measuring a plane sole flatness?

[bugbear]

I have a passing interest (some might say obsession :-)
in making woodworking plane soles flat.

(aside; they clearly need to be "fairly flat";
no-one is quite sure "how flat" they need to be;
I take the view that "too flat" is "flat
enough" ;-)

http://www.geocities.com/plybench/flatten.html

I have (for a while) had a Chinese surface plate,
like this one:

http://www.leevalley.com/wood/page.aspx?sid=&ccurrency=3&page=32526&category=1,43513

I now have a Mercer G.303 dial indicator (second hand)

http://www.cromwell.co.uk/MER3003187V

And 2 less accurate dial indicators, one with long, linear travel,
but only 1/2 thou resolution,

I also own some surface gauge stands, both branded and
apprentice made.

My workshop is a (messy) mixture of woodworking and
metalworking stuff.

Loading Image...

How can I go about measuring the shape
of my (hoped to be flat) plane sole
as accurately as possible?

BugBear

[Nick Mueller]

Post by bugbear
I also own some surface gauge stands, both branded and
apprentice made.

Here's the method to check for flatness with a gauge stand and a dial
indicator.

Put the dial indicator in each corner and rotate it by 90° after you have
adjusted the stand's arm to reach nearly the other corner (of the short
side). Reapeat with the stand standing in the centre, rotating 360°. If you
do have a very long surface to check, you can also put the stand at 1/2 or
1/3 lengths of sides.

An other method is with a long ruler with exactly parallel sides(that
costs), and a dial indicator riding on the ruler. I have a picture of that,
if you want. Made that thing for checking flatness of a lathe's bed.


Nick

[bugbear]

Post by Nick Mueller

Post by bugbear
I also own some surface gauge stands, both branded and
apprentice made.

Here's the method to check for flatness with a gauge stand and a dial
indicator.
Put the dial indicator in each corner and rotate it by 90° after you have
adjusted the stand's arm to reach nearly the other corner (of the short
side). Reapeat with the stand standing in the centre, rotating 360°. If you
do have a very long surface to check, you can also put the stand at 1/2 or
1/3 lengths of sides.

So the surface gauge is sitting on the surface being measured - no
requirment for a surface plate?

I'm not getting the picture here - since a (e.g.) #5 plane
is 14" by around 2 1/2" I don't see how anything gets turned through 90 degrees,
but since my visualisation of what you're describing is so poor,
that may be natural!

Can you (for this ignorant person) be more explicit about where the surface gauge
base is, and what point is being contacted by the dial gauge, and how the
various dial gauge reading can be translated/interpreted
into a quantative maps of the bumps and hollows?

Post by Nick Mueller
An other method is with a long ruler with exactly parallel sides(that
costs), and a dial indicator riding on the ruler. I have a picture of that,
if you want. Made that thing for checking flatness of a lathe's bed.

When you say ruler, do you mean cast iron straightedge, wide enough for things
to sit on?

Loading Image...

BugBear

[Nick Mueller]

Post by bugbear
So the surface gauge is sitting on the surface being measured - no
requirment for a surface plate?

Yes!

Post by bugbear
I'm not getting the picture here - since a (e.g.) #5 plane
is 14" by around 2 1/2" I don't see how anything gets turned through 90
degrees, but since my visualisation of what you're describing is so poor,
that may be natural!

OK, its a "bit" on the long side. So the method I tried to describe in poor
wording might not be the best. :-))

Post by bugbear
Can you (for this ignorant person) be more explicit about where the
surface gauge base is, and what point is being contacted by the dial
gauge, and how the various dial gauge reading can be
translated/interpreted into a quantative maps of the bumps and hollows?

OK, new game, new luck.
Put the stand in one corner. Adjust the arm to reach out a bit less than the
sole's width (2 1/2"). Now the dial's tip sits on the opposing corner where
the stand is. Adjust to zero. Rotate stand 90°. You know what direction to
rotate? :-)

Now you get a difference. It shows you almost (not completely, but quite
good) wether the sole is bent upward or downward.
Move the stand along the longer side in such a way, that if you rotate the
stand, the dial's tip reaches the place where the stand was standing
before. Read the dial, rotate 90° (reaching the opposing side), read,
rotate further 90°, read, move stand, ... Do that all along the sides of
the sole. Now you did get some kind of map. Try to figure out how the sole
has to be warped and bent to get the readings. That method is a bit
complicated and is better to *verify* flatness.

