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  1. Quote Originally Posted by Clive S View Post
    What an epic build well done ..Clive
    Speaking of epic build, hows your build coming along? :-)

  2. #22
    Well thanks to your work on the machining for the gantry its now just about alive with all axis running. Watch this space and I will try and get a build log up soon. Working on the control box now.
    Thanks again for the great machining work you did for me. ..Clive

  3. Quote Originally Posted by Clive S View Post
    Well thanks to your work on the machining for the gantry its now just about alive with all axis running. Watch this space and I will try and get a build log up soon. Working on the control box now.
    Thanks again for the great machining work you did for me. ..Clive
    Any time Clive look forward to seeing it in all it's glory

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  5. Jonathan, this is awesome. A master class in how to do it properly!

    Cheers Joe
    Last edited by JoeHarris; 19-02-2014 at 08:07 PM.

  6. #25
    I am tinkering on the design, as i find it great. I am wondering if i can build something similar, simplifying it a bit?

    Like:
    - 2 x 100x100 steel box for the gantry
    -The bearing blocks and rails on the gantry to be at the upper side/or at the lower side/ so i can use epoxy and level them easy
    -2x ballscrews at the gantry near the rails

    What worries me most is the Z, making the z box and adjusting rails and fitting everything in place there. maybe using some ready box section and fit the spindle inside and fix the bearing blocks to the sides of it.

  7. #26
    Quote Originally Posted by george uk View Post
    1. To stiffen up Z and Y ( when in action together ), i was thinking off adding rails to the inside edge of the X top support. ( i may want to add an impact head to it in the future ). Any opinions ?
    It's hard enough to align 2 rails let alone four. If you really need the higher load ratings, it's easier to just use bigger rails.

    Quote Originally Posted by george uk View Post
    2. any idea when the files will be available, am eager to have a crack at this.
    Soon. Sasha's still sorting them out but he's more interested in making the enclosure for the machine at the moment!

    Quote Originally Posted by silyavski View Post
    - 2 x 100x100 steel box for the gantry
    Could do, but clearly that makes getting an accurate surface to mount the rails on more difficult. An early design for this machine did use 60*60 box section, but we decided not to use it as aluminium is much easier to machine.

    Quote Originally Posted by silyavski View Post
    -The bearing blocks and rails on the gantry to be at the upper side/or at the lower side/ so i can use epoxy and level them easy
    Definately lower side as you want to keep them as close to the bed as you can to minimize the overhang.

    Quote Originally Posted by silyavski View Post
    -2x ballscrews at the gantry near the rails
    I presume you're referring to the Y-axis? If so then yes it will make a noticeable difference to the stiffness of the Y-axis, but bear in mind it's already exceptionally strong so it's by no means mandatory. You could achieve the same by increasing the spacing of the Y-axis bearing blocks quite significantly.

    Quote Originally Posted by silyavski View Post
    What worries me most is the Z, making the z box and adjusting rails and fitting everything in place there. maybe using some ready box section and fit the spindle inside and fix the bearing blocks to the sides of it.
    We used separate plates as they can be adjusted to get the rails parallel. Also it means you can machine features inside the Z-axis and you're not restricted to limited standard sizes.
    Last edited by Jonathan; 20-09-2013 at 06:41 PM.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

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  9. #27
    Quote Originally Posted by Jonathan View Post
    It's hard enough to align 2 rails let alone four. If you really need the higher load ratings, it's easier to just use bigger rails.
    I mentioned something similar to you in an email Jon and feel the machine would benefit from 1 more rail on both Y & Z axis. One Higher up on Y axis and on 3 sides of box on Z axis but more to help with resonance and vibration in all cutting directions rather than increase load ratings.?

    Would also add another ballscrew to Y axis rather than increase bearing plates has the action of 2 screws pushing/pulling together would be smoother than widening the plates.?

    Like you say it's very strong already but feel these changes would make it the close to ULTIMATE strong machine.!

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  11. #28
    Hi

    Thanks for your reply Jonathan. To add a second rail, i was going to set it up and level it following your excellent instructions, then use the level surface prepared for the first rail, to mark the second. I was thinking of adding the second rail 90deg relative to the first ( on the side ) for the reasons stated in JAZZCNC above.

    In fact, if i get the first rail level, and use it to mark the second, it would be quite hard to make it to far out ( as long as am carfull ). The main reasons i require stiffnes to the gantry is so i can add a B/C head or plate if needed. Am also adding a turret/lathe to the bed.

  12. #29
    A couple of questions as i am designing my own build, using your ideas:

    -so you believe 3kw spindle would be better than 2.2kw?
    -how you did the oiling system? did you use the original nipples and modify them? why not grease? how much oil is used under operational condition? What oil?
    -where did you get that spring shims that make the preload? what are the specifications? how did you calculate the distance between the 2 nuts , so that they would be mirroring each other exactly and the shims to fit in?

