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Manual Surface Grinder Skills

Discussion in 'TOOL GRINDERS & SURFACE GRINDERS' started by electrosteam, Jan 16, 2017.

  1. electrosteam

    electrosteam Australia Steel Registered Member

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    I am starting to get familiar with my SG and seeking some advice on skills that used to be learned on the shop floor from more experienced c0-workers.

    When I put a new job on the chuck, I need to test the surface for the high point.
    This seems to take forever as I move the wheel head randomly over the job slowly dropping the head to achieve first contact.
    What do the experts do ?
    Is it beneficial to start with a stationary wheel, or a wheel slowly rotating (I have a VSD) ?
    Is a shim stock like paper or plastic film inserted between the job and the wheel useful ?

    It is annoying when the last pass on a two-sided job requires the job to be slid off the chuck, scratching the bottom side.
    I know, it doesn't matter, but how can I minimize it ?
    Would thin plastic film, or other material, minimize the risk of this ?

    The stepover percentage that should be used is a mystery to me ?
    What are the trade-offs for large versus small stepover ?, as related to cut and finish ?

    If I take the job off the chuck for measurement then replaced, the next cut is always more than I expected.
    I have made special effort to clean everything to no avail.
    Is it me or a characteristic of the process ?
    What is it about me or the process that must be improved ?
    Or is it just a fact of life ?

    Is there a reference book available online that deals with this type of practical skill ?

    Regards from sweltering Sydney,
    John
     
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  2. projectnut

    projectnut United States Active Member Active Member

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    I'm not an expert, but I can tell you some of what I've learned over the years. First I would start the machine and get it up to speed about 10 minutes before attempting to use it. The warm up period will allow everything to normalize. Any expansion of parts will be completed before you start grinding. When you are ready to start grinding I would shut off the machine, move the table out from under the wheel and stone the chuck with an extremely fine oil stone. Then wipe it with a soft cotton cloth before placing the work piece on it. I would also run a fine file across all surfaces and edges of the work piece to knock of any burrs. Then wipe it clean before placing it on the chuck. If you have a permanent magnet chuck you might want to consider putting a piece of paper on the chuck before putting the work down. Then when it's time to remove the work there's less chance of scratching the chuck.

    As I'm typing this I realize the post could go on for pages and become so boring it would be useless. There are several good sources of information available. I would suggest getting a copy of the book "Grinding Technology" by S.F. Krar and J.W. Oswald. It was published by Delmar Publishers in 1974. It covers many types of grinding including surface grinding. It also gives insight as to what types of grinding wheels are available, how they are constructed, and which ones should be used on different materials. It's a great reference book. I've used it many times to select a proper wheel and learn tricks for securing and positioning odd shaped work pieces.
     
  3. rgray

    rgray Active User H-M Supporter-Premium

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    The tool and die guy site has great info/video on it http://www.thetoolanddieguy.com
    It's not free but I found it very cheap for the learning I got from his site.
    Suburban tools on youtube has video on surface grinding.

    I often use a sticky note. The ones from my bank have their printing at the top. the paper is .002 thick and when you touch the colored part and it starts removing the color it is easy to see. Mostly this is helpful when you want to be about .001 off the chuck cause you are facing with a wheel made to face on it's side.
    Most other times I just go down slowly till I "touch off" the surface. Not to worried about the high spot as anything going on to the grinder should be within .005 of flat anyway. If not the high spot might be obvious and it is then your starting point.

    If your really needing to be careful with stock removal then it would be faster to sweep for the high spot on a surface plate first so you know what you are up against.
     
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  4. intjonmiller

    intjonmiller United States Active Member Active Member

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    +1 all around. Warm up is good (minor clarification: not all part expansion is done before you start working, as the workpiece can also expand), paper is a quick way to find when the wheel is about to make contact on a piece that is already pretty flat, your surface plate can speed up that process and let you know if you need to focus on one area or even tip the part slightly before grinding one side, and Suburban Tool (on YouTube) has an excellent set of videos on surface grinding theory and practice, including shimming with cigarette paper (typically 0.001") to correct for parts that are slightly out of square.
     
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  5. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    Putting a piece of white paper that is well lit behind the work, and then bending down so your eye is parallel with the chuck will let you get within a few thousandths quickly. Then follow the advice above. I typically just lower it slowly with the wheel running just over the edge of the work and traverse the table while looking and listening for first contact. Disclaimer: I am a rookie at this...
     
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  6. machinejack

    machinejack United States Iron Registered Member

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    I use loose shims of varying thickness sliding around under an irregular work piece with the chuck not turned on to support the part if it is irregular. Just crank the wheel down until you get a spark back up a few thou and proceed across the part. You will find that the cut will get heaver or lighter adjust accordingly. Heat buildup will cause a long thin part to buck up. Take it slow. I also use small blocks similar to 1,2,3 blocks to block and support the part. With 40 years of tool making and countless hours form grinding and just squaring up parts I still use cation using the surface grinder it is one of the most dangerous machines in the shop. Just the other day I had a wheel explode because I did not give it a ring test. Also I have several machinist friends that have missing fingers. So be careful.
    Jack
     
  7. chips&more

    chips&more United States Active User Active Member

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    Make sure the part is good and stuck on the mag chuck! Block the part if you can. Your part/project can fly off the mag chuck in the blink of an eye and do some real damage to you, project and or machine. Please be careful, make sure your project is stuck good on the mag chuck!…Dave.
     
  8. schor

    schor Canada Active Member Active Member

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    Some good advise above. I have watched a few videos on grinding on youtube and I also have a friend that is a tool and die maker explain quite a bit to me about the grinder.

    Warming up is something you should always do, stoning the chuck is a must, dressing the wheel every time.

    As for the getting close to start, the piece should already be very flat, most you would need to do it check the corners and the middle to get your touch-off.
     
  9. intjonmiller

    intjonmiller United States Active Member Active Member

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    I have pieces of a grinding wheel that "detonated" when I was careless once. I keep it on a shelf with other reminders of mistakes or surprise accidents. I recommend doing this with any parts that get messed up through any sort lapses in safety judgment.
     
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  10. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    I etch it firmly in my mind, and then destroy the evidence before anyone else sees my screw up... :-|

    Not really, I am open about my past mistakes to help keep others from future mistakes. I do throw away the evidence, unless it is funny enough to make others laugh when I show them...
     
  11. Chips4Lips

    Chips4Lips United States H-M Supporter - Premium Content H-M Supporter-Premium

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    After having a good number of years using several different sizes and brands of horizontal surface grinders, I tend to pronounce it as one of the most dangerous tools in your shop. I don't mean to be "mean spirited or trying to scare you from taking on the learning curve but it is without a doubt one of those tools that you will be "surprised by" at some time, some day when you least expect it - and even when you've been exceptionally careful with your setups thinking that this would be your saving grace. The primary reason is that regardless of the brands of wheels you find - you can never quite tell just how "robust" that wheel is by looking at it. If you hold it by sticking something like an 1/8" allen wrench thru the inside and then tapping very lightly on the outer rim area there should be an almost "bell like" sound to a good wheel - you won't be playing "The Sound of Music" with them but this can help to identify wheels that get loaded up with someone using it improperly by maybe not dreswsing it down thoroughly enough to get the grains back to a clean an clear area. There's a tendency sometimes to think about that diamond that you're dressing it with and how much money you paid for it (so you don't tend to use it too much) but you should - the entire purpose of dressing the wheel is to remove those areas where the metal particles are still imbedded in the partical grains of the wheel. Sometimes you will also see a glazing on the grinding surface that is almost like someone polished it... this too is not a good situation because that "glazing" is made up of many of those particles from the previously ground steel but also from the adhesive and grains of the wheel you're looking at. Having that type of surface will seldom ever do what you want in the way you want because it's just an opportunity for generating more heat and with surface grinders in particular, heat is never you friend. Keeping things cool is cool and should be done in whatever means possible - whether that is a flood coolant that will drown your magnetic table (good thing) or even just a spray mist like you would use on your mill to flush particles away from the cutting area. The coolant liquid is doing the same thing in the grinding operation by flushing those surfaces (you wheel and your stock for removal) continuously which is always good. I've often used a light coat of WD-40 that can work sometimes better than other depending on the steel types you're grinding. So just when you get this cooling details firmly planted in your planning and your grinding, you'll start thinking that this isn't so hard.. the grinder's doing all the work and you just have to keep two hands doing two different things in a steady motion and pace and then the provervbial stuff will not only hit the fan but wipe it off the mount you made on the wall to keep things cool in the shop.. the wheel can explode when you least expect it and I'd guarantee you won't be expecting it but when it happens you'll remember it and once your heart rate settles back down you can do some shop cleanup operations and find a better wheel to continue with. There may be no visible proof of anything you did wrong, but the wheels (to me) are the achilles heel in that they age, they get loaded up with such a mix of liquids, particles and grinding "junk" that you can never quite tell when it's likely to be a problem. I've seen people try to flush a wheel in a parts cleaning tank and then use an air hose with about 90+ psi pressure to try to blow thru the conglomerate to clean it - partially helpful on coarser grit wheels but rather doubtful on anything above a 100 grit zone.

