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 ?

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

On Fri, 19 Jun 2020 02:15:37 -0700, Tricky Dicky wrote:

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

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.

On 19/06/2020 11:17, Smolley wrote:
On Fri, 19 Jun 2020 02:15:37 -0700, Tricky Dicky wrote:

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

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.

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

--
"Nature does not give up the winter because people dislike the cold."

ۥ Confucius

On 19/06/2020 10:15, Tricky Dicky wrote:
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

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.

On Fri, 19 Jun 2020 11:23:26 +0100, newshound wrote:

On 19/06/2020 10:15, Tricky Dicky wrote:
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

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.


I have ordered a glass cutter with a diamond head.

On 19/06/2020 11:23, newshound wrote:
On 19/06/2020 10:15, Tricky Dicky wrote:
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

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.

yes, it is. But be careful



--
Climate Change: Socialism wearing a lab coat.

On Fri, 19 Jun 2020 09:00:14 -0000 (UTC), Smolley wrote:

I need to cut some glass 4.5mm (a mirror), do I need to score both
sides or just one side.

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

Can I use washing up liquid for lubricant instead of oil ?

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.

--
Cheers
Dave.

On Fri, 19 Jun 2020 12:53:18 +0100, Dave Liquorice wrote:

On Fri, 19 Jun 2020 09:00:14 -0000 (UTC), Smolley wrote:

I need to cut some glass 4.5mm (a mirror), do I need to score both
sides or just one side.

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

Can I use washing up liquid for lubricant instead of oil ?

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.

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.

In article ,
Tricky Dicky wrote:
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.

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

--
*Bigamy is having one wife too many - monogamy is the same

Dave Plowman London SW
To e-mail, change noise into sound.

On Fri, 19 Jun 2020 13:43:53 +0100, Dave Plowman (News) wrote:

It also depends how old the glass is.

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

New cuts much more easily than old.

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

--
Cheers
Dave.

On 19/06/2020 12:53, Dave Liquorice wrote:
On Fri, 19 Jun 2020 09:00:14 -0000 (UTC), Smolley wrote:

I need to cut some glass 4.5mm (a mirror), do I need to score both
sides or just one side.

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

Can I use washing up liquid for lubricant instead of oil ?

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.

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.

Yes usually slightly curved I notice.
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Tricky Dicky" wrote in message
...
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

In article l.net,
Dave Liquorice wrote:
On Fri, 19 Jun 2020 13:43:53 +0100, Dave Plowman (News) wrote:

It also depends how old the glass is.

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

New cuts much more easily than old.

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

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?

--
*It is wrong to ever split an infinitive *

Dave Plowman London SW
To e-mail, change noise into sound.

On 19/06/2020 10:00, Smolley wrote:
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 ?

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.

On 19/06/2020 10:00, Smolley wrote:
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 ?

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


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 19/06/2020 12:53, Dave Liquorice wrote:
On Fri, 19 Jun 2020 09:00:14 -0000 (UTC), Smolley wrote:

I need to cut some glass 4.5mm (a mirror), do I need to score both
sides or just one side.

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

Can I use washing up liquid for lubricant instead of oil ?

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.

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).

On Friday, June 19, 2020 at 7:07:38 PM UTC+1, John Rumm wrote:
On 19/06/2020 10:00, Smolley wrote:
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 ?

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


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

I saw a car windshield cut to fit a different car on wheeler dealers.
Here is curved laminated glass cut:
https://www.youtube.com/watch?v=kTM8Xy4HYAI

On 19/06/2020 10:00, Smolley wrote:
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 ?


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

On Friday, June 19, 2020 at 10:00:16 AM UTC+1, Smolley wrote:
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 ?

i've watched youtube videos, planning to try soon
(will now get email updates on this thread)
[g]

There was an example of glass cutting on the Repair Shop, specialist glazer was brought in to cut some panes for a Victorian gas lamp. He scored the glass with a single stroke of a diamond no lubricant. He simply held the glass in his fingers either side of the score and with a slight twist of the wrists it split cleanly.

Richard

On 20/06/2020 10:02, Tricky Dicky wrote:
There was an example of glass cutting on the Repair Shop, specialist glazer was brought in to cut some panes for a Victorian gas lamp. He scored the glass with a single stroke of a diamond no lubricant. He simply held the glass in his fingers either side of the score and with a slight twist of the wrists it split cleanly.

