It's interesting to know that you can make a glass from a bottle, engraving a cut all around the circumference and splitting it in two with a few tricks. If you plan to make many glasses and if you wish to obtain a perfect flat cut, you can preferably build your own cutting device.
The main advantage of using a jig like this one, is that you can obtain a perfectly flat cut very simple to refine with sandpaper (see image).
I will explain here how to make the jig from common and cheap objects.
Step 1: The Sketch
After measuring some bottles, I planned to leave about 12 cm between supports, with the possibility to increase this distance to 17 cm. This is enough to cut the standard little beer bottles and also the 1 liter ones.
My design is very simple. my intent was to build a jointed arm which could also shift along the axial direction, and sturdy enough to maintain the position while you push the cutting blade into the glass.
So I decided to use what I already had in my house, and the device took gradually shape.
Step 2: The Components
The wheels diameter has to be not more than 4 cm, and it should be cool find wheels with a rubber surface.
The wood beams are:
- one piece about 25 x 4 x 2 cm (length, high, width)
- one piece 11 x 4 x 2 cm
- about 25 cm total length of a 1 x 2 cm section beam
Then you need only some glue, different types of screws, a bolt and four rubber feet.
Step 3: First Holes
All the holes on this device are made by hand, but you could better use a column drill to obtain perfect perpendicularity.
I added a new hole in the bottom part of the wire conduit, so a total of three holes cover the full length, but you can also add two more holes, since they will hang better the "rail" on the wood board.
Then I also made four little holes in the top cover, which is 8 cm long. These holes are not centered on the shorter side, to avoid interference between horizontal and vertical screws.
Step 4: Let's Make the Joint...
A pair of long screws acts as joint of the wood arm. So cut a couple of wood pieces 3 x 2 x 1 cm and, about 7 mm from the border, drill an hole in the direction of the longer axis. Dispose the pieces on a flat surface, and mark the holes position from the conduit cover. Then drill the four holes for the screws.
Step 5: ...and the Arm
Let's refine the arm head so that it could keep handy the cutter. I tried to use the cutter as it is, avoiding to drill it. A big screw keeps it steady into a groove engraved in the wood. Since I made some upgrades to improve the operation of the tool, I also replaced the screw with a bolt, and I tilted more the cutter, as you can see in the first picture of the next step.
Step 6: Let's Assemble the Cutter Mechanism
My first attempt was to screw the two little wood blocks directly on the conduit cover. This doesn't work, because the two-parts pivot (the two long horizontal screws) has more play than a single pivot, the plastic cover isn't rigid enough, and the arm was not very steady. So I added an additional wood beam to reinforce the device.
After screwing the horizontal pieces together insert the arm and insert the long screws in the holes so to mark the position where to drill the hole in the arm.
Step 7: Glue the Beams
Place the "rail" over the bigger wood beam and mark the positions of the holes. Drill the holes but wait to glue the pieces to screw the rail in.
Put two wheels on the board to have the exact position where to glue the big beam. I used two-elements glue to be faster, but you can also use normal wood-glue.
Step 8: The Rollers
Meanwhile the longer beam fastens you can drill the holes for the rollers. I used very short screws so they don't stick out the bottom surface of the board. The last two rows of holes are to shift two wheels so that a larger bottle could be held.
Step 9: Rail and Rubber Feet
Now assemble all the four wheels, screw the rail in place, add four rubber feet, clean the surfaces... the main piece is almost ready.
Step 10: Some Finishing
Since the trolley cover moves loosely along the rail I decided to glue two nylon stripes inside the longer edges. I've cut the stripes from a nylon cake tray. You can also smooth them with sand-paper.
Use cyanoacrylate glue, and to be sure the stripes are kept pressed during the drying, apply the cover on the rail as soon as applied the glue.
This solution works great, and you can set up the resistance of the movement simply moving fast the "trolley" to and fro, since the heat will consume a bit the plastic, mitigating the opposition force.
Step 11: The Bottle Stop
Glue the last wood beam so that it will act as stop for the bottle. Check that it's high enough to reach also the biggest bottles. This beam will also act as bracing for the rail, so add some glue between the two boards.
Step 12: Test It!
Unfortunately there were a couple of mistakes in my design:
- as I explained before the arm joint was not very sturdy
- the cutter's blade wasn't reaching the glass of biggest bottle, because the steel frame touched at first
- blade route was a bit misaligned with the circumference, and it drifted out of it
Step 13: Solve Issues
- I added the 8 cm wood beam between conduit cover and wood blocks, that makes the joint stronger
- I re-designed the arm with a tilted groove
- I filed the groove surface with more attention to alignment, and I added a more reliable bolt as connection for the blade
Step 14: What's Missing?
Glasses? Yeah, you're right... since I'm not very skilled in this technique, despite the perfect groove, I've broken all the bottles I've at home!
You've to wait some time, that I'll drink more beers and I'll try again... meanwhile you can look the many good step-to-step and video instructables about this same topic.
Step 15: I Did It!! [UPDATE]
Finally I did it! After engraving a SINGLE cut around all the circumference I rotated the bottle over the little burner, after half minute I paused ten seconds, then I let some drops of cold water fall over the cut, and I heard the crick, I put the bottle over the flame again and it split!
Anyway, there is enough space between the two sets of wheels to contain a common tea light, so that you can heat the bottle spinning it on the same gear. I will try that solution next time.
With medium and fine-grained sandpaper I refined the border sanding it on a flat surface and removing the sharp edges. After that it appears awesome! ...yes, this is a tiny cup for coffee, nothing special... but it's funny anyway!
Step 16: Last Improvement [UPDATE]
To obtain a perfect cut, I had to change the wood arm into a sturdier metal brace, and with the use of a column drill I built a new carriage with perfectly aligned joint. I was so lucky that I found in my junk that metal U profile with perfect length and with already the four holes! :-)
I had to smooth out the wood edges under the arm to let it moving. In addition this carriage is higher than the first one, so that I can cut bigger bottles with less bending of the blade, and pushing it from above and not from the side.
Step 17: The End?
This new solution works very good, since the joint is made by a single steel bar passing through all the length, and you can lock the blade on the arm without worrying about the wood deformation.
When you push the blade against the glass it remains exactly on the circumference, and at the end of the rotation you'll hit the start point of the trace, this is essential to make perfect splitting.
Since I've a good spring which fits well on the side of the arm, I'm planning to add it so that the arm will lift when you release the pressure, that will be cool... stay tuned ;-)