    Having a reliable and proper functioning digital readout is a definite plus but without it, the grinder can still do an excellent job if you pay very close attention to the scales on both the vertical and Y-Axis travel to gain an understanding of exactly what happens when you move the dial by .001" or by .0001" - you need to know how well the threads and the bed works together after years of use. That too depends on how maintenance might have been handled by previous owners. The part people forget about is that if you break off one very small particles of grit from a wheel and put it in the wrong place, the grinder will feel like you just submerged it in your kids sandbox... all of the ways and channels under the main table are there for a specific purpose in making two fairly heavy pcs of steel slide together as though the top one was floating on air... when it feels that way, it's probably getting oil where it should be and you can become extremely sensitive with your own fingertips about what is clean and what is not. Regrinding the magnet is probably one of the jobs that will improve the accuracy if it's done correctly but will be one of your worst nightmares if it's not. You are relying on the grinder as a final step in a sequence of steps that are all intended to gain accuracy so if the magnet surface is not flat and true with the final grind operation, you will trying to obtain dimensional results that will drive you nuts in the process, but be patient, be particular and be persistent in marking surfaces, dealing in tenths or better for a valid reason and you can be rewarded with one of the best tools in your shop. When you can trust it to do what you ask and get the results without taking 3 days instead of 3 hours, then you'll feel rewarded for all of those extra steps you took to get it right.

    As for the grinder being any more dangerous than anything else in the shop, it's probably not but it demands a healthy level of respect for what it can do in a split second.. not just to your nearly prized pc of steel but to your hands, eyes and the rest of your facial features! I've seen people forget to turn the magnet on when their intending to dress the wheel and they get the diamond just every so slightly off-center (to the right) of the wheel and if you do this, I guarantee you will know the value of an anal transducer attached to the power plug! Just pay attention to what you're doing and don't get distracted by your music or your kids or your schedule.... when you get the work done that you wanted to represent your best efforts, then it will be done when you're done with it!!! There are some good books about grinding and I would suggest finding a couple and learn what you can about basic and sound examples of setups that stay in place, don't vibrate while you're passing over them multiple times and this is one case where some of the older books are probably as good or even better than something written last year - by last year everyone was convincing themselves that they had to have a CNC controlled surface grinder.. I'd say NOT true ... learn to be good without it and you may be even better someday but there's a lot to learn about proper techniques and retaining all ten fingers and getting thru those chapters should take the better part of the next 5 to 10 years... don't be discouraged - be the student you need to be to be good with this tool and you'll be glad you did. And above all, don't hide your mistakes - they are golden opportunities to learn more and that's what you will do as you learn more and begin to push your own skill boundaries more and more.

    Follow up with some notes in another 6 months or so and let all of us know what has been the more challenging portions of your experiences with the grinder and what are the areas where you've learned more and improved your skills within this timeframe. We can all learn from each other in that way and it will give you a reasonable goal and timeframe to work in to see your own progress. Thanks and work safe.

    Chip4Lips -
     
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  12. Chips4Lips

    Chips4Lips United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Just saw this bit of information that was posted by "Glenn Brooks" - good tip on a place to start with some reading...

    For a good (free) reference book on grinding, search Google books on line for "Advanced Grinding Practice" written by Hamilton in 1915. It's free through Google Books, and contains many chapters regarding how to do precision grinding. Also there are some newer references available through on line booksellers, but cost money to purchase. I've found this 1915 reference to be a very useful resource for learning how to use my OD grinder.

    Thanks Glenn for the tip and don't let that date of 1915 throw you off... the people doing grinding then learned both "what to do and what not to do" and many of those things are absolutely still valid for us today.

    Chips4Lips
     
  13. Dabbler

    Dabbler H-M Supporter - Premium Content H-M Supporter-Premium

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    Here's the link for the PDF from archive.org, as it is out of copyright: advancedgrindingpractice

    Just bought my first surface grinder, a Brown and Sharp 6X12, still in my truck. Thanks for the info!
     
