Page 1 of 4 123 ... LastLast
Results 1 to 10 of 39

Thread: Scraping - How to take to the next level?

  1. #1
    Join Date
    May 2011
    Location
    North East, UK
    Posts
    216

    Default Scraping - How to take to the next level?

    Hi folks,

    Been learning to scrape over the last month or so, I bought the Sandvik carbide thing in the photo. I also made an HSS 'pull' scraper but I'm struggling to get results with that one.

    I've spent about 8 or 9 hours practicing on cast iron and some cast steel and I've got to the point where I can achieve the sort of effect below quite easily.

    Problem is I can't seem to get it any better! Spent an hour tonight making this piece in turn worse, then back to below, then worse again, but never better. Just pushing the blue around.

    Is this because the Sandvik scraper blade has a large radius (I guess it's about 6 inches)? Or am I just being careless?

    I have bought a diamond wheel on which to re-profile one side of the insert if required. Thusfar I haven't blunted all 4 edges so still have sharp ones available for now.

    I'd just like to get the spots smaller and a more even distribution - you can see there are patches where the density is real low.

    Would appreciate any advice.

    Cheers,
    Rich


  2. #2
    Join Date
    Feb 2008
    Location
    MI
    Posts
    254

    Default

    I've taken a class but I forgot to stay at the Holiday Inn (North A. TV commercial joke).

    My first guess is you have too much blue on your surface plate. There are some big holes (blank spots - 30% of the lower long edge) that should not be scraped until it becomes more even.
    Rob

  3. #3
    Join Date
    Oct 2002
    Location
    Bremerton Washington
    Posts
    4,938

    Default

    The end radius of the stock Sandvik scraper tip is a bit flat for small scale scraping like that little plate. I suggest you get a couple extra tips ($$$) if the budget will stretch and grind one edge of one tip to about 2/3 the factory R. See how there are no blue indications along the edges of the plate in your photo? I think you may be over-scraping the edge. If you avoid the edge you get a row of indications along it. It's a happy medium thing.

    If you are serious about scraping you might consider a motorized lap for finishing the edge of your scrapers. The difference in keenness between a ground edge to a lapped edge in like night and day.

    Look at the second photo down for my version of a diamond lap.

    http://prowave.blogspot.com/2007/05/scraping-class.html

    The lap as shown is cast iron but most any metal will do. Diamond is in hardness to most metals as metal is to bar soap. I use the green (9 - 12 micron) diamond lapping compound smeared on with a finger tip.

    Also I think Muel1 is on target. It appears you have too much blue on the surface plate. You want enough blue for vivid color at the same time thin enough to clearly see the texture of the plate's surface.

    Finally, don't over-scrape. Scrape off only the blue and if the spots are too large remove only the center. I hesitate to get into "spot reading" but a bearing spot has definite anatomy. The actual bearing "point" (actually an area) may have a greyish-blue color where the pigment is mashed by contact between the work's high spots and the surface plate. Then there is the "beach" where the pigment tapers from the actual bearing area to the thickness of the flim on the plate. The remainder is the trailing smears and ragged edgees from the viscous blue being dragged into filaments depending on blue thickness.

    If you get too obsessive reading these indications you lose time and productivity. It's best to be aware of how a bearing "point" appears, learn how to treat it, then turn that part over to your subconcious mind. Learn to scrape like you drive. The actual process of driving (scraping) evolves from anxious obsession with every detail to a subsconcious process directed by a supervising eye. You won't learn it over-night but in a few days it will come.

    Anyway scrape off the actual bearing point and leave the non-contacting beach un-scraped.

