1/2 and it says in reference to skewing the iron"..This has exactly the same effect as lowering the bevel angle, because it lowers the cutting angle."
Reduced Cutting Angle
Steve Elliott
>Yes, it does lower the effective cutting angle somewhat, but it still reduces tearout due to other factors. If you have Leonard Lee's book on sharpening, take a look at pages 9-10 and 13.
My most-used plane is an Ulmia smoother bedded at 49�, and I find it helps a lot to skew the plane if tearout is a problem.
Re: Reduced Cutting Angle
Lyn J. Mangiameli
>Though skewing is often effective, for all the reasons referred to, it is not without a drawback. By skewing the plane the mouth is no longer orthogonal to the direction of travel. What this does is effectively greatly increase the size of the mouth (i.e. unsupported area directly before a given point on the blade edge). In contrast, a skewed blade in a plane traveling straight forward has the skew advantages while retaining its set mouth size.
Re: Skewing the iron *LINK*
L. Hanson - N. Idaho
>There's a nice little treatise by John Whelan from one of his books on the effect of skewing the iron at the link below...
L. Hanson
www.norsewoodsmith.com
John Whelan on skewing
Geometry...my head hurts
jim_reed@marietta
>How does rotating the blade lower the angle??? It has been a few years since my last geometry class, but my head is hurting from all these calculations.
Get the Exedrin
Steve Elliott
>If you follow the link in L. Hanson's reply, there is a good explanation of why the effective cutting angle is reduced. To really make your head hurt, it explains that "the sine of the effective pitch is the product of the sine of the actual pitch and the cosine of the skew angle."
Also...
Scott Burr in Ben Lomond CA
>Your are also narowing the blade width also, so it takes more work (passes) with a plane held at a skwewd angle.
If you can get hold of...
Scott Burr in Ben Lomond CA
>Jim Kingshott's "Handplane video". He explanes is as simple as pie. My interpretation: Instead if riding a bike straight up a hill, you ride side to side up the hill (think switchback turns here) It makes planing easier (climbing the hill) easier.
Re: Mouth Width With Skew
Todd Stock
>30 degree skew angle results in a 15% increase in effective mouth width, while a 45 degree skew would open the mouth by 41%. For a tight mouth (.005 to .010), width would increase on the order of .00075 - .0015 with a 30 degree skew angle and .002-.004 with a 45 degree skew angle. All in inches, of course.
Is this significant, Lyn? Also - any idea what effect the cross-grain levering action has on tearout in non-rowed stuff?
Re: Geometry...my head hurts
Todd Stock
>Set your plane cross-grain (90 degree skew angle). This is a zero degree effective bedding angle - the chip or shaving is not lifted at all as it is cut.
If you skew the plane a few degrees closer to normal, you can see that the shaving now has to change direction a 1/16" or so upward to follow the blade.
Clear as mud, right?
Re: Mouth Width With Skew
Lyn J. Mangiameli
>Thanks for the math, that will be useful in other situations as well. The answer to your question is that it depends. Really.
The lower the effective cutting angle, the more mouth size becomes an issue with a blade perpendicularly oriented to the direction of travel. Does this carry over to a skewed plane? Well, not exactly. The blade is no longer severering adjacent wood fibers at eactly the same time, so there is some (though modest) side support to the point at which an individual fiber is cut. This will actually reduce the need for a tight mouth. On the other side, a skewed blade often is not traveling orthogonal to the grain, and in these situations, mouth size becomes even more important. So the need for a tight mouth is very wood dependent and whether the direction of the grain is exactly parallel to the direction of travel (which it usually won't be).
In the real world, most woods will respond adequate to skewing of the plane (because they are relatively insensitive to effective cutting angle), and endgrain inclusions will usually respond very well. But other woods will respond very poorly to a skewed plane, particuarly woods with pronounced grain and relatively weak connection between parallel fibers, ash is often like this; or woods with wavy and/or reversing grain. Often the woods one may most be prone to consider using a skewed plane for are the very woods that will least respond to it. Such woods do require a small mouth and a higher, rather than lower effective cutting angle.
Skewing more often results an easier cutting action, rather than a better cutting action.
OK, so why skew?
Robin Frierson
>Jeez, my head hurts too from all this math. So bottom line, why do we skew? We all know it makes the plane easier to push, but seems you are giving up the benefit of the higher effective cutting angle of a high angle smoother. And like Lyn points out, making the mouth wider.
Do when do most of you employ a skew cut? I find myself skewing the plane slightly most of the time, except with a jointer. With a high angle smoother seems it would be better not to skew at all, to keep the effective cutting angle high to prevent tearout? And conversely, if you want a lower angle for end grain you should skew end grain cuts?
And If I understand this correctly?, a plane that is skewed does lower the effective cutting angle, but a plane with a skewed iron does not?
Sorry, my head still hurts
jim_reed@marietta
>So skewing the blade does not lower the angle, just the EFFECTIVE angle. I never learned about that in geometry class. I am sorry, but woodworkers should use ENGLISH. This is about as bad as PREDRILLED holes.
Re: OK, so why skew?
Bob Hackett
>The most simple explanation I`ve heard is to think of chopping versus slicing.In a straight ahead planing motion you chop through the wood fibers,skew the plane and you slice.Hope this helps.
Mainely,Bob
Re: Sorry, my head still hurts
Todd Stock
>Let's go for a bike ride...imagine you are facing a hill that rises 50 feet for a run of 50 feet.
You can choose to:
- Ride straight up (50 ft rise/50 ft run = 45 degrees...tough!)
- Ride at an angle to the hill (covers more distance, but same rise, so the angle of the slope that YOU see is less...a 150 ft run with 50 ft rise reduces the angle of the hill to around 19 degrees.
So straight up the hill is like using a zero degree skew angle, while angling across the hill is like skewing the plane.
Take some Advil and get a good night's sleep.
Re: OK, so why skew?
Tim of San Leandro
>Robin,
I often run into chatter problems with high angle beds at the beginning of a board so I'll enter the cut skewed and then once started, straighten the plane out for the remainder of the stroke.
Tim
Re: OK, so why skew?
Moses Yoder in White Pigeon, MI
>I don't have a high angle plane, but may eventually. The angle is still higher when skewed than it is with a regular 45 degree plane that is skewed. If you think of cutting pipes, which is woodgrain, hitting the edge of the pipe at an angle will slice more cleaning than pushing into it straight on, as mentioned above. The higher angle of the high angle frog will force the wood upward sooner (at a higher angle) , causing it to break in shorter lengths, thus causing less tearout than a 45 degree frog. I think I can manage theory better than practice ;)