Keeping drilled holes aligned

[Mr Ron]

I am gang milling 8 items in brass. The holes are #41 spaced 0.375" apart in a straight line. I can layout the holes using my DRO; so far so good. Here is where I am stumped; I need the holes to be exactly in line, but a #41 drill will drift off location unless I prick punch first; 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". Prick punching will get me ±.005". Is that as close as I can get it? Books don't tell me how to do it. You "old timers" must have a secret way of doing it.

[whateg0]

It'll take longer but a spot drill or a small center drill would get you started. I might be tempted to cut off a #41 and regrind it, depending on how thick the material is you need to get through.

Dave

[John Hasler]

It'll take longer but a spot drill or a small center drill would get you started. I might be tempted to cut off a #41 and regrind it, depending on how thick the material is you need to get through.

Dave

Or just use a stub drill (carbide if you've got it).

I don't think I have a #41 stub drill so I'd spot drill with a small center drill. It's too short and stiff to wander.

[toglhot]

Use an optical centre punch followed by a centre drill to spot start the small drill

[NP317]

I spot drilled the small rivet holes for my locomotive.
Used the DRO and spotted the multiple rows, then went back, changed to the drill bit, and drilled them.
That minimized tool changes and required table motions only one axis for each row. The DRO made it all very simple for my brain.
And I did re-sharpen the drills before using them. My standard practice.
RussN

[Harold_V]

The notion of using a center punch for locating holes isn't recommended unless you have no other options. It is a huge waste of time and offers a high degree of error. Holes can be located within less than a thou, consistently by other means. You're hard pressed to hold .005" with a center punch. Also, there is no need to *lay out* holes. They can be located perfectly well by trusting the screws of the machine, or, in this case, the DRO. If in doubt, a quick check with a ruler will reveal a mis-location.

In this case, it's been made clear that there's a DRO equipped machine that would reliably locate holes and allow them to be drilled on location. All that is required is that the drill either be extremely short, so it isn't flexible enough to not drill where it's pointed, or the hole should be started with a center drill or a spot drill. Neither has an advantage over the other, in spite of many suggesting that a center drill doesn't work properly.

One of the options a person has when faced with making multiple changes, a Wahlstrom chuck can be chosen. It is capable of making changes while the spindle is in operation, so going from a center drill (or spot drill) to a drill takes but a moment. They offer the added bonus of having a powerful grip, although, in this instance, that isn't a requirement.

H

[SteveM]

Tubalcain (aka MrPete222) did a video on hole location using various methods. Marking and centerpunching was the least accurate, as Harold mentioned.

As to books, there is one: "Precision Hole Location" by Robert Moore of Moore tools.

I don't have the book handy, but one of the things I remember is that they recommended Russ's approach of center drilling all of the holes first, doing one tool change and then doing the next operation. The machine and the operator should be accurate enough and competent enough to relocate the work for each operation and you won't spend 90% of your time doing tool changes.

Steve

[GlennW]

I don't have the book handy, but one of the things I remember is that they recommended Russ's approach of center drilling all of the holes first, doing one tool change and then doing the next operation. The machine and the operator should be accurate enough and competent enough to relocate the work for each operation and you won't spend 90% of your time doing tool changes.

And you will most likely catch it if you mis-located a hole on the first pass. Gives you a second chance to verify location.

[whateg0]

... Also, there is no need to *lay out* holes. They can be located perfectly well by trusting the screws of the machine, or, in this case, the DRO.
...

H

While not required, I still do often layout holes. Unlike OP, I don't have a DRO and counting turns over several inches often leads to mislocation by 0.1" this way or that. Depending on the shape of the part being worked, it may not be easy to measure with a ruler on the machine.

Dave

[John Hasler]

I also often lay out holes for the same reason Dave does. I don't (usually) center punch and I drill by the dial and not by the layout, but it keeps me from committing howlers such as producing a mirror image part.

[NP317]

Looking at the photo I posted above, you can see layout notes and scribe lines for the rows.
These provide my brain a visual positioning double check. This greatly cuts down my errors...
RussN

[Mr Ron]

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