Glass Cutting query

On Wednesday, July 31, 2013 4:03:46 PM UTC+1, Adrian Brentnall wrote: <snip>

Agreed - you want to avoid stress concentrations apart from the one along your cutting line... If you happen to have some pliers like these http://www.toolbox.co.uk/maun-4860-160-flat-nose-plier-2870-76920 then use those rather than ordinary pliers - but still put a piece of gaffer tape on each jaw. (I hadn't realised they still made them - mine came from a secondhand shop many years ago...)
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On Wed, 31 Jul 2013 14:53:20 +0100, Bertie Doe wrote:

I read it that a small section of the radius was done then the score taken straight to the edge of the waste, then repeated. I must admit I'm dubious about the tapering to zero bit that this requires...

I wouldn't think so, glass is actually pretty strong and flexible but extremely brittle so when it goes, it goes suddenly and completely.
Cutting is no more than a controlled break, the score gives a weak point and increasing the stress by flexing to open the score produces crack propagation from the bottom of the score through the thickness of the glass and along the length.
--
Cheers
Dave.
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On 31/07/2013 16:06, Dave Liquorice wrote:

It can work..... and sometimes does The thing with glass is that it's an odd material, and it's all about persuading it to break along the line that you want. Not like 'cutting' (say) a piece of timber - where you're more or less in control of it.

There's two types of pliers in glasswork. The 'grozing' pliers have one flat jaw and one curved jaw - and that's the ones that he's using to cut the arc in the video. Make sure that the score is on the top of the glass, and the flat jaws are also on the top-side of the glass. The pliers are used the other side up to 'groze' (= roughly grind) away at the edge of the glass if it's a bit on the large side. Only works well if the finished edge of the glass is going to be concealed (e.g. in a timber frame or lead-section). If you need to remove small amounts from the edge and still have a clean finish then you use a diamond-grinder (not an angle-grinder!) running in water.
The cut-running pliers are used across the score-line, and have jaws that are vee-shaped, to apply pressure to the score-line. You sometimes find cheap versions used for snapping ceramic tiles - these'll do for occasional use on glass.

True. It helps to imagine the glass like a balloon - with a thin 'skin' on the top & bottom surfaces. Scoring the glass correctly weakens the top 'skin', and applying the right amount of pressure to the glass in a controlled fashion enables the glass to fracture along the score-line.
Straight line cuts (e.g. windows) are less critical, and you can often get away with simply scoring and then snapping the glass over a lath or ruler.
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"Dave Liquorice" wrote in message
On Wed, 31 Jul 2013 14:53:20 +0100, Bertie Doe wrote:

I won't bother with the breaking plier, I'll try Adrian's method with duct tape on an existing pair.
What type of cutter do you use, diamond or wheel? I just phoned Homebase and their OB version has a single hardened wheel and sells at £5. Ebay has a lot to offer in that price range, including a German one, with 5 replacement wheels. Not worth spending on a high-end model, due to low usage.
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On 31/07/2013 16:55, Bertie Doe wrote:

Should be OK - take it gently!

Most glass folks will use a variation on a wheel-based cutter.
I use mostly pistol-grip cutters (3rd one along on this page) http://www.warm-glass.co.uk/advanced_search_result.html?y=-63&x=-796&keyword=glass+cutter&search_in_description=1
but that's just because I find them easier, and it's less strain on the wrists after a day cutting glass. The 'pencil-grip' type should be fine for what you're doing. Experiment to find a way of holding it that lets you get enough pressure, without stopping you from being able to 'guide' it.
Find a spare bit of window-glass, and cut a 2"-wide strip. Then start off making short cuts across the glass to make it into 2" squares (if it's a bit second-hand, don;t forget to clean it well first. The slightest bit of grit on the glass will make your cutter 'skip', and that's not going to help.)
Once you've got a stack of perfect 2" squares. Cut yourself another strip, and then practice cutting 's'-shaped lines across it.
Once you've done that, you'll have got the feel of it, and you should be able to have a go at the actual job.
Adrian
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"Adrian Brentnall" wrote in message

Google brings up 'Toyo' a lot in the mid-price range:-
http://www.ebay.co.uk/itm/Toyo-TC-10-STYLE-Pistol-Grip-Cutters-in-Colours-/110807644926?pt=UK_Crafts_Glass_Art_Supplies_CV&var=&hash=item19cca67afe
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On 31/07/2013 22:20, Bertie Doe wrote:

Yes - that particular one is a 'Chinese copy' - see the line "These are not TOYO HEADS OR HANDLES just same style".
But - having said that, they're half the price of the genuine item - and would be perfectly fine for occasional use. I have both the pukka Toyo, and 'copy' Toyo cutters in the workshop, and I tend to use whichever one's closest at the time - I'm not sure I can tell the difference between them.
If you're feeling extravagant <grin>, the same supplier will do you a pair of 'no name' grozing pliers for under 9 quid.
Adrian
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"Adrian Brentnall" wrote in message
On 31/07/2013 22:20, Bertie Doe wrote:

Still at the project planning stage. I'll try using tape on some bull-nosed pliers. The duct tape will also come in handy, if I run out of Elastoplast.
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On 01/08/2013 09:42, Bertie Doe wrote:

See - you're getting the hang of it already! <grin>
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On 31/07/2013 16:06, Dave Liquorice wrote:

I believe the crack propagates at the speed of sound in the material.(Googles ...) - yes, approx 11,000mph for glass.
--
Reentrant

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A diamond cutter is the best. You must get the cut in a single "stroke". If you do it again, the crack runs off the line. You can also get a tool like pilers that "folds" the glass to break it.
Cutting a hole requires a "compass" device to get a single circulat cut that joins exctly. More smaller concentric scores are made and about twelve radial ones. They must not cross the outer ring. The glass is broken out from the centre by tapping it. Only works on new glass. I have had a high cockup rate too.
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On 31/07/2013 11:01, Bertie Doe wrote:

Nothing to it. Dead easy.
If you sign a pact with the Devil....
--
Dave - The Medway Handyman www.medwayhandyman.co.uk

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