I described the fabrication of a holder for a flexible shaft tool used for drilling horizontal and vertical drilling. They are both excellent ways to put a great little tool called the flexible shaft to work for us, but unless you are using one of the more heavy duty 1/4 HP flexible shaft carving units like the Foredom and some others you will not be able use or even drive drill bits and milling bits larger than 1/8" diameter, the maximum capacity of their collets. If you own one of these larger more powerful units, you can put one to work simply by making a holder that will accept your particular size handpiece. With these, you can chose between a collet chuck or a 1/4" adjustable chuck. I would opt for the later, as you would then be able to use any size drill bit from 0 to 1/4".
I wanted to see if I could come up with a design using a heavy duty spindle with ball bearings at each end, a threaded end to accept a 3/8" chuck and the other to hold a pulley. The whole thing is powered by a piggy back mounted sewing machine motor driving a small pulley via a vacuum cleaner belt. The reduction is about 2:1, giving a 1725 rpm speed with higher torque at the bit. Basically the fabricated spindle is mounted in line with the lathe bed on a thick aluminum base and the motor is mounted on top, sitting on a platform over four columns. Let's begin with the spindle unit since it requires the most work. The spindle housing is built around two types of surplus bearings that can be obtained from American Science & Surplus in Milwaukee, Wis. The bearings are 1-7/8" outer diameter, 25/32" bore diameter and 9/16" thick, #24272 $3.00 a pair. This bearing is open so it requires dust cover. The second available bearings are also 1-5/8" diameter but with a 11/16" bore and is 3/8" thick # 23253 $1.75 ea. The spindle housing is made out of 2" diameter steel (C12Ll4 ) or aluminum about 2-1/2" long. Chuck and face and center drill both ends and set up the workpiece between centers. Take a truing up cut all along the length. Set the work up in a four jaw or an accurate three jaw chuck and begin to drill out the center all the way through if you can. If not you can perform all the drilling and boring as far as you can reach and continue by flipping the workpiece over and drill out the other end. The through bore is to be about .050" larger than the 3/4" diameter stock the basic spindle will be made out of. Once the hole has been completely bored through the work, you can begin to bore the bearing housing. the pocket for the bearing must be made very accurately. It must accept the bearing as a light press fit and be only a couple of thousands deeper than the thickness of the bearing so when the bearing cover is installed over it, it will secure the bearing against any possible horizontal movement. Bore the opposite end and after removing all burrs, put it aside while the dust covers are made. Glue on a 2" faceplate a small piece of 3/16" thick aluminum large enough to allow a 2" circle to be turned and turn it to the same diameter as the spindle housing and face it smooth. Heat with a torch and remove the dust cover from the faceplate, re-chuck it and face off the glued side. Locate and drill three equally spaced holes about 5/32" from the edge with a clearance size drill bit for a 4-40 screw. Drill and bore out the center of the dust cover to 1/32" bigger diameter than the bore of the bearings you decide to use. With some double stick tape between the spindle housing and the front dust cover to temporarily hold them together, transfer punch the three hole locations, drilled them and tap them to 4-40 thread.
