Accurate work requires accurate setting up of the machine. This is important even for DIY work. I find that sometimes it is difficult to line up the tailstock with the headstock and chuck centre, locate centres on work in the milling attachment, or set up height of tool bits in the tool post. Traditionally depth and height gauges are used. Without an z-axis DRO, I find it much more handy to use an inexpensive laser to do the work.
Step 1: What Are Required
The following are needed:
One 5V DC small tubular "industrial" alignment laser, red light
Power supply - any surplus phone charger rated at 5V DC 100mA+/-, or battery box with 3 "AA" batteries
Small piece of brass shim
Small "Industrial" alignment lasers are available from e-stores at very reasonable prices. These are similar to the pen pointers which you can pick up from any dollar-store. They are however focusable and are housed in robust metallic cylinders which can be mounted accurately in the lathe chuck. The one I bought needs only 5V DC and very little current. This can be supplied either from a discarded phone charger rated at 5V for a few hundred milliamps, or a battery box with 3 AA batteries (4.5V which is good enough, in fact the laser would probably operate on 3V).
Step 2: Make Pinhole Aperture for Laser
The laser arriving in its box is focusable to a narrow beam of maybe a few millimetres. For alignment work on the lathe, this is not sharp enough. Nevertheless, it is quite simple to reduce the cross section of the beam to less than a millimetre, even to a fine point.
The aperture of the laser housing comes to about 8mm in diameter. Take a small piece of brass shim and punch or cut out a disk of the same diameter. Using a sharp steel pin, puncture the brass piece at its exact centre with a tiny hole, say 0.1mm in diameter.
Unscrewing the laser aperture cap, you can see the focusing lens. Place the small brass disk over the lens and replace the cap. The disk should sit snugly inside the screw-on cap.
Step 3: Test Use and Conclusion
I connect up the laser with a phone charger. The positive lead on the laser is usually red and the negative black. On the charger, the leads are usually black, with the positive lead marked with a continuous or broken white line running along its length. If there are no distinctive markings, then it will be necessary to test for polarity with a multimeter. If the polarities are correctly connected, the laser lights up as soon as the phone charger is plugged into the wall socket.
A narrow red beam is emitted from the laser and can be projected onto a flat surface many feet away as a tiny dot. This can be reduced further in size by turning the laser cap to refocus the beam.
I put the laser in the self centering 3-jaw chuck. I place a card in front of the tailstock, firstly to refocus the laser, and then also rotate the chuck and laser by hand at least 360 degrees to make sure that the laser dot remains in the same spot, indicating that the laser is concentric with the chuck and there is no runout. Indeed I find out that the label stuck on the laser prevents the tube to be chucked concentrically so I inserted only the bare part of the cylinder. I have since removed the label so that I can insert the laser more fully into the chuck.
A bright laser dot appears to be a little fuzzy because of glare around the fringes. However if viewed through a pair of laser protection goggles the glare is cut out and the tiny spot becomes crisp and crystal clear.
I put a dead centre in the Jacobs chuck on the tailstock. The laser dot falls slightly to one side which indicates that the tailstock is not quite concentric with the headstock. I am able to adjust the tailstock until the laser dot falls squarely onto the dead centre.
I am also able to align the tip of a tool bit mounted on the tool post so that it is just illuminated by the laser beam.
I intend to use the laser to line up work, particularly those mounted on the milling attachment, to locate drilling or milling centres accurately.
Step 4: Epilog: a Little Embellishment
The laser focusing lens is held in place by a helical spring and is liable to be disturbed from time to time. Also, even though the laser cylinder is reasonably round and great care has been taken to pierce the pinhole aperture and lined up at the exact centre of the lens, I found that the narrow laser beam still had a minute deviation from true centre.
I therefore took a steel rod about 19mm (3/4") in diameter, 45mm long. I turned it on the lathe to make it round and concentric with the headstock. I bored a 12.5mm cavity 36mm deep at one end and drilled a 3mm hole through from the other end. I tapped three M4 holes at 120° intervals on the side wall. I secured the lens and cap with a drop of locktite blue on the threads. I placed the laser, lens side first, into the cavity. I then inserted three grub screws into the tapped holes to hold the laser cylinder firmly in place. I used two black and one silver grub screws. The silver colored screw helps the laser orientate at the same location in the chuck everytime.
I mounted the laser with its new housing in the chuck and pointed the laser dot onto a card placed in front of the endstock. By tweeking the three grub screws, I was able to move the laser dot into a fixed position which does not change nomatter how I rotated the chuck. I then secured the grub screws with a few drops of locktite blue.
I am now confident that the laser will remain true everytime I use it.