Surface Grinding Technique for Dummies - Page 2
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  1. #21
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    And always rember what Dennis said....

    Buck

    Re:
    Always keep in mind, heat is the enemy while grinding.

    Dennis

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    I agree, plunge grinding produces a LOT of heat. Another trick for flattening warped work is doublesided tape. Beats the hell out of fooling with shims and crap. I certainly would not plunge on it though.

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    Perhaps this isn't what you were asking but I do have a suggestion concerning grinding. While the other posters have offered some excellent advice I begin a grind with determining whether I can secure the workpiece (or what's holding it) well enough on the mag-chuck. Yes the finish, wheel selection, depth of cut, and feed are all very important. So is ensuring that you don't launch the piece off the chuck. As others have correctly stated, heat is to be controlled while grinding. Heat can cause a piece to "suck up" into the wheel (warp) and it may cause the wheel to launch it off the chuck. If you're grinding fairly thin, flat pieces there's a greater chance of this than a chunky (technical term) piece. One of the things I do is to see if I can move the piece when it's on the mag-chuck BEFORE I start power to the wheel. If I can move it with my fingers so can the wheel. You'll want to have some sort of fixture or larger pieces of steel that are thinner than the workpiece but have a large enough surface area for the mag to grip. Ensure there's no grinding dust on the chuck or workpiece sides (a small paintbrush works well) and slide these into contact with the workpiece on either side (in the X axis) to prevent any movement of the workpiece. If the workpiece is moved by the wheel it can get grinding dust under it and that means it's being lifted off the mag-chuck. Any time you remove the workpiece you need to have clean surfaces where the workpiece contacts the mag-chuck. You'll have plenty of opportunity to develop good grinding techniques, make sure you can secure the workpiece by whatever means you need to. Just don't rely on the mag-chuck to hold things all the time by itself, it won't. Also, if you use D-2 for anything it will not stick to the chuck well enough for grinding, always secure it in/on something that's A-2, CRS, or anything that won't move around on the chuck. Hope this was of some help, good luck.
    Last edited by AD Design; 07-29-2013 at 10:08 PM. Reason: Incoherent thoughts

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    Quote Originally Posted by allloutmx View Post
    Trying to find you on the world wide web...I love a good blade, i carry an over priced ontario xm-1. would love to see your product. Also, ever though of throwing a picatinny rail on a fixed blade? I keep thinking to throw something together for my AR.
    Check out Larry Mensch if you like custom made knives.
    Larry and Knives, Pg 1 - A WebsiteBuilder Website

    I'm not a collector, but I've done some machining work for him in the past.

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    I am just lurking and learning on this thread, but wanted to tell you guys that I am learning so much reading your posts here. I wish I could meet you all and learn from you in person, but I can say that I am sure absorbing so much from you. Wow. Thanks
    Bernie

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    tape for flattening warped work..

    I use double-back, first time ordering a special tape made for grinding and big bucks then just used carpet tape that worked as well.
    Problem is that grinding produces a lot of pressure and will spring a thin part. Good check is to set a part over a bridge of two blocks and then with a tenth indicator at center push down with two fingers.. If it springs away then when grinding it will also spring away..
    With that spring away from grinding pressure, grinding out a warp may be impossible. That is where the shim under is needed.
    Some materials 1/4" stock will spring away with grinding... for a long part 1/2" and more will spring away.
    You might use tape, a shim under to fill the possible spring gap and a stop block at the go side.

    Might even be needed to grind away only part if the warp then flip/ flip if relieving stresses is included in the the grinding or getting close to finish size.

    non grinding...
    Another way to flatten is to bridge the part then push (press) to a set of shims (stack) to get the exact press amount.. keep decreasing shim by a very small increments (perhaps only a few thou) till the part bends. Yes it might crack but I have saved hard parts with no grind-stock this way.
    Heat and splash works also but with needed hardness can be chancy. Bump with a carbide or tool steel chisel also works but leaves marks.

