grinding techniques
Close
Login to Your Account
Page 1 of 2 12 LastLast
Results 1 to 20 of 22
  1. #1
    Join Date
    May 2021
    Country
    UNITED STATES
    State/Province
    Delaware
    Posts
    80
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    20

    Default grinding techniques

    People,

    I hope all is well. Here is a debate; a co-worker claims that in order to achieve the flattest, most accurate part, one must grind/spark out dry, without coolant. YFI we are grinding silicon carbide with VIT bonded diamond wheels. We generally have the part directly on the mag chuck, and use parallels to block the part in. I understand the theory, but my thoughts: 1)the wheel will get hot/warm and glaze over, thus not cut as free. 2) with the mag chuck on, without coolant, it itself will get warm and distort. Again, the dry technique come from the thought that the coolant works its way under the part, and lifts it away from the chuck....opinions, please.

    I would be of a mind to try to use a vacuum chuck to hold the part, a buffer from the heat of the chuck....

    Mark

  2. #2
    Join Date
    Apr 2018
    Country
    UNITED STATES MINOR OUTLYING ISLANDS
    Posts
    9,166
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    4450

    Default

    Quote Originally Posted by M. Roberts View Post
    People,
    Maybe. Then again, maybe not. We could be your alien lizard overlords, ya know

    I think your guy is playing with himself. Not surface grinding but ... Maag gear grinders, the most accurate, blah blah, used to grind dry using just the edge of the wheel for accuracy. Nowadays Hofler gear grinders run wetter than wet with a big hose at the interface, form grinding. Get the same result. Reishauers used oil. P&W's used water base. All came out the same (when properly done, of course).

    I would look more into the wheels themselves ... something like cubitron where all the grains are sharp, is going to make more of a difference than wet or dry, imo.

  3. Likes eKretz liked this post
  4. #3
    Join Date
    Oct 2010
    Country
    UNITED STATES
    State/Province
    Oregon
    Posts
    5,805
    Post Thanks / Like
    Likes (Given)
    5769
    Likes (Received)
    2239

    Default

    I'm not a grinding expert, but thoroughly disbelieve the notion that grinding coolant forces the wheel away from the work. Even if it did, it wouldn't much matter because the effect would be repeatable, and therefore a consistent process will produce consistent parts.

  5. Likes tdmidget liked this post
  6. #4
    Join Date
    Jan 2007
    Location
    Flushing/Flint, Michigan
    Posts
    10,887
    Post Thanks / Like
    Likes (Given)
    640
    Likes (Received)
    8742

    Default

    Not sure how you find a wheel that works both wet and dry.
    When Blanchard grinding silicon-nitride, ceramics and cermets in a plate they will float.
    The wheel pushes them back down but the leading edge will be a touch smaller and you can see it in the surface by looking at a overhead florescence tube like a mirror. You see a bent tube.
    In plate they are not held as the holes in the plate .005 bigger than the parts so they are free.
    Using a ring and keepers with each part sort of clamped this is not a problem.
    If the part blocked only front and one side I could see the argument for this on a SG.
    I have seen people mill a hatch pattern on the chuck surface so the coolant can not build up under the part and has somewhere to go.
    For me dry grinding anything outside of a bench grinder is a absolute last resort.
    In surface grind as you noted wheel heat and the dreaded "sucking up".
    Bob

  7. Likes Richard King, michiganbuck liked this post
  8. #5
    Join Date
    Mar 2005
    Country
    UNITED STATES
    State/Province
    Indiana
    Posts
    6,398
    Post Thanks / Like
    Likes (Given)
    2264
    Likes (Received)
    2378

    Default

    I think this would depend on the size and mass of the parts. Something heavy is not likely to float up. Little lightweight parts probably will. This is with respect to nonmagnetic parts. Any parts attracted to the magnet, coolant will generally not get under if they're flat.

