Glass Cutting?

Hi All,

I have a need to make various small discs in thin glass to replace broken faces in small compasses, instruments etc, also some small rectangular windows in a couple of plane table compasses I have in my 'to be fixed' cabinet.

The glass varies between 2 & 6mm thick and the circles needed between 30mm and 150mm.

I have a variety of cutters including VITREX circular wheel cutters and diamond point cutters by Sharrat & Newth, Shaw etc but so far have only managed to break a lot of glass and get very frustrated.

Can anyone please give me any pointers, tips etc?

Some of these do need to be pretty accurate dimension wise.

Cheers, Martin

What is shown on the movies does not work, looks good but that's all.

Mark the hole with the glass cutter then nibble in to the marks to form quadrants you should then be able to remove the sections leaving the disc.

Bob

Hi Martin When I last had some glass cut the guy sprayed some sort of lube on the sheet before cutting.

When I have tried it I found a new wheel cuts better than an old one. Have a look at sites that cover stained glass cutting as a hobby might have useful info.

I use a diamond blade circular saw for cutting all sorts of glass ceramic stone parts

Very cheap from b&q as a tile cutter

stick a paper sticker on the glass mark out and then trim away then use the side of the blade to gently sand away

I did bit of stained glass work many years back. You do tend to make quite a few scrappers, especially at first. Actually if you watch the professionals, even just cutting square panes for windows they toss quite a few in the bin. Sometimes the cut just decides not to follow the score. I would mark the circle as Bob suggests, then mark some tangential lines to the edge of the piece. Bust them away a piece at a time with grozing pliers. (They have flat faces. ) Sometimes you can tap at the score with the wooden handle of a glass cutter and see the crack follow the score around, but it doesn't always work that well. Inside curves are naturally harder than outside, and of course with stained glass work you often want an inside curve.

You can grind glass. They do that for the exposed edges of mirrors. Ideally you would use a wet diamond wheel, which I have but I don't suppose many others do. You don't want to let it get hot, so take it quietly, but assuming you have got a circle pretty right but with a few bits sticking out, you can grind them off. If you are nervous about doing it under power, use an ordinary oilstone. It will take longer but is less likely to lead to fragments

One thing you could consider for the small ones...see if you can get a diamond hole saw with an inside size that is right. These are used for cutting holes in tiles. I used one for making holes for stanchions to go through brick tiles on my steps, and they were cutting lovely for circles in hard material. I haven't tried on glass, but have on glazed porcelain tiles, which are so hard that carbide won't touch them. They are used with water running onto the job.

John

As far as window panes are concerned you'll have a job finding someone to do it today. Most of it is done on machines, you just order what size you want and pick it up when ready.

As for compasses and so on you might try slide covers or similar. They are very thin but I suppose you might be able to use a few together after sealing the edges??

A little trick I was taught many years ago was once the cut lines had been scribed, run a bead of water over the lines and a nice clean break will occur. You can even use a finer wetted with spittle for speed.

However, do the same but using paraffin and you can guarantee that the break will be somewhere else but not the scribe lines.

Mike

Sorry, I was a bit misleading when I said 'windows', they are about 150mm x 20mm is all. Sounds like it is going to be a lot of trial and even more error! I have a lot of diamond honing stones so they might help.

What do the watch and clock makers do for their glasses?

Martin

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Martin,

So far as I am aware, the rough circles are produced by nibbling o a scribed line, and then ground to size and finish in a 'lathe'.

It may be worth you contacting one of the jobbing opticians.

MichaelG.

Last manual glass cutter I went to made the statement that ld glass never cuts as well as new glass. He also brushed soem liuid (water?) across before scribing and snapping.

edge ginding for things like bathroom shelves he did on a wet grooved disc.

If you ever get to see the guys that do the fancy cut glass (some of the best from the czech republic) - they don't hang about doing it. They sit in front of a set of discs of different hicknesses for the line/shape types

about 20 mins in before they cut...

Laser cutting

Neil

I've never done this so I'm an expert.

In a lathe, mount a bit of MDF in the four jaw. Stick the glass to it with PVA. Using a diamond tile cutter blade edgeways on in the tool post take a series of little plunge cuts to bring the shard down to diameter. Soak the MDF overnight in water to release the glass roundel.