    Yes a grinding heat burn will put in stresses and warp a part. One government test suggested 200,000 tons of stress can be set to a part with a grinding burn.

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    Buck, I'll differ with you there. If you are producing that much pressure grinding, you are doing it wrong. Grinding should produce the least tool pressure of any machining operation, other than maybe EDM. Too much deflection = too much depth of cut. How much deflection could .0001 depth of cut produce? You must tailor your technique to the job. One reason why grinding is besot with so much "witchcraft and black magic".

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    This is a tip related to getting parts flat when surface grinding. Something I picked up off a grumpy ass ole tool maker. lol..

    One morning at my last job I walked into the crib witch just so happened to double as our tool room, the place where jigs and fixtures were made for the parts we machined.

    I rounded the corner just in time to see one of our older tool maker standing at the surface grinder with a cigarette cellophane with white powder in it holding it about eye level kinda squishing it around with his fingers. I said wtf have you got there? He just grinned and said nothing at all to me what so ever. Of course by now he has my attention but he looses track of me, I keep an eye on him seeing what he was going to do. Well long story short, baby powder is what he had. He put that powder on the magnetic chuck then laid his plate on top of the powder then did a few figure eights with the plate then turned on the magnetic chuck and ground his piece. His plate was trapped on the chuck as to not slip off.

    The powder fill the voids so when the magnet was turned on it acted as shim. Flipped the piece over then ground it flat. I thought that was pretty slick.

    The only other thing I remember about this guy is he was always putting vix vapor rub on his nostrils, said he could breath better. Smart man he was..

    I didnt read the whole thread and maybe this isn't new to anyone but I just thought I'd share it with you all. Thanks for reading..


    Brent

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    Quote Originally Posted by tdmidget View Post
    Buck, I'll differ with you there. If you are producing that much pressure grinding, you are doing it wrong. Grinding should produce the least tool pressure of any machining operation, other than maybe EDM. Too much deflection = too much depth of cut. How much deflection could .0001 depth of cut produce? You must tailor your technique to the job. One reason why grinding is besot with so much "witchcraft and black magic".
    One simple test of grinding pressure is to hand push a part into a bench grinder wheel with feeling the pressure used to produce a noted amount of sparks. Then on a surface grinder with the same amount of contact to a part produce the same amount of sparks. Yes using a wheel of the same grit and hardness.

    A certain amount of pressure is required to force the abrasive particles to penetrate the work piece material.

    Yes wheel pressure is directed three ways, down to the chuck, to the go direction and resisting the cross feed direction if that is being used.

    Another good test is to place a part across two blocks on a plate, set on a tenths test indicator to the center of the part and then push down with one finger then with two two fingers to note the deflection or bend to the part.

    Another good test for all machining not just grinding is to place a tenths indicator to a standing cutter spindle or even a machine collum and give a full hand push to see if there is deflection.

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    One government test suggested 200,000 tons of stress can be set to a part with a grinding burn.
    Buck, I'll differ with you there. If you are producing that much pressure grinding, you are doing it wrong. Grinding should produce the least tool pressure of any machining operation, other than maybe EDM.
    Given the tensile strength of steel, that actual number does not sound plausible in tons or lbs.
    But I think Buck's point was the stress set up in the metal due to heat contraction from grinding wrong ("burn"); not the actual pressure on the part.
    Similar to torch straightening shafts, or bendiing large beams. So I guess since they did not specify the material section in area, maybe big numbers on big (huge!) parts would be possible. Small red-hot bead on one side of a massive I beam, quenched. Do a number of them and the beam gradually bends. same effect on grinding parts.

    Or maybe I missed which post was being replied to.

    smt

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    That figure was from government test most likely at a university or the Grinding Wheel Institute and reported I believe in a book by Kenneth B Lewis. I still have the books but did not note the page so would have to re read them to find it. I think it was in "The Grinding Wheel".
    In the test they heavy burned a piece of steel by surface grinding. Measured the stress induced warp age..Then cold honed away the burn to beyond the stress and re checked the residual stress and distortion to come up with that figure..I know it seems impossible...The test concluded how much pressure would be needed to cause the damage with methods other than grinding.

