My Scraping Education

[rolfinator2002]

Thought I'd post my (cast iron) scraping eductation so far, some hard learned, some passed along by others with experience. Hoping to save others my frustrations and mistakes.

First, hard won lesson:
Never use prussian blue spotting fluid; if you have those little tubes from permatex or wherever, give or throw them away. I have 2 brand-new tubes if anyone wants them.
*I forgot just how hard it is to clean up anything after using it. Impossible to get stains out of anything but metal.
*Use Canode spotting ink. Non-drying, water soluble ink, works great. I clean up my straight edges and work with just a damp cloth or running water. Got a stain out of the carpet fairly easily too.
Dapra sells it, but were very expensive with all the other related items, so I bought mine from Volk.com for $10 for 1/2 pint (lifetime supply).
2nd:
You'll need a rubber roller (2" to 3" wide, your preference) to apply the ink. Not very critical, I bought one from the craft store for $2 as opposed to spending bucks online.
3rd:
Try to use a carbide scraper to reduce your downtime dressing the tip.
There is nothing wrong with using a steel scraper from Enco.com, but you'll need to grind a radius on the nose to avoid end-gouging.
4th:
Scraper dressing is all important. Dress the tip with a 140-300 mm radius to begin your work or large areas and dress it to 60mm radius for spotting those canode spots toward the end of your journey. A DVD/CD is a perfect template for 60mm radius.
5th:
Scraper dressing pt.2
You must dress the tip so that the scrapes have no streaks or scratches (not issue with steel scraper). Grind the nose of the tip between 1-4 negative degrees, and grind it so the working edge "sees" the lead side on the grinding wheel to prevent carbide breakdown, then flip the tip over and repeat. The finished tip will have a little edge-nose to it, and the carbide won't break-out, leaving nicks. Can't stress how clean and sharp tip must be; lathe sharp is not good enough. If you can see any nicks under a 20x loupe, no good.
6th:
Carbide blanks are usually dull, no good. Faces must be ground and polished; inserts for Biax scrapers come mirror bright, which is why they are expensive.
7th:
My homemade scraper will accept anywhere from 3/32 thick to 1/8 thick blanks, so I can use cheap ebay carbide or the good stuff. The standard biax insert is 3/32 thick, with 3/4" x 1" being the most popular (most people seem to use the inserts dressed with the 3/4 side as the cutting edge. They are ground with 4 work edges, so don't get too frightened if you order some inserts from Dapra; you might grind that insert once if you do this for a hobby.
8th:
I use a granite straight edge for the box ways and flats because it is a whole lot cheaper to get accuracy/foot with granite. Regardless of the straight edge, always run a sharpening stone (any kind) lightly across the surface before touching with your master, even if you haven't started scraping, otherwise you risk scratching the master (like I did). A few scratches don't hurt, but they add up. Brush off the surface also beforehand.
9th:
Apply spotting fluid to the master sparingly, everybody always starts out with too much. Use a small amount and take your time spreading it out with the rubber roller. A good spot with show light color in the center, with blue around the edges, not all blue.

When I think of more screw-ups and lessons, I'll post for anybody who wants to scrape their own machines.

[TOTALLYRC]

Do you have any before and after pics or a video or 2?


Mike

[rolfinator2002]

I learned on some scrap class 40 iron, didn't take pics, but starting to take pics on latest iron. This is pretty new for me too, by no means an expert, just an engineer whose profession puts him in touch with a lot of prototyping equipment and machinists.

Brand new lesson regarding biax scrapers:
Bought an electronic variable speed; just had to speed up the process for reasons I'll disclose in the future.
There are still single-speed power scrapers floating around. Do NOT buy one unless you can get an external speed control. Why? Tough to use for any higher point work, turcite, or smaller parts, even with stroke turned down to 2mm. The level of skill required to operate a power scraper is directly proportional to it's speed. The variable speed version is so much easier to use; my hand work to finish up will probably be the last 1 or 2 passes if at all.

[TOTALLYRC]

I will keep watching since I will probably want to scrape a machine or 2 in the future.

