Laser Instructions/Rotary Tutorial
In order to engrave cylinders using the laser cutter (bottles and other round objects), the rotary attachment is used. This replaces the Y axis with a rotating spindle.
FIXME - Need a photo of the rotary attachment. Also need step-by-step photos for setup.
This was contributed by Pavel Krasnopolski by email, and has been uploaded un-edited (with permission). If anyone wants to tidy it up, go for it.
I did quite a bit of laser engraving of glasses with the rotary stage. I was using settings around 50 for speed, 50 for power. The lower speed setting was due to my suspicion (possibly wrong) that the stage skipped some steps on a higher speed. You will need to go to the Settings menu (I think, it's under 'File') and change the step of the Y coordinate to correspond to the diameter of your glass. I usually do it by trial and error, by pressing "Run Box" and observing the angle of rotation that my engraving would cover, then figuring out the math of how much I need to correct the Y step by. I am attaching the settings I used in one of my runs. Please note, that I also decreased speeds and accelerations just in case. Obviously, you need to return them to the original settings for the next person using the laser. It sometimes requires a restart of the program for the settings to take effect.
Starting with the usual condition of laser with the flat table. Run Z datum with the aluminum cylinder. Measure the distance between the worktable and some convenient point on the gantry or cutting head (careful). Lower the table all the way down (long and boring process, just keep pressing that button). Remove the honeycomb table (very careful not to touch the lens!). Remove the grid, which the honeycomb rests on. It's rather broken and tries to fall apart at every opportunity. Now you have a flat surface to put your rotary stage on. Align the stage visually with the Y-directed beams on that flat surface. This gives sufficiently precise orthogonality to X direction. Before you disconnect the linear Y stage, align it with the axis of the rotary stage. You want the red spot to be on the axis of rotation. Now disconnect the Y stage and connect the rotary stage in its place. The connector is to the right of the table just under the control panel. Note that connector has a collar, which needs to be unscrewed before you can unplug it.
Fixing the glass into the rotary stage is more of an art. Usually, I use external edges of the chuck to gently grab the inside of the lip of a glass through some soft pads made from paper towels. Obviously, it's very easy to overtighten and break the glass. For a light wine glass this is usually sufficient, but for a beer glass you will need to improvise a holder from a piece of plywood, which has a hole for the center (the rotating cone on the stage), and several wood screws that grab the bottom of the glass. Next, you choose an average height level that you want to be in perfect laser focus and position your Z height accordingly. That's where you use the measurement you did in the beginning. The laser is forgiving of 2-3 mm of height error (out of focus), which allows to engrave curved wine glasses. For a highly conical beer glass, I sometimes raise one end of the rotary stage.
You may notice the rotary stage has a significant play. That happens when the pulley on the chuck axle shifts along the axis. IIRC, it gets tighter when you pull it away from the chuck.
It's a good idea to set your origin at the left bottom corner instead of the default left top. This will eliminate any effect of the play, because the stage will rotate continuously in one direction from start to finish, except for the final quick return.
There is a well known software glitch in the laser, which SOMETIMES makes it skip any empty spaces in Y direction (empty horizontal lines of pixels). It occurs only on certain days, depending on the current oil prices and phases of the Moon. To be on a safe side, design your engraving not to have such spaces (decorative lines, frames, etc. work well).
I discovered the laser changes its power with time. The power settings that work initially result in cracking glass after about 1.5 hours of the laser system being turned on (while not necessarily lasing). Turn it off and let it cool for about 15 minutes.
Unfortunately, there is no chance you will get the settings right at the first try, so bring 2 extra glasses that you will practice on first. I've ruined several projects, when I brought only the necessary number of glasses. If you make a set of 4 glasses for a family, bring a set of 6 at least. They WILL get cracked. And the power setting should also be adjusted to give satisfactory contrast and line width. Start with power 50, speed 50 on a test glass, but be prepared to do several attempts.