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Cutting Glass

I need to cut some glass 4.5mm (a mirror), do I need to score both sides or just one side. Can I use washing up liquid for lubricant instead of oil ?

Reply to
Smolley
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I once saw a professional cut a mirror at a local glaziers and he just scored one side. Unlike window glass I think mirrors have to have the edges ground/polished before being handed to the customer which would probably take out any fraying of the silvered layer.

Richard

Reply to
Tricky Dicky

This is a mirror that I ordered and It arrived broken, the vendors don't want it back, so I thought I would trim it up.....I can always seal the edge of the silvering with super glue.

Reply to
Smolley

put it in a picture frame to hide the edges and mastic it from the back...

Reply to
The Natural Philosopher

The traditional way of cutting glass is, of course, scoring and snapping. But I have often cleaned up and made safe "chipped" edges on glasses, etc. with abrasive. I have sometimes wondered whether it would be possible to cut glass sheet with something like a tile cutter, perhaps using a diamond wheel. Or, say to take off a corner, with a diamond disk in a Dremel.

Reply to
newshound

I have ordered a glass cutter with a diamond head.

Reply to
Smolley

yes, it is. But be careful

Reply to
The Natural Philosopher

One and I'm pretty sure the non-silvered side for a mirror.

Glass cutting uses crack propagation to perfom the "cut". The score starts and then guides the crack as it grows when the glass is flexed to open the score line. For something 4.5 mm think score the glass well supported then slide a thin (5 mm ish) lath under the glass, align one edge of the lath with the score then starting near one end of the score press down on the unsupported glass 6" or more from the scrore. You should see a crack start to grow, keep gently pressing and moving along the line. Thinner glass can be scored and lifted and gently tapped with the cutter underneath the score line, the weight of the glass and the impact causing the crack to grow.

The score needs to be done in one single and very firm pass with the "cutter". The skill is in the firmness of that pass. Too light and the score doesn't reliably guide the propagation. Too heavy and the score has many cracks to propagate. More than one pass also introduces extra cracks.

The oil isn't really a lubricant but a "wedge" to help the crack propagate from the bottom of the score. ie the molecules of oil flow into the growing crack keeping it open and the maximum stress (hopefully) in the right direction.

Trying to trim less than an inch or two off can be tricky as it's harder to apply the flexing pressure over a long enough section of the score. There is a tendancy for bits to break off forming a "scalloped" edge.

Reply to
Dave Liquorice

Thanks for that info Dave, my plan is to clamp the mirror to the kitchen worktop and clamp two thin 'lats', one either side of the glass sheet, so the applied force is distributed evenly over the width of 14". The mirror corner is missing to a depth of 2" with a large crack propagated down to about 4" . My plan is to take off 6". I shall do this with the break line over the sharp edge of the worktop. I shall use the clamps as handles to apply the breaking force.

Reply to
Smolley

It also depends how old the glass is. New cuts much more easily than old.

Reply to
Dave Plowman (News)

Yep, old glass has lots of surface scratches than can divert the cut.

They both cut the same, except old glass might not cut where you want it to. B-)

Reply to
Dave Liquorice

Oops, sorry about the copy of your post!

I was just going to add that I watched a professional doing this, and ISTR he did the single pass with the glass cutter, then he tapped the glass near the cut before snapping it.

Reply to
GB

Yes usually slightly curved I notice. Brian

Reply to
Brian Gaff (Sofa)

I was told there was more to it than that. Very fresh glass cutting more easily than that in stock for a while. So not always to do with scratching or whatever in use?

Reply to
Dave Plowman (News)

I've cut an old mirror with a normal glass cutter and it was fine- score the non-silvered side and snap it as normal. I took a bit off the cut edges to smooth them with a oilstone like you'd use to sharpen a chisel, IIRC, but it was about 35 years ago. I'd found an old, framed dressing-table one and cut it square.

Reply to
Chris Bartram

I have seen it suggested that white spirit will work...

Reply to
John Rumm

The other useful technique is, after making the score, to gently tap along the line of it with something like the ball of a ball pein hammer. Done correctly, it will cause the surface defect to propagate through the thickness of the glass. You can see when this has happened by viewing from different angles. Do this all or almost all along the crack, then the glass will crack very easily (but still using the lath technique). Masters of the technique make this look really easy (they typically use the back of the cutter).

Reply to
newshound

I saw a car windshield cut to fit a different car on wheeler dealers. Here is curved laminated glass cut:

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Reply to
misterroy

Score only on the non-silvered side - ideally using a carbide-wheel cutter against a straight-edge.

You need to keep the cutter vertical and apply the right amount of pressure - you do not want to press so hard that you see glass chips along the score-line.

Use any sort of oil - I use good old 3-in-1 oil, but any light oil (even cooking oil) will do at a pinch.

Having scored the line (in one single confident stroke - do not go back over the line) then tap firmly on the underside of the glass under the score at both ends. You should see the score start to run though the glass.

Lay something (like a thin lath or even a thin metal rod) underneath the score and apply downward pressure to the sides of the glass. The crack should run along, under the score.

Mirror is very susceptible to the dreaded 'creeping black-edge' - where the silvering detaches from the glass and the reflective effect is marred by the black area. Grinding the edge of a mirror makes this more likely to happen, as does the use of any type of 'acid-cure' mastic. Best to seal the edges with a cellulose varnish or clear nail-polish.

Thing is - it's a fairly specialised skill, and if you're only doing it once then there's limited opportunities for developing that skill.

Any glass merchant would do it for you for a fiver - and get it right. I'd do it - but you'd have to get it over to me in Ireland!

Adrian

Reply to
Adrian Brentnall

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