Mike

[jalessi]

YouTube- Kitamura Machinery - Hand Scraping Techniques on a Horizontal Machining Center

YouTube- Kitamura Machinery - Hand Scraping Techniques on a Horizontal Machining Center

YouTube- Kitamura Machinery - Handscraping Techniques on a Vertical Machining Center

YouTube- Kitamura Machinery - Handscraping Techniques on a Vertical Machining Center

[skullworks]

Could you post some close up pics of the insert after grinding?

[rolfinator2002]

I have a lot of irons in the fire at the moment, so the project is going to be stretched out a bit.
Lost my job for christmas (all of us); seems my company is selling part and shutting down the remaining part of a division, so a job search is going to take a lot of focus with near 20% unemployment in this area. The US unemployment rate is very deceptive because it only counts people who have been unemployed for 6 months or less, not very accurate in this economy. I digress.

The biax paperwork I found on an EU website suggests grinding the carbide insert to -3.5 degrees for cast iron. Here is a closeup of a standard 3/4" biax carbide insert as ground to show you what I meant in a previous post regarding the shape. Grind it so that the grinding wheel "sees" the flat sides first. Some people grind just one work edge, preferring to grind sideways (see nick Mueller), but I like this method since I can flip the blade over for another working edge.

[rolfinator2002]

Here are some pics of my homemade scraper. It cost me about $6 in material and my time as opposed to the $75-$100 for either an Anderson or Dapra. I purchased carbide blanks on ebay, with extra blanks for form tools or whatever. They are NOT the standard biax thickness(3/32), which is hard to find for cheap. These blanks are approx 1/8" thick, so I can shim to clamp biax inserts. Was not happy with the results until I got the hang of grinding the inserts, now very happy with the function.

Here is the mill saddle of the present project, after measurement to determine what needed to be scraped and after rough scraping. Scraping starts as rough scraping to remove tool marks (whether grinding or milling according to the biax folks), then plane scraping, followed by finish scraping, then oil film scraping.

Last, I'm not far enough along to determine if I really needed a straight edge to "spot" the dovetails in the saddle top and table ways, so it would be unwise to purchase a straight edge (>$2,000); I was losing my job where I had the resources to fabricate a straight edge, so I decided to at least rough-in a tool in the evenings after work before the layoff day.
It was made from G2 dura bar cast iron (similar to class 30-40) which I purchased from a local supplier. Milled it square, clamped it in a large set of v-blocks and split the bar across corners on a vertical bandsaw. Then proceeded to both side-mill and face-mill the sides to get a 90 degree, 50 and 40 degree triangle, carefully setting up the mill to ensure precise angles. Turned some handles out of 3/4" scrap, threaded to 9/16-18, drilled and tapped holes in the bar to match. The dura bar supposedly comes stress-relieved, but I didn't want to take chances so the metallurgy dept let me use an oven to stress-relieve it at 1100 deg F to be sure. It was then milled again to touch it up. It will be scraped when/if I need it for this project, but certainly in the future for another mill.

[tobyaxis]

A true Art Form to say the least.

[rolfinator2002]

This was suppose to be a straight cnc conversion for a taiwanese vertical mill, but when I started to strip it down for power washing, it became clear that the saddle had moved from 20 years of aging. The center of the box way was depressed by .010" and the top side surface had the same issue, with flaking still intact where it had sunk.

Now I own a power scraper, learning the art and certainly appreciating the craft because I won't be that good at it, but would like to avoid the $1100 or more for a total regrind and scrape by sending it out. I figure that the lathe in my future will probably need similar attention. The mill at my former employer is a mess in terms of stick-slip; they just pump it with a grease gun, now I understand why some mills are more accurate than others.

Hopefully all this effort will yield a cnc mill that will accurately mill everything without oil film "rise-up" or stick-slip issues.

[Eson]

I wonder what your thoughts are on scraping brass or aluminum just for getting started if you don't have any cast iron laying around? Also how much difference is there between scraping cast iron and say carbon steel?

What is 'oil film scraping'? Is that frosting or flaking? Im trying to learn the glossary.

[rolfinator2002]

Internet is a great place, except if everybody has a different opinion on a topic that really needs to be in one track. Check your IM. I sent you the US (english) biax scraper how-to manual, which includes different materials.
Cheers.