Chris Lindquist wrote:
I've been trying to find out exactly what process was used for
originating a surface plate in the good old days. I expect it involved
careful hands and a large amount of scraping, but what provided a
reference for "flat"? And how flat was flat around the turn of the
century?

I'm not planning to try this at home, of course. My Chinese granite
plate is plenty flat enough, thanks. But I've been going through my
books looking for an answer to this chicken-and-egg question without
finding a solution.

Can anyone help?

Thanks!

Greetings,

You don't make one plate, you make 3 of the same size. Match plate A to
B, B to C, and A to C. It's an iterative process, bringing down the
high spots on each plate a bit at a time. The same method can also be
used to generate straight edges, and with some variation master
precision squares.

Cheers,
Stan

Yeah, and it was being done a lot further back than "the turn of the
century". Sir Joseph Whitworth was one of the first to publicize flat and
straight edge making, but it didn't originate with him, probably. For
details, get one of Lindsay's books, "English and American Tool Builders"/

Bob Swinney

"Dave Baker" wrote in message
...
Subject: Early surface plates: How were they made?
From: (Chris Lindquist)
Date: 21/08/03 20:43 GMT Daylight Time
Message-id:

I've been trying to find out exactly what process was used for
originating a surface plate in the good old days. I expect it involved
careful hands and a large amount of scraping, but what provided a
reference for "flat"? And how flat was flat around the turn of the
century?

I'm not planning to try this at home, of course. My Chinese granite
plate is plenty flat enough, thanks. But I've been going through my
books looking for an answer to this chicken-and-egg question without
finding a solution.

Can anyone help?

By lapping 3 plates against each other with grinding paste until all three
are
flat. The same way as reference plates are made now. The ancients could
make a
plate as flat as we can now. The technique requires no special technology.


Dave Baker - Puma Race Engines (www.pumaracing.co.uk)
I'm not at all sure why women like men. We're argumentative, childish,
unsociable and extremely unappealing naked. I'm quite grateful they do
though.

On 21 Aug 2003 20:07:34 GMT, a (Dave Baker) wrote:

Subject: Early surface plates: How were they made?
From: (Chris Lindquist)
Date: 21/08/03 20:43 GMT Daylight Time
Message-id:

I've been trying to find out exactly what process was used for
originating a surface plate in the good old days. I expect it involved
careful hands and a large amount of scraping, but what provided a
reference for "flat"? And how flat was flat around the turn of the
century?

I'm not planning to try this at home, of course. My Chinese granite
plate is plenty flat enough, thanks. But I've been going through my
books looking for an answer to this chicken-and-egg question without
finding a solution.

Can anyone help?

By lapping 3 plates against each other with grinding paste until all three are
flat. The same way as reference plates are made now. The ancients could make a
plate as flat as we can now. The technique requires no special technology.

Yes, in fact a quartz (?) sphere (12" diameter) was hand made by the
chinese I believe over 1000 years ago and is very nearly perfect.
It's in the Smithsoanian. Very interesting to imagine how the did it.

John

Please note that my return address is wrong due to the amount of junk email I get.
So please respond to this message through the newsgroup.

In article , Dave Baker says...

By lapping 3 plates against each other with grinding paste until all three are
flat. The same way as reference plates are made now. The ancients could make a
plate as flat as we can now. The technique requires no special technology.

Not strictly true, Dave. Read the description about flat
surface generation in Moore's book, they go into considerable
detail on this.

1) they use cast iron plates, specially ribbed and supported.

2) the square plates are spotted against each other with a
marking medium, and are hand scraped to each other.

3) the exact sequence of operations matters, and there is 90
degree rotation included between each cycle. This prevents
a saddle error from developing.

4) once the plates are spotted and hand scraped as well as
possible, each plate is then futher corrected using several
additional steps, to get down to roughly one micron flatness
level. Unless one includes these steps, they say that ten
or so microns is all that can be achieved.

Probably the *most* important technologies that we have, that
were not available to the 'ancients' are a) more accurate
metrology, and b) temperature controlled environments for
doing the measuring in. The second is probably the most
important.

Moore's book give considerable engineering detail about what
is now pretty trivial stuff, but when the book was written is
was state of the art, he talks about feedback loop control
of HVAC systems in their plant.

Jim

==================================================
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JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

I read that scraping results in better accuracy when making true planes,
than does surface grinding.
I find that hard to understand.
Can someone explain why that would be so?

Jordan

In article ,
(John Flanagan) wrote:

Yes, in fact a quartz (?) sphere (12" diameter) was hand made by the
chinese I believe over 1000 years ago and is very nearly perfect.
It's in the Smithsoanian. Very interesting to imagine how the did it.

Something similiar is done in the mountains by hillbillies. It involves
a small stream of water falling into a 'pot' in the rock and a stone in
the pot that turns in response to the water flow.

