[Newbie] My First Attempt At Scraping

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Standingbear

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image.jpeg Frirst I want to say hello to everyone this site has been very interesting reading thru all the good information. It has been a big help just reviewing all the old posts. I made my first attempt at scraping today and it was very addicting chasing the blue.

My first project is scraping a 4" angle plate. I did not get a pic when I started but only the corners touched. About my 3 time scraping the blue dots started covering the entire area. My questions is my dots seem to be small in comparison to some of the pics I have seen on here. I will add a pic for some feedback. Also when I rub on my granite surface plate I notice what looks like small scratches in the ink? Not sure if this is normal.
 
The small scratches in the ink is debris. Right before you take the impression, take the palm of your hand and wipe the surface clean on the angle plate and gently do the same on the bluing applied to the surface plate. Doing this should stop the scratching you are seeing. The scraping is looking fine. One thing to do before you go any future. Rock the angle plate in a twisting motion about 10-15 degrees on the angle plate. doing this should establish a hinge point that is about 2/3's the way from the end, or 1/3 from the end. If you are getting this, you are about as close to flat as it comes. If it spins in the middle, you have a convex scraped into your flat surface. If it hangs on the ends, you have a convex scraped in your flat surface. Keep working at it until you get the hing action needed to tell if it is flat.
Ken
 
Standingbear - that looks great! Did you start with a chi-com angle plate? What method are you using to make sure the plate stays square as well as flat?

I appreciate your input as a beginner scraper - I have done a small bit, but have projects in the future!!

John
 
image.jpeg Ken thanks for the help. I added a photo to see if I'm following you correctly on holding at approx 10 deg and rock. In the photo I would hold like that and rock forward? Should I just go off feeling or using the blue? Sorry for all the questions.

John I appreciate the feedback. It is just a cheap chi-com angle plate. I may have jumped the gun but I have only scraped one side and was waiting for a granite square I ordered to do the other side. I'm sure there is a way to do it without one but I am just kinda learning as I go. Sounds kind of crazy but I was anxious to get started. Big plan is once I get better at this I want to do a K&T universal mill that is is bad shape.
 
The hinge test is done with the work flat on the surface plate. You push sideways on the work close to one end with a low placed finger and watch where the center of rotation is located as the part twists on the plate. If it is about 2/3 of the distance to the opposite end of the work, that is correct. It it is in the middle of the work, the work surface is convex. If it pivots at the end of the work, the part is concave. The hinge point should also be in the center of the work, side to side. A heavier side like an angle plate makes that a bit more fussy, and contamination gives false results. You can also tap the corners of the work sharply downward with your finger. If there is any bouncing noticeable in the part by feel and/or sound, the part is convex or there is contamination under the part.

For your first scraping job, that looks great!
 
Here is another tip that will help with the scratches you saw: After you have done your scraping, try running a fine stone lightly over the entire surface to remove any very tiny burrs that are left over from scraping. After lightly stoning the surface, rub your hand over the entire surface to remove any foreign material from it as Ken mentioned.
 
After each scraping pass, I lightly debur the surface with a fine and flat ceramic stone and generic Windex, then wipe off with paper towel followed by the palm of my hand, making sure it is dry and clean, then back on the surface plate for hinge test and marking.
 
I was given this pdf primer on scraping which is very informative.
 

Attachments

  • Scrapping, How to.pdf
    8.7 MB · Views: 142
Thanks everyone for helping. Last night laying in bed thinking about blue dots I had the the moment it came to me about the hinge test. When I get off work today I will give it a try.

Emilio thanks for the PDF it is helpful.
 
looking good!
here's something else to try , blue up your part like normal on the ink.
then go to a part of the plate that has no ink and rub the part on the bare plate.
you will see some very shiny points across the surface of the angle plate, those are your highest points
the second highest points are very dark blue to black in appearance.
you are going to spend most of your time on those 2 observations
keep up the good work!
 
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