Scrapping finish

[DaveSohlstrom]

I have been scrapping this sub table for my mill. As you can see from the photo I am getting micro scratches on the piece. Is this normal. My scraper is carbide and lapped to a very smooth finish. I can not feel any nicks on the cutting edge with my finger nail.

Dave

 

[Richard King]

Those are blade scratches. I wish you showed me the scraper blade too. I am assuming it's an Anderson brand carbide blade? Or is it one you made? You say the blade is lapped? How? Hand Lap or electric power? I hate to guess here but the edge is not sharp enough and is scratching. Some of those blades have are not side lapped and has rough sides. I use a Glendo grinder and tip the housing back with the 600 grit wheel facing up and I push down on the side of the blade to shine it flat and it has a mirror finish.
http://www.accu-finish.com/seriesone.html the picture on bottom left. Another possibility is you are not picking up the blade and as you pull the blade back it scratches caused by the chips from the scraping.
What grit lap are you using? Take a picture of it and the blade. Your scraping needs some help too. Send those pictures and then I will write some more.

20 PPI 45% contact 40 PPI 45% POP

My first attempt of downloading pictures on here... If you can do a close up on here you will see no scratches and the size of the high blue spot is the same size as the low spot. The checkerboard look is the secret to 20 and 40 Points Per Inch - PPI --- and Percentage of Points - POP - We scrape conventional machine or less precision to 18 to 22 PPI and Jig Bore precision to 38 to 42 PPI. We try to get 40 to 60% for best contact.

 

[DaveSohlstrom]

Rich

Thanks for the reply. The scrapper is one made by Forrest. 1/8X1 blade tip. diamond ground to 60mm R at 94 Degree. Face and end power lapped to mirror finish. Green diamond lap past loaded using an ball bearing to set the diamond on the wheel. Will take photos of scrappers and lap on Monday.

Dave

Dave,
It's spelled SCRAPER...what you are spelling is "SCRAPPER" which means the guy who takes junk to the junk yard.

When you scrape do chips stick to the blade? It might be magnetized and the chips are fouling the cuts. Didn't you order a DVD from me, or maybe you didn't get it yet? When you get it look at how I separated the scrape marks to get the checkerboard look. You need to practice diagonal lines with a scrape mark and then an opening the same size and same length to get the percentage right. We strive for 50% high spots and 50% low spots.

The High spot carries the weight of the sliding part and the low spot hold the oil. If the blade was too flat or the radius was too flat that could be why its got low percentage. You have maybe 10% contact and 90% not touching or bluing up. You should grind the blade to have a 60 mm radius or the approx 4 1/2" circle with a neg. 5 deg. angle. and a line running down the middle so you have 2 cutting surfaces. I will add a picture of a properly sharpened blade later. If the blade is to flat you might suspect corner gouges from rolling the blade. But those are scratches from a bad blade or your not picking up the blade at the top of the stroke and siding the chips back and scratching. The lap might be dirty and that's scratching the side. You might be doing the fingernail text wrong. Maybe use a utility knife blade and lightly slide it along the corner or right angle of the edge and see if you feel it hitting nicks. It doesn't take much.
Many new scrapers have a tendency to get a magnetic charge. You will need to buy a cheap demagnetizer.
Lets compare photo's next and see what we can find out. Richard

 

[DaveSohlstrom]

Rich

There are days I feel like a Scrapper rather than a Scraper.

I checked the angles on my scrapers. Diamond wheel is set to 4 degrees and the lap is set to 5 degrees.





I discovered today that more pressure gives less scratching. Chips are not sticking to blade. I received my DVD today and have watched it twice.

Here are my scrapers made by Forrest. As you can see they are very stiff. One is ground to 60mm and one to 40mm.







Things look better but still having trouble getting that 40% spot area.




The piece I am working on is a sub table for my milling machine to set work at a 45 degree angle without having to rotate the head. It is a real PITA to get the head back into tram.



Dave

 

[Richard King]

It is what I suspected the side of the blades are rough. The 3rd picture down shows the problem. The side shows the silver solder and that side needs to be lapped so it is shinning like a mirror. As shinny as the top of the blade and smooth. Its easy to do by first filing off the solder that is sticking out and then with the diamond wheel shut off press the side of the carbide up against the it and find the right angle, then tun on the wheel and carefully press the side of the blade against the wheel.
That should get rid of the scratches. I have seen this problem before with Anderson blades also. The Biax and Sandik blade sides are so shinny they look like a mirror. I would also put a rubber pad on the scraper handle and wrap the handle with some electrical tape. Some will use the tape that is thicker they use to insulate the wiring connections and then wrap it with the thinner shinny tape. Your hands will not hurt as much gripping the handle. Some men wear gloves too.
The close ups of the scraping looks better then the first ones. Fix the sides of the blades and you will see an immediate cure. Rich

 

[DaveSohlstrom]

I'm getting an average of about 35 PPI but only about 20% coverage.

Dave

 

[4GSR]

Dave,

You got better than 20% coverage there, more like 100% coverage in my book. Bearing points per sq in not bad either!

My scraping doesn't come near that good. Generally 70-90% coverage with 15-25 bpi.

BTW- Nice job there!

 

[DaveSohlstrom]

Ken

I may of used the wrong term. I'm talking about the area of blue spots to area with no blue. I'm only getting maybe 20% blue and would like 40%.

Dave

 

[4GSR]

Dave,

Let's let the Richard chime in and give his expert opinion.

Your scrapers look very familar to a couple my Dad use to have many years ago which he made. I don't know what happen to them. I know he used them a lot over the years at one place he used to work at. The only thing i have left from his stuff is a spotting or flaking tool he made and a Sandvic scraper. I still use them and have added several other scrapers to my collection over the years.

Ken

 

[Richard King]

The charts I thought would be at the bottom of the page ended up here. ...at least they are here..ha ha


View attachment ScrapingPercentagevsOil.pdf View attachment ScrapingPOPChart.pdf


I will try to download a couple of charts I have inside my hand-out for my classes that should help you understand percentage % versus points per inch PPI and POP or % percentage of points. The best scraping is when we have the same number of low spots and high spots. High for weight and lows hold the oil. You see the 1/2 moon flaking on ways also. 1/2 moon is a extra deep oil pocket we put in to hold and distribute the oil evenly. It's also used to make things look pretty. Some dishonest used machine dealers will also flake worn ways to make them look new. That's been called a Chicago Job for years. The 3rd row to from left is the best row...

It was nice talking to Dave on the phone.
I sometimes prefer a phone call as I can explain thing in more detail then writing them. You beginner scrapers need to remember scraping is a trade and it takes a while to learn how. I do know I can teach you to scrape in a week, but I am there standing behind you and tweeking what your doing. I want my students to not only earn to scrape, but I want to teach you how to scrape a machine part. The last class several of the guys scraped SB lathe compounds. A class that just shows you how to scrape seems to me ..it would leave you frustrated when you go home...and have to guess how to scrape your machine.
Happy Scraping all Rich