Is there a consolidated opinion on the amount to nudge a piece of work
sitting in prussian blue in order to encourage marking? Procedurally
I have been using (in compass points) 1 inch north, then 1 inch south,
then 1 inch east, then 1 inch west. I use the rubber handle tips of a
pair of needle nose pliers to apply the force as much as possible to
either the x or y axis (e.g. with no pushing down on the piece). Is
this a good procedure, or should I try something different? (BTW -
when I do no nudging whatsoever, there appear some number of dots on
the surface, but so faint that I often need a magnifying glass in good
light to see them. The dots using the method outlined above are good
- but more smudges than dots. This fact is bothersome, I think. The
examples I have seen are clearing circular-ish dots).

Also, I have a light piece I am working on - 6 inches by 3 inches by
3/8 inch. I found that it does not mark well. Noticing the type of
surface plates and other things that are usually scraped, I think
usually the work is much heavier. Therefore I tried placing a couple
of matching pieces of the work on top after it is placed in the blue.
I seem to get a much more uniformly good marking. Is this procedure
acceptable? When the piece is not weighted, there are times that when
nudged, it will ride the surface like an air hockey puck with just the
lightest of nudges and I have to grab it to keep it from going off the
side. I think there is some sort of air pocket induced when this
light work is not weighted....

Thanks in advance. I have read every scraping post on this group and
now I can say that my eyes are as bleary as my hands blue. I have
spent an amount of time on this "effort" to which I am almost becoming
embarassed to admit. But now it is a matter of pride. This work will
go flat! So any help or opinions would be greatly appreciated.

it will ride the surface like an air hockey puck with just the
lightest of nudges

It sounds to me like you are using too much blue compound.

ss wrote:
Is there a consolidated opinion on the amount to nudge a piece of work
sitting in prussian blue in order to encourage marking? Procedurally
I have been using (in compass points) 1 inch north, then 1 inch south,
then 1 inch east, then 1 inch west. I use the rubber handle tips of a
pair of needle nose pliers to apply the force as much as possible to
either the x or y axis (e.g. with no pushing down on the piece). Is
this a good procedure, or should I try something different? (BTW -
when I do no nudging whatsoever, there appear some number of dots on
the surface, but so faint that I often need a magnifying glass in good
light to see them. The dots using the method outlined above are good
- but more smudges than dots. This fact is bothersome, I think. The
examples I have seen are clearing circular-ish dots).

It depends on the condition of the piece. But, you may have too
much dye on the surface plate. You want it VERY thin. I use my
hands to move the part, not tools. I sometimes lift up to reduce the
downforce, if the part is very heavy. Other times, especially when
the spin test shows a convex part, I will press down on one end and
lift up on the other, to show where the highest spot is. The spin
test is simply to see if the part will swivel on its center. If it
swivels, there is a pronounced hi spot in the middle of the part.
By moving the part in all 4 directions, you force both ends to
touch down as the part rocks, making you think it is roughly flat.
The press down/lift up trick will cause marking on only half the
part, if it is convex. The mark closest to the center is the
highest spot. Just scrape there, and repeat. I usually use a
circular or oval movement, and often make 3 circles of the part.
(That is an orbiting motion, not actually spinning the whole piece.)
Again, it depends on the condition, and what the marks have been
looking like.

I have stopped using the Prussian blue, it is just too messy (and
long lasting on the hands.) I use Canode dye, which is made for
marking & scraping purposes. It is not as good as the Prussian blue,
as it will ball up after being on a surface plate for a while.
(I guess that means there is latex in it.) But, it washes off,
and I find the performance of the stuff to be quite good, otherwise.
I spread it out with a rubber roller called a "Speedball Brayer"
apparently available at any art supply outfit.

One thing that may work just a little better with the Prussian blue is
the variations in the density of the mark. Modest high spots that
are just high enough to touch the dye get a dark mark. Higher
spots that really support the part by contact through the dye
to the surface plate leave a thinner mark in the center, with a dark
ring around it. Sometimes you also get a brown or gray color to it,
as some iron has rubbed off and mixed with the dye. These are the
highest spots, and more attention should be made to those marks.


Also, I have a light piece I am working on - 6 inches by 3 inches by
3/8 inch. I found that it does not mark well. Noticing the type of
surface plates and other things that are usually scraped, I think
usually the work is much heavier. Therefore I tried placing a couple
of matching pieces of the work on top after it is placed in the blue.
I seem to get a much more uniformly good marking. Is this procedure
acceptable? When the piece is not weighted, there are times that when
nudged, it will ride the surface like an air hockey puck with just the
lightest of nudges and I have to grab it to keep it from going off the
side. I think there is some sort of air pocket induced when this
light work is not weighted....

