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View Full Version : What is scraping? How is it done and what for?



Belstain
03-07-2003, 04:39 PM
I saw a thread on hand scraping the other day and haven't got a clue what that is.

lynnl
03-07-2003, 05:02 PM
There are many more better qualified to answer, but since I'm here first I'll start. Scraping, in very general terms, refers to applying a very hard, sharpened hand tool (think of the end of a large file ground to, say a crescent profile) to a reasonably flat surface on which the high spots have been marked, and manually scraping those high spots, removing mere thousandths or tenths of thousandths of material thickness at a time. After going over the entire surface, it is rechecked and high spots again marked and process repeated, over and over again until the high spots (all in the same plane) are sufficiently dense to make the surface "flat enough" for use as a bearing surface. As you might guess, it's not a task for the impatient person. Obviously it requires some other reference surface, and a marking medium, to detect and mark those high spots each cycle. In the early days of machine tool development this is 'how it was done', and tho it may sound crude, the skilled and patient hands of those old masters are ultimately responsible for the precision we enjoy today.

Belstain
03-07-2003, 05:16 PM
Where can I learn more about how to do that?

Tibertus
03-07-2003, 05:26 PM
You need to read the old threads. One of the better books on scraping is the famous "Machine tool reconditioning" that has the record amounts of posts on this BBS. You can search using "scraping" and find the other threads on this subject.
There is also an individual that will teach you but you have to travel to his location and pay a fee to learn.
good luck

Peace

Uncle Dunc
03-07-2003, 08:55 PM
Also search the article index at http://www.homeshopmachinist.net/artind.cfm There was a series a few years back about reconditioning an old shaper vise. It had a good description and a lot of photos. They might still have the back issues.

Quick Change
03-08-2003, 11:56 PM
Belstain,
Lindsay Publications also sells several reprints of old books on scraping.

tattoomike68
03-09-2003, 12:29 AM
in collage we had a scraping progect first and realy weeded out the lazy.
we had to scrape and square within than .001 . the drills, you hade to shapen drills that hold -.000 to plus.005. then the profeser would buzz the end off and you do it again. you do it right or do it again.
many of the night classes had home shopowners and olny needed to do some trigonometry to go to the shop.
the first 11 creadits in machne tool tech. half of in the first quarter was scraping, you hade to do it right or do it again.
it was tough.
it is an art and an science all to self.
get a block and a old file and you can scrape all you want and do nice stuff.



[This message has been edited by tattoomike68 (edited 03-09-2003).]

steve schaeffer
03-09-2003, 05:48 AM
how would you mark high and more importantly low spots on a lathe bedway? i understand using a surface plate for high spotting a piece of metal, but how do you "guage out" your lathe or mill ways? also, say on a bridgeport, are the entire surface of the ways scraped, or is it just the areas where you see the "flaking"? or is the flaking a secondary function after scraping ?

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extreme tractor racing

Don Warner
03-09-2003, 08:32 PM
<font face="Verdana, Arial" size="2">Originally posted by tattoomike68:
in collage we had a scraping progect first and realy weeded out the lazy.
we had to scrape and square within than .001 . the drills, you hade to shapen drills that hold -.000 to plus.005. then the profeser would buzz the end off and you do it again. you do it right or do it again.
many of the night classes had home shopowners and olny needed to do some trigonometry to go to the shop.
the first 11 creadits in machne tool tech. half of in the first quarter was scraping, you hade to do it right or do it again.
it was tough.
it is an art and an science all to self.
get a block and a old file and you can scrape all you want and do nice stuff.

[This message has been edited by tattoomike68 (edited 03-09-2003).]</font>

A Friend of mine who was a machine tool builder in Chicago that came from Germany in the 50's, told the story that when he was an apprentice they gave him cube of steel approximately 24mm square and he had to hand file to a perfect 20mm sphere +/- .01 mm at the end of the apprentice term.

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