I have a Starrett precison level I think is not perfectly flat on the
bottom.
What is the proper procedure for checking the flatness of a part using
a surface plate? For example:
Do you coat the part with Prussian Blue? How, a finger tip, what
thickness?
How do you test it on the surface plate - press it down gently, slide
it, rotate it, what?
How would you prepare the surface plate - clean with alcohol, use a
damp kem wipe, what?
Do you test flatness on different sections of the surface plate?

I hope these are not to basic. Any other hints, tips, cautions, would
be sincerely appreciated.

Gil

geebee509 writes:

What is the proper procedure for checking the flatness of a part using
a surface plate?

Step one is, "buy or borrow a copy of Connelly's _Machine Tool
Reconditioning_".

Do you coat the part with Prussian Blue?

That works, and you can get it at an art supply place. But it is a
horrible, horrible mess to use, and not really any better than what I
improvised. It is toxic. It dries quickly (you don't want that for
marking/scraping). It stains your skin. It is impossible to completely
clean off of you or your tools.

I made my own compound by simply mixing red iron oxide pigment powder
with a little light machine oil. A tablespoon in an old candy tin would
be a lifetime supply for most people. Works great, cleans up with soap
and water, doesn't stain you chemically, doesn't dry out, not toxic.

How, a finger tip, what thickness?

Yep, rub it on the granite very thin. You'll quickly figure out how
much with practice.

Clean the stone first. Running your hand over the stone will be quite
sensitive to detect any debris.

How do you test it on the surface plate - press it down gently, slide
it, rotate it, what?

Set the part down without sliding, nudge it around a few millimeters,
and lift off, again without sliding. Again, practice and you'll see.

You need a way to vise the work without distorting it.

How would you prepare the surface plate - clean with alcohol, use a
damp kem wipe, what?

Not alcohol, you need a fast-drying, non-polar solvent. Paper towels,
and WalMart store brand camp stove fuel (cheapest source of naphtha) in
a Sure Shot sprayer. Don't get cheap on the paper towels. Wear old
clothes, they'll be ruined.

Do you test flatness on different sections of the surface plate?

The plate should be flat to better tolerance in all directions than you
will be able to scrape to, so it shouldn't matter what direction you're
marking from.

To clean up your hands, scrub with lots of liquid soap and a Scotch
Brite pad. Try not to scratch your nose while you're working!

It your work item is not flat, it is a bit hard to judge how much off it
is and where by simply marking, unless it is way off enough to, say,
slip feeler gages underneath.

Made my own scrapers just as good as the hideously priced European
imports: handles by flattening and drilling the end of 1/2 EMT, and
epoxying a sphere (found as: old trackball, craft shop "doll heads", old
billiard balls) to the other end. For the bit I used 1/8 x 1 inch mild
steel bar, with a carbide strip brazed on the tip (refill from Warner
scraper from paint dept at Lowes). Cadmium braze and flux from
Grainger.com brazes carbide to steel with just a propane torch. Grind
the carbide square, on a round radius of about 6" inches or less (that
is, the plan view is shaped like the letter "D", with a sharp-cornered
blunt edge, not a knife edge); you'll need at least a green wheel on a
tool grinder, or a diamond wheel, for this. A sharp edge is critical,
so shortcuts won't do; you have to resharpen frequently, like every hour
or so. Before carbide they used just tool steel scrapers, but that
requires much more frequent sharpening. Scraping is simply pushing down
and away at a low angle, producing crispy crumbs on cast iron, or thin
shavings on steel, removing a fraction of a thou per scrape.

If this sounds good to you, I have lots of photos I took while scraping
my Bridgeport back to new, but never put onto my Web pages. Maybe if
there's any interest here I will do that.

Richard J Kinch writes:

You need a way to vise the work without distorting it.

I should explain, to hold it while you are *scraping* it, not while marking
it.

At the very least, can you put the pictures in the dropbox?

I'd use a dial indicator or electronic gage and height transfer
stand to locate the high or low points. I clean the surface plate
with naphtha.

geebee509 wrote:
I have a Starrett precison level I think is not perfectly flat on the
bottom.
What is the proper procedure for checking the flatness of a part using
a surface plate? For example:
Do you coat the part with Prussian Blue? How, a finger tip, what
thickness?
How do you test it on the surface plate - press it down gently, slide
it, rotate it, what?
How would you prepare the surface plate - clean with alcohol, use a
damp kem wipe, what?
Do you test flatness on different sections of the surface plate?

I hope these are not to basic. Any other hints, tips, cautions, would
be sincerely appreciated.

Gil

geebee509 wrote:

Do you coat the part with Prussian Blue? How, a finger tip, what
thickness?

You coat the plate with touching blue (I think you call it that way).
About a fingertip on wipe that you spread over the plate (area where you
want to touch).
The thicker the blue is, the less precise results you get. Imagine
having a layer of 1mm on the plate.*) :-))


How do you test it on the surface plate - press it down gently, slide
it, rotate it, what?