When you get it very flat, the air bearing effect can be pronounced.
Also, when it bites through the air, and sticks to the dye, you almost
need tools to pry it off!

If you are trying to get it absolutely flat, so that you get a
consitent blue color across the entire part, dream on! You will never
get there. This will achieve a flatness of about 10 uInches across
the part, which has no use unless you are trying to make your own
gauge blocks. Getting .0001" flatness is fairly easy, and it sounds like
you may be there, already.

Jon

"Tfmccarley" wrote in message
...
it will ride the surface like an air hockey puck with just the
lightest of nudges

It sounds to me like you are using too much blue compound.

"do no nudging whatsoever, there appear some number of dots on
the surface, but so faint that I often need a magnifying glass in good
light to see them"

or not enough blue. blue is the consistency of oil paint and would tend to
be sticky instead of allowing something to float. If your surface plate is
flat it doesn't much matter how much or in what direction you move it as
long as you move it through a the blue enough so the reading is effected by
any differences in how thick the blue is at various places on the plate.
3x6 is plenty big enough to scrape. I don't know why you'd expect dots
rather than smudges.

imo you're making this too complicated, the principal simple, you are using
paint to indicate where one piece isn't flat by comparing it to a flat
piece. spread some blue on the plate, lightly grip the work by the edges
and move it around. The spread of blue will be heavier when you start which
is more aggressive and as you to get it closer to the finished state, the
lesser amount of blue left on the plate will show more detail. If you are
getting a circle of blue, either your plate has a high spot, or the blue
isn't even close to evenly covering the plate. don't weight it down, you're
just bending it to the shape of the plate. think about it - how is bending
the work to the plate going to show you what's high and low?

two things to consider 1) if the piece is so flimsy that you're concerned
about your grip distorting it (i.e., why are you using tweezers), what's the
point of scraping it? its going to bend in use or conform to what ever
shape its bolted to, and 2) this is a flat thin piece, there may be enough
internal stresses that its constantly changing shape, it least enough to
mess you up trying to scrape it down to a tenth of a thou (which may be the
case if you're putting the blue on so lightly you can barely see it). You
don't say what material it is, but I'd use cast iron if you have a choice.
What is the intent anyway for this piece??

In article , Michael says...

imo you're making this too complicated, the principal simple, you are using
paint to indicate where one piece isn't flat by comparing it to a flat
piece. spread some blue on the plate, lightly grip the work by the edges
and move it around. The spread of blue will be heavier when you start which
is more aggressive and as you to get it closer to the finished state, the
lesser amount of blue left on the plate will show more detail.

Well, it is a *bit* complicated. But mostly 'feel.'

Like you say, the amount of blue on the surface plate
(and its consistency) really matters.

For starting out, when I am roughing a piece, I tend
to have the prussian blue fairly heavy on the plate
and also fairly sticky, or thick.

By heavy, I would mean a dab or two on the plate,
not cut with any oil, and spread around evenly by
gloved hand.

Then the part is pretty much just touched down, and
the real high spots get a pretty deep blue mark.

As time goes on and the part gets flatter and flatter,
I try to reduce the amount of marking medium and also
to thin it out a bit more with some wd-40 so the
consistency is more even and thin. Then I need to
move the part around more to get a decent mark, but
the mark is still much lighter and shows finer
detail than in the example above.

I've found that most of my mistakes in the beginning
were using the wrong degree of marking, ie. I would
be trying to spot very finely and accurately, when I
had a thousanth or two to move. Or, using too much
marking compound when the part is very flat. Then
it just shows up all blue, there's no contrast.

Jim

==================================================
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==================================================

In my very limited experience in scraping I found the most critical factor
in getting good high spot indications with prussian blue film was the
eveness and thickness with which it was spread. A gloved finger (not
fabric) seemed to work the best for me. I never tried a roller.

John.

"jim rozen" wrote in message
...
In article , Michael says...

imo you're making this too complicated, the principal simple, you are using
paint to indicate where one piece isn't flat by comparing it to a flat
piece. spread some blue on the plate, lightly grip the work by the edges
and move it around. The spread of blue will be heavier when you start
which
is more aggressive and as you to get it closer to the finished state, the
lesser amount of blue left on the plate will show more detail.

Well, it is a *bit* complicated. But mostly 'feel.'

Like you say, the amount of blue on the surface plate
(and its consistency) really matters.

For starting out, when I am roughing a piece, I tend
to have the prussian blue fairly heavy on the plate
and also fairly sticky, or thick.

By heavy, I would mean a dab or two on the plate,
not cut with any oil, and spread around evenly by
gloved hand.

Then the part is pretty much just touched down, and
the real high spots get a pretty deep blue mark.

As time goes on and the part gets flatter and flatter,
I try to reduce the amount of marking medium and also
to thin it out a bit more with some wd-40 so the
consistency is more even and thin. Then I need to
move the part around more to get a decent mark, but
the mark is still much lighter and shows finer
detail than in the example above.

I've found that most of my mistakes in the beginning
were using the wrong degree of marking, ie. I would
be trying to spot very finely and accurately, when I
had a thousanth or two to move. Or, using too much
marking compound when the part is very flat. Then
it just shows up all blue, there's no contrast.

Jim

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

On 17 Oct 2003 13:57:36 -0700, jim rozen
wrote:

In article , Michael says...

imo you're making this too complicated, the principal simple, you are using
paint to indicate where one piece isn't flat by comparing it to a flat
piece. spread some blue on the plate, lightly grip the work by the edges
and move it around. The spread of blue will be heavier when you start which
is more aggressive and as you to get it closer to the finished state, the
lesser amount of blue left on the plate will show more detail.

Well, it is a *bit* complicated. But mostly 'feel.'

Like you say, the amount of blue on the surface plate
(and its consistency) really matters.

For starting out, when I am roughing a piece, I tend
to have the prussian blue fairly heavy on the plate
and also fairly sticky, or thick.

By heavy, I would mean a dab or two on the plate,
not cut with any oil, and spread around evenly by
gloved hand.

Then the part is pretty much just touched down, and
the real high spots get a pretty deep blue mark.

As time goes on and the part gets flatter and flatter,
I try to reduce the amount of marking medium and also
to thin it out a bit more with some wd-40 so the
consistency is more even and thin. Then I need to
move the part around more to get a decent mark, but
the mark is still much lighter and shows finer
detail than in the example above.

I've found that most of my mistakes in the beginning
were using the wrong degree of marking, ie. I would
be trying to spot very finely and accurately, when I
had a thousanth or two to move. Or, using too much
marking compound when the part is very flat. Then
it just shows up all blue, there's no contrast.

Jim

================================================= =
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
================================================= =
Greetings Jon and Jim,
I have been trying, with a carbide scraper, to scrape a little. I have
read that book about machine tool rebuilding by Connely. But it seems
to take a lot of force. I do have bad wrists so maybe it is not as
hard as I think. I have looked at one page about scraping that has
been posted several times here but it doesn't tell me enough. Could be
that I'm just dense. Anyway, can either of you point me to a place for
some better info? I did try to order that video and book from Michael
but he was never able to respond I guess.
Cheers,
Eric R Snow

Thanks for the insights.

be sticky instead of allowing something to float. If your surface plate is
flat it doesn't much matter how much or in what direction you move it as
long as you move it through a the blue enough so the reading is effected by
any differences in how thick the blue is at various places on the plate.

If there was a high spot and I moved the piece too much, I just
assumed that after a certain point, too much blue would cling such
that it would spread to a neighboring low spot and affect the reading.
I was trying to control the degrees of freedom in my procedure.

3x6 is plenty big enough to scrape. I don't know why you'd expect dots
rather than smudges.

Both the scraping video demo (machinerepair.com??) and the tony's
precision scraping page show dots that are clearly circularish. These
are the only markings that I have seen, other than my own. As an
aside, I did try cutting the blue with oil, and now the paint is very
smooth and the marking is much more than what I expected. Without the
oil, I noticed that small clumps would form on the plate and roller
that had to be periodically removed. With the oil in the mix, I can
spread it with no clumping, and arbitrarily thin.


imo you're making this too complicated, the principal simple, you are using

I agree 100%.

paint to indicate where one piece isn't flat by comparing it to a flat
piece. spread some blue on the plate, lightly grip the work by the edges
and move it around. The spread of blue will be heavier when you start which
is more aggressive and as you to get it closer to the finished state, the
lesser amount of blue left on the plate will show more detail. If you are
getting a circle of blue, either your plate has a high spot, or the blue
isn't even close to evenly covering the plate. don't weight it down, you're
just bending it to the shape of the plate. think about it - how is bending
the work to the plate going to show you what's high and low?