  13. #30
    Quote Originally Posted by JAZZCNC View Post
    I mentioned something similar to you in an email Jon and feel the machine would benefit from 1 more rail on both Y & Z axis. One Higher up on Y axis and on 3 sides of box on Z axis but more to help with resonance and vibration in all cutting directions rather than increase load ratings.?
    As I'm sure you're aware, you can improve the response of a resonant system in just two ways - either raise the stiffness to reduce the magnitude of the deflection, or increase the damping so the error dies away faster. Therefore comparing the stiffness of each option is very much related to comparing the overall response for resonant conditions.

    The linear guides do have some damping effect, due to the oil layer between the bearings and rail. Adding rail with two bearings, as you suggest, would therefore increase the damping factor, as it increases the surface area in contact. Instead of adding an additional rail and two bearings, you could increase the stiffness and damping by adding one bearing to each of the existing rails which is likely more cost effective. This also has the added slight bonus of evening out errors in rail straightness and generally aligning two rails is a easier than three. Either way, this damping effect isn't that large as the surface area in contact is small, so you're probably better off improving damping in other areas such as joints in the frame. You can also add non-load bearing sliding contact bearings to further improve the damping effect, which will make a bigger difference as sliding bearings will have a much greater surface area in contact.

    If you take the load ratings from the Hiwin datasheet and plot them versus rail size, it seems that the load rating is proportional to the rail size raised to the power 1.7. So if we assume the stiffness of the rail is proportional to the load rating and that the magnitude of the force on each linear bearing is similar, to increase the stiffness by the same factor as adding one additional rail (i.e. 50% as you're spreading the load between 6 bearings instead of 4), you only have to increase the rail size by 27%. So for example going from a 15mm rail to 20mm, or 20mm to 25mm would gain slightly more stiffness than adding the additional rail. Similarly if you want to double the stiffness, then instead of going from two rails to four, you could increase the rail size by 50% (e.g use 30mm rails instead of 20mm).

    Looking at it a different way, if you plot the price of the linear rails and linear bearings versus their size, it's a pretty convincing linear relationship. So by increasing the rail size you have an exponential gain (x^1.7) in stiffness for a linear increase in price. If you add more rails you have a linear gain in stiffness for a linear gain in price.

    Quote Originally Posted by JAZZCNC View Post
    Would also add another ballscrew to Y axis rather than increase bearing plates has the action of 2 screws pushing/pulling together would be smoother than widening the plates.?
    Both methods would work. If the bearing spacing is made large enough to prevent racking, then the stiffness of the axis would also be greatly increased since the deflection for a given force due to the bearings is proportional to the bearing spacing squared (based on combining the formulas in the manufacturer's datasheets). Similiarly, adding the extra ballscrew would eliminate racking and thus increase the stiffness, however it cannot increase the stiffness further so the former or a combination of both is required if the axis stiffness is still not sufficient.

    Quote Originally Posted by JAZZCNC View Post
    Like you say it's very strong already but feel these changes would make it the close to ULTIMATE strong machine.!
    Got to draw the line somewhere.

    Quote Originally Posted by silyavski View Post
    -so you believe 3kw spindle would be better than 2.2kw?
    Yes, if one or more of the following are true:
    1) You need to get more power than the 2.2kW spindle can deliver at low speed, e.g. for cutting steel, but still require a high speed spindle.
    2) The machine is rigid enough for the stiffness of the spindle to be the limiting factor.
    3) The machine is rigid enough to make cuts which exceed the power rating of the spindle.

    Number 3) is definately the case for the macine in this thread. I'm not yet certain about the rest so wont comment.

    Quote Originally Posted by silyavski View Post
    -how you did the oiling system? did you use the original nipples and modify them?
    No, if you look carefully in the photos you can see that to save space new nipples were machined which were the correct size for the tube to just push on to it and not fall off.

    Quote Originally Posted by silyavski View Post
    why not grease?
    Oil is much less viscous, so it requires less pressure to push through the system which in turn makes the oil distribution system easier to manufacture. Oil also allows higher speed, but that's not really an issue here. Grease is commonly used for the linear bearings, but oil seems more common for ballscrews.

    Quote Originally Posted by silyavski View Post
    how much oil is used under operational condition? What oil?
    Very little. The datasheets for the ballscrews and linear bearings do give recommenced values. Bear in mind the oil is also good at flushing out foreign bodies from the nuts, so certainly no harm in oiling them regularly. You can find the correct oil to use in some of the ballscrew datasheets, but I wouldn't worry too much about what you use as, although not recommended, the ballscrews will last a long time without oil, so anything will be a lot better than nothing. You probably don't want something with too low a viscosity as that would drain out quickly.

    Quote Originally Posted by silyavski View Post
    -where did you get that spring shims that make the preload? what are the specifications? how did you calculate the distance between the 2 nuts , so that they would be mirroring each other exactly and the shims to fit in?
    I got them from Lee Spring, spring manufacturer for a variety of uses. The preload force is set as a percentage of the screw's rating, so you need to find the rating for your screws and then find disc springs which can apply that force without being fully squashed. I didn't calculate the distance, instead a gap is left, measured, then a spacer made to the correct thickness to squash the springs by the calculated amount to obtain the required force.
    Last edited by Jonathan; 26-10-2013 at 08:35 PM. Reason: Formatting

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