Adjustable mouth and plane sole flatness

[ali27]

Some planes have an adjustable mouth by loosening the front knob and moving the front part
forward or backwards. Does this not affect the flatness of the front edge. Or better said how does
that front edge remain coplanar with the rest of the sole?

Ali

 

[Peter Sefton]

I am no engineer but I do think this must be one of the trickier elements of plane making to get right.

Cheers Peter

 

[Vann]

Some planes have an adjustable mouth by loosening the front knob and moving the front part
forward or backwards. Does this not affect the flatness of the front edge. Or better said how does
that front edge remain coplanar with the rest of the sole?

Surely, if the machined surfaces of the sliding piece (and it's matching sufaces in the plane) are parallel to the machined sole, then that piece will be parallel with the sole. If the sole is then given a final (parallel) surface grind, that sliding piece will always coplanar and flush with the sole (unless you get grit/gunk in between the machined surfaces).

Or are you referring to the vertical face on the front of the sliding piece? That piece sticks out or in depending on the size of the mouth opening - or, in the case of more recent Veritas planes, is hidden behind a front lip (part of the sole casting). I can't see that front face is important - unless you often run your plane into some obstruction, at speed...

Cheers, Vann.

 

[ali27]

Some planes have an adjustable mouth by loosening the front knob and moving the front part
forward or backwards. Does this not affect the flatness of the front edge. Or better said how does
that front edge remain coplanar with the rest of the sole?

Surely, if the machined surfaces of the sliding piece (and it's matching sufaces in the plane) are parallel to the machined sole, then that piece will be parallel with the sole. If the sole is then given a final (parallel) surface grind, that sliding piece will always coplanar and flush with the sole (unless you get grit/gunk in between the machined surfaces).

Or are you referring to the vertical face on the front of the sliding piece? That piece sticks out or in depending on the size of the mouth opening - or, in the case of more recent Veritas planes, is hidden behind a front lip (part of the sole casting). I can't see that front face is important - unless you often run your plane into some obstruction, at speed...

Cheers, Vann.

Yes, the first part I is exactly what I am referring to. If all these things you mention are done well, then
the adjusting mechanism will not change the flatness of the sole. I wonder though whether that is
actually so easy to do.

It seems to me reasonable that to make it really accurate, one would need to change the size of the mouth
and then with a straight edge check if anything changes and how much and based on that slightly file away
any ''unparalellism'' (if that is a word).

Of course it can be done to very high precision(by guys like Karl Holtey), but how precise this is for
example in like LN and LV planes.

Ali

 

[Scouse]

I think that from a manufacturing point of view, it's probably easier than you think. Seventy or so years separate my LN jack and my no18 knuckle joint block and they are both flat and stable, but, as noted by Vann, the machined surfaces need to be kept clean.

 

[bugbear]

Surely, if the machined surfaces of the sliding piece (and it's matching suffaces in the plane) are parallel to the machined sole, then that piece will be parallel with the sole. If the sole is then given a final (parallel) surface grind, that sliding piece will always coplanar and flush with the sole (unless you get grit/gunk in between the machined surfaces).

Yes, but words like flat(planar), coplanar and parallel are easier to say than do!

Veritas' moving frog approach to adjustable mouths in their bench planes is a clever solution; moving toes, whilst good for planes with short toes (e.g. block planes) must eventually become impractical in larger planes.

BugBear

 

[Vann]

Surely, if the machined surfaces of the sliding piece (and it's matching suffaces in the plane) are parallel to the machined sole, then that piece will be parallel with the sole. If the sole is then given a final (parallel) surface grind, that sliding piece will always coplanar and flush with the sole (unless you get grit/gunk in between the machined surfaces).

Yes, but words like flat(planar), coplanar and parallel are easier to say than do!

I guess it all comes down to how flat is flat enough? - and therein lays a root of a massive discussion. But Stanley did it successfully for years, and Veritas do it successfully now. I think I've heard of a Rider with ill-fitting toe-piece, and I can imagine that Stanley have probably let QC slip on their non-Sweethart range of block planes

...moving toes, whilst good for planes with short toes (e.g. block planes) must eventually become impractical in larger planes.

The moving toe in the Veritas LAJ must be one of the largest around. Larger planes such as their BUJ only have a short moving portion, just in front of the mouth.

Cheers, Vann.

 

[Cheshirechappie]

Bear in mind that machine tools - including very large ones - have been constructed not just occasionally but as a matter of course to have slideways aligned to split-thou tolerances over distances of many feet, making a sliding mouth-piece for a block plane to stay in alignment is, in egineering terms, pretty trivial.

If anybody needs to tune a vintage plane or a new budget plane, strip out the mouthpiece and see that there are no burrs or surface roughness on the mating sliding surfaces, and that the threads and nut run free and true. Then reassemble, and correct the sole for flatness if it needs it. That will ensure that the sole stays flat and the mouth-piece moves freely when it needs to. If the plane is a real cheapy, it may be wise to check the blade bed for flatness, burrs and surface roughness, then install the blade and check the mouthpiece rear edge against the blade for even mouth opening all across, and correct if needs be with a fine file.