Keeping drilled holes aligned

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Mr Ron
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Keeping drilled holes aligned

Post by Mr Ron » Sun Jan 12, 2020 11:26 pm

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.
Mr.Ron from South Mississippi

whateg0
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Re: Keeping drilled holes aligned

Post by whateg0 » Sun Jan 12, 2020 11:49 pm

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
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Re: Keeping drilled holes aligned

Post by John Hasler » Sun Jan 12, 2020 11:57 pm

whateg0 wrote:
Sun Jan 12, 2020 11:49 pm