    There's a way to calculate the amount of blue to put on the plate if you're interested in numbers. Post #4 in this link:

    http://bbs.homeshopmachinist.net/thr...blue+thickness

    I strongly suggest you get either the Micheal Moore book on how to scrape. Order a copy of Rickard King's DVD from Dapra Corp or, if you can, take his class. Big money but lots of training:

    Richard is affiliated with Dapra:

    http://www.dapra.com/contact/scraper_training.htm

    and, if you contact them they have (I think) his Basic Scraping DVD for sale.

    http://handscraping.com/

    Also: http://smartflix.com/store/video/596...r-Way-Scraping

    And if you branch out into machine tool scraping: http://www.ebay.com/itm/Scraping-For...item4aac0e1282

    PM me with a phone number if you like and we can talk about it.

    Adding, are you scraping from alternate directions? That is one cut 45 degrees from one edge then the next cut 45 degrees the other way? The object os to develop a sort of checker board of bearing points.

    These points randomly dispersed over an area to form little bearing surfaces that collectively constitute a near exact plane. In between the bearing points - call them "islands" for a moment - are little "lagoons" left from the passage of the scraper that form reservoirs for lubricant or blue.

    I see you have the plate lightly gipped in a vise. Even a light squeeze can distort a plate enough to mak a difference when scraping. Are you removing it to take a print from a surface plate?
    Last edited by Forrest Addy; 08-28-2012 at 11:13 PM.

  4. #4
    Join Date
    Jul 2007
    Location
    West Michigan
    Posts
    1,821

    Default

    Forrest,

    I have read your posts for many years now and am always amazed with your depth of knowledge and your ability to put it into words that are easy to understand.
    Thanks so much for sharing your expertise with us.

    Brian
    OPEN EYES, OPEN EARS, OPEN MIND

    THINK HARDER

    BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

    MY NAME IS BRIAN AND I AM A TOOLOHOLIC

  5. #5
    Join Date
    Oct 2002
    Location
    Bremerton Washington
    Posts
    4,938

    Default

    Quote Originally Posted by bborr01 View Post
    Forrest,

    I have read your posts for many years now and am always amazed with your depth of knowledge and your ability to put it into words that are easy to understand.
    Thanks so much for sharing your expertise with us.

    Brian
    Thank you for that. It's all part of paying forward what my mentors gave to me.

    Adding I just re-read this post 6 hours after I first wrote it and it sounds trite, saccharine. That may be trite but it is still the truth. Older farts like Brian and I have a positive duty to bring along the younger farts even indirecly for the noobs and lurkers.
    Last edited by Forrest Addy; 08-29-2012 at 04:07 AM.

  6. #6
    Join Date
    Aug 2012
    Location
    Cottage Grove, Minnesota, USA
    Posts
    318

    Default

    I would like to add a few things to what Forest has said. Thanks for the plug Forest :-). I have had the privilege to have known Forest for 30 years or so. He and I get a bit upset at each other sometimes...but he has contributed to the machining community and he will go down in history along with Connelly, I am sure.

    The reason one sees a flip flop or come and go bluing is generally caused by not enough depth of the scrape mark or cut or you stoned it to hard to remove the burr. Many European scrapers do not use a sharpening stone to de burr the scrape cut. If you look at the DAPRA.com site under scraper accessories you will see a "control gage" It's a handy little tool: The square hole in the middle is used to count points, 3 sides are used in checking the scraper blade radius when your sharpening the blade. The sides are R/120, R 90, R 60 metric circle radius and the straight knife edge is used to de-burr the part. (I also grind it to a R/40 when scraping 40 PPI) I use it plus a Norton MS-28 medium grit sharpening tapered slip stone to remove the burr left at the end of the scrape mark.

    I tell my students to sharpen your blades an R 60 or approx. 2 3/8" circle.. to get 15 to 20 points in 1 square inch (PPI) read thru middle hole of the control gage. Your Sandvik scraper is a bit stiff so I would put a rubber pad on the end of the handle. I usually use a 4" dia. rubber orbital sanding disc. It already has a hole in it and you can screw it on the plastic handle with a sheet metal screw. With the pad you can push the scraper with your body and not your arms.