Post by bugbear
When you say ruler, do you mean cast iron straightedge, wide enough for
things to sit on?

I should have said straightedge? Some precision ground flat steel. Not the
ones with a knife that you use against the light. You get them in different
grades. I do have one 1m long in grade 0 (actual deviation 0,007mm). A
500mm straightedge grade 1 should be by far good enough for you and would
put you back at about 50.- EUR. Unfortunately, they are very bad at using
them with touching blue. But very good at checking straightness *along* *a*
*line*.
You can always use that straightedge on the diagonals to show twist.
Sorry, I don't know the right word in English for that "ruler".


HTH somehow. :-)
Nick

[bugbear]

Post by Nick Mueller

Post by bugbear
So the surface gauge is sitting on the surface being measured - no
requirment for a surface plate?

Yes!

Post by bugbear
I'm not getting the picture here - since a (e.g.) #5 plane
is 14" by around 2 1/2" I don't see how anything gets turned through 90
degrees, but since my visualisation of what you're describing is so poor,
that may be natural!

OK, its a "bit" on the long side. So the method I tried to describe in poor
wording might not be the best. :-))

Post by bugbear
Can you (for this ignorant person) be more explicit about where the
surface gauge base is, and what point is being contacted by the dial
gauge, and how the various dial gauge reading can be
translated/interpreted into a quantative maps of the bumps and hollows?

OK, new game, new luck.
Put the stand in one corner. Adjust the arm to reach out a bit less than the
sole's width (2 1/2"). Now the dial's tip sits on the opposing corner where
the stand is. Adjust to zero. Rotate stand 90°. You know what direction to
rotate? :-)
Now you get a difference. It shows you almost (not completely, but quite
good) wether the sole is bent upward or downward.
Move the stand along the longer side in such a way, that if you rotate the
stand, the dial's tip reaches the place where the stand was standing
before. Read the dial, rotate 90° (reaching the opposing side), read,
rotate further 90°, read, move stand, ... Do that all along the sides of
the sole. Now you did get some kind of map. Try to figure out how the sole
has to be warped and bent to get the readings. That method is a bit
complicated and is better to *verify* flatness.

Ah; each measurement is measuring a local gradient, and these
can be integrated to reveal a curve. I understand.

Post by Nick Mueller

Post by bugbear
When you say ruler, do you mean cast iron straightedge, wide enough for
things to sit on?

I should have said straightedge? Some precision ground flat steel. Not the
ones with a knife that you use against the light. You get them in different
grades. I do have one 1m long in grade 0 (actual deviation 0,007mm). A
500mm straightedge grade 1 should be by far good enough for you and would
put you back at about 50.- EUR. Unfortunately, they are very bad at using
them with touching blue. But very good at checking straightness *along* *a*
*line*.
You can always use that straightedge on the diagonals to show twist.
Sorry, I don't know the right word in English for that "ruler".

A ruler is "ruled" i.e. it has divisions in inches, or millimeters.

A straight edge doesn't. Good rulers may be used as straightedges.

Straightedges come in two main styles; "ground flat stock"

http://www.bowers.co.uk/products/show/577

and the ones which are really long, narrow surface plates, either
camel back cast iron:

http://www.gandmtools.co.uk/cat_leaf.php?id=3284

or granite blocks:

http://www.tru-stone.com/pages/smp.asp

I can see how to use that for simple checking,
but I don't understand hwo to use it as you said

Post by Nick Mueller
An other method is with a long ruler with exactly parallel sides(that
costs), and a dial indicator riding on the ruler. I have a picture of that,
if you want. Made that thing for checking flatness of a lathe's bed.

I admit, I had envisaged setting up the plane (upside down)
to the sole was parallel to the surface plate, and using a dial indicator
from above, with the indicator support sliding over the surface plate.

