Fixings in uPVC window frames

[Random Orbital Bob]

Am I correct in assuming that regular wooden fixings ie screws and similarly drills are good for dense plastic like window frames. Or.....because the material is dense, do machine screws or at least tight wound screws work better like those designed for hardwoods?

Thanks

 

[Phil Pascoe]

Are you fixing the frames in or fixing things to them?

 

[Random Orbital Bob]

Fixing French blinds to them (not mine either so i don't really want to cock it up)

 

[MusicMan]

I've used self-tappers, to hold up curtain poles, seems to have worked ok (been up a year).

 

[Phil Pascoe]

That's what I thought you meant - there was another post after that that disappeared (I'm getting used to that happening). As above - I've always used self tappers.

 

[Racers]

Hardened wood screws are nearly as tough as self tappers, I have used them my self into upvc.

Pete

 

[MusicMan]

Pete, you are right on the hardness and toughness of course. My reason for choosing self-tappers was that they have, relatively, a narrower shaft and deeper threads, thus designed to hold better on thinnish sheets.

 

[CHJ]

Am I correct in assuming that regular wooden fixings ie screws and similarly drills are good for dense plastic like window frames. Or.....because the material is dense, do machine screws or at least tight wound screws work better like those designed for hardwoods?

Thanks

Rob, are they just plastic or is there a load bearing aluminium insert in the verticals. Might influence choice and positioning of fixings.

 

[Random Orbital Bob]

Not sure until I get the cross sectional drawings. But beyond this specific job, I'm interested in a general rule about sensible choices of screw for uPVC

 

[Woody2Shoes]

I'd use a coarser, tapered cutting thread like a self-tapper or a woodscrew, rather than a smoother, finer, parallel thread like a machine screw. Another possible gotcha is that sometimes there are bits of steel lurking inside the UPVC profile (e.g. for improved structural/security performance) - also some bits of the profile will be thicker/thinner than others - so I guess you'll need to see all the design details to be sure. Cheers, W2S

 

[Random Orbital Bob]

Understood. Think that's what Chas was referring to. Various manufacturers reinforce the profiles with steel historically and more recently a plastic composite to add rigidity for structural and security reasons which obviously might the halt the passage of any given poorly designed for the job screw. What I'm really after is the holy grail of holding power. Which type of fixing is going to deliver the greatest holding power (thread type etc) in this difficult to fathom material.

 

[Woody2Shoes]

I think that most window frames are made of uPVC which is not particularly dense, although denser than most timber, relatively ductile, and of moderately low tensile strength. I'm guessing that the shear strength (which is what screw fixings rely [heavily?!] quite a lot on) is not great either.

https://www.makeitfrom.com/material-pro ... uPVC-PVC-U

I'd use whatever fixing distributed the forces as widely as possible across the material, with no hot-spots/point loads. A larger number of bigger holes is better than a smaller number of smaller holes. I'd use a fastener with maximum surface area contact with the hole it's in - fatter being preferable to thinner. A bit like trying to fix something to thermalite block.

I think that any application that is pushing the limit of what's achievable might be worthy of a re-think. Cheers, W2S