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SOLVED: Glass cutting... advanced tips needed.


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Hey all,

I have started cutting 6mm glass, but the break is not perpendicular. to the surface. The break edge is angular.

I'm using a new oiled glass cutter and a straight edged aluminium cutting bar as a scoring ruler.

I have tried these 2 ways of breaking the glass:

a) using a large opened paperclip end as a lever point under the score line - break is clean along the score line but is uneven peperndicular to the surface.

b) using a 16mm MDF board longer than the glass pane so the edge of the mdf board is directly under the score line - break is clean along the score line, but still not perpendicular to the surface. It is much more even than a), break is slanted the complete length of the break like 2mm at the bottom edge.

Has anyone got any advanced tips on cutting/breaking 6mm glass so that the break is perpendicular to the surface?


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Hi Marko

It all depends on how much you are trying to cut off the piece of glass.

The thicker the piece of glass (say 6mm) it's hard to break off a piece 20 mm wide evenly. If it was 4mm the same length would break perfectly. If you go to the hardware and buy yourself a pair of tile breaker pliers, they will help heaps. ou place them directly on the score mark and gently press. Make sure you support the other end too where the glass will break. Its practically impossible to break glass neatly if it's a thin strip on thick glass. Also, the shorter the length of glass, the easier it is. Hope this helps you

giszmo44 smile.gif

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Also to the last response, im pretty sure that most glass edges in the industry that are smooth and un-sharpened, have been polished.

You can get a glass edge polisher from most decent hardware stores.

Hope this helps.

Cheers, and be careful.


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hi marko

it's as simple as this;the glass will break following the line you score, if your line is 'straight' [across the pane] it will break straight. if your line through the thickness [6mm] is not staight the glass cannot break straight. the break can only follow line you make. doe's this make sense? no? ok k.i.s.s. make sure that you hold the cutter perpendicular to the pane [staight up down] if you slant the cutter left or right you will get an angled cut." practise makes perfect"..have fun;colfish

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Guest Panga

hi marko,

i would also like to add to this, never score the glass more than once.

i have couple of friends that are glaziers and they gave me that advice when i was cutting glass.

HTH Troy biggrin.gif

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Just to add:

* Old glass has "hardened" and is less predictable/manageable when cutting.

* A cheap alternative to properly polishing the edges, but still taking the danger out of them, is to use a sharpening stone run along the edge, shaping it slowly.

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Thanks for all your comments...

I have 4 sheets of Tinted 6mm Glass each 3ft11in wide - from damaged window at work.

Lengths are between 3ft and 6ft.

I want to make some 24x18x18in tanks with clear front glass.

I have worked out that I can cut glass strips 18in high across the 3ft11in wide glass (then remove the ecxess of the ends and cut/break to make 24x18in and 18x17.??in panels.

I have researched on the net about glass cutting (most info is regergitated)... even read stained glass sites - there is not much out there for thick glass.

I follow these rules:

* Glass cutter is new - Tungsten Carbide Wheel (oil lubricated wheel for cleaner score)

* Only score the glass once then break.

* Break glass as soon as possible after scoring. I have been doing it in 2-3 minutes.

* Wet the score line with water to help break (yes it is true!)

When scoring:

* Use a straight edge ruler/bar to score a straight line (as the glass is 3ft11in wide! I have a 4ft aluminium bar 5mm thick clamped with small QuickGrips to the glass, 2 sheets of newspaper between bar and glass to protect the glass.)

* Use enough pressure to score glass. Do not use too much pressure!

* Do not start/stop/change scoring motion or pressure.

* Do not rescore after scoring

I am doing all the right things...

It is just the breaking methods that I have done in my 1st post have given me 2 different bevels in the cut - and these breaks were accross the pane so 3ft11in long. a) (using a point of fracture at one end) the bevel changed pitch through the length of the glass between 2-3mm.

but in b) (using a full length hard edge to fracture the pane) the bevel was straight at 2mm off perpendicular

I have already experienced the glass thickness vs minimum width/strip that you can break off.

My 1st attempt (method a) 1st post) was for a 3ft11in fracture to square/straighten one edge that was wavy (hand scored/cut by glazier when removing the pane from a window). The fracture failed at the far end using method a) and there was about 6in or 'extra' glass that was still attached as the width was only 1cm from score at that end and 6cm at start!

My 2nd attempt was 5-6cm from the 1st fracture... so I was giving it a better chance not to fail at the far end of the pane. Using method b) to fracture along the score, I did not fail! It was a clean fracture... it is just that the fracture is not perpendicular! DOH!

So I have improved my glass cutting skill by using a sharp edged board directly under the score to help the fracture along. This is better than the method a) Which BTW is the most common method for cutting glass as most glass cut is <3mm thick (picture framing, Stained Glass, Standard House window glass) - I thought I'd give it a go anyway!

