Creating stronger screws?
Hi Folks,
Quick bit of advice required - one of the toilet flushes in the house has broken and the culprit was a little plastic screw and thread that held the flush in place, you can see the screw part and thread in the image here:
A perfect opportunity for my 3d printer, I thought!
I've modelled an identical replacement in fusion 360 and printed it off in PLA - this worked great, but unsurprisingly is too brittle for this use - so I've printed it off in PETG (Prusament) with 100% infill. I fitted this and all seemed fine, but has snapped after a day of use.
As the bolt part needs to be hollow to allow the flush handle through it, it's a little more challenging.
One thought I've got is that it may be the direction of the layers that is contributing to its weakness - ie if I printed the screw part horizontally along the threads then the layer lines would go against the sheer force and be much stronger? I'm not really sure how I could print it horizontally though as there'd need to be a mass of supports that might not be easy to remove from between the threads...
Any thoughts most welcome!
Re: Creating stronger screws?
You can split the screw portion lengthwise and it will still hold tight when the nut threads on. And since you're in Fusion, you can do the split and make tabs to ensure alignment. Not as clean as a solid part, but will certainly help the strength with loads being placed along the extrusion rather than the layer bond. And supports - probably not needed - would be on the bearing surface and pretty easy to remove.
Another trick I've heard - untried by me - is to use the highest layer height your nozzle will produce. Apparently this improves layer to layer fusion and bond strength.
Re: Creating stronger screws?
Ah, that's a really good tip (ie split in half) - makes a lot of sense, will give that a shot!
Interesting thought re the layer height - can see the nut of logic in it, although not entirely convinced how radical a difference this would make (ie fewer fracture points, but nonetheless they'll still be there) - when I get a spare moment it'll be interesting to print off a ton of variants and do some stress tests on this sort of stuff...!
Re: Creating stronger screws?
PS am I being daft - how can I create alignment tabs in 360? Can't see the option for the life of me!
Have split my screw in half, can manually model it in worst case, but sure there's the option...?
(part of the problem is that as most UIs like Fusion 360 are full of 'tabs' for the interface, when I google it struggles to differentiate!)
Any pointers most welcome
Re: Creating stronger screws?
Making "tabs" would be a manual process to draw them after you've split the part ... similar to adding pins for alignment. But my assumption was the threaded area is too thin for pins; after some thinking, tabs might also be problematic. A couple of pins in the bezel would probably be better, and where you want good alignment, too. Easiest way to make pins is plan on using filament as the pin, so model the holes for the 1.75 mm you're printing with.
Re: Creating stronger screws?
That looks quite a hefty screw. Are you printing petg hot enough for good layer adhesion?
Re: Creating stronger screws?
Well remember it's a hollow screw as it needs the toilet handle to go through it - probably more of a bushing than a screw technically!
I've given up an ordered a plastic replacement - I feel Ive failed!
Re: Creating stronger screws?
Don't. To mit that part seems like it simply wasn't meant to be 3d printed. I wouldn't even attempt to do so. There is a correct technology for everything...