Granite surface plate/flattening/where to buy?

[Ttrees]

One of the best ways to get an idea of flatness without needing a guaranteed plate, or straight edge and feelers,
provided some sort of surfaces are available, i.e checking against cast iron tables or whathaveyou.
The method does what it says on the tin, and is a basis for flattening something, whether it be precision or rough like belting a rusty metal plate with a big hammer.

 

[Jacob]

@Jacob
I'd be quite surprised the book you sold didn't mention this?
https://www.ukworkshop.co.uk/threads/david-charlesworth-furniture-making-techniques.136495/

There you go - as i said, one of the new books!

 

[Jacob]

One of the best ways to get an idea of flatness without needing a guaranteed plate, or straight edge and feelers,
provided some sort of surfaces are available, i.e checking against cast iron tables or whathaveyou.
The method does what it says on the tin, and is a basis for flattening something, whether it be precision or rough like belting a rusty metal plate with a big hammer.

Nobody needs "a guaranteed plate".
Straight edges occasionally useful but not essential. Edge of a combi square is useful for checking for flatness.
Feeler gauges no use to woodworkers.
Straightness is assessed by "looking" at the thing. Twist with winding sticks.

 

[Ttrees]

Agreed Jacob, nobody needs such a plate, if they have the ability to make something quite flat for themselves.
I have feelers, but only bought them to make my own surface plate.
It's quite evident with pivoting/hinging, tapping, and using ones eyes with good lighting, to get close, and such methods can be utilized the whole way through to unmeasurable standards for the non machinist, who doesn't have such equipment.

For planes and things, one could argue that the lapping on abrasive is more foolproof than using a deburring wheel alone, or other method of "targeted removal" (where-ever @D_W is?)
as a high spot is obviously going to have more contact,
and the material from the centre can be removed more evenly, leaving it a simple matter of
erasing however much material one leaves on the edges
i.e how much one feathers the ink off the edge, or infact occasionally runs off the abrasive
if using a smaller area of contacted surface than the item (plane) is.

(the edges being the reference as anything the opposite is pretty much unmeasurable)
i.e if one feels the need to do the test like Cosman shows beforehand,
because after say 10 few swipes on a large abrasive would throw whatever feelers
(one thou shim stock in Cosman's case) one would be getting beyond an "Prussian blue" test if one has a permanent marker around.

One can see most of the edge disappear with one or two short strokes of the larger area,
as abrasion will favour the edges and eliminate the witness marks one has been careful to keep an eye on.

 

[Jacob]

Agreed Jacob, nobody needs such a plate, if they have the ability to make something quite flat for themselves.
I have feelers, but only bought them to make my own surface plate.
It's quite evident with pivoting/hinging, tapping, and using ones eyes with good lighting, to get close, and such methods can be utilized the whole way through to unmeasurable standards for the non machinist, who doesn't have such equipment.

For planes and things, one could argue that the lapping on abrasive is more foolproof than using a deburring wheel alone, or other method of "targeted removal" (where-ever @D_W is?)
as a high spot is obviously going to have more contact,
and the material from the centre can be removed more evenly, leaving it a simple matter of
erasing however much material one leaves on the edges
i.e how much one feathers the ink off the edge, or infact occasionally runs off the abrasive
if using a smaller area of contacted surface than the item (plane) is.

(the edges being the reference as anything the opposite is pretty much unmeasurable)
i.e if one feels the need to do the test like Cosman shows beforehand,
because after say 10 few swipes on a large abrasive would throw whatever feelers
(one thou shim stock in Cosman's case) one would be getting beyond an "Prussian blue" test if one has a permanent marker around.

One can see most of the edge disappear with one or two short strokes of the larger area,
as abrasion will favour the edges and eliminate the witness marks one has been careful to keep an eye on.

View attachment 136698

It's called "over-thinking". Elaborate solutions to an imaginary problem.

 

[Ttrees]

Toolmaking is what it is.

 

[Ttrees]

...and that is why the tolerance of those planes in the Cosman video is there,
i.e specifically biased so one can lap them on float glass or some such thing with a
wide and long strip of paper, and end up with whatever tolerance they wish,
should they feel the need to even work it atall.
Cosman shows these right off the bat and still does his trademark thing pinching shavings.

It's inbetween this and the smallest fraction of convexity which is likely for most, unnoticeable for all who don't have such want for finer tolerances,
It makes an interesting topic to me, but said hard to get an answer .
I'd like to see what Rob would make of it, should he wish to give that wide plank planing video
another go and demonstrate everything he knows, not just hints of such working.
Maybe he still makes a good few quid from the old video?

Point being he has a stout bench suitable for the job, and thus able to have a true reference and ability to note what one shaving will achieve,
not that one needs a plane of this tolerance, I've dimensioned some timbers with a scraper plane, before I knew how to use the cap iron,
it's all about speed and surety for fine tolerance things which have no room for error,
and I haven't been/yet to be swayed by anyone's opinion of how much of a tolerance or indeed how much convexity one has made their longer plane(s) who thinks works different than what I find suitable, (i.e duplicating the surface of the bench which Cosman does suggest but that might not have come across for some folks)


But yet there maybe a lot more ways this might be noticeable, which I'm not even properly given credit to, as is always the case with woodworking...
Take flipping the work around... for making up a wide panel, seat, guitar or whathaveyou, can one achieve the same gapless result without excess hollowing, so one can change their minds without without a load of faff re-matching what could be a multitude of timbers
(laminated or edge joined bench or table tops comes to mind)
say one plank got some damage at a later date than anticipated.

This I'd guess would be up there for the most noticeable of all reasons to want a bias,



Tom

 

[ivan]

What's a perfectly flat plane sole for, if you could scrape it so?
Take a final shaving from a flat board; the No.7 is running on a narrow part of the sole just in front of the mouth, and the heel right at the back. However, once running on the board, all downward pressure is at the tote. This can flex the sole downward. If the sole is very slightly hollow it still flexes down to the timber surface. If too convex, the plane might not cut. So provided the sole is either flat or slightly hollow over the full length, perfect flatness is not required as the sole is not perfectly rigid! Less true with shorter planes, but then these are not required to produce critical flatness as for edge jointing, say.
Picked up a calibrated chinese granite plate from Axminster about 450x600x100 V-V-heavy! Took 2 to put it in my van. Bought for metalwork some years back. For non critical use I found some granite place mats in Aldi/Lidl, glossy surface appeared V flat checked by using it as a mirror. Plenty good enough for abrasive backing.

 

[Inspector]

Granite and cast iron surface plates are for measurement. Not lapping tools on sandpaper! If you did that where I worked you would get roasted. Lap on something else and check with the surface plate. Bunch of barbarians and heathens.

Pete