    The scrape marks should be approx. 1/4" long and 1/8 wide. You should practice scraping the checkerboard pattern with no blue and you should measure the depth of the scrape mark. The depth should average .0005" deep with a minimum of .0002". If you are looking inside the DAPRA catalog, look for the ink roller. It looks and works the same as a 4" long x 1" dia. hard foam paint roller and using a roller you can apply the blue on evenly.

    As stated, apply the blue to your plate so you can see through the ink and see the plate. Looking at your part, it looks like the bottom right is a false reading or a smeared area and lower then the rest. You need to "hinge" your part on the plate and use a .001" feeler gauge to feel for open spots. Take the part out of the vise and rub it on the surface plate, you can use circle motion, figure 8, up or down or left or right. The longer you rub it the more you will see the different heights of the blue.

    The higher the high spot the more it polishes of the ink. If you have an area of the plate clean, after you blue up the part, rub it on the clean spot, this will really polish off the ink and the shinny one or reflect like a mirror are the highest ones. The black is 2nd highest, then same color of blue is 3rd highest and a thick glob is a false reading and to thick, so wipe off the blue in that area...The hinge I mentioned is the "rotation of points" or if you were to set you part on the plate and hold onto one end of the plate with your fingers move it to and fro and watch where the part pivots on the plate.

    It should rotate or pivot 30% from that end and and then do the same thing with the other hand and it should pivot 30% from the opposite side. If it pivots in the middle the parts looks like the bottom of a rocking chair and it rocks side to side and blues up the edges and they are false. All of this info is in my DVD and it can be purchased from DAPRA, on my site and I also sell it on E-Bay. Mention you saw this on the board ad I will give you a $5.00 off discount.

    The secret is to get the checkerboard look. The more points are achieved by generating shorter strokes. The European method was to push forward or pull backwards and lift the blade out at the end of the 1/4 long stoke then move over 1/8 and put in another scrape and when you put in the next line be sure that line of scrape marks does not touch the first line so you get individual marks. You will hear the blade hitting the part and you will hear the tap tap sound. When you have the marks all going the same direction, like a platoon of soldiers standing at attention. change direction 45 degree's and put down another group the same way and the part will have X X X X marks or cross hatched checkerboard look.

    Rob can explain this as he learned how well this method worked at the class he attended. One more thing, if your scraping gray or soft cast iron I would sharpen the blade with a 300 to 600 grit diamond wheel with a 5 deg neg. edge the same as your blade is now sharpened but at a 60 Radius. I never have my beginning students use the flat blade that the new blades are sharpened at as the corner can easily dig in and you gouge the iron.

  7. #7
    Join Date
    Apr 2010
    Location
    Sunnyvale, CA
    Posts
    127

    Default

    A few other things to consider (I learned from Richard at his class) that got me from the "can't scrape at all" stage to the "I can see the light" stage:

    • You may be rocking your piece and getting a false blue pattern. Put the part on the table at try to slide your narrowest feeler gauge under an edge. If you can get a 0.002" in there, you don't have the even blue pattern you think you have in the picture. Think of it this way: if you had a perfect cylinder and you rolled it through the blue, it would blue up fine. But it wouldn't be flat. Always be on the lookout for bad bluing technique before you scrape away.
    • On the same bluing technique issue, if you push the piece at one edge, it should pivot 1/3 of the way from the opposite edge. If it doesn't, it isn't sitting flat, over an even area. Push it on both sides and check it out. Turn 90 degrees and try again. If it pivots at an edge or in the middle, you are sitting on a high spot. It's super easy to do and should be in every bluing cycle. I would have never thought of this, and it is so simple once you know... It catches high spots amazingly well.
    • If you don't know if you are in the 0.0002 - 0.0005" range, put your part on a surface plate, scraped side, up and sweep it with an indicator. You can see the individual scrape spots and check them for depth. I certainly didn't scrape deeply enough at the beginning.
    • If you are feeling really frustrated, you might even try bluing the part, taking a picture, cleaning the part, then bluing it again. Take another picture and compare. Are you getting consistent bluing patterns? If not, you need to figure that out before you touch your scraper.