Gently lay the part on the plate. Move part with little circular or
longitudinal (depending on shape of part) gentle movements. Try not to
tilt the part or you will get false results. If the part tilts/rocks,
you might get it roughly in shape using a straight edge before
proceeding with the plate.
Touching surfaces _can_ get very tricky!


How would you prepare the surface plate - clean with alcohol, use a
damp kem wipe, what?

There are special cleaning agents. I use petroleum.


Do you test flatness on different sections of the surface plate?

Not on mine, I know that it is flat everywhere. :-)

*)
I have seen that in a report about a famous airplane manufacturer when
they fitted wings to the body. I won't tell names to protect our
European industry. ;-)


HTH,
Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO // Eigenbau-Digitalanzeige
http://www.yadro.de

geebee509 wrote:
I have a Starrett precison level I think is not perfectly flat on the
bottom.
What is the proper procedure for checking the flatness of a part using
a surface plate? For example:
Do you coat the part with Prussian Blue? How, a finger tip, what
thickness?
How do you test it on the surface plate - press it down gently, slide
it, rotate it, what?
How would you prepare the surface plate - clean with alcohol, use a
damp kem wipe, what?
Do you test flatness on different sections of the surface plate?

I hope these are not to basic. Any other hints, tips, cautions, would
be sincerely appreciated.

Gil


Put a tiny speck of prussian blue on the surface plate after a very
thorough cleaning. Wipe the plate 3 times with your fingers to detect
any speck of dust before applying the dye. If you can find a "speedball
brayer" (used in the printing and silkscreen industries) this is the
best thing ever to spread the dye evenly.

The coating will be about .0001" thick for this type of work!
The part to be tested has to be completely clean of dust specs,
again, use your fingertips to make a last test of the part before
placing it on the plate. Place the part very gently on the plate,
do NOT press down at all, and move it sideways by pressing against
the bottom. You want to slide it, not rock it. Then lift off from
one corner, or just straight up for small items like this.

You can also test the part on the clean part of the plate (no dye
needed) with the "spin test". Place the part and gently turn it
from one end. If it pivots around the far end, the part is concave,
which is good for scraping. If it pivots around the middle, it is
convex, and will rock and give a false reading when tested with dye,
unless you take precautions to prevent it.

I have some chemical surface plate cleaner. I think it is mostly
detergent and water, but I don't know exactly. I suspect alcohol will
work fine. Watch out for all types of wipes, they leave lint. You have
to remove the lint after the plate dries. A tiny speck of grit or lint
will completely foul up a reading of this type.

If your surface plate is in good condition, you don't need to test at
different locations. Most granite surface plates, even cheap ones, are
incredibly flat. You have to test diagonally across the entire plate to
find any error of significance. Cast Iron plates, on the other hand,
can warp and wear over time, and can't be trusted until you have
verified their accuracy.

Jon

Prussian blue is for depressed Teutonics machinists. Get some water based
marking compound from Dapra
http://www.dapra.com/biax/scrapers/accessories.htm

MSC will drop ship it for you.

Starrett seems to scrape their precision levels so the base is not flat, but
has a gentle curve so the bottom actually hogging. If you want a flat base
you would have to grind or scrape yourself, thats what I did.

Tony


"geebee509" wrote in message
ups.com...
I have a Starrett precison level I think is not perfectly flat on the
bottom.
What is the proper procedure for checking the flatness of a part using
a surface plate? For example:
Do you coat the part with Prussian Blue? How, a finger tip, what
thickness?
How do you test it on the surface plate - press it down gently, slide
it, rotate it, what?
How would you prepare the surface plate - clean with alcohol, use a
damp kem wipe, what?
Do you test flatness on different sections of the surface plate?

I hope these are not to basic. Any other hints, tips, cautions, would
be sincerely appreciated.

Gil

Richard,
Thank you for the detailed information. I would be very interested in
your pictures as I'm certain others would. Please post them if you
will.
Thanks,
Gil

Jon,

That's a good tip on the brayer. I wondered how to get a smooth
coating. Too thick and you get a false reading. Think I'll buy one. For
15 bucks it sounds like a good tool if you're going to blue the plate
often.

Does your chemical cleaner remove the blue stain from the surface
plate? Mine left a blue tinge on the pink surface!!! I hate when that
happens.

The KimWipes (I misspelled it earlier) are low lint, non-abrasive,
delicate surface wipes made by Kimberly Clark.I thought they would be
suitable for cleaning but I would be interested in what you would
suggest.

I see your point on using the spin test. It would be easy to rock the
part and get a false reading. You'd end up scraping and having it get
worse.

Sounds like you've been there and done that. It's tips like these I
wanted to get. Many thanks.

Gil

"Richard J Kinch" wrote in message
. ..

| To clean up your hands, scrub with lots of liquid soap and a Scotch
| Brite pad. Try not to scratch your nose while you're working!