Cut a piece off 3/4 " diameter 12L14 steel shaft about 5" long, chuck, face and center drill both ends. Mount it between centers and begin to turn the first 1-1/2" to accept one of the bearings as a slight press fit. This diameter is from the shoulder for a distance to match the thickness of the bearing. The rest of the shaft is further reduced to 1/2" to accept the belt pulley as a slip fit with about a 1/4" overhang. through the pulley. Make sure that a really square shoulder is created where the two diameters meet. After testing the fit of the pulley on the end, flip and re-mount the shaft between centers and set the depth stop so the second end is turned so the distance between the two shoulders created is exactly the same as the distance between the bottoms of the two bearing housings of the spindle body. Remove the spindle and chuck with a four jaw chuck by the pulley end and indicate as close to zero as possible and support the opposite end with a steady rest. Take a facing cut and turn the end down to 3/8" for one inch. Thread the resulting one inch long stub with a 3/4-24 die using a die holder on the drilling guide to insure near perfect centering of the thread. Chamfer the end of the threaded stud and reduce the diameter to the thread depth on the first 1/8"where the stud meets the shoulder. Screw the chuck onto the stud and check for run out. If the chuck's rear mount is not hardened, it can be mounted by gripping it by the body in reverse and the rear mount can then be faced true to help make it seat square against the spindle. It is time to test fit everything together. Find some pipe with an inner diameter 3/4" and outer diameter about one inch, cut two one inch long pieces, face all the ends clean and square and chamfer the edges with a file. Insert the spindle so the drill chuck end is on the dust cover end of the spindle housing and insert the two bearings on each end of the spindle. Place the two pieces of pipe at each end with the use of a large vice, carefully press the whole assembly home. The spindle should turn freely with zero lateral wobble. If you are using sealed bearings you will not need to lubricate them but the open type will require a good dose of bearing grease. Locate the dust cover and secure it with three 4-40 1/2" long machine or cap screws. If the cover is a bit larger than the rest of the housing, you can re-chuck and turn down the cover until it blends with the housing. The pulley end can also have a dust cover as with the drill chuck end, or you can make the pulley itself assume the roll of the rear dust cover by doing the following. Chuck the large pulley ( I used a 3" diameter pulley ) by the front end that has the set screw hole and machine a recess a hair larger in diameter than the housing and about 1/8" deep. When you insert the pulley into the rear shaft, just slide the pulley do the recess overlaps around the end of the housing, thus becoming a sort of rotating dust cover. It works just fine. Next time I will make the motor and cross slide housing for the spindle.
Take your finished spindle and housing and with fiber or other heavy duty adhesive tape, cover all the exposed area where there might be any chance of machining chips getting into the bearings. Clamp the spindle housing by the ends and check that it is level. Use spacers or parallels underneath to provide leveled support and orient the spindle's long axis with the Y axis of the milling machine and check for squareness. If you can not gain access to a milling machine, you may be able to clamp it to the vertical milling vice so that it is oriented in a vertical axis and mill with the head spindle. Admittedly, it is a lot easier operation when performed on the milling machine. In my case, I mainly use a SHERLINE and it will handle just about any job I throw at it. The task that needs to be accomplished here is to mill a perpendicular 1-3/4" wide flat slot across the middle of the round housing to provide a place to mount a rectangular plate the will ultimately attach to the cross slide and hold four vertical posts or columns onto which the upper that will house the motor, will be screwed into. The motor will have to sit in a line behind the spindle unit so that both pulleys are in line with each other If you have access to a reversing switch like the ones provided on certain sewing machines, you will be able to run the motor in reverse and simply mounted directly over the spindle, with its pulley facing toward the rear of the spindle.