BugBear

[p***@hotmail.com]

Post by bugbear

Post by Nick Mueller

Post by bugbear
So the surface gauge is sitting on the surface being measured - no
requirment for a surface plate?

Yes!

Post by bugbear
I'm not getting the picture here - since a (e.g.) #5 plane
is 14" by around 2 1/2" I don't see how anything gets turned through 90
degrees, but since my visualisation of what you're describing is so poor,
that may be natural!

OK, its a "bit" on the long side. So the method I tried to describe in poor
wording might not be the best. :-))

Post by bugbear
Can you (for this ignorant person) be more explicit about where the
surface gauge base is, and what point is being contacted by the dial
gauge, and how the various dial gauge reading can be
translated/interpreted into a quantative maps of the bumps and hollows?

OK, new game, new luck.
Put the stand in one corner. Adjust the arm to reach out a bit less than the
sole's width (2 1/2"). Now the dial's tip sits on the opposing corner where
the stand is. Adjust to zero. Rotate stand 90°. You know what direction to
rotate? :-)
Now you get a difference. It shows you almost (not completely, but quite
good) wether the sole is bent upward or downward.
Move the stand along the longer side in such a way, that if you rotate the
stand, the dial's tip reaches the place where the stand was standing
before. Read the dial, rotate 90° (reaching the opposing side), read,
rotate further 90°, read, move stand, ... Do that all along the sides of
the sole. Now you did get some kind of map. Try to figure out how the sole
has to be warped and bent to get the readings. That method is a bit
complicated and is better to *verify* flatness.

Ah; each measurement is measuring a local gradient, and these
can be integrated to reveal a curve. I understand.

Post by Nick Mueller

Post by bugbear
When you say ruler, do you mean cast iron straightedge, wide enough for
things to sit on?

I should have said straightedge? Some precision ground flat steel. Not the
ones with a knife that you use against the light. You get them in different
grades. I do have one 1m long in grade 0 (actual deviation 0,007mm). A
500mm straightedge grade 1 should be by far good enough for you and would
put you back at about 50.- EUR. Unfortunately, they are very bad at using
them with touching blue. But very good at checking straightness *along* *a*
*line*.
You can always use that straightedge on the diagonals to show twist.
Sorry, I don't know the right word in English for that "ruler".

A ruler is "ruled" i.e. it has divisions in inches, or millimeters.
A straight edge doesn't. Good rulers may be used as straightedges.
Straightedges come in two main styles; "ground flat stock"
http://www.bowers.co.uk/products/show/577
and the ones which are really long, narrow surface plates, either
http://www.gandmtools.co.uk/cat_leaf.php?id=3284
http://www.tru-stone.com/pages/smp.asp
I can see how to use that for simple checking,
but I don't understand hwo to use it as you said

Post by Nick Mueller
An other method is with a long ruler with exactly parallel sides(that
costs), and a dial indicator riding on the ruler. I have a picture of that,
if you want. Made that thing for checking flatness of a lathe's bed.

I admit, I had envisaged setting up the plane (upside down)
to the sole was parallel to the surface plate, and using a dial indicator
from above, with the indicator support sliding over the surface plate.
   BugBear- Hide quoted text -
- Show quoted text -

If you make up a little block - say 1"x 1" and drill and tap one face
with 3 screws in a triangle to another face at 90 degerees to the
first, you fix a piece of front silvered miror. Now turn the plane
over and mark it out in pencil in 1" squares, next put the block in
one square standing on the screws and shine a builders lazer at the
mirror from about 10ft and plot the reflection from the lazer beam on
a piece of card by the lazer, so the light has travelled 20ft. You
will be able to easily calculate the error in each square.
For grearer accuracy repeat with the mirror standing at the junction
of each square. I hope you find something more interesting to do over
christmas
Peter

[mark]

