I need some M4 x 12mm countersunk plastic screws. The obvious easily obtained material is nylon but I see that some other plastics are also available - e.g. clear acrylic.
I'm not expecting metal strength but it would be good to know which (reasonably priced) plastic is going to be stronger. I'm aming to use the screws through a sheet of closed-cell plastic to pull things 'into' the plastic (rather like upholstery buttons).
Acrylic is very brittle and propagates cracks easily - not what you want for a screw.
Nylon (polyamide/PA) is pretty good as a mechanical element. There's also various forms of fibre-reinforced nylon (GFR PA) which are stronger but not sure you can make a sensible fibre lay-up for a small screw.
Don't overtighten, as I think that's a common cause of nylon failure - the screw head shears off.
Theo
Pretty much all there. I found acrylic as will, but if it is a low grade plastic screw nylon seems to be most used
In the model aircraft arena, the ability of nylon bolts to shear in a crash is desirable
I actually found that at least with cross heads, the screwdriver could not exert enough torque to shear them - the heads just mashed first.
I sometimes specify PEEK fasteners, mainly because of temperature. They're pretty strong, though unreasonably priced.
The good news is that the patent will expire pretty soon, assuming this is the key one:
What about Delrin? aka Polyoxymethylene or POM
This is advice from CoPilot.
Q: What is the best material to use to make a uV-resistant screw ?
A: The best materials for making a UV-resistant screw are plastics like Acrylic (PMMA), Polycarbonate, PTFE, HDPE, Polyetherimide, Polyphenylene Sulfide, and Polyvinylidene Fluoride. These materials are known for their excellent UV resistance and are suitable for outdoor applications where exposure to sunlight is a concern.
For instance, Acrylic and Polycarbonate are both strong and durable, with Polycarbonate being particularly noted for its impact resistance.
If you’re considering metal screws, stainless steel screws are a good option as they offer exceptional rust resistance and can withstand outdoor conditions.
It’s important to choose the right material based on the specific requirements of your application, such as strength, flexibility, and environmental resistance.
As that article mentions, it depends on the application and also reliance on the material not being too malleable or brittle. If trying to hold two pieces together that have a natural tendency to pull apart you will not want to use a material that may stretch over time or when fitting, nor when attempting to tighten that last quarter of a turn just snaps.
It's much like the "plastic" back washers that come with many taps these days. Great that they will not rust* but I've found when in an awkward position and trying to tighten them the internal tread can deform and jump back a tread effectively loosening the nut as you tighten. Once this has happened once the chances of tightening are zero. I always throw away the plastic back nuts and purchase the brass* versions.
I could not find anyone making screws out of that.
Yes 100%. I have a wobbly tap with an untightenable cracked plastic nut that is in such an awkward place it been waiting around 6 years to be replaced...
Quite! OP here, the basic choice for easily obtained (and not stupidly expensive) screws seems to be between nylon and acrylic. Having found a few sites with information I think nylon is almost certainly the way to go for my application.
Is it wobbly enough to get a squirt of silicone under the flange to bond it to the sink.
BTDTGTTS
It just unscrewed even more
Is this an outdoor application ?
White nylon seems quite UV sensitive (a problem after one year). Black nylon is better, but they don't make screws of it (at least 4 to 5 year life).
You may want to review thread design, in case what was tapped into the steel, is different than how they cut the plastic ones.
No, it's inside and hidden under panelling so will be kept in the dark! :-)
Interesting. I've just now received spam email advertising a frying pan with PEEK non-stick coating. Fifty-seven quid, so not outrageous.
I got that spam too. I didn't read it, so I thought PEEK was a brand of frying pan.
Seems like PEEK is being touted as a replacement for PFAS which have environmental problems. Also seems to be better at high temperatures, something PFA/PTFE coated bakeware struggles with.
Theo
It's long been used in industrial valve seats.
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