DRILLING WITH THE CROSS CARRIAGE

 

Drilling on the lathe is normally accomplished by mounting the drill chuck in lieu of the dead or live center. On the TAIG, it screws directly to the sliding dead center and is then actuated via the drilling lever. It is a nice system as it gives the operator a very good feel on how the drilling is going by direct feed back from the drill bit. Most other lathes utilize the knob or crank system to move the center or drill chuck to and from the work. They both have their good and bad points. In my own view, they are both lacking in one very important point. They do not provide an easy way of accurately judging drilling depth. I suppose one can rig up some sort of elaborate dial indicator / depth gauge affair to it but it would seem to be more work than it's worth.

The better alternative still uses a dial indicator, but mounted on a simple "pot" magnet, available for a few bucks in many sizes from all mail order industrial tool companies. It sits to the right of the tool post with the tip of the dial indicator bearing on the right side of the carriage to measure its longitudinal travel. To perform the actual drilling operations, you need to make a tool post type holder that will hold the drill chuck. Two choices are available here, as there are two types of drill chucks. Those with threaded mounts and those with tapered mounts. After the tool post is made, you will have to either buy or make the arbor or adapter that will link the drill chuck to the post. If your chuck has a tapered mount, it might be best to just purchase a straight shank to Jacobs taper adapter. For the threaded types, you can either buy a threaded stud, available at many large home centers in their hardware departments or from a tool supply house. The studs are normally double threaded at each end with an un-threaded center section. The one you would need is the 3/8 - 24 for 3/8" chucks or the 1/2- 20 for 1/2" chucks. You could of course machine your own. The first thing to do is to build the actual tool holder. If you refer to the boring bar holder article, you will get the idea of what you will need. It is built exactly the same. Make the tool post out of a 2" square length of aluminum or steel by first facing the ends. Drill a central through hole for the hold down cap screw, reverse chuck the work and machine a 1/16" deep recess, leaving about 1/8" of material from the edges. Screw and align the tool post to the cross slide and center drill for a hole that will miss the central vertical hole, sort of half way between the edge of the post near you and the edge of the center hole. Drill and ream the hole to fit the straight shaft of the tapered Jacobs adapter. If you are using the threaded stud, start by turning the threads down on the opposite end of the stud to the next smaller fractional size and drill that size hole on the tool holder so it will accept the newly turned end of the threaded stud. Drill and tap two vertical set screw holes in line and center along the hole that will tighten the arbor in place during use. To use the drill chuck holder, you have to first align it square to the spindle center line and axis of rotation by aligning the front edge of the tool holder parallel to the front edge of the cross slide. When I say "front", I am referring to the head stock end of the lathe. The drill chuck should have its corresponding arbor, whether threaded or tapered, firmly attached. The straight end of the arbor is inserted into the horizontal hole of the tool holder so the base of the chuck is flush against it. Tighten the two set screws to lock the drill chuck/arbor in position. Because the horizontal arbor hole was drilled with the lathe, it will be automatically be aligned vertically. We have to bring it into horizontal / lateral alignment by adjusting the cross slide. Several ways of rapidly achieving this are, inserting a pointed center on the spindle and a second pointed rod in the drill chuck and lining up the two points by adjusting the cross slide. My favorite and I believe, fastest method is to have previously center drilled the end of the arbor stud that should now be protruding through the other side of the tool holder and align it with the tail stock dead or live center. If the tail stock center is in line and you have brought the tool post so you can insert the center point into the center drilled hole of the stud, and the pointed tool in the drill chuck also lines up with the center of a faced off surface to be drilled on the lathe chuck, you are in business. If you do it this way, you will not have to disturb any work piece on the lathe chuck during this chuck aligning procedure. It takes ten times the time and effort to explain it than to actually do it. To drill, you just advance the carriage toward the revolving work piece. To measure depth. I set up a little pot magnet on the tail side of the lathe bed and attach a small dial indicator so the plunger is almost fully depressed and bearing against the tail side of the tool post. With the drill point lightly touching the work piece and the indicator needle zeroed. As you drill, the cross carriage will move toward the head, gradually allowing the dial indicator plunger out, giving you a direct reading in thousands of an inch of the depth of any blind hole as long as it is less than the maximum dial travel of your indicator. Small blind holes for miniature screws are a constant requirement in the building of model engines and they would otherwise be at the least, difficult to drill to specific depths without some sort of measuring arrangement like this one.