    The stress cause the sample to retain the warp even after the entire burn was removed.

    We were discussing grinding out a warp and I added that (the stress comment) to illustrate the possible cause of a warp.

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    It is worth mentioning here since several have had it wrong, that the crossfeed is "Z" and the down feed is "Y". This is in conformance with the worldwide specification that the "Z" is the axis of spindle rotation . The "X" is the largest of the 2 remaining axes . Thus the down feed is "Y".

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    Quote Originally Posted by yardbird View Post
    This is a tip related to getting parts flat when surface grinding. Something I picked up off a grumpy ass ole tool maker. lol..

    One morning at my last job I walked into the crib witch just so happened to double as our tool room, the place where jigs and fixtures were made for the parts we machined.

    I rounded the corner just in time to see one of our older tool maker standing at the surface grinder with a cigarette cellophane with white powder in it holding it about eye level kinda squishing it around with his fingers. I said wtf have you got there? He just grinned and said nothing at all to me what so ever. Of course by now he has my attention but he looses track of me, I keep an eye on him seeing what he was going to do. Well long story short, baby powder is what he had. He put that powder on the magnetic chuck then laid his plate on top of the powder then did a few figure eights with the plate then turned on the magnetic chuck and ground his piece. His plate was trapped on the chuck as to not slip off.

    The powder fill the voids so when the magnet was turned on it acted as shim. Flipped the piece over then ground it flat. I thought that was pretty slick.

    The only other thing I remember about this guy is he was always putting vix vapor rub on his nostrils, said he could breath better. Smart man he was..

    I didnt read the whole thread and maybe this isn't new to anyone but I just thought I'd share it with you all. Thanks for reading..


    Brent
    A reasonably feasible idea and worth a try for those with an open mind. Closed minds need not apply.

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    Default Starting a grind

    Quote Originally Posted by ARCustomKnives View Post
    I'm sure this has been covered extensively before, but after much searching, I figured I would just ask:

    How do you start a grind?

    Let's assume we have something like a 5x5x1.6" block of steel mounted on our magnetic chuck. I want to take it down to 1.5" thick.

    I dress my wheel (let's say for the sake of argument that it's 1/2x7) and I'm ready to start surface grinding.

    Do I....

    Start somewhere inside the edge of the block and work my way out to one edge and back to the other? I'm assuming that this way (granted that the block is already mostly parallel) I'm using the full cutting width of the wheel initially, until I come off of the edge of the block and start working my way back... correct?

    OR

    Do I start with my wheel outside of the block of steel completely, and start working my way in from the outer edge, using just the corner of the wheel at first?


    Now the reason I'm including dimensions is simply that I don't know what I do not know... I'm not sure if certain grinding applications/techniques are determined by how much your're grinding or needing to take away, so I figured that setting a specific scenario may yield more specific information...

    Thanks in advance!
    Hey, what you seem to be talking about is what we call a touch off. Theoretically your supposed to use the paper touch off method with your wheel off, some goofs like to leave it on to watch the paper fly but it's dangerous. I personally use a 14 x1.5 wheel and i just look to see when the light disappears between the part and wheel, i know I'm with in .003 give or take. So what you do is mark your highest point on your part, topographically speaking and put that section in the back where it's easiest to touch off.
    It's very important if your grinding really wacky saw cut crap that you measure your high point and touch off, it only takes a second to progress from a .002 cut to .025.
    Use your paper to get close, back the wheel off of the part, start your wheel, get your table going and feed on to your part and expect it to hit in approximately what ever the papers thickness was.
    Also a rule of thumb when grinding is with light cuts you can use full wheel to two thirds of the surface. When heavy cutting use one third to two thirds, we use automatic grinders so it's easier to guage but not an exact science. Also do understand the different styles of dressing a slow medium and fast pace. The slower the better the ra but the faster the more predictable the cutting when it comes to minimizing tool pressure.


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