What is Scraping?

R

Richard King

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Hi Everyone,

I wrote this few days ago on another site I write on and thought I would share it with you.

Someone asked "What is scraping anyway?"

my Answer:

It is the precision fitting of ways on a machine tools and it provides even oil lubrication film on the ways (also used on Babbit and bronze bushings bearings, etc. Over the years it has been discovered that hand fitting or scraping of the ways is the most precise method so machines wear and function properly. We use a carbide tipped "scraper" that resembles a file or wood chisel. We scrape pockets approximately .0002" deep to form weight carrying high spots and the low spots are for oil. A good scraping job resembles a chess / checker board one spot is high and the next spot is low. Our goal is to get 50% high spots to carry the weight and 50% low spots for oil.

We fit the machine way clearance from .0002" to .001" so oil can squeeze between both sides of the way surfaces so the ways move smoothly and do not wear. We also test the squareness and alignment using levels and gages.

It's a trade, but it is pretty easy to learn if your mechanically inclined and have a good teacher. Scraping is easy but knowing where to scrape and how much to take off is the hard part. I also say in my DVD, start small on a surface plate and then start an easy project like a lathe compound.

Most conventional machines like lathes and mills are scraped to an accuracy of .0002" per 12" and straight edges and jig bore super precision machines are scraped to .00005" per 12". The high spots are classified as High Points per 1 sq. inch and on the conventional machine we try to get 12 to 20 point per inch (PPI) and jig bores / super precision we try to get 38 to 42 PPI If you ever look at the ways of a Bridgeport you see 1/2 moon spots, well those have 2 functions, the main being extra deep oil pockets plus they look nice. they are approx .002" deep.

I was talking to a reader and he asked about a Scraping Seminar in the UK sometime, so I just wrote a friend of mine in NE England who works at a used machinery company and asked him is he could host a class next summer. I await his response. So all who live in the UK pass the word and let me know if your interested in learning to Hand / BIAX power scrape, 1/2 moon flake and learn to repair your machines. When we have more info I will advertise it on the area Tony talked about.

Mechanics that scrape are called Machine tool builders, fitters, or machine rebuilders. I am a Journeyman Machine Tool Rebuilder. I apprenticed under my Father who lerned from a German born Journeyman during WW2 a a Defense Plant here in MN. I started to rebuild machines and scrape when I was a child...50 years ago...I am now 62 and have been teaching scraping for over 30 years for companies like GM, Timken, Cummins, John Deere, worked with several new machine builders in the USA, Europe and Asia; Spinner, Hardinge, Kent, Paragon, Hartford, Sharpe, Chevilier, plus taught several hobbyists and home machine shop owners.

I hope to help all of you repair your machine tools on his site. I like this site as there are no bullies allowed as seen on other sites.

There are others who teach scraping, I am one of them.
 
Richard: Would you happen to know of anyone who teaches a scraping class in the south east. I live in Fl. but would travel to Georgia , South Carolina , Alabama , to take a class. Thanks. Roger

Hi Roger,

I taught a class north of Birmingham 2 years ago and was going to have another on there last year, but we didn't get enough interest. The host Tommy Gamel who builds street rods < gamelstreetrods@bellsouth.net > has a nice shop and wanted to re-Turcite his Fadal VMC. We were going to have a week long class, starting on a Sat. Some who only wanted to learn to scrape over the weekend and the rest of the week for those who wanted to learn to scrape and rebuild machines. Maybe you can contact Tommy and see if he wants to host one next spring. We did the first one then so we didn't need heat or AC. I believe there is a guy in SC who teaches, but can't remember his name. Micheal Ward, I think.
My old friend Forrest Addy teaches classes in Seattle and is planing one next spring.

I drove down to Alabamma and never realized how far it was from MN, it took me I think 24 hours.... If you can go to Missouri, we are talking about doing one in Columbia next spring at a former students home shop. When it is a for sure thing we will advertise it on the paid site on here. I need to ask Tony how to do it.

I am always looking for hosts for the classes. In a couple we have had at home machinists, we did them in there 3 car garage, both of the guys had a work shop in one stall and we put up work tables in the other 2 spaces where we scraped.
Take Care....Rich

PS: Lets do one in Florida in January or February when it's 20 below and 6' of snow up here in MN, ha ha ha
 
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Thanks for the info on scraping. Just a comment, there is a 10 part series on scraping in The Home Shop Machinist magazine with the last part (part 10) in the November/December 2012 issue. The article author is Michael Ward.
 
This is really great. I have an old Atlas lathe that requires quite a lot of work. When I first got it, I could rock the compound slide almost 1/16" on a surface plate. I finally got it to +-.001 on four corners, not perfect but other areas require work as well and I'm pressed for time. This the first time I've seen such great info on scraping, I learned what I could from a book. My scrapers are made from old files and some carbide tool bits welded to 3/4" rods. They're not as pretty as I've made them sound. Anyway, I'll proceed as time allows but I really wanted to thank everyone that has posted questions, answers and pics. Very informative and encouraging. Many thanks.
 
"My scrapers are made from old files and some carbide tool bits welded to 3/4" rods. They're not as pretty as I've made them sound."




That's exactly what we did in most shops.
This way, you can make them any size, weight, angle; that is needed.
 
I have used the Anderson, Sanvik and Biax hand scraper plus home made ones my Dad and I made over he years. I have used spoon scrapers, hook / pull scrapers, Home made 1/2 hand flakers and the Biax Power scraper and power 1/2 moon flaker. I prefer the BIAX Hand Scraper that uses the Biax insert blades. They bolt on and when one gets dull you exchange it with a sharp one. I say I don't care how you scrape or what tools you use, as long as you get the same quality in the same amount of time.
 
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Hi Richard,

Have you ever considered making a series of instructional videos, either for sale or on Youtube? For example on youtube, "machine shop tips" by mrpete222 aka tubalcain is a series of over 100 videos on various machine shop topics.

Anyway, I'm hoping to learn how to scrape eventually because I have several WWII era machines that I want to bring back to accuracy. Know of any resources in Northern California?

thanks,

Brook
 
Brook,
He already has...


Tadd, We don't advertise or sell anything directly on this site openly. Sorry.
Rich
 
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Brook,

There are DVD's an Books about scraping that can be purchased on E-bay and on the net. Open advertising is prohibited on this site. If you care to email me, we can talk about it privately off the site. Those You Tube helpful hints are cool, But I work full time rebuilding plus teach classes from time to time. I don;t have the time to do something like that. I want this forum to be about learning, sharing and not selling. I have some things I recommend but there are several products that work too.

Richard
 
Thanks guys,

Im new here so didnt mean to insult anyone or break any rules. Should have looked you up before replying Richard. I'll get in touch.

Brook
 
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