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Thread: Parallelism and Perpendicularity in Vertical Mills

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    Registered bonmotwang's Avatar
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    Parallelism and Perpendicularity in Vertical Mills

    I am going to design and DIY a vertical mill cnc. There are a lot of useful information and guidence I found on this forum.
    But in most of the building logs, I didn't find how to adjust the parellelism and perpendicularity for the X, Y and Z axis.
    I thought there should be a step(s) of verifying/adjusting the parallelism and perpendiculatiry somewhere in the process.

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    That kind of thing is done constantly throughout the process, every time two pieces of metal are assembled (and before they're assembled) they're checked for square and position.

    If you're wondering about the parallelism of eg. linear guide rails, the install manuals for those rails typically have a guide for that.

    Also, there are various techniques described in build threads here and in the CNC wood router section for determining parallelism.

    I think most people skip it for the same reason they skip descriptions of installing a bolt... it's pretty basic for the most part. The best way to learn this stuff is to get a good book like "Machinery's Handbook" and read. Lots of great stuff in there.

    If you have a specific question on the best way to measure a particular part of your machine while assembling to ensure it's parallel, then post and ask.

    Taking a half step back, you might want to start with a solid wood cutting router table instead of a vertical mill. If you don't have enough experience with milling machines and machinist's skills to already have a bunch of different methods for checking parallel and square memorized, you're probably not going to be happy with the result you get when designing your own machine from scratch. There's a lot more to it than just arranging an X/Y table and Z quill of the size you want.

    Maybe buy some plans from someone? Ever read the gingery books?

    Erik



  3. #3
    I agree with Erik, but to try to answer you a bit in addition, most methods use some type of indicator to check the measurement you're interested in. For example, to check the squareness of the z axis movement to the table, you could put a dial test indicator in the spindle, put a cylindrical square on the table (from a quick google search, here's an example: MAGNETIC CYLINDER SQUARES by Suburban Tool, Inc.), and move the z axis with the indicator tip against the square. A refinement of that technique, iirc, would be to reverse the square (rotate 180 degrees) and indicate that side as well. The average of the two measurements would be the deviation of the z axis from perpendicular movement relative to the table. The reason you check off both sides is in case the cylinder has taper along its length. You could do the same thing with a test bar in the spindle and the indicator mounted to the table. Other techniques would include using an autocollimator and an optical square or a laser interferometer with angle measurement optics.

    A good book for this kind of information is Connely's Machine Tool Reconditioning: Machine Tool Reconditioning for Machine Tools by Machine Tool Publications

    CNC mill build thread: http://www.cnczone.com/forums/vertical_mill_lathe_project_log/110305-gantry_mill.html


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    Registered bonmotwang's Avatar
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    Thanks for the replies.
    I own a 400mx400mx100m router, so I have been through how to measure if they are square and how much they are off.
    But it is tricky to do the fine adjustment if it is not designed for that.
    I am trying to have this thinking in the design to make sure I can do fine tuning in my next CNC.
    Yes, I will make sure it is straight and square in every step. But errors accumulate, so instead of praying for the errors canceling out each other or just simply shim it. I am looking for (dreaming?) some general guidance.
    Specific question would be great, but I am not at that stage yes. Everything is still in my Solidworks so far.



  5. #5
    Connely's book talks about accumulating error, for example on a knee mill, and how to make sure the errors add so the final machine is in spec. Basically you just have to be able to measure the actual error at each stage, keep track of it, and make sure that you are correcting for it so that the finished product will be within the tolerance range you desire. For various types of machines, there are various typical tolerances at each step plus at the end, but since this is your design those tolerances are up to you. As far as how to design in adjustment, you can:
    - design it so everything's adjustable with grub screws
    - have bolted joints that you can shim, slide or rotate around
    - align parts to each other during construction with grub screws, secure them with bolts and then grout them together (inject filled epoxy into the gap between parts)
    - scrape parts based on spotting them with reference surfaces and mating surfaces and checking alignment with various indicators and gages, keeping track of the errors as you build the machine (this is the traditional way)

    I'm sure there are other ways as well. Grouting would be my choice, as that gives the possibility to produce the stiffest joints.

    Personally I would just think through each step of alignment, what tools you'll use and how you'll set them up, and make sure it will be possible to align everything. Assume everything will need tweaking and that nothing will start out flat / parallel / perpendicular. This could also lead you to specific questions on how to align a part that it would be easier for people here to answer.

    CNC mill build thread: http://www.cnczone.com/forums/vertical_mill_lathe_project_log/110305-gantry_mill.html


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    Registered bonmotwang's Avatar
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    Thanks JSH
    Very appreciate your thoughts about "how to adjust". Maybe this is as simple as how to install a bolt for some of the zoners here. But for me this is exactly what I wanted to hear to start my thinking.



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