I do not have a milling machine per se, but I have been able to use a small drill press as well as my small 4" Taig micro lathe to perform most of my milling cuts on small workpieces and many of the small components needed for my model steam engines projects. Although the drill press setup does allow you to take only relatively light cuts on small to medium size workpieces, it really isn't designed to do that, as the spindle and bearings of a drill press are only intended to absorb direct thrust along the axis of rotation such as those encountered when drilling, rather than the side loads applied in most milling jobs. Persistent use of the drill press for other than normal drilling operations will do nothing but promote the possible early demise of the spindle bearings and the quill. The speed that this will occur will be dependent on the overall size of the drill spindle and its bearings as well as the volume of milling done with it. Obviously, if you are using a small, cheap 8" capacity imported bench unit to mill metal with, it will probably not last more than a couple of years of constant use compared to an industrial quality floor unit possibly weighing a thousand pounds but costing twenty times more. Even though neither unit was originally designed for milling, the larger, heavier machine will certainly perform as a pretty good milling machine, as well as last infinitely longer than the small cheap unit. The problem is that you will have to invest maybe thousands of dollars to equip your shop with one of these large machines as opposed to as little as $50 ( Harbor Freight price ) for one of these little drill presses.
A lathe spindle is designed to not only efficiently handle the forces encountered along the axis of rotation but also the strong side forces of a heavy turning or facing cut. It is because of this type of spindle that the lathe can be made to double as a perfect milling machine substitute. In fact small model making machine brands like Sherline and the old Unimat as well as several others make their vertical milling machines with basically the same head stock spindles used on their lathes. The biggest problem with the drill press is the chuck which can extend three or more inches past the spindle mount. That's why it can and does flex in any direction as much as .010" when a side load is applied. This produces a harmonic type of vibration during certain surface milling conditions that creates a pattern on the cut surface instead of a nice smooth machined surface. Most larger drill presses have a hollow morse tapered spindle much like those found on most lathes so a matching morse tapered milling bit adapter can be inserted in place of the chuck. This eliminates most of the side flex by placing the end mill much closer to the spindle bearings. The spindle of the lathe, if in good condition will not display any detectable lateral flex in any direction. This I have checked with a TPI bearing against my lathe spindle and even when applying heavy side forces ( with my hands against the chuck ) I could not make the needle deflect. Yet the drill press spindle showed about .006" to .008" deflection with a medium amount of side force applied to it. It's not that the spindle or the bearings are bad. It's that the relatively small diameter connection between the Jacobs taper adapter on the spindle in the back of the chuck does allow for some flex. If you could remove that situation and directly insert the mill and adapter into the spindle taper, you would probably eliminate or at least reduce the effects at that weak point.
The Taig microlathe as well as many other similarly sized lathes provide you with a milling option by offering a milling accessory which is nothing more than a regular slide mounted vertically on a heavy housing so it can be attached to the cross slide or compound of the lathe carriage and oriented to the lathe spindle. This vertical milling attachment will house any small capacity vice or any arrangement of "T" bolt clamps to enable you to position and hold the work. This arrangement seemed to work pretty well on the Taig lathe itself, allowing me the versatility to build small scale simple steam engines without actually having to use a real milling machine. I then figured that it could also be adapted for use on the bigger machine like the HF minilathe. Yes, other vertical milling slides are available by Palmgreen and though being of excellent quality, they do cost a whole lot more. I also could have built my own but here we had a case where it's easier to just buy Taig milling slide rather than build one from scratch. A much larger spindle diameter of well over 1" on the Minilathe, compared to around 5/8" on the drill press, translates to larger, heavier duty bearings for a much sturdier operation. Heavier possible cuts coupled with much smoother surface finishes are just some of the immediate benefits of using the lathe. The adaptation couldn't have been simpler. After laying out the location for the taig unit's two mounting holes on the cross slide surface. I drilled and threaded them to 10-32. After removing the two "T" nuts on the milling slide's mounting bolts, it's was a simple matter of setting the milling unit on top of the cross slide, in line with the bolt holes and tightening the cap screw down. I made sure that there was just enough play in the mounting holes to allow the unit to be aligned to the spindle. Squareness of the unit to the spindle needs to be set with a test dial indicator, making small adjustments until you get not movement of the needle along the total front surface of the slide to insure that the attachment's vertical surface is exactly parallel to the cross slide travel or Y axis. The inner surface of the stationary vice jaw must also be set at a perfect horizontal position unless a tapered cut is desired. The TDI is also used to set this adjustment. The third check is the squareness of the jaws to the vertical surface of the milling slide. This can be done with a small accurate machinist's square and shims can be added if required to square up the jaws so they are a perfect 90 degrees to the slide surface. Cheap vises are notoriously out of square so don't skimp here. I milled the vice's bed and the stationery jaw surfaces after mounting and aligning it on the vertical slide so now I can be 100% sure of the trueness of its surfaces in relation to the lathe spindle. Once I had the vice jaw milled perfectly square, I milled two horizontal "V" grooves of differing depths so I could instantly mount round stock while being assured that it is being held straight and square. Of course, there is a certain degree of inconvenience to using a lathe as a milling machine since you must always change over from turning to milling operations every time you need to mill. You can minimize the time needed to change over by taking the time to master the squaring up procedures involved in the change over.
