My first Taiwanese drill press was a bench model. I liked it right away from a usability perspective because you could crank the table up and down, the table had T-slots and a central hole, and the spindle was a standard 2 Morse taper. In addition it had 3 pulleys which gave 15 speeds, and an integral light.
I used that drill press for a long time but was frustrated by its three major failings. Its quill rattled and shook during extension, the entire machine vibrated excessively, and there was excessive runout in the spindle taper. It was possible to do good work with the tool, but it was frustrating. Here are some of the problems that manifested from the conditions described above.
To precisely locate a hole in a drill press, you can use a wiggler. (See http://www.loganact.com/mwn/howto/wiggler/wiggler.html for Mike Rehmus's excellent writeup on a wiggler). I learned about a wiggler, got excited, dug around my old tooling and found one, put it in my drill chuck and discovered that it would run true when the quill was retracted but as soon as the quill was lowered and the rattling would start, the wiggler would fly into its "helicopter" position. This was discouraging. In practice, it meant I could not use a wiggler. I will discuss this condition and how to diagnose it below.
This drill press, as I mentioned, was a bench model. It sat on a sheet metal tool stand, which sat on a wooden floor. If I put a cup of water on the drill press table with the machine turned on, you could easily see standing vibration waves on the surface of the liquid, at least until the cup "walked" off the edge of the table, it was that bad. Vibration to this degree is common in inexpensive machines. It reduces bearing life, increases power consumption, and makes it more difficult to get good finish.
Finally, when I measured the runout in the spindle (measured in the internal taper) I found about .007" TIR. Not bad, but not good either. This condition manifests itself in the point of the drill bit wavering around in a little circle when you are trying to get it to start in a center-punched hole. Once it starts it should run true, though.
When it came time to buy another drill press, I considered upgrading to a heavy precision US-made tool, but the cost was prohibitive for my needs. Since I like the usability of the import drill press design, I decided to analyze the source of the problem conditions I have found and to look for a machine on which these conditions either do not exist or can be corrected easily and within my overall budget.
Anyway, with the quill fully retracted, and no power to the machine, if you grip the chuck and rotate it one way and then the other, you should not feel a loose "slap". It should feel solid and not loose. Then, holding the chuck with your left hand and the downfeed lever in your right hand, slowly lower the quill through its entire extension, repeating the back/forth rotation, looking for areas where there is excessive play. If there is, you will certainly notice it. The noise will sound different, and you will feel the difference. If you think you detect wear in the splines, then turn on the machine and lower the spindle slowly, listening to the sound. If you are looking at a machine with significant spline wear, you will absolutely hear it while lowering the spindle under power with no load. In my opinion spline wear is a showstopper.
If you hear sheet metal rattle under power, try opening and closing the lid of the belt guard slowly, feeling the vibration. I have seen a case where there was little vibration in a machine but it happened to be at the resonant frequency of the belt guard. Wide open, it was fairly quiet. Fully closed, it rattled slightly. But open 1", it sounded like an amplified hornet. The condition of resonance can only be cured by adding or removing mass or stiffness. For the above case, the rattle was greatly reduced with some magnets. For many imported drill presses, the simplest way to deal with resonant vibration in the sheet metal belt guards is to put a chunk of lead on top when they are closed.
If you really want to try to get to the root of the problem, and if the tool vendor will let you, you can put the motor on a bench and run it. Loosen the end cap screws slightly to allow the bearings to align themselves, then slowly and carefully retorque them. I have done this with excellent results, which proves that assembly technique can be related to motor vibration, especially for inexpensive motors with sheet metal end caps.
If the motor is not the source of excessive vibration, it is time to examine the pulleys.
With the belts removed, grasp the middle pulley on the top of the machine. This is the one that acts as an idler between the motor pulley and the spindle pulley. Pull up to see if there is excessive play between its mounting pin and the corresponding hole in the head. I have seen machines where there is over .025" of play. This condition manifests itself as pulley misalignment, and causes vibration. The hole in the casting should be bored parallel to the spindle, and the mounting pin for the center pulley should fit solidly in the hole with little "rock". The pulley should swing smoothly about the mounting pin, and should always remain aligned with the spindle pulley.
If the plane of movement of the center pulley is not perfectly horizontal, it will not be possible to have it in alignment in all positions. A bad drill press will have over 1/4" of misalignment of these two pulleys. Look for one that is well within 1/16". If the drill press you are examining has severely misaligned pulleys, it will require correction to run true.
Note that there are different designs of the center pulley shafts. On one model I looked at, the pulley was pressed onto a bearing so adjustment in the vertical direction was easily done in a bench vise by just lightly pressing the pulley to move it in the desired direction. If the entire pulley sits slightly too low, it should be possible to slip a washer under the part of the center shaft that inserts into the head casting, thus raising the pulley slightly.
It is also possible that the pulleys are imbalanced. It is possible to correct this, however, shop time at a precision balancing shop is expensive. It is also possible to balance pulleys using the knife-edge method, in a home shop. However, the spindle pulley, being mounted on a taper, will be difficult to balance inasmuch as it will be difficult to put it on a shaft to balance it.
