First time scraping

I'm a nurse by trade but I love messing around in the garage , I always wanted to learn how to scrape. I got myself a grade a surface plate and a biax hand scraper. This was taken off of the mill , it had a lot of surface imperfections.... I just wanted to get the feel for it. How am I doing?
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I think I see a lot of scratching, but the pictures aren't the clearest. Is that iron? If so, you might want to describe your scraper sharpening method. If it's steel you'll maybe need to tweak your scraper edge geometry a bit.

Yes there are scratches , I think those came from the stone I was using to remove burrs. I'm just using a biax 20 blade . This is steel, it came off the mill , surface finish was shit.

Steel is tough to scrape without scratching. As I recall, one of the guys here posted a thread about the geometry he found to work pretty well. I believe it was a somewhat substantial positive rake on the front of the scraper with a small flat ground at the bottom so it didn't have so much clearance.

eKretz said:

Steel is tough to scrape without scratching. As I recall, one of the guys here posted a thread about the geometry he found to work pretty well. I believe it was a somewhat substantial positive rake on the front of the scraper with a small flat ground at the bottom so it didn't have so much clearance.

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When I scraped steel back in the day I used a scraper with a cutting blade made out of a large power hacksaw blade. As you say it had a substantial positive rake on the cutting edge. You could also use the same scraper on cast iron but you needed a negative rake on the blade then. You didn’t get many scrapes out of it on cast iron before it needed re-sharpening.

Regards Tyrone.

I'd look at your scraping from two perspectives: What are you scraping, and How are you scraping.

What are you scraping has to do with getting the right geometry in your cutter and scraping implement for the kind of material, and knowing "where" to scrape. Where to scrape involves a lot of measuring, printing, and general detective work to determine how far to go to reach the desired precision. If you are trying to make something flat, then you need to be able to measure your progress. You also need to know what it's flatness refers to. Is it flat to the part, to the machine or assembly it mounts to, or will it stay flat when in use?

How to scrape has to do with how to work efficiently and how attractive the results are. Bear in mind though that you can make something look really pretty scraping, but if you're not measuring what you're doing then it can have no effect on making a machine or other surface actually work, or even make it worse.

I'd recommend learning to work in 'lines' rather than moving around at random. It helps to be able to see what is going on as the light hits scrape marks differently at different angles. Use a sharpie and a ruler to lay out a grid at 45 to the work and follow the lines as you scrape. Once you get a feel for it you won't need the lines and you can use the previous scraping marks as a guide for the next pass.

Scraping steel is tricky, but it also isn't as common. I'd recommend starting with a piece of iron as it's easier to do and much more common in application as most scraping jobs involve refinishing or improving castings. You can find a used or imported angle block or small iron surface plate for cheap to learn on and end up with a usable tool when you are done.

You can get convenient sized pieces of durabar from McMaster. For first scraping work a 4"x4" by however thick block will be great. You won't believe how nice it is to scrape after starting with steel!

When you can pinpoint scrape that move on to correcting geometry. It's only about 8x more skull sweat and effort than making a surface flat, haha. (Something like a Hardinge split bed where you gotta hit 3 surfaces and alignment at the same time will make you wonder why you got into this...).

Last week I taught a class up here in MN and one of the students works for Siemens Turbine repair and scrapes steel. I taught him to grind the blade tip to a positive rake of 25 degree's (looks like a wood chisel) with a 60 mm radius. M B one of my A+ students is right about moving in a straight line to get a checkerboard look. There is a "sticky" above on where Ballen learned to scrape and he has several pictures on how to scrape the checkerboard pattern. You also need to use a 260 grit diamond wheel to grind the blade and then to use a 1200 grit wheel to finish the blade so it doesn't scratch. Using a 5 deg/ rake will always scratch or leave small scratches in the scrape mark. If you hand scraping use the 5 deg rake and not the positive rake. Using the # 20 blade 3/4 x 3" is a bit more difficult to hold the scraper. I would buy a 20-150 3/4 x 6" blade and use it as it flexes more. The photo is a 25 x 25 mm Sanvik insert ground to a pos 25 degs. in a DAPRA blade holder. We used a 20 150 blade and I didn't snap a picture of that.

Hold the scraper a little lower in back then normal level position. I will try to down load some photo's of the blade. I also describe this on my Facebook forum - King-Way Scraping Consultants. Join and learn there too.

Hi Richard,

Richard King said:

There is a "sticky" above on where Ballen learned to scrape and he has several pictures on how to scrape the checkerboard pattern.

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I want to compliment you again on your generosity and willingness to pass on your trade to others. I keep seeing this over and over again, kudos for your patience!

Sasanifab, the people here have a few centuries of collective scraping experience. Rich has spent a lifetime behind a scraper and has taught thousands of people how to scrape. So if you pay attention and put in some time, you can definitely learn to scrape from this group.

Cheers,
Bruce

Ballen is also a A+ internet and in person student. He took a class I taught in Austria.