How to use a drill press to drill with drawing layout

Question

I want to make a part with 3mm thickness aluminum plate (about 10 by 10 cm).

On my first try, I painted the plate with permanent ink and drew the layout using a tungsten pen and a square ruler.
After having made a cross mark, I used a center punch, took it to my drill press, and started drilling with a 3mm drill bit at first, then a 5mm drill bit.

On my second try, I printed my layout and stuck it to the plate with latex glue, then used the center punch on the paper, and used the drill press just like during my first try.

My first try lacked precision due to the imprecision of my hand and ruler.
During both of my attempts I also had a problem with the drill press as I wasn't able to position the center punch mark to the drill bit accurately enough.

My drilled holes are usually off-center by almost a millimeter.

I usually make my part with a 3D printer. This metal working is quite new to me.

Am I missing anything? How should I have done this?

Note this is my design

Answer 1

On thin material, sometimes it's easier to get precise placement by drilling with a handheld tool because you can adjust the bit location as you start to make the hole, then the hole will guide you and the drill (and being perfectly perpendicular to the piece usually isn't critical on thin material). With a drill press, the hole will end up where you position things, so precise positioning is critical.

If your workflow or requirements pushes you to using a drill press, there are a few things that can make the job easier.

• If you need to make a lot of holes in a pattern, use fixtures for alignment. This is useful for multiple holes the same distance from an edge, or multiple pieces with a hole in the same location. Fine tune positioning with scrap pieces (can be any cheap material of the same dimensions).

• Making a location guide mark for a drill press works a little different from doing it for handheld drilling. The drill press will force the hole to the position you set up. If you use a center punch and don't then position the piece precisely, you can get an off-center hole, an angled hole, or a broken drill bit.

  With a drill press, the hole will be where the drill press is aligned (unless it's forced off-center by making the drill bit buckle, like too much pressure too fast and a dull bit). You don't need a center punch if you have a way to precisely align the piece. There are a couple of positioning strategies that can help.

  • Make a very shallow guide or just location marks on the piece. Start with the clamps loose enough so you can slide the piece around for adjustment. Position the piece as accurately as you can. Iterate some initial, very shallow surface drilling just enough to confirm that the hole will be centered, adjusting if necessary. Tighten everything once you're confident in the positioning.
  • A variation on that theme: start with the smallest drill bit you have (for the minimum error off-center), then enlarge the hole in several steps. The initial hole only needs to be deep enough to center the next bit.
  • Make a really deep divot with a center punch. Leave the clamps loose enough so the piece can slide its position but not rotate with the drill bit. With the drill press off, lower the bit, center it in the divot by moving the piece so the bit is not being deflected in any direction (visible when lowering the bit into the divot). Start drilling. Let the piece center itself (while the hole is still very shallow, nudge the piece if necessary if the hole isn't quite centered). Once the hole is accurately centered, you can tighten the clamps, although that might not be necessary for small holes; the hole will act as its own guide. Just prevent the piece from rotating or vibrating.

• If you're making systematic error (the error is always in the same direction), practice with some scrap. Make a series of holes and measure the error. Then position the way you normally do, and make a manual adjustment to compensate for your normal error. Even if you don't make the precise same error each time, if you are normally off in roughly the same direction and by roughly the same amount, compensating for the average error will improve your precision.

• If this kind of drilling will be a recurring requirement, you can invest in a cross slide vice. This is a vice mounted on an XY screw adjustment that lets you fine-tune the position. If you carefully align the orientation of the drill press table with the drill, and the vice with the table, you can also use it to position the first hole, then use the adjustment screw to translate the piece to make other holes across the piece the same distance from the edge and at an accurate interval.
  ^{image courtesy Harbor Freight}