Page 2 of 7 FirstFirst 1234 ... LastLast
  1. #11
    It's an interesting design and if you really want to do the Z axis that way then I would add a reinforcement panel on the front outer face of that RHS box to spread the load of the spindle out to the edges (I assume the spindle is mounted just on the front face and not sandwiched between the front and rear faces?). Say a 8-10mm thick aluminium plate as wide as the RHS and enough height to pick up on the 4 spindle mounting bolts. Otherwise the loads will go into the weaker membrane panel and not be transferred to the stiff edges. If you simplified your loading condition on the analysis this will not show up.

    Same could be applied to the rails, I would add a thin strip of say 6-8mm thick steel, by 30mm wide on the inside of the RHS directly where the rails mount and screw the rail bolts right through into it.

    Also in post#9, first picture, the upright bracket holding the ballnut to the Z axis is too thin. It needs to be approaching the length of the ballnut and then bolted down in 4 places. It should be a 'boss' not a 'bracket'. Also the plate it sits on is on the small side if you are trying to maximise performance. This needs a better connection to the upright Y axis plate. As drawn it will twist when loaded. Maybe a similar plate parallel to the current plate but above the ballnut would work trapping the ballnut in-between 2 plates.

    Keep exploring, it's good to see something different every now and again.
    Last edited by routercnc; 05-05-2016 at 05:43 PM.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  2. #12
    Quote Originally Posted by routercnc View Post
    It's an interesting design and if you really want to do the Z axis that way then I would add a reinforcement panel on the front outer face of that RHS box to spread the load of the spindle out to the edges (I assume the spindle is mounted just on the front face and not sandwiched between the front and rear faces?). Say a 8-10mm thick aluminium plate as wide as the RHS and enough height to pick up on the 4 spindle mounting bolts. Otherwise the loads will go into the weaker membrane panel and not be transferred to the stiff edges. If you simplified your loading condition on the analysis this will not show up.

    Same could be applied to the rails, I would add a thin strip of say 6-8mm thick steel, by 30mm wide on the inside of the RHS directly where the rails mount and screw the rail bolts right through into it.

    Also in post#9, first picture, the upright bracket holding the ballnut to the Z axis is too thin. It needs to be approaching the length of the ballnut and then bolted down in 4 places. It should be a 'boss' not a 'bracket'. Also the plate it sits on is on the small side if you are trying to maximise performance. This needs a better connection to the upright Y axis plate. As drawn it will twist when loaded. Maybe a similar plate parallel to the current plate but above the ballnut would work trapping the ballnut in-between 2 plates.

    Keep exploring, it's good to see something different every now and again.
    The spindle mount is bolted from the front and the rear of the large square steel tube. However I'm not satisfied with it because the mounting of the plate can maybe drag the clamping around the spindle apart. I also need to make tramming possible.

    The nice thing with the steel square tube is all the space for mounting parts. If I eventually want to add a 3:1 belt reduction on the spindle, for steel. (whisfull thinking)

    Plates on the inside for the rails sounds like a good idea.

    The upper ballnut connection is made of 3 layers of 10mm aluminium plates, where the lower one is bolted to the large steel tube. The grabCAD model should show it better. Or I'm misunderstanding something.

    Thanks for the comments it have helped me removing a lot of weak points.

    Edit: I see I forgot to add the mounting holes for the backside of the spindle attachment on the square tube.
    Last edited by PotatoMill; 05-05-2016 at 06:43 PM.

  3. #13
    Now the whole thing begins to come together again. I have done some more FEA on the whole frame. I will just add that they are approximations and gives a rough overview. Joints and mounting points will add to the deflections.

    Click image for larger version. 

Name:	compleate assembly 100 + g i X retning aluminium base med enkelt støtte.PNG 
Views:	81 
Size:	166.0 KB 
ID:	18408
    Base:
    I did some test with and without the side supports. The side supports make the base a lot more rigid. However, without the side support the deflection on the base is still insignificant compared to the gantry and the y and z carts. I also looked at how steel would increase the rigidity, but since the deflection on the base already was insignificant on the total frame, the increased stiffness from the steel was very small on the whole frame. The base is about 57kg with aluminum and 105kg with steel.
    Click image for larger version. 

Name:	compleate assembly 100 + g i X retning.PNG 
Views:	82 
Size:	225.7 KB 
ID:	18407
    Gantry:
    The gantry have a lot to say on the stiffness of the frame especially torsion that add to deflection on loads in the x axis. The gantry is changed from a frame with a lot of 60x60mm square tubes to a single 300x200mm t=6 rectangular tube. The stiffness of the new setup is about the same, but it makes the assembly a lot easier. Which means there is less areas to make mistakes the rigidity of the machine will suffer from. I had to go for steel on the gantry to get it rigid enough, an aluminum rectangular tube was just not enough. Casting aluminum could be possible, but that will again make it more complex and prone to errors. The gantry is still movable on its own, but it is now at 50kg. The Y and Z cart is at 20kg so in total the gantry and Y and Z cart will be 70kg.


