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  1. #31
    Yes, Nema 23 max axial load is 15 N. This means -

    For Z stepper motor:
    This has to react the Z axis parts which move up and down - if 3 kg then this is 30 N down
    When plunging / drilling into wood this is typically 60 N up (giving 30 N in the other direction)
    Drilling holes repeatedly takes the force from +60 N to -30 N which will work those bearings
    Machining with helix cutters will also apply axial loads (due to the helix) - up to 20 N from memory

    For X and Y stepper motors:
    These have to react the horizontal cutting forces which for wood can be up to 50 N

    All of these loads are well over 15 N so this is why everyone is recommending that the leadscrew has it's own bearings.

    I seem to remember that steppers can have a bit of axial play in them, even when brand new. This means that there will be positional accuracy limitations. Angular contact bearing blocks on the ballscrew can be tightened up to remove this.

    The final comment to make is that the leadscrews are usually not perfectly round, plus it would be difficult to align them perfectly with the axis of the motor shaft. This means there will be fluctuating forces being applied to the bearings each time the shaft rotates.

    Finish the machine, run it for a month or so and report back how you get on, what worked, and what didn't.

    References:
    http://www.motioncontrolproducts.com...tors.php?cat=1
    (max axial load)

    http://ac.els-cdn.com/S1877705812021...5afb04f23aa36d
    (drilling force in wood 4th page)
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  2. #32
    Quote Originally Posted by routercnc View Post
    Yes, Nema 23 max axial load is 15 N. This means -

    For Z stepper motor:
    This has to react the Z axis parts which move up and down - if 3 kg then this is 30 N down
    When plunging / drilling into wood this is typically 60 N up (giving 30 N in the other direction)
    Drilling holes repeatedly takes the force from +60 N to -30 N which will work those bearings
    Machining with helix cutters will also apply axial loads (due to the helix) - up to 20 N from memory

    For X and Y stepper motors:
    These have to react the horizontal cutting forces which for wood can be up to 50 N

    All of these loads are well over 15 N so this is why everyone is recommending that the leadscrew has it's own bearings.

    I seem to remember that steppers can have a bit of axial play in them, even when brand new. This means that there will be positional accuracy limitations. Angular contact bearing blocks on the ballscrew can be tightened up to remove this.

    The final comment to make is that the leadscrews are usually not perfectly round, plus it would be difficult to align them perfectly with the axis of the motor shaft. This means there will be fluctuating forces being applied to the bearings each time the shaft rotates.

    Finish the machine, run it for a month or so and report back how you get on, what worked, and what didn't.

    References:
    http://www.motioncontrolproducts.com...tors.php?cat=1
    (max axial load)

    http://ac.els-cdn.com/S1877705812021...5afb04f23aa36d
    (drilling force in wood 4th page)
    Thanks for the comments and info in the links

    cheers Dave

  3. #33
    Quote Originally Posted by Steel View Post
    I just looked at the z axis on my 3020T and the lead screw is supported with one bearing on the top plate and either a bearing or sleeve on the bottom plate and the motor is connected with a flexi coupler so those bearings are being used to support axial loads even though there radial bearings. I cant see the difference by using the stepper bearings to replace that type of set up.
    And two wrongs don't make it right.!!

  4. #34
    Quote Originally Posted by Steel View Post
    please show me one youtube video of a fixed gantry draw slide build made of steel please, you wont find one !!!
    Quick google brought this up.....found one



    Question....if you've got decent linear components, why are you making this one?
    Neil...

    Build log...here

  5. The Following User Says Thank You to njhussey For This Useful Post:


  6. #35
    Fun video to skip through.

    Look at how much the motor wobbles at 4:34 - that's a great example of what routercnc was saying about alignment causing extra load on the bearings!

  7. #36
    Quote Originally Posted by Zeeflyboy View Post
    Fun video to skip through.

    Look at how much the motor wobbles at 4:34 - that's a great example of what routercnc was saying about alignment causing extra load on the bearings!
    Ok so maybe ill try this setup ? this is not the finished setup but you can get the idea.

    Click image for larger version. 

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  8. #37
    That's a just a set of 2 thrust bearings I assume? Which end are we talking there?
    Last edited by Zeeflyboy; 06-03-2017 at 08:11 PM.

  9. #38
    Quote Originally Posted by njhussey View Post
    Quick google brought this up.....found one



    Question....if you've got decent linear components, why are you making this one?
    Ok i was wrong there are a few out there after all

    In answer to your question I saw one on youtube and thought to myself I want to make one of those and so here i am, Since i cant seem to sell my rails and ball screw kit maybe one day i will have the space and time to turn it into a decent machine but for now this build and my aluminum melting barbecue i put together on Saturday i should have enough to keep me busy in my free time.

    Click image for larger version. 

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ID:	20988Click image for larger version. 

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  10. #39
    My very first machine, made from bits I had laying around to see if I was serious about building a cnc machine, used something like that. A pair of thrust bearings either side of a plate to resist the axial loads. The stepper was then connected to the ballscrew using a very stiff and tight fitting piece of rubber tube to act as an alignment coupling. Something off a car engine cooling circuit ?

    The coupling worked fine for many months, but the thrust bearings became noisy and needed regular adjustment. I think this is because they were held there by a locking collar and did not apply a preload. Your picture has a preload nut so this will be better. By all means try it as it is much better than using the stepper bearings.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  11. #40
    Quote Originally Posted by Zeeflyboy View Post
    That's a just a set of 2 thrust bearings I assume? Which end are we talking there?

    Top end, i think ill put a radial bearing in the middle to keep the shaft centered plus some sort of aluminum cap on both thrust bearings so i can bolt everything to the plate.

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