  14. ghostdncr

    ghostdncr United States Active Member Active Member

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    When I put a new job on the chuck, I need to test the surface for the high point. I use a good test indicator (B&S .0005" in most cases) mounted on a magnetic base attached to the spindle.

    This seems to take forever as I move the wheel head randomly over the job slowly dropping the head to achieve first contact. Mark the high spot of your part with a Sharpie or similar permanent marker. This way you're not "air grinding" the whole part when touching off.

    Is it beneficial to start with a stationary wheel, or a wheel slowly rotating (I have a VSD) ? Once I get the machine warmed up and the wheel dressed, it won't be turned off until I'm either finished or need to change wheels. It's extremely difficult to restart a grinding wheel and have it remain true, but I have watched a coworker get good luck at restarting using a skateboard wheel fitted to a 1/4" die grinder. The wheel was brought to bear against the face of the wheel and the spindle brought up to speed, and then he'd switch on the grinder.

    Is a shim stock like paper or plastic film inserted between the job and the wheel useful ? I have used shim stock many times on badly out-of-square parts. I keep a pack of cigarette rolling papers in my toolbox that will precisely crush down to .0015" under the pressure of most common magnetic chucks.

    It is annoying when the last pass on a two-sided job requires the job to be slid off the chuck, scratching the bottom side. I know, it doesn't matter, but how can I minimize it ? I use one of two precision screw vises to lay upside down across the part, clamp, and then lever the part out of contact with the residual magnetism of the chuck. No scratching, and total control of the process. And actually, it DOES matter! Scratches in either the workpiece or the magnet don't simply go down into the metal, they raise a significant burr to either side of the scratch and there goes your flatness and along with it, any hopes of accuracy.

    Would thin plastic film, or other material, minimize the risk of this ? May be worth a try, but the method detailed above works great and alleviates the need for it. At some of the levels I've ground, I'd be skeptical of finding a commercial film consistent enough to be repeatable.

    The stepover percentage that should be used is a mystery to me ? There are formulae to calculate this, but I've never used them. Listen to the grinder and if it sounds aggressive during the cut, you're probably taking too much. Too much cut is hard on your motor, spindle bearings, and injects way too much heat into the process to ever achieve decent accuracy. There are exceptions to this rule, such as when doing cutoff/slitting operations or plunge grinding, so don't consider "aggressive" to be verboten.

    What are the trade-offs for large versus small stepover ?, as related to cut and finish ? I generally prefer light cuts with heavy stepover on most materials, but some material types will produce a better finish with a very light stepover. If surface finish is an issue, a bit of experimentation early on will show which is best in a given circumstance.

    If I take the job off the chuck for measurement then replaced, the next cut is always more than I expected.
    I have made special effort to clean everything to no avail.
    Is it me or a characteristic of the process ?
    I suffered terribly from this phenomenon when first starting out. A number of techniques can be used to minimize it, though. Most importantly (as you are doing), clean everything! I usually keep a spray bottle of acetone at the grinder for this purpose. Lightly passing a fine, flat stone over both the workpiece and the chuck will help smooth things out. Confirm part height with the spindle-mounted test indicator mentioned earlier. I also keep a small copper slug approximately 1" OD x 3" long to tap down my part onto the magnet. This seems to help seat the part onto the magnet's face and get everything back in order.

    What is it about me or the process that must be improved ? To be perfectly blunt, everything. Time and experience seems to be the only solution for that, so don't doubt yourself. Just realize that attaining true precision with a surface grinder is a very complex thing having many, many differing factors at play. Learning to manipulate all these factors simultaneously and, usually on an incredibly fine scale, takes a lot of practice.

    Or is it just a fact of life ? The only fact I'm aware of is that most are either unwilling to put in the work and practice, or they simply cannot perceive working at the level of accuracy attainable with an average surface grinder in decent tune. You seem to be on track and asking the right questions at this point. Keep at it!
     
    Last edited: Apr 16, 2017
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  15. Bob Korves

    Bob Korves H-M Supporter - Premium Content H-M Supporter-Premium

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    My surface grinder is powered with a VFD. I also added an external spindle on/off switch and an external potentiometer to control the spindle speed (output Hz). I slowly reduce the spindle speed to a stop with the pot and the wheel never slips in the hub.
     
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