Beginner scraping question on scraper design
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    Default Beginner scraping question on scraper design

    I've been watching a lot of videos lately on scraping and working on gearing up to do some scraping of my own. I've noticed that about half seem to use a rounded scraper tip and about half have a straight tip with just the corners rounded off. I haven't been able to find any explanation as to why I should be using one or the other.

    So, is it just personal preference or are there specific situations in which using one or the other is the "right" choice?

    Sorry if this has already been asked, I did some searching but didn't find anything.

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    Nobody else has taken the bait here......

    Rounded for "push" scraping. That allows you to vary the width of the area scraped for each stroke, by varying the angle of the blade to the surface being scraped.

    As far as I know, the straight type are more along the lines of "pull scrapers". I've tried straight for push scraping, (just because) and did not like it. It may be useful for some types of "frosting", or finishing with a pattern, but I do not fool with it.

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    The radius on the tools depends on your target spot density (points per inch). The Biax blades come from the factory with four or five different radii ranging from 20mm (very narrow, for pin-pointing) to 150mm (rather broad, for large area scraping). Smaller radius and shorter strokes for smaller spots, especially when finishing. Larger radius and longer strokes for larger spots, especially when roughing.

    Don't obsess about it. Go to a smaller radius on the tool if you reach a PPI plateau that's too low for your objective.

    Always radius the tool or at least knock the corners off to avoid gouging the work.

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    Thanks for the replies. I'll probably just fabricate a pull scraper with a straight blade from some scraps and inserts to try that out too. Right now I've got a 3/4 anderson scraper with a 3" nose radius ground on it that seems to be working alright but I only tried a scrap of aluminum plate I had so far. I picked up a pair of old 4x4x4 cast angle plates that I'd like to try restoring soon.

    There is a youtube video from Japan that has a whole shop of guys using large push scrapers with straight edges too but that's the only one I can recall like that and their scrapers and techniques were different from anything else I've seen in many other ways too.

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    My Starter Pack


    Make that a 2" Radius


    The task at hand.


    Business end

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    I see you have EZE-laps for sharpening. Not too bad. You might want to make something to hold the lap so the angle is consistent, about a 5 degree negative rake seems to be a common one for the scraper "edge".

    Your aluminum block is not bad, considering how nasty I think it is to scrape. You might vary the direction of scraping more often, and to more angles. I usually do three directions, unless the surface makes that too difficult (like a surface that runs under a dovetail).

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    Yea I'm using the laps to finish it up, I did most of the shaping on my bench grinder but the wheel was suffering so I'll need a better solution long term. I'll try it with a bit of rake, it was basically 0 for the aluminum.

    The aluminum was coming in nicely but I did just kind of stopped abruptly when I started having issues spotting with it being such a small light piece and possibly my hand heat effecting it. I couldn't spot it twice in a row and get the same result anymore, it was time to get a real work piece.

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    Quote Originally Posted by KVandy15 View Post
    Yea I'm using the laps to finish it up, I did most of the shaping on my bench grinder but the wheel was suffering so I'll need a better solution long term. I'll try it with a bit of rake, it was basically 0 for the aluminum.

    The aluminum was coming in nicely but I did just kind of stopped abruptly when I started having issues spotting with it being such a small light piece and possibly my hand heat effecting it. I couldn't spot it twice in a row and get the same result anymore, it was time to get a real work piece.
    Your strokes are too long for a 50 mm radius blade, shorten them to about 1/4" or shorter, keep them about 1/8" or less apart. For roughing keep the stroke 1/2" to 3/4", you should use a 90 to 100 mm blade and keep the strokes 3/16" to 1/4" apart. You should be able to make the cut about the same width. Try to lay down rows at 45o in both direction. A basket weave patter emerges quickly if you keep things even. Before you get to 20 PPI just concentrate on bringing down the high areas, once you have an even 20 PPI, switch to a 50 to 60 mm blade, start splitting flats and also start concentrating on the highest spots. Have fun .

    first pass on my Starrett 199 level:

    img_2281.jpg




    dee
    ;-D

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    Thanks for the tips, I think I am going to cut another wider blade as well to go with this smaller radius. I've also got a 1" scraper because I have no self restraint so I'll probably do a wider blade for that.

    Also a lot of the longer scrapes seen in that shot were more or less me just messing around, I didn't really intend for that to be the focal point but I love the feedback. I'll be sure to put up some pics of the angle plates once I get started on them.

