cutting circles out of glass - tips ?

Your safest bet is to core drill the hole. Do not try to scratch it.

Randy Hansen SC Glass Tech. Scam Diego, Comi-fornia

i did this. i took a 3" hole out of the interior of a 16" disk.

draw out the interior hole with a sharpie. use a minibit on your grinder to drill a sequence of holes around the perimeter of this line, and a few on the interior of the circle in a small area. score around the perimeter. make lots of scores between the perimeter holes and the interior holes, and across the diameters in a lot of places. CAREFULLY break out the small areas between the interior holes with grozers. work on grozing out the rest of the interior pieces. use the large grinder head to smooth out the perimeter.

if you do it wrong, you just start over.

ps: i heard of someone just scoring the interior cut, and then just punching out the hole with a fist.

even after repeated attempts and should you be successful, the doughnut (hole) will always be at risk for cracking. Add heat from a soldering iron and for sure a recipe for a crack.

Watch how they "cut a hole" on TV or the movies ....they usually show a sliding door, and we all know that is safety glass, cannot cut a hole in it.

\if they could tap on the inside (other side) of the glass why would they have to cut a hole to gain entry......

MUST BE TRUE< MARTHA, I saw it on TV!!!!!!!!!!!

BUT, I too have succumbed to the hole cutting in glass fro an "unusual" effect.....

-- snipped-for-privacy@yahoo.com In the words of the IMMORTAL USED CAR DEALER: THERE IS AN ASS FOR EVERY SEAT!

Although it's easier to just drill the hole out, you can cut a circle out from inside a piece of glass. Here's a method I use as a demo in my Cutting Clinics. It's very effective at demonstrating "impossible" cuts.

1. Score the circle you want. Unless you're EXTREMELY good cutting by hand, I'd suggest using a circle cutter.

1. Turn the glass over, lay it flat on your table, and tap the circular score until it has cracked completely along the score.

2. Turn the glass back to the original side and score an "X" and a "+" to divide the circle into 8 pie-shaped pieces. (BE CAREFUL to NOT run the score past the original score for the circle. Stop those scores about 1/8" short of the circle score.

1. Turn the glass over, again lay it flat on the table, and tap those scores until they have all completely cracked.

2. Stand the glass up vertical and tap the center where the scores intersect. The pie-shaped pieces will fall out leaving a hole in the glass.

You can also use this same method to cut out extremely complex shapes other than circles.

As I tell my beginner students.... all those cat burglar movies where the guy scores a circle and suction cups it cleanly out are BS.... you need to be on the inside of the window to tap it!

Hi Randy

Thanks for the advice..... ....unfortunately I don't have a core drill. I'm going to need to be able to do this to produce a range of specific sizes - might involve quite a few core drills.

Time is the one commodity that I have plenty of - I'll just have to try the other techniques that people have suggested - but thanks for the suggestion anyway....

Regards Adrian Suffolk UK

HI Howard

Yes - I suppose that's where the core drill solution wins - in that there's no extra stresses induced in the glass.

Thanks Adrian Suffolk UK

Hi Charles Thanks for the comments

Same principle, I'm looking at 1" holes from a 3" x 2" rectangle

= glass cutter ?

Sounds like a plan. The problem I was getting was that the circular score was OK, then I made scores across the circle like spokes of a wheel - and they ran OK

- but they wouldn't break out because they had 'nowhere to go'.

I guess that the ground out holes help with that....

I've had plenty of practice at that step !

Sounds like a recipe for a trip to the Emergency ward! Don't think I'll try that

Many thanks Adrian Suffolk UK

Hi Dennis Thanks for the detailed reply.

yes - was going to use a circle cutter anyway...

I've been running the crack by tapping with the 'blunt end' of the glasscutter - your way sounds more controllable - I'll try it.

Tried this with 4 sectors - but not been able to get 'the first piece' to come out - I'm sure that, once one piece is out then the rest will follow without too much drama

Presumably to the accompanyment of a drum-roll - certainly sounds like Magic! - I'll gve it a try.

I think I'll stick to circles for the time being - but what kind of shapes were you thinking of ...?

Many thanks Adrian Suffolk UK

One possibility would be to use a Taurus bandsaw with a sectional blade. You'd have to drill a small starter hole in your work piece to thread the blade through, and then you could saw the circle.

Also, you could drill a hole in the work piece that would be big enough to get a small grinder bit started, and just use your tabletop grinder to grind out the hole from the inside, increasing the bit diameter as you go.

If you have sandblasting capabilities, you could just mask off everything BUT the circle you want cut out (on both sides of your work piece) and blast the hole into the glass,

Hi Moonraker Thanks for the comments.

Of the three options I only have a grinder - that might be a plan.

I had considered a sort of composite approach - score a circle, then use the grinder to make a starter hole in the centre (on secord thoughts - probably hole first _then_ score circle!).

At least that would give the 'scrap' glass somewhere to go - st the moment I do quite well with the scoreing and running - but the darned thing won't come out of the centre.

Eventually I give it one tap too many and the piece of glass that I want ends up as three pieces of glass. Very frustrating!

I'll have a 'play' with the grinder method.

Thanks Adrian Suffolk UK

How well the blunt end of your cutter works for tapping depends on how small that end is. The screw cap on Toyo cutters is enormously too large to be used for tapping. Some old style glass cutters had a ball on the handle end. Those are fine for running straight lines but considerably too large for curves. The old style metal cutters WITHOUT a ball end are perfect. If you can't get one of those, a Phillips screwdriver (X end) works beautifully. The object is to have a tip small enough to be able to strike ONLY on the line to be scored.

As pointed out by Moonraker, you MUST tap on the back of the score. Although some tappers hold the glass upright while tapping, you'll have much better success if instead you lay it down flat while tapping. Tapping will often cause small chips where the glass breaks. To ensure those chips are only on the scrap side, tap just slightly (about 1/16") on that side. (another good reason why a small tapping head is helpful). That way all the chips will be on the side you plan to trash and the other side will have only small overhangs that can easily be taken off with a carborundum stone or on a grinder.

If you're having trouble getting the pie pieces to start coming out, it helps to score another concentric circle about half the size of the original one. The smaller the pieces inside the circle, the easier they start popping out. You're right - once the first is out, the rest fall away.

As to other possible shapes - just about anything. Another demo I like to do is to debunk the opinion that you can't cut a "V" into a piece of glass. Take your cutter and score in from an edge, stop, turn the cutter and score back out leaving a 90 deg corner. If you're patiently careful, you can tap out that piece. It CAN be done, but it's NOT something that should be done. The remaining piece WILL break out from the "V". It's an effective way to demonstrate why saws shouldn't be used for conventional stained glass. "Any cut that can't be done by hand, shouldn't have been done at all".

I would think that scratching would be near impossible for a 1 inch hole if the glass has any thickness to it. Anything thicker than say 3 mm. If this is the case, you might try Charles suggestion.

A 2.5 inch hole might be easier.

I say this with a limited experience of scratching, and a lot of experience of working with glass. The others that have responded have much more experience in this arena. Please let us know what works best for you.

Randy Hansen SC Glass Tech Scam Diego, Comi-fornia