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  1. #51
    fifa's Avatar
    Lives in bristol, United Kingdom. Last Activity: 4 Weeks Ago Has been a member for 0-1 years. Has a total post count of 30. Received thanks 2 times, giving thanks to others 0 times.
    Few comments:
    - I do not understand why you are using AL profiles and AL plates, check stiffness...
    - design of lower (x) rails is .... You need to grind both surfaces to get perfect parallelism, otherwise will linear bearings feel the load caused by angular displacement of both rails , put them on the top of the table, in same plane - much easier for DIY,
    - design of gantry (y) - it must be closed beam - it has no sense to do a "nice look" without functionality,
    - side brackets, what is the method for setting the "true" right angles? Do you expect that everything will be machined within few microns? , y length tolerance stack is problematic anyway
    - foots: do you expect that desktop is planar?, machine must be stable, it looks nice, but

    Before design set the requirements i.e.
    - max work space
    - max space for machine
    - max tooling dia
    - material of machining
    - define what you wish to do ( mirror surfaces, engraving...)

    and the start with design.

    regards

  2. #52
    Quote Originally Posted by fifa View Post
    Few comments:
    - I do not understand why you are using AL profiles and AL plates, check stiffness...
    Why alu profile, because it is available cut to length at sizes larger than I can handle myself with decent precision and also with ground surfaces from misumi. GFS (high rigidity) profiles are being used, they have substantially more mass than normal profiles.

    Why alu plate, because I can process aluminium plate myself and I can buy it in ecocast form with a high flatness tolerance, again readily available. If I pay for every part of this machine to be made up in steel to high tolerances by someone else then I will not be able to afford it, even if the material itself is cheaper... which i'm not sure it is when you start talking about milled tooling plate.

    - design of lower (x) rails is .... You need to grind both surfaces to get perfect parallelism, otherwise will linear bearings feel the load caused by angular displacement of both rails , put them on the top of the table, in same plane - much easier for DIY,
    Both surfaces are ground...

    - design of gantry (y) - it must be closed beam - it has no sense to do a "nice look" without functionality,
    I don't understand what you mean here.

    - side brackets, what is the method for setting the "true" right angles? Do you expect that everything will be machined within few microns? , y length tolerance stack is problematic anyway
    That little mounting plate at the bottom of each side has an eccentric nut on one end and a DIN shoulder bolt at the other, which will allow the entire gantry to be trammed fore/aft, while the side arms and mount plates are both made from eco-cast plate which will have to sit flat to each other when bolted together. Further adjustment is available on the spindle mount for tramming left/right.

    - foots: do you expect that desktop is planar?, machine must be stable,
    On a machine this small I think adjustable feet are more trouble than it's worth. Better just to make sure you have a flat level surface for it to sit on... depending on what I can find I will either sit it on a granite block or pour a self levelling base block for it which will form the bottom of my enclosure.

    Before design set the requirements i.e.
    - max work space
    - max space for machine
    - max tooling dia
    - material of machining
    - define what you wish to do ( mirror surfaces, engraving...)

    and the start with design.

    regards
    My design requirements were of course set out before I started to design it... the majority of what you list there was mentioned in the very first post. I'm not sure how you can even start designing a machine without knowing what you want it to do...


    Thank you for the feedback but I do think there is a danger sometimes of losing sight of reality on this forum. For what is ultimately a small hobby desktop machine the rigidity of a 50x100mm GFS extrusion and 20/25mm alu plate is hardly going to be the limiting factor... This machine will be an order of magnitude more rigid and precise than my current one while expanding the work area, which is really all I'm after.
    Last edited by Zeeflyboy; 22-02-2017 at 10:51 PM.

  3. #53
    A few frame details... made up using 50x100 and 50x50 milled profile now.

    Bottom screw nut mounting plate will probably become a single piece once I have a machine large enough to make it.






    Gantry fore/aft tramming adjustment (both sides)... undecided whether to go this way or just rely on shimming for this bit.

    Last edited by Zeeflyboy; 22-02-2017 at 10:53 PM.

  4. #54
    fifa's Avatar
    Lives in bristol, United Kingdom. Last Activity: 4 Weeks Ago Has been a member for 0-1 years. Has a total post count of 30. Received thanks 2 times, giving thanks to others 0 times.
    Sorry I am not native English speaker, therefore I can be easily misunderstood.

    X rails: pre-machining rails do not count due:
    - rails must be parallel - your design is frame from 4 profiles. Forget on straightness (you are assuming this will help with using expensive profiles.) think about other two elements which are connecting both profiles.
    You have 2 plates - potentially nonparallel, two profiles Mitsumi + two profiles catted and machined by... as I said check the stiffens of the bearing, lets assume the total error of non-parallelism is 100 microns, and that half of this error must be compensated by bearings, the other half by brackets. This means 25 microns per bearing - now check the stiffness and you will see the load which is in the "system". If you wish to remove error, you need to do machining in the assembled condition...

    Check the I (Area moment of Inertia) of profile and plate, most likely 25 mm thick plate is stiffer than 50 mm profile or it is close to it. And whatever will you do: If the profile and plate are not planar, when they will be assembled the result will be non-straightness of the rail "bed" surface.

    Y gantry: problem is torsional load not the bending - check the I and calculate displacement applying 100 N force at the end of the tool
    The second problem is: Y gantry length must meet X rail width - within micron range otherwise you are facing with additional load to the X bearings... Not mentioned that both side surfaces must be parallel, - if not additional load on X bearings again

    Regarding the idea of setting the true angles with bolt - by definition this means you are incorporating elasticity in relative stiff system. Means also you have nice oscillation.

    You are right system is relatively rigid. I am escalating problems caused G&T and consequences of those.

    regards

    regards


    ,

  5. #55
    Well I think that compared to my machine, which is welded steel frame with a bit of epoxy for levelling the rails and some 20mm tooling plate for the gantry, this is far more of an engineered and well thought out solution. Thought has gone into how to assemble the machine and the OP is very realistic with respect to the area they want and what they want the machine to do.

    I think gents that everyone is getting a little too nit picky (which, don't get me wrong, can be a good thing) and getting a little bit too bogged down in ultra precision engineering and forgetting that this is a hobby machine..............there is nothing here in this design of machine which couldn't be sorted with the help from a few beers an assortment of shims and a bloody big hammer
    Neil...

    Build log...here

  6. #56
    Absolutely agree. There may be some minor adjustment needed at the end but there would be with ANY machine (except possibly a Datron). It looks more well planned than most other DIY machines that have turned out just fine.
    ZeeFlyBoy your skills with Fusion 360 are incredible.

  7. #57
    Thank you chaps! Neil I think you summed up my thoughts quite eloquently - especially the beer and hammer part lol.

    I am of course after critique, it was the main purpose of sharing this design before starting to build it rather than vice versa - and I am extremely glad I did.

    The complete change to the Z-Axis for example is not something I would have thought of but I can definitely see the benefits... but ultimately yes, one needs to keep sight of the fact that this is a hobby machine to go in the Man Cave, not an industrial interferometer calibrated machine.

    I am confident that the design as it now stands will fall within the alignment error ability of the linear rail carriages, and with some tweaking I think I can get probably get it to within my ability to accurately measure.

    Jumper - Thanks but I'm still just an amateur with Fusion, but I do find it refreshingly easy to use for the most part!
    Last edited by Zeeflyboy; 23-02-2017 at 03:35 AM.

  8. #58
    Quote Originally Posted by fifa View Post
    Sorry I am not native English speaker, therefore I can be easily misunderstood.

    X rails: pre-machining rails do not count due:
    - rails must be parallel - your design is frame from 4 profiles. Forget on straightness (you are assuming this will help with using expensive profiles.) think about other two elements which are connecting both profiles.
    You have 2 plates - potentially nonparallel, two profiles Mitsumi + two profiles catted and machined by... as I said check the stiffens of the bearing, lets assume the total error of non-parallelism is 100 microns, and that half of this error must be compensated by bearings, the other half by brackets. This means 25 microns per bearing - now check the stiffness and you will see the load which is in the "system". If you wish to remove error, you need to do machining in the assembled condition...
    All profiles are going to be from the same place (mitsumi now, given I want the milled stuff) actually, given that they almost certainly should be cutting the bracing profiles one after the other without re-positioning the cutting gate they should be very, very close.

    They can always be massaged with my current machine which will happily repeat to substantially better than your stated 100 micron example (as confirmed by some fairly expensive glass scales mounted to both X and Y axis). It should be fairly easy to get them to within 10's of microns rather than 100's...


    Check the I (Area moment of Inertia) of profile and plate, most likely 25 mm thick plate is stiffer than 50 mm profile or it is close to it. And whatever will you do: If the profile and plate are not planar, when they will be assembled the result will be non-straightness of the rail "bed" surface.

    Y gantry: problem is torsional load not the bending - check the I and calculate displacement applying 100 N force at the end of the tool

    This is a bit beyond me, I have never used any simulation software and not sure where to start.

