This is another excellent article by Mikey, a frequent contributor to MachinistBlog.com and winner of our “Machining Metal as a Hobby” contest.
The Craftsman 15″ Drill Press, Model 137.229150, is a floor model commonly found in many home shops. Made by Rexon of Taiwan for Sears, Grizzly and others it is a typical consumer grade drill press. When new this machine is quite functional and if you use it to drill holes in wood and the occasional piece of metal then this drill press will give you years of service. However, if you are a metal worker and need more accuracy in your machine it’s a whole other ball game.
The accuracy of these machines when new is not too bad but in a few short years mine developed significant run out, with 0.003″ total indicator run out (TIR) at the spindle and double that at the chuck. That may not seem too bad but let me tell you, 0.006″ of run out at the chuck is enough to visibly see the bit wobbling! My spindle bearings had developed play that I could hear and feel and I knew it was time to do something about it.
While it may appear to be daunting it turns out that restoring it is not difficult. However, it does require access to a hydraulic press and a puller for the spindle pulley so take that into consideration. Other than these tools no special tooling is required beyond that found in the typical home shop. If you or your friends don’t own a hydraulic press all machine shops and most auto repair shops do; the cost to press the bearings off and on should be minimal.
If we consider where run out could come from it will likely be the spindle assembly, the arbor or the chuck. The spindle assembly is basically the drive sleeve that drives, supports and guides the spindle at the top, the solid spindle itself, and the four bearings that support these components. I suppose the quill could contribute but unfortunately there is no provision for improving the accuracy of the quill so it’s a moot point.
The manual does not list part numbers for the above components but you can order them from the Sears Parts Direct website at reasonable cost using their illustrated parts breakdown. I suggest replacing the spindle, the drive sleeve and all four bearings at this time.
I also suggest you obtain precision after market bearings instead of using the OEM bearings. You will need 3 each 6204ZZ and 1 each 6203ZZ. I chose to replace one of the 6204ZZ bearings with a 6204-2RS; this bearing is sealed and resides at the bottom of the quill where it is exposed to chips and cutting fluid. All of these bearings are available from your local supplier but are cheaper on eBay. I prefer to use Nachi bearings for their quality but this is a personal choice.
If/when I need to rebuild my drill press again I will use an angular contact bearing to replace the lower quill bearing; the near equivalent for the 6204-2RS is the slightly longer 5204-2RS. Note that I have NOT done this yet so I’m not sure if the bearing would protrude a few millimeters. If it did you could chuck the quill in the lathe and bore the bearing recess deeper, or live with a little protrusion. Only the lower bearing needs to be an angular contact bearing; radial bearings are fine for the upper spindle bearing and drive sleeve. Why an angular contact bearing?
Angular contact bearings are designed to take both axial and radial loads, unlike radial bearings which are made for radial loads only. Consider that when using a drill press to push a drill into a work piece both axial and radial forces are at work. Sort of makes you wonder what the designer was thinking, doesn’t it? Take a look at a good American drill press, like a Clausing, and you’ll find an angular contact bearing at the end of the spindle.
The chuck arbor is another potential source of run out and I typically change it to a new Albrecht or Jacobs arbor when installing a new chuck. The OEM spindle requires a #2 Morse Taper.
If you are using the OEM chuck for woodworking or general use then it may suffice. However, I would consider replacing it if you need to drill a precision hole. You can use a keyed chuck, like the Jacobs Super-Chuck 14N on the right, or a keyless chuck like the very accurate Albrecht on the left. Both are far more accurate than your drill press will ever be and can be had on eBay at reasonable cost. If I could only have one chuck I would choose the Albrecht for the obvious convenience and accuracy it provides.
In summary, we are going to replace the parts in the drive train that could be causing run out and consider replacing the arbor and chuck, which are additional sources of potential run out.
Okay, let’s get this thing apart! As always, please work carefully and proceed at your own risk.
- Use your arbor wedge to knock out the arbor and chuck. If you don’t have one you can make one from 1/8″ thick mild steel.
- Remove the light bulb from its socket.
- Loosen the two set screws that hold the head to the column and move the head to your work bench. It is heavy so try to have another person assist you if possible.
- Open the belt cover and remove the belts. Now remove the nut at the top of the spindle – this is a LH thread. You can insert the arbor wedge into the slot in the quill to hold the spindle still.
- Remove the spindle pulley. You will need a pulley puller for this.
Remove the quill.
- Loosen the quill adjusting set screw just to the right of the spring.
- On the left side of the head find the quill return spring assembly. It has two nuts; the outer one is a jam nut. Remove the jam nut.
