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    Default steel finishing

    Greetings. I need to finish 3" x 3" pieces of 4140 steel, about 40 Rc. They need to end up mirror like and flat. What's the best way to start on a mill?

    I tried a 5-cutter indexed surface cutter, not good, probably due to some slight chatter. Then I tried a single point fly cutter that was better but still not very smooth.

    So what's the best way to prepare the plates for polishing? Thanx.

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    Not in a mill,you need a grinder,...my 2cents...Phil

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    1. Have mill
    2. Don't have the kind of grinder I'd need.
    3. So?

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    try aluminum inserts.

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    No matter what kind of insert or technique you use, you will be a long way from mirror finish using just a mill. If all I had was a mill I would try to devise some sort of lapping wheel.

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    Does the part need to be dead flat or just shiny? If very flat, get a lapping plate and use it after milling. If it just needs to be shiny and local flatness isn't super critical, use a buffing wheel.

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    Quote Originally Posted by dian View Post
    try aluminum inserts.
    They'll chip out almost instantly. BTDT.

    Regards.

    Mike

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    You could try a burnish face mill. Cogsdill makes some and it might get you where you want, or at least closer

    Diamond Burnish Face Mill Tools by Cogsdill

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    Use a fly cutter with a high-speed steel tool bit ground with positive rake and a generous radius. Keep your surface feet below 60. Feed as necessary for your desired finish.

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    Quote Originally Posted by gbent View Post
    Use a fly cutter with a high-speed steel tool bit ground with positive rake and a generous radius. Keep your surface feet below 60. Feed as necessary for your desired finish.
    That is about as good a solution as I could suggest, with just a mill. Personally, I prefer brazed carbide tool bits in my fly cutters, and I use a diamond wheel grinder to keep the radius sharp.

    Another key is to use a fine power feed, which will give a more uniform surface. Obviously, the milling machine has to be in good shape to get best results.

    I have several NOS "Superfinisher" devices for milling machines that are supposed to get a ground finish. I never tried one, but I would be glad to sell one for $100. They come with several sets of rubber bonded abrasive wheels in different grits. The instructions say you do not need coolant for polishing.

    Larry

    dsc02390.jpg dsc02391.jpg dsc02386.jpg

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    Quote Originally Posted by abstruse View Post
    1. Have mill
    2. Don't have the kind of grinder I'd need.
    3. So?
    find someone who has one.
    other then that its a ton of manual labor sanding/polishing

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    I've seen guys put grinding stones in their mill.

    Cover your ways, and any other nearby equipment...

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    Quote Originally Posted by abstruse View Post

    I tried a 5-cutter indexed surface cutter, not good, probably due to some slight chatter.

    So what's the best way to prepare the plates for polishing? Thanx.
    What is the diameter of the 5-cutter? Feed rate? Spindle speed? Hand or machine feed? Lubricant? ????

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    Quote Originally Posted by CAMasochism View Post
    You could try a burnish face mill. Cogsdill makes some and it might get you where you want, or at least closer

    Diamond Burnish Face Mill Tools by Cogsdill
    Depending on qty ^ those will certainly do it, but be prepared for sticker shock, especially in larger diameters.

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    roloc pad with sandpaper then scotchbright, or cratex wheels. Then quick pass on buffing wheel.

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    For a one or few up using automotive wet abrasive paper by hand then finish with 3000 dry paper should work.

    A large radius insert can help. having the cutter face (each insert) run to <.0005 can be a big help.

    Having a wiper blade, one with being flat for .030 or so. and that blade .0002 high. with this high blade honed with a .005 flat and .0002 high can help.

    Indicating blades /inserts on a plate only works if your spindle nose runs at close to zero.

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    Are you sure they need to be “mirror like” in order to be “prepared for polishing?” I just want to make sure you’re not overdoing the surface prep if the customer is expecting these parts to go through some belt sanders next...

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    Quote Originally Posted by Finegrain View Post
    They'll chip out almost instantly. BTDT.

    Regards.

    Mike
    i put some aluminum seht't in a facemill a while ago and use it for steel occasionally, no chipping so far.

    op should look at finishing inserts (pvd coated, cermet, wipers). even one wiper in a facemill works. if tabletop mill and 40 hrc good luck. maybe we should look at Ra values.

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    Quote Originally Posted by abstruse View Post
    Greetings. I need to finish 3" x 3" pieces of 4140 steel, about 40 Rc. They need to end up mirror like and flat. What's the best way to start on a mill?

    I tried a 5-cutter indexed surface cutter, not good, probably due to some slight chatter. Then I tried a single point fly cutter that was better but still not very smooth.

    So what's the best way to prepare the plates for polishing? Thanx.
    If you are stuck with using a mill may be you can try to rotate the pieces 90 degrees after the milling pass and repeat pass at same depth, that should get surface bumpy, rather than scratchy; if you know what I mean. You will have to grind it smooth no matter what, but bumpy rather than scratchy surface should be easier to grind smooth. IK thing they have grinding attachment for end mill, that will be your best bet.

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    Speed and a rigid machine. The photo is of A36. The harder the material the less speed and easier it will be to get a good finish.

    The finish in the photo was around 1700 SFM with an old school Valenite shoulder mill (less than ideal tool).
    Attached Thumbnails Attached Thumbnails screenshot_20210124-151538_messages.jpg  

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