square AND round rails!?


Results 1 to 12 of 12

Thread: square AND round rails!?

  1. #1
    Member
    Join Date
    Mar 2018
    Posts
    68
    Downloads
    0
    Uploads
    0

    Default square AND round rails!?

    I built my first CNC machine (gantry style) recently and had a blast. It is great for wood and small cuts in aluminum. Now want to build something more rigid dedicated to aluminum, I'm sure you've heard this story before...

    My next build is likely going to be a C style mill with a pretty small work envelope to try to achieve max rigidity.

    After watching this video (ignore the title for a moment, seems to have some good advice for driving rail systems and alignment)

    :

    This has me thinking a lot about dual rail setups where one rail floats.

    I've ordered some 20mm profile rails and I wanted to ask if anyone has paired one profile rail with one supported rail as the "floating" rail. This gives my old sbr16 rails a home and simplifies alignment.

    Similar Threads:


  2. #2
    *Registered User* Joe_Ohlandt's Avatar
    Join Date
    Jun 2018
    Posts
    6
    Downloads
    0
    Uploads
    0

    Default Re: square AND round rails!?

    What is going to keep the floating rail in the proper place? I can see it walking away due to so many circumstances.
    Why not just get ONE strong set of profiled rails and carriages?



  3. #3
    Member
    Join Date
    Mar 2018
    Posts
    68
    Downloads
    0
    Uploads
    0

    Default Re: square AND round rails!?

    Quote Originally Posted by Joe_Ohlandt View Post
    Why not just get ONE strong set of profiled rails and carriages?
    everyone does this. it works! 2 parallel rails also seems to cause lots of problems per the folks in the video. I'm flipping the question around to ask why not use one square primary and one supported rail (which I already have) as a floating rail thus eliminating alignment issues. Maybe no one has ever tried it (i doubt that)?



  4. #4
    Member ger21's Avatar
    Join Date
    Mar 2003
    Location
    Shelby Township
    Posts
    35538
    Downloads
    1
    Uploads
    0

    Default Re: square AND round rails!?

    Because it's less rigid than two fixed rails, and the most important thing in a CNC machine is rigidity.

    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)


  5. #5
    Member
    Join Date
    Jun 2010
    Location
    Australia
    Posts
    4252
    Downloads
    4
    Uploads
    0

    Default Re: square AND round rails!?

    2 parallel rails also seems to cause lots of problems per the folks in the video.
    Perhaps they are selling something?
    The advice I got from the local agent was "don't do it".

    the most important thing in a CNC machine is rigidity.
    Perzackly.

    Cheers
    Roger



  6. #6
    Member
    Join Date
    Mar 2018
    Posts
    68
    Downloads
    0
    Uploads
    0

    Default Re: square AND round rails!?

    Quote Originally Posted by ger21 View Post
    Because it's less rigid than two fixed rails, and the most important thing in a CNC machine is rigidity.
    I can see you are implying that it is less rigid enough to not do, but how much less rigid will it be? Assuming there is a top Y and bottom Y from what I can see via a dial test indicator and FEA almost all of the torque from the cutting forces hits the bottom rail and the beam. I'm quite the newb a this but my first iteration of my machine showed the same measurement while cutting. My spagetti like rigidity fixed gantry first attempt moved all over on the bottom Y rail, the top hardly moved acting like a pivot joint. I may be completely wrong about this.

    Also of note is my z-trucks were mounted on the Y gantry with moving Z rails. This arrangement appears to keep the majority of force on the bottom rail. The moving Z truck argument seems to move the twisting forces depending on the Z height but there are like 600 post on that topic already.

    So, is it 500% more rigid with 2 profile rails vs 1 profile rail and one supported rail, or is it 100% more rigid? What is the tipping point here for the engineering tradeoff? I've seen you post several times saying that 15mm profile rails are overkill for most hobby machines.

    P.S. last night I tried this out with 2.5" x .25 T6 aluminum tube a HGH20CA bottom Y rail and a SBR16 top rail. Compared with the C-Beam I was using it seems much more stable to twisting but I have to get it back on the machine to test it out... Worse case I just build up my forearms doing all the tapping.

    P.P.S Thanks for replying and being open to data driven debate!



  7. #7
    Member
    Join Date
    Jun 2010
    Location
    Australia
    Posts
    4252
    Downloads
    4
    Uploads
    0

    Default Re: square AND round rails!?

    C beams twist all over the place. Square tubing is much, much more rigid.
    Doubling up on profile rails does make for huge complications of alignment. You can avoid all those by just going to a bigger profile rail.
    And I do NOT agree that 15 mm is overkill; more likely underkill.

