wobbling problems


Page 1 of 2 12 LastLast
Results 1 to 20 of 22

Thread: wobbling problems

  1. #1
    Member
    Join Date
    Apr 2015
    Posts
    11
    Downloads
    0
    Uploads
    0

    Question wobbling problems

    Hello!

    I've been building a CNC router for a while (gantry type, stationaty table), and got it ready enough to run some wood routing this summer (worked like a charm!)

    Now I've been thinking about milling som aluminium, spent yesterday evening with some cad/cam and tried today: catastrophy.

    It cut downward in a spiral to get to the right depth, started to spiral outwards and then it went crazy, wobbling all around the place.

    I'm new to milling/routing so the basics on feedrates and spindle speeds come from sporadic googling, not a solid education.

    I am pretty sure this is a major construction issue, that the gantry is to weak and give room for some movement.

    However, I now ask you if there could be anything I can improve without rebuilding the entire machine.

    Lubricant, feedrate, spindle speed, type of tool, climbing cutting or not.

    Hope you have som constructive opinions!

    Similar Threads:


  2. #2
    Member ger21's Avatar
    Join Date
    Mar 2003
    Location
    Shelby Township
    Posts
    35538
    Downloads
    1
    Uploads
    0

    Default Re: wobbling problems

    First, we need to know what you mean by "wobbling"?

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  3. #3
    Member awerby's Avatar
    Join Date
    Apr 2004
    Posts
    5728
    Downloads
    0
    Uploads
    0

    Default Re: wobbling problems

    It sounds like your machine just isn't rigid enough to mill aluminum; most routers aren't. Either stick to wood, or consider building another machine that's a lot stiffer.

    [FONT=Verdana]Andrew Werby[/FONT]
    [URL="http://www.computersculpture.com/"]Website[/URL]


  4. #4
    Member
    Join Date
    Apr 2015
    Posts
    11
    Downloads
    0
    Uploads
    0

    Default Re: wobbling problems

    Yes, as mentioned before, that would definitely be my first guess as to what is the main error.

    However I thought maybe there are "settings" that will enable better circumstances and in some cases ease the sumptoms of this weakness.

    As an explanation, the center of the endmill revolves arount the Z-axis (a 4mm endmill makes a 6-8 mm hole, after that I suppose it loses the "grip" on the material and "springs" back to center.)

    I'm not sure if it revolves in the same direction as the spindle or the other way, but I would guess the other way.



  5. #5
    Gold Member LeeWay's Avatar
    Join Date
    Jun 2004
    Location
    United States
    Posts
    6618
    Downloads
    2
    Uploads
    0

    Default Re: wobbling problems

    What does the machine look like?
    What is the construction? What motors and other electronics are driving it?
    What kind of spindle does it use?

    Lee


  6. #6
    Member ger21's Avatar
    Join Date
    Mar 2003
    Location
    Shelby Township
    Posts
    35538
    Downloads
    1
    Uploads
    0

    Default Re: wobbling problems

    You're trying to plunge a 4mm endmill into aluminum to make a 4mm hole? You'd be better off using a 2-3mm endmill, and using circular interpolation to make the hole.
    How deep are you trying to go in one pass?

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  7. #7
    Member
    Join Date
    Apr 2015
    Posts
    11
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by LeeWay View Post
    What does the machine look like?
    What is the construction? What motors and other electronics are driving it?
    What kind of spindle does it use?
    Built with aluminium beams, round linear rails, ballscrews (double for X-axis), stationary work area with a gantry that moves in x-axis, y axis on the gantry and at last z axis on a y-axis plate (a bit similar to this: https://ae01.alicdn.com/kf/HTB1eTceNXXXXXX0XFXXq6xXFXXX7/set-of-8-Aluminum-Gantry-Plates-kit-for-Kyo-s-Sphinx-CNC-machine-Kyo-Sphinx-DIY.jpg ), with air cooled, vfd driven er16 ac-spindle, nema 24 steppers, separate driver for each, controlled with mach3 via smoothstepper ESS.


