Announcement

Collapse
No announcement yet.

Fly cutter design

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Fly cutter design

    I'm going to make a fly cutter and I have 1-1/2" (40mm) square stock and my largest round stock is 1-1/4" (30mm). Bigger is better & the square fly cutter would look like this:
    Click image for larger version  Name:	Fly cutter.jpg Views:	43 Size:	14.3 KB ID:	1938817
    (I'm planning on using a right hand lathe turning tool.)

    Anybody see a disadvantage to using square stock?
    Last edited by Bob Engelhardt; 04-16-2021, 12:27 PM. Reason: "Right hand" tool, not left - looking at bottom is confusing.

  • #2
    Makes perfect sense to me Bob.

    Ian
    All of the gear, no idea...

    Comment


    • #3
      Your indication of rotation is not right for the tool placement. Your dashed line circle indicates that the arbor in this view is away from us so this is the work piece's end on view of the tool. That means the tool is correct for cutting in normal forward rotation but the arrow indicates reverse rotation.

      Assuming a 1/2" square tool bit and that the set screws for securing it will go into the suggested 1/4" wall I might suggest a slight change. Flycutters are very often out of balance anyway. So why not offset the arbor and slot for the cutter by 0.1" and use that to bulk up the skinny side of the slot? Yes, this makes it a little more lop sided but it's a flycutter. But for this style of flycutter it's wildly out of balance anyway due to the cutting bit and offset needed to put the cutting tip on a radial line from center. So what's another tenth inch between friends?

      Click image for larger version  Name:	Flycuter from square.JPG Views:	0 Size:	24.3 KB ID:	1938828
      PS: If it's not clear I've also shown the arbor size as being 0.750 to further stiffen things up.
      Last edited by BCRider; 04-16-2021, 11:36 AM.
      Chilliwack BC, Canada

      Comment


      • #4
        Re: rotation - yes, I'm showing the tool end. And I meant the lower left corner to be the cutting edge. So CW rotation.

        The 1/4" wall drives the cutter, so the clamping screws will be opposite it and force the tool against it. But that 1/4" could be more - I dunno.

        It will be held with a 1/2" collet (no option), so that fixes the shaft size.
        Last edited by Bob Engelhardt; 04-16-2021, 12:28 PM.

        Comment


        • #5
          Ok, you say arbor size .75- why not turn a matching taper on the square stock so it can be inserted directly into your spindle instead. Maybe I'm missing something-

          Everything I've done with flycutters shows me that stiffer is better. Nothing wrong with using square stock for the body of it. It looks like you want to make it adjustable, so balancing will be something to consider- although if you're sweeping a large radius, the rpm would be lower. One of my good flycutters is a fairly large blob of steel with a tapered portion to fit the spindle taper, plus it has a recess to fit over the nose of the spindle. In that recess is a pin which fits up into a notch in the spindle to give it a positive drive. The effort I put into making it this way was worth it.

          In your case, using the square stock, you'd have to machine a piece to add to it to allow this extra rigidity. That of course is going to mean turning a portion of the body round so you can press on this extra piece. But this also gives you a convenient way to align the extra piece so your taper fits tightly at the same time this recessed piece snugs up on the spindle nose. I mated the parts using JB Weld.
          Last edited by darryl; 04-16-2021, 12:43 PM.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

          Comment


          • #6
            Originally posted by Bob Engelhardt View Post
            Re: rotation - yes, I'm showing the tool end. And I meant the lower left corner to be the cutting edge. So CW rotation.

            The 1/4" wall drives the cutter, so the clamping screws will be opposite it and force the tool against it. But that 1/4" could be more - I dunno.

            It will be held with a 1/2" collet (no option), so that fixes the shaft size.
            Ah, so that's what the little bevel on the cutter indicated. Fair enough. Clearly I misread your description.

            And the smaller swept diameter you are indicating with that point on the tool means that it'll be more in tune with the required 1/2" arbor. I'm seeing it end up at around a 2" swept diameter. So relatively small by most standards but in keeping with your limit on the shank diameter.

            It does mean that you'll be rotating in the reverse direction. Not a big deal other than remembering to push the right button or flick the switch the right way.

            I'm really tempted to make one as per my drawing since I've got some 1.5" square stock on hand. But I've got a perfectly fine fly cutter already. Plus if I'm going to make chips it really should be focused on making more special holders for my recent QCTP. Or finally making my first steam/air engine that I keep promising myself.....

            One other thing you might consider since you're limiting the diameter and shank size and thus working within the rigidity limits. If you swap your 1/2" square cutter for a 3/8sq that would also give you a beefier thin side due to the smaller cutter. And for the size of the sweep a 3/8, or even 1/4 square tool bit would be just fine.
            Last edited by BCRider; 04-16-2021, 02:05 PM.
            Chilliwack BC, Canada

            Comment


            • #7
              Hi Guys,

              I posted my fly cutter design on here a little while ago !

              Click image for larger version

Name:	New_Flycutter-1.JPG
Views:	969
Size:	145.6 KB
ID:	1938862
              Click image for larger version

Name:	New_Flycutter-2.JPG
Views:	758
Size:	157.0 KB
ID:	1938863 I also posted a drawing, but don't seem to be able to locate it at the moment.

              The shaft on this one is 20 mm and the disc is 20 mm thick. I'm using 1/4" square hss tool bits.
              Best Regards:
              Baron J

              Comment


              • #8
                And here I was going to say "just make sure you built it so the set screws don't get the load of the cutter tool" another words build it so the set screws push the cutting tool into the flycutter base for the direction of rotation when cutting...

                But after post 7 I think we got way bigger fish to fry as in square peg in a round hole type fish lol

                Comment


                • #9
                  Hi Guys,

                  I've been using this design for quite a while now. It was designed to overcome several fly cutter failings. It is very well balanced so it doesn’t suffer the vibration that often occurs, the large and quite heavy disc has a useful flywheel effect. Of course you still get the characteristic thump when taking a cut particularly if its a deep one. 0.5 mm in steel is typical. It also doesn't suffer the deflection like other fly cutters, helped by the thick shaft pressed into the disc.

                  Whilst I'm here, how does the search function work ? I posted a drawing as part of a response to a thread but can't seem to find my own replies to a post.
                  Thanks:
                  Best Regards:
                  Baron J

                  Comment


                  • #10
                    Click image for larger version

Name:	Fly Cutter Drawing.jpg
Views:	770
Size:	120.3 KB
ID:	1938871
                    Found It ! This is the drawing I posted
                    Best Regards:
                    Baron J

                    Comment


                    • #11
                      The fly cutters that utilize cheap triangular positive rake inserts work a charm on light milling machines, either make one or buy one and you will not be disappointed.
                      Similar to this
                      http://www.kristitool.com/shop/b-52-fly-cutter/

                      Comment


                      • #12
                        Hi,

                        I also recommend a flycutter like Bented linked to. if you don't mind buying those cheap inserts. They do work extremely well and can be run at ludicrous speeds and feeds for a near mirror finish. But there a bazillion different styles of flycutters and they mostly all work just fine.
                        If you think you understand what is going on, you haven't been paying attention.

                        Comment


                        • #13
                          Many have noticed that the BB's search function does not work very well. You will find a post faster using Google or one of the other search engines.



                          Originally posted by BaronJ View Post
                          Hi Guys,

                          I've been using this design for quite a while now. It was designed to overcome several fly cutter failings. It is very well balanced so it doesn’t suffer the vibration that often occurs, the large and quite heavy disc has a useful flywheel effect. Of course you still get the characteristic thump when taking a cut particularly if its a deep one. 0.5 mm in steel is typical. It also doesn't suffer the deflection like other fly cutters, helped by the thick shaft pressed into the disc.

                          Whilst I'm here, how does the search function work ? I posted a drawing as part of a response to a thread but can't seem to find my own replies to a post.
                          Thanks:
                          Paul A.
                          SE Texas

                          And if you look REAL close at an analog signal,
                          You will find that it has discrete steps.

                          Comment


                          • #14
                            This is a fly cutter I made for use on my SB-9 lathe. Before purchasing my mill, I did a lot of milling work on that lathe: this is both an example of that work and was made to use there for other tasks.

                            It was made from rectangular steel stock.

                            Click image for larger version

Name:	P08crop.JPG
Views:	724
Size:	99.0 KB
ID:	1938883
                            You may notice that I solved the balance problem.

                            Another photo:

                            Click image for larger version

Name:	FlyCutter4In.JPG
Views:	712
Size:	145.8 KB
ID:	1938884

                            It can accept either HSS, braised carbide, or insert tools.

                            The "RPS = FPS" is a feature that I only discovered after I had built it. The overall diameter is about 4" and the diameter at the tool tips is about 3.8" which is also 12" / pi. So the cutting speed in FPS is also equal to the RPM used.

                            If I recall correctly, the slots for the 3/8" tool bits were cut with the sides that the top of the tool bit rests against are on a radius/diameter of the tool. That means that the angles made while grinding the tool bits (rake, clearance, etc.) are the ones that are presented to the work while using the tool. No calculations are needed when making or sharpening the tool bits.

                            I used this tool for milling work in my lathe. I also made a smaller one with the same design for use on my Unimat. One of these days I may get around to making an adopter so I can use it on my Grizzly mill. Frankly, it works a lot better than the four bit cutter that came with that mill.
                            Paul A.
                            SE Texas

                            And if you look REAL close at an analog signal,
                            You will find that it has discrete steps.

                            Comment


                            • #15
                              I like Baron's design and It doesn't get any easier to make!
                              Why didn't I think of that.

                              Comment

                              Working...
                              X