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  1. #151
    So boyan, 22 teeth will not work with the 1 in ball screw. Anything larger will not let the bearing slide over the gears.

  2. #152
    There is a reason we do it like we do it. Now you know it.
    project 1 , 2, Dust Shoe ...

  3. #153
    Quote Originally Posted by Boyan Silyavski View Post
    There is a reason we do it like we do it. Now you know it.
    You should just have designed it for him!
    Oops! You Did ;-)
    You think that's too expensive? You're not a Model Engineer are you? :D

  4. #154
    Still working on it Boyan, and thanks for all your help as well as Jonathan. I made the Inner diameter of the RBN to be 1.0787. That would be 2mm of space for the ball screw as you suggested. Then I made the outer diameter of the RBN to be 1.3720 in which is about .006 smaller for the 7207 to fit nicely. Still as you can see, at the HTD gear part, The wall is about .0421 in in thickness. I think since both sides of the gear are attached to 1.3720 it will be strong enough. What do you think. MutzyClick image for larger version. 

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  5. #155
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 2 Days Ago Has been a member for 9-10 years. Has a total post count of 2,147. Received thanks 236 times, giving thanks to others 5 times.
    Just over a mm wall thickness. You might get away with it in steel, but I'd expect aluminium to sheer.

    By the time you consider axial loading due to bearing preload/dynamic loading, then the belt/nut causing some sheer/twist/radial loading, that part is going to be under a fair bit of stress under high loads. And that's before you consider stress points due to not being a smooth shaft.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  6. #156
    Thanks for the input M_C. How much minimum thickness do I need in Alluminum vs steel? If I bring the numbers to what Boyan suggested in the previous posts to 27mm ID it would leave the thickness at about .054. not too much more, but it helps. mutzy

    Would it make sense to use a slighly smaller Ball Screw?
    Last edited by mutzy; 26-12-2017 at 10:44 PM.

  7. #157
    Please take some important notes:

    In reality the screw is 25.00mm. And as all must be lined up to under 0.01mm/ 0.02mm could be felt as tightening at certain point/ so you can use 26mm of the center hole with no problem.


    You must not make the parts smaller than the fitted part! |I have made that mistake and is impossible to fit correctly. Make all parts "press fit" 0.02mm bigger That means shaft must be 0.02mm bigger than inner bearing and bearing bed must be 0.02mm smaller


    You know what i am saying? This is not a skateboard wheel. All your design is based on "esy to service", but in reality it must be based on "precision"




    I dont know why the worry about the thickness. Let's speak in mm as this Imperial system gives me a headache

    If i am not wrong ~ = The bearing has 35mm internal diameter. 22t pulley has ~35mm OD and ~31mm diameter on the tooth lowest point/35- 2x~2mm/ . So if the hole is 27mm that gives a 1 mm clearance from the 25mm ball screw, then (31-27 ) /2 = 4mm wall at the pulley thinnest point, so whats the big deal?
    Even so where the tooth is its thicker by 2mm so...???
    project 1 , 2, Dust Shoe ...

  8. #158
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 2 Days Ago Has been a member for 9-10 years. Has a total post count of 2,147. Received thanks 236 times, giving thanks to others 5 times.
    Quote Originally Posted by Boyan Silyavski View Post
    I dont know why the worry about the thickness. Let's speak in mm as this Imperial system gives me a headache

    If i am not wrong ~ = The bearing has 35mm internal diameter. 22t pulley has ~35mm OD and ~31mm diameter on the tooth lowest point/35- 2x~2mm/ . So if the hole is 27mm that gives a 1 mm clearance from the 25mm ball screw, then (31-27 ) /2 = 4mm wall at the pulley thinnest point, so whats the big deal?
    Even so where the tooth is its thicker by 2mm so...???

    I was just going by the drawing, which put the thinnest point at 0.0421", or 1.06mm.
    It probably would be ok in aluminium, but as I mentioned, by the time you allow for all the forces likely to be acting on the shaft, it is quite a highly stressed part. I wouldn't be comfortable with it unless a FEA showed a good bit of safety margin, but it seems to be a lot of work just to avoid boring out a pulley.
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

  9. #159
    Happy New year to all coming up. May we all have a great year of designing and learning.

    Boyan, I did reset the OD of the shaft back to 35 mm + .02mm on both sides of the gear.
    The inner diameter hole was set to 26 mm.

    The pulley is 33.899 mm outer, 29.533 at the tooth lowest point
    Wall thickness from lowest tooth point to inner dia is ~1.85 mm.

    Yes M_C, I was doing this to eliminate the pulley step and as Jonathan posted earlier to lower the moment of inertia. (hope i didn't open another can of worms by saying that.LOL
    mutzy
    Click image for larger version. 

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  10. #160
    m_c's Avatar
    Lives in East Lothian, United Kingdom. Last Activity: 2 Days Ago Has been a member for 9-10 years. Has a total post count of 2,147. Received thanks 236 times, giving thanks to others 5 times.
    In the grand scheme of things, is the amount of inertia saved likely to make that much difference? Is a couple hundred grams of pulley, going to be that significant in relation to a 30KG+ gantry?
    Avoiding the rubbish customer service from AluminiumWarehouse since July '13.

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