    Quote Originally Posted by ger21 View Post
    You're trying to plunge a 4mm endmill into aluminum to make a 4mm hole? You'd be better off using a 2-3mm endmill, and using circular interpolation to make the hole.
    How deep are you trying to go in one pass?
    No, trying to make a pocket with dimensions 30x40mm, 4mm deep, taking maximum 2mm vertically and 0,8mm horizontally each pass. It starts by cutting a downwards spiral, making a hole of about 8mm ø, 2mm deep, then starts to cut a horizontal spiral out from that hole. However, when it starts to wobble, it rips up a groove (?) Horizontally, that would have an approx diameter of 6-8mm.



  8. #8
    Member ger21's Avatar
    Join Date
    Mar 2003
    Location
    Shelby Township
    Posts
    35538
    Downloads
    1
    Uploads
    0

    Default Re: wobbling problems

    Can you post some pictures?

    Gerry

    UCCNC 2017 Screenset
    [URL]http://www.thecncwoodworker.com/2017.html[/URL]

    Mach3 2010 Screenset
    [URL]http://www.thecncwoodworker.com/2010.html[/URL]

    JointCAM - CNC Dovetails & Box Joints
    [URL]http://www.g-forcecnc.com/jointcam.html[/URL]

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


  9. #9
    Member
    Join Date
    Apr 2009
    Location
    USA
    Posts
    5516
    Downloads
    0
    Uploads
    0

    Default Re: wobbling problems

    20% radial stepover may be too much; sometimes it's better to use less stepover and speed up the federate. And yes, I recommend some type of lubricant when cutting aluminum, and yes, climb-milling.



  10. #10
    Gold Member LeeWay's Avatar
    Join Date
    Jun 2004
    Location
    United States
    Posts
    6618
    Downloads
    2
    Uploads
    0

    Default Re: wobbling problems

    You didn't mention if the round rails are supported or not. That can make a big difference. Even supported round rails leave a lot to be desired in the rigidity aspect of a router, though the later can probably pull off machining some aluminum if designed well.
    Sounds like the spindle should work okay with high speed.
    Along with high speed comes the need to get a proper chip load per tooth when cutting. That will require a fast moving machine too, so it has to be very well designed. Otherwise, you will have issues and or your machining will not look very good.
    Backlash is another major contributor to getting good aluminum parts machined on a router.

    The machine link you posted has roller bearing on aluminum extrusion for guide rails. It will more than likely act different than a machine with round rails. Not much life expectancy on such a machine either. The addition of steel flat bar would greatly increase its rigidity and lifespan.

    Lee


  11. #11
    Member
    Join Date
    May 2005
    Location
    USA
    Posts
    3920
    Downloads
    0
    Uploads
    0

    Default Re: wobbling problems

    You need to post pictures as your descriptions leave a lot to be desired.

    That being said I'm not sure how a machine so wobbly could have been doing a good job in wood. If at all possible pictures of that 8 mm hole cut with a 4 mm end mill might also help. It would be nice to know how round that hole is. Also is the final pocket over sized.

    Your problem is so ill defined that it could be anything at the moment. However i suspect general stiffness sucks. If the machining of Aluminum is to be a focus of your work i suggest that a new machine is in order. Keep the new machine as small as possible so that you can maximize stiffness and keep costs down.

    Since we don't know exactly what is happening with your machine it is hard to make suggestions. However the first thing to consider is minimizing step over. Also chip extraction can impact quality seen on a loose machine as chip recutting adds a variable to the systems load.

    Edit:

    I might add that the word: wobbling, kinda implies a significant problem that might indicate the machine will never be suitable for milling aluminum.



  12. #12
    Member
    Join Date
    Apr 2015
    Posts
    11
    Downloads
    0
    Uploads
    0

    Default Re: wobbling problems

    Sorry for slow answering. Been busy with work, kids, etc...

