Thread: Having trouble understanding low-angle vs high angle planes

Originally Posted by wsal

Title says it all!
I know this topic has been discussed quite a bit but there's one thing that I just don't understand: manufacturers make 'low angle' planes with bevel up blades yet, when the bevel angle + blade angle are combined it comes to be equal to or even higher angle than your everyday stanley bevel down plane? I would have thought the point of a low angle plane is having a low angle? Or is it all just about the whole 'blade moving in the direction of the plane avoiding chatter' issue?
I apologize that this question probably sounds massively ignorant but I've still never been able to figure out the answer! Please correct me if I've got my facts mixed up.
Cheers
Will

Gidday Will,

There are all sorts of considerations that apply to the bedding angle of a plane, and whether it is made bevel up or bevel down, and I'm in no way claiming any expertise in the field, but the simple answer to your question is that generally a plane described as a 'low angle' plane will have a cutting angle that is lower than a standard angle bench plane.

Generally a 'standard' bench plane will be used bevel down and they normally have a cutting angle of 45 degrees, and a 'low angle' plane will be used bevel up and have a cutting angle of 32 degrees (individual planes will vary).

As you've noticed, just because a plane is designed to be used with the blade bevel up, doesn't mean that plane will necessarily have a lower cutting angle than a standard bench plane. So in other words, 'bevel up' doesn't necessarily equate to 'low angle'.
As you've noted, a bevel up plane may actually have a steeper angle than a standard bench plane, and it can be made steeper just by altering the pitch of the bevel on the blade. This versatility means that bevel up bench planes can have different blades used for different purposes (eg really steep angle for difficult grain).

Have a look for some of Derek Cohen's posts about the Veritas Bevel Up Smoother for further discussion. Eg here https://www.woodworkforums.com/showth...bevel+smoother

to be quite honest Will..... which way its bedded doesn't really amount to much importance.

Different pitches works, but its not overally practical changing blade angles all the time. A high angle setup for difficult grain is rarely done anyway because the higher the angle the harder it is to push etc.

Mostly it gets all very anal in terms of actually making things. Success is still governed mostly by practise with a trully sharp blade on a tuned plane, with the same pitch setup......... most commonly found planes can be made to work well like this

When a plane is "Bevel Down" (BD), the bed is standard at 45 degrees. The cutting angle of the plane is the same as the bed - 45 degrees. It does not matter what the bevel angle of the blade is, the cutting angle remains the same.

Rule: Cutting angle = Bed angle

When the plane is "Bevel Up" (BU), the bedi is usually 12 degrees. The cutting angle is now the total of the bed (12 degrees) plus the bevel angle of the blade (say 33 degrees) to get to the same cutting angle of 45 degrees.

Rule: Cutting anle = Bed angle plus bevel angle

With a BD plane, the cutting angle is pretty much a fixed affair (I'm keeping it simple for now) since the bed is not adjustable.

(OK, to complicate matters a little, a BD plane can also use a back bevel, which can increase the cutting angle, but this is more complicated as now you have to hone two bevels).

With the BU plane, the cutting angle is easy to vary since all you need to do is alter the bevel angle on the blade.

The range of BD cutting angles is limited to a minimum of 45 degrees (even when increasing the cutting angle with a back bevel, you still are limited to a minimum of 45 degrees).

The range of a BU plane runs from a low 37 degrees (12 degree bed plus 25 degree bevel) to as high as you like (for hard and interlinked Aussie timber a 60 degree cutting angle is generally recommended).

Where a BU plane scores is that you can swap out a couple of blades quite easily as they are less complex (no cap iron to set), and you can use it with a low cutting angle on end grain (eg. block plane or shooting board), and then for smoothing interlinked and difficult grain with a high cutting angle. Very versatile. The BD plane generally can do only one thing well. It is far less versatile, but that does not mean that it is less capable, just less flexible. By-and-large, however, most BD planes have bed angles that are too low for Australian hardwoods.

I use both types, with BU planes for the upper and lower extremes, and BD planes for the middle range of cutting angles.

Commenting on a point of Jake's, a high cutting angle (I might use about 65 degrees at times) is not hard to push on a smoother since one is taking very fine shavings. I find BD planes with veruy high cutting angles do, however, feel different and more difficult.

Especially with interlinked timber, it is impossible to ignore the benefits of a high cutting angle (unless you are willing to put up with tear out.... or sanding). Whether BU or BD makes no difference. You just want a high cutting angle. Then BU planes are easier to set up.

Similarly, when cutting end grain, you camn use anything really. But a low angle makes it easier and leaves a smoother finish. Again, it is easier to achieve on a BU plane.

Still, there are a few pros and cons, which I shall not touch on here.

Regards from Perth

Derek

Wsal,

What they said generally works but don't be afraid to experiment because occasionally you will be planing a tricky piece that doesn't appear to obey the rules.

You can generally get good shavings by trying BD's (use a higher angled frog too), BU's (with the different bevels) and plane at different angles to the grain.

Vary the Cap Iron on BD's and the mouth on both BU's and BD's.

When you draw yourself a diagram it becomes obvious.