Boomerang Shaped Grind Marks On Bridgeport Ways
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  1. #1
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    Default Boomerang Shaped Grind Marks On Bridgeport Ways

    I have ALWAYS wondered how they get those boomerang marks on the ways on Bridgeports. Nothing looks prettier than the ways of a brand new Bridgeport.

    If anyone could educate me on this, it would clear up something I have been wondering for years.
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    It's called flaking. While I suppose there's a machine for this, they are usually merely scraped there with the end of what looks like a file with no teeth.

    Their purpose is to create little divits to hold lubricating oil as the parts slide to and fro.

    Their secondary purpose, is to look pretty. Really. Getting all those half moons so identical and visually well spaced, was the trademark of a skilled scraper, although them looking so nice isn't nearly the important part of the whole process. It's the simple concept of taking pride in the WHOLE process...

    It's part of a process called "scraping", which is a method of getting a surface flat, by scraping away the high spots. It's an entire trade, and a very difficult one reserved in the old days for those with lots of mechanical aptitude, patience and diligence. Not a lot of hand scraping is done anymore.

    Power scraping merely replaces the hand file looking thing, with a handheld power tool that takes away some of the effort. It still looks pretty hard!

    Google metal scraping and you'll start to get an idea.

    Tools

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    Yes, there is a machine for this - a Biax HM-10 half moon scraper which can be gotten from Dapra. It can also be done by hand by rocking the scraper.

    Here's a good description of the scraping process.

    http://www.moglice.com/newsite/frame...ightframe.html

    Steve.

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    Talking

    They are very bad. All of the good mills have them worn flat.

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    It might not be a popular opinion but I think that heavy, machine applied, flaking completely ruins the appearance of a machine. It isn't part of scraping. A scraped finish will already hold way oil. That's down to the number of spots per inch that the ways are scraped to and the depth of the cutting used to reach that number.

    Flaking tends to get used on machines that have ground ways as a way of breaking up the surface of the ways. Some people then claim that the ways have been hand scraped. This isn't strictly honest, is it?

    If you just want pretty on a scraped surface, use frosting on the final pass. Much nicer.

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    Last year got a tour of the Hardinge factory where they now make Bridgeports. They have at least one guy with very big arms that scrapes the ways entirely by hand. And it is like watching an artist while he works. While there, I also got a peek at how they apply those perfectly spaced marks to the tables. It's ingeniously simple and a kick to watch. They mounted a Biax scraper on the head of a standard Bridgeport that's been converted to CNC. Then they mount a new table on the machine's table and program the mill to move the Biax into contact with the table, make a mark, then move to the next spot and do it again. and again and again. All perfect spaces and perfect marks. At first it's a little unnerving watching the Biax scraping an brand new table. But then it becomes almost hypnotic watching all those perfect little markings going on one at a time.

    Rick

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    Talking If you want to do it your self

    Another way to do it is (and its hard to explain here) take a 12" file and grind a radius on the end at a sharp angle. Make sure its sharp then take a 1" x 4" x 1/4 thick crs tack weld it 3/4's up from the radius. Tack weld this across the file. get a big file handle biggest you can find. Then wrap the hole thing with duct tape. (not the Radius) Hold the handle with your dominant hand make a fist with your other hand. Push the handle with your hand on it against your tit muscle hold firmly, now hit the cross bar with your fist sharply on one side. Pushing your weight against your part at about a 45 degree angle. Try this on a junk part over and over untill you master it. The guys I worked with when we learned this took about an 8 hour shift to make the tool and learn the trick. Then as we did it it became easy. When you get done every body will be like how'ed you do that, it looks great. With just a little practice you can do it in no time.

    Have Fun

    Gerald

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    I used to do the "flaking" with this Borel Dunner Unit after scraping with a Biax. My dad and uncle could "flake" by hand but quickly went to the machines when they became available. They would spend a lot of time scraping their "master straightedges" against each other using red lead and dykem. Martin

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    There is an old tradition of using scraper marks for decoration on machine tools. The Hardinge Brothers Cataract lathes and mills (1903-1938) were decorated on every unpainted machined flat surface on the cast iron parts. The marks were made by pressing a flat-ended scraper against the iron and rotating the tool about the center of the sharp edge. Most of the visible decoration is on surfaces that did not require particular accuracy, did not contact other parts, and had no need for oil pockets. Like I said, it was decoration. The old Hardinge catalog illustrations show the dazzling effect of the decoration. Usually the existing machines have lost most of the original scraping. But here is a picture of my set of Cataract headstock and tailstock raising blocks from about 1920. Lack of use combined with dry storage has let them keep most of their original finish.

    Larry


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    My take of Flaking (frosting)

    Here's one of the best kept secrets of the machine tool rebuilding racket: that pretty flaking pattern so much admired on exposed hand scraped ways is strictly for appearance and it works against the owner, shortening the life of the machine.

    I've heard old hands sincerely speak in glowing terms of a "proper flaking job" as though it was both the crowning glory of a machine's appearance and a conscientiously applied means of retraining oil and reducing friction. Given a free hand a master scraper would apply an artistic scraping pattern to all exposed bare metal surfaces much as a prideful bosun's mate applies fancy rope-work to a vessel's quarterdeck fittings and appurtenances.