--
free men own guns - slaves don't
www.geocities.com/CapitolHill/5357/

How perfect is perfect? Somebody can consider that a 1/32" accuracy is
perfect enough whil another isn't happy with an accuracy of a 1/4 wavelength
of green light.
Making a sphere isn't a hard chore at all. Rubbing another piece of
material over the surface will quickly produce a spherical surface to the
size of the grit used and gradually to a fair bit more accurate than that.

--
Bob May
Losing weight is easy! If you ever want to lose weight, eat and drink less.
Works evevery time it is tried!

In article , Bob May says...

How perfect is perfect?

One micron rms, over four feet square.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

jim rozen wrote:
In article , Bob May says...

How perfect is perfect?


One micron rms, over four feet square.

Read "The Perfect Machine: Building the Palomar Telescope"

In article , Jim Stewart says...

One micron rms, over four feet square.

Read "The Perfect Machine: Building the Palomar Telescope"

Right, but could they put a one hundred pound straight
edge on the mirror and still have it hold tolerance?

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

On Fri, 22 Aug 2003 10:28:26 +0100, Jordan wrote:

I read that scraping results in better accuracy when making true planes,
than does surface grinding.
I find that hard to understand.
Can someone explain why that would be so?

Jordan

PRO:-
the table on a surface grinder follows the ways to some extent and will also
vary in height if the oiler has been used.
Grinding also produces heat which will distort the object being ground,
Scraping three plates against each other is a primary method rather than a
secondary method i.e. It is not dependant on the accuracy of any other piece
of equipment.
Scraping isn't limited by the size of your surface grinder.

CON:-
If the piece will fit the grinder at work then I can get better results with
an hour of surface grinding than I can with a week of evenings spent scraping.

I burnt my hand on a carbide scraper blade that I was using (hard) for some
rough scraping last week :-(




For true planes you have to go to the primary method of generation which is
the theory that the only surface which can be congruent to an identical
surface in all orientations is the plane surface and the corollary that the
only surface which can be congruent to its reflection in all orientations is a
plane surface. This means scraping three surfaces against each other. Anything
else is an approximation..


Mark Rand
RTFM

Subject: Early surface plates: How were they made?
From: (Chris Lindquist)
Date: 21/08/03 20:43 GMT Daylight Time
Message-id:

I've been trying to find out exactly what process was used for
originating a surface plate in the good old days. I expect it involved
careful hands and a large amount of scraping, but what provided a
reference for "flat"? And how flat was flat around the turn of the
century?

I'm not planning to try this at home, of course. My Chinese granite
plate is plenty flat enough, thanks. But I've been going through my
books looking for an answer to this chicken-and-egg question without
finding a solution.

Can anyone help?

During my apprenticeship I had the 'priviledge' of resurfacing a number of
4'x6' cast iron surface plates. (1 was standard, I was the bosses
'favorite').
*
We were able to get a good start by cutting below the patina of the badly
warped plates on a single point planer. Then they were left to soak and
settle for a couple months.
*
For the plates in better shape, we just started in. Using three plates
(five is better, I'm told) the program says that you blue one plate to
another, and scrape away the blue on one plate. Then take that plate and
blue it to the third plate and scrape that one. Then take the third and
blue it to the first one and scrape the first one. Then you turn one of
the plates 180 degrees and start all over. This continues until all three
blue evenly to each other in all orientations. Then you usually flake the
surface to break it up to keep it from being too smooth (and to give a
place for minute dirt to collect).
*
Now - this takes a long time. Especially when the boss loans out the power
scraper. It took two of us 6 weeks to hand scrape approximately .003. A
paper coffee cup of shavings was a good days work.
*
I still have the scrapers I made for all that. Drew out some 6150 to about
1" X 24" X ~ 3/16 and brazed some carbide on the end. Made about a half
dozen to get one with just the right feel.

In article , TreeMoose says...

Then you turn one of
the plates 180 degrees and start all over.

I always thought it had to be 90 degrees. A saddle
error will not resolve for a full 180 rotation,
right?

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

In article , Mark Rand says...

For true planes you have to go to the primary method of generation which is
the theory that the only surface which can be congruent to an identical
surface in all orientations is the plane surface and the corollary that the
only surface which can be congruent to its reflection in all orientations is a
plane surface. This means scraping three surfaces against each other. Anything
else is an approximation..

The 'in all orientations' part is quite critical. This is
why a) surface plates generated this way are either round
or square, not rectangular. And b) why there has to be
a 90 degree rotation during the scraping/spotting cycle.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

jim rozen


TreeMoose
Then you turn one of
the plates 180 degrees and start all over.

Jim
I always thought it had to be 90 degrees. A saddle
error will not resolve for a full 180 rotation,
right?

