Interesting plastic drilling

[GrahamRounce]

Interesting? A disc of perspex, 8mm thick. I drilled a 2mm hole all the way through, then a shallow 3.5mm one for the screw head. Put a drop of superglue into the bigger hole and pushed the screw through so it sat flush.
Then noticed all the junk that seems to have penetrated and spread into the perspex itself! Note especially the hair-fine slivers apparently floating several mm into the bulk! Any ideas?

 

[Lons]

Hi Graham

Drilling acrylic (it will be cast acrylic at that thickness) is never a clean hole as it slightly fractures as it cuts, normally not a problem but putting superglue into it affects the acrylic and penetrates the cracks. Superglue also turns white in that situation and I'd suggest the brown marks are from residue off the drill bit and or screw if you inserted that while the glue was wet..

You shouldn't really use superglue on acrylic unless it's one of the specialised varieties as it reacts chemically and weakens it.

 

[niall Y]

Hmm .... I used to work with Perspex, but in the days before superglue. In this instance I would have drilled , threaded and countersunk. the screw .
The problem is obviously the superglue which is a form of Acrylic itself, though it doesn't seem to have reacted very well with the Perspex disc. You might have done better with "Tensol" with some Perspex swarf dissolved into it
I am far from being an expert on the chemistry of Perspex, but I seem to recall that flat sheet - as opposed to components like thin tubes, have slightly different formulas. They certainly smelt different when you cut into them, with the tube having that rather unpleasant smell that is more akin to superglue.

 

[Vulcan]

You have to work with what you’ve got but I always avoid Acrylic. PETG is much nicer to work with.

 

[GrahamRounce]

I should have said there could have been (apparently was) crud on the drill and also the wood supporting it while drilling.

It's the way tiny pieces have migrated into the perspex - or you think those are fractures, not pieces? But "floating", disconnected ones?

PPS, I'm not complaining, it's not a problem. I'm just curious.

 

[Keith 66]

They look like fractures caused by the drill pulling itself into the hole. If you want acrylic to drill cleanly take a normal twist drill & grind a negative rake flat on the cutting edge, you can also use a diamond file. A drill ground this way scrapes rather than cuts & will drill fast clean holes in acrylic without breaking it.
The two types of Acrylic are Cast & Extruded, not sure what the chemical difference is.

 

[Lons]

Definitely fractures in my experience and the crud has migrated into those pulled in by the superglue which soaks in an melts into the fractures. If you drip superglue around the top surface of a hole it will often craze the surface.
Like Niall I worked in the industry for several companies as branch manager of plastics distribution companies, long before superglue but we cut quite a lot and fabricated some We distributed ICI perspex and I've visited the factories on numerous occasions but to long ago for me to remember the chemical differences however the properties of cast sheet and extruded is different and that of course includes extruded tube, as Keith says, your nose is a good guide as it is with many plastics when heated.

I'd also have drilled tapped and countersunk as suggested and while what Keith said about grinding drill bits is absolutely correct, I never bother as is occasional use and just ensure the bit is sharp, clean and speed is slow.

 

[Cabinetman]

Also possible to heat it up in an oven and push the screw through then let it cool, it will push up the surrounding surface though.
It’s a memory plastic so all sorts of clever uses can be made of it.
Ian