To make a long story short, I now have a very nice set up for milling parts of many shapes and sizes, providing cuts that are far smoother than with any previous set up I had used in the past. The best thing about using this lathe is the variable speed motor this particular unit comes equipped with, enabling you to make large or minor speed adjustments on " the fly ". Advances of the carriage to set the depth of cut are easily done with a new hand crank I built for the lead screw. More on that on a later article. You simply clamp the half nuts and turn the crank to either advance or retract the carriage into or away from the cutter. A dial indicator bearing against the side of the carriage body is used to measure the exact carriage movements. All in all, I am perfectly happy with this particular arrangement for the majority of my milling needs. I presently do not have a "real" milling machine per se but have arranged several other ways to accomplish the same. The drill press is one way that comes the closest to a real milling machine. There is some degree of vibration in the system that I hope I can get rid off by upgrading to a heavier duty, sturdier and larger drill press. Still cheaper than the smallest real milling machine.
To provide the X/Y movements, I used to use a 4" capacity cross vice which did let me perform some basic milling. The lead screws were bad as well as the dials on the advance handles. Later, I upgraded the cross vice with a regular X & Y milling slide table which did much to improve the quality of my cuts. A good machining vice thrown in and I can't complain too much, at least for now. This is my set up at the present time and although it is several times better in all respects than the old cross vice method, it still does not produce that elusive perfect cut, but then again, what does. The Taig lathe can also be used to mill in five different distinct ways. The first and most direct way is to use the vertical milling attachment designed for it although the set up is not as sturdy as on the larger lathe. You must take light cuts and move slow to get the very best results. The second method involves a motorized heavy drilling spindle which was shop made, mounted to the cross slide, aligned to center height but adjustable radially (by advancing or retracting the cross slide). It's intended for drilling spaced holes for cylinder heads or drilling in line along the diameter or radius and the like. Spacings between holes or milling cuts are controlled with an indexing plate attached to the outer pulley of the head stock spindle. The third method uses a flexible shaft tool in a special housing that is bolted to the vertical slide so that work can be milled or drilled from above by raising or lowering the slide. Another holder using the flexible shaft tool bolted to an adapter block and to the cross slide at center height gives a fourth method to mill horizontal grooves along the long axis of shafts and similar workpieces. The last and more conventional method involves the placing of a miniature high speed jeweler's drill press along side and behind the lathe bed so the drill head can be rotated and placed over a vice mounted to the cross slide. Once the head is locked, light milling jobs can be done on work held on a small 1-1/2" capacity vice or milling plate bolted to the Taig cross slide's "T" slots. Drilling jobs can also be easily done without changing the workpiece set up.
What level of accuracy can you expect from these arrangements? Pretty damn good results ( within .0005"to .001" of specs ), but it takes constant checking and adjustment to keep the surface or bed of the vice as well as the stationary jaw surfaces perfectly square to the spindle. A quick check or two with the TDI before you start machining plus a few minor adjustments if needed should be more than sufficient to insure the desired accuracy of your parts. I am applying the term accuracy to the squareness of the parts thus produced and not to the exactness of the their dimensions. That aspect will come as a result of careful work and monitoring during the milling processes. As an example. I placed a rough piece of square aluminum stock on the vice and began taking fly cuts along each of the four sides, each time rotating the work 90 degrees. Two final end cuts to square up the end surfaces and de- burring of all the edges finished the test block. Now came the testing of the surfaces for squareness and taking measurements across the widths to check for tapers. Corners 1-2-3 were square and #4 showed the tiniest bit of daylight against the square. #4 represented the accumulative error between the first three surfaces. It still was very, very small so I was well pleased. All ends were square to all four sides. I was very satisfied with the results achieved. By the way, the sides were over 1" square and I was able to take a full facing cut of about .015" without any problem at all. Not something I could have done on the drill press.
During the coming Summer, I will be involved in the production of a video series on the very subjects I have and will be discussing in these and future article. Specially the projects involving the different modifications and tool making for the Taig and 7 x 10 Minilathes. They will be available at a very reasonable price directly through mail order but more on that as that develops. I have over 25 years of experience in most areas of photography which I worked on while in the military.
If you pick up anything from this short article is that you can achieve a given result with what sometimes may be considered as a minimum in tooling. The great Rudy Kohoupt began making his incredible engine models with nothing more than a Unimat and a small 8" drill press for power tools. You wouldn't know it from the results!
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