Subject: File hardness, hand scrapers

From: [email-masked] (Peter Monta)
Date: 09 Dec 1993 08:00:35 GMT

I've been reading recently about hand scraping and the making of
surface plates (in Gingery's books and a few others), so I thought
I'd give it a try.  I'm having a problem getting good scraping action.

The suggestion is to hollow-grind a file to make a scraper.  I did
this (only at the tip, to about 1cm back), and was careful not to let
the area get too hot.  The resulting edge takes great effort to push
across cold-rolled mild steel, tends to stop and "dig in" slightly,
and in general doesn't scrape cleanly or at all deep (it would take
forever to scrape down any distance; most of the time the tool looks
like it's simply burnishing the work, with zero cutting action).

I tried to assess the tool's hardness by filing it with another file.
I was able to do so, and there was no damage to the other file.  As a
control, I filed a tiny section of the unground area (teeth), and did
see some mutual damage, so there's a definite difference.

Question 1: are files surface-hardened, not hard all the
way through?  (If so, why is the tang "blued"? A case-hard file would
not need an annealed tang.)  Question 2: if files are only hard on
their surfaces and teeth, are they at least high-carbon steel, so that
I could harden completely the top part?

Question 3: is there some description of what effective scraping feels
like?  Is the chip continuous, a tiny ribbon?  Does the scraped area
have a fine finish?  How much is taken off per scrape, approximately?
A few microns?

Thanks for any hints or references.  I've a new respect for
large hand-scraped machine tools.

Peter Monta   [email-masked]
MIT Advanced Television Research Program

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From: [email-masked] (David Jenkins)
Date: 9 Dec 1993 08:39:32 GMT

In article <[email-masked]>, [email-masked]
(Peter Monta) writes:
|> I've been reading recently about hand scraping and the making of
|> surface plates (in Gingery's books and a few others), so I thought
|> I'd give it a try.  I'm having a problem getting good scraping
|> action.
|> 
<stuff about using files deleted>

Using files is an excellent idea, but pick a high-quality one.  I
would pick anything made by a reputable UK company, and I assume that
you could find many similar USA ones.  DON'T go for the 3rd-world
stuff.

|> Question 1: are files surface-hardened, not hard all the
|> way through?  (If so, why is the tang "blued"? A case-hard file would
|> not need an annealed tang.)  

Files are high-carbon steel throughout. your grinding probably 
softened it.

Question 2: if files are only hard on
|> their surfaces and teeth, are they at least high-carbon steel, so that
|> I could harden completely the top part?
|> 

See previous answer.  Be prepared to grind your file to the point
where you'd be wanting to finish it with a stone, then heat treat it
to a hard temper (light straw colour).  When you've finished, then
stone it.

|> Question 3: is there some description of what effective scraping feels
|> like?  Is the chip continuous, a tiny ribbon?  Does the scraped area
|> have a fine finish?  How much is taken off per scrape, approximately?
|> A few microns?
|> 

Hard to describe - imagine very slight curls.  You are only removing a
thou maximum if you're doing it right, often less.  The important
point to remember is that you should have tried to get the surface as
flat as possible by other means before you try scraping, e.g.
best-quality milling or even surface grinding.

Even if you're not trying to get a flat surface, you can get a nice
"frosted" finish with a scraper.

-- 

David Jenkins

* I'd rather be steaming... *

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From: [email-masked] (Michael J. Edelman)
Date: 9 Dec 1993 12:55:19 GMT

>across cold-rolled mild steel, tends to stop and "dig in" slightly,

This seems to indicate that perhaps your cutting edge isn't straight.

>like it's simply burnishing the work, with zero cutting action).

Don't expect to cut deep. A scraper is for trimming a few tenths at a 
time.

...
>like?  Is the chip continuous, a tiny ribbon? 

No. It takes off fine chips. 

>... Does the scraped area
>have a fine finish? 

Mmm.  It's not a *polished* finish, if that's what you mean.

Kitts tools seels a nice assortment of scrapers at $1.89 each. Can't beat 'em,
really. Therey also sell an assortment of 5 (I think) at a slightly reduced price.

--mike