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  1. #91
    Thanks so far for your opinion and for your advices. I have one main question.
    You told me not be afraid of the gantry weight. Not to try to lighten the steel pieces as weight is not such a big problem. I want to ask then why many people try to build the gantries with aluminum that it is lighter than steel and aslo more expensive. Why many people try to make their gantries as light as possible without of course having compromises with stiffness. Finally why nearly every Z axis is made from alluminum and not ftrom steel. In my project i think that with or without the offcuts, the difference in weight will be nearly 20 kgr. If that mass isnt important and have small impact to the performance of the machine, then i have no reason to laser cut the parts the way i show before as the cost for lasercutting is not small.

    Thanks again

    Vagelis
    Last edited by ba99297; 03-04-2014 at 04:15 PM.

  2. #92
    Ger21's Avatar
    Lives in Detroit, United States. Last Activity: 9 Hours Ago Has been a member for 5-6 years. Has a total post count of 508. Received thanks 68 times, giving thanks to others 0 times. Referred 1 members to the community.
    I want to ask then why many people try to build the gantries with aluminum that it is lighter than steel and also more expensive.
    Because aluminum is much easier to work with for most people.

    Why many people try to make their gantries as light as possible without of course having compromises with stiffness.
    Because they don't know any better.

    Finally why nearly every Z axis is made from aluminum and not from steel.
    Again, aluminum is usually much easier to work with. You can cut it with woodworking tools, or even very lightweight cnc routers if you take your time. Steel requires different tools, or you need to pay someone to do the work.

    The Z axis is one place where lighter weight is helpful. But I think ease of fabrication is still the main reason aluminum is used.
    Gerry
    ______________________________________________
    UCCNC 2017 Screenset

    Mach3 2010 Screenset

    JointCAM - CAM for Woodworking Joints

  3. #93
    I have to admit I did not know the answer to Vagelis' questions but now Gerry has replied I agree with what he says but don't know if that's the full story. I found the Hiwin blocks seemed to move easier with more weight applied so maybe mass and preload of the bearings work together ?
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  4. #94
    Ger21's Avatar
    Lives in Detroit, United States. Last Activity: 9 Hours Ago Has been a member for 5-6 years. Has a total post count of 508. Received thanks 68 times, giving thanks to others 0 times. Referred 1 members to the community.
    I found the Hiwin blocks seemed to move easier with more weight applied so maybe mass and preload of the bearings work together ?
    When bearings have a high preload, they will have a "stiction" force that needs to be overcome before they move. Adding weight makes this "stiction" appear less. Unless you have high preload bearings on a lightweight machine, this issue is more "perceived" than actual.

    While it's certainly possible to build a gantry that's too heavy, it's rather unlikely. Especially with a servo powered machine. If you keep the gantry weight under 125-150Kg, you should be fine.
    Gerry
    ______________________________________________
    UCCNC 2017 Screenset

    Mach3 2010 Screenset

    JointCAM - CAM for Woodworking Joints

  5. #95
    After so many months of studding the cnc world, i finally realize that that the myth about lightweight gantries ( that i had in mind ) bites the dust. I am talking about my machine and not for every cnc. Thanks to Deans advices and thanks to Jonathan calculator, i see that 20-30 and even more kgr at the gantry weight doesn’t affect torque needs of the motors. I understood that the most torque will be needed to move pulleys and ballscrew than the gantry that slides on the carriages. Also Syliavsky Eddy, and Ger21 mention that. Thank you every one. After that i will make some changes to Y axis and then go on with the Z axis. So far my gantry weights about 65-70 kgr( without the motors ballscrews of y axis and without the Z axis that need to be designed.
    A last photo of the gantry
    Click image for larger version. 

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    Vagelis
    Last edited by ba99297; 07-04-2014 at 11:28 AM.

  6. #96
    Hi Vagelis,

    Sorry I've not been replying to your emails or thread but I've been very busy. I've just today managed to open the file you sent me so have a better idea and can see it's mostly what you posted here.

