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Stupid Mill question (about cutting a square hole)

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  • Forrest Addy
    replied
    Drill the corners first then chomp out the stock center. If you look at the mating feature you can determine the corner radius in the mating part you can accept for function. In any case don't drill the corners using the part corner coordinates as the drill center. That leaves Mickey Mouse ears in the corners.

    Locate the drill center inside the part feature (square) so the drill periphery circumscribes the square's corners or the corner radius. Size the drill about 1/10 to 1/8 the size of the square. Use a mill about 1/2 the size of the square to clear stock off the walls. Use a smaller end mill to clean up the remainder when the drilled corner hole perifiery intersects the square.

    It's not a big deal but it does take a bit of math and fiddling and you finish with a very tidy square with little over-cut in the corners.

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  • Forrest Addy
    replied
    Drill the corners first then chomp out the stock in the center. If you look at the mating feature you can determine the corner radius in the mating part you can accept for function. In any case don't drill the corners using the part corner coordinates as the drill center. That leaves Mickey Mouse ears in the corners.

    Locate the drill center inside the part feature (square) so the drill periphery circumscribes the square's corners or the corner radius. Size the drill about 1/10 to 1/8 the size of the square. Use a mill about 1/2 the size of the square to clear stock off the walls. Use a smaller end mill to clean up the remainder when the drilled corner hole perphfiery intersects the square.

    It's not a big deal but it does take a bit of math and fiddling and you finish with a very tidy square with little over-cut in the corners.
    Last edited by Forrest Addy; 04-06-2016, 10:30 AM.

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  • becksmachine
    replied
    Or do the square hole sleeve trick.

    Dave

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  • Illinoyance
    replied
    Haave you considered a rotary broach? I found links to several shop made rotary broaches in this forum. They ranged from very simple to fairly complex. I built one from plans I found there. It was one of the more complex designs. It worked well for a .170 square holes in brass.

    Leave a comment:


  • Gary Paine
    replied
    Originally posted by bobthecooldad View Post
    will try drilling holes (with center) then doing the slot. thank you for the replys i will let you know when i get more material (in a few days)
    If you have to wait for more material, I assume you are giving up on salvage of the workpiece you have? Must be a blind hole.
    There are chisels that could clean out the corners for you. A shaper could work the corners out. Heat it red hot and pound in a form tool?

    Leave a comment:


  • J Tiers
    replied
    That's a lot of co-incidence, that the DRO was compensated by the way it shifted just enough not to show anything..... "Possible"..... maybe not "likely".

    We know drills deflect easily....

    Which explanation is more likely, or which requires less complicated special conditions?

    Leave a comment:


  • Paul Alciatore
    replied
    It is not strictly true that the DRO not changing means that the work did not move. The work is more or less centered under the quill while the DRO scale is offset a number of inches from that position. If the gibs are not completely free of slack, then the table can rotate in a manner that the work piece and the DRO scales will move by different linear amounts.

    Put a DI on the end of the table and then try moving that end back and forward and see how much the DI changes. You may be shocked. The movement will be less under the quill, but it can still be present. But you say you had the locks on so this is probably not the case.

    If I were cutting out the corners with a small end mill, I would use an end cutting milling cutter and do a plunge cut, not a sideways one. Drills will walk but end cutting end mills do not. And use a high enough spindle speed so that the depth of cut per tooth is not too great for the end mill to handle.

    Of course, you could always file it.

    Also there are other ideas for square or rectangular holes. Here is one:





    Originally posted by J Tiers View Post
    If the DRO says it was not walking, then it must be drill deflection or the work moving. Probably drill deflection.

    Start each hole with a spotting drill, or a "screw machine length" drill of any fairly close size. Just pit the center dimple in and the other drill should follow it. An actual center drill will work if it is small, and you only use it to dimple the surface.

    Yes, there are square hole drills. Most leave the corners with a tiny radius, and they are generally only easily available in inch sizing (I have, for instance, a 12.7mm square drill). Also they are expensive.

    Leave a comment:


  • bobthecooldad
    replied
    Originally posted by J Tiers View Post
    If the DRO says it was not walking, then it must be drill deflection or the work moving. Probably drill deflection.

    Start each hole with a spotting drill, or a "screw machine length" drill of any fairly close size. Just pit the center dimple in and the other drill should follow it. An actual center drill will work if it is small, and you only use it to dimple the surface.

    Yes, there are square hole drills. Most leave the corners with a tiny radius, and they are generally only easily available in inch sizing (I have, for instance, a 12.7mm square drill). Also they are expensive.
    will try drilling holes (with center) then doing the slot. thank you for the replys i will let you know when i get more material (in a few days)

    Leave a comment:


  • J Tiers
    replied
    If the DRO says it was not walking, then it must be drill deflection or the work moving. Probably drill deflection.

    Start each hole with a spotting drill, or a "screw machine length" drill of any fairly close size. Just pit the center dimple in and the other drill should follow it. An actual center drill will work if it is small, and you only use it to dimple the surface.

    Yes, there are square hole drills. Most leave the corners with a tiny radius, and they are generally only easily available in inch sizing (I have, for instance, a 12.7mm square drill). Also they are expensive.

    Leave a comment:


  • Chris Evans
    replied
    Your approach is nearly right try drilling 4 holes on each corner at say 3mm diameter then drill the 13mm hole. This leaves very little to mill out with your small cutter. Was it the machine slides moving or the job moving on the table? If the machine was moving it need attention to the slideway GIB strip adjustment and the lead screw backlash sorting. If the job will stand the corners missing you could drill on the exact corner positions.

    Leave a comment:


  • Stupid Mill question (about cutting a square hole)

    I need to drill a 13mm square into an steel block.. i have used a 13mm slot drill but i get a 13mm radius at the top and bottom and i cannot make the block any bigger to compensate for thethe radius, tried with a small 3mm end mill to reduce the corners but it shattered so i went to a 4mm and the square hole kept walking (even with the mills locks on and the dro telling me it isnt walking) so i was wondering if there is a tool to make a 13mm slot into a square hole or a tool to cut a square in a block of steel.
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