Begin to mill the slot to 1-3/4" wide and about 3/16" deep and orient the spindle so the three screws that hold the front dust cover in place are situated in pyramid style. This of course, does not matter in the least and is done only for esthetics reasons than anything else. Once the slot is finished, you will need a 1/4" thick rectangle 1-3/4" wide and 3-1/2" long. Temporarily attach the rectangle across the slot with double stick tape and locate four hole positions to for a one inch square. Drill with a #21 drill bit deep enough to go about 1/4" to 3/16" into the spindle housing. Remove the plate and the tape and tap the resulting holes for 10-32 and enlarge the plate holes to #11 and counter sink them to accept flat head machine screws. Install the plate and check for squareness and adjust if needed. Locate four corner holes 3/16" in from each corner so if a 1/2" square piece of bar stock is placed centered over the area, you will have a 1/16" space from each edge of the plate. Drill the holes with a #11 bit. One of the crucial measurements will have to do with the length of the columns and the determining factors will be the length of the pulley belt. the size of the pulley you use and the center height of the motor spindle as it sits on top of the motor platform. To figure this out, I take the motor with its pulley and belt in place and I loop the belt around the spindle pulley and raise the motor, keeping it level until the belt is tight. I measure the distance between the motor base and the floor of the bottom spindle mount. I then subtract about 1/8" for a hard sheet rubber motor mount plus the thickness of the motor platform. The resulting measurement is the what the four columns need to be. Cut them slightly longer to allow facing cuts to square them and bring then down to identical length. As they are faced the final time to the correct length, drill them through will a #11 drill. The top motor platform will need four matching holes on one end of the plate. My top plate is 1/2" thick and 4" by 7". I simply placed the bottom plate in the same orientation as it sits on the cross slide so it was flush with the left 4" wide edge and transfer punched and drilled the #11 holes. I cut four pieces of 10-32 threaded rod measuring the distance from the bottom edge of the bottom plate and the surface of the top motor mount plus 3/4". I faced the ends of the rods clean and proceeded to assemble the unit. With the spindle mounted on the bottom plate, I threaded the threaded rods through each of the four vertical supports and placed each one over each of the corner holes of the bottom plate, passing the threaded rod through the holes and threaded an glued a 1/8" x 3/8 square nut on each of the rod ends with CA glue. I then placed the top motor mount in place by passing the top ends of the threaded rod through each of the four mounting hole and tightened the hole thing with four 10-32 wing nuts. I placed the flat sewing machine motor with its pulley facing the spindle, aligned it over the spindle pulley and secured the motor with fiber tape to keep it from moving. The belt will need a rectangular slot through which to pass through to the spindle pulley. After laying it out, I drilled a hole and proceeded to cut the slot with a metal cutting blade on my hand held jig saw. I was slow going but it did a good job. Now is the time to secure all the components permanently. I removed the top mount and the motor and put it aside for now and took the wing nuts and vertical columns off. The columns were epoxied in place in line and square with the corner holes and allowed to cure. After curing, the rods with the glued nuts were smeared with grease and passed through the columns from underneath. The top surfaces that come in contact with the under surface of the motor platform were smeared with epoxy and the top was inserted through the threaded rod and pressed flush against the columns. After adjusting the top motor platform to square it to the bottom plate, the whole thing was secured with the wing nuts and allowed to cure. The grease on the threads of the rods kept the epoxy from freezing the rods into the hollow of the columns. To install on the cross slide you just loosen the wing nuts to allow the rods to drop enough to let the " T " nuts engage the " T " slots on the cross slide. Square it up with the spindle and tighten the wing nuts. The motor pulley was a normal sewing machine pulley with its flanges turned down enough to let the belt ride over the rims of the " V " groove. This way the belt can be easily removed or installed without having to disassemble the motor platform. The motor was temporarily mounted over a rectangle of 1/8" hard foam rubber with a few loops of heavy duty fiber tape and the on/off switch was attached to the side of the platform for easy and convenient access. When I tried to drill a hole on the center of the workpiece I found the center line of the drilling unit to be 3/16" below the lathe center line so I build a small frame around the base of the spindle mount out of 3/16" square brass tubing and epoxied the whole thing together, forming a frame on the bottom of the mount to effectively bring the drill point up to the lathe center point. Unlike the smaller flexible shaft drilling unit the can only effectively drill 1/8" diameter and smaller holes, this unit will drill all sizes from the smallest #80 to a 1/4 inch" hole. The drill chuck that I am using on it is a Sears Craftsman keyless 3/8 chuck and 3/8 - 24 threaded mount to accept the spindle thread. This unit was originally designed for use as a horizontal rig, drilling along the lathe spindle axis but I suppose it could be re-designed so the spindle axis is a right angles to the lathe axis ( Y axis ) and clamped via " T " bolts to the vertical milling slide vise. With the spindle machined to accept involute gear cutters, it could be used to make gears out of a blank held by a simple arbor. The cutter would cut across the top edge of the gear blank and the piece would be indexed with a division plate screwed to the head pulley. Several bushings to accept different diameter arbor holes could be made to screw to the spindle end so many different types of cutters could be used on the same spindle.