    The rails are supported, and you'll get some idea of the machine from the picture (I don't need any comments on poor image quality or poor workshop order, and won't give you any lame excuses for it either)
    Also a picture of the workpiece, for reference the pocket is about 12mm in diameter.

    Wizard: Im not really clear on what you mean by "Also is the final pocket over sized", could just be me not familiar with cnc terminology. could you clearify please?

    I'm now in the process of redesigning the machine, with a lower and a lot stiffer/stronger gantry. Along with longer distance between the linear bearings in each pair, to relieve stress/bending of the rails.
    Would that be a proper first step in your opinion? Although as Wizard pointed out, this machine may never be suitable for cutting aluminium.

    Thanks a lot for all the answers so far!





    Attached Thumbnails Attached Thumbnails wobbling problems-img_20170826_220545_787-jpg   wobbling problems-20171101_125922-jpg  


  13. #13
    Member
    Join Date
    Jun 2011
    Location
    US
    Posts
    692
    Downloads
    0
    Uploads
    0

    Default Re: wobbling problems

    Is the flat on the top right of the circle intended?
    Was the tool path actually supposed to be spiral or a series of circles where it steps outward at each circle?
    If it's actually a spiral tool path my guess would be that the work piece moved on you. What seems like a well secured workpiece when things are cutting smoothly might slip once enough vibration comes into play.



  14. #14
    Member
    Join Date
    Apr 2015
    Posts
    11
    Downloads
    0
    Uploads
    0

    Default

    It was supposed to be spiral, and no, the dent or whatever you want to call it is the result of the "wobbling" and not indended. I never thought of the possibility of a loose workpiese. I clamped it hard as hell! But I will look into that. Thank you!



  15. #15
    Gold Member LeeWay's Avatar
    Join Date
    Jun 2004
    Location
    United States
    Posts
    6618
    Downloads
    2
    Uploads
    0

    Default Re: wobbling problems

    I think doing as you mentioned with a redesign is the first step in resolving these issues. Your rails would likely be stiffer if you just mounted them to straight sections of a 4 x4 post. Much stiffer than the extrusions you have. I know we all have budget contraints and that is why I mentioned the 4 x 4's. Lowering the gantry and spreading the bearings will all certainly help and I would imagine the t=issues you are seeing right now will virtually disappear.

    Oh and tie the two gantry beams together with a plate or plank. That addition right there would be would give you a big jump in the right direction.

    Lee


  16. #16
    Member
    Join Date
    Apr 2009
    Location
    USA
    Posts
    5516
    Downloads
    0
    Uploads
    0

    Default Re: wobbling problems

    Quote Originally Posted by ellobo91 View Post
    Sorry for slow answering. Been busy with work, kids, etc...

    The rails are supported, and you'll get some idea of the machine from the picture (I don't need any comments on poor image quality or poor workshop order, and won't give you any lame excuses for it either)
    Also a picture of the workpiece, for reference the pocket is about 12mm in diameter.

    Wizard: Im not really clear on what you mean by "Also is the final pocket over sized", could just be me not familiar with cnc terminology. could you clearify please?

    I'm now in the process of redesigning the machine, with a lower and a lot stiffer/stronger gantry. Along with longer distance between the linear bearings in each pair, to relieve stress/bending of the rails.
    Would that be a proper first step in your opinion? Although as Wizard pointed out, this machine may never be suitable for cutting aluminium.

    Thanks a lot for all the answers so far!



    A plate tying the two extrusions on your gantry would stiffen it up some, and prevent each one from translating relative to the other. Also the plate at the base of the gantry legs could be of thicker material, wider block spacing, and gusseted to help support the gantry leg.

    Also, I can't tell what kind of tool you used, but if you used a ball endmill, your rDoC (stepover) should be about 50-70% of what it would be for a straight endmill. Also use a stub endmill, the shorter the tool is, the stiffer it is and the cleaner it will cut. Too many times I see guys cutting 1/8" material, and the tool is sticking out at least 1".



