skew angle on rebate (rabbet) planes

[Howard Pollack]

I'm thinking of making a pair of skew rebate planes for the woodie build-off. Looking around on the web I find the skew angles vastly different on these planes. For example Terry Gordon's is skewed at 4*, while the Veritas skew-block is 15* and the Veritas Skew Rabbet is skewed at 30*. Quite a difference. I'm wondering, in terms of usage, what difference these angles make. Thanks.
-Howard

[Chuck Nickerson]

Mathematically, the greater the skew angle the lower the effective cutting angle.

However, I suspect that greater skew angles are tougher to build in a wooden plane.
This is ONLY a suspicion on my part. It does seem to be born out by the data points you mention.

[Jim Neeley]

The difference between them? I don't know; I have the 18* Lie Nielsen skew block (w/ fence and nicker).

In addition to the skew angle lowering the effective cutting angle, when cutting rabbets it also tens to pull the plane into the corner of the rabbet, making it easier to keep the rabbet corner square.

[James Taglienti]

Mathematically, the greater the skew angle the lower the effective cutting angle.

However, I suspect that greater skew angles are tougher to build in a wooden plane.
This is ONLY a suspicion on my part. It does seem to be born out by the data points you mention.
I never understood how that worked can you explain it? I just dont get how toe cutting angle is less

[Chris Griggs]

It's like walking up a hill at an angle instead of straight up the hill. Much less steep right? There is less rise (vertical distance) to your run (movement forward). The greater you direct your movement across the slope of the hill, the less distance you progress up the hill with each step forward you take - (e.g. the angle at which you are traveling upward is less steep). Similarly, the wood isn't hitting the blade bevel dead on, rather its going partially across the bevel as it engages so the rise to run is less steep. I bet Dave W can explain it better - hes a mathematician. I'm just a former middle school math teacher.

[Jessica Pierce-LaRose]

It just kind of is. Take a block and cut it off at a rough angle. Measure a plane blade with a protractor against your bench top, then skew the plane and measure it again. Or use a block cut off at an angle.

The way it had always been explained to me was to think about walking up a hill. If you go straight up, it's steeper than if you climb up at an angle to the slope. . .

EDIT: That's what I get for not hitting refresh before reply - Chris beat me to it!

[David Weaver]

I bet Dave W can explain it better - hes a mathematician.

That's stretching it!

The only easy way I can explain it is to take an iron and draw a line straight back while it's 90 degrees to a cut (draw the line up the bevel, but not onto the iron).

Then turn the iron 45 degrees and draw a line straight back in the direction the cut would be if you were cutting with the iron skewed 45 degrees.

The second line will be longer, but will reach no higher in height. The only way for that to be the case is for the effective angle to be lower.

The extreme case, that may make it easier for someone to understand if they still don't see it after that is to turn the iron just shy of 90 degrees. It takes nearly the width of the iron to rise to a height that is less than the iron's thickness. That's really shallow.

[Chris Vandiver]

The moral to this story is to not walk straight up the hill, if you can avoid it.:)

[Jim Matthews]

There's a reason to use rabbets perpendicular to the plane body - the rabbet will cut a constant side wall, rather than attempt to make a series of "steps".

Also, without a fence, a skewed rabbet will attempt to pull itself into the work with each pass.

[Larry Williams]

I'm thinking of making a pair of skew rebate planes for the woodie build-off. Looking around on the web I find the skew angles vastly different on these planes. For example Terry Gordon's is skewed at 4*, while the Veritas skew-block is 15* and the Veritas Skew Rabbet is skewed at 30*. Quite a difference. I'm wondering, in terms of usage, what difference these angles make. Thanks.
-Howard

Like Chuck said, skew angle impacts the cutting geometry. It also effects how much the plane will tend to drift in the cut, which can be a problem if you're trying to start the rabbet free-hand without a batten. If you're making wooden planes one big issue you need to consider is what angle you have your floats skewed at. You're dealing with a compound angle and the skew of the float will result in a different skew angle for the different bed angles. I'm really never working with or considering the actual skew angle of the plane, I'm trying to stay true to the skew angle of the floats. Keeping the mortise with the proper size parallelogram shape is something I find pretty challenging. I have 1/8" and 3/16" thick pairs of left and right hand floats made with several different angles but can't tell you what exact skew angle plane they'll make at the different bed angles. I'd sit and do the math but it's not something I use. Maybe I can remember to measure the skew angle of some of the planes we have and try to remember which floats were used to make them.

On edit. The breast and bed or bed and wear on skewed planes are actually cut at different angles because they're at different angles to the sole. I cut the bed to the float skew angle and work my way into fitting the wedge at its front edge. I don't have floats made to all the angles for the front of the mortise. If I did, at some point I'd be working with the wrong float for what I'm working on.

[Joe Fabbri]

Larry, I'm curious, I read in Whelan's book, which my brother got me as a gift, that you can use triangular saw type files as floats. Anneal them, and grind/sand it smooth, and cut teeth into it. Have you tried this, or do you find it doesn't provide enough clearance still? It seems like it might work okay, though.

On another note (but which also might be of interest to Howard), what's your preferred method of cutting the conical escapement, Larry? Do you use a multiple blade pipe reamer, or do you step drill it and use a rasp/gouge?

Joe

[Bob Strawn]

The more skew, the smoother the cut and the smaller the area cut. Think of it as leverage. A larger skew means more blade passes but less wood is cut.

When working rough wood with a straight plane, I tend to angle it much more that when I am working easy wood. The angle that works best for you on the worst wood you cut might be a good angle for the skew. It is nice to have at least enough cutting width remaining after the skew, to cut the entire face of the rebate you normally make.