So again How do I get the fracture to be perpendicular!

My thoughts...

Method a) shows some promise as the first few inches of fracture were perpendicular... then the rest of the fracture just went wavy bevel sad.gif .

Method b) well the whole fracture has an even bevel.

So I'm thinking back to method a) but with a full length thin Stainless Steel rod! This way the pressure point of the rod on the back of the glass is full length for the fracture and hopefully will give me a full length perpendicular fracture!. Method b) differs as the board edge is not cuasing any pressure on the fracture point till I Flex the glass with my body weight - hence I presume the clean beveled fracture!

What do you guys/gals think?


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I have sovled my own problem. Experiment and you will triumph!

So for all you DIY tank builders... here is another tip...

Due to Glass thickness, cutting/breaking glass needs extra attention - especially when you want a nice perpendicular fracture edge.

I think I need a long enough rod or edge that was straight and 4ft long.

This is to be placed directly under the score line so when breaking long pieces of glass (and even short pieces) there was an edge support the whole length of the score line.

This bottom edge support provides a pressure point to aid in the fracturing of the glass when breaking. So betten the score line and bottom pressure point the fracture will be perpendicular... or so my thinking goes!

What I think I need is a 2-4mm Stainless Steel rod.

Being round and thin the contact point on the glass pane would be a nice tangent. Stainless stell is also very tough and will not rust so I can use it for future DIY jobs.

I could even look at angle edgeing made in aluminium or steel.

Stainless steel rods are hard to find unless going to a specially metal shop.

Angle edging might not be available at a local hardware store.

So yesterday I went to Bunnings on a 'dicovery' mission.

What I found was:

* 4mm wooden dowel - not good as the grain gave uneven thickness and lines... this would mean a pressure point that was not straight, even being slightly off could generate a frature run - an uneven edge and worse off wavy edge or scolloping of the edge... so any wood product is no go.

* 6mm steel rod - nice - It is coated in oil, but any rust spots will change the straight line pressure point. Will rust - not future use for glass breaking, oiling will mean storage problems.

* Right angle edging - available in Steel or Aluminium. Steel is off the list. so I sized up a 2meter long 3mm thick 12mmx12mm edge in Aluminium. As Aluminium is soft and easily damaged I searched throught the selection and found one with a straight edge with no dings or imperfections. Total cost $7.20 (it aslo comes in 3m lengths ~$10.50)

Ok how to use it...

Well as soon as I score the glass...

I lay the angle edge so that the point (90deg angle) is at the top.

I position the glass pane so that the score line is right over the angle edge.

I put a few telephone books on the main glass pane to weight it down and get better contact with the angle edge.

I then break the glass... and wow... it is pretty close to perpendicular and very clean.

This is much more suitable for a DIY tank!


I have done some minimum width edge tests and have found that with 6mm thick glass I can get a perpendicular break:

- 10mm break-off piece from edge for a 50mm wide strip (offcut).

- 2.5-3in break-off piece from edge for a 3ft wide pane.

Note - the longer the score line the wider the break-off piece will need to be. Otherwise you will not have enough even pressure to snap the break-off piece cleanly and your edge will be wavy and worse... you will only snap a small piece off and leave the rest.



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hi Gigitt, I make all of my own tanks from fry 12"x12"x12", breeding tanks 18"x18"x18", grow-out tanks 6'x18"x14".

I have used 'old' glass from discarded windows which does not break clean. New glass breaks clean 100% no probs. I have a sheet of wood which i lay the glass on, scour the glass and snap along edge of wood holding both ends of glass approx. 3-4" in from edge. For smaller cuts of glass for lids ect. i usually hold glass approx. again 3-4" high and drop along the sharp edge of a piece of timber (1/2"x4") again no probs.

hope this helps, keep it simple.

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I tied that see b) in my first post - break was clean but beveled.

My Glass panes are 18 years old.

My new method works a treat.

* Lay Glass on mdf board.

* Measure Size, mark with masking tape edge under the glass.

* Layup the straight edge rule so that the glass cutter wheel is cutting along the masking tape positions, and clamp down.

* Score the glass.

* Remove the clamps and straight edge rule.

* Tilt up glass so I can place the aluminium angle directly under the score mark.

* Add some phone books for weight on the other side of score line - adds even pressure on aluminium angle.

* Wipe a water soaked tissue over score line.

* Cover score line with newspaper - to stop glass splinters flying about.

* Hold glass evenly, and lith light even pressure bend offcur down.


* Glass is cut cleanly and perpendicular.

* Finish off glass edges by rubbing Wet and Dry paper with a block.


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