  9. #6
    Join Date
    May 2021
    Country
    UNITED STATES
    State/Province
    Delaware
    Posts
    80
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    20

    Default

    Guys,

    Thank you for your replies and reinforcing my thoughts...yeah, my coworker has a PhD in BS, and is extremely versed in convincing less knowledgeable people of his intelligence....

  10. #7
    Join Date
    Jul 2005
    Location
    Cottage Grove, MN 55016
    Posts
    8,568
    Post Thanks / Like
    Likes (Given)
    4498
    Likes (Received)
    5042

    Default

    I learned something a few years ago when I taught inside the Stefan and Franz Luftingers shop " Maschratur OG" in Laakirchen, Austria. They would always set magnetic parts on 3 leveling jacks and indicate in a part before blocking it in and grinding it. I have always used 3 points in rebuilding, but they used it to eliminate any magnetic distortion. Then they knew the part was flat and would flip it over. I use coolant in almost all operations of grinding unless it is Turcite. Heat will get you every time. I have seem some tool makers grind small parts and not use coolant. I always ground cast iron and it would grow from the heat.

  11. Likes Janderso liked this post
  12. #8
    Join Date
    Mar 2005
    Country
    UNITED STATES
    State/Province
    Indiana
    Posts
    6,398
    Post Thanks / Like
    Likes (Given)
    2264
    Likes (Received)
    2378

    Default

    Yeah, shimming some parts on the grinder is necessary to get them flat, just like on any other machine tool. Grinding has much less tool pressure but it's still there also. Another way that works is to flip the parts repeatedly. Every grind and flip you'll grind out a bit more of any distortion. For majorly warped stuff it's best to do shimming for the first step then flip back and forth until flat. 3 points would work fine on something that's stiff but won't do any good on something that flexes a lot under its own weight. Those types of parts can get tricky.

  13. #9
    Join Date
    Mar 2001
    Location
    Switzerland
    Posts
    2,776
    Post Thanks / Like
    Likes (Given)
    3254
    Likes (Received)
    1312

    Default

    My mentor always talked about putting a sheet of newspaper (coolant soaked) between the part and the chuck. He also mentioned forgetting to block the part once and a hole in the wall....

  14. #10
    Join Date
    May 2021
    Country
    UNITED STATES
    State/Province
    Delaware
    Posts
    80
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    20

    Default

    Thanks for the input guys. Richard King: I have a vision in my head of your description....all of the leveling jacks that I have been exposed to are at a minimum of 0.500" tall...how big of parts were you working on?

  15. #11
    Join Date
    Jun 2012
    Country
    UNITED STATES
    State/Province
    Michigan
    Posts
    14,224
    Post Thanks / Like
    Likes (Given)
    4844
    Likes (Received)
    5125

    Default

    You don't hear of people precision grinding Silicon Carbide often.

    Parts not thick enough to maintain their own form/shape/flatness need under support, or support in the direction they might be pushed.

    Even a long piece of tungsten carbide will bend with wheel pressure, often the mag chuck suck-down will distort steel.

    It is surprising how much pressure is exerted on a steel or carbide part with grinding.

  16. #12
    Join Date
    Aug 2017
    Country
    UNITED STATES
    State/Province
    Connecticut
    Posts
    89
    Post Thanks / Like
    Likes (Given)
    4
    Likes (Received)
    21

    Default

    Quote Originally Posted by eKretz View Post
    Yeah, shimming some parts on the grinder is necessary to get them flat, just like on any other machine tool. Grinding has much less tool pressure but it's still there also. Another way that works is to flip the parts repeatedly. Every grind and flip you'll grind out a bit more of any distortion. For majorly warped stuff it's best to do shimming for the first step then flip back and forth until flat. 3 points would work fine on something that's stiff but won't do any good on something that flexes a lot under its own weight. Those types of parts can get tricky.
    Assuming we're all grinding ferrous materials for the most part I've seen lots of flatwork parts where the operator socked down 100 percent on the magnet, cleaned one side, flipped it over and cleaned the other side and then was surprised to find the part was sprung. Using less and less magnet and flipping the part usually will allow you to grind flat. Shimming the sprung area works as well, as does using a piece of plastic shim stock and blocking the part in on either side with thinner cleats direct on the chuck. Dry wheel will always introduce heat. Mass of the part and how close you need to hold your tolerance are always variables to be kept in mind. We used to spray lube some parts with hand spray bottles just to get enough coolant on the part to keep the heat down. Worked better than you'd think it would on the right sized parts.

