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Large diameter boring

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  • Large diameter boring

    Greets all.
    got a little job i've been putting off for a while because i wasn't sure how to bore some holes:

    3" diameter, FLAT bottom (blind).

    i dont have a boring head for my mill,
    or a 4 jaw chuck for my lathe.

    any recommendations? i may have to put out
    the $300 for a boring head, eh?

    if a boring head is the only way to go,
    how much can these things cut? (1HP mill)

    the largest drills i've got are about 2"
    and they wont get me the flat bottom i need.
    i have this funny feeling that if i get the $300 head, i'm going to be making a 2" hole and then spending the entire afternoon opening it up to 3", a scratch at a time.

    any good homebrew boring head ideas out there?

    thanks yet again.

  • #2
    If you have a flycutter, grind the toolbit so it is relieved enough to have a slight flat bottom and relieved enough so the area that would come in contact of the wall is cut back slightly so as not to scrape the wall. Scribe your diameter and clear most of the bore out with an endmill that use the flycutter to finish bore. You just need a good eye to set the size, or if you have a height gage, vee block, and some math skills you can set it that way also. Easiest way for the DIY to get it done on the cheap.

    If it's not good enough for you, it's sure not good enough for anyone else.


    • #3
      Put it on a lathe faceplate?

      Or, if you have a rotary table...mill it out with an end mill.
      Try to make a living, not a killing. -- Utah Phillips
      Don't believe everything you know. -- Bumper sticker
      Everybody is ignorant, only on different subjects. -- Will Rogers
      There are lots of people who mistake their imagination for their memory. - Josh Billings
      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
      Don't own anything you have to feed or paint. - Hood River Blackie


      • #4
        rotary table?

        you could drill holes just inside of your scribed line, then knock out the slug and bore to size. drills are fast metal cutters,
        if you get the boring head, you can take heavy cuts until you get close, especially in alum. i take up to .250.300 inch per pass roughing cuts . just feed the tool slow. end result is a quicker machine time rather then taking a bunch of light cuts.
        extreme tractor racing


        • #5
          Here is a suggestion: buy "The Shop Wisdom of Rudy Kouhoupt" volumn two. On page 102, Rudy describes how to build a compact boring head. Build your own.
          Richard Montgomery
          Robert, LA


          • #6
            I've typed in a response here twice, and erased it each time, thinking that it's too dangerous a procedure to give as advice. I'm posting this now to see if anyone else has done the same, and what their experience with it was. Baically, it involves rotating the workpiece on a pivot point mounted in the t-slot on the mill table. Rotating it by hand, against the endmill, that is. I clamp the piece down to hog out most, almost all, of the meat, then remove the clamps and rotate the workpiece by hand, to finish mill the desired circumference. I've used the process many times, in wood, plastic, and aluminum, with good results. I still have all my digits, all 21 of them, both eyes and ears, and no scars from errant flying metal chunks. A major problem doing this is that the cutter wants to rotate the work in the same direction as the cutter, thus doing climb milling, so if you lose your hold on the piece, it will spin, rip the pivot point out, probably wreck the cutter, and throw the workpiece and the broken off piece of the endmill at you. If that doesn't happen, you'll end up with a hole milled perfectly round, limited by the play in the pivot point. A usually minor annoyance is that you'll have a small hole through the center of your piece, which can be filled, if req'd.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-