1. #1
    Sherpa's Avatar
    Lives in Lampeter, United Kingdom. Last Activity: 4 Weeks Ago Has been a member for 0-1 years. Has a total post count of 8.
    Good Evening All,

    Firstly and a bit presumptuously thank you all in advance for the help and support that I am going to need during this build, seldom do I say that I feel part of this community before I even begin the help I have had to date has been amazing and I again would like to thank you all

    So like any successful project it needs a catchy name so given that this is what I am going to be in for the next X months or Years I decided to call my CNC Machine "Deep Thought".

    I have started to put pen to virtual paper bit rusty on my CAD skills but it is coming back - slowly. I now have the early look / feel of a machine sub frame, interestingly this has already thrown out a huge number of questions some answered by looking at other build logs other not. It is funny to think that I started in Sketchup going "This will be a few hours and I will be done" two days later I am like " hmmm - (goes of to look at MyCNC Forum) but all very very enjoyable.


    The DESIGN BRIEF

    Use case statements - bit of my job coming through!!

    “ As a user I want the ability to use my CNC machine to cut Wood (hard and soft) , Aluminium, Plexiglas and Wax blocks. I need to be able to construct the machine myself (or buy parts I cannot tool). The design should enable me to prototype in wood first to provide confidence in my measurements. It’s size needs to fit in with my workshops space without reducing the overall usable area too much. I need the machine to be able to replicate the same cuts with as little deviation as possible to keep accuracy of the end product, I would like to spend no more than 1000 on the build if possible”

    I would guestimate that the overall material usage would be 50% wood 50% other materials listed.

    The CNC bed size is 630 x 1000 mm (appreciate cutting size will not be the same)

    The key element to my machine (not unique at all I would have thought) is its ability to consistently and accurately (within reason of a self-build machine) reproduce parts that I require for my small business that will in turn lower some product overheads.

    I think that about covers it, but if you cleaver people need more to provide support and guidance please let me know what other information would be useful.

    DESIGN Trouble

    So going to try and articulate this in the correct language to try and make the question easier to answer. First some wide angle pictures of the design so far:

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    Question 1 - I am a bit confused with regards to this design section, i intend to use two Y axis motors to provide much greater stability and to reduce the "racking" i think it is called or the gantry pulling or twisting that could be encountered on a single centered ball screw. Accepting that having two stepper motors increases the cost and increases the complexity of the build slightly, as well as needing to calibrate them occasionally as i understand it two is overall more beneficial that one (part A question is my thinking correct here?).

    Part two is in two parts A) how should i be connecting the ball screws to the lower cross beam on the gantry, should they be on top to provide extra support / stability ( a bit worried that it might "strike the plate" or should it be attached to the bottom as per the picture below.

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    Part B) i am just not clear at all as to how i am meant to design this area, mainly as i'm not sure how the ball screw assembly is meant to be put together, so am unsure of diameter of cutouts needed for bearings, and how the ball screw would be fastened / driven by the stepper motor. I would be grateful if this could be explained- looking at other build logs it is hard to visualize as while i can see the basic principle the pics are taken far way so not able to see the layout / connectivity. Am i also right to put both ball screws as close to the gantry guide rails as possible as per picture below:

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    EDIT - looking back at the picture above i need to redesign this to protect the rail from debris from the bed!

    So this is where i am up to for now until i can address these questions, cant go any further in the tooling plate design etc as this is all centered around how ball screws work.

    Would love your feedback to see if i am designing something viable or something that is destined to the scrapheap :) will not be offended in anyway, if you think i need to overhaul the design so far just let me know why so i can correct it in version 2!

    Look forward to your opinions / answers

    Kind Regards
    Sherpa
    Last edited by Sherpa; 25-09-2016 at 09:26 PM.

  2. #2
    Quote Originally Posted by Sherpa View Post
    Question 1 - I am a bit confused with regards to this design section, i intend to use two Y axis motors to provide much greater stability and to reduce the "racking" i think it is called or the gantry pulling or twisting that could be encountered on a single centered ball screw. Accepting that having two stepper motors increases the cost and increases the complexity of the build slightly, as well as needing to calibrate them occasionally as i understand it two is overall more beneficial that one (part A question is my thinking correct here?).
    You haven't mentioned the size of the beast. If it isnt too large the received wisdom is to use a bigger stepper and a belt to drive the two Y screws. This avoids racking and sync problems.

    My agolopies if there are typos, but it it Sunday night and two stonking G&T's and a glass or three of a very robust red wine (Batturica from LIDL) have mellowed my typing skillll;s.

    Rob
    It takes all sorts to make a world, I am just glad I am not one of them.

  3. #3
    Sherpa's Avatar
    Lives in Lampeter, United Kingdom. Last Activity: 4 Weeks Ago Has been a member for 0-1 years. Has a total post count of 8.
    Hi Rob - thanks for that added bed dimensions 630 X 1000mm - just watched a good video too on ball screws so that is sort of falling in place

  4. #4
    From the project name I assume it incorporates 42 of something?
    ;-)
    If you will not be swayed by logic or experience simply pick the idea you
    like best, but ask yourself why you sought advice in the first place and,
    for a simple life, perhaps consider not doing so in future

  5. #5
    Sherpa's Avatar
    Lives in Lampeter, United Kingdom. Last Activity: 4 Weeks Ago Has been a member for 0-1 years. Has a total post count of 8.
    Ok making some progress now fixed issue with rails being exposed with a bed overhang - read allot about ball screws so going to tackle that next - feel the learning curve is huge and keep going back to the design and tweaking, feel like this is never going to get finished . And as i type this i am thinking i have no cable tracks (are they called "energy rails") so another snag added to my list!!

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    Sherpa

  6. #6
    Energy Chains also known as Power Chain, Drag Chain & Cable Chains
    It takes all sorts to make a world, I am just glad I am not one of them.

  7. #7
    Sherpa's Avatar
    Lives in Lampeter, United Kingdom. Last Activity: 4 Weeks Ago Has been a member for 0-1 years. Has a total post count of 8.
    Well final update on this thread because ... A) just figured out posted in wrong place and B) Gone back to the drawing board so the original design brief has changed so will do it all again once my plans are complete.

    So today i spent time in the workshop getting things tidy again and man it is lick the floor clean in there now lol !!!
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    New post should be up in the Build Log section by the end of the week :)

    Speak soon

    Sherpa

  8. Nice workshop! You should have a look at this thread : Finished builds picture menu
    http://www.mycncuk.com/showthread.php?t=10066
    Last edited by JoeHarris; 10-10-2016 at 08:21 AM.

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