Well, the old, old texts don't have any answer.

In case anyone's still interested:
The accuracy of cast iron surface plates, based on the three-plate scraping
method, is not one person's invention. That it was employed by English
mechanics during the 1700s, before the time of identifying method to person, is
sure.

Its systematic use is identified with Henry Maudslay by Samuel Smiles (the
great nineteenth-century English biographer of early industry), through whom
Joseph W. Roe, the author of "English and American Tool Builders," took much of
his content.

In any case, some of the early info on surface-plate generation comes from
James Nasmyth, an apprentice of Maudslay, who wrote

"The importance of having Standard Planes caused him [i.e., Maudslay] to have
many of them placed on the benches beside his workmen, by means of which they
might at once conveniently test their work. Three of each were made at a time
so that by the mutual rubbing of each on each the projecting surfaces were
effaced. When the surfaces approached very near to the true plane, the still
projecting minute points were carefully reduced by hard steel scrapers, until
at last the standard plane surface was secured. When placed over each other
they would float upon the thin stratum of air between them until dislodged by
time and pressure. When they adhered closely to each other, they could only be
separated by sliding each off each. This art of producing absloutely plane
surfaces is, I believe, a very old mechanical 'dodge.'

Nothing as to plate rotation in the scraping sequence. (Obviuously not a
technical text, either)
I suspect Moore's method may have added some footnote, with its 90 deg.,
square plate rotation consideration.

As TreeMoose points out, at some point you need to scrub the accuracy of the CI
plate, and frost it for use.

Cast iron has long lost its status as an ultimate measurement medium, in any
case.
Frank Morrison
(who still has a IC surface plate)

"Fdmorrison" wrote in message
...
jim rozen


TreeMoose
Then you turn one of
the plates 180 degrees and start all over.

Jim
I always thought it had to be 90 degrees. A saddle
error will not resolve for a full 180 rotation,
right?

Well, the old, old texts don't have any answer.

Jim is right, if you get the rotations wrong in a certain way, you wind up
with anticlastic saddles. I made a model of this once, in thin cardboard,
and wrote down the required rotations. I think it's 180 deg. between one and
two and one and three, and then 90 deg first (and then 180 deg) between two
and three. Or something like that. g

My uncle made a set of three aluminum plates, 6 in. square, to demonstrate
this. You can make the saddle quite pronounced if you work at it. But you
have to be a real bungler to do it by accident.

Ed Huntress

On 21 Aug 2003 21:30:24 -0700, jim rozen
scribed:

Hey all:

Great thread!

When I worked in Switzerland as an apprentice, we would lap Stainless
Steel height gage bearing surfaces down to near millionths flatness
using a chunk of (relatively flat) cast iron with some deep file
scores in it... And diamond paste...

Think of a cast iron gauge stand, take off the column, scratch a few
deep lines in it with a file edge, criss-cross, slap some diamond
paste and kerosene on the work surface and go to town... Took a few
hours or so, but with the fine paste, kerosene as a lubricant, we
could achieve some pretty good results... A nearly mirror finish, with
exceptional flatness. 1st hour was getting all the high spots, 2nd
hour was to polish it with the slurry, last hour was to dilute the
paste enough to get a nice polish on the column.

Goal was to get 1um flatness over 600mm in the checking fixture...

OBT Priceless: Cleaning the lapping slurry out of every nook and
cranny of your body after lapping a few of these a day...Ugh...

Best,

Fred

In article , Dave Baker says...

By lapping 3 plates against each other with grinding paste until all three are
flat. The same way as reference plates are made now. The ancients could make a
plate as flat as we can now. The technique requires no special technology.

Not strictly true, Dave. Read the description about flat
surface generation in Moore's book, they go into considerable
detail on this.

1) they use cast iron plates, specially ribbed and supported.

2) the square plates are spotted against each other with a
marking medium, and are hand scraped to each other.

3) the exact sequence of operations matters, and there is 90
degree rotation included between each cycle. This prevents
a saddle error from developing.

4) once the plates are spotted and hand scraped as well as
possible, each plate is then futher corrected using several
additional steps, to get down to roughly one micron flatness
level. Unless one includes these steps, they say that ten
or so microns is all that can be achieved.

Probably the *most* important technologies that we have, that
were not available to the 'ancients' are a) more accurate
metrology, and b) temperature controlled environments for
doing the measuring in. The second is probably the most
important.

Moore's book give considerable engineering detail about what
is now pretty trivial stuff, but when the book was written is
was state of the art, he talks about feedback loop control
of HVAC systems in their plant.

Jim

================================================= =
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
================================================= =

Tony's precision scraping page:


http://www.csgnet.net/toolroom/scrape1.htm

http://www.csgnet.net/toolroom/scrape2.htm

http://www.csgnet.net/toolroom/power.htm