Post by bugbear
I have a passing interest (some might say obsession :-)
in making woodworking plane soles flat.
(aside; they clearly need to be "fairly flat";
no-one is quite sure "how flat" they need to be;
I take the view that "too flat" is "flat
enough" ;-)
http://www.geocities.com/plybench/flatten.html
I have (for a while) had a Chinese surface plate,
http://www.leevalley.com/wood/page.aspx?sid=&ccurrency=3&page=32526&c...
I now have a Mercer G.303 dial indicator (second hand)
http://www.cromwell.co.uk/MER3003187V
And 2 less accurate dial indicators, one with long, linear travel,
but only 1/2 thou resolution,
I also own some surface gauge stands, both branded and
apprentice made.
My workshop is a (messy) mixture of woodworking and
metalworking stuff.
http://i48.photobucket.com/albums/f234/bugbear33/workshop.jpg
How can I go about measuring the shape
of my (hoped to be flat) plane sole
as accurately as possible?
   BugBear

I say your going over the top ........for a stanley plane

the plane may end up perfect
.but wood will never be ........swelling and changing with the
moisture content within hours of you getting it bang on .

if you want to go to the trouble.. do it with a plane that's going to
be worth a lot of money at the end of all your hard work.

stephen thomas in the practical machinist forum builds bespoke wood
planes..........search his posts ..


all the best.markj

[dave sanderson]

Post by bugbear
I have a passing interest (some might say obsession :-)
in making woodworking plane soles flat.
(aside; they clearly need to be "fairly flat";
no-one is quite sure "how flat" they need to be;
I take the view that "too flat" is "flat
enough" ;-)
http://www.geocities.com/plybench/flatten.html
I have (for a while) had a Chinese surface plate,
http://www.leevalley.com/wood/page.aspx?sid=&ccurrency=3&page=32526&c...
I now have a Mercer G.303 dial indicator (second hand)
http://www.cromwell.co.uk/MER3003187V
And 2 less accurate dial indicators, one with long, linear travel,
but only 1/2 thou resolution,
I also own some surface gauge stands, both branded and
apprentice made.
My workshop is a (messy) mixture of woodworking and
metalworking stuff.
http://i48.photobucket.com/albums/f234/bugbear33/workshop.jpg
How can I go about measuring the shape
of my (hoped to be flat) plane sole
as accurately as possible?
   BugBear

I maybe missing something, but why dont you use the traditional method
of bluing and then scraping the high spots? It will get you as flat as
the
reference with a little patience.
I assume you dont really care about the mapping of the surface, just
that
it is flat?

Dave

[Charles Lamont]

Post by bugbear
How can I go about measuring the shape
of my (hoped to be flat) plane sole
as accurately as possible?

Rest it sole down on the surface plate and see where you can get a
feeler gauge under it.

Or, if it is very good, rest on cigarette papers and see which ones are
touching and which not.

Or blue it up and and see where the high spots are.

[Andrew Mawson]

Post by Charles Lamont

Post by bugbear
How can I go about measuring the shape
of my (hoped to be flat) plane sole
as accurately as possible?

Rest it sole down on the surface plate and see where you can get a
feeler gauge under it.
Or, if it is very good, rest on cigarette papers and see which ones are
touching and which not.
Or blue it up and and see where the high spots are.
--
Charles Lamont

Or bung it on a surface grinder (or even decent flat belt sander) and
skim to a clean up cut, and accept it'll be perfectly adequate for the
job thus freeing up time to worry about things worth worrying about
<G>

AWEM

[Tony Jeffree]

On Mon, 22 Dec 2008 22:43:35 -0000, "Andrew Mawson"

Post by Andrew Mawson

Post by Charles Lamont

Post by bugbear
How can I go about measuring the shape
of my (hoped to be flat) plane sole
as accurately as possible?

Rest it sole down on the surface plate and see where you can get a
feeler gauge under it.
Or, if it is very good, rest on cigarette papers and see which ones

are

Post by Charles Lamont
touching and which not.
Or blue it up and and see where the high spots are.
--
Charles Lamont

Or bung it on a surface grinder (or even decent flat belt sander) and
skim to a clean up cut, and accept it'll be perfectly adequate for the
job thus freeing up time to worry about things worth worrying about
<G>

I've never felt the need to measure a sole for flatness, or even bung
it on the surface grinder for that matter. A couple of minutes in the
frying pan, then a squeeze of lemon juice is all that it needs <G>

Regards,
Tony

[Andrew Mawson]

Post by Tony Jeffree
On Mon, 22 Dec 2008 22:43:35 -0000, "Andrew Mawson"

Post by Andrew Mawson

Post by Charles Lamont

Post by bugbear
How can I go about measuring the shape
of my (hoped to be flat) plane sole
as accurately as possible?

