Cutting Glass

[Paul King]

I've got several sheets of 3mm Horticultural glass which need reducing in size. Standard size Greenhouse glass, about 2'6" x 2' (750mm x 600mm for the metricists). I need to reduce them to 2'3" x 2'. I score the line and break off the excess 3" x 2' piece but it never comes away cleanly - I have to nibble away bits to get a straight line - the 3" strip breaks into several pieces.

Just how do I get it to cut cleanly, leaving me with two intact pieces of glass?

All suggestions welcomed.

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[Mungo "two sheds" Toadfoot]

Have you tried supporting the underneath of the 2' all along its length, with a piece of thin dowel for example, then tapping along it until it breaks?

Si

[Christian McArdle]

What do you score the line with? I bet you'd get a better line with a "contractor" grade tile cutter than with a 99p score and snap.

Christian.

[Dave Plowman]

I'd guess it's old glass which never snaps cleanly.

[Mouse]

[stuart noble]

A decent cutter, dipped in white spirit or meths. One light but continuous score. With a 3" offcut you should be able to grip it with finger and thumb either side of the cut

[Bob Mannix]

Basically you don't. Slow crystal growth in glass (which is a supercooled fluid)makes it impossible to cut cleanly once it has aged. That's why glass merchants do it so successfully - theirs is brand new.

[Mike Harrison]

Essential to use a good quality carbide cutter (Shaw), make ONE clean score from edge to edge, and support the beak line with something like dowel. Tapping along the score line also helps (this is what the ball on the end of the cuter is for)

The guy at the local glass shop said that new cutters need to be 'run in' with a few dozen scores on scrap glass before they work well. The pro's also score under oil.

3" is quite a small piece to cut off though - you may need to use something (piece of wood) to apply even pressure along the length of the cutoff piece.

[Paul King]

Thanks all for the replies. Took the advice and bought new (Shaw) cutter. All glass now cut cleanly and fitted in place!

Thanks again.

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[jacob]

Not true that old glass is difficult to cut - I've cut acres of the stuff but it has to be very clean etc as previous posters have said. Use 'glaziers' cleaner from a spray bottle, not windolene or whatever. If you are removing a narrow strip glaziers 'grozing' pliers help. You apply gentle pressure with the pliers near one end and watch the cut open slightly, then move along a bit and do it again. Eventually the whole strip comes away but it's a bit of a fine art to remove a narrow piece (less than say 10mm) in one. Wider pieces no prob if you follow previous posters advice.

cheers

Jacob

[Jerry Built]

I know you've done it, but (if you ever need to cut glass again) use a single-point diamond cutter which is far, far, far better than the wheeled ones. As you've found, old glass cuts easily once scored properly. It does not "flow" to make the bottom thicker than the top, or develop new crystal structure, or anything like that, in other than geological timescales.

J.B.

[Dave Plowman]

Perhaps you'd explain just what the ageing process is then that makes it much more difficult to cut when old?

[jacob]

There isn't any ageing process in real time, only geological time, except for weathering, wear and accumulation of dirt and other deposites. I've cut acres of old glass and once cleaned it cuts like new. The only prob is hard deposites which prevent a clean score, or simple defects like spalls and incipient cracks. There may also be very impure glass which deteriorates for all I know, but I've never seen any. The oldest window glass i've cut was from about 1650 and was no prob.

cheers

Jacob

[Dave Plowman]

I'm no expert, but cutting new glass is easy peasy. Old stuff that I've tried, not. And I really can't see what deposits would stop a diamond cutter. Oh, and I'd always clean it first - there's not much point in using say scratched glass. Are you saying it's an urban myth that new glass isn't easier to cut?

[jacob]

Yes without a doubt, except for rare occurences of poor quality glass. Also a myth that glass creeps with age although it sometimes looks as though it has because old glass tends to be irregular and glaziers always fit it fat end down and also the bottom lead came is the one which will hold water (if the seal has gone) and which will be expanded by frost action. If you have a prob with cutting old glass then its probably not clean enough - and the cutter (diamond or not) tends to slide over rather than cut properly. Use that powerful cleaner you get from a glass supplier - it's a bit too strong for ordinary window cleaning as it takes off the paint surface like sugar soap

cheers

Jacob