  17. Likes eKretz liked this post
  18. #13
    Join Date
    Jun 2012
    Country
    UNITED STATES
    State/Province
    Michigan
    Posts
    14,224
    Post Thanks / Like
    Likes (Given)
    4844
    Likes (Received)
    5125

    Default

    Quote Originally Posted by M. Roberts View Post
    Guys,

    Thank you for your replies and reinforcing my thoughts...yeah, my coworker has a PhD in BS, and is extremely versed in convincing less knowledgeable people of his intelligence....
    Ph.D. in Business Analytics but has he /she ever touched a grinder?

    Sometimes as-in-theory does not relate to as-in-actual-practice.

    Offhand I don't remember grinding silicon carbide it is very hard and often porous.

    I have ground ceramic cutting tools and have ground them with diamond wheels and wet.
    Dry grinding ceramics tends to make micro-fractures in a sharp edge.
    Even grinding diamond cutting tools wet seems better.

  19. #14
    Join Date
    Sep 2018
    Country
    UNITED STATES
    State/Province
    Michigan
    Posts
    168
    Post Thanks / Like
    Likes (Given)
    32
    Likes (Received)
    85

    Default

    I think what he is referencing is that in theory a fine wheel such as diamond/cbn types "could" hydroplane on the coolant.

    In practice its nonsensical because....
    - A decent grinder can probably wetgrind to a flatness beyond most shops measuring capabilities
    - CBN Wheels load up without coolant, creating more serious issues than a water/oil film.
    - as mentioned above by Bob/Emanual - different wheel types and dressing styles are typically used for wet vs dry grinding.

  20. #15
    Join Date
    Jun 2012
    Country
    UNITED STATES
    State/Province
    Michigan
    Posts
    14,224
    Post Thanks / Like
    Likes (Given)
    4844
    Likes (Received)
    5125

    Default

    YFI...yellow fever immunization

    QT"[I would be of a mind to try to use a vacuum chuck to hold the part, a buffer from the heat of the chuck]

    Qt Op; opinions, please.

    Some clarity of what the part might be could help.
    Last edited by michiganbuck; 09-25-2021 at 03:53 PM.

  21. #16
    Join Date
    Jan 2007
    Location
    Flushing/Flint, Michigan
    Posts
    10,887
    Post Thanks / Like
    Likes (Given)
    640
    Likes (Received)
    8742

    Default

    Quote Originally Posted by michiganbuck View Post
    .
    Much most of the silicon carbide I have experience would not hold on a vacuum chuck
    .
    Would need solid stops or blocking on the vacuum plate unless a very good side surface area part.

    Imagine a 2 x3 inch of non-magnetic material on you chuck.
    Blocked in but not 100% covered or shielded all around (as blocked parts always are).
    Now take a power washer and spray it at the seam between part and chuck where there are gaps.
    Will it lift or "float"? Darn sure it will unless the blocking can produce enough side clamping force and grip.

    When off the right side of the part that coolant coming off the wheel is going pretty fast.
    One trick here is to have a blocking strap on the right side wider than the part is so this water or oil has no place to "get under" and lift.
    This is a real problem on non-magnetic parts. It is not wheel float it is part float or more accurately water pressure getting underneath.

    Try grinding the top of a SPG-632 Silicon Nitride insert or even a TPG-322 in carbide. One can not block tightly as the sides are at 11 degrees.

