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    Default How do you get point size larger

    When you are scraping and you point sizes are small, say smaller than 1/16", how do scrape to make the point sizes larger.

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    Normally you would go the other way, but the parameters to change (as I have been taught) are blade radii and stroke length. So I would think you could experiment with going to a blade with larger radii and at the same time lengthen your strokes.

    As far as I can remember some have written to flatten the strokes, ie. lower/lessen your angle of attack, which should give a broader cut. maybe that is easier.

    BTW, I was also taught to use the same downward force, ie. consistent depth of cut, so this should stay the same throughout.
    But.. maybe others can have a different opinion on this?

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    With a flat tipped pull (shoulder) scraper it's pretty easy to get the contact points larger. The pull scraper can really skim tiny amounts off with a lot of control, and hit an area larger than radius tips without digging in. If you are power scraping then you definitely don't want a flat tipped blade- I've done some small reference flats with the Biax and just go for a very high concentration of points, and if I want them larger, spend a bit of time with a stone slip that's been flattened on a diamond hone. Sounds sort of sacrilegious but the prints prove it out.

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    Many times when i see those small points it is because the scraper or your not moving the blade sideways fast enough to get a spacing of the cut or low spot and no cut high spot. This again is you have to use the checkerboard pattern when finishing and not roughing. There are many things to remember when scraping but once you master basic hand scraping the checkerboard x x x x pattern you will discover you will scrape faster and the appearance will look super. Lets start by saying you need to grind your blade tip radius at 60 Mm circle radius with a 5 deg neg rake. Your blade is 20 Mm or 3/4" wide. Scrape a low spot 1/4" long and your width of the scrape mark is 1/8" then you move the blade over 1/8" and then scrape another low spot and keep going sideways at a 45 deg angle to the part. So you have a low spot as wide as your high spot. Many times when someone scrapes the get the spacing to close and the high spots get small. I teach and make my classes say it loud and often in a class exercise. Have them repeat the 4 RULES of scraping. If you can remember these 4 RULES you will scrape faster and better. 1) Individual scrape marks or points (as I said above) 2) Individual scrape lines (meaning the spacing from the line above and below the one your scraping can not touch the line before or after, if they touch you will get long openings or ruts). 3( Depth of the scrape mark or cut. (I have all my students measure how deep they scrape. We take a surface gage and set it on the top of the test bar we practice on and use a .0001 indicator to measure how deep the scrape mark or pocket is. On average they should be .0002 to .0004" deep and as Jan said keep the same pressure down all the time to keep the pattern for coming and going) 4) Hinge the part. (To find the Airy points or as some of the guys say the spin point. I like to see the pivot on each end of the part of our practice bar or your straight edge at 30% from each side edge.) If you fail to hinge or swivel the part you have no idea if the part is high in the middle. high in the middle is one of the worse things that can happen to a machine your scraping as the part will rock or tip like a rocking chair when your moving the slide one way and then reverse the travel. PLease note the Individual scrape marks and lines that create the checkerboard pattern. The 2nd picture is a Babbitt shoe from a power plant generator. On Babbitt we recommend scraping 3 ways to avoid "Chatter" as we discussed in the "Shatter" thread and the leading edge of the shoe is scraped lower so as the generator turns the oil "wedge" flows into the bearing to lift to get the continuous oil film and no wear. Rich
    Attached Thumbnails Attached Thumbnails 20150127_124542.jpg   20140903_160708.jpg   img_0572-1-.jpg   dsc01920.jpg  
    Last edited by Richard King; 02-23-2015 at 11:30 AM.

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    If you have depth of .0004 to .001" you can wet stone it to spread out the points. Think of the high points a pointed mountain and you et stone it to flatten it a little. I teach you only wet stone it ever 4 TH or 5 TH time when you have this issue. if you wet stone it every time you will get to much contact or percentage of points. You want to get as many low spots as high spots or 40 to 60% contact as you can see in the above photo's. Some one once called it "basket weave" and after repeated backet weave over and over again in the same area (checkerboard) the pattern comes and stays. If it goes away you violating rule 1, 2 and 3. It take lots of practice. Rich

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    Are there any variations or points to note when using a Biax rather then hand scraping, Richard?

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    I teach in the classes the BIAX scraper takes away all the work we need to physically push the hand scraper. The new models have a reo-stat to slow them down to the speed of a hand scraper would use. But what or why would you need a power scraper for if you slow it down to a creep?

    As in hand scraping you need to practice using a Power Scraper to get hand and eye coordination so you can hit the high points. This is why scraping the checkerboard technique works so good. As you are using the same motion all the time...you repeat it and repeat it. Look at it as a Tick Tack game. It has a pattern that is easy to follow now if my 5 year old grandson looked at the Tick Tack board and he started to draw circles and zig zag lines it would be confusing as heck to play the game. Same goes for scraping.

    When I teach in Taiwan I have to speak in pictures as I have been told the Chinese Language is bassed on telling a story using pictures in your speech. Over there their are many Motor Scooters, so I use for an example driving a scooter...and driving a Bicycle . You pedal a Bike and it gets tiring and you have a motor on a scooter, but you steer it the same way. Same technique as a BIAX scraper, you hold it differently but you use the 45 deg to the part motion the same way you do it when you hand scrape.

    For many years BIAX was used to rough scrape and you finished by hand. Now BIAX has perfected the scraper and you can get 60 points with one of you wanted to. The old Blue Biax's were made to rough, but some of us who owned them bought speed controls and slowed them down so BIAX started to install VS motors. In the future more changes will be added to them to help the scraper hand get a better job done and faster.

    The most important thing on a Power scraper is to be the detective and figure out how far your part your scraping is off. This will effect what stroke you use and what blade tip radius you grind it to. In a general rule of thumb, I say if the part is out more then .005" machine it. I guess if you have a way grinder or a machine handy if it is out .002" machine or grind it. Then start to scrape by hand or power with long 3/4" for a expert and and 1/2" for a beginner with biax or 1" by hand long checkerboard angles and i say scrape like your scraping paint off.

    You are roughing now and don't need think about Rules 1 and 2 as your scrape marks can touch each other now and you don't need to blue it up every time, you can use the Yellow Canode Highlighter or Red lead to "blind" and "step" scrape until your part is flat to .001" and running the speed at about 1/4 off the fast VS switch. (5 on the green BIAX's). You still should rough using the 45 deg angle and next time scrape 90 deg to that 45 angle to keep your body and technique an X pattern. I will move the BIAX in a circular motion so you move the scraper in a 1" circle overlapping each other as you move from one side to the other. Also move into the work as you will cut off the burrs compared to moving backward as you will leave burrs.

    Then you shorten the stroke and begin to use rule 1 & 2 and gradually get more and more points and your bluing it each time between scrapes . Shortening the stroke, lowering the speed (I slow to about 1/2 speed, but new students like 1/3 the fast speed) and the more points you slowly shorten the stroke, speed and blade tip radius. 90 to 60 Mm blade tip Radius for for roughing to .0002" flat to 20 PPI and 20 to 40 radius blade tip for 20+ points. Look at the pictures and you can see the length of the stroke and the points per inch for reference. The BIAX manual and my work booklet shows this as Jan spoke of. Rich
    Last edited by Richard King; 02-23-2015 at 04:41 PM.

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    Quote Originally Posted by Richard King View Post
    I teach
    Indeed you do!

    What was not covered in these few posts held within it the guidance to go and find the rest, and the motivation to action that.

    May I suggest 'sticky' status to our moderator?

    Bill

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    Thanks Bill !

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    Quote Originally Posted by Richard King View Post
    If you have depth of .0004 to .001" you can wet stone it to spread out the points. Think of the high points a pointed mountain and you et stone it to flatten it a little. I teach you only wet stone it ever 4 TH or 5 TH time when you have this issue. if you wet stone it every time you will get to much contact or percentage of points. You want to get as many low spots as high spots or 40 to 60% contact as you can see in the above photo's. Some one once called it "basket weave" and after repeated backet weave over and over again in the same area (checkerboard) the pattern comes and stays. If it goes away you violating rule 1, 2 and 3. It take lots of practice. Rich
    well, the percentage of contact is still not clear no me. in my experience it varies something like +/- 30%, depending on the amount of blue you use. in the extreme case where you rub without blue, for example, you get tiny shiny spots. but when blued up "thin", bearing might be 70%.

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    That generator shoe looks like a Kingsbury bearing segment

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    Yes it is. I did a scraping seminar at American Babbitt in West Virginia aprox. 6 months ago. I have also taught a class at Kingsbury in Philadelphia several years ago. As far as the percentage goes. On a bearing shoe you leave the leading edge low or no bearing points. This is the leading edge of the bearing and as the turbine turns into the shoes a wedge of oil lifts the turning armature up. The shoes are in an oil sump and the only time. It would wear is on the initial start. Many new design s have a pressure oil lift so there is no wear when it first spins. Rich

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    Quote Originally Posted by dian View Post
    well, the percentage of contact is still not clear no me. in my experience it varies something like +/- 30%, depending on the amount of blue you use. in the extreme case where you rub without blue, for example, you get tiny shiny spots. but when blued up "thin", bearing might be 70%.
    keep in mind with the thin wedge of oil there shouldn't be contact. With the blue, what appears as contact will change with the amount used - same with the viscosity of the oil. Ideally you want the right viscosity and the right small variance between highs and lows such that there isn't metal to metal contact
    Last edited by Mcgyver; 03-20-2015 at 11:25 PM.

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    Sorry to digress, but where does one find the gage used as a window to count the number of points? I realize that it is also for finding the scraper radius as well. I've looked in ebay with no joy.

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    They can be purchased at in Europe from a Biax distibutor. In the thread I talk about the trade show I will be attending a Rebuilding Seminar next month in Germany there is a link to Filipp P. The BIAX sales manager. Write him and mention my name and he should be able to. Help. BIAX will start selling my DVD in Europe now too. We plan on a joint we DVD and book to come out in 2016. Rich

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    I was going to add words of wisdom about scraper sharpening, technique, checker board pattern, etc but Richard beat me to it. Well done Richard.

    The best I can offer are general remarks to beginners that may not pertain to the OP.

    Scraping does take practice and physical effort. I suggest beginners start with surfaces having plenty of scraping stock or material on which can learning mistakes on. Skill hasto be built a bit before transistioning to critical work..

    It takes real effort witg the scraping strokes to remove actual stock. It does no good to scrape off the blue without removing the underlying high spot. Actual chips have to be made albeit small ones. Rough scraping swarf should look a bit like coarse ground pepper or coffee grounds and the beginner should be stiff and sore in the mornings 'til he gets used to the work.

    There's an order and sequence to scraping for machine tool rebuilding. Most start with the milling table of a knee mill for example but the best order and sequence generally starts with the coliumn ways and getting them in accurate geometry with the horizontal milling spindle; next working the knee, saddle and table is a definite order.

    One thing seldom mentioned in these general scraping threads is most precision scraping requires working with two or more scraping references plus levels and alignment tooling if an accurate muturally perpendicular system of machine tool axes are to be generated.

    "Learning to precision scrape" is not something to be learned over a week-end or take a one week class in and be assured of competence. That's just the start. Precision scraping is a large part of a whole trade. Machine tool rebuilders used to serve a four year 8000 hour apprenticeship with scraping and alignment comprising about a third to a half of the areas and elements of practical shop floor experience.

    Home shop guys can work in isolation and teach themselves the scraping process re-inventing the wheel many time along the way but there is no need to. Help is at hand for those who reach out. Many regulars posting here started from a bare bench and a desire. In the course of a few years they developed into competent efficient scraper hands, veterans of several tricky projects. Scraping aint rocket science but it does require dedication. There are classes, books, resources, tools, oodles of scraping videos on the internet, and websites like this one. There is no longer any need for an aspiring scraper hand to labor in solitude.
    Last edited by Forrest Addy; 03-21-2015 at 11:33 AM.

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    Quote Originally Posted by partsproduction View Post
    Sorry to digress, but where does one find the gage used as a window to count the number of points? I realize that it is also for finding the scraper radius as well. I've looked in ebay with no joy.
    Not as durable as the real thing, however a serviceable version is readily made by scribing a square on a bit of clear plastic - cd jewel case works perfectly for this

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    Quote Originally Posted by Mcgyver View Post
    Not as durable as the real thing, however a serviceable version is readily made by scribing a square on a bit of clear plastic - cd jewel case works perfectly for this
    Yes, that works and I've done it but there was one unexpected liability. I'd set it down somewhere and then couldn't find it again because I was looking right through it.

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    I guess knowing the three radii is the only thing keeping me from making my own, a piece of 1/16" spring hardened steel, which I happen to have, should do well. There appears to be one edge that is flat, either as a small straight edge for quick checking or as an area scraper to remove loose crap om the surface. That blue temper steel is about 45 RC so it can be cut, though the Dapra part is probably harder and perhaps thicker.

    The talk about learning basics over time rings true for me, because I know I've wasted many hours with tentative scraping when what was needed was rapid and somewhat ugly material removal, and the more time one "invests" the harder it is to get realistic and lengthen the stroke. It is so pretty and oh so flat, but it's not aligned! Under those conditions it is a bit painful to be ruthless with it.


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