The following are the features I look for in a drill press.
I don't know what marketing genius came up with the useless concept of measuring a drill press capacity in swing, but it has become the standard. The swing is the maximum Diameter disk you can drill the center of -- basically the distance from the center of the chuck to the closest edge of the column (throat distance) times two.
I find that a 400mm [16"] swing or 200mm [8"] throat capacity is the minimum needed to prevent resorting to a hand-held drill more than 10% of the time.
There is very little cost increase for a floor standing drill press and the height is useful for assemblies, end-drilling, and supporting one or more jigs -- if you have the space. This is particularly true in a woodshop environment.
I suggest no less than 100mm [4"] quill travel (plunge range). You might think that you will never drill a hole deeper than 50mm [2"]. This may be true, but you will want the additional quill travel so you can drill the bottom of a part that has sides -- like a drawer. To drill a part that has deeper sides than your quill travel you will have to lower the table, place the part, and raise the table into the bit providing the sides don't hit another part of the machine before you get it raised far enough.
I suggest no less than 12 speeds, 200 RPM or less to 3500 RPM or more. Variable speed machines are the most convenient, but also more expensive.
Until recently, variable speed was achieved through several mechanical systems -- mostly with belt drives. Drill presses with variable AC drives have been introduced in the last few years and are the most expensive. Alas, cost constraints limit the majority of drill press purchases to stepped-pulley belt driven machines.
You should look for easy belt changes on these machines. Look for belt guards that are not a pain to open and belt tension systems that are easy to adjust.
Wood Magazine has a Drill Speed Chart that shows recommended speeds for various bits and materials.
I find that 3/4 HP motor is a minimum. TEFC (Totally Enclosed Fan Cooled) is very desirable in a woodworking shop due to dust. I would avoid open motors entirely.
The quill of a medium-duty drill press should accept a #2 or #3 Morse Taper for chucks and large drill bits. These sizes are the most common and make it easier to find accessories that will fit the machine.
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Chuck capacity should be 13mm [1/2"] plus, most floor-standing drill presses come with 16-20mm [5/8"-3/4"]. I am a big fan of keyless chucks (chucks that are tightened by hand and do not need a chuck key).
The most respected keyless chuck is made in Germany by Albrecht and are expensive -- you can expect to pay over US$200 for a 1-13mm [1/32"-1/2"]. I took a chance on a 0-13mm [0-1/2"] keyless chuck sold by SPI (Swiss Precision Instruments) that is made in Taiwan. It is a beautiful piece of work and sells for about US$80. It is an excellent addition to any drill press.
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A quill lock is a very handy feature for doing setup, essentially a third hand. The problem is finding one. Very few new drill presses have them until you get into the industrial grade machines from Wilton, Delta, General, and Powermatic. I have modified some of the common Taiwanese-made medium duty drill presses with excellent results. A description is provided under Modifications.
An easy-to-use and fast acting depth stop is a great advantage. The best I have seen is on a Delta industrial variable speed press, which I purchased as spare parts and retrofitted to a 20" Jet (described under Modifications).
I am not a fan of rotating collar-style depth stops that are on the quill lowering shaft. I find them harder to accurately adjust and you cannot use measuring devices or work pieces to set drill depth like you can with the simple vertical threaded rod and stop.
Table Height Adjustment
Mechanical assistance for raising and lowering the table is the norm for any decent drill press, usually rack and pinion.
The two major styles of drill press tables have open slots or closed T-slots. Closed T-slots usually match tooling slots on machine tools like vertical mills. These tables are usually larger than the open slot style and have a moat around the table to collect and recycle cutting fluid.
Open slot tables may be round or rectangular and are most common on 400mm [16"] and smaller machines. Attaching to them requires bolting through rather than using t-slot fittings. Drill presses used for woodworking are well served by attaching an auxiliary table with a fence and T-slot hold-down.
Table Angle Adjustment
Many people like a table that can be angled/rotated, but I rarely use it because it is time-consuming to align it square (a dial indicator is needed if you are picky).
A work light is very handy, but can be added.
I would not purchase a new drill press if the manufacturer did not guarantee that runout will be under .12mm [.005"] at the chuck. Runout is the "wobble" measured at the chuck. Often the chuck is off and the quill is fine so you can get them to send a new chuck. You will require a dial indicator to check this.
If it comes down to two machines that are equal in your judgement, go for the one that weighs more. The added mass absorbs vibration. I built a steel base that raised it 150mm [6"] for a more comfortable operating height. I filled the base with a bag of Redi-Mix concrete, which made it much less top heavy and feel more solid. See Mobile Base Modification for details
Run the machine before you accept it if you can. A plastic cup with a 6mm [1/4"] of water should sit on the table with barely a ripple when the press is running under no load. You can often reduce vibration on existing belt-driven drill presses with link-belts. Conventional V-belts take a "set" over time and are a frequent cause of disconcerting vibrations.
All of the consumer-grade radial drill presses I have seen are not rigid enough to be useful for the work I frequently do. As an absolute minimum, you should not be able to push the quill down against a block of wood (when not running and no bit) and perceive any movement at all. I feel that deflection under these conditions should be less than .2mm [.008"] when measured with a dial indicator.
I have never seen medium-duty radial drill presses sold. They are either consumer grade or massive machines found in large machine shops that weigh tons and cost thousands of dollars.
Fit and Finish
Consider the overall fit & finish. It can say a lot about overall quality of things you cannot see without disassembly.
Naturally, you need to look at the work you do and make sure the capacity meets your needs. In drill presses, more capacity is always better (and never enough). Used presses are usually worth consideration, but it is hard to find a decent price in many areas.