Keeping drilled holes aligned

[Frank Ford]

. . . drill bits that small don't have split points, so How do I get all the holes to stay in a straight line? Brass especially is "slippery" so a drill bit will skate on the surface if I try to "peck".

My #41 drills have split points. I'd try a split point screw machine length drill, say from McMaster-Carr: product number 2896A555

[John Hasler]

A carbide stub drill won't skate because it won't bend.

For maximum precision do as everyone is telling you and spot the holes with a center drill or spot drill and then drill with a stub ("machine length") drill. Need not be carbide.

[Harold_V]

If I use a carbide spot drill, will it stay on location, or will it "skate" on a slippery brass surface?

First, it need not be carbide. One made of HSS will work perfectly well. So will a #1 centerdrill, or even an 0 centerdrill. All that is required is that you create a dimple, which can be smaller than the hole diameter. That will keep the web of the drill on location. It's the web that causes skating, as it does not cut. It displaces metal, which is then removed by the lip of the drill.

Because you have created a depression, the drill will have no reason to skate. Yes, it will cut on location. I have drilled thousands of holes by this method, holes that were subject to 100% 3rd party inspection. It is a tried and proven method of locating holes. And while double drilling is risky in brass, holes that are inspected for size are best double drilled, starting with a slightly undersized drill, with the hole opened to size by the prescribed drill size. By eliminating web contact, which one does by double drilling, the second drill has no option but to orient on the margins, which are circular ground and not inclined to cut. That way you achieve a hole that is sized according to the drill size., as winging is eliminated.

H

[John Hasler]

If I use a carbide spot drill, will it stay on location, or will it "skate" on a slippery brass surface?

An HSS spot drill will be adequate. I suggested a carbide stub drill only if you do not spot drill.

[pete]

First there's not enough information Ron. You need to quantify how "exact" that exact is. Different levels of +- accuracy dictate how it needs to be done. A big difference between a visually in line row of holes to run small bolts through @ + - .002", and better than .0002" to line two precision bores up to each other. A drilled hole isn't going to be exact for size, straightness and roundness no matter how accurately it's initially located. As exact as possible in a home shop probably needs single point boring at the minimum. If the hole depth isn't more than about .300"- maybe .500" solid carbide boring bars are an off the shelf item to do exactly that and to the size diameter you require.

[whateg0]

First there's not enough information Ron. You need to quantify how "exact" that exact is. Different levels of +- accuracy dictate how it needs to be done. A big difference between a visually in line row of holes to run small bolts through @ + - .002", and better than .0002" to line two precision bores up to each other. A drilled hole isn't going to be exact for size, straightness and roundness no matter how accurately it's initially located. As exact as possible in a home shop probably needs single point boring at the minimum. If the hole depth isn't more than about .300"- maybe .500" solid carbide boring bars are an off the shelf item to do exactly that and to the size diameter you require.

I can't fathom boring a hole less than 0.100". It may be done, and for shallow bores, is probably fine, but knowing how much a small drill will deflect, and how my 1/8" boring bar behaves, that's gotta be a tedious process.

Dave

[SteveM]

I can't fathom boring a hole less than 0.100".

I couldn't find the picture, but Harold has a boring bar that's about the size of a straight pin.

Steve

[NP317]

Carbide is rigid and should hold position nicely. The shorter the better for accuracy.
Make sure the cutting edges are sharp.
RussN

[Harold_V]

I can't fathom boring a hole less than 0.100".

I couldn't find the picture, but Harold has a boring bar that's about the size of a straight pin.

Steve

The smallest diameter hole I've bored was .062", in some coin silver (for you folks who don't know, that's 90% silver, 10% copper). Many moons ago, when I was employed by Sperry Utah Engineering Laboratories. I do not recall the tolerance, but boring was required. I was fortunate to have been assigned to a virtually new Monarch EE, which really helped.

A simple boring bar for small holes can be made easily from what's left of a small diameter drill. While the shank of twist drills is usually not hardened, the portion that adjoins the flutes is, so you have a reasonable amount of material to fashion the boring bar.

H

[Bill Shields]

I am on the side of 'do not center punch...use a spot or center drill (HSS is OK if that is what you have) then have at it with whatever drill you have of the correct size'.

700 rivets in using DRO / center / hss 3/32 drill

[spro]

Hey! That is beautiful!
I should leave it there but center punching does also compress the metal which we need drill through.

[Bill Shields]

i do not 'disagree' with center punching...only that when I DO center punch...i never seem to get the 'punch' exactly where I want it...hence find it more detriment to the finished product than a benefit.