In the factory washrooms they keep taking the Scotchbrite pads out, and
I hear that they're really bad for you. Don't know why, I don't get myself
that dirty usually.
The other option for stubborn stains is hand lotion. Seems to get the
most aggressive sealants right off your hands.

"geebee509" wrote in message
ups.com...
Jon,

That's a good tip on the brayer. I wondered how to get a smooth
coating. Too thick and you get a false reading. Think I'll buy one. For
15 bucks it sounds like a good tool if you're going to blue the plate
often.

Does your chemical cleaner remove the blue stain from the surface
plate? Mine left a blue tinge on the pink surface!!! I hate when that
happens.

The KimWipes (I misspelled it earlier) are low lint, non-abrasive,
delicate surface wipes made by Kimberly Clark.I thought they would be
suitable for cleaning but I would be interested in what you would
suggest.

I see your point on using the spin test. It would be easy to rock the
part and get a false reading. You'd end up scraping and having it get
worse.

Sounds like you've been there and done that. It's tips like these I
wanted to get. Many thanks.

Gil

Before you do any scraping or other alteration, it is a good idea to repeat
your test in a different orientation and/or with a different method to be
sure your indications are not the result of your technique rather than an
actual fault.
Don Young

On Wed, 19 Apr 2006 00:34:55 -0500, Richard J Kinch wrote:

snip


If this sounds good to you, I have lots of photos I took while scraping
my Bridgeport back to new, but never put onto my Web pages. Maybe if
there's any interest here I will do that.


Yes please! It may give me some tips and encouragement for when I have to do
my Beaver VBRP mill.


Regards
Mark Rand
RTFM

On Wed, 19 Apr 2006 00:34:55 -0500, Richard J Kinch
wrote:



Not alcohol, you need a fast-drying, non-polar solvent.

Why is a non-polar solvent preferred? Which solvents are polar
besides alcohol and water?

Don Foreman writes:

Not alcohol, you need a fast-drying, non-polar solvent.

Why is a non-polar solvent preferred?

I assume the marking compound base is non-polar: linseed-oil-based prussian
blue, my shopmade iron-oxide-in-light-machine-oil.

As someone else pointed out, there are water-based marking compounds, which
would be solved by water or ethanol.

I prefer the machine oil marking compound, since it doesn't dry out like
water-based or artist paints. When you have a sub-thousandth layer, it
dries quickly.

A brayer is OK to spread it, but your fingertips are more accurate and
even, if you aren't squeamish about clean-up.

What's that Lassie? You say that geebee509 fell down the old
rec.crafts.metalworking mine and will die if we don't mount a rescue
by 18 Apr 2006 18:57:29 -0700:

I have a Starrett precison level I think is not perfectly flat on the
bottom.
What is the proper procedure for checking the flatness of a part using
a surface plate? For example:
Do you coat the part with Prussian Blue? How, a finger tip, what
thickness?

Prop your part up on 1-2-3 blocks, like you are making a bridge.
Get a test indicator, mounted on a stand, and run the tip on the
underside of your part.

If your surface plate is flat, and your 1-2-3 blocks are matched, you
should be able to read how flat it is.

Dan H.
--

Dan

geebee509 wrote:

Jon,

That's a good tip on the brayer. I wondered how to get a smooth
coating. Too thick and you get a false reading. Think I'll buy one. For
15 bucks it sounds like a good tool if you're going to blue the plate
often.

Does your chemical cleaner remove the blue stain from the surface
plate? Mine left a blue tinge on the pink surface!!! I hate when that
happens.

The KimWipes (I misspelled it earlier) are low lint, non-abrasive,
delicate surface wipes made by Kimberly Clark.I thought they would be
suitable for cleaning but I would be interested in what you would
suggest.

I see your point on using the spin test. It would be easy to rock the
part and get a false reading. You'd end up scraping and having it get
worse.

Sounds like you've been there and done that. It's tips like these I
wanted to get. Many thanks.

Gil

Get some shim stock and put a couple of thou. under each end. Then use
another piece and run it under the piece. You can feel the high and low
spots very easily. Unless you have a little experience in scraping and
measuring you can get the wrong readings by looking only at the spotting
on the surfaces. Also, any dirt, dust or anything on the surface will
screw up your readings and blueing transfer.



John

carl mciver wrote:

"Richard J Kinch" wrote in message
. ..

| To clean up your hands, scrub with lots of liquid soap and a Scotch
| Brite pad. Try not to scratch your nose while you're working!

In the factory washrooms they keep taking the Scotchbrite pads out, and
I hear that they're really bad for you. Don't know why, I don't get myself
that dirty usually.
The other option for stubborn stains is hand lotion. Seems to get the
most aggressive sealants right off your hands.



I used to wear rubber gloves but bluing is like tar, no matter how hard
you try not to get any on you it will show up somewhere on your body.


John