    As I told you before and now others have also confirmed for you that Gantry weight is not such a big issue with Servo's so won't go further on about this.! . . What I want to point out thou is that your complicted Jigsaw puzzle won't really stop the steel from warping while welding.
    10mm plate needs serious heat to weld even with Tig and you will experience some warping and for this reason I suggest you design the gantry so it can be welded up completely then important surfaces machined after it as stablised.
    Because of your welded and fixed ridged gantry design then you have less areas of adjustment so it becomes important surfaces are machined true and parallel.

    I think I've said this before but really for cutting wood then this design is massive overkill unless your planning on attaching a high powered spindle cutting deep and fast 12hrs a day.!
    I know your thinking to cut Aluminium with the machine but even then the gantry will be strong enough for light/medium duty work. If you want deep depth's of cut and high quality finish then the size of the machine and Gantry router design will be more the limiting factor not just the Gantry design or strength.

    End of the Day you CANNOT have the perfect all round machine at this size so My advise Again is to build it to be the very best it can be for the Purpose you intend to use it for most.! . . . . . . I would rather have a machine that is excellent at one thing than just average at anything and you will only have one or the other.!!
    Last edited by JAZZCNC; 07-04-2014 at 08:24 PM.

  7. The Following User Says Thank You to JAZZCNC For This Useful Post:


  8. #97
    Dean you are right. I am trying to make an all purpuse machine. In my country they said "you can not carry two watermelons under one armpit". That is what i am trying to do BUT as i am going to spend money for a machine, i am trying to achieve the best value for money project. Every day because of asking i find out things that help me avoiding mistakes. I will go on with z axis and come back. If anybody see something that should be mentioned, I will be glad to hear it. Meanwhile if you have any supplier for belts and pulleys tell me. The main problem with me ( among others ) is that I have no lathe or mill for some main machining, so I am trying to avoid that cost by sketching laser cut steel puzzles. As I see it is difficult to avoid machining. Next week I will take my plans and make a research about milling cost. Thank you so far for your help


    Vagelis
    Last edited by ba99297; 07-04-2014 at 10:47 PM.

  9. #98
    Here is some progress.
    Ganty side plates 10mm steel. Doyou think i need a second side plate each side?
    Gantry body 210mm height, made from two tubes 120X60X4 ( up down) and 1 tube 80X80X4 (middle) welded together
    All gantry will be welded and then apply epoxy in order to have bottom side carriages in the same level
    Z axis from 20mm aluminium and some parts from 10mm steel.
    Y axis upside carriages at 400mm distance
    Y axis bottom side carriages at 250mm distance
    Z axis travel 200mm
    Spindle plate 200mm wide

    On Friday i will confirm my order to Chai for ballscrews dimensions leave 50mm for pulley attach and easy alignment
    I will be glad to hear any advice or comment
    Thank you for your time

    Click image for larger version. 

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    Last edited by ba99297; 30-04-2014 at 11:36 PM.
    The creative adult, is the child who survived

  10. #99
    Have you thought how you will access the mounting bolts on the Z rail blocks (4.jpg) it looks like the Y rails blocks will restrict them. On another point it seems like you are use angle iron for the rail blocks (Y) are you sure that they will be at true right angles and that the inside edge is flat and parallel to the outside edge. ..Clive

  11. #100
    Quote Originally Posted by Clive S View Post
    On another point it seems like you are use angle iron for the rail blocks (Y) are you sure that they will be at true right angles and that the inside edge is flat and parallel to the outside edge. ..Clive
    Aluminium angle is a lot more accurate than steel so maybe you could use a thicker section aluminium angle instead.
    Do you need the full Z travel ? if not I would move the Z Hiwin blocks further apart.
    Also now is the time to work out where your cable drag chain (energy chain) will sit, you'll need three lengths of the stuff and will need to know the lengths, bend radius, internal dimensions.

    Looks like it's coming together nicely.
    Last edited by EddyCurrent; 01-05-2014 at 09:14 AM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

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