Hand Tools Archive

Subject:
Not so ...

Derek Cohen (in Perth, Australia)
Dennis has requested a clarification of my comment about a ramped board offsetting the benefits of a cutter skewed to the direction of cut. Look at the photo of ramped board in the "eagle has landed" post. If the skew was designed to cut optimally at say 20 degrees, ramping the board either up or down marginally changes the angle that the wood "sees" the cutter. This obviously changes the designed cutter skew angle relative to the direction of the end grain. If the skew angle is truly a calculated value determined by the tool's designers, than the maker of the shooting board has unwittingly discarded the intentions of that design by slanting the board and the workpiece. Also remember that a shooting board fails if it does not have a fence that fully supports the trailing side of the workpiece against spelching. The more slant and skew present at the point of exit of the cutter, the greater the chance for unsupported wood on the trailing side blowing out. DAMHIKT.

One thing I do like about ramped boards in that they may tend to help keep the plane perpendicular to the workpiece during the cutting stroke. In fact, I would say that is their only real virtue.

The value of spreading the blade wear over a slightly greater length of the cutting edge is negligible on typical 3/4" to 1" stock, a few inches wide, so why even bother with the ramp in the first place?

Hi Michael

mmmm ... I don't buy any of what you write.

There was a thread recently on Saw Mill Creek in which the observation was made that the ramp and the skew angle of the #51-type shooter cancel each other out. Perhaps you are taking a lead from this. It is not an accurate reflection of what happens.

1. First of all, the ramp angle of the shooting board is about 5 degrees, and the angle of the skew on the plane is 20 degrees.

Secondly, the main advantage of the ramped board is to reduce the impact as the plane blade hits it. In a flat board with a square blade the impact would be square on. That produces maximum impact vibration. The ramping of the shooting board platform enables the blade to enter the wood progressively, that is, at an angle of 5 degrees, and this reduces the jarring from impact. A plane with a skewed blade, such as a #51-type, would enter the wood on a flat board at a progressive 20 degrees. On the ramped board this gets reduced to 15 degrees. For entry purposes this is insignificant. I would argue, nevertheless, that the main benefit from a ramped shooting board would be found for a shooting plane with a square blade.

The fact that there is a change of angle at impact does not mean that there is any change in the cutting performance of a skewed blade on a ramped shooting board. Once past the impact zone, the blade continues to cut as it always does. It is the shearing action of the skewed blade on the plane that is the strength of the #51-type shooter. The angle at which the work piece is held should not have any effect.

You may wish to read a comparison I made between three shooting planes (LN #51, LN #9 and LV LA Jack) on both flat and ramped shooting boards: http://www.inthewoodshop.com/Furniture/ShootingPlanesCompared.html

Scan down to "Cutting Angles and the Effect of Skew".

2. The second point of yours was made about spelching being affected by slant and skew. Again I disagree. Spelching has to do with the trailing edge being unsupported during a cut. I do not understand how a ramped board reduces the support of the fence. Perhaps Australian geometry is different, after all we do things upsidedown. :) Care to elaborate?

Further, while a fence may aid in supporting the workpiece, it is not necessary to prevent spelching. A simple chamfer at the rear of the board will have the same, perhaps better, effect. Indeed, I believe that one should always chamfer the trailing edge since the supporting edge of the shooting board will get nibbled away as one takes a deeper slice of the edge being shot. As soon as you return to a lesser projection of the blade, the trailing edge is unsupported by this difference. (This is one of the arguments for having a fence that adjusts to take up the gap, rather than a fixed fence that must be replaced).

Perhaps others will chime in as well - these were interesting points you raised. Thanks.

Regards from Perth

Derek

Messages In This Thread

The Veritas Shooting Plane - Reviewed
An OT question
Re: An OT question
Re: An OT question
Just furniture? :D
Re: An OT question *LINK*
Re: An OT question
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Re: The Veritas Shooting Plane - Reviewed
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Re: The Veritas Shooting Plane - Reviewed *PIC*
Re: The Veritas Shooting Plane - Reviewed
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Re: The Veritas Shooting Plane - Reviewed
Thanks for the review
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Re: Thanks for the review
Stanford deserves a compliment here
Re: Thanks for the review
The eagle just swooped down..... *PIC*
Re: The eagle just swooped down.....
Negates much of the benefit of the skewed blade?
Re: Negates much of the benefit of the skewed blad
Not so ...
Derek is right
Varieties of ramped boards
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Re: Another way to shoot veneer ..
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Thanks, Roger! *NM*
Re: Chiming in.....
Re: Chiming in.....
The way I see it
That's a pretty plane, Roger
Re: The Veritas Shooting Plane - Reviewed
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Give it up, Fellas...
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Methodology, I got a chuckle...
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Funny, my take-away...
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Re: On arrows
Shooting Star
Excellent review and discussion, Derek
A doddle?
Re: A doddle?
Re: A doddle = Bobz your uncle
Bravo, Derek! *NM*
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