Richard


All depends on the glass - the thinner the glass the easier it snaps.
I use some 2mm glass in my fused-glass jewellery, and it snaps as easily
as a chocolate bar - 2mm picture-frame glass is equally cooperative.

Modern 'stained-glass' glass tends to be 3mm - again, fairly easy to
work with.

4mm float / mirror glass takes a bit more effort. Scoring the surface of
the glass creates a line of weakness along which you'd like the glass to
break. Bending the glass by as little a 2 - 3 degrees causes it to break
along this line of weakness (hopefully).
In glasswork we use a pair of 'running pliers' - like the ones unsed in
ceramic tile work, which are designed to apply the correct pressure to
run the score..

Given that this is the op's first attempt, and he's only got one chance
to get it right, he probably needs all the help he can get!

It's probably just me getting old & crabby, but the more often I see
anything on TV that I know a little about (like stained-glass on the
Repair Shop), the more often I find myself shouting "You don't do it
like that!" at the TV.
These programs are produced for entertainment, not education....

On 19/06/2020 11:17, Smolley wrote:
On Fri, 19 Jun 2020 02:15:37 -0700, Tricky Dicky wrote:

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

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.



How thick is the glass?

There are some very cheap large mirrors[1] around where the glass is
only around 1mm thick and nearly impossible to lift from a supporting
backing without it bending and cracking. I have the T shirt when I
thought it a good idea to remove a mirror in order to paint the frame.


[1]
The mirror glass is 1 metre x 0.75 metres in a frame for around £25. The
Range often used to have them piled high on their shop floors and I have
seen them elsewhere. It's the frame and backing that allows the mirror
glass to stay intact.

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On 19/06/2020 19:59, newshound wrote:


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.

I was shown how to do this with quarry tiles and used it when fitting
the same. Score the glazed top surface with a glass cutter in the same
way as glass and then use a very small light weight hammer

https://tinyurl.com/ya54ypa9

to repeatedly gently tap the back of the tile in the area with the score
on the top surface. The tile will start "ringing" with the note changing
as the crack propagates and breaks along the score line. Not suitable
for just taking off a small amount but OK for a 1/4 of the tile width or
more.


--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On 20/06/2020 10:38, Adrian Brentnall wrote:

These programs are produced for entertainment, not education....


More so when they completely edit out the boring bits that in a process
are essential for producing a decent finished article or even edit out
bits that the "experts" don't want the DIYer to know.

I find that I get annoyed when labour costs are not included so that £50
profit would be more like a £200 loss even at minimum wage. Worse is
when that ream of gold leaf comes "free" because it was left over from
another job or the sand blasting and powder coating of the ocean liner
was done free as a small favour to the presenter.


--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

In article ,
alan_m wrote:
On 20/06/2020 10:38, Adrian Brentnall wrote:

These programs are produced for entertainment, not education....


More so when they completely edit out the boring bits that in a process
are essential for producing a decent finished article or even edit out
bits that the "experts" don't want the DIYer to know.

I find that I get annoyed when labour costs are not included so that £50
profit would be more like a £200 loss even at minimum wage. Worse is
when that ream of gold leaf comes "free" because it was left over from
another job or the sand blasting and powder coating of the ocean liner
was done free as a small favour to the presenter.

Repair Shop doesn't charge for repairs. Unlike many of the classic car
progs where they claim to have made a profit.


--

--
*Save the whale - I'll have it for my supper*

Dave Plowman London SW
To e-mail, change noise into sound.

On 20/06/2020 11:08, alan_m wrote:
On 19/06/2020 11:17, Smolley wrote:
On Fri, 19 Jun 2020 02:15:37 -0700, Tricky Dicky wrote:

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

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.



How thick is the glass?

The original poster said 4mm

On 20/06/2020 11:21, alan_m wrote:
On 19/06/2020 19:59, newshound wrote:


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.

I was shown how to do this with quarry tiles and used it when fitting
the same.Â* Score the glazed top surface with a glass cutter in the same
way as glass and then use a very small light weight hammer

https://tinyurl.com/ya54ypa9

to repeatedly gently tap the back of the tile in the area with the score
on the top surface. The tile will start "ringing" with the note changing
as the crack propagates and breaks along the score line. Not suitable
for just taking off a small amount but OK for a 1/4 of the tile width or
more.


The sort of glass cutters we use in stained-glass tend to have a
weighted brass 'head' (the opposite end to the cutter) - and this can be
used to start the score running.

