Shooting boards - Ramped vs skew

[Steve Maskery]

Morning all

This is spin-off from Derek's thread over on Hand Tools.

First of all, sorry Derek, I didn't mean to hijack your thread! That's why I've started a new one. Nor did I mean to imply anything detracting about your SBs. I think they are beautiful, as is everything I've seen of yours. As I said before, I fully accept the notion that a ramped board spreads the wear on the blade and sole of the plane, but it's this issue of it producing a skewed cut that I have a problem with. I don't think it does and I hope that this explains why.

This is a normal shooting board shooting endgrain:

The blade is square on to the direction of travel and the angle of the blade will be 45 degrees.

If we ramp the workpiece 10 degrees it looks like this:

The blade is still 90 degrees to the direction of travel and the pitch of the blade is still 45 degrees - nothing is different about the cut. The position of the workpiece along the blade is slightly different, more of the blade will do some cutting, and at different times during the cut, but the cutting action itself is still 45 degrees EP, square on to the travel.

So we ramp a bit more, to 45 degrees:

Still the cutting action remains the same.

We can ramp as much as we like - 90 -

or even 110:

It's all essentially the same.

Now let us consider skewing the blade. This means the blade itself is not facing the direction of travel of the plane.

Skewed 10 degrees:

Skewed 45 degrees:

It should be clear now that the cutting angle is no longer 45 degrees, it is less than that (35.264 to be precise, and, I hope, accurate). This is why skewing produces a cleaner cut on end grain, it's because the cutting angle is effectively reduced.

To take it to extremes - skewed 90 degrees:

The EP is now zero, the plane is no longer cutting at all, I would just get a score line down the timber

and, ridiculously, 110:

in which case I'm actually dragging the plane backwards.

If anyone can tell me what is wrong with my logic, I'm quite prepared to be corrected, and I really hope I've not upset anyone with this, it is not my intention!

 

[Paul Chapman]

QED :wink:

Cheers :wink:

Paul

 

[newt]

Steve to me your logic is entirely sound. I think I read somewhere before (probably on another forum) that ramping only increases the area of the blade used. I like you drawings very realistic.

 

[Jake]

Yup, you convinced me in the other thread last night, with the 'blade that would score a line' point. Pictures illustrate it well!

 

[Racers]

Hi, Steve

You are right, I found it difficult to work out untill I imagined the wood to be circular like a dowel then everything made sense, ramped boards have the same effect as turning the stock round so you are plaining from a different angle straight across the stock.

Pete

 

[Pete W]

Steve, I'm not arguing with your point because I think you're right (and illustrated it beautifully ) but...

It seems to me that the ramped shooting board skews the blade in the sense that a skew chisel is skewed. In other words, at the point of impact of blade to wood, there's less steel in action, reducing the friction/resistance and therefore allowing an easier cut (and perhaps a slightly cleaner cut).

Or is that another conceptual illusion?

 

[Steve Maskery]

Or is that another conceptual illusion?

I'm afraid it is, Pete.

A skewed chisel is the same as a skewed plane, the effective angle is reduced because of the skew, the edge approaches the work at an angle, not square on.

On a ramped SB the edge is always square on, no matter how ramped the workpiece. It's not the same.

S

 

[Jake]

I almost hesitate to say it, but I think Pete is right - it isn't a reduced effective angle point - but the seperate 'ease of start of cut point' that with a ramped board, the cut starts with the tip of one corner, and progresses diagonally across until it's cutting the whole board - rather than just banging straight into a whole edge shaving.

 

[Steve Maskery]

Ah, OK, yes, but it lasts for just a mm or two, doesn't it?

It's a fair point, but doesn't affect the skew issue.And once you get to the top corner it's actually harder as the shaving is wider.

I've thought of another downside, too, although I've no idea if it is enough to make any practical difference. The more the workpiece is ramped, the greater the chance of breakout on the upper surface.

As I say, I don't know how much difference that would make in practice.

I'm not trying to say ramped SBs are no good nere. I've not got one so I can't speak from experience. But if they are better, it's not because they cut skew, because they don't. It's a myth that I've seen many times before and I just think it needs de-mything.

S

S

 

[Racers]

Hi,

Which Pete are we talking about?



Pete M

 

[dennis]

Steve

I went to the wrong thread first,I had convinced myself that there was a minimal amount of skew on a ramped board but having seen your brilliant explanation must agree with you.One way to create skew would be to use a parallel shooting board and make a wedged shape sled to sit the plane in.

Dennis

 

[Steve Maskery]

Dennis
You've got it!


S

 

[johnjin]

Hi Steve
Very well demonstrated and explained perfectly.
And Dennis is exactly right as well

All the best

John

 

[Philly]

I've had in-depth discussions with Bugbear on this - he says a big advantage of the skew is as the blade exits the work. More of the end grain fibres are supported as a smaller amount of blade is leaving the work.
Hope this makes sense,
Philly

 

[Tom K]

Hi Steve, very nice illustrations but surely most of them are irrelevant, provided the blade passes through the grain at any angle below 90 it surely must be skewed by definition :? Your logic seems to dictate that the angles of cut the blade produces will be different from one side to the other? Must get myself some shed time to test it in the flesh.

Regards Tom

PS Oh yeah I know "Doubting Thomas"

 

[dennis]

One example would be if you had a piece of wood in a vice and held the plane at an angle and with the right hand side of the blade flush with the right hand side of the wood and keeping this angle but finishing the cut with the left hand side of the blade ending flush with the left hand side of the wood,this would be the same as using a ramped board and the plane would be drifting accross the wood not skewing.But if you set off again holding the plane at the same angle with the centre of the blade in the centre of the wood and with your fingers underneath holding the plane in this position and finished the cut with the blade still in the centre of the wood and still angled,this would be skewing.

Dennis

 

[Tom K]

Hello Dennis, I understand the mechanics what I can't quite understand is this.
Within the capacitys of the shooting board and the plane blade, that is that your blade passes through the grain from end to end maintaining the same skew what is the difference in the cut produced?
I just want that light bulb moment :lol:

Regards Tom

 

[bugbear]

I almost hesitate to say it, but I think Pete is right - it isn't a reduced effective angle point - but the seperate 'ease of start of cut point' that with a ramped board, the cut starts with the tip of one corner, and progresses diagonally across until it's cutting the whole board - rather than just banging straight into a whole edge shaving.

Yes; that effect is genuine and very useful. And both rampedSB's and skew cuts provide it.

That fact that they have something in common doesn't make them identical.

Conversely, a ramped SB distributes wear over the blade width, which a skew cut doesn't.

They're similar - confusingly so - but not the same.

BugBear

 

[Steve Maskery]

provided the blade passes through the grain at any angle below 90 it surely must be skewed by definition :? Your logic seems to dictate that the angles of cut the blade produces will be different from one side to the other?

My point is that none of the ramped cuts are skewed at all, because the blade is always square on to the direction of travel and thus not skewed at all.

But by skewing the plane the actual pitch of the blade is altered, the more it is skewed the lower the effective pitch.

That fact that they have something in common doesn't make them identical.

I couldn't have put it better myself.

Thank you all for your contributions to this. As well as sorting it out in my own head beyond doubt, I've also learned something about ramped shooting boards.
Cheers
Steve

 

[Shultzy]

I think using a skewed blade is similar to the drawfiling technique in metalwork where the file is angled progressively to produce finer cuts.