That is a good point. I wasn't trying to bend, just kind of eliminate
any hydroplaning or air-pocket riding. I tried doing a thought
experiment with the 2 extremes - light and heavy. I thought that it
should be possible to scrape a coin, like a quarter, but that a piece
this light might ride the paint a bit. Also, I see that a lot of
scraping goes on with 100+ pound surface plates. Therefore I figured
that weighting it a bit should not change the reading, but might
eliminate any float. I am pretty new to all of this, so my logic
might be a bit warped....


two things to consider 1) if the piece is so flimsy that you're concerned
about your grip distorting it (i.e., why are you using tweezers), what's the
point of scraping it? its going to bend in use or conform to what ever
shape its bolted to, and 2) this is a flat thin piece, there may be enough
internal stresses that its constantly changing shape, it least enough to
mess you up trying to scrape it down to a tenth of a thou (which may be the
case if you're putting the blue on so lightly you can barely see it). You
don't say what material it is, but I'd use cast iron if you have a choice.
What is the intent anyway for this piece??

The piece started as hot rolled steel (I think). It's intent is
twofold, one as a practice scraping piece, and two as the part of the
carriage on the Gingery lathe that rides the ways (that is if I don't
practice scrape it down to nothing!). I don't know anything about the
metallurgy in general, or about the suitability of this piece for the
purpose, I just know that it is the only metal I can reasonable get
right now (I am overseas). Any comments on practicality would be
appreciated.

As time goes on and the part gets flatter and flatter,
I try to reduce the amount of marking medium and also
to thin it out a bit more with some wd-40 so the
consistency is more even and thin. Then I need to
move the part around more to get a decent mark, but
the mark is still much lighter and shows finer
detail than in the example above.

I've found that most of my mistakes in the beginning
were using the wrong degree of marking, ie. I would
be trying to spot very finely and accurately, when I
had a thousanth or two to move. Or, using too much
marking compound when the part is very flat. Then
it just shows up all blue, there's no contrast.

I have found exactly the same thing. I have just discovered using
oil in the mix, and it makes a big difference. As a beginner, I
never gave much thought to the paint. Paint is paint,right?
But I don't think the batch of paint I have can be spread very very
thin - it is just too thick and clumpy at that level. But with a
drop or two of oil, I can now smooth out the paint very nicely.

Greetings Jon and Jim,
I have been trying, with a carbide scraper, to scrape a little. I have
read that book about machine tool rebuilding by Connely. But it seems
to take a lot of force. I do have bad wrists so maybe it is not as
hard as I think. I have looked at one page about scraping that has
been posted several times here but it doesn't tell me enough. Could be
that I'm just dense.

The Connelly book is too old and not terribly specific about the
tools available now. As for force, it should not take much force
to scrape cast iron. I scraped in the Michael Morgan straightedge,
and it took a long time, my wrists DID get tired, but not very
quickly. I could scrape for 3 hours at a stretch before I was sore.

I am now scraping a lathe cross slide that is cast steel, and was
flame sprayed with hard Chrome. The scraper blade literaly could
not even scratch the Chrome, but it scrapes the steel pretty nicely
now that I've rubbed the Chrome off with a Cratex grinding wheel.
(I had to remove the Chrome because the flame spraying operation
warped the part!) I can only scrape this part about an hour at a time,
it takes more force than cast iron.

But, if your iron part is too hard to scrape, there must be something
wrong with your scraping blade. It should be flat and polished on the
wide sides, and have a very wide radius on the end. You hold the
tool nearly flat to the work and push it in small strokes across the
surface. The first pass or two are harder, as there are lots of
hills to dig into. You approach the work from varying directions
each pass to prevent rows of hills from developing. Once the
surface begins to flatten out, it gets pretty easy to do the scraping,
and it shouldn't take much downforce to make the tool bite lightly
into the work. You don't want to take cuts like a lathe or shaper
tool! You should get dust mixed with the spotting dye, but never
curly chips, except on the first pass of a badly roughed piece.
If you need to make chips, do that work with a powered machine,
like a mill or shaper, and leave the last .001" or less for the
scraping.

And, if you are trying to hand scrape a steel part, you certainly want
to anneal it first!

Let us know a little more about what you are trying to so, and maybe
we can offer more specific help.

Jon

In article , Eric R Snow says...

I have been trying, with a carbide scraper, to scrape a little. I have
read that book about machine tool rebuilding by Connely. But it seems
to take a lot of force. I do have bad wrists so maybe it is not as
hard as I think. I have looked at one page about scraping that has
been posted several times here but it doesn't tell me enough. Could be
that I'm just dense. Anyway, can either of you point me to a place for
some better info? I did try to order that video and book from Michael
but he was never able to respond I guess.