In a previous life I made electroplated diamond tools; it is possible to make small trepanning tools that cut to dead to size using a sacrificial mount as above. It's common enough in fibreglass work. If you have enough of one size to do it would be worth doing.

Eug

Edited By Eugene Molloy on 20/03/2015 09:16:34

I have cut small discs by using a bit of copper tube and some grinding paste, the tube in the drill press, and the glass on a bit of wood, can't remember how long it took, but it worked. It drilled a hole through the hard face of a valve lifter too.

Ian S C

Re. watchmakers glass cutting - there is a trepanning-type tool that is used for varying sized perspex disc cutting. The cutting tool can be micro adjusted for diameter and the 'knife' is driven by a rotating handle. I had one such in one of my destroyed sheds. The recovered items are in shambolic 'storage' at the moment so I don't know whether it survived

Rgds

Bill

Buy a new glass, they are available in 0.1mm diameter increments so you should be able to find something that fits

When I have seen it done they strike a number of tangental lines from the scribed circle and snap then nibble the edges, The glaziers I normally use has what is best described as a "wet linisher" for finishing odd shapes.

Water jet or CNC machines knock them out now.

The lucky ones in Oakland California have these guys !

MichaelG.

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In the U.K. ... try here

Edited By Michael Gilligan on 20/03/2015 10:38:09

My Father showed me a few tips when glass cutting. His experience with glass was mainly repairing windows that where broken while playing ball games as you did in those days! 😱 The first thing he pointed out was never attempt to cut glass if it below ambient temperature or if it's just brought in from the cold. It seems more brittle when cold. Another point he made was the older the glass the more difficult it is to cut cleanly. The glass pane must be flat and preferably laying on several thickness of newspaper. Lastly, if your using the roller type glass cutter keep it well oiled.

Edited By Johnboy25 on 20/03/2015 11:22:07

I visited a place that made a variety of glass products many years ago. One of them in particular were glass discs about 6mm thick and about 40-45mm dia. The glass sheet was first cut into squares and then had the corners knibbled off with pliers. Fifteen or twenty of these rough billets were then stuck together with beeswax and mounted in a conventional Lathe, a Boxford I believe. The whole column of glass was then turned down to size and then the wax was melted to separate them. Sadly I don't know what tool was used to turn them though! Properly supported on both sides this leads me to think you may be able to turn them down with the correct tool?

Many years ago and quite by accident I discovered that it was possible to cut thin glass, like microscope slides for example, underwater using stout scissors to run round quite complex shapes. Those with teeth worked best and It does nothing for the scissors of course

Yes, there were failures and the thicker glass just squeezed out of the jaws of the scissors, but it was an interesting observation. The water was essential, in the dry the glass just shattered uselessly.

I have no idea how it works, but after cutting rub down the sharp edges on fine wet and dry paper

Brian

Many myths abound about glass cutting.
I was a glazier for 30 years from the age of 14. (and have the stitches to prove it).

For circles use a decent compass cutter with a well oiled axle and not too much side play in the wheel, take a couple of spins to leave a 1.5" or so ring of waste (cullet). Tap the final cut open and 'run' it all round, either with a wooden point or a knuckle. Then make a small tangential cut and tap it open to spring off the last ring off like a circlip. This leaves a small point where the final cut meets up which can be stoned down or is more often lost in the pollishing.

The wheel axles are sintred bronze and apreciate being kept in thin oil or parafin as prefered.
If the wheel has a 'skip' (flat spot) replace it, or the cut will litterally be 'hit and miss' with gaps where the vent can run off instead of following the line of micro fractures produced by the wheel pressure.
A good cut can be heard, it has a particular hiss, rather than a scratch. Old glass has a ruined surface, cuts have a greater chance of running off.

For bench work in a cutting shop a diamond if usually used. A wheel can wear out in a day, sometimes in a morning if you have several tons of glass to cut to standard sizes. Diamonds are sent off once a year to be reset onto a new point.

A diamond or grit fed core drill can produce discs. Keep it wet and cut half way through from each side making sure the bit is square to the glass, the final break through leaves a little sprue round the edge, very sharp.