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  1. #1
    Totaly new to this so pass a few ideas by you lot and see If they are good or crap!
    Building a fairly big CNC for wood working so need a large bed size
    In a perfect world 10ft x 5ft I do have the space in the workshop for that
    BUT a bit over optimistic for my first attempt LOL so 5ft long x 3ft wide
    With hopefully 2ftx4ft working area for MK1
    The bed or base will be kitchen cabinates with a strong top as I am a cabinate maker
    and so thats very easy for me to make
    But the linear slides ,,, HUMM
    Seen the skate berings and ali angle thing ,, works but
    The V grove berings are better but at more than 12 each !!
    Proper suported rails ECT is out of the question at the lenths I need
    SO been brain storming and come up with ....
    An aluminum I section thats 54mm x 25mm that has a 6mm hi x 4mm wide rib on the 25mm face running right along the lenth
    I could use the skate berings in a V on ali angle , but its ugg ugg
    I could use V berings but at 12 quid each and hardened steel on ali
    would not last very long !
    So skate berings with tyers? , replaceable nylon tyers
    Ant thoughts or sugestions
    thanxs

  2. #2
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 10 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,833. Received thanks 192 times, giving thanks to others 5 times.
    Problem with using nylon wheels, is you risk losing rigidity due to flex in the wheels.

    I wouldn't worry too much about running hardened bearings on an alloy extrusion. Provided you keep them clean and spinning, you shouldn't experience any major wear. You're only likely to experience major wear if things start sliding.

  3. #3
    Quote Originally Posted by m_c View Post
    Provided you keep them clean and spinning, you shouldn't experience any major wear. You're only likely to experience major wear if things start sliding.
    That is very true and easier to accomplish when you have bearings with way wipers sliding on rails.

    So unless you enclose all the running gear in bellows you will embed dust to the tracks/bearings that will give very stiff jerky movement.

    Very expensive are bellows and awkward to implement.

    Phil

  4. #4
    skate berings with tyers?
    i like the idea personaly, might be worth it on a large x axis.. bit bulky to impliment but if you have three way apposing wheels i imagine you could pre-load them against each other with enough force to prevent them flexing any more than your frame / gantry etc

    the tyres (+ the larger diameter) would smooth out any of the smaller rail inperfections

    might be a winner if your after saving the brass

    its allways a gamble though when you try something new

  5. #5
    chris, have a look at "routercnc" build log, looks like he is running plain bearings on alli profile, looks like a winner :)

    he seems happy with it anyway

  6. #6
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 10 Hours Ago Has been a member for 9-10 years. Has a total post count of 1,833. Received thanks 192 times, giving thanks to others 5 times.
    Quote Originally Posted by M250cnc View Post
    That is very true and easier to accomplish when you have bearings with way wipers sliding on rails.

    So unless you enclose all the running gear in bellows you will embed dust to the tracks/bearings that will give very stiff jerky movement.
    One random idea I've had for such situations in a dry enviroment, would be a suitable air supply aimed to blow any dust of the rails either side of the bearings. For shavings/dust, a gentle air supply would be enough to blow any rubbish of the rails. Off course, there is the issue that you'd need a compressor to provide the air supply.

  7. #7
    Hi C Cunningham,

    As Mark points out I am running bearing races directly onto Ali profile, but I always knew it was a short term solution and a small witness mark is appearing on the profile where the bearing runs over it. Not the best long term solution, although a hardened running strip might give better service.

    Stray dust and chippings do get engrained on the top ali surface, and aligning the whole gantry (90 deg to bed, same height from bed at each each etc) took some fiddling. Once the extractor shoe is working that should solve the dust problem. The top and bottom bearings are fitted to short axles which run in adjustable slots in the side pieces. This allows complete alignment adjustment vertically. Side to side location is from single bearings set into holders, with one side fixed and the other side on an adjustable pressure plate. A bit like these :

    http://www.axminster.co.uk/axminster...all-prod21223/

    Linear motion, cnc and cheap are a difficult combination.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  8. #8
    Ross77's Avatar
    Lives in Devon, United Kingdom. Last Activity: 11 Hours Ago Has been a member for 8-9 years. Has a total post count of 689. Received thanks 25 times, giving thanks to others 40 times.
    Linear motion, cnc and cheap are a difficult combination.
    Aint that the truth

    I had promised my self not to post untill I actually start building again, but maybe I have an idea that might be worth exploring.

    If the machine was solely for woodwork and the correct feeds and speeds could be achived with the rest of the system, then surley the loading on the bearings could be reduced and then a small nylon or delrin "Tyre" wouldnt be such a bad idea and allmost a cheap throw away maintainance part if wear occurs. (it could even have a rib that runs in the profile channel to proved some lateral restraint)

    If the section was thin enough it shouldnt compress to much and if it was made wider than the bearing it could spead the load over a wider section on the ali profile.

    Im not saying that it is a perfect solution but for this application and accuracy I'm sure it would be worth a try.

    Later

  9. #9
    (it could even have a rib that runs in the profile channel to proved some lateral restraint)
    nice one ross, that sounds like a great idea!
    that alli profle is pretty accurate, it sounds like it would work a treat

    i cant see acetal/delrin wearing a grove in your alli to quickly

    with the price of skate bearing being the way they are id be tempted to use two on each wheel and make the wheels as wide as possible

  10. #10
    Quote Originally Posted by routercnc View Post
    As Mark points out I am running bearing races directly onto Ali profile, but I always knew it was a short term solution and a small witness mark is appearing on the profile where the bearing runs over it. Not the best long term solution, although a hardened running strip might give better service.

    Stray dust and chippings do get engrained on the top ali surface,
    Would you say it's the dust build up that's is causing the witness mark ?

    Phil

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