If you're doing a straight 'edge-to-edge' cut then you shouldn't need to
do any more than tap at the start and end of the score - and the section
in-between will follow the line of the score, if the score has been done
properly.

If you have a sinuous score then tapping at strategic points along the
curve can ensure that the glass behaves - rather than cracking off in
random directions where it wants to..

On 20/06/2020 11:21, alan_m wrote:
On 19/06/2020 19:59, newshound wrote:


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.

I was shown how to do this with quarry tiles and used it when fitting
the same.Â* Score the glazed top surface with a glass cutter in the same
way as glass and then use a very small light weight hammer

https://tinyurl.com/ya54ypa9

to repeatedly gently tap the back of the tile in the area with the score
on the top surface. The tile will start "ringing" with the note changing
as the crack propagates and breaks along the score line. Not suitable
for just taking off a small amount but OK for a 1/4 of the tile width or
more.


I had never heard of that. I love the acoustic aspect. Quarry tiles were
a right ******* in the days before tile cutter machines.

On Fri, 19 Jun 2020 19:59:48 +0100, newshound wrote:

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 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.

Wasn't sure if that would work well with 4.5 mm thick glass, I guess
it should and might be a bit more controlled that applied pressure.
The thickest glass I've cut would be 3 mm the lift and underside tap
worked well.

--
Cheers
Dave.

On Sat, 20 Jun 2020 10:38:10 +0100, Adrian Brentnall wrote:

On 20/06/2020 10:02, Tricky Dicky wrote:
There was an example of glass cutting on the Repair Shop, specialist
glazer was brought in to cut some panes for a Victorian gas lamp. He
scored the glass with a single stroke of a diamond no lubricant. He
simply held the glass in his fingers either side of the score and with
a slight twist of the wrists it split cleanly.

Richard


All depends on the glass - the thinner the glass the easier it snaps.
I use some 2mm glass in my fused-glass jewellery, and it snaps as easily
as a chocolate bar - 2mm picture-frame glass is equally cooperative.

Modern 'stained-glass' glass tends to be 3mm - again, fairly easy to
work with.

4mm float / mirror glass takes a bit more effort. Scoring the surface of
the glass creates a line of weakness along which you'd like the glass to
break. Bending the glass by as little a 2 - 3 degrees causes it to break
along this line of weakness (hopefully).
In glasswork we use a pair of 'running pliers' - like the ones unsed in
ceramic tile work, which are designed to apply the correct pressure to
run the score..

Given that this is the op's first attempt, and he's only got one chance
to get it right, he probably needs all the help he can get!

It's probably just me getting old & crabby, but the more often I see
anything on TV that I know a little about (like stained-glass on the
Repair Shop), the more often I find myself shouting "You don't do it
like that!" at the TV.
These programs are produced for entertainment, not education....

It took me three attempts to get a half decent edge and taking off about a
foot of glass. I bought a 'professional diamond glass cutter' and it was
crap. It became blunt very quickly. I ended up using a new, tungsten
carbide tipped two fluted end mill, which gave a deep score.

On 20/06/2020 13:09, Smolley wrote:
On Sat, 20 Jun 2020 10:38:10 +0100, Adrian Brentnall wrote:

On 20/06/2020 10:02, Tricky Dicky wrote:
There was an example of glass cutting on the Repair Shop, specialist
glazer was brought in to cut some panes for a Victorian gas lamp. He
scored the glass with a single stroke of a diamond no lubricant. He
simply held the glass in his fingers either side of the score and with
a slight twist of the wrists it split cleanly.

Richard


All depends on the glass - the thinner the glass the easier it snaps.
I use some 2mm glass in my fused-glass jewellery, and it snaps as easily
as a chocolate bar - 2mm picture-frame glass is equally cooperative.

Modern 'stained-glass' glass tends to be 3mm - again, fairly easy to
work with.

4mm float / mirror glass takes a bit more effort. Scoring the surface of
the glass creates a line of weakness along which you'd like the glass to
break. Bending the glass by as little a 2 - 3 degrees causes it to break
along this line of weakness (hopefully).
In glasswork we use a pair of 'running pliers' - like the ones unsed in
ceramic tile work, which are designed to apply the correct pressure to
run the score..

Given that this is the op's first attempt, and he's only got one chance
to get it right, he probably needs all the help he can get!

It's probably just me getting old & crabby, but the more often I see
anything on TV that I know a little about (like stained-glass on the
Repair Shop), the more often I find myself shouting "You don't do it
like that!" at the TV.
These programs are produced for entertainment, not education....

