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Trouble at the mill...

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  • Trouble at the mill...

    Oh, dear, what kind of trouble?

    Something's gone askew on the treddle.

    What's that mean?

    I don't know, I was just told to come in here and say "Something's gone askew on the treddle", I didn't expect the Spanish Inquisition!

    Sorry, I couldn't resist it. I've been struggling/fighting with my new Sherline 2000 mill, and it's winning.

    As I'm completely new to this, I don't know which variable(s) I've got set wrong. What am I trying to do?

    Bore a 3/4" hole 1" deep (a through hole) in 1018 CRS. I first drilled the hole through with a starter drill, then three progressively larger drills until it was 3/8" wide. So far, so good.

    Then I moved to the sherline boring head, with the sherline boring cutter. I set it for a .05" cut, set the speed to 500 rpm, and went on my way. I'm getting chatter, grinding, stalling, smoke, and shuddering of the mill.

    Obviously, not all simultaneously, but still, it's a bit disconcerting. I've changed speed from about 100 to 1000 rpm. I've reduced the depth of the cut down to about .01", and up to about .08". I've varied speed from glacial to obviously too fast.

    As best as I can tell, the small cuts chatter, and the large cuts dig in, stall, and move the table over. This table movement obviosly exacerbates the problem, leading to a vicious loop wherein I have to storm upstairs and ask for advice.



  • #2
    I'm not familiar with milling machines but we a have a key cutter at work and if everything isn't tightened down well we end up with the same kinda things happening as what's happening to you, the bit will actually wander off line if you feed it too fast and somethings loose, otherwise it just chatters. If the bits not sharp the same kinda thing can happen as well.....just a thought....


    • #3
      I'd suggest a slower speed, although if you're starting with a 3/8" hole, 500 rpm may not be totally out of line.

      Are you talking 0.050" on the radius, or on the diameter? That is, is the resulting chip 0.050" thick, or 0.025" thick? I suspect, with the size of setup you have, a 0.010" chip thickness may be plenty.

      How are you setting the angle of the cutting edge relative to the work? You may want to play around with that a bit, to see if experimentation in that area helps any.
      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
        It sounds like you have some slop somewhere. Make sure everything is tight, from vise to cutter. Your table is locked down, the tool is sharp, and so on, right? Stick to a light cut until you isolate the problem.
        Location: North Central Texas


        • #5
          I'm not familiar with the Sherline boring equipment, but anytime I've have problems with a boring tool it was because I had the cutter mounted in such a way that that the cutting edge did not project beyond the clearance, and rubbing ensued. i.e. I had no clearance.
          Lynn (Huntsville, AL)


          • #6
            Well it sounds to me like you are making it bite off more than it can chew,or maybe you have a boring bar that is too long?
            Even in a b-port a boring head will chatter,so it might need a bore with an undersize endmill first,then finish it up with a few .001"passes,just a thought.
            I just need one more tool,just one!


            • #7

              A .o50" cut is way too much for a wee mill like yours in steel. Try no more that .oo1-.oo5" and watch your surface speed <500sfm with HSStooling and >400sfm with Carbide tooling). A little lube or suds will help reduce chatter.

              This is a great learning experience for you - enjoy it while you can. Some day you will be much better than you are now and will beable to look back and chuckle at how easy it is once you know how. Remember to share your lessons with others.


              • #8
                I think you've got it, Joel. After a lot of (painful) experimentation, I found that the table is moving. I'm not sure why, I've got it locked down... but it is. A call to Sherline seems to be in order.

                Thrud: Thanks for the size thoughts. That seems to be the biggest problem I'm having, conceptually. What is the "right size" cut? Any clues are useful.

                Thanks, all.



                • #9
                  I've got a Sherline and have done boring-- but first: isn't it "One ought flay rod's out of skew on treddle!" ?

                  Anyway: yes, .05" is way too big a cut for the Sherline boring setup. They even say so in the instructins that comes with the boring tool. I find .01" is the most I can do without lots of chatter, but that's in Al; in steel, keep it down to .005 or less. And I also agree, make sure everything is tightened down, including the Z axis.

                  Another point: the boring head has two different configurations; make sure you are using the one with the least overhang.


                  • #10
                    Try about .010 cut or even less on this little machine, and run about 500 RPM, bit of oil if a HSS tool.

                    Quality takes time, but the sherline can give it. Those sherlines will make you a better machinist by nothing else but learning patience.
                    CCBW, MAH


                    • #11
                      Jeastwood: Nothing makes me hit the books faster than an accusation of a misquote, and here I think we both have to apologize to the comedy gods. As per "Monty Python's Flying Circus - All The Words", it's "One on't cross beams gone owt askew on treddle."

                      I think we both did pretty good, though.

                      Thanks, all, I'll be locking this thing down, taking a smaller cut, and seeing what happens. I'll let you all know. Or maybe I won't... Because as you know, my chief weapon is surprise... surprise and fear... fear and surprise... and a ruthless efficiency...