Surface Grinding Thin Parts
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    Default Surface Grinding Thin Parts

    I am wondering if anyone is willing to share how they surface grind thin parts. I use my surface grinder almost exclusively on thin stock. My issue is that the magnet is strong enough to suck the part flat so when I grind it any small warp is retained. I know the grinder is good because when I grind thicker parts they come out perfectly flat. If I test a thicker part the surface is well within .0005" which is plenty for me.

    I know this is a common(ish) issue because I have found some info about it online. I have read all the threads I can find on the topic. I have seen and tried a few suggestions with varying success. So far I have not been able to get a perfectly flat thin part. I have had the best luck by frequently flipping the part to help remove some of the warp.

    I have heard of people gluing a part down, using tape, placing something under the part like paper etc. Ideally I would like to find a way to fixture the part and grind one side perfectly flat then use the mag chuck to grind the other side. Flipping the parts produces OK results but its time consuming and makes it hard to hit a precise thickness.

    My machine is a small 18" manual reid from the 40's that I restored with the help of a few people on this forum. the chuck is a manual magnet chuck. In case it isn't obvious from my beginner question I have no / minimal machining or grinding experience so please forgive any oversights I may have made.

    I am also interested in workholding methods for non ferrous materials, specifically titanium.

    Most materials I grind are .150" or less in thickness.

    Any advice is greatly appreciated, thanks.

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    If you are using cold-finished (CR) material, you will have to rough off both faces before you have any chance of grinding a flat part. Once that's taken care of, you should shim the initially not-flat part so the magnet cannot suck it down. Get some thin shims and a pair of tin snips and put stuff under the high spots of the part so when you turn the magnet on they remain high. Surface grind the upper face. Then flip it. If the bottom of the part (the face you just ground) rests flat on the chuck with the magnet turned off, then you can just grind the upper face and probably be done. However, if the bottom has high spots that raise up off the chuck, you will have to repeat the shim-grind-flip procedure.

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    Get a second opinion on your wheel selection, this will make the world of difference for many reasons, if the parts are taking too long.

    Have you used sets of mag blocks to reduce the mag power? Or even used half and quarter strength chucking? You’d benefit from a open pole chuck too opposed to close pole to help reduce the mag power.

    Do your parts allow for holding with a grinding vice or bolting to a angle plate?

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    I'm not the last word in grinding but I'll try to offer something useful. First off what material are you grinding? I'll presume that you're making knives and using the most common materials. Is your grinding done on stock that's unhardened, hardened, or at both stages? Warp is a consideration for both soft and hardened materials and you'll have to deal with both. Part of the warping is due to stress in the material when it left the mill, stress relieving can/will help reduce this. The other part of warping is due to whatever stress you put into the material from material removal. Any heavy cuts from milling will induce stress that can show up before and/or after heat treatment.

    Do you have a variable control for the mag-chuck? These can reduce the amount of magnetic force on the workpiece but it's also a bit risky as you approach that borderline between holding the piece and launching it out of the grinder (scary & dangerous). If you're laying the piece parallel to table travel that isn't a good strategy. The longer the wheel is in continuous contact with the work the more heat builds up and can lead to warping. It's more work but it helps greatly to shorten contact time by laying the piece perpendicular to table travel (if possible) or at an angle to travel so time-per-pass is reduced. Yes it means many more passes but sometimes that's the nature of it. If you're grinding D-2 I would strongly suggest using a fixture or vise because D-2 is not held by the magnet even if it seems like it, do not trust it. Some materials are more difficult to grind than others and your choice of wheel composition, hardness, and grit size can/will make a big difference. You need to state what you using on what. A fixture may be required here as well to assure a secure hold. Are you grinding the bevels/angles or just the spine/flats?

    Are you grinding wet or dry? Depth of cut per pass? How much step over per pass? Are you blocking the piece in? How flat/parallel does it need to be? More details from you get better answers. Mag control show below, click on it for bigger image.

    chuck-control.jpg

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    Lots of good ideas so far. Here are a couple more:

    Open grain style wheels are a must. 46 grit would be the finest I would go. More open would be better.

    If you're not using coolant, you're toast. You will never get there from here.

    If parts are soft, straighten them before you grind them. And when you do grind take very small passes,(.0002-.0004) moving the table quickly. Dress the wheel often.

    Reduce heat any way you can. The heat is your enemy.

    If the parts are hard, sandwich clamp them when you heat treat them, and don't take them apart until the temper is finished.

    I routinely grind hard D2 plates. (1 X 2 X .025-.035) on an old crappy Boyer from the 50s, so it can be done.

    Patience grasshopper.

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    Quote Originally Posted by Thunderjet View Post
    I routinely grind hard D2 plates. (1 X 2 X .025-.035) on an old crappy Boyer from the 50s, so it can be done.

    Patience grasshopper.
    -While it may be "possible" it's not good advice to give someone new to grinding. My advice was "not to trust it". That you have avoided disaster should not serve to encourage others to attempt duplicating your good luck. Try to help the OP develop safe working habits rather than testing where the tipping point of disaster is with one of the most dangerous machines in the shop.