    The design on GrabCad is now updated https://grabcad.com/library/z-and-y-cart-gantry-cnc-1. However, the ball screws for moving the gantry is not finished yet. And I see that mounting of the rails for the Y cart makes it impossible to attach the Y cart so I have to find a solution for that. Moreover, it would be great if someone have a good suggestion.
    Last edited by PotatoMill; 07-05-2016 at 09:41 PM. Reason: Grammar and structure

  4. #14
    Given that the additional cost and effort is low I'd add the side supports anyway as there may be a significant reduction in resonance under circumstances for which you have not calculated.
    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. #15
    Quote Originally Posted by magicniner View Post
    Given that the additional cost and effort is low I'd add the side supports anyway as there may be a significant reduction in resonance under circumstances for which you have not calculated.
    Indeed, that's why I will probably build them anyway, but it can also be easily added later. The only minus is the added with, if I can get it trough a door on wheels whitout removing the gantry and tipping it on the side it would be nice. Else than that it is only positive with the added rigidity for unforseen deflections. Hovewer the base is already more than strong enough, it's the torsion on the gantry that is the weak point.
    Last edited by PotatoMill; 08-05-2016 at 01:12 AM.

  6. #16
    I'm currently considering making a stationary gantry design. Since the weight of the gantry pluss the z and y cart comes inn at 80kg (mostly in steel).
    The cons will be;
    -Longer machine
    -Longer rails
    -Potensial for sag in the bed

    Pros
    -Less weight to move for the steppers
    -Simpler design
    -Less twist on the z axis, the largest factor for displacement

    The reason i'm posting this is because it probably a lot more pros and cons than I can come up with, that I hope someone here will add.

  7. #17
    So I have been working on redesigning the whole machine. I'm currently going for a stationary gantry design.
    Click image for larger version. 

Name:	Stationary gantry.PNG 
Views:	132 
Size:	183.0 KB 
ID:	18718
    Due to the fixed gantry design the heaviest moving part is now the base plate with 30kg. I'm going to use 20mm HIWIN profile rails on all axis.
    There will be one lead screw on each axis, no need for two on the X any more due to the stationary gantry. Here i'm going to use 1605 ball-screws. To drive the axis i'm currently looking at using servos in the 200-400W range. There is not the same amount of information on servos av steppers so I hope someone here have some knowledge on servos. Seems like JMC produce the cheapest servos and drives, but I cant find a lot of data on them. If there servos from JMC are good enough i'm probably going to use them. BST automation also seems to have a ok selection on servos, but again there is little documentation to find.

  8. #18
    Quote Originally Posted by PotatoMill View Post
    BST automation also seems to have a ok selection on servos, but again there is little documentation to find.
    If you send them a msg Fred will be more than happy to help and send you what you need.

    .Me
    .Me

  9. #19
    Quote Originally Posted by PotatoMill View Post
    Click image for larger version. 

Name:	Stationary gantry.PNG 
Views:	132 
Size:	183.0 KB 
ID:	18718
    It looks like you have the rails on the base and the carriages moving on the X-axis.
    If you have the carriages fixed on the base and the rails moving under the X-axis you can have maximum support and rigidity where you need it most at all times.
    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

  10. #20
    I can give some info about that. I have one 60ASM200 at home. My computer is not enough fast for this resolution, so that is why it looks slow on a video. The electric gear ratio is 1:1. https://www.youtube.com/watch?v=qyrEdBIpqx8

Page 2 of 7 FirstFirst 1234 ... LastLast

Similar Threads

  1. Cast aluminium gantry router
    By jrcast in forum Gantry/Router Machines & Building
    Replies: 17
    Last Post: 17-02-2017, 07:13 PM
  2. BUILD LOG: Aluminium Framed Router
    By lucan07 in forum DIY Router Build Logs
    Replies: 34
    Last Post: 04-05-2016, 08:06 PM
  3. 600 x 400 Aluminium Profile Gantry Router
    By Journeyman in forum Gantry/Router Machines & Building
    Replies: 0
    Last Post: 02-03-2016, 03:28 PM
  4. RFQ: RFQ: Aluminium parts for my CNC router
    By biketrialsdave in forum Projects, Jobs & Requests
    Replies: 0
    Last Post: 12-10-2014, 09:06 PM
  5. BUILD LOG: Aluminium Extrusion CNC Router Build
    By joshendy in forum DIY Router Build Logs
    Replies: 9
    Last Post: 10-04-2012, 07:26 PM

Bookmarks

Posting Permissions

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