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  1. #21
    No problem on the length of the rail for the bearings mate, irving will be the man when it comes to the maths on rail lenths as he has looked into rail flex before.

    If it was me and i was looking to use 16mm rail, i would only use it on the Z axis with an overall length of 300mm MAX. For the 20mm rail i would goto say 6-700mm MAX.

    Irving if you please
    .Me

  2. ive got a few lengths of more substantial rail and block with end caps for sale 25mm i dont think that would flex over 3ft! but i could be wrong:whistling:

  3. #23
    Quote Originally Posted by AdCNC View Post
    ive got a few lengths of more substantial rail and block with end caps for sale 25mm i dont think that would flex over 3ft! but i could be wrong:whistling:
    How much would they be?

  4. Quote Originally Posted by progomez View Post
    Thanks for the replies. What would be the maximum length for the 20mm and 16mm bearings as they seem quite cheap, at least for a small cnc.
    Hi, been away for a few days...

    how long is a piece of string? It all depends on the rigidity of the mountings, what they are bolted to, the spacing of the trucks and the weight of what is running on the trucks.

    As a guide, a pair of 800mm long, 20mm round rail on SK20 supports at each end deflects approx 0.5mm under a 10Kg load. If thats your X rails, your Y/Z gantry and router/spindle is likely to weigh 15 - 18Kg! If you are carving shapes out of MDF then don't expect better than 1mm accuracy vertically or 0.5mm horizontally. For most things you'll want better accuracy than that.

    I use 16mm rail on my PCB mill but thats a moving table, fixed gantry design and the load on the table is tiny. On that I get 0.05mm deflection under 4Kg of load which is purely cutting forces as PCB's weigh nothing!

  5. #25
    I have decided to make a smaller machine to test out the delrin nuts I bought off ebay. They are 10x2d and round. How do people mount round delrin so it doesnt spin? Should i flatten one end.

    I have bought some trapezoidal rod from merchant dice size 400,400,200. Im thinking of encasing the machine in mdf and trying out a moving table design. The size should fit on my desk and the casing should stop some of the dust and noise(my main problem with my original router).

    Ill only be able to make items less than 300x300 but will be good for testing. thanks for the advice.

  6. Quote Originally Posted by progomez View Post
    I have decided to make a smaller machine to test out the delrin nuts I bought off ebay. They are 10x2d and round. How do people mount round delrin so it doesnt spin? Should i flatten one end.

    I have bought some trapezoidal rod from merchant dice size 400,400,200. Im thinking of encasing the machine in mdf and trying out a moving table design. The size should fit on my desk and the casing should stop some of the dust and noise(my main problem with my original router).

    Ill only be able to make items less than 300x300 but will be good for testing. thanks for the advice.

    I have the same nuts. I drilled out a chunk of mdf the diameter as the nut, slit it on one side, drilled through and used a couple of M5 bolts and M5 teenuts (captive recessed nut) to put the 'squeeze' on the delrin. 4 mounting holes in the corners allows ot to be bolted to the underside of the table/gantry/etc.

  7. #27
    Quote Originally Posted by irving2008 View Post
    I have the same nuts. I drilled out a chunk of mdf the diameter as the nut, slit it on one side, drilled through and used a couple of M5 bolts and M5 teenuts (captive recessed nut) to put the 'squeeze' on the delrin. 4 mounting holes in the corners allows ot to be bolted to the underside of the table/gantry/etc.
    Thanks for the reply.

    Would it be worth me shaving one side flat? Does the mdf hold it solid? have you got a picture of it?

    Also is a moving table design better for accuracy?

  8. Quote Originally Posted by progomez View Post
    Thanks for the reply.

    Would it be worth me shaving one side flat? Does the mdf hold it solid? have you got a picture of it?

    Also is a moving table design better for accuracy?
    No need to shave it, it holds it fine, just roughen the mating surfaces. Can use some loctite if need be. My cutting forces are low.

    Sorry no pics, I didnt take any but I might have the first trial one somewhere....

    I dont think moving table v moving gantry is ab accuracy issue. Moving table (in X only on mine) is easier to implement in my view and with lightweight workpieces and low cutting forces (e.g. PCB milling) can get away with lower cost unsupported rails.

  9. #29
    Ive picked up a cheap wood lathe with 4 jaw chuck off ebay so will try and make a ridge on the delrin nuts (once I figure out how to centre the nut)

    I also decided to make a smaller 400/400/200 cnc and then in time buy one of the kits off ebay (from china) which has the supported rails and make a 4'by2' cnc.

    Ive also joined a cnc course at my local college. Its shows how to manually program haas machines but also in time Im hoping to be able to use these machines to mill some parts out of alu.

  10. Quote Originally Posted by progomez View Post
    Ive picked up a cheap wood lathe with 4 jaw chuck off ebay so will try and make a ridge on the delrin nuts (once I figure out how to centre the nut)

    I also decided to make a smaller 400/400/200 cnc and then in time buy one of the kits off ebay (from china) which has the supported rails and make a 4'by2' cnc.

    Ive also joined a cnc course at my local college. Its shows how to manually program haas machines but also in time Im hoping to be able to use these machines to mill some parts out of alu.
    To centre the nut you need a dial gauge and stand which can be got off ebay relatively cheaply. basically the trick is to adjust one pair of opposing jaws until rotating the chuck 180deg produces no offset, then repeat for the other pair.

    Be careful not to crush the nut tho...

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