    Cheers
    Roger



  8. #8
    Member
    Join Date
    Apr 2013
    Location
    Sweden
    Posts
    1899
    Downloads
    2
    Uploads
    0

    Default Re: square AND round rails!?

    Quote Originally Posted by jschoch View Post

    After watching this video (ignore the title for a moment, seems to have some good advice for driving rail systems and alignment)
    Watching a 55 minute long video selling plastic bearings...? You must have a lot of time...

    If you want to mill aluminium you need a rigid machine. Forget about plastic bearings. Would not use them for 3D printer. Build/upgrade to highest possible rigidity, get the best, most rigid pair of rails you can afford (not less than MGN15), align them properly and that's it.

    https://www.youtube.com/c/AdaptingCamera/videos
    https://adapting-camera.blogspot.com


  9. #9
    Member ger21's Avatar
    Join Date
    Mar 2003
    Location
    Shelby Township
    Posts
    35538
    Downloads
    1
    Uploads
    0

    Default Re: square AND round rails!?

    So, is it 500% more rigid with 2 profile rails vs 1 profile rail and one supported rail, or is it 100% more rigid? What is the tipping point here for the engineering tradeoff?
    If I had to guess, I'd say closer to 5x more rigid, if not much higher. But the only way to know is to build them, and test them.

    As for what's good enough? That depends entirely on your expectations. What more than good enough for one person can be unacceptable for someone else.

    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)


  10. #10
    Member
    Join Date
    Mar 2018
    Posts
    68
    Downloads
    0
    Uploads
    0

    Default Re: square AND round rails!?

    Quote Originally Posted by A_Camera View Post
    Watching a 55 minute long video selling plastic bearings...? You must have a lot of time...

    If you want to mill aluminium you need a rigid machine. Forget about plastic bearings. Would not use them for 3D printer. Build/upgrade to highest possible rigidity, get the best, most rigid pair of rails you can afford (not less than MGN15), align them properly and that's it.
    I make as much time to learn and consider different ideas as I can!

    I'm not planning on plastic bearings for a cnc mill. I'm using HGH20CA rails and i have some SBR16 rails from my last attempt that I'd love to put to use.



  11. #11
    Member
    Join Date
    Mar 2018
    Posts
    68
    Downloads
    0
    Uploads
    0

    Default Re: square AND round rails!?

    [QUOTE=ger21;2191466]If I had to guess, I'd say closer to 5x more rigid, if not much higher. But the only way to know is to build them, and test them.

    [QUOTE]

    wow, that is quite a lot! I wonder what the best way to test this is? Can you think of a good jig design that is easy to build?

    Quote Originally Posted by ger21 View Post

    As for what's good enough? That depends entirely on your expectations. What more than good enough for one person can be unacceptable for someone else.
    My last build was like a wet noodle and I was able to do aluminum with the right feeds/speeds. My main objective is to learn and have fun but I want to temper that with not having to babysit a machine for long operations which is really a waste of time. This brings up an interesting question that I don't often see asked. here. How much time is saved for a given rigidity improvement? i've seen ppl tweaking FEA simulations 60+ times for a few thousands. How much quicker can you cut for a given rigidity improvement? How much does .0001" less moment deflection get you?



  12. #12
    Member
    Join Date
    Apr 2013
    Location
    Sweden
    Posts
    1899
    Downloads
    2
    Uploads
    0

    Default Re: square AND round rails!?

    Quote Originally Posted by jschoch View Post
    I make as much time to learn and consider different ideas as I can!

    I'm not planning on plastic bearings for a cnc mill. I'm using HGH20CA rails and i have some SBR16 rails from my last attempt that I'd love to put to use.
    My CNC (moving table type) is based around SBR16 (2 on each axis) and 1605 (one on each axis), the working area is pretty small, 310 x 270mm and the Z clearance is 160mm, giving me the possibility to use a good vise and the total machine weight is about 90kg, so it is not a light table top machine. I am milling aluminium, and it is working just fine, but as I said earlier, the more rigid the better, meaning you can use the SBR16 you have (2 on each axis) but if you can get real rails then don't get anything less than 15mm, especially not for the X and Z. Perhaps for the table, assuming you plan to make a moving table type, maybe 12mm is OK, but I would not use so small rails on a CNC. I am using MGN12 on my 3D printer, and it may be overkill for that purpose, but I think not. If I ever upgrade my CNC with real rails I'll use MGN20.

    https://www.youtube.com/c/AdaptingCamera/videos
    https://adapting-camera.blogspot.com


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

square AND round rails!?

square AND round rails!?