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    Quote Originally Posted by KVandy15 View Post
    Thanks for the tips, I think I am going to cut another wider blade as well to go with this smaller radius. I've also got a 1" scraper because I have no self restraint so I'll probably do a wider blade for that.

    Also a lot of the longer scrapes seen in that shot were more or less me just messing around, I didn't really intend for that to be the focal point but I love the feedback. I'll be sure to put up some pics of the angle plates once I get started on them.
    BTW that first pass on the level was with a 90 mm radius blade. the 60 mm is a lot narrower and shorter strokes, you can see pictures in this thread: Scraping in a precision master level

    dee
    ;-D

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    Quote Originally Posted by KVandy15 View Post
    I've been watching a lot of videos lately on scraping and working on gearing up to do some scraping of my own. I've noticed that about half seem to use a rounded scraper tip and about half have a straight tip with just the corners rounded off. I haven't been able to find any explanation as to why I should be using one or the other.

    So, is it just personal preference or are there specific situations in which using one or the other is the "right" choice?

    Sorry if this has already been asked, I did some searching but didn't find anything.
    I prefer straight tipped scraper but that's just me and people get good results with both. Also, HSS tips can be sharpened FAR better than carbide ones and that makes a HUGE difference in how easy you'll get to scrape accurately while producing a visually pleasant pattern. I find pull scraping to be decidedly superior but again, people get good results with both. The height of the work is much more critical for pull scraping though - bit of an inconvenience. The sharpening of the scraper is what held me back for a while a decade or two ago - you might try to find a professional scraper who can show you how it's done. From real sharp to so-so is a massive difference. Not to confuse the touching up of the edge you see on YT with proper sharpening.

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    Quote Originally Posted by KVandy15 View Post
    Yea I'm using the laps to finish it up, I did most of the shaping on my bench grinder but the wheel was suffering so I'll need a better solution long term.
    3pcs set 240/600/3000 grit 6" diamond grinding disks is less than 15 dollars from ebay and works amazingly well on carbide. 240 or 600 grit for shaping and 3000 grit for finish and re-sharpening. 1/2" mounting hole matches the cheapest bench grinders. AFAIK For optimum results you should run slower than typical bench grinder but my results have been really good even on 3000 rpm grinder.

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    Quote Originally Posted by AlexO View Post
    I prefer straight tipped scraper but that's just me and people get good results with both. Also, HSS tips can be sharpened FAR better than carbide ones and that makes a HUGE difference in how easy you'll get to scrape accurately while producing a visually pleasant pattern. I find pull scraping to be decidedly superior but again, people get good results with both. The height of the work is much more critical for pull scraping though - bit of an inconvenience. The sharpening of the scraper is what held me back for a while a decade or two ago - you might try to find a professional scraper who can show you how it's done. From real sharp to so-so is a massive difference. Not to confuse the touching up of the edge you see on YT with proper sharpening.
    If i was pull scraping i would use a very large radius blade, something like 150 to 200 mm with rounded corners, say .5 mm or less corner radius. If your blade is completely flat you will have no valleys nor peaks, you will have plateaus and flat ditches, your flats will be the same size as your scrape blade width and your stroke length. It might be completely fine for you, but i would be concerned about getting a good PPI. With a radius blade you can make different width marks by adjusting the attack angle and scraping depth, with a flat blade you need a different width blade to change mark width. If you look at the images from Wyler it looks like the pull scrapers they use have a blade with a radius, not completely flat, The marks seem to start with a radius and not a straight line. I am not 100% certain, i am just reading the tealeaves.



    It would be interesting to get confirm or deny form people who work(ed) as , or know Wyler scrapers.