- The manual recommends that you place a screwdriver into one of the slots to control the spring as you release tension but I just used a gloved hand to grab hold of the spring housing and, while controlling the spring tension (turn the housing slightly CCW), remove the nut. The tension is not that strong and is released in about a single turn. It will look like this when removed [photo 4].
- Turn the feed handle and catch the quill as it drops out.
- You can now disassemble the quill. There is a piece of plastic tubing on top of the assembly which looks suspiciously like a Taiwanese anti-grease slinger device. Under that is the spindle nut, a nut lock washer and a flat washer – in that order.
- The Nut Lock will have one of the ears bent up to keep the Spindle Nut from turning; using a punch, carefully bend it down so the nut can be removed.
- Now remove the spindle nut (RH thread). Note: the tension on this nut is minimal. It is run down to contact the bearing and turned until one of the tabs on the nut lock can engage a slot. Typically, this arrangement is used to preload a bearing but in this case I think it just keeps the bearing from being displaced.
- Now remove the nut lock and flat washer and set them aside.
- Here is where you will need your hydraulic press. Drive the spindle out of the quill from the top. Once the spindle is out you can tap the bearings out of the quill with a brass punch or hardwood dowel. You will notice the two bearings inside the quill differ; the upper one is smaller – the 6203ZZ – while the lower one is the 6204ZZ. This lower bearing is the same as the paired bearings on the drive sleeve. [Photo 6]
Remove the drive sleeve from the head.
- The drive sleeve [photo 7] is held in place at the top of the drill press head by two “Circlips”, one on top and one underneath the Drive Sleeve. Remove the upper clip by grasping one ear of the clip and slipping a slim screwdriver behind the clip. Carefully work the clip out. The one under the drive sleeve can be left in place.
- Use a hardwood dowel and tap the drive sleeve assembly [photo 8] out from below – that is, stick the dowel into the head from the bottom side and use a dead blow hammer to tap the drive sleeve out toward the top. It is a loose press fit but tap evenly so you don’t cock it as you drive it out.
- Now press the drive sleeve out of the two bearings. Note that you need to position the unit with the threaded part down. Support the bearings and then use a piece of stock smaller than the inner bearing race that bears on the center column of the sleeve so it can be pressed out. The two bearings are separated by a plastic ring that you need to retrieve even if you are replacing the drive sleeve and bearings.
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Disassembly is now complete and all parts can be cleaned and inspected.
Assembly is basically the above procedure in reverse.
Use grease sparingly during assembly. You need to grease the spindle but remember that the spindle is moving up and down through the drive sleeve during operation and the belts are subject to flying gobs of grease as this occurs.
- Press the drive sleeve into the two drive sleeve bearings with the plastic ring between them.
- Clean the socket that will receive the drive sleeve.
- Install the drive sleeve assembly into the head. Put a light coat of oil on the outer bearing race of the drive sleeve bearings and push the drive sleeve assembly into place from the top. Try pushing it into place manually; if the bearings align correctly you can push or gently tap the assembly into position. If it won’t go in easily then you can pull it into place using a threaded rod passed through the assembly. Use a scrap of wood or metal below and a washer and nut on top and tighten the nut to pull the assembly down. You only need to get it in far enough to install the upper circlip. Do not distort or damage the lower circlip.
- Install the quill.
- Assemble the quill and spindle with their bearings.
- At the top of the spindle, install the flat washer, the nut lock, and then the spindle nut. Snug the spindle nut then back it off to engage the nearest tab on the nut lock that will engage and bend that up.
- Re-install the plastic tubing. Clean the quill itself, with attention to the teeth on its side and apply a light coat of oil.
- Insert the quill into the head and engage the handle to crank the quill up.
- Install the quill return spring assembly – essentially the reverse of the above. Remember to preload the spring about one turn before locking the nut down. Install the jam nut.
- Re-install the pulley and belts and re-install the head onto the column. Adjust the quill set screw to minimize play but be sure the quill moves freely.
- Re-install the light bulb.
- Install your arbor and chuck and you are … Done!
I would recommend doing a rebuild if you are having run out issues. It’s not hard to do and the cost is more than acceptable (if you don’t count a new chuck). The improvement in performance is significant – run out at the arbor on my drill press is now less than 0.0005″ TIR and that drill bit looks like it’s standing still!
Update: It is now February 2010 and the run out at my arbor is still under 0.0005″ TIR despite hard use in a typical hobby machine shop. I believe the use of high quality bearings minimizes wear on the spindle and drive sleeve and help to maintain accuracy. At this rate I may never get to try that angular contact bearing!