    Perhaps not dry but a very reduced amount of coolant flow. We do this sometimes.
    Bob

  22. #17
    Join Date
    Jun 2012
    Country
    UNITED STATES
    State/Province
    Michigan
    Posts
    14,224
    Post Thanks / Like
    Likes (Given)
    4844
    Likes (Received)
    5125

    Default

    Top Grinding a part with 11* sides as Bob described would a be a tough call with using conventional grinders like surface grinders and Blanchard type machines because of lightweight and non-mag of Silicon, along with the inability to block-ii as would be a straight sided part
    A double disk rotary lapping through feed machine might do for production parts of silicon carbide.
    Tungsten carbide has the advantage of higher weight so aiding a grinding process. Controlling the direction of grinding forces likely would be a key asset.
    NTK Technical Ceramics Characteristics Table (Representative value) - Products | NGK SPARK PLUG CO., LTD.
    3.6 is more than 3x times heavier than water(water =1.0).
    Silicon carbide might be graded as low as 2.75
    Back in the 70s I thought NTK was producing the best ceramic cutting tools and worked with Sam Beto (USA rep) testing them for machining, mostly for heat-treated parts, 43 to 63 Rc (about). (Yes, I may have spelled sam's last name wrong). light cuts and high surface seed were often applied.

    Diamonds adhere to a greased pallet, I wonder if Silicon carbide might do the same...just thinking out loud.

  23. #18
    Join Date
    Jun 2012
    Country
    UNITED STATES
    State/Province
    Michigan
    Posts
    14,224
    Post Thanks / Like
    Likes (Given)
    4844
    Likes (Received)
    5125

    Default

    Thin film coolant rather than flood might be better for some grinding applications.
    A nozzle is evenly positioned so to be about .002away from the wheel but covering the wheel width and positioned close to the part.
    The wheel seems to suck in the coolant and tends to hold it rather than slinging it off quickly.
    The coolant aid is furnished to the grinding action, but the amount of coolant to fixturing and the set-up is greatly reduced.

    Diamond selection might also help. I think natural diamonds were more free-cutting than manufactured ones.

  24. #19
    Join Date
    Jun 2012
    Country
    UNITED STATES
    State/Province
    Michigan
    Posts
    14,224
    Post Thanks / Like
    Likes (Given)
    4844
    Likes (Received)
    5125

    Default

    Diamond wheels don't glaze over in the same way as an AO wheel does. Often the diamond edge gets Dull and finally, that diamond breaks free from the holding bonding. As that happens the holding bonding gets higher and so fills the open space where a ground chip should be free to roll off the part, be held in that open space, and be ejected at first chance.

    A soft material is applied to the diamond wheel to knock down the bonding so the diamond's sharp edges are sticking up higher than the bonding.

    Agree you cant achieve this diamond wheel dressing in all grinding applications but when you can it reduces grinding forces/pressure on the par and make the wheel last longer.

    A green silicon carbide grinding stick is a very good dressing device for lowering the bonding.

    A diamond wheel can load up/glase-up with grinding steel, brass, aluminum, and other soft mareials.

  25. #20
    Join Date
    Jul 2005
    Location
    Cottage Grove, MN 55016
    Posts
    8,568
    Post Thanks / Like
    Likes (Given)
    4498
    Likes (Received)
    5042

    Default

    Quote Originally Posted by M. Roberts View Post
    Thanks for the input guys. Richard King: I have a vision in my head of your description....all of the leveling jacks that I have been exposed to are at a minimum of 0.500" tall...how big of parts were you working on?
    Sorry, I just checked old posts and I missed this one before today. They used the pointed jack screw. STARRETT Jack Screw Set, Leveling Work And General Tool Room Use - 6NAY5'|'S191 - Grainger

    I can see using auxiliary perimeter jacks on the outside to support the 3 pointed ones and they would be finger tight. Not disturbing the 3 point geometry. I used to make jack screws from fine tread set screws and nuts. Or flat head bolts. I would grind off the hard type stamp on hardened bolts. I used them as jack screws.


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •