Cutting CD case plastic to make meter glass replacements?

[G6Tanuki]

It seems that whatever acrylic is used for CD cases, while clearly very amenable to being moulded, deeply resents any sort of cutting/machining/filing operations - it either melts or cracks!

Any suggestions? I've got a 1950s moving-iron centre-zero ammeter with a cracked glass and so far all my attempts to cut a disc of plastic from a CD case as a new 'glass' have failed.

[Goldie99]

I've no first hand experience with them, but I suspect they're polystyrene based rather than an acrylic.
Possibly a hot wire cutter may be the best option (?), or maybe source a small sheet of acrylic instead, as used for picture framing.

[mickm3for]

Hi a fine tooth hacksaw light pressure take it slow, use the blade only with the cutting stroke towards you support close to cutting edge Mick

[The Philpott]

The wrong sort of plastic can cause havoc with static and i speculate this includes acrylics. The problem is i don't know what the correct type of plastic is.. Discuss!

I've kept a few random circular glasses, what diam./thickness is it? (or is there a cutout at the bottom..)

Dave

[G6Tanuki]

I hadn't thought about the static issue - have had this problem in the past with glass-fronted meters which have been polished too-zealously!

It's 51mm diameter, about 2mm thick, just a plain circle (it's for a 1950s ammeter on a tractor).

[Goldie99]

Sounds like the usual size for a lot of classic Lucas m'cycle ammeters - 2" diam. I'm sure there are replacements available from some of the classic bilke parts suppliers - possibly a simpler option ?

[Hartley118]

I've had success in cutting a CD case for a meter glass application using a fine-tooth junior hacksaw blade followed by different grades of 'wet & dry' paper to smooth the edges. As yours is circular, maybe careful use of a fretsaw might be best.

Static charge producing spurious deflection of the pointer has been a problem from time to time though. I guess it's worth trying some anti-static polish. Or avoid using it on very dry days!

Martin

[G6Tanuki]

Thanks for all the suggested options, but I have found a better solution - the pile of stuff awaiting the WEEE skip contained an old rubber bodied flashlight that had succumbed to the dreaded leaky Duracell disease, but the plastic disk in front of the reflector is exactly the right size for what I need!!

Thread can therefore be closed.

[David G4EBT]

You can buy 2mm thick Perspex discs in 1mm increments from 13mm to 201mm at the link below.

EG, 50mm £2.22 + 95 P&P.

https://www.ebay.co.uk/itm/234219455...MaArh6EALw_wcB

Might save a lot of faffing about.

Hope that helps.

Ooops - too late!

[Uncle Bulgaria]

If you go to your local glazier they will cut you the relevant shape for very little cost. Even better, get a circular cutter and cut your own from a sheet of 2mm glass. I've been buying a lot of various sorts of glass for DIY windows recently from historic cylinder glass to toughened and laminated and there are always offcuts at the glazier's that I've been given when asked. I'm intending to do just the same thing for my Ferrograph tape counter which has a broken dial glass.

[G6Tanuki]

I'm hoping that this will be a one-off, so spending money on specialist tooling seems less-than-ideal.

A friend has a 'thing' used for cutting holes in tiles for shower-controls, taps etc; it's a rubber sucker that fits at the centre of the tile then has a round-and-round hand-cranked arm with a Diamond-tipped cutter. He got through quite a few tiles before making a good cut without the outer part of the tile [the wanted bit] breaking when he tried to push the centre disc out.

[Uncle Bulgaria]

Yes - one of those spy film window-breaking 'things' would do. Glass is rather easier than tile as it's homogenous. Tiles can be a complete bear and I'd use a diamond hole saw rather than try to score and crack a circle out of one.

Speaking of which, that reminds me that I've used a diamond hole saw (only a cheapo market special) when drilling through glass blocks to make lamps - not an area where scoring and cracking is suitable! Those holes were at least 50mm across to get the lightbulb and fitting through, and I got lovely circles every time.

I tried a piece of some sort of acrylic for my Ferrograph initially - sawn then cleaned up with a file while the circle was chucked on an electric drill (the counter knob comes through the front so a central hole was needed anyway). It just didn't have the right lustre compared to a piece of glass so I'll be trying a 'thing' or a holesaw next.

[wd40addict]

I once used plastic cut from a CD case to replace the glass in a Bell and Howell meter. Took two goes, but second attempt was fine.

[mark_in_manc]

2mm picture glass will cut under water with scissors (!). You can get close to a circle, and finish holding it in-line with the belt on a linisher.

[Julesomega]

That's an amazing claim, Mark: I have an ancient VVM coming in the post, not to mention a couple of nice PSUs in store, all need glass replacement. Can you offer any guidance on the technique, such as type of scissors, temperature of water, type of water...?

[kalee20]

I've heard of cutting glass underwater with scissors too - never needed to try it.

Strong scissors are reportedly needed, and the whole operation a foot under water.

As for the OP's question, I wouldn't use a CD case - I'd look on ebay and get a small piece of clear polycarbonate sheet - it's tough!

[The Philpott]

-and a decent permanent marker, given that colourless glass can become invisible underwater! Feels counter-intuitive, but so often mentioned that there must be something in it.

Dave

[mark_in_manc]

Originally Posted by Julesomega

That's an amazing claim, Mark: I have an ancient VVM coming in the post, not to mention a couple of nice PSUs in store, all need glass replacement. Can you offer any guidance on the technique, such as type of scissors, temperature of water, type of water...?

I saved up a few scraps of 2mm picture glass from broken picture frames I found in various bins. I did it in the washing up bowl in the kitchen, with cold water (I think - maybe it was a bit warm to make it more comfortable!) and a fairly heavy old pair of scissors I didn't care too much about.

The bloke who suggested it to me, thought maybe the water damped the glass and stopped cracks propagating somehow. You get a bit of a smashed-up edge - so I cut a series of straight cuts which got no closer than 2 or 3mm from the edge of the circle I wanted, and then used the belt linisher to clean it up as I mentioned. I don't suppose it did the belt much good. Hold the glass edge vertically in-line with the belt - hold it flat to the belt and it is more likely to snap.

Having a bit of a flange to glue the glass into, covered up the dodgy edge - it was not a clean circular cut.

So, that's what I know. Have fun!

[Cathovisor]

Small clock/watch glasses? However, I'd just visit my local friendly glass merchant.

[Richard_FM]

I did wonder if some thick acetate sheeting would be suitable, the sort sometimes sold in A4 sheets to be used to protect bound documents.