Part design for longevity

I have a question that I have not seen come up. I often design tool holders (ABS) and lets say I make a holder for a Dremel bit and I make a hole where the bit press fits nicely so it won't fall out. Problem is that over time (not to long) the hole wears out and the bit can then fall out. I got to thinking there must be a way to design in a plastic spring like system into a hole so that it could spring back and forth when the tool is inserted while only causing minimal wear so the tool can be held properly for many insertions and removals.

I am just curious if anybody has done any testing for a design like this and if so what were the results and do you have any examples you could show. I would rather not re invent the wheel so to speak if I don't have to.

Thanks

Edited 1 time(s). Last edit at 08/16/2014 01:07AM by tmorris9.

The easiest way would be to find a design which doesn't require press fit. A hole with a closed bottom, for example.

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My designs already have a closed bottom, problem is when the holder is inside a portable tool box and is tipped on its side dumping out all the bits. And this is just an example not a one shot project. Just wondering for future projects as well.

My Dremel project is being solved with small magnets glued into the bottom of the hole.

I've successfully used an M2 tap on PLA. So how about tapping a side hole and using a set/grub screw to hold the tool in?

Andy

Edited 1 time(s). Last edit at 08/16/2014 06:03AM by ajayre.

I design springy structures all the time for this sort of thing. I'm not quite sure what your tool holders look like, but I'd create a couple of flexing fingers with a circular contour between them to hold the bit. I also find that PLA works better for flexing structures because it is harder and seems to creep less over time. If you post a picture of your version, I'd be happy to show what a springy version might look like. (Of course, it helps if you've got access to nice CAD software .)

OK, so the screen grab shown below shows my idea for a tube oversized with inward facing walls to act as springs, it's really tiny though and the walls broke after repeated use (they also taper inward towards the bottom to be stiffer). The photo is of my finished product (printed overnight) and this one will have 1/8" x 1/4" magnets glued into the holes and when the bits are slid inside they will hit the end of the magnets to hold them in place.

... look out for 'snap-in'-designs ...

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perhaps something like this? the cylider wall is slightly slanted into a cone shape, allowing part to flex and hold something.



code written in openscad file is attached as well:


james villeneuve snap example compensates for tolerance and wear.



difference(){
cube(size=[10,10,5],center=true);
cylinder(r1=7/2,r2=7/2,h=12, $fn=20, center=true);
}
difference(){

cylinder(r1=6/2,r2=6/2,h=5, $fn=20, center=true);

cylinder(r1=5/2,r2=5/2,h=6, $fn=20, center=true);
cube(size=[10,1,8.1],center=true);
cube(size=[1,10,8.1],center=true);
}


difference(){

cylinder(r1=8/2,r2=6/2,h=5, $fn=20, center=true);

cylinder(r1=5/2,r2=4.5/2,h=5.1, $fn=20, center=true);
cube(size=[10,1,8.1],center=true);
cube(size=[1,10,8.1],center=true);
}

Edited 2 time(s). Last edit at 08/16/2014 07:31PM by jamesdanielv.

Here's another way you could do it.

That's a really good idea. Thanks

I have created a similar part once, it consisted of two halves that were held together by a rubber band. The Dremel bits clamped in between the two parts. On both halves there were cuts where the rubber band fitted in so that it didn't extend beyond the perimeter of the two halves.

Maybe an idea for you to design something similar? It can be a good idea to not only use printed plastic, but add a second material that has different qualities and fits inside a hole in the bit holder?

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Quote
tmorris9
My designs already have a closed bottom, problem is when the holder is inside a portable tool box and is tipped on its side dumping out all the bits.

The trick is to design the closing lid in a way this can't happen. For example another hole which aligns with the bottom one when closing, so when closed, you have a cavity closed on all sides. Or design a downholder into the closing lid.

Regarding press fit ... well, it's cheapo plastics, which was never known for its wear resistance. Either you can find a way to get away without strong friction or you have to choose another material. Steel, for example.

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