Thread: DIY mill...

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  1. #21
    Can you re-arrange and centre support those rails? Would make it lots stronger.

    Have you considered reinforced concrete for the base? A bit of granite worktop would be nice. Sand and liquid epoxy if you have the pioneering spirit.

    Looks a tadge flimsy as is.

  2. Robin, how would you support a round rail with a linear bearing that fully encloses the rail?

    these are 16mm carbon steel rails supported at each end - according to my calcs a single rail will deflect no more than 0.04mm under a 35kg central point load and a) I dont plan to load them that much and b) the load is distributed across two pillow blocks on two rails so expect the deflection to be <0.01mm...

    Where's the flimsy bit come in?

    Irving...

  3. #23
    Lee Roberts's Avatar
    Lives in Wigan, United Kingdom. Current Activity: Viewing Moderator Control Panel Has been a member for 9-10 years. Has a total post count of 2,545. Received thanks 161 times, giving thanks to others 652 times. Made a monetary donation to the upkeep of the community. Referred 10 members to the community.
    lol, OI YOU LEAVE MDF ALONE !!!

    Yes it is Delrin.

    Yea i used delrin as a drive nut under the table as well mate.











    Just let me know when you need anything ill quote you happy !

    Lee

  4. #24
    Lee Roberts's Avatar
    Lives in Wigan, United Kingdom. Current Activity: Viewing Moderator Control Panel Has been a member for 9-10 years. Has a total post count of 2,545. Received thanks 161 times, giving thanks to others 652 times. Made a monetary donation to the upkeep of the community. Referred 10 members to the community.
    Forogt to say, i also sell ACME Delrin Drive nuts as well.

    They work jsut as well for ACME, i think you may have got ballscrew from Dice.

    or was it Anti-Backlash x3pcs 10x2 Trapezoidal + Delrin Nuts CNC ?
    Last edited by Lee Roberts; 27-07-2008 at 05:11 AM.

  5. #25
    Lee Roberts's Avatar
    Lives in Wigan, United Kingdom. Current Activity: Viewing Moderator Control Panel Has been a member for 9-10 years. Has a total post count of 2,545. Received thanks 161 times, giving thanks to others 652 times. Made a monetary donation to the upkeep of the community. Referred 10 members to the community.
    Ahh yes there it is: View Item

  6. #26
    Quote Originally Posted by irving2008 View Post
    Robin, how would you support a round rail with a linear bearing that fully encloses the rail?

    Where's the flimsy bit come in?

    It's not so much the load, it's sympathetic vibration that may give you headaches.
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  7. Quote Originally Posted by Robin Hewitt View Post
    It's not so much the load, it's sympathetic vibration that may give you headaches.
    Robin,

    Its an interesting point. a centre support will reduce the deflection but as we already know thats tiny. But I hadn't considered the resonance aspect. I'll do some calcs to find the resonant freq of the bar and see if theres any issue.

    Irving...

  8. Quote Originally Posted by CNCUK View Post
    Ahh yes there it is: View Item
    Hey, thats cybersnooping :) in 20/20 hindsight I think I paid over the odds for these, although they sell 3 nuts for 24 alone and the screw is ~1/100mm so by their prices 21 wasnt so bad.

    I'm sure, Lee, you could have done it cheaper and your block 'nut' is easier to mount than the round one (haven't thought how I'm going to mount it yet).

    Irving...

  9. Quote Originally Posted by irving2008 View Post
    Robin,

    Its an interesting point. a centre support will reduce the deflection but as we already know thats tiny. But I hadn't considered the resonance aspect. I'll do some calcs to find the resonant freq of the bar and see if theres any issue.

    Irving...
    Well the natural, undamped frequency for a single rail is roughly 287Hz so I'm not sure theres any issue here - all the possible drivers forcing oscillation are at at a considerably lower frequency (min cutter speed 2800rpm - 46rps) so the damping coefficients for forced excitation are large. Also with the two pillow blocks attached there is a significant damping coefficient. There may just be issues with a combination of cutter speed at 17000 rpm (single flute), 8500 rpm (2 flute) or (4250rpm (4 flute) and/or stepping rate of 172mm/min. (Its years since I did any of this stuff at college... makes my brain hurt just reading the equations!)

    Of course the proof will be in the actual result...
    Last edited by irving2008; 27-07-2008 at 05:26 PM.

  10. #30
    Maybe I'm just tied up thinking you're going to make deeper cuts in harder materials than you actually are. A speed control can help prevent chatter, but without big heavy slides I'm thinking you really want to get as much spring out of the system as you possibly can :D

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