Glass/mirror cutting

What skills to learn, what tools to get
Post Reply
jacob
Site Admin
Posts: 11335
Joined: Fri Jun 28, 2013 8:38 pm
Location: USA, Zone 5b, Koppen Dfa, Elev. 620ft, Walkscore 73
Contact:

Glass/mirror cutting

Post by jacob » Mon Feb 26, 2018 1:00 pm

I'm trying to cut a big 1/4" thick mirror. The cut is 25" long. The mirror itself is about 40x25"

I've used a $2 glass cutter and scored the line (one continuous motion). I tried tapping underneath hoping that the part would snap clean off. After some failed attempts, things were looking ridiculous so I decided to make it more ridiculous and brought out the heavy machinery: a 1 pound ball peen hammer. I hit the glass harder than I would comfortably hit my hand. Nothing!

What to try next?
https://www.amazon.com/C-R-Laurence-Pla ... 001Q5HMAE/ (big ass running pliers)
http://crlaurence.com/crlapps/showline/ ... elID=13595 (8" running pliers)
A ghetto solution that involves a bar clamp and some strategically positioned wood or metal blocks to apply pressure analog to the running pliers

I don't mind sacrificing the mirror in the name of science.

PS: I don't think the mirror is tempered. I've also cut thinner glass in the past, no problem, but this one defies me.

Toska2
Posts: 272
Joined: Fri Nov 20, 2015 8:51 pm

Re: Glass/mirror cutting

Post by Toska2 » Mon Feb 26, 2018 2:09 pm

If you have the wood... Make a giant one

Three 2x4 30" long
Two 2x4 10" long
Two large C- clamps (8-10")
One 1" pipe 25" long.

Make an rectangle with two 30" and two 10" 2x4s.
Cut a notch in the third 30" 2x4 for the pipe to wedge/stabilize.

Placing the rectangle so the gap is centered over the scored line. The long edges touching the glass. Some hot glue might help with holding the pipe-2x4 together. Place the third 2x4 and pipe underneath and evenly squeeze together with the C-clamps on each end.

Campitor
Posts: 863
Joined: Thu Aug 20, 2015 11:49 am

Re: Glass/mirror cutting

Post by Campitor » Mon Feb 26, 2018 6:42 pm

I've had success cutting large pieces of glass by scoring deeper than usual then placing the score line over a nice straight piece of wood that spans the entire scoreline. Press down firmly but quickly near the center of the scoreline - the glass should break clean unless it's too thick or your cutter wheel is dull. I've cut glass successfully this way but it does take a bit of "feel" to get it just right if you've never done it before. Here is a youtube vid that mirrors my technique (I used gloves instead of slippers): https://youtu.be/442A8BEDoVs

Riggerjack
Posts: 2671
Joined: Thu Jul 14, 2011 3:09 am

Re: Glass/mirror cutting

Post by Riggerjack » Tue Feb 27, 2018 2:01 pm

Not much experience, here, but...

Did you clean the mirror? Even dust can interrupt the score and cause problems.

Did you hear the scraping sound when scoring? You have to press hard enough for the blade to provide an even score. And you scored the glass tace, not the silvered face, right?

Did you use a cutting oil of some kind? Again, for a better score.

Did you wipe the score with kerosene, and set it ablaze? Sounds wrong and dangerous, but I have heard of people doing this successfully. The theory is a temperature change, causing stress at the weak point you created. I have never tried it, and would recommend doing more research before trying it, but it's an idea.

When I replaced the inserts in my front door, I went to an art glass place, picked out the glass I wanted, and paid to have it tempered. Cut glass has a sharp or ground or ground and polished edge. Tempered glass has a unevenly round edge, as it was heated til soft, then tempered.

Hope that helps. Good luck.

Campitor
Posts: 863
Joined: Thu Aug 20, 2015 11:49 am

Re: Glass/mirror cutting

Post by Campitor » Thu Mar 01, 2018 10:11 pm

@ Jacob

What was the end result of your experiments? Did you manage to break the mirror cleanly?

jacob
Site Admin
Posts: 11335
Joined: Fri Jun 28, 2013 8:38 pm
Location: USA, Zone 5b, Koppen Dfa, Elev. 620ft, Walkscore 73
Contact:

Re: Glass/mirror cutting

Post by jacob » Fri Mar 02, 2018 1:39 pm

Well, I broke it alright, but not cleanly. The next breaker-jig will have to be more elaborate. I think it's key to get the groove as deep as possible and make the "wedge" from the unscored side as wedgy as possible for maximum force concentration towards the score. Otherwise, given the thickness of the glass, the scored microfracture is too free to "wander"---which is what happened.

Campitor
Posts: 863
Joined: Thu Aug 20, 2015 11:49 am

Re: Glass/mirror cutting

Post by Campitor » Fri Mar 02, 2018 10:53 pm

I've cut tons of tile for bathroom and kitchen renovations. I used to be a big fan of tile saws -they are very good. But the manual tile cutters can make straight cuts in thick tile very cleanly without all the mess and noise. The simplicity of its design makes it possible. Below the cutter head, which is suspended on metal rails, there is a 1 millimeter thick metal edge that is raised roughly 1 millimeter above the bed; its makes for a very sharp and narrow edge which the snapping fins can put pressure against when snapping the tile. An adjustable edge on the cutter bed holds the tile in place so the scored line doesn't shift away from the metal edge underneath.

Perhaps you can jury rig a plywood board and a metal edge for the same effect. You can use a circular saw to make a thin kerf in the plywood that you can wedge a metal strip or perhaps a hardwood strip. Look at this tile cutter on Amazon for details: https://www.amazon.com/QEP-10630Q-24-In ... B008O0W7RC. Zoom in on the bed of the cutter and you will see that thin metal edge in the middle of it - hopefully this can give you some ideas on what I'm talking about and inspire a suitable duplicate you can build. Here is a video of a tile cutter in action: https://www.youtube.com/watch?v=_YgfKBaDUiY.

I feel somewhat silly making the above suggestion - I'm sure you've probably used a tile cutter a few times and perhaps you've forgotten about this simple but effective design.

Post Reply