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flycutter question

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  • flycutter question

    Evans recent post on his flycutter makes me ask this question about the conventional ones, Im in the process of building my own (in my head right now) and am going conventional BUT am wondering about the drastic angle that is used for the tool bit slot, im going to be using inserts with the option of just grinding my own HSS, even the tips of my inserts hang down farther than the rest of the insert holder -- so why do I even need to angle the flycutter head?

    If I dont need to I would rather have the cutter as close to the spindle bore as possible to keep rigidity, To me flycutting presents some big tooling leverage ratio's and I want my quill all the way up and locked and a cutter with minimum vert. extension... even though i plan on taking baby cuts.

    Are they doing this just to make it handy when grinding your tools as they will already have clearance because they are on an angle?

  • #2
    There are no set rules or laws about how to build tooling. Your desire to shorten your holder for maximum ridgity is good. Then you must figure what you want to accomplish on your particular job. Small radius, larger radius, clearance, etc. You might have to make several to do a wide range of jobs. Just my thoughts. JIM


    • #3
      The angle of the flycutters usually seen is to facilitate sharpening the cutter. I have several shop made flycutters with the cutter slot milled vertically on the edge of the base, and these work just as well as any.

      There is no particular magic involved. Just set the leading edge of the cutter on the centerline and install the setscrews from the front so cutting forces are applied to the solid portion of the flycutter body.
      Jim H.


      • #4
        I think the angle on most commercial jobs may also play a roll in how well the bit stays in the cutter. If you aren't making a one piece non-adjustable one I see no reason to worry about it flying out.

        I bought a large one off eBay for $17.00 then later found out I could have purchased a set of 3 for about the same money !! (I'm not boasting here!)
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        • #5
          I like a flycutter with adjustable radius. I primarily use them for appearance sake. I have a multi-insert face mill for getting most of the way there. For best appearance, I make a shallow cut with a flycutter whose radius will let me do the final surfacing in a single pass. For the rigidity reasons you suggest, I'll adjust the cutter, or use a smaller cutter, to keep the radius as small as possible while still make a single pass over the plate.

          Here are the two cutters I own:

          The plate was just cut with the smaller radius, so you can see the "seam" where I had to make two passes. I did that to demo the effect. I then mounted the larger cutter and cleaned it up with 1 pass.

          Another thing to note. Flycutters are sensitive tram indicators. The longer the arm, the more sensitive. Eventually it gets very hard to tram the machine so it cuts on both sides of the circle:

          Still, if you don't have a surface grinder, the flycutter leaves a pretty decent finish. That was for a 12" disc sander table, a project I'm working on at the moment:



          Try G-Wizard Machinist's Calculator for free:


          • #6
            Bobs flycutter, the one on the right, is similar to the ones I use a lot. When you see that grinding relief on the 'bottom' and the 'side' of the cutter allows you to bore as well as face, it becomes more useful. I just use HSS in mine, and grind to suit both surfacing and boring. I find it quite rigid in use, and because it's quicker to mount it's the one I reach for most often (as long as it will do the job properly) It's not a substitute for an adjustable boring head per se because it doesn't have an adjustment dial, but other than that it's fine. I make use of the fact that the cutter sticks out the side of the body so the whole thing will go in the hole. It produces at least as good a finish as a real boring head. It's only because of the straight toolbit that the angled slot is needed, but- if the toolbit is long and the tail end of it needs to clear the workpiece, this could then be another advantage. You'd be limited to the depth you could bore because of this, but whatever.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-