Scraping Class, Part I (was Scraper's Elbow)
John Hofstad-Parkhill
Dennis Danich, (teacher), Me (idiot), Jim Quick (metal head) and Bruce
VanSloun (galoot)
Objective:
Make a 36" hand-scraped straight edge, of suitable quality for machine tool
rebuilding, but mostly for the joy of being able to accomplish such a feat
at all (see idiot).
Test Bed:
2" x 12" Cast iron parallel, rough machined (in every sense of the word) by
the now embattled Jet JMD-15 mill/drill.
The Tools & Materials
The Scrapers
The scrapers we are using are all the replacable tip kind, about 15.. 18" in
length. The blades are 3/4" and 1" wide with a radius that matches the biax
scraper gauge, in millimeters - might as well be miles. I think he said
somewhere around 90mm
In this case all the blades are HSS. Dennis uses carbide as well. I can't
grind carbide. Actually Dennis uses the Biax power scrapers.
I purchased a couple of the 10" scrapers from J&L, the one-piece made in
India variety. Dennis did not think they would work well, so they are not
currently in use (more on that later). The problem being they are too rigid
and not thin enough, at least at the working end.
I tried every catalog I have and was unable to come up with the replacable
blade scrapers. Enco used to carry them and Dennis says you can order them
by phone from Enco. I saw them in my old Enco catalog, that I no longer
have.
Dennis uses Anderson Bros. scrapers and speaks well of the Enco blades.
We are using the arm scraping technique, not hip scraping, or using your
body. This primarily due to his age & height... too hard on the back. I
think the bulbous handle scrapers are a bit more friendly in use than those
that look like an ordinary file handle.
The stone:
Oil stone, unknown grits (two sided), used exclusively for scrapers as
sharpening them rapidly wears a deep groove. I'd guess about a 200..240 grit
on one side, and about a 400 grit on the other. For my purposes I've been
using medium and fine diamond lapping plates.
GoJo:
One 4.5 lb cannister of hand cleaner. Used in lieu of cutting oil on the
stones. I've actually been trying it on the diamond and ceramic stones
myself. It does clean up nicely compared to water. I suspect the 4.5lbs will
outlast this project... and then some.
Marking compound:
(brand name worn away) #2243 Water Soluble Non Etching Die & Bearing Ink
Washes Off With Soap & Water from King-Way Technical, Inc. 10855 68th St.
So. Cottage Grove, MN 55016 (612) 459 9428. This bottle is so old, it may be
area code 651 by now. Also available from Dapra, the folks that market Biax
over here. Biax scrapers fetch about $1500, the scraper blade sets about
$300-$400 depending on the variety.
Dykem Hi-Spot Blue #107 (one tiny little tube)
Prussian Blue oil paint (from local graphics art supply)
Dennis likes his water soluble stuff, we found that the Dykem leaves a
sharper contrast that I found easier to pick out. It also dries rapidly when
compared to the others. Prussian Blue seems to serve very well, I can't find
any discernable difference in the markings between the Prussian Blue and
Dykem. Dykem contains (linseed?) that slows down drying to nearly a complete
halt.
Rags. Lots and lots of them.
Deburring stone, I'd guess about a 200..240 grit stone, flat.
Surface plate. In this case the only big one I have, a 24" x 18" Starrett
pink granite tool room surface plate.
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Sharpening the scraper.
The radius is gentle, as soon as I can measure it I'll post it as things
progress. Grinding is performed such that a small "V" is formed on the
cutting edge of the tool. Holding the tool straight in to the grinding
wheel, elevated to about 5-deg. and making a pass, then flipping the tool
over and making another pass at 5-deg will form this "V".
Honing. For right-handed folk, the handle is grasped in the left hand, the
other end is grasped with the right hand, near the cutting edge. The blade
is held perpindicular to the stone, but canted 5-degrees (to match the
grinding you just did... Duh). As you draw your right hand towards you, you
push away with your left hand, then reverse the motion, push away with your
right as you pull with your left. This makes the pivot point about the
center of the tool.
Also flatten the tool face on both sides, straight across in a side-to-side
motion, nearly flat with the stone, elevated about 2-degrees.
For early work, moving to the next finer grit should be all it takes. Later
you may want to work on a polish with a ceramic or very fine oil or water
stone.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Sidebar: The one-piece scraper from India exhibited a tendency to scratch
early and often, leaving the individual scrapes scarred. Bruce surmised that
it might be too brittle, heated the tip to a light straw to pull the temper
and we tried it again. Much improved. Light straw looks exactly like the
rest of the steel to my eyes. I cannot discern the difference. This made me
purse my lips.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
I attempted to modify one of the India scrapers to hold a blade. I ground
the sides fairly flat with respect to the shank of the tool and ground the
face of the tool such that a blade would lie flat. I softened it up - a
bit - so I could drill & tap 6-32. I then took a hunk out of a Stanley iron,
used for woodworking planes, thinking that it would hold a suitable edge for
scraping. I cut and filed it, then attempted to harden it. I took out my
array of BTU generating devices, from propane, mapp and mapp+O2. I heated
and quenched. Nothing. The cast iron laughed and chased the edge away,
significantly rounder and more burnished than before.
I then had Bruce try his hand, since he can see colors I cannot. Heated
steel until magnet no longer attracted, quenched. Still nothing. Won't get
hard. I find this very peculiar, bits of the Stanley logo were still
visible.
I gave up on that piece and obtained a 1" blade from Dennis. The whole thing
was hard as a damned rock, so I needed to anneal it enough to drill. So I
heated it, hot, then really hot and let it cool. Still hard as a rock.
Possibly it's cooling too fast, but I didn't want to lose the temper on the
cutting end. Managed to drill through it with some carbide tipped drills
(they weren't happy, one broke). Mounted it, ground it and honed it. The
working side is plenty hard and scrapes well. Success... sorta.
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The strokes. Dennis did the roughing strokes, long (width of the casting at
45-degrees) steady, perfectly spaced. Then repeated the same the opposite
direction, cross hatching the surface.
"breaking up the surface"
Still really roughing in. Aiming for a scrape, about 5/32" wide, much wider
than you might expect. To achieve this you can: 1) Drop the tool lower so
that it's closer to parallel to the work surface 2) Push down harder, or 3)
Re-hone the tool.
Equal strokes, angled in with rows set at 45-degrees, about 1/4" to 5/16"
long, with an ever-so-slight gap between each. Repeated in the opposite
direction to again effect a cross hatch.
Practice this until your brain hurts more than your arms. Then lay off, and
practice some more. Practice 8 hours/day until it's second nature. (this is
heresay)
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Spotting. Forget what Ed says about spreading blue with your fingers. Use a
small rag. Sure, 90% is soaked up in the rag, the results & speed are worth
every penny. Still use your fingers to detect any stray particles but apply
the stuff with a rag. I used good 'ol cotton of the t-shirt variety. Works
wonders.
Finding the real high spots and not the smears. Once you see one they're
fairly easy to find, at least for us at this stage of the game. Were quite a
distance from the finer points. They are identifiable by a distinct ridge
around the high spot. The tip of the high spot will be a lighter, somewhat
shiny blue, around the base of this little hill will be a ring of darker
blue. This is a true high-spot. This can also be uncovered by spotting the
piece on marking compound then taking the spotted piece to a clean section
of the surface plate and rubbing it again (this is an adaptation of the
other method of spotting where the surface being scraped has the bluing
applied to it). Anyway, the high-spots will really show up for you to see.
Making progress.
I'm now flipping between making regular passes across the entire surface
(practicing strokes) and spotting. I'm quite happy to report that I've not
yet hit a wall. Every time I run through a cycle I end up with more spots.
This tells me that I'm not doing everything wrong.
The elbow:
Still not sore. I think the lower angle of attack has something to do with
it. It's only been two days however.
Lighting. Have not hit on the perfect light supply. Often the spots are just
hard to see - at all. Or if I can see them, I can see them only from an
angle that prevents effective scraping (can't get to it).
There are still areas that scrape easier than others due to the way I'm
holding the scraper. Once you're over a large enough area things proceed
well. On edges or ends it's problematic, since I can't rest my left hand
(the guiding hand) on anything.
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Disclaimer: This account is my own world perception of what's happening
through Dennis's kind assistance. I don't offer it as a treatise on
scraping, but only as helpful bits of information that may help you fill in
the rest of the story.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Scraping Video: It's not my idea, I've got nothing to do with the scraping
video. It's Dennis and Guy Lautard. I offered to pick up recommendations on
Dennis' behalf so that those of you who may actually fork over for the video
might have some suggestions, ideas, i.e. I N P U T into how it might take
shape. I told Dennis I would forward any suggestions you may have
mull...@advinc.com
"John Hofstad-Parkhill" <jhpar...@sihope.com> wrote:
> Finding the real high spots and not the smears. Once you see one they're
> fairly easy to find, at least for us at this stage of the game. Were quite a
> distance from the finer points. They are identifiable by a distinct ridge
> around the high spot. The tip of the high spot will be a lighter, somewhat
> shiny blue, around the base of this little hill will be a ring of darker
> blue. This is a true high-spot.
I have seen this as well - my take on it is that (especially on surfaces
with large height variations, as when one is first starting out) the
marking medium is transfered to the high spot, and partly rubbed off it,
at the same time. So the tip of the high spot will appear *less* blue,
ie. the bulls-eye effect you mention.
I have found this tends to dimimish as the height variations even out
and the surface improves. This effect can also be diminished by using
less, or thinner, marking medium (blue) as well - but then you will
spot and see only the really hight tips that need scraping, and it
takes forever to rough out that way.
Sounds like you are having a great time - is this a real scraping
class, or just a bunch of folks who got together to try to learn from
a pro?
Jim
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John Hofstad-Parkhill
>class, or just a bunch of folks who got together to try to learn from
>a pro?
In this case I'm unable to discern a difference.
R Hudiburg
>steel until magnet no longer attracted, quenched. Still nothing. Won't get
>hard. I find this very peculiar, bits of the Stanley logo were still
>visible.
>
That's because the irons are really 2 piece: about an inch of good tool steel
on the business end welded to a mild steel on the name end. If you really
polish the back you can see the joint(but just).