So, while you can copy another planes skew, you can also make a skew that suits your style of woodworking.


I am thinking about making a pair of skew planes that don't reach into the corner. That way I can use them on a shooting board. I am not sure how the lift movement that a skew can make will work out on a shooting board, but I could always take down the side and turn them into skews for rebates if the idea does not work out.


Bob

[Jessica Pierce-LaRose]

Why not skew them so that the skew pulls the plane down onto the bed of the shooting board, rather than up?

[Bob Strawn]

That seems to be the best method, but that might also tend to lift the wood being planed. I will not know for sure until I do it. With a right and left plane, I can try both, and if it fails, I end up with two of the largest skew rabbets anyone has seen!

Bob

[Jim Koepke]

For shooting use I think the traditional method has been for the skew to be so the top of the blade hits the work piece first.

This will have the effect of pushing down on the work and thus holding it more securely.

Of course if you have a left and a right hand skew you can make a double sided shooting board that is handy for shooting miters.

jtk

[Jim Neeley]

Howard,

Matt Bickford discusses skew angles on rabbet planes here: http://musingsfrombigpink.blogspot.com/2011/01/skewed-rabbet-vs-straight-rabbet.html

In this section he infers that the angles are superior for cut quality when cutting across the grain but he prefers straight because of how it performs when going with the grain. Interesting read.

Jim

[Larry Williams]

Larry, I'm curious, I read in Whelan's book, which my brother got me as a gift, that you can use triangular saw type files as floats. Anneal them, and grind/sand it smooth, and cut teeth into it. Have you tried this, or do you find it doesn't provide enough clearance still? It seems like it might work okay, though.

On another note (but which also might be of interest to Howard), what's your preferred method of cutting the conical escapement, Larry? Do you use a multiple blade pipe reamer, or do you step drill it and use a rasp/gouge?

Joe

Joe,
I don't think the float with 60º sides is a good idea. I tried making side floats with only a 15º angle on the float edges and found the bidirectional cutting a problem. With the fine points on the sides make for an incredibly aggressive float. By the time you realize you've over-cut, you've gone way too far. I kept trying and made them in three different sizes and even tried it on the small cheek floats. I ruined planes with all of them. I don't mess with that any more, it was an expensive flop.

I do the initial shape of the conical escapement with eccentric single edge reamers I made at different angles. Different body widths require different angles. When cutting circles in wood you'll have two areas where you're cutting against the grain. I tried different geometries on the cutter and the one that causes the least tear out is close to a scraping type cut. It's slow cutting and the reamers get hot in use so I don't rough many without letting the reamer cool. I clean up the surfaces with 00 cut half round files. Even as slow as the reamer cuts, it's the fastest method I've found. The reamers were made from 1 1/2" O-1 drill rod. I can't really say how eccentric they are because the eccentricity was hand ground by eye, going slowly until I had reamers that worked well.

[Jim Matthews]

From the "Musings from Big Pink" responses;

*Bob Rozaieski (http://www.logancabinetshoppe.com/blog.html)Jan 28, 2011 05:43 AM (http://musingsfrombigpink.blogspot.com/2011/01/skewed-rabbet-vs-straight-rabbet.html?showComment=1296222202237#c47741167646 39844791)

*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.

I take the advice of both Bob and Matt seriously. We should all defer to Mr. Williams, the dean of side escapement hand planes, today.
I love the way Big Dogs visit this forum.

I found, in practice, that I was wandering around with a straight rabbet trying to stay on line. Either a heavy score line or Snipe's bill were necessary to get started.

A straight rabbet wants to cut straight. A skewed rabbet will be drawn in the direction pointed by the leading edge.
I'm looking for a moving fillister with a skewed blade to act as a rabbet plane. I just don't have enough shop time
to learn how to properly handle the unfenced versions.

[Bob Strawn]

For shooting use I think the traditional method has been for the skew to be so the top of the blade hits the work piece first.

This will have the effect of pushing down on the work and thus holding it more securely.

Of course if you have a left and a right hand skew you can make a double sided shooting board that is handy for shooting miters.

jtk

This would make sense to me, especially because angled shooting boards tend to have the slight skew effect produce a downward force on the board being planed.

Bob

[Andrew Pitonyak]

I never understood how that worked can you explain it? I just dont get how toe cutting angle is less

Two equations are frequently found in print and Mr. Hock was wondering which was correct and which was wrong, so, I created a paper that at least shows the math (complete with pictures, drawing, and arrows) that demonstrates this if you are interested.

I did silly things like take a piece of 2x4 to act as the plane and then sent it through a table saw to show the angles and such. Not sure what I was thinking.... Must have had too much time on my hands. I even enlisted a super smart Physicist who pretty much never gets this stuff wrong to check my math and he came up with an even more elegant solution.

[Joe Fabbri]

Thanks for the information, Larry. Sorry for the delayed response, but I've been away from the forum for a few days.

I guess it's almost always the case that ideas that seem too simple probably won't work, haha. I didn't really think of the sharpness of the sides of a float being a problem. I wonder, though, if using the blunt chisel technique (I forget who came up with that) would work. Have you ever tried taking a triangular file, and grinding the front 90 degrees and scrape down the skew mortise? It would take a little while, but I'd think it might be a pretty safe way of reaching the angle desired.

Joe

[Bill Houghton]

The moral to this story is to not walk straight up the hill, if you can avoid it.:)

Especially not barefoot in a snowstorm while carrying your brother on your back. And, if you must, just don't do it both ways.