    I'm simply going on the basis that common sense Garden Shed engineering tells me a combined total of 32mm of solid aluminium plate and 40mm of heavy profile that makes up the gantry cross section is overkill for a 550mm span gantry on a relatively light duty table top machine. Certainly it is at least as beefy as most DIY machines of that scale that I have seen.

    The second problem is: Y gantry length must meet X rail width - within micron range otherwise you are facing with additional load to the X bearings... Not mentioned that both side surfaces must be parallel, - if not additional load on X bearings again
    I don't really see this being an issue as long as it's longer rather than shorter. All it requires is to try inserting a shim brass sheet of various thicknesses between the gantry arm and mounting plate until you find a thickness that slots in snugly.

    Regarding the idea of setting the true angles with bolt - by definition this means you are incorporating elasticity in relative stiff system. Means also you have nice oscillation.
    How is it incorporating elasticity? Once the angles are set the bolts on the respective parts are torqued down clamping everything rigidly in place... you aren't relying on the part just resting on an eccentric bushing. Where does the elasticity come from?

    You are right system is relatively rigid. I am escalating problems caused G&T and consequences of those.
    You've lost me again lol - what's G&T when it's not in a glass with some ice?
    Last edited by Zeeflyboy; 23-02-2017 at 05:19 AM.

  9. #59
    I dont see a problem, as far as your face and back plate are actually machined on a mill.


    Not that we are getting picky, but when some one sees that machine design, its obviously to a higher standard. So in order to maintain that standard and result to be incredible machine, one should aim high.

    I said once somewhere, you may laugh but the most imprecision in a build comes from not wiping the dust correctly from rails when mounting, when you are alone and tired, in a rush and no one to help you.
    project 1 , 2, Dust Shoe ...

  10. #60
    Quote Originally Posted by Zeeflyboy View Post
    Ok great, thanks - glad you agree with my thinking then!

    I've just done a mass analysis on the finished machine and its coming in at just shy of 190kg... I know mass is but one suggestion of rigidity but that's not far off 3 times the mass of my current machine.

    I've also taken the opportunity to change to a HGR25 rail and HGR25HA carriages on the Y-axis since there is more space now.

    Had a quote back for all motion parts, it was pretty reasonable for ground screws and HIWIN rails. Think I'm good to pull the trigger on those parts?


    This is certainly going to be one of the most beautiful and best machines I have seen. Seeing and following your posts I am sure that the quality will match the beauty and it will not just be a "beautiful blond" with only good looks and sexy appearance, but it will also have massive quality and accuracy attributes.

    I also like the idea of protective side covers, I think this is important because of several reasons, apart from the most obvious that it keeps most of the chips inside the working table area, it also works pretty efficiently when the cutter is broken and comes flying at you like a deadly projectile at high speed. I also have side walls around mine and that have stopped two such projectiles already from hitting me, so it is definitely a good idea to design that protection from the start. I actually don't understand how other people dare to run these machines without any protection at all, some not even using protective goggles. Perhaps they never make mistakes and never break a mill bit, I don't know, but that's their business.

    The only thing I'd do differently in your design regarding the walls is that I'd make them easily removable, preferably without the need of unscrewing. This is because it helps placing the work piece/vice/measuring instruments and so on on the table more easily. It also allows working on longer than the table work pieces if you would need it some day.

    The other thing you should consider is the mass. 190kg is a very heavy thing, which is very good for a machine, but it sets some requirements for the table also. No point building such heavy machine if the table it is on is not stable enough, which I am sure you know very well also.

    The other thing about the mass you have to consider is the ability to move it around. Perhaps it is a non-issue, but anyway, if you one day have to move it just a little bit, it is going to be a very difficult task if you haven't thought about that during the design. My machine is only about 90kg but to move that around on my own is not possible, so I have to lower the machine on wheels to do that, and even so it is not something which is done in a minute or two, first I have to lift the machine then remove the wooden blocks it is standing on then lower down on two wheels and do the same for the back, or the front part, depending on where I start. Mine is standing on it's own feet, so it is a bit easier than it would be for yours.

    Perhaps you have these questions covered/solved already, but before starting the machine build, I'd build the table to build it on and made sure the table is extremely easy to rotate and move around during the work. It is going to be necessary to have easy access to all sides, that's for sure.

    Anyway, it is very interesting to follow up on your work and see the progress. Good luck with the rest of the work as well, and don't forget too keep us updated, both here and on the Zone.
    Last edited by A_Camera; 23-02-2017 at 10:49 AM.

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