  17. #17
    Member
    Join Date
    Jun 2011
    Location
    US
    Posts
    692
    Downloads
    0
    Uploads
    0

    Default Re: wobbling problems

    I think the question of is the pocket oversized meant if the operation finished, (which maybe it didn't, I don't know if you stopped the operation when it jumped like that or if it finished,) was the diameter of the pocket the intended diameter?
    It may not have been the work piece that moved, it may have been a loose shaft or something else. It doesn't look like just the result of deflection. I'd look for anything that could have slipped in that direction.

    Lots of good advice already, quite a bit can be gained for not much money. I'd say in best bang for the buck order, shortest tool stickout you can get away with. Make sure your spoil board is well secured to the base of the machine all along the frame rails. This will add quite a bit of torsional (resisting making the base into a trapezoid) stiffness to the base. Plate to tie the gantry extrusions together (will help keep the gantry from deflecting sideways.) Beef up the verticals, just some rectangular aluminum tubing attached with a bunch of T-nuts will help a bit.

    Another thing that wouldn't cost much, but would take some time, why is the gantry so tall, but then the carriage sticks way down? You aren't really getting any extra clearance by having the gantry up so far. I'd lower the gantry and raise the gantry carriage accordingly. Keep the bottom of the carriage where it is in relation to the frame, but lower the gantry so the bottom of it is at about the same height as the gantry carriage. This will get you a lot of stiffness if you don't have a reason for it being so tall.



  18. #18
    Member
    Join Date
    Apr 2015
    Posts
    11
    Downloads
    0
    Uploads
    0

    Default

    The pocket was supposed to be a lot bigger, I had to stop the machine when it started to wobble.

    Yes, I thought of adding a plate between the beams to get rid of, did you call it trapezoidal movement? However, I dont think that will be enough. Sure it improves the stability innthe Y-axis, but the flexibility in the X-axis is just as severe, if not worse. Some of that I believe is because the lower gantry beam/extrusion is only 60x30mm, standing. Which means pressure on the spindle innthe x-axis direction bends the lower Y-rail and the beam behind it.

    The gantrys height was originally intended to give the machine a proper work area height (cant come up with a better word for that...), And this, along with the space between the bearings is another reason for the flexibility in the X-axis.

    The idea for the reconstruction is to replace the 60x30 horizontal gantry beams with 60x60 or 60x120, and move them down a bit. I also plan on replacing the vertical gantry beams with 15mm alu plates that allows for wider space between the bearings on the X-axis bearings. My strongest concern about this is the rigidity of the 15mm plates. But I believe that can be reinforced later on...



  19. #19
    Member
    Join Date
    Apr 2015
    Posts
    11
    Downloads
    0
    Uploads
    0

    Default

    Also, maybe a bit off-topic though, do you have any tips on where I could read/learn some basics on feedrates, spindle speeds, behaviour of materials and cutters etc. Better to read some basics and come back here a bit better educated than to post more stupid questions than needed. Have heard some here about if i decrease stepover I need to increase feedrate? In my ignorance i thought the lower, the better (on both stepover and feedrate)



  20. #20
    Gold Member LeeWay's Avatar
    Join Date
    Jun 2004
    Location
    United States
    Posts
    6618
    Downloads
    2
    Uploads
    0

    Default Re: wobbling problems

    I don't think this is quite true.
    There really are no set speeds and feed for any materials until you actually calibrate your machine to do them. A limber machine like yours is currently cannot hope to achieve anything close to optimized parameters for any material other than possible foam, wax, etc. Not even great in those.
    I hate to say it to you, but you are expecting way too much out of your machine.
    A machines basic movements needs to have a pretty solid frame and gantry and mechanicals just to change the direction of travel with any authority. Not even cutting anything yet.

    Here is a little test for you.
    Clamp the table to something solid. Then grab your spindle and push and pull on it in different directions. Raised and lowered.
    Tell me what you see.

    Lee


Page 1 of 2 12 LastLast

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

wobbling problems

wobbling problems