That's a shame. Most of the practical advice for this,
I got from Michael's book. I purchased the connely book
quite a while ago, but IMO it does not give much real
information on the very basic aspects of hand scraping,
like how to sharpen the tool or how to use it. The
sort of things that one would learn as an apprentice,
for example. The connely book is great at the higher
order stuff, like how to re-work an entire milling
machine, what to do in what sequence and so on. But
not, 'this is how you make a piece of cast iron flat,
starting with a dull scraper, a tube of prussian blue,
a surface plate, and some un-flat cast iron.'

Is he really out of the business of supplying those books
and videos?

Jim

==================================================
please reply to:
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==================================================

In article , Jon Elson says...

The Connelly book is too old and not terribly specific about the
tools available now.

Yes. As I mentioned before, it does not do a very
good job of explaining the *real* basics of how to
take a stroke with a scraper, or how to sharpen one.

But, if your iron part is too hard to scrape, there must be something
wrong with your scraping blade. It should be flat and polished on the
wide sides, and have a very wide radius on the end.

This was really, really non-intuitive for me. I had tried
to make a small scraper blade from HSS toolbits before having
read Morgan's book, and it bore no resemblance at all to
what he showed they are supposed to look like. It was not
clear to me, either, that the correct blade would perform
at all in the way it should (but of course they do) from
a preliminary examination.

I guess what suprised me is that all of the hand scraper
operations are *negative* rake cuts. The rounded end
of the blade is is ground such that the cutting edge is
formed between the side of the blade, and the end surface
that the user grinds into it.

And that the end surface is really two two grinds that meet
along the centerline of the blades thickness, and the
actual cutting edge is slightly more than 90 degrees.
That, combined with the angle that the scraper makes
with the workpiece, gives a large negative rake angle on
the cut. And I was suprised at how well one can remove
metal with such a configuration.

You hold the
tool nearly flat to the work and push it in small strokes across the
surface. The first pass or two are harder, as there are lots of
hills to dig into. You approach the work from varying directions
each pass to prevent rows of hills from developing. Once the
surface begins to flatten out, it gets pretty easy to do the scraping,
and it shouldn't take much downforce to make the tool bite lightly
into the work. You don't want to take cuts like a lathe or shaper
tool! You should get dust mixed with the spotting dye, but never
curly chips, except on the first pass of a badly roughed piece.
If you need to make chips, do that work with a powered machine,
like a mill or shaper, and leave the last .001" or less for the
scraping.

That's right, Morgan makes it clear that one has to have the
surfaces within a thousanth or so by other means, before scraping.
Also that grinding is a very poor way to prepare a surface for
hand scraping, as it gives local hard spots. As you say,
milling is prefered.

Jim

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==================================================

In article , ss says...

I have found exactly the same thing. I have just discovered using
oil in the mix, and it makes a big difference. As a beginner, I
never gave much thought to the paint. Paint is paint,right?
But I don't think the batch of paint I have can be spread very very
thin - it is just too thick and clumpy at that level. But with a
drop or two of oil, I can now smooth out the paint very nicely.

I am indeed using prussian blue *paint* from an artists supply
store. I also suspect this is not the best material, because
it has other substances in it (thickeners, dryers?) that make
it good for artists but maybe not the best for machinists.

But thinning it a bit with a non-drying oil - sometimes
I use wd-40, sometimes ATF - seems to make it work well.

But there are special purpose marking media shown in catalogs,
and I think I might try a small bit of that next time I get
into a hand scraping project, to see if it makes a difference.

Jim

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==================================================

"jim rozen" wrote in message
...
In article , Eric R Snow
says...

snip

Is he [Michael Morgan] really out of the business of supplying those books
and videos?

I had email from Michael a few weeks ago indicating that his Bridgeport
repair book was going into editing, but his web site seems to be dead.
Anybody else heard from him lately?

Mike

On 18 Oct 2003 09:00:30 -0700, jim rozen wrote:

snip

That's right, Morgan makes it clear that one has to have the
surfaces within a thousanth or so by other means, before scraping.
Also that grinding is a very poor way to prepare a surface for
hand scraping, as it gives local hard spots. As you say,
milling is prefered.


From recent experience you _can_ scrape down 5 thou or so. It just seems to
take about 25 times as much effort as starting at 1 thou. You really do have
to remember that you don't even think about accuracy until _all_ of the area
has shown blue at least once. Until that point, you don't really know how deep
the hollows are.


Mark Rand
RTFM