Add Mill Function to a Drill Press

Getting a mill for a home workshop is hard to justify. Like many other people, I've been using a drill press and a sliding vise to serve the same function. This Instructable shows how to modify a drill press so it can better serve as a mill. I developed this for my Ryobi drill press, but the same approach can be used for any drill press that uses a set screw.

Ryobi drill press uses a M10-1.5 set screw, with M6 screw segment on the bottom to attach it to the press. To use it as a mill, you set the two depth nuts to the right depth, then hold the press down while you operate the sliding vise. This is cumbersome and imprecise, since the nuts have no markings to indicate how far have they turned (every turn changes the depth by 1.5mm) and are prone to moving from the vibrations.

In this Instructable, we'll replace the set screw with a M10-1.0 screw and add a second nut to block the head at the desired depth. The second nut will be marked to indicate changes in 0.1mm increments and will be lockable. The two drill depth nuts will be replaced with a single nut that can also be locked.

Note that we can't just change the nuts on the existing set screw, since it lacks thread on the part where the new nut is supposed to go.

If you prefer to go with inch screws, you don't have to match the metric sizes exactly, a rough approximation should work fine.

Materials:

M10-1.0x85 screw or rod

2 M10-1.0 nuts

2 M6x25mm screws

4xM4 inset hex set screws, such as used in 3D printers

Selected tools:

drill press

sander

hacksaw

rotary tool, such as Dremel (optional)

M6 tap

M4 tap

M10-1.0 tap is useful, but not required

drill press vise

triangular file

To replace the old set screw, we need to cut the new screw to length, drill a hole on each end and tap the holes for M6 screws. I drilled the first hole before cutting the M10 rod to length, since a longer rod was easier to make vertical for drilling.

It doesn't matter if the M6 holes are not perfectly centered in the M10 screw, but try to make them reasonably parallel with the M10 axis. I used a 13/64" drill bit for the holes. The holes should be at least 1cm deep.

To tap the holes, stabilize the M10 screw with a couple of nuts. I used cutting fluid and my usual tap block to help keep the tap vertical. I used a low-strength steel M10 rod, which was easy to tap.

Screw the M6 screws in tightly and cut off the heads. Wrap the upper screw with tape, since it's a little too thin for the Ryobi depth gauge to fit snugly.

One nut will be used in drill press mode to set the depth. We just drill two holes (I used a 1/8" drill bit) and tap for M4 thread. After tapping is done, you need to clean up the screw in the nut. I found the M10 tap handy, but you can also do it using a M10 screw - best use another screw and not the new set screw you just made, since any burrs may damage the thread.

The depth-holding screw to be used in a mill mode needs a bit more processing. We want to mark the rim with 10 marks, so we can set the depth precisely. For this, we first need to make the outer perimeter circular, instead of hexagon. I threaded the nut onto a M10 rod and locked it with another nut. Put into a drill and spun against a sander yielded the circle quickly. I finished by briefly hand-sanding the surface with a 400 grit sandpaper.

On a piece of paper mark 10 lines (one every 36 degrees), center the nut and mark the line locations on the nut. Then use a triangular file to cut a notch at each location. You can also use a rotary tool, but I found it hard to keep the grooves straight. I did start each groove on one end with my Dremel, so the file didn't wander when cutting the groove.

You might mark each groove with a felt tip pen or paint to make them stand out more.

Finally, drill two holes on opposite sides of the nut and tap them for M4 thread, as with the other nut. I elected to put these lock screw holes between the grooves.

Two M4 set screws go into each nut. These screws are commonly used in 3D printers to lock various parts to motor axles.

Remove the old set screw if you haven't done it already. Initially, I removed the whole assembly, but there is no need to do that, all the nuts can be removed and the whole screw pulled out. Put the new screw in place, but screw on the grooved nut in place before threading the lower M6 screw through the collar and fixing it with the nut (the original nut and washers will fit). Screw the new top nut on and fit the depth indicator onto the top M6 screw - it should fit snugly.

Make a mark on the housing above the nut. It doesn't really matter where, it just serves as a reference as the nut is turned. When you want to change the depth each the distance between grooves on the nut corresponds to a 0.1mm difference in depth.

During testing, I found that I could reliably set the depth to a 1/4 distance between grooves, or depth of a 0.025mm - roughly a thousandth of an inch, a pretty precise control! This could probably be made even more precise if the nut diameter was a little bigger (it can't be much, since there is limited clearance around the screw) and the markings on the nut were finer.

Here's an update after using the mill function for a few months.

The main issue I had was rigidity. The shelf supporting the vise flexes under pressure. There is also considerable vibration resulting in tool marks. My solution was to build a support for the shelf. The original was banged together from aluminum stock that I had on hand and was not designed too well - to make it stiff, I had to tighten a plethora of screws and it also wouldn't let me fully lower the shelf. Vertical space is always at premium, and it became even more so after I switched to a keyless chuck that was longer than the original keyed one.

I just finished the second version. Based loosely on a car jack, it uses 1 inch steel bars. The support lets me fully lower the shelf and also fully raise the shelf, even assuming I remove the vise.

The attachments are steel angle profiles, while the axles are 8mm stainless steel rods from a 3d printer. The screw is 9/16 inch, 11TPI.

I cut the steel using a table saw with a blade made for steel and a bandsaw with 24TPI blade. Axle holes were drilled slightly undersize with a 5/16 inch drill bit and brought to size using a 8mm reamer bit. Each of the 8 leg pieces is 6 inches long. If you look closely, you'll see that corner edges are rounded so they won't interfere with the angle profiles.

Two short pieces hold the screw. One is drilled through. The axle on that side is in two parts, since it would otherwise interfere with the screw. The axle is off center, so there is more space to seat axles on each side. Eagle-eyed viewers will notice that I inadvertently installed this piece upside down!

The other screw holder has a hole for the screw that doesn't go through, so there is a through axle. The axle hole is positioned off center to match the other piece. A M4 screw, not visible in pictures, holds the screw in place. This piece is installed the way I planned it, so the screw is not perfectly horizontal. While the whole contraption works fine, I'll flip one of the pieces at some point, purely for esthetic purposes.

I raise and lower the shelf using the drill press handle, then tighten the nut to hold everything rigid. There is a second nut so the screw could be blocked from both sides, but the upper legs interfere with it. I might make the through piece longer if this proves to be a problem.

So, how does it work?

Well, it's not a real milling machine, that's for sure. Some of the original commenters pointed out, quite rightly, that we don't have a draw bar and that a taper is not designed for such use. Another good point is that the drill press bearings are not designed for side loads. Neither of these, I believe are the limiting factor here, because you can only generate light forces. Well, I might destroy bearings at some point, but they are a few dollars each.

The real limiting factor is still rigidity. With the new jack, the vise is rock solid. However, the rest of the press vibrates and I still get chatter and tool marks. I can do light passes in aluminum or similar soft metals. I don't think this can handle even mild steel.

However, I found the whole milling function really useful. Even for drilling, I can position holes within a fraction of millimeter. In all three dimensions, I can make 0.025 mm or so steps, something close to a mill (a thousandth of an inch) if I'm careful. I made a bunch of small aluminum parts for various projects that would otherwise be completely out of reach.

I hope this helps provide some perspective if you're thinking of making this.