  8. #8
    Join Date
    May 2011
    Location
    North East, UK
    Posts
    216

    Default

    Thanks a lot for the help folks, much appreciated.

    I did consider buying Connelly's book but on account of the fact it only seems to be available during a full moon in exchange for 200 of rare Amazonian Frogs legs I do appreciate being able to get help on here!

    Richard- Would be interested in your DVD but can you post to the UK? How do I order?

    Quote Originally Posted by Erik Brewster View Post
    If you are feeling really frustrated, you might even try bluing the part, taking a picture, cleaning the part, then bluing it again. Take another picture and compare. Are you getting consistent bluing patterns? If not, you need to figure that out before you touch your scraper.
    That's a good point which I figured out by myself actually. I am able to get the same pattern each time, but also, every single iteration I've been taking a snap on my mobile phone so that I can compare, and I can see a logical progression with each pass, until I kind of 'stall' at the level above. I found this really helpful to confirm I was actually getting somewhere.

    First things first I need to get a smaller radius and some proper sharpening equipment I think, and I think it sounds like I need to check the depth I'm scraping, then I'll come back and re-read all of this!

    Cheers,
    Richard

  9. #9
    Join Date
    Mar 2005
    Location
    Toronto
    Posts
    6,572

    Default

    Quote Originally Posted by loply View Post
    First things first I need to get a smaller radius and some proper sharpening equipment I think, and I think it sounds like I need to check the depth I'm scraping, then I'll come back and re-read all of this!

    Cheers,
    Richard
    there's varying opinion on the radius - I find a large radius honed super sharp can help 'find' the point. I think what strikes me as maybe the important issue is how fine an edge you are putting on the tool. If the next level is more bearing points per sq in, this is difficult to do if the depth of cut doesn't also start to get reduced and to do that you need a finer edge. On finished things the surface won't move a tenths indicator...but you're not going to get there without less and less depth of cut. The more the work is toward finishing, the more I find I'm sharpening the tool - and that's using a power cast iron lap with diamond (homemade) that puts a mirror finish on the tool. I like having several scrapers handy and sharpen them all at once - when all of sudden you realize the scraping is no longer that pleasant, grab a fresh scraper and smile goes back on your face
    Last edited by Mcgyver; 08-29-2012 at 10:54 AM.
    .

  10. #10
    Join Date
    Aug 2012
    Location
    Cottage Grove, Minnesota, USA
    Posts
    318

    Default

    I disagree, The 4 Rules of scraping a 20 to 40 point bearing with 50% touching and 50% low area's are:
    1. Individual scrape marks
    2. Individual scrape lines
    3. Depth of cut (.0002" to .0005")
    and a new one I've added in the past 3 years
    4. Hinge the part.

    I have been scraping for 50+ years and rebuilding machine tools for 41. I have been teaching scraping classes for 30+ years and I also still rebuild machine tools. I specialize in scraping precision machine tools like Moore, Sip Jig Bores. I manufacture cast Iron Straight Edges and scrape them. No Depth is the reason the part flip flops, or comes and goes. Think about gage blocks and how they ring together when you stack them up. Super flat and they stick. Ways scraped to flat gull up and get stick slip. We scrape straight-edges deep so they can be used over and over again and not wear out. We scrape ways that way so they can support the weight plus oil flows in the low area. I am sorry if this offends mcgyver and his opinion, but these are facts and if you were to measure the scraping on a new Moore or Sip, a Brown and Sharpe Straight-Edge you would see they are .0002 to .0005" deep.

    I bought a Glendo Accu-Finish I grinder / Lap 20 years ago and use a 600 grit wheel. I use it in my classes and when I am rescraping machines in my profession. I have replaced the wheel maybe 2 times. Those home made laps work well though and are cheap to make. I also use a double end grinder like a Baldor brand with a 300 grit wheel. Most pro's use these types. The finer the wheel the better, but not needed to get a good bearing.
    Last edited by Richard King; 08-29-2012 at 11:39 AM.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •