Ramped shooting boards - do they really work better?

[MusicMan]

Tom, they don't match. You have to include the direction of the plane relative to the angle of the blade, and then they do not match.

Keith

 

[Tom K]

Tom, they don't match. You have to include the direction of the plane relative to the angle of the blade, and then they do not match.

Keith

The blade intersects the grain at the same angle its the same cut. the direction of push when doing a true skew cut
enable the blade to maintain position it doesn't create the cutting action it enable it as does the ramp angle.
The ramped board will be very limited in the material it can process thats why the aren't more popular.

 

[ED65]

You were right first time Tom, there was never a skew cut.

If you do a drawing of a plane cutting a board skew and then one of the board ramped using the same angles then overlay them they match (you do of course need to rotate them) so the blade intersects the grain at the same angle.

They actually don't match once you factor in that the angle relative to the board changes. That's where I went wrong with the diagram that I posted and then deleted, I neglected to rotate the arrow showing the direction of travel. A ramped shooting board gives you a diagonal cut only, just as in the rightmost image in MusicMan's post on the previous page.

Look at it again with your head tilted to the left, if that still doesn't convince you the posts from Wilbur Pan in this thread on the WoodTalk forum might.

The only way to get a skew action going is to rotate the cutting edge relative to its direction of travel, not relative to the angle of the board.

 

[MusicMan]

Tom, I don't understand your 'explanation' at all, sorry. But the essence of a skew or slicing cut is that the blade has a component of velocity along its edge as well as perpendicular to its edge, hence it slices the grain. This happens with a skew iron pushed straight along the board, or with a straight iron held at a skew angle and pushed along the board. It does not happen with a straight iron pushed at a diagonal angle but in the direction the plane is facing, which is what happens on a ramped shooting board. That is just a straight cut at a diagonal direction.

It is nothing to do with the intersection of the blade with the grain, but the slicing component of the blade's motion.

I can't explain it any better than that. ED65's explanation may also help.

Keith

 

[condeesteso]

Just a thought - for any slicing at all the cutting edge must be at an angle other than 90 degrees to its direction of travel.

 

[Tom K]

Unfortunately I don't understand what you dont get ? Cutting edge intersects grain at less than 90 degrees nothing else happens in either example. A little like Woody Allen cloning the nose.

 

[condeesteso]

Unfortunately I don't understand what you dont get ? Cutting edge intersects grain at less than 90 degrees nothing else happens in either example. A little like Woody Allen cloning the nose.

Sorry to hover over this: I think I do understand so what am I missing. I'm saying forget the stock, orientation (flat, ramped etc irellevant) - there is only skew when direction is NOT at 90 degrees to the edge.
A further check - when I plane a top at an angle, that is not a skew cut - rotating the plane off it's long axis is the only source of skew.

????

 

[Tom K]

Unfortunately I don't understand what you dont get ? Cutting edge intersects grain at less than 90 degrees nothing else happens in either example. A little like Woody Allen cloning the nose.

Sorry to hover over this: I think I do understand so what am I missing. I'm saying forget the stock, orientation (flat, ramped etc irellevant) - there is only skew when direction is NOT at 90 degrees to the edge.
A further check - when I plane a top at an angle, that is not a skew cut - rotating the plane off it's long axis is the only source of skew.

????

Hi C, first lets clarify the statement for me it all starts with " a ramped shooting board works by simulating a skew cut" the important word is simulate it can never be a true skew because the planing direction is wrong. Will come back to this post after work to carry on with my thoughts

 

[bugbear]

If we're to continue analysing wether a ramped board does, or doesn't provide a skew cut,
perhaps the participants would all care to define a skew cut.

Otherwise I don't see how a conclusion can ever be reached, regardless of thread length.

BugBear

 

[Steve Maskery]

Good idea.

A skew cut is when the blade is presented to the work at a different angle to that at which it is being pushed.

S

 

[bugbear]

Good idea.

A skew cut is when the blade is presented to the work at a different angle to that at which it is being pushed.

S

"blade" or "edge of blade" ?

BugBear

 

[Tom K]

http://www.thefreedictionary.com/skew

 

[MusicMan]

Edge. I put it equivalently a few posts back: a skew cut occurs when the blade edge has a component of velocity parallel to itself as well as perpendicular. It is this parallel motion (slicing) that changes the nature of the cut.

The topic has been thoroughly investigated by Prof Atkins of Reading University, who found that the effort required to cut a fibrous material decreases the higher the ratio of parallel to perpendicular motion. So when you slice a turkey, it's best to move the knife quite rapidly back and forth, not just push down. A similar.effect occurs in wood (especially cross-grain cutting) which is why we bother about skew cutting.

Keith

 

[ED65]

If we're to continue analysing wether a ramped board does, or doesn't provide a skew cut,
perhaps the participants would all care to define a skew cut.

Already done a few times, My contribution from the previous page:

rotate the cutting edge relative to its direction of travel, not relative to the angle of the board.

http://www.thefreedictionary.com/skew

Tom, that's a general definition of the word. For this we need a woodwork-specific definition.

I'm like a reformed smoker now, wanting to spread the good word Just having the plane at an angle does not equal skewed planing because it doesn't take into account the direction the plane is then pushed.

Can I just ask, you have used skew planing on occasion yes? Just close your eyes and think about the motion. You angle the plane to one side then push it straight along the board, not along the axis of the plane itself. So the side of the plane faces the direction of travel. Only this is skewed planing.

Any time the plane is pushed straight along its length there is no skew involved and that is why a ramped shooting board doesn't have any skew action. It is merely a slightly diagonal cut.

 

[Tom K]

No you are confusing skew cut with skew planing. The first is an outcome the second is a means to that end.

 

[condeesteso]

If we're to continue analysing wether a ramped board does, or doesn't provide a skew cut,
perhaps the participants would all care to define a skew cut.

Otherwise I don't see how a conclusion can ever be reached, regardless of thread length.

BugBear

My final: a skew cut occurs ONLY if the angle between cutting edge and direction of travel is NOT 90 degrees.

 

[Jacob]

My final - the tiny slope of the so-called "ramp" would not make the slightest difference to the cut. If it was steep enough to make a difference it'd most likely spelch out on the bottom edge and you wouldn't want to use it anyway.
The whole idea is slightly bonkers, but that's normal for arm-chair woodwork theorists!
Happy christmas all!

 

[Derek Cohen (Perth Oz)]

A proper skew cut has a shearing action.

A a plane with a straight blade on a ramped board does not cut with a shearing action.

A straight blade on a plane on a ramped board enters the work piece at the angle of the ramp (only a plane with a skew blade does cut with a shearing action). The means that the straight blade enters the wood progressively. This is the major benefit of a ramped board (it is significant). A secondary benefit is spreading the war on the blade (valuable, but less important).

Regards from Perth

Derek

 

[MusicMan]

Jacob, by your own admission you haven't used a shooting board for 15+ years, didn't like it then and have never tried a ramped board. So who is the armchair theorist? ;-)

I agree that a 5 degree skew would only have a small shear component, about 8%, and be unlikely to make much difference anyway, though I have not tried it. And the ramp does not skew cut anyway. But a 5 degree progressive entry could, and Derek has actually got out of his armchair and tried it and reports that it does make a significant difference.

 

[monkeybiter]

MusicMan.........ever wish you hadn't started? (hammer) :wink: