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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > G0704 Z ballscrew drops when taking heavy cuts
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  1. #1
    Join Date
    Dec 2013
    Posts
    47

    G0704 Z ballscrew drops when taking heavy cuts

    I rarely post here but im having a problem that I think is getting worse.
    The heavy the cut I take my z axis seems as if its dropping down some. My machine is a g0704 with 570 xy motors z has the 960. Ide say month and a half ago I up graded my motor and went to a TTS style Power draw bar
    So lets say I take a doc @ .100 and face off a 4 inch square with a 5/8 / .625 indexable endmill @ 25ipm . By the tim i get to the end of the operation and go back to were I started im .030 deeper into my stock.
    Mach still reads 0 . I let my head sit raise all night with a dial indicator on it at zero I returned in the morning it still read 0. Im at the point were im just going to tear it down.
    What to hear if any one had any opinions that may help me Thanks

  2. #2
    Join Date
    Sep 2012
    Posts
    323
    To me it sounds like the cutter moving, not the Z axis.

    So either the cutter is pulling out from the tool holder, or the tool holder is pulling out of the TTS collet.

    What are you using for a tool holder? A holder with a set screw or an ER collet holder?

    How much load are you using to hold the tool holder?

    Andrew

  3. #3
    Join Date
    Dec 2013
    Posts
    47
    Im not saying your wrong but I dont get how thats possible.
    Im using a tool holder with a set screw. The tool bit hits the end of the tool holder and there is a set screw on the flat. The tool holder its self is up against the spindle. So neither have any were to go.
    My cuts dont have gouges in them the drop into the work is slowly tapered.
    I forgot the exact amount of # per im using but what ever hoss has in his plans I doubled that by taking two set and stacking them like this (())(())(()). The air cylinder im using is over kill so I can add more or arrange them different if need be.

  4. #4
    Have you checked for backlash in the Z?
    That would be quite a bit to have but if the gibs are too tight you could get stick slip.
    It would slowly creep down from the vibration of the mill running as it went along and mach would still think it was in the same place.
    Just a possibility.
    My other guess would be pullout too of the tts holder, that would be easy enough to see after the cut with a gap between the spindle and toolholder.
    One other thing, if you are using a vise could it be pulling the part out of the jaws a bit?
    Hoss
    http://www.hossmachine.info - Gosh, you've... really got some nice toys here. - Roy Batty -- http://www.g0704.com - http://www.bf20.com - http://www.g0602.com

  5. #5
    Join Date
    Oct 2004
    Posts
    298
    Maybe I'm interpreting your comment wrong, but it sounds like you're facing off a block, and when you check the left and right side, they differ in thickness. Is your head trammed?

  6. #6
    Join Date
    Dec 2013
    Posts
    47
    Hoss , Cowanrg thanks for the replies.
    I sat at my machine for hours. First thing I thought also was tramming the head and pull out. First I trammed my mill even though it was in tram. But lets say it wasnt. Eventually all the material would come off yes it may have lines and un even spots but in my case the head just keeps drooping and dropping slowly with no end.
    I sat there for an hour trying to face off this block never getting it to a point were it was even.
    I also checked the tool for slipping ever time the tool is were I left it butted up against the tool holder and the tool holder butted against the spindle.
    Ive have owned this machine for a year and a half its has been converted to cnc for the whole time. I went to the TTS system few months ago. I have never had this problem.
    Hoss Im going to try tightening my gibb but its pretty darn tight. My back lash is almost nothing at .001 last I checked I should recheck it.
    Is there a way to stack my washers for more force / holding pressure from (())(())(()) to maybe ((()))?

  7. #7
    Tightening the gib more is the opposite of what i was saying, if it's too tight it will stick and not move smoothly which is what you want.
    (())(())(()) will give you double the force and the same movement needed to release the tool, ((())) will give triple the force but only 1/3 the movement needed.
    Are you seeing a gap between the spindle and toolholder face?
    If not then you aren't getting pullout, it won't go back on it's own.
    What springs and air cylinder are you using?
    Hoss
    http://www.hossmachine.info - Gosh, you've... really got some nice toys here. - Roy Batty -- http://www.g0704.com - http://www.bf20.com - http://www.g0602.com

  8. #8
    Join Date
    Nov 2009
    Posts
    4415
    The flat on the end mill is long. When installing the end mill into the TTS holder, do you push the end mill "up" against the set screw? Or pull it down?

  9. #9
    Join Date
    Dec 2013
    Posts
    47
    Hoss I was thinking tighten the gib if the head was moving on its own from the force of just gravity.
    Right now my Disc springs are (())(())(()).Im going to change them to ((())) just cause ill feel better. My air cylinder is 4 stage 4 inch( 4 1 inch cylinders) adjustable stroke fabco model . I think when I checked it had a pretty high rating of up around 4000lbs . I know not experiencing tool pull out though. The tool and the tool holder are exactly were they were when I installed them. There not moving.
    Fastest1 my tools set screw is touching the end of the flat it has no room to travel and at that the tool is butted up to the end of the tool holder . Neither the tool holder or tool have room top travel.

    I did notice something today I never thought of . When I did the install I read you documents bout the bearings . Mine were not getting warm at the time of the install of the PDB a few months ago. I sat in the garage today . Turned the machine on. Ran my cutter to the tip of the work piece cleared out a small spot. Put my dial indicator on the spindle(the part that used to hold the DRO) . I let it sit there @4200 rpms for 15 mins . I found out two things . With no cutting force I watched my spindle slowly come down .0175 make a small circle. I then felt the spindle when removing the tool and it was so hot I couldnt keep my hand on it more than a second.
    My bearings are shot. I take it Do you think the heat would expand / reduce the metal so much it woulds make a difference?

  10. #10
    Can you grab the spindle (when it's cool) and feel any movement up and down?
    Maybe put an indicator on it to see if it moves.
    Another question is your quill locked good and tight?
    Hoss
    http://www.hossmachine.info - Gosh, you've... really got some nice toys here. - Roy Batty -- http://www.g0704.com - http://www.bf20.com - http://www.g0602.com

  11. #11
    Join Date
    Dec 2013
    Posts
    47
    I took an insert from you used a set screw when I did the conversion. The quil is probally tighter than it should be. Theres is no movement up or down while cool or hot (I used a shop rag)
    Man I just thought bout it I hope my Z ball screw nut mounts bolts didnt loosen up

  12. #12
    Join Date
    Dec 2013
    Posts
    47
    Every one thanks for your help. I tore down my z axis to find I must have over tighten my gibb ridiculously tight . When I unbolted my head from the ball screw nut it just hung there on the middle of the column.
    I loosened it up. All works as it should now.
    The day wasnt lost though I now know a little more and my TTS system is a lot stiffer and tighter. And my bearings are shot.
    Now I can finish the project at hand making my back plate for my 3jaws / rotary table.

  13. #13
    Join Date
    Nov 2009
    Posts
    4415
    On the topic of end mill installation you say, "my tools set screw is touching the end of the flat it has no room to travel and at that the tool is butted up to the end of the tool holder . Neither the tool holder or tool have room top travel."

    If I understand this correctly, you mean the tool and or tool holder have nowhere to travel upwards. In my understanding generally the end mills we use are ejecting the chips upwards above the work piece. For this to happen the force is pulling the end mill downwards into the work.

    I was always informed to pull the end mill down against the set screw and then tighten it. Doing this will insure that the Z never goes too deep unless the holder were to pull out. Truth is, the TTS system holds very well for the size tooling it is designed to hold.

    Not trying to negate the need for your other repairs or finds. This is just an additional detail to watch. Then all you have to do is watch your plunge rate;-), and feed rate and RPM.

  14. #14
    It's been my experience that indexable endmills don't pull into the material, quite the opposite actually.
    Glad to hear your problem is solved R.M.S.
    Hoss
    http://www.hossmachine.info - Gosh, you've... really got some nice toys here. - Roy Batty -- http://www.g0704.com - http://www.bf20.com - http://www.g0602.com

  15. #15
    Join Date
    Nov 2009
    Posts
    4415
    Good point Hoss. The indexable mention had slipped by me. I have no experience with indexable tooling (or very little with face mill).

    I was stating what I had learned with traditional end mills. Correct me there too if I am wrong. My results sure don't show a god like skills. Better than last time though ;-)
    A lazy man does it twice.

  16. #16
    Join Date
    Dec 2013
    Posts
    47
    Yeah honestly I haven't owned the tts style system long. I searched tool pull out on you tube there is nothing.
    You bring up a valid point that makes allot of sense . lll be sure to give it a try .
    If you haven't tried using indexable end mills there great . I personally love them Im able to take allot more aggressive cuts in ruffing with out worry of breaking a end mill and if you chip a insert just flip it around.
    Ive noticed I still get better finished using a regular end mill . You should really try them out I love mine.
    I purchased mine from shars but you could honestly make some with some simple math and the correct inserts.

    I used the machine a today every thing seems ok .

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