Tips on precision drilling?

[hapki]

Well, I've screwed up several MHS pieces this week. I drilled a hole for a blade retention screw in a new blade holder. I got it exactly in the right place. But then when I tapped it, the 10-32 tap broke off in the hole. I destroyed the piece trying to get it out.

Then I decided to cover over the mess with a shroud. That went well. So I drilled two small holes on each side of the shroud to expose the blade holder--thinking I could add electrical pins for a cool effect. But then when I tried to drill the tiny holes in the blade holder, I got one off target by about 1.5 mm. So now I will re-do the shroud to cover another mess.

What are some tips for drilling precision holes? I have tried using a Dremel with a very small bit to get the hole started. I have also tried getting a hole started by knocking a divot in the metal with a small nail. I can get the bit to drill in the right place only about 49% of the time. So that means I screw up a lot of nice pieces. I have a drill press, but it is even less accurate, because the bit walks around too much. I'd like to stop ruining expensive pieces.

[Silver Serpent]

Get a center punch tool. A nail works, but the point isn't always as precise.

Be sure your drill bits aren't getting dull. Sharp bits cut better. When you first make contact with the metal, go slowly to help prevent the bit from walking.

[darth_chasm]

I use a center punch to mark the spot, then a center/spot drill bit to do the pilot hole. They are short and stubby, and are much less prone to walking. Once that's done I move up incrementally in bit size until the hole is the desired size. All on drill press.

If you have a tap wrench for your taps you can set that up in the drill press to help keep the tap straight. The wrench should have a dimple on the top which you can center a drill bit in to hold the tap in place. Here are a couple videos that go over this and a couple other methods:

https://www.youtube.com/watch?v=WWjaoW7VJxY
https://www.youtube.com/watch?v=KBrrVnYBPOQ

[xl97]

Along with DC's comments...

I suggest starting small!

So if you wonder a bit or the angle is slightly off.. it -may- be corrected by going to the next larger bit size.

[jbkuma]

Lubricate, especially when tapping. You will be surprised how much better things go for you when you lubricate.

[Avidgrant]

Lubricate.... With?

Alternatively.... Buy extra parts. Just kidding.... Although I did indeed buy extras in case this happened to me.

[PhoenixHawk]

Lubricate.... With?

WD-40 works fine as a cutting lubricant if you cant find cutting oil.

[jbkuma]

You should be able to pick up cutting oil at any hardware store. I usually just use mineral oil. There's a number of more or less reputable concoctions that pros and DIYers will swear by depending on the material.

[Greenie]

When tapping, just a couple of turns then back out to clear the thread and always lubricate. Cutting oil, engine oil, duck oil, cooking oil, WD40, grease. They will all work better than using nothing.

[Sevinzol]

1. A nail is not good for centering because it is only work hardened mild steel, not tempered. People are mentioning Center Punches. There are several types. I have 3 myself: one designed to center a mark relative to an existing hole (like a door hinge). second is a spring loaded Automatic Center Punch, and the third is just a solid old one piece Center Punch. My suggestion is use the old fashioned one piece with a (small) hammer. You'll have better control with how hard to hit. remember Aluminum is soft.

2. Use your drill press, you have one. If the bit is drifting then choke up on it (stick it as far in the chuck as you can). If the bit is wobbling then your chuck is seated crooked, you need to remove and reseat it (this can take hours). There might be a set screw inside the chuck but many are just pressure fit. consult your manual. Make sure to set your speed right. metal is not wood. Use some oil. I use 3-in-1, WD-40 is not oil its designed for rusty bolts. it is too thin to work as a cutting oil. the oil is there as a lubricant, a heat sink, and to help suspend the metal particles.

3. Make a "V" block. if you don't have a machinist vice to hold the piece solid then cut a piece of 3/4 plywood, lengthwise with the blade at a 45 degree angle, glue and screw these pieces to a third, wider piece and clamp this to the drill press platform.

4. Go slow and use the drill bit size you need. I don't recommend sneaking up on it by making a smaller hole first. because this can contribute to chatter and might mess up the roundness of the hole. DeWalt sells Pilot Point HSS drill bits.

5. When you tap. Practice on a scrap piece. Double check you have the right sized hole. If its even slightly too small you will probably break the tap by forcing it. Use oil. Turn the tap only 1/4 - 1/2 turn then back it out a 1/4 turn. This breaks the little shavings you are creating and helps prevent them from jamming up the tap. If its going right, it should feel smooth and not resist, if you have to crank it, then back it out to clear the shavings, add oil and go again. considering how thin an emitter is, you shouldn't have to do that.

... and remember we're having fun.