It took me three attempts to get a half decent edge and taking off about a
foot of glass. I bought a 'professional diamond glass cutter' and it was
crap. It became blunt very quickly. I ended up using a new, tungsten
carbide tipped two fluted end mill, which gave a deep score.


Strangely, a lighter score (so it's only just visible on the surface of
the glass) works better, and you're more likely to get an accurate break.

I had it described to me once, that the glass is like a toy balloon -
the outer layers (top & bottom) are the rubber - the main body of the
glass is the remainder of the thickness.

All you're doing with the glass 'cutter' is to create a line of weakness
by cutting into the outer skin. Then, with the correct amount of force /
angle, you'll persuade the main body of the glass to break along the
line of the score..

Scoring the line too deeply causes the surface glass to splinter (you
can see fine glass-dust along the score-line) and then the core is
likely to run off in random directions.

When I've taught people who to do stained-glass, we spend an amount of
time with sheets of horticultural (greenhouse) glass - learning just how
much pressure is required when scoring. Straight lines first, then arcs
and onto snakey-lines!
Different colours and types of glass require different pressures - after
a while you instinctively adjust the scoring pressure to suit the piece
of glass you're cutting.

On Fri, 19 Jun 2020 14:51:59 +0100, Dave Plowman (News) wrote:

It also depends how old the glass is.

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

New cuts much more easily than old.

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

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?

Maybe but it only takes a single scratch to divert the cut,
particulary if the angle between the scratch and score is small.

--
Cheers
Dave.

On 20/06/2020 18:48, Chris Hogg wrote:
On 20 Jun 2020 17:07:09 GMT, Tim Streater
wrote:

On 20 Jun 2020 at 14:41:03 BST, Chris Hogg wrote:

The stress intensity at the tip of a microcrack is very high, due to
its almost atomic scale radius; opening it up by etching increases
that radius and reduces the stress. The fine flaw produced by a
glass-cutter is in effect just a long flaw, and fine, even invisible
scratches will divert the line of fracture. Old glass, such as the
greenhouse glass I referred to in an earlier post, is full of
invisible microcracks and almost impossible to cut by conventional
methods. I used a diamond wheel tile cutter with great success when
cutting down panes of old greenhouse glass for re-purposing.

Can it be annealed by heating, and if so, at what temperature?

No idea. Annealing will relax any stresses in the glass, but I don't
know if it heals microcracks. Don't know what temperature either - I
was going to guess 600C or thereabouts, but wiki says upper 400's.
https://en.wikipedia.org/wiki/Annealing_(glass)


IIRC "flame polishing" as carried out by glassblowers aims to take the
surface just to dull red heat, which ties in with your 600C. I don't
think "annealing" would deal with the cracks.

On 19/06/2020 20:43, misterroy wrote:


I saw a car windshield cut to fit a different car on wheeler dealers.
Here is curved laminated glass cut:
https://www.youtube.com/watch?v=kTM8Xy4HYAI

Changing the subject, I was amused to see on TV last night some firemen
taking the roof off a crashed car with what looked like an bog standard
cordless sabre saw. Through the door pillars and straight across the
windscreen as well.

On 21/06/20 10:02, newshound wrote:
On 19/06/2020 20:43, misterroy wrote:


I saw a car windshield cut to fit a different car on wheeler dealers.
Here is curved laminated glass cut:
https://www.youtube.com/watch?v=kTM8Xy4HYAI

Changing the subject, I was amused to see on TV last night some firemen
taking the roof off a crashed car with what looked like an bog standard
cordless sabre saw. Through the door pillars and straight across the
windscreen as well.

I assume they'd identified the car as diesel or battery-powered. The
pincer-type cutters were designed to cut into metal where a sabre or
other saw might cause sparks which could ignite any petrol around.

--

Jeff

Cutting glass with a diamond is something requiring a lot of skill and familiarity with the cutter. I could cut glass with my own diamond but not with my fathers. There was a subtle variance in the angle to hold it.
Much easier to use a wheel type cutter where the world and his dog had every chance of success.
Forget clamping and creating stress in the glass. Lay it on a flat clean sheet of wood with a cloth cover such as baize. Use a straight edge to guide the cutter to score a line from edge to edge of the worksheet. Carefully insert a bit of dowel under the score when the score will crack through and the two pieces separate. Old glass is a lot more difficult due to brittleness.
Don't press too hard, there's a correct pressure which you can learn with practice on scrap pieces.