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  1. #21
    I had the spindle mount lower down in my original pics. Iíll put it back where it was. Thanks


    Sent from my iPhone using Tapatalk

  2. #22
    I have now moved the spindle mount lower onto the backing plate, how does this look?:

    Click image for larger version. 

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    I have done a bit more digging into why people within the Joe's community have moved away from ball screws to R&P, the reasoning appears to be about speed, ease of assembly / maintenace and price more than anything. Looking at the pricing of C7 leadscrews on BST Automation they seem to be cheaper than using the CNC routerparts rack and pinion system (although the postage costs are about as much as the screws!) - I'm confused as to which way to go, any suggestions please? Would I be looking at 2010 for the longest axis, it will be 1600mm long? This comes out around 1000RPM critical speed - is this too low?

    All help gratefully received.

    Cheers

  3. #23
    Are you confusing lead screws and ball screws?
    Joe's used to use lead screws and went to R&P ,ball screws are better than both but way more expensive!

  4. #24
    Looks ok to me with that spindle mount position. One thing I did on my Mk3 was to drill and tap a second set of holes a bit higher on the Y plate so I had the option of mounting it higher for very tall work. Of course you can only reach across that work an amount until the Y plate may hit it but it is a quick feature to add at the build stage. I also added tapped holes along one edge of the Y plate to allow me to bolt a reference strip and maintain spindle tram alignment whilst adjusting the spindle holder. Never used it of course! But worth a mention

    Canít help on the ballscrew a that long and r&p as havenít used them.

    If you search the forum that sort of thing has been asked before and Jazzcnc has given advice
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  5. #25
    As far as I can tell Joe's Hybrid machine used lead screws, the Evo used ball screws and the EVO MKII uses R&P, just wondering why they would move away from ball screws if they are the best?

    Good shout putting extra holes for spindle mounting, I'll definitely do that.

  6. Hello, I am new to this forum and I was looking for information of "pinion & rack & gear reduction with spring tension" -packs - similar to cncrouterparts version of
    PRO Rack and Pinion Drive, NEMA 34.
    Reasons why I decided to use rack & pinion were exactly those that JF mentioned above (+ the option to make extensions later). So if anyone can help me where can I get as ready sollution as possible I am interested to hear. Nema 34 and module probably 1.25 with straight teeth (the rack can be cut with laser).

  7. #27
    Been making very slow progress on my design lately and I'm looking at redesigning my frame but can't decide what size tubing to use. Originally I was using 50x50x3 for most of the frame with 100x50x4 for the rail support, I'm toying with increasing this to 50x50x4, 50x50x5 or possibly even 60x60x5. Obviously there is a cost difference associated with each option so I'd like to do some sort of stress / deflection calculations to work out whether the cost is justified. Can anyone tell me what sort of loading I should be applying to my design to work this out please? I have seen example calculations with 50N as the load on the spindle which seems more than enough from my experience using a hand router - is this a good number to work with? If so I don't imagine I will get much flex from the frame using 50x50x3 let alone the heavier sections, I think most deflection will come from the bearings and aluminium extrusion gantry. What is an acceptable amount of deflection? I understand the argument for increasing mass to reduce vibration but if I can reduce the material costs for the frame and find another way of adding mass to it (sand / epoxy filling the frame?) then I can spend the money elsewhere.

    Thanks for your help!

  8. #28
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 9 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,688. Received thanks 291 times, giving thanks to others 11 times.
    I know that you've had a look at my write-up already. I used 3mm wall thickness. If I were doing it again, I might have used 4mm for some of the parts (like anything that has a rail bolted you it) just for better damping. However, from a strength point of view I am happy with what I have, remembering that my machine is very much hobby class, not commercial/production. Just recently I have been machining quite a lot of small steel components. I use small (2-4mm three-flute coated carbide designed to run without coolant) cutters at around 7-8K RPM and am getting good results. Again, not production-style heavy cuts but the ability to machine more complex profiles (with some 3D work as well) means that I use the router in preference to my vertical mill. My gantry is quite stiff (three 50x50x3 sections). I'm pretty happy with the overall capability which is much more than I might have expected and way beyond what I had hoped to achieve.

    This is just one data point from one user so consider it alongside other opinions and designs but it emphasises that engineering design is as much about compromise as ultimate performance in one aspect. After all, my machine is too slow for an ideal woodworking machine and much too light for decent metal cutting. The fact that I can get acceptable results, even if not optimum, owes more to luck than judgment...

  9. The Following User Says Thank You to Neale For This Useful Post:


  10. #29
    The thicker the better as it significantly dampens vibrations which translates into cleaner cuts and longer tool life.
    Don't be messing around with sand etc because while it dampens vibrations slightly the cost in performance due to the extra weight is too expensive for the returns.
    Spending a little extra for Thicker steel will pay dividends in quality and stiffness.

    For a machine this size I'd go with 60x60x5 as a minimum. It will give you a much stiffer machine than using 50x50. I've built machines this size using both sizes and 60x60 is the better choice.

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


  12. #30
    Neal / Jazz - thanks for the feedback.

    I'll look at thickening things up, it does add up quite a bit - going from 50x50x4 to 50x50x5 to 60x60x5 each jump adds about £100 but I only want to build it once so want it to be right.

    Jazz - I was only thinking of sand filling the static parts, I wasn't intending to fill the gantry - I'd be much happier not to have to do this. The gantry will be the same 160x80 ali extrusion whichever way I go with the frame.

    Is the 50N loading a fair number?

    Cheers!

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