Rest it sole down on the surface plate and see where you can get a
feeler gauge under it.
Or, if it is very good, rest on cigarette papers and see which ones

are

Post by Charles Lamont
touching and which not.
Or blue it up and and see where the high spots are.
--
Charles Lamont

Or bung it on a surface grinder (or even decent flat belt sander) and
skim to a clean up cut, and accept it'll be perfectly adequate for the
job thus freeing up time to worry about things worth worrying about
<G>

I've never felt the need to measure a sole for flatness, or even bung
it on the surface grinder for that matter. A couple of minutes in the
frying pan, then a squeeze of lemon juice is all that it needs <G>
Regards,
Tony

That's because you don't have a soul - we all know that <G>

AWEM

[Tony Jeffree]

On Tue, 23 Dec 2008 08:11:48 -0000, "Andrew Mawson"

Post by Andrew Mawson

Post by Tony Jeffree
I've never felt the need to measure a sole for flatness, or even

bung

Post by Tony Jeffree
it on the surface grinder for that matter. A couple of minutes in

the

Post by Tony Jeffree
frying pan, then a squeeze of lemon juice is all that it needs <G>
Regards,
Tony

That's because you don't have a soul - we all know that <G>

Ah - but I do have a kipper <G>

Regards,
Tony

[bugbear]

Post by Charles Lamont

Post by bugbear
How can I go about measuring the shape
of my (hoped to be flat) plane sole
as accurately as possible?

Rest it sole down on the surface plate and see where you can get a
feeler gauge under it.
Or, if it is very good, rest on cigarette papers and see which ones are
touching and which not.
Or blue it up and and see where the high spots are.

I've done that. My site that I linked
to explains how to do it.

I wanted to measure, quantitively, how
good (or bad) a job I'd done.

To those telling me not to bother, I would
point out that most model engineering is done
for the sake of the achievement, or enjoyment of
the task itself, not because the final item is
intrinsically "needed".

I am also well aware of the debate concerning
how flat a plane's sole needs to be, and also
how much effort it's worth putting into
a low-value second hand tool, and what the economic
return might be.

BugBear

[Charles Lamont]

Post by bugbear
I've done that. My site that I linked
to explains how to do it.
I wanted to measure, quantitatively, how
good (or bad) a job I'd done.

Your measuring method needs to be an order of magnitude more
accurate than the thing you are measuring. You need a Talysurf.

[Don Young]

Post by bugbear

Post by bugbear
How can I go about measuring the shape
of my (hoped to be flat) plane sole
as accurately as possible?

Rest it sole down on the surface plate and see where you can get a feeler
gauge under it.
Or, if it is very good, rest on cigarette papers and see which ones are
touching and which not.
Or blue it up and and see where the high spots are.

I've done that. My site that I linked
to explains how to do it.
I wanted to measure, quantitively, how
good (or bad) a job I'd done.
To those telling me not to bother, I would
point out that most model engineering is done
for the sake of the achievement, or enjoyment of
the task itself, not because the final item is
intrinsically "needed".
I am also well aware of the debate concerning
how flat a plane's sole needs to be, and also
how much effort it's worth putting into
a low-value second hand tool, and what the economic
return might be.
BugBear

To be theoretically correct, shouldn't the back and front of the sole be
offset from planar at the blade by the depth of cut thickness? I think
planing machines actually do this, since they have significant depths of
cut. You might also want to evaluate the change from flat due to the
frictional heat of the planing and the bending pressure exerted on the
handle(s). ;>)

Don Young (USA)

[Tony Jeffree]

Post by Don Young
You might also want to evaluate the change from flat due to the
frictional heat of the planing and the bending pressure exerted on the
handle(s). ;>)

If you are going to that kind of extreme for what is, at the end of
the day, a pretty crude a hand tool, then you might also want to get a
life ;-)

Regards,
Tony

[bugbear]

Post by Tony Jeffree

Post by Don Young
You might also want to evaluate the change from flat due to the
frictional heat of the planing and the bending pressure exerted on the
handle(s). ;>)

If you are going to that kind of extreme for what is, at the end of
the day, a pretty crude a hand tool, then you might also want to get a
life ;-)

This *is* the forum for people who
make 1/5 scale bicycles, yes?

