Skew block query

[Anonymous]

But, not that it matters. Unless one is making a plane and

I am 8)

Thanks for the spreadsheet Shady, much appreciated :wink:

Basically the bed angle should be the difference of subtracting the front to back bedding angle from the skew angle.

In the case of the LN 140, subtracting the 12 deg bed (back to front) from the skew angle of 18 deg leaves 6 deg. angle right (leading) to left (trailing).

Not sure I see what you mean here Mike. What is this 'bed angle' of 6 degrees?

2. I think Garrett Hack suggests that, because your effort is now going into a longer area of blade (the skew increases the length of edge in contact, all other things being equal), the 'force per unit length' equation changes in your favour. Seems counter-intuitive (ie, more fibres to cut, should be harder), but there we go.

Counter-intuitive and wrong acording to the Newton's laws of physics. The force spread across a greater area results in less force being applied to each fibre (given the same force from the user's hand). Also, the applied force and inertia force (opposite reaction force), which are vector quantities (have both magnitude and direction), are split into two components due to the skew. This reduces the force per fibre to an even smaller value. The 'force per unit length' equation does not change in your favour, just the opposite in fact.

I think the advantage is the slicing action alone which effectively reduces the force require to cut through the wood fibres.
This is easily demonstrated in the kitchen, cut a carrot by pressing down on the knife, and then cut it again by slicing across it with the same knife - same contact area but lower force required the second time.

 

[Neil]

Practising on your carrots again, eh Tony? :wink: :lol:

Neil

 

[Alf]

Not sure I see what you mean here Mike. What is this 'bed angle' of 6 degrees?

The bed angles over from one side to the other slightly. It's not just a normal "flat" wedge that just happens to have a skewed end, it's a compound angle. At least I think so... But you folks are definitely going into territory where my feeble brain dare not tread, so I'll just read and try to understand one word in ten... :lol:

Cheers, Alf

P.S. No carrots were harmed in the making of this post.

 

[bugbear]

Now that's a nice shaving in yer' avatar, Alf!

BTW, one "obvious" (?) result of a skew when working cross grain is that any particular wood fibre (assuming "normal" grain) is removed gradually, from one end to the other, instead of suddenly.

So for cross grain work, skew is good (e.g. the hallowed and rare #289, #46)

Further, for end grain work, esp. shooting, a skewd blade reduces the shock at cut entry and exit, making the planing stroke smoother, and reducing spelching.

BugBear

 

[Chris Knight]

Some thoughts here

 

[Anonymous]

Practising on your carrots again, eh Tony? :wink: :lol:

Neil

Of course I thought everyone practiced their joints on carrots :?:

 

[Shady]

Alf - the bed has to have that slight angle across the axis of the plane (or cant, as I described it earlier) - otherwise it won't be a flat plane. This is due to the geometry of making 2 flat planes (sole of the plane and the bed of the blade) meet at a skew angle. If it were 'straight across' when viewed from behind, the side edge running to the shortest part of the skew would have to run at a steeper angle than the other side edge (going to the longer end of the skew)...Now that would make for an interesting blade!!

I've got a sketchup diagram showing this somewhere, if anyone's really interested.. More unnecessary trivia as a result of sad shady's inquisitive nature....

 

[Alf]

Folks,

Heard back from the man himself (small delay due to wrong buttons being pushed for sending the email which we'll gloss over, but it wasn't me... ) and:

...checked some other skew blocks on
the shelf (they were fine) and went over the prints with machinists. There
are several things that could be wrong with your tool. The most likely
problem is that blade is ground at the wrong angle (it should be 18
degrees), the 'frog' the small flat seen when looking underneath the blade) may be tapered instead of parallel, or the angle of the mouth may be wrong. It seems something is!
<snip>
I'd be happy to send you a new blade or send you a new tool <snip> Let me know which you prefer, and I'll get it out tomorrow.

So that's good. =D>

Cheers, Alf

 

[Midnight]

good result...

 

[MikeW]

I'm glad that things seem to be working out--nothing worse than a (new) tool that causes frustration.

 

[Alf]

Replacement plane arrived at lunchtime. Took it for a quick spin and it's a total doddle compared to the struggles I was having with the other one. Huzzah! Glad I decided to follow it up, and thanks to L-N for the speedy replacement. =D>

Cheers, Alf