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    Quote Originally Posted by AD Design View Post
    -While it may be "possible" it's not good advice to give someone new to grinding. My advice was "not to trust it". That you have avoided disaster should not serve to encourage others to attempt duplicating your good luck. Try to help the OP develop safe working habits rather than testing where the tipping point of disaster is with one of the most dangerous machines in the shop.
    I was trying to give advice derived from passed knowledge. I was not assuming that the user was "new to grinding". My Bad.

    If you would have read my recommendations regarding the operations he was trying to accomplish, maybe there were some improper directions that were inferred. If so, I apologize.

    I was was trying to direct him in the best way I knew how to accomplish his task.

    If I was in error, please recommend the proper way to do the job at hand.

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    I will second the angle placement.And block the work in.Fortunately my grinder has hydraulic feeds so that makes it a lot easier.

    Grinding thin stuff and crs is trickiest thing I have run into in my limited experience.

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    Boss picked up a nice flat set of mill parallels. They're called "ultra-thin" and are 1/32" nominal thickness. D-2 or shimmed or any of that death-defying nonsense is a tiny bit better with the 1-5/8 x 1/32 thick parallels on the downwind side of the work (blocking from a scoot disaster). And I'm spoiled with our variable magnet control to help on the warp cleanups.
    Be careful, but too slow on table feederate makes mega-heat almost instantly and as well-stated by prior posts "Reduce heat any way you can. The heat is your enemy." and "The longer the wheel is in continuous contact with the work the more heat builds up..."
    Once the heat starts to radiate out ahead of the wheel (vertical centerline) the thermal expansion in the steel out ahead of the wheel causes your perfect .0002 or .0003 per pass to increase, causing more immediate heat, which radiates out ahead of the wheel, etc. etc. and **@##XXXX##*@@!

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    There's even a point in the overheat cycle where the material starts raising up into the wheel through thermal expansion, warping, or both. The pass starts ok but rapidly gets worse as you travel. It can even be with a DOC that's been working, but some threshold is reached and it's going to get burning ugly or "launch" if you continue with the pass. I've had to raise the wheel head up in the middle of a pass for fear of ruining/launching the piece.

    The shortest grind path across a workpiece is usually the best approach to begin the job. Only experience and vigilance will tell you what you can/can't get away with. Two different pieces from the same batch may grind/behave differently too.

    Blocking in with parallels, available stock in the rack, or special made "grippers' are always the safest bet. Using them on both sides of the piece will allow you to see any change in position upstream by a gap that shows up between the parallel and the workpiece. Once the workpiece moves there's a good chance it's riding up on some grinding "dust/crud" and won't be parallel if you continue to grind. Better to stop, clean, and re-situate everything.

    Grinding mishaps/accidents happen faster than with any other machine in the shop and by the time you notice/hear it's usually too late.



    Thunderjet- you did ok with your reply, sorry if I was rough and/or rude with you.

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    Quote Originally Posted by AD Design View Post
    Thunderjet- you did ok with your reply, sorry if I was rough and/or rude with you.
    No problems.

    It is an art to grind ultra thin pieces, no doubt.

    Angled placement is also a must for a good outcome.

    There are even cooled magnetic chucks that are offered now, if you want to go that far.

    And yes, there are those pieces that just won't cooperate on the chuck.......throw them in the parallel box and move on.

    BTW, I would kill for a lever actuated manual grinder.....they rock.

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    Inspect your part completely before putting it on the surface grinder. A surprise on the grinder means you were inattentive. For fussy grinding you need to inspect the part after you turn the mag on. I have a surface gage where the base is made from bronze, so its nonmagnetic. I will use the surface gage and indicator to check various spots when engaging the mag, and shim so there is no movement. I have also used a disc grinder to flatten parts before putting on the mag.

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    Thanks for all the replies,

    Ill provide a little more detail about my situation.

    I am grinding knife blades. They are framelock blades so they are pretty short, About 5". The blades are made from m390 steel which is magnetic. They start out at .152" and I try to remove as little material as possible to make them flat. They come Blanchard ground so there is no scale and they are pretty flat, just not perfect. I have tried with and without coolant and I didn't notice any difference. I take light passes .00025" to .0005" and I cant feel any heat build up with my hands. I do occasionally spray some coolant on them from a bottle. I used to run a mister but it made a huge mess and I figured if my parts are staying cool to the touch there was nothing to gain. Perhaps I am incorrect in this assumption. I am using an 80grit wheel but I also have a 46. I forget the exact hardness but I can find out. I like the 80 because it leaves a nicer finish that I can blast over but maybe the 46 is a better choice.

    I have thought about getting a disk sander to get the first side flat. I am having a hard time finding one in Canada for a reasonable price. I really like the AMK tactical one but they wont ship outside the US. I did get pricing to ship it here myself but it is cost prohibitive.

    I assume that when people are talking about work orientation they mean its best to orient the parts perpendicular to the path of the wheel. I have not been doing this but its an easy change to make.

    I am not familiar with any type of vise that can hold my parts but if anyone is aware of anything please let me know.