BugBear

[David Littlewood]

Post by Tony Jeffree

Post by Don Young
You might also want to evaluate the change from flat due to the
frictional heat of the planing and the bending pressure exerted on the
handle(s). ;>)

If you are going to that kind of extreme for what is, at the end of
the day, a pretty crude a hand tool, then you might also want to get a
life ;-)

Could it just be that your irony detector was switched off?

David

[bugbear]

Post by Don Young
To be theoretically correct, shouldn't the back and front of the sole be
offset from planar at the blade by the depth of cut thickness? I think
planing machines actually do this, since they have significant depths of
cut.

Indeed. On a mailing list, someone proposed the "manx jointer",
a hand plane (on this handtool only list, "tail" is a euphemism
for power lead, and manx cats have no tail) that had
the sole-heel step you propose.

http://swingleydev.com/archive/get.php?message_id=56589&submit_thread=1#message

Post by Don Young
You might also want to evaluate the change from flat due to the
frictional heat of the planing

Discussed here:

http://swingleydev.com/archive/get.php?message_id=66114&submit_thread=1

Post by Don Young
and the bending pressure exerted on the
handle(s). ;>)

Discussed here:

http://swingleydev.com/archive/get.php?message_id=6920&submit_thread=1#message

You thought you were joking, didn't you :-)

BugBear

[Don Young]

Post by bugbear

Post by Don Young
To be theoretically correct, shouldn't the back and front of the sole be
offset from planar at the blade by the depth of cut thickness? I think
planing machines actually do this, since they have significant depths of
cut.

Indeed. On a mailing list, someone proposed the "manx jointer",
a hand plane (on this handtool only list, "tail" is a euphemism
for power lead, and manx cats have no tail) that had
the sole-heel step you propose.
http://swingleydev.com/archive/get.php?message_id=56589&submit_thread=1#message

Post by Don Young
You might also want to evaluate the change from flat due to the
frictional heat of the planing

http://swingleydev.com/archive/get.php?message_id=66114&submit_thread=1

Post by Don Young
and the bending pressure exerted on the handle(s). ;>)

http://swingleydev.com/archive/get.php?message_id=6920&submit_thread=1#message
You thought you were joking, didn't you :-)
BugBear

Yes, I did. But I am often surprised at how much knowledge and information
actually exists that I am unaware of. ;-)

Don Young (USA)

[p***@yahoo.com]

On Mon, 22 Dec 2008 11:20:48 +0000, bugbear

Post by bugbear
I have a passing interest (some might say obsession :-)
in making woodworking plane soles flat.
(aside; they clearly need to be "fairly flat";
no-one is quite sure "how flat" they need to be;
I take the view that "too flat" is "flat
enough" ;-)
http://www.geocities.com/plybench/flatten.html
I have (for a while) had a Chinese surface plate,
http://www.leevalley.com/wood/page.aspx?sid=&ccurrency=3&page=32526&category=1,43513
I now have a Mercer G.303 dial indicator (second hand)
http://www.cromwell.co.uk/MER3003187V
And 2 less accurate dial indicators, one with long, linear travel,
but only 1/2 thou resolution,
I also own some surface gauge stands, both branded and
apprentice made.
My workshop is a (messy) mixture of woodworking and
metalworking stuff.
http://i48.photobucket.com/albums/f234/bugbear33/workshop.jpg
How can I go about measuring the shape
of my (hoped to be flat) plane sole
as accurately as possible?
BugBear

Not to sure of the necessity for extreme flatness of your sole
plate. However a very convenient visual check is the ancient
plate glass methylated spirits capillary test.

Lay a thick piece of glass on your sole plate with one edge of
the glass propped up on a thin spacer chosen to give an airgap
slope of about 1 in 100.