    The master surface plates at Hunter's Point Shop 31 scraping bench had a handsome logo scraped in the center of their reference faces and the logos and all had near perfect bearing.

    I've seen case hardened machine tool purchasers of vast experience be so taken with a beautifully flaked way surface they completely ignore the hazard it represents to machine tool longevity. They admire its glistening iridescent surface, run their hands over its hypnotic indentations and breathe "It takes a master scraping hand to do this."

    I think BS, I used to do that by the acre with a Biax half moon power scraper and the brilliance of the scraping came from lapping the scraping edge with 9 micron diamond compound to a mirror finish. You can cover up a multitude of machine discrepancies with pretty flakiing. It's eye-catching and beautiful. It's also the used machine tool sales equivalent of putting a banana in the rear axle of a used car to silence failing gears.

    Most machine tools feature way wipers either of felt or sophisticated molded rubber designed to exclude grit and chips plus retain oil at the ends of the ways. Flaking done with a heavy hand may go as deep as 0.002 below the scraped surface and if done for maximum effect the depressions have abrupt intersections ideally configured to trap dirt.

    I'm a firm believer of flaking as much as 5% of the area in any fully housed way bearings as a means of lubricant retention and reducing "stiction" but never in ways intended to be exposed to chipflow or airborne dust. There, the ways should remain scraped smooth so the way wipers can better conform to the surface, excluding dirt and retaining oil. When the hand scraping pattern fades from the exposed ways in a few years, it's time for a re-scrape.

    The secret to flaking is practice and preparation. Those pretty half moons are a product of hard core consistency. I've Biax half-mooned about an acre (subjectively speaking) of way surface but still I'm no expert.

    If I was learning flaking all over again, I'd first get several days of practice in one hour sessions to teach my muscles what to do. The actual learning takes place in the small hours of the morning when you're asleep. This part of skill building can't be rushed. Find any piece of flat scrap cast iron and practice running lines of flaking striving for consistent motion with the tool, perfect starts, and perfect stops. Hitting the work every time with the scraper running and in motion while making the first half moon the same in size and shape as the middle and the last will come but not for several days.

    On a ground surface you get only one chance to make perfect display flaking. It's a Zen-like occupartion where abstract concentration and focus leads to the perfect manipulation of the tool.

    If you've going after raw beauty in a display piece you need to diamond lap (9 to 12 micron (green) lapping compound) the scrapers to mirror finishes and dead keen edges. Only then will the flaked surface glint and sparkle for as long as you can keep the rust and tarnish off.

    A handsome piece of decorative flaking requires some layout and some carpentered jigging. Decide the orientation and spacing of the flaking on the work.

    Decide if you want to lay down parallel rows of flaking in one direction and then shift orientation and flake to other, or some combination in alternation. I've found a "twill" pattern is effective. Run some practice patterns before you make your decision.

    Decide the scale of the flaking. Too small and the flaking looks busy, too large and it loses esthetic appeal. Ideally the flaking should commence and end right at the edges. Believe it or not, once you get the rhythm it's not difficult to start and stop right on the edges of the work without dinging them up. Just don't try to do to on purpose. Let muscle memory and Kentucky windage (and Zen) guide your hands.

    Decide the spacing. Parallel rows should have about 1 1/2 times the pitch as the width of the flaking in my opinion. Here again you'll have to experiment.

    Make a hardwood straight edge to guide the tool. Clamp it in place and practice using it. Use the straightedge for every row of flaking. This ensures linear perfection letting you ignore one variable so you can concentrate on those remaining.

    If you have trouble with the starts and stops, clamp cast iron blocks to the edges flush with the surface for the scraper to start and stop on. This protects the crisp edges from taking a beating should you happen to blow the start.

    Keep the chips vacuumed up. Running over chips leads to chipped scraper edges and scores in the scraped depressions.

    Clean the surface thoroughly and lightly Arkansas stone the surface going in the direction of the ground finish. Use WD 40 for a cleaning and stoning lubricant. This stuff is in a class by itself when used for stoning.

    As with any risk laden skill, knowledgeable cheaters always prosper.

    The powered flaker is a marvelous tool. Customers love a pretty flaking job and the Biax HM-10 certainly shortens the time to do it.

    Given my choice, I never frost or flake finish cuts of a routine scraping job. I can get the surface interruption for fully closed way bearings using a hand scraper or the Biax 7-ELM by selecting the right radius of the scraper edge and the way I manipulate it.

    Whenever I got instructions for a nice "half moon flaking job" I'd bum the Biax HM-10 flaking tool and scrapers from my ex-employer and give the customer what he wanted. That’s at a surcharge and I’d give a written caution that half moon flaking is detrimental to the performance and life of way bearing wipers.

    I made it a point to do a beautiful job of flaking for the customer knowing that the service life of way bearings exposed to the chip/coolant wash would be cut by a third or a half given usual shop negligence in servicing way bearing wipers. A thing of initial beauty is sometimes a compensation for reduced production life.

    I'd give some detailed how-to but this post is long enough.


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