Finally, even if the machine has high quality balanced pulleys, and if the center pulley seems tight and is aligned with the spindle pulley, there may still be vibration due to the pulleys being eccentric. I found a couple of real bad pulleys by just lightly touching the edge of them with a finger while the machine is running. If the pulley isn't round or if its hole isn't centered, you will feel a distinct "buzzing" on your finger. Also, the belts will look like they are "hopping" instead of appearing motionless as they should. Of course, it is possible to check this condition with a dial indicator. If a pulley is only slightly off it can probably be trued up in a lathe, or even be replaced.
I found an article on a mechanism called a "dynamic absorber" which looked like it might work for a drill press. I am not going to describe this in mathematical detail but I will briefly describe the technique and give the reference and hopefully it will be easy to find the reference if needed. This information is below, in Appendix B.
Vibration causes excessive noise and shortens bearing life. I also believe it detracts from the finish of the hole being drilled, and can make it more difficult to align the bit with the workpiece. I am of the opinion that it is well worthwhile to go through a machine and remove the vibration. It makes the tool much more pleasant to be around.
Remove the drill chuck, insert the test indicator, and rotate the spindle by hand. Note the extreme values. Their difference is total indicated runout, or TIR. A good spindle will have less than .0005" runout. A bad one can have over 1/32" runout. My old one had .007" which isn't that bad but I wanted better for metal working. Look for a machine with less than .001" TIR on the internal spindle taper.
It is possible to fix this condition by removing the quill completely, entirely disassembling the head, mounting it on some machine tool and boring out the spindle cavity, and then sleeving it. Of course, it is also possible to build a drill press from scratch. In my opinion I would recommend choosing a drill press without excess play over taking on such a restoration project.
I started by leveling my surface plate carefully. If you don't have a surface plate, you can use the top of a table saw or some other flat surface you can level. I bought a piece of 1/8 by 1" O1 ground flat stock and machined a 45 degree bevel on one end. (I did this with a 12" disc sander with a tilting table - a milling machine may be much faster.) I cut the 18" beveled stock in half, giving me 2 roughly 9" pieces. I used 4 3/8-16 screws and washers as rough "clamps" on the sides of 1-2-3 blocks. I then clamped a block to the end of each knife. I lined up the knives so they were flat and parallel and level.
I then put the motor's armature (aka "rotor") on the knives. I saw that the two ends of the shafts were of different diameters. On one such motor there was a narrow area close to the rotor body where there were equal-sized shaft diameters. I used those. On another such motor I had to turn a suitable bushing in the lathe. Anyway, once on the knives the rotor with the static imbalance immediately tumbled to its position with the heavy side down. I drilled round the rim on both ends of the rotor to bring it as closely back into balance as I could, frequently checking the balance on the knives. Reassembled, that particular motor ran far more smoothly.
One more note on home balancing - it is possible to remove weight from the heavy side by drilling as just described. In a couple of cases I have not been able to remove enough weight this way and I have found a method that worked well for me, to add weight to the light side. Start with an old wheel weight. Then, on the light side, make a cone-shaped indentation with the drill (i.e. start a hole but don't penetrate through). Then take the whole thing to your kitchen, and pick your rattiest kitchen spoon. Cut off a chunk of the wheel weight about 1/4" cubic, and melt it in the old spoon, then pour it into the hole you drilled. It will not bond, but it will sit there and bead up on top and will exactly fit the indentation. Then, after everything is cool, put a drop of superglue into the indentation and then put the just-cast weight in, just as you poured it. Hold it there for 30 seconds or so. This glue worked just fine for me. I was able to make the light side just slightly heavy in this manner, and then hit the raised part of the weights with the belt sander a "kiss" at a time until the part came balanced on the knives.
Here is my design. It can be used as is for drill presses with NEMA 143 frame motors (3/4" shaft, 4" bolt hole separation in the direction parallel to the shaft, 5 1/2" bolt hole separation in the direction perpendicular to the shaft). I made mine all from 1/8 by 1" mild steel flat bar. I cut two pieces of flat bar so that they bolted onto the motor mounting bolts, and had 7" sticking straight down below the motor. This is the cantilevered spring, albeit split into 2 parts. I then cut 4 pieces 8 1/2" long, and drilled 4 3/8" holes to bolt them. Starting from an end, the holes are in 1/2" and 2 1/2", so they straddle the springs hanging down. I cut 1 1/2" pieces of 5/16-18 allthread, and used nuts and washers to bolt the 4 pieces together, clamping over the springs. All together, the 4 pieces of flat bar, the allthread, the nuts and washers form a weight. A weight suspended from a spring forms a system which has a natural frequency.
You can "tune" the frequency by adding washers, or by moving the weight up or down. When I get mine within 1/16" of the right spot, it really takes off. When it is operating, soaking up the vibration, I can balance a nickel on the table of my drill press.
The design equations were published in a book titled, "Practical Solution Of Machinery & Maintenance Vibration Problems" by Ralph Buscarello, pub. 1979. I found this book in the Seattle Public Library.
Email: Grant Erwin
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