Carefully introduce a small amount of methylated spirits into
this airgap. Very little is needed - the amount carried in a
small artists brush is sufficient. Capillary action will draw
the spirits to the touching end of the airgap. Add enough for a
band of liquid about 1/2" wide. Surface tension causes the free
edge to have uniform thickness so the height of the free edge is
a direct indication of 100:1 amplification of the airgap at the
edge height.

Because the meths is flowing in a very small gap it
takes a little time to settle into its final position. The
smaller the slope the greater the amplification and the longer
the settling time.

The flatness quality of the glass can first be checked by
the same method on your surface plate. The glass doesn't need to
be very thick because it's fully supported along its length.
1/4" or more is OK.

The best glass to use is genuine plate glass as this has
been ground flat and polished on both surfaces. This is not too
easy to find.

Most current glass is float glass. This process inherently
produces glass with two precisely parallel surfaces
but the flatness is dependent on the precision of the mechanical
alignment of the outfeed rollers. This may introduce a small
amount of twist or bow. Its quality as a flatness standard is a
bit variable so selection is necessary.

A much better bet is mirror glass (e.g. an ancient dressing
table mirror). Twist or bow in a reflective surface is
unacceptable so quality mirrors are either plate glass or float
glass selected for minimum twist/bow.

The problem is removing the backing. The silvered surface is
protected by a copper plate layer followed by a paint or resin
film. The film can usually be removed by a methyl chloride based
paint stripper but nitric acid is needed to shift the copper and
silver coating.

For precision work with fine ground optical surfaces a 1 in
1000 slope can be used. For coarser work a similar method is
possible but with a 1 in 20 slope and the meths replaced by a
handful of identical smallballs.

The method is still usable with glass that is not dead flat.
If the workpiece is stationary and the glass position is
changed, workpiece errors stay put, glass errors move with the
glass.

Jim

[bugbear]

Post by p***@yahoo.com
On Mon, 22 Dec 2008 11:20:48 +0000, bugbear

Post by bugbear
How can I go about measuring the shape
of my (hoped to be flat) plane sole
as accurately as possible?
BugBear

Not to sure of the necessity for extreme flatness of your sole
plate. However a very convenient visual check is the ancient
plate glass methylated spirits capillary test.

I thought I'd read several "older" books on precision
engineering, but I've never read of this technique - thank
you very much!

BugBear

[Cowtown_eric]

what is the diameter of small balls mentioned. The smallest I can find is .4mm

[F Murtz]

Post by bugbear
I have a passing interest (some might say obsession :-)
in making woodworking plane soles flat.
(aside; they clearly need to be "fairly flat";
no-one is quite sure "how flat" they need to be;
I take the view that "too flat" is "flat
enough" ;-)
http://www.geocities.com/plybench/flatten.html
I have (for a while) had a Chinese surface plate,
http://www.leevalley.com/wood/page.aspx?sid=&ccurrency=3&page=32526&category=1,43513
I now have a Mercer G.303 dial indicator (second hand)
http://www.cromwell.co.uk/MER3003187V
And 2 less accurate dial indicators, one with long, linear travel,
but only 1/2 thou resolution,
I also own some surface gauge stands, both branded and
apprentice made.
My workshop is a (messy) mixture of woodworking and
metalworking stuff.
http://i48.photobucket.com/albums/f234/bugbear33/workshop.jpg
How can I go about measuring the shape
of my (hoped to be flat) plane sole
as accurately as possible?
BugBear

Then put a blade in it which is usually hand ground and stone finished
and therefore imperfect.
PS you can get a plane with a flexible sheet base which can be adjusted
concave or convex what do you do then?

[bugbear]

Post by F Murtz
Then put a blade in it which is usually hand ground and stone finished
and therefore imperfect.
PS you can get a plane with a flexible sheet base which can be adjusted
concave or convex what do you do then?

Its performance, in terms of predictable behaviour
and surface quality will be less good.

BugBear

[bugbear]

Post by bugbear
How can I go about measuring the shape
of my (hoped to be flat) plane sole
as accurately as possible?

In the end I did this:

http://geocities.com/plybench/flatten_practice.html#measure

Thanks to all for the input.

BugBear