Drilling Precise Holes on Ridged Al. Angle

[js530]

I'm new to machining, so far I only have a $50 HF drill press, a 8" caliper, and a set of drill bits. I want to make some linear bearings based on the THK aluminum angle design, with two parallel holes on each side. One problem I have is drilling precisely. What is the best way to lineup holes? Right now I'm using a carpenders square with a pencil, but I just can't drill a hole where I want one. Usually an 1/8" or more out of line . What about blue layout paint with a scribe? What is the prefered method? Thanks...

[DareBee]

A scriber will mark aluminum (or steel ) quite nicely without using layout blue. Don't forget to center punch the spots to be drilled so the drill has somewhere to start without wondering around.

[Mcgyver]

And so starts the addictive path of acquiring tools. You can manually layout holes to a thou or two accuracy, but you'll need snazzy stuff like a surface plate, height gauge and optical centre punch, etc (all of which you may eventually acquire in the pursuit of better workmanship)

Darabee's nailed your problem - the drill wandering. Consider buying a Starrett prick and centre punch; they're not very expensive and the Starrett quality means they'll come with a nicely formed point. When you have two intersecting layout lines scribed, the finer prick punch will "pick up" (you can feel it) the intersection - give it a light tap with a ball peen hammer followed by a heavier tap using the centre punch. The prick punch finds the interestection and the centre punch forms a crater for the drill to start in - really the same tool, just different point angles. For belts & suspenders, start the hole with a centre drill (stubby and won't flex like a twist drill) or more correctly a spotting drill.

Finally, consider picking up a book like the amateur’s workshop or a senior year high school machine shop text - a lot of the frustration goes away with knowledge and this is all chapter 1 stuff

[take a cut]

if you are making linear bearings the only thing that is really critical is that the two sets of holes have the exact center to center location and this can be accomplished by simply clamping the two pcs of angle back to back and drilling the holes together. Ill bet they come out within .001 of each other unless you drill them at a really weird angle. It would take a good machinist and good tools to do as good as that when doing them individual.

[2muchstuff]

You can take the drilling one step further by using a jig to drill your holes on your drill press. Jig: something that is securely mounted and will hold your material in a specific location. In a block of metal drill 2 holes 8" apart. For the sake of argument lets say they are 1/4" in diameter. In one hole put in a 1/4" steel dowel pin such that it is at least 1/4" above the surface of the block and super-glue it in place. Secure another dowel pin in your drill chuck. Lower your drill chuck and pin into the other hole in the block. Secure the block to the drill press table. Raise up chuck and replace pin with drill bit. On your material drill your first hole where you want it. Place that drilled hole over the pin on the block. Spot drill (center drill) first and then follow with 1/4" drill. After that hole, move that hole over the pin and repeat the process. This way your holes will all be equally spaced down the line and in line.