    The steel is ground soft first so I can do some pre heat treat machining, then hard. I run the steel at 63 HRC so it becomes very difficult to move. I usually dress the wheel after each blade.

    I have one in heat treat today so Tomorrow I will try the shim method and see if that helps. I will post a picture of the blades to try to give a better idea of what I am working with.

    Thanks everyone for your responses I appreciate them a lot. I feel I have a lot to learn from the people on here.

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    20200212_205447.jpg
    Here are some blades after the first round of grinding. The blades are in the annealed state here.

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    20200201_160343.jpg
    Here is a completed knife. In order for it to function properly all the mating surfaces must be flat and parallel. The handles are titanium and I order it precision ground so I don't need to modify it. It would be nice to have a way to surface grind it in case I ever get a bad piece or If I need to modify the thickness.

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    guess no one wants to give up the double sided tape trick!

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    Quote Originally Posted by cyanidekid View Post
    guess no one wants to give up the double sided tape trick!
    I have heard of this. The tape I tried was gorilla tape but it was thick and had some give. The part warped badly and the tape let go. I don't think it was the right thing to use. Is there a specific kind of tape that works best?

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    If you wanted to play around, you could make a little box, set two parallels across, lay the blade down on those then fill the box with wax up to almost the surface you want to grind.

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    First off I’ll have to state that I’ve never made a knife, or anything else, from M390. My reading up on it tell to be an excellent material, but my experience with the properties are zero so use your own experience/judgment with any of the following comments.

    Grinding has many variables and all relate to the time/money ratio. Time spent can mean more in operating cost per piece IF that’s an important consideration. Reducing time per piece may/may not be important depending upon how much trouble gone through for how much time saved.

    Money spent on better tools/equipment can save time but will enough time be saved to make it worth the money spent? Only you can answer this question. Having said all that consider the following:

    Orientation of work- Yes it’s a best practice to orient the work perpendicular to wheel/table travel to reduce time-in-grind for a given pass and reduce the generated heat. If not much heat is generated and warping or burning marks aren’t present the work can be set parallel for less overall grind time.

    Not much perceived heat- That’s likely because you’re only taking .00025-.0005 depth of cut (DOC). If you’re ok with how long it takes then no change is needed. If you want to reduce the time then a deeper DOC will be required. This may generate more heat and call for measures to counter the heat.

    Coolant- No perceptible difference? If you increase the DOC you may very well want to use it

    Double sided tape- Only used it for rubber or other non-ferrous work, never trusted it due to generated heat loosening the adhesive

    Wheel Grit- Using an 80 is most often used for finer detail dressed on the wheel or very minimal grinding. I’ve very rarely used an 80-100-120 grit wheel and only when a form had to be closely matched or I was “picking out” the geometry of a detail. Flat grinding like you’re doing doesn’t require a fine grit. Yes you may get a better surface finish with the 80 but you’re using less than .001 DOC. Use of 46 wheel is for greater DOC (less time grinding) with less heat.

    Surface Finish- Just based upon looking at the photos (I may be wrong here) you should be getting a better finish with the 80 @ DOC you’re using. You need to use a sharp diamond for dressing the wheel and there are techniques for dressing that affect the final surface finish. Dressing the wheel at .0015-.002 per pass is good (variables here too). How fast you traverse the wheel while dressing affects the surface finish too. Are you verifying the entire periphery of the wheel is being dressed? Photos look like either vibration, skipping, or partially dressed wheel showing “waves” in surface. How are finishing the surfaces after heat treating and grinding?

    All of the above are to reduce the amount of grinding time. If you’re ok with what you’re doing then no change is needed and also may not be worth the money spent. That’s all up to you to decide.

    Vise- I didn’t elaborate on a vise because I needed to see what you’re making. It appears that a custom set of jaws would need to be made to contact enough points/surfaces. This will only serve to better hold the knife blank when grinding. Increasing DOC also increases the force that’s pushing on the blank. Might/might not be worth the trouble and expense for custom jaws dedicated to ONE model. Blocking in is cheaper but doesn’t grip like a vise/fixture will. This is especially true when grinding the bevels.

    You state that M390 is magnetic (good) but how magnetic is it? When on the mag-chuck how much force is needed to move it? This is where the balance of DOC, heat, and blocking all come into play.

    My apologies for the long-winded post. I hope some of this helped. Others may have additional thoughts. I’m not the last word in grinding, especially on an unfamiliar material like M390

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    Working at a tool and die shop for a couple of weeks I made some parallels for my personal use. To deal with heat treat warping I was told to set them up on magnetic parallels first and take very light cuts till I got the first side flat.
    Finishing those knife blades after heat treat, I could see making a custom magnetic fixture out of brass with a pin to catch your blade pivot hole and drilling a bunch of holes on either end of the fixture to fill with nails to provide hold down for the blade ends. Finish grinding you fixture after pressing in or Loctiting the nails. Put the blade with high spot in the middle for the first pass. Saw one of the guys at that shop with shop made magnetic parallels and he said common nails were very good for transferring the magnetic force.
    Last edited by FredC; 02-17-2020 at 09:07 PM. Reason: cleaned it up a little.

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