18mm lens spacer and adjusting the air nozzle
Posted: Tue Jan 03, 2012 6:29 am
My previous adventure with disassembling the lens had me doing lots of test firings with and without the air nozzle. I noticed that the spots fired with the nozzle were ever so slightly elliptical. With very short, low power shots into paper you would see a clean hole with a dark elliptical halo. Today I verified by removing the nozzle that the halo goes away.
To permanently eliminate the halo I did two things:
1. Finally cut a spacer ring (DXF attached) to center the lens in the holder. It's actually a slotted 18-22mm ring cut from 1/16th acrylic. It sort of snaps in past the threads and leaves a perfect 18mm opening for the lens. This is far superior to my previous attempts to center the lens! For one thing I verified that my spot moved slightly when I reassembled.
2. I zip-tied a laser pointer to a dial indicator base and set it up (parallel to the gantry, between the gantry mirror and the carriage) so that the red spot coincided with the test firing of the laser. This allowed me to test-fit the air nozzle several times. With the cheap red laser pointer there was always a "halo" effect around the spot, but I could readily see from that how well centered the spot was. I used 1/4" copper foil tape to shim the air nozzle until the red spot/halo were as centered as I could get. Trying to just aim the nozzle before tightening it didn't work because it would always register itself against one of the mating faces. It actually took quite a few layers of tape (in my case above the screw clockwise from the air input) to get it aligned.
Finally after that I shot a new test spot with the nozzle in place and it's nice and sharp with no halo. I'm curious to see if I pick up some extra cutting power as well.
To permanently eliminate the halo I did two things:
1. Finally cut a spacer ring (DXF attached) to center the lens in the holder. It's actually a slotted 18-22mm ring cut from 1/16th acrylic. It sort of snaps in past the threads and leaves a perfect 18mm opening for the lens. This is far superior to my previous attempts to center the lens! For one thing I verified that my spot moved slightly when I reassembled.
2. I zip-tied a laser pointer to a dial indicator base and set it up (parallel to the gantry, between the gantry mirror and the carriage) so that the red spot coincided with the test firing of the laser. This allowed me to test-fit the air nozzle several times. With the cheap red laser pointer there was always a "halo" effect around the spot, but I could readily see from that how well centered the spot was. I used 1/4" copper foil tape to shim the air nozzle until the red spot/halo were as centered as I could get. Trying to just aim the nozzle before tightening it didn't work because it would always register itself against one of the mating faces. It actually took quite a few layers of tape (in my case above the screw clockwise from the air input) to get it aligned.
Finally after that I shot a new test spot with the nozzle in place and it's nice and sharp with no halo. I'm curious to see if I pick up some extra cutting power as well.