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Reinforce Hole for Self Tapping Screw?  

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Wingsy
(@wingsy)
Eminent Member
Reinforce Hole for Self Tapping Screw?

I'm building an enclosure for a circuit board. The board will rest on the surface of the standoff and be held with a self tapping screw in the hole in the center of the standoff. The way I understand what will happen is, when that standoff is printed it will be filled with a selected pattern, but there will be a relatively thin solid surface surrounding the hole. But I'd like the standoff to be solid (at least in the upper half of it) so the screw won't rip out the hole due to insufficient wall thickness (or is this just an imagined problem?). I've been into Slic3R for MK3 and don't see how to specify something like this without turning off infill for the entire part. How would I do it?

Posted : 27/05/2018 7:25 pm
Joe Prints
(@joe-prints)
Estimable Member
Re: Reinforce Hole for Self Tapping Screw?

I usually lean towards extra perimeters, giving the screw holes more wall thickness.
If you are looking to reinforce just the top area of the holes, raise the number of top solid layers

Anything can be made better
https://www.myminifactory.com/users/Joe%20Prints

Posted : 27/05/2018 9:03 pm
Martin Wolfe
(@martin-wolfe)
Reputable Member
Re: Reinforce Hole for Self Tapping Screw?

What you need to do is selective infill.

To do this you will be making small cut-outs from the model to trick the slicer into placing extra local perimeters.

The Model

Sliced

The key things to keep in mind when doing selective infill are:-

  • Printed filament width (0.45mm with a 0.4 nozzle)

  • Layer height (in my example 0.2mm)

    I hope this helps.

    Regards,
    Martin

  • Martin Wolfe

    Posted : 27/05/2018 9:57 pm
    Erik
     Erik
    (@erik-3)
    Estimable Member
    Re: Reinforce Hole for Self Tapping Screw?

    How tight are you wanting this screw? I've had no problems with 2 perimeters on 0.20mm layers holding for an M3 screw. I make the hole exactly 3mm, and an M3 screw bites in getting well. I can't pull them out with pliers, but you can usually overtorque it and strip the hole if you try pretty hard.

    Posted : 28/05/2018 12:56 am
    Wingsy
    (@wingsy)
    Eminent Member
    Topic starter answered:
    Re: Reinforce Hole for Self Tapping Screw?

    Thank you very much. Appreciate that.

    Posted : 28/05/2018 9:25 pm
    Makan
    (@makan)
    Active Member
    Re: Reinforce Hole for Self Tapping Screw?

    Wauw, great tip on the selective infill, Martin!
    Thanks for that.

    Posted : 28/05/2018 11:38 pm
    Wingsy
    (@wingsy)
    Eminent Member
    Topic starter answered:
    Re: Reinforce Hole for Self Tapping Screw?

    OK, this is what I've come up with. It looks fairly sturdy to me but what do you think? The slice you're looking at is somewhere in the middle of the screw hole. I know it's going to use more material and slow things down a bit, but the only other printing that will be done in this part is 4 walls 3mm thick and 20mm tall ( a box).

    Everything else was left at the default values. (Just want you folks to know that I've learned more from your suggestions in this thread and where it's taken me than I have elsewhere in the same amount of time.)

    Posted : 29/05/2018 3:25 pm
    neil.e
    (@neil-e)
    Estimable Member
    Re: Reinforce Hole for Self Tapping Screw?

    I really think you are overengineering this. If the goal is to just secure a board into a case and it won't be subject to crazy stress you just need two walls and you're good to go, as karl.w2 mentioned. I've done this many times for things like Pi3 cases etc and it's just fine. Make the hole 3mm, ensure you're printing two or three perimeters in your slicer (you likely are already) and call it a day.

    Posted : 31/05/2018 7:25 am
    rob.l6
    (@rob-l6)
    Honorable Member
    Re: Reinforce Hole for Self Tapping Screw?


    I really think you are overengineering this.

    Yup, absolutely. No need to reinforce just for your purposes. But great tip all the same.

    Posted : 31/05/2018 7:35 am
    arthur.c2
    (@arthur-c2)
    Trusted Member
    Re: Reinforce Hole for Self Tapping Screw?

    To me it's not a problem of wall thickness, it's just that M3 screws has a really small pitch so you can't tight them too much without snatch the plastic (the length of your screw has an influence too).

    If I want to tight well, I use thermoplastic screws that have a bigger pitch.

    And if I want to bolt a part with torque, I make a cylindre in a separated body around the hole and affect 2 differents process on Simplify3D to fill it.

    Posted : 31/05/2018 1:35 pm
    Wingsy
    (@wingsy)
    Eminent Member
    Topic starter answered:
    Re: Reinforce Hole for Self Tapping Screw?

    I appreciate you guys taking them time to pass on your experience. I've had the feeling for a while that this was really a non issue or there would be many posts about it.

    If I were to build a bridge it would have so much concrete & steel in it that it would only support 1 car at a time.

    Posted : 31/05/2018 4:14 pm
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