Announcement

Collapse
No announcement yet.

How to cut a trough in the face of work

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

  • How to cut a trough in the face of work

    There's a joke in there somewhere.

    Anyway, if I have a piece of acetal chucked, what's the right way to turn a groove in the face? The groove (ideally) would be flat-bottomed, about 1/4" wide, and about as deep.

    Do I grind a trepanning tool?

  • #2
    Use a grooving tool that has side relief on both sides less than the tip cutting edge and the outside relief side ground to an arc to less than the OD of the groove. Done that a lot and have several ground up for just that job. Setup and rigidity is important.

    You are talking about doing it in a lathe, right?
    It's only ink and paper

    Comment


    • #3
      Yeah, it's all I have!

      Setup and rigidity is important.
      I have an Atlas. Yer killing me. But it's acetal so I'm ok.
      Last edited by Tony Ennis; 11-05-2011, 11:17 AM.

      Comment


      • #4
        I recently did exactly what carld said in aluminum on my 10" Logan. I managed to get about 1/2" deep before breaking the tool. That didn't make me feel too bad since the bit I was using a 1/8" square HSS bit with clearance ground at front and sides to accommodate the approximately 2" radius. I haven't worked acetal but imagine it would machine easier than aluminum. I did reduce my RPMs to eliminate chatter and it probably would have gone better had I used a different bit with more rigidity. Something bigger in cross section ground where it needed to be for side clearance on the radius. Perhaps something shaped like a comma?

        Comment


        • #5
          Ah...by a different name, same grind "profile" as a bit I used for counter-boring (fair bit of chatter since it was more or less a plunge in at the start of process, still, flat bottom which was the "important" issue to be solved at the time)

          Comment


          • #6
            You can largely avoid chatter issues by grinding a V shaped bit that when plunged creates a v groove the correct depth and width. Then use the trepanning tool to clean up the corners.
            Free software for calculating bolt circles and similar: Click Here

            Comment


            • #7
              One can easily grind a round bar (of the correct diameter) to half a diameter at the end and grind a relief. Works good on small depths (1-2D) and easily made from a round HSS blank or carbide. The round shape provides the necessary side clearance.

              And run the lathe in reverse with the tool upside down, as that eliminates chattering about completely. Because if the tool tries to grab, it will bend away from the work and thus it won't dig in more.
              Amount of experience is in direct proportion to the value of broken equipment.

              Comment


              • #8
                You won't have any troubles cutting a 0.25" groove in the acetal. I can't count the number of ASA o-ring grooves I've cut this way, most of them in 316 SS. A fair number were done with a lantern style post in a small Colchester lathe. That was a b*tch, but I cut a fair number in polycarbonate, acrylic, HDPE, etc. and they were all super easy. Like everyone has said, just make sure you have the proper side clearance for the diameter of the "trough".

                Comment


                • #9
                  I use a tool ground something like this only with a flat on the leading edge.



                  The tool shown was for cutting a groove wider than the tool and getting a flat bottom without a lot of chatter. Of course the groove has to be wider than the width of the tool plus the radius on the sides.
                  It's only ink and paper

                  Comment


                  • #10
                    Perhaps I'm showing my ignorance here, but for a groove 1/4" wide x 1/4" deep with a flat bottom, I would just use my .093" wide cut off tool and plunge it to depth, then move it over, repeating untill I had the desired width. Did I misunderstand the question?
                    Brian Rupnow

                    Comment


                    • #11
                      Brian - I think we are talking about trepanning tools. A parting off tool will definitely not work
                      Bill

                      Comment


                      • #12
                        I've used my parting tool to make shallow grooves. 1/4" should be no problem with a good relieved parting tool.

                        For deep stuff I use a second lathe and an endmill.
                        Andy

                        Comment


                        • #13
                          Originally posted by brian Rupnow
                          Perhaps I'm showing my ignorance here, but for a groove 1/4" wide x 1/4" deep with a flat bottom, I would just use my .093" wide cut off tool and plunge it to depth, then move it over, repeating untill I had the desired width. Did I misunderstand the question?
                          This groove is to be cut in the face of the stock. A parting tool won't work unless you were cutting a shallow groove at a very large diameter or had a lot of relief ground in your parting tool. Even then, the relief is only helps if you are cutting a relatively large diameter, shallow groove. You really need clearance on either side of the tool.

                          Comment


                          • #14
                            Here's a great example of face grooving (trepanning.)

                            http://www.youtube.com/user/walterto.../7/3Hra3g_vA8A

                            I've got a similar insert tool, but haven't had the opportunity to try it yet. The manufacturers give you a diameter range for the "first cut". Once you make that you can go bigger or smaller.
                            Last edited by PixMan; 11-05-2011, 10:14 PM.

                            Comment


                            • #15
                              I just took a drill bit and ground the shank end into a half moon shape when looking at the end of the drill. Since i was cutting aluminum at the time i heated the shank end up cherry red and quenched it to make it harder but for acetyl you can probably just re-leave the end and sharpen. The half moon shape gives the side relief.

                              Comment

                              Working...
                              X