Announcement

Collapse
No announcement yet.

Boring off center.

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

  • Boring off center.

    Here's the problem.
    12 inch Troyke rotary table position locked down after every index. Bridgeport axis are locked. Bridgeport boring head pulled up tight in the spindle. Boring head has some serious miles on it. Initial bore was drilled to 3/4 with a 3/4 ball end mill. opened the holes to 1.125 with a larger end mill. Indexed back to zero and ran the end mill into the same hole to check center. End mill cleared the hole. Enter the boring head. I'm using the boring head to counter bore the holes 1.750 diameter .125 deep. The counter bore is about 1/16th off to one side and which side isn't consistent from hole to hole. There are nine holes. I ran the 1.225 end mill through each hole to see if the rotary table was off. It isn't the end mill went through each hole with just minor resistance every 40 deg.
    Right now my money is on the boring head or the bar.
    Any ideas?

  • #2
    That 12 inch rotary table is probably crushing the knee and the knee is just about ready to blow apart and everything is going to far down. Do you have a rotary table that doesn't weight 900 tons?

    Comment


    • #3
      Originally posted by 3 Phase Lightbulb View Post
      That 12 inch rotary table is probably crushing the knee and the knee is just about ready to blow apart and everything is going to far down. Do you have a rotary table that doesn't weight 900 tons?
      Machine shop version of the China Syndrome?

      My money is on the worn boring head. I'm assuming you are locking the screws of the head for each cut? If not that would be the first step. If that doesn't help then check to see if the boring head's bar can be shifted even with the screws snugged down. It may be worn such that it's pivoting on a high spot or a particular locking screw even when snugged down.

      Given that you're getting a random 1/16" shift it should be easy enough to feel that much play in any part of the system. Just for giggles pull and tug mightily on the table to see if it "clicks" in any manner too. A recent thread on here found that the mill's gibs has come quite loose and the table was able to "click" a good 3/16" back and forth at the ends due to the play.
      Chilliwack BC, Canada

      Comment


      • #4
        Originally posted by Rustybolt View Post
        Right now my money is on the boring head or the bar.
        Any ideas?
        That's where I'd be looking. Are the holes round but just off-set or are they oval?
        You did check the screws, balls and dovetails , right? Could be the d'tails are worn enough to allow the balls to jump in and out of pockets.

        Comment


        • #5
          Originally posted by CCWKen View Post
          allow the balls to jump in and out of pockets.
          I hate when my balls jump out of my pocket.

          Comment


          • #6
            BC everything tightend down as far as my 66 year old muscles can do it.

            CCKen the counter bores are round. That's what I'm finding puzzling. Oval I can deal with.

            Comment


            • #7
              Not that I know anything.... prove that daily....

              sounds like you need a new rotary table. Lots of moving parts in those things. And just because it has ball locators... doesn't mean they are right either. I always thought those were just a ball park thing.

              Second thought would be gibs....

              Comment


              • #8
                Drill or end mill does not put any sideways force on things, but the boring head does. Something is moving.

                It's probably not the boring bar or the head, because any deflection from a rotating part should just give you a smaller bore - but one still centered on the original hole.

                My first guess would be the quill, as I'm assuming you are using that to feed the cut and it therefore is not locked. Try locking the quill, and feed by raising the table (but with gibs somewhat snug) and see what happens.

                Comment


                • #9
                  Yeah, something is moving. Head tram bolts tight?

                  Comment


                  • #10
                    OK. Found it. CCKen gave me the idea.
                    I grabbed hold of the boring tool to see if I could move the whole head.
                    Yep. It moved. I dismounted it and found some new divots on the taper of the shank.
                    This is what happens in a company where just anybody can walk up to a machine and start turning handles.
                    I looks like somebody decided the boring head would make a good hammer.
                    The part isn't ruined. I can sink the rim to flat again but this sets the whole thing back for a couple of days.
                    I ordered a new boring head combo.
                    It's going to live in my locked tool box for awhile.
                    I hope I remember to give it back when I leave.

                    Thank you guys. this is what I like about this place. A lot of ideas and helpful people.

                    Comment


                    • #11
                      My best guess would be the tram on the head, the stick-out of the boring head is likely to be significantly greater than the endmills. I think this would apply if feeding with the quill or the knee, so check the tram next.

                      I would still be suspicious that the tram is out as well.
                      Last edited by Robin R; 04-12-2018, 03:33 PM. Reason: More info

                      Comment


                      • #12
                        If the shank of the boring head was bad it would be a good idea to check spindle taper for damage.

                        Comment


                        • #13
                          First thing I did was to put the end mill back in and index the plate to all 9 holes. It slid in perfectly. I will check tram again- thanks Robin- Since it is a Bridgy and they are notorious for being made out of rubber.

                          Comment


                          • #14
                            If the counterbore is eccentric to the hole something has shifted in your setup. Is everything clamped down tight? Since you are moving the RT from hole to hole are you always going the same direction so backlash in the worm & gear doesn't affect you? If you move the table to get clearance to mount the boring head, is the table returning to zero?

                            I may have a counterbore I could loan you. I can check the sizes tomorrow. You woud have to make your own pilot. I don't have one of the size you need.
                            Last edited by Illinoyance; 04-13-2018, 05:13 PM.

                            Comment

                            Working...
                            X