    With hand scraping sharpness, carbide HSS no matter what you use, is paramount, as soon as the scraper is dull you are fighting it. I tend to sharpen my carbide almost every pass, especially during roughing. Once the radius and relief angle is established it is just 3 swipes or so on the lows speed 1200 grit diamond wheel. It is not mirror polished but very sharp. You do not notice a dull blade that soon with a Biax, you can cover a lot more territory before the blade tells you to quit.

    dee
    ;-D

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    Quote Originally Posted by dcsipo View Post
    If i was pull scraping i would use a very large radius blade, something like 150 to 200 mm with rounded corners, say .5 mm or less corner radius. If your blade is completely flat you will have no valleys nor peaks, you will have plateaus and flat ditches, your flats will be the same size as your scrape blade width and your stroke length. It might be completely fine for you, but i would be concerned about getting a good PPI.

    dee
    ;-D
    The blade is never really flat - because of the way it's sharpened it is actually very slightly round and overtime gets rounder and rounder. At some point I take it to the grinder and straighten it again. Both systems make for good results but I scrape small surfaces and one of my concerns is to keep valleys to the minimum. Look at fresh areas on a SIP jig borer ( under the columns...) - there are practically no valleys. All you'll see is "shadows" of a very wide, VERY sharp, flat scraper. For me, the "PPI" doesn't mean that much and in general I think it gives a misleading sense of quality. What matters to me is the percentage of surface between two highs. The problem as I see it is how the surface starts to wear. But that's a long story...

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    Sounds like I am going to want to try a straight blade on the push scraper too. I think I have spares to try that with the Anderson scraper as well. I did get a couple of HSS blades as well but I haven't tried those yet either. I've got an extra day off this weekend so hopefully I can spend at least one of them in the shop.

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    Quote Originally Posted by KVandy15 View Post
    Sounds like I am going to want to try a straight blade on the push scraper too.
    It gives you a lovely smooth surface but ONE mistake and it takes ages to put right that gouge. Also tends to pick up material under the blade which can cause gouges too. Try it with very short strokes and keep cleaning the swarf off the blade.

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    As always this subject has been written about several times before:
    In a class I taught 2 weeks ago in Stuttgart Germany one of the students brough 3 pull scrapers that he inherited from a old scraper he referred to as the "old Man"

    The old man had shown the German Student how to pull scrape as he had pulled scraped in his past career in Switzerland. The old man was 70 when this student knew him. Anyway, after the "old Man" trained student learned how to push scrape the BIAX method of hand and then power he put away the pull scraper and said he would only pull scrape the last couple of passes to get the pull scrape look. He said that but in reality he never did during the class. I have seen this before too.

    Pull scrapers switching from pull to push and BIAX power after finding out the "old way" sucked. I have worked with Sip Techs and they scraped the exact way I teach using the BIAX Power Scraper to get 50% high and low scrape marks at 40 PPI and then they used their pull scrapers to get their "Signature Look" that Sip used on all their machines. See below in the documents a Swiss student gave me about how to pull and push scrape and they geometry of the blade. It is in French, Swiss and German I am told.

    PULL Scraping

    Pull Scraper Geometry

    "50+ years experience scraping with over 30,000 students so far"

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    Thanks for the extra info Rich. I figured it had to have been asked before but apparently my searching abilities suck. I assume that push scraping will be my go to choice but it won't cost me much extra to whip up a pull scraper to try out. Even if I don't do it often it becomes another tool in my bag.

    On the subject of the BIAX scrapers. I've been watching ebay for a decent deal on a biax but all of them so far seem to go for like $750 or more and that's often not including any blades. Is that just what it's going to cost or should I keep holding out for a better deal? Maybe look somewhere else?

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    Keith Rucker just bought a Green Motor Biax for $200.00.So if you keep an eye open you can find them. Even a old blue model is easier to use then a pull scraper. Pull scraping has a place in scraping. If you think about it, how many pro's use it to rebuild machines. I have just spent 3 weeks in Germany teaching at 2 - 1 week seminars at German Machine Rebuiders who have BIAX power scrapers and a few hand scrapers. Pull scraping might be fun to screw around with and fun to try now and then, but if your trying to do a job fast and comfortably you will only "play" with them. Check out the Germany and UK class thread next Monday as I will be downloading several pictures over the weekend. KV please share your idea's so new people can learn from your experiences. When looking for info on scraping. "google it and add practical machinists to the search and you will find years of posts listed. Rich

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    Quote Originally Posted by KVandy15 View Post
    On the subject of the BIAX scrapers. I've been watching ebay for a decent deal on a biax but all of them so far seem to go for like $750 or more and that's often not including any blades. Is that just what it's going to cost or should I keep holding out for a better deal? Maybe look somewhere else?
    I don't think that's to bad of a price, a new Biax 7ELM is around $3500. Its an opportunity cost... buy one now and have it and use or wait a year or two for a screaming deal to come up.


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