[cpcp]

Hi,

I would like to cut out a glass table top but it would be too large for my CNC router. The glass to be used must be of the newer "low iron" type i.e. almost colourless -but also weaker than usual.

Is a possible solution to CNC a guide and then apply this to the glass and hand rout? I have no idea of the type of tool to use, coolant/lubrication requirements, clamping requirements or (perhaps most importantly!) safety issues.

Thanks for any knowledge.

[ZipSnipe]

What thickness? How big and what type of edge do you want? Diamond coated cutters is what you want to use and turpintine for coolant. But if the glass is 1/4" to 1/2 inch then just a regular glass cutter(diamond wheel type) and hand cut it with the cutter and straight edge. If its a funky shape then have your cnc machine cut out a template leaving 1/16 to 1/8 " short of the size you need and then hand cut it. You need a orbital sander with diamond sand paper to smooth out and polish the edge.

[cpcp]

Hi ZipSnipe,

The thickness will be about 1/2" and the shape will be quite curvy and complex. From what you say I have to score a diamond wheel around a CNC pattern -right? I seem to have trouble cutting a STRAIGHT edge in glass so this could be tricky for me! I guess I have to get the score correct first time.

Does the diamond sandpaper need to be lubricated to cut back better?

If I wanted a rolled edge do I go around the edge with a diamond routing bit?

Thanks again.

[kkenny]

Have you considered water cutting?

[ZipSnipe]

1/2 curves are very hard to cut. If you have never cut glass before then I suggest getting like a small section of 1/4 glass practice cutting a few times. For curves I usually cut the top side first then I flip the glass over and I take a pair of pliers that have a rubber grip and I position the handle so that it is centered up with the score on the other side then I press down until a crack appears , I keep pressing around the score always pressing behind the crack and not out in front of it. Be prepared as cutting glass requires skill. You have to think like glass and picture where it going. Glass prefers to go the straightest path. For sharp curves, instead of running the cutter around the bend of a pattern, I,ll run it at a slight curve and off the glass. I,ll the just grind the sharp curve with a sander. Some wd 40 is what I use for a sanded polish look(smooth frosted). Let me ask you this why don,t ya make the pattern and take it to a glass shop and have them make it for ya, I,ll give ya an example of cost here in the states. Your probably lookin at $50 for a pattern charge and for 1/2 super clear like you want with polished edge is about $25.00 per sq. foot.
Good luck

[cpcp]

Thanks ZipSnipe,

It sounds like a steep and probably expensive learning curve for my skill base and so (even though I like to do almost everything myself) I think I will have to sub-contract this one out. Thanks very much for the ballpark costs as it will help me negotiate a competitive rate and all your help has saved me time and expense.

Kkenny I think you are right, all the big cutting companies tend to use water-jet cutting.

Thanks again

[ZipSnipe]

Out of all my vendors only one has a cnc water jet machine(they are also the highest price and so I never buy from them). Most shapes can be cut by hand but when dealing in thicker glass it is usually a very experienced hand that cuts it. I never cut 1/2 glass , I always just order it cut to size(lot easier). You never did say how large it was or if it lays on top of a surface, on top of pedestals or inset?

[blackc1]

I work in a laser optics laboratory and we machine and shape glass exclusively.
If you have a cnc machine to cut the template why not use it to cut the glass? what we do is use wax to affix the glass to another piece of glass then to a piece of metal (aluminum, steel) then you can use clamps to hold the metal so you don't have to clamp directly onto the glass.the reason we wax the glass to another piece of glass is so you can cut into the second piece of glass all the through the top piece of glass. the drills we use are a sintered metal diamond mix. the feed rates are pretty slow (1/2 IPM or less) and we use a synthetic oil/water mix for coolant.

[cpcp]

It is to be a table top resting on the table skirts and leg tops -the size is about 1 metre (3 feet) by 2 metres (6 feet.)

I initially was going to use acrylic but there is a consumer prejudice about how acrylic (even the newer tough surface grades) scratches. It is a little annoying because glass scratches also of course but I have to be pragmatic and "give em what they want."

That is the reason I was looking at the 1/2 inch but it occurred to me today that perhaps if thinner glass was easier I could just veneer a shapped acrylic top with shapped glass. This may just be complicating things as: two cutting jobs are required and also shrinkage of bonding material may crack the glass over that large surface area.

One other aspect that I probably need to cost out too is to get the cut piece(s) "hardened" for safety.

[JEST]

Bonding would be tough
If the edges are exposed, it is hard to hide air gaps.
If you have no air gaps, the bonding needs be completed in a vacuum to prevent fogging (moisture drops).
This is assumming you arent going to try to do a complete surface bond. I can't imagine how to prevent bubbles/dust getting trapped.

CNC is not too bad for unskilled "curve" cuts in glass. (assuming you are CNC adept). Use the outer edges of you glass for edge pressure testing. (how much material at what feed rate with how much coolant for your tools...)
I would try cheaper thinner glass for initial tests. Glass is a crystalline structure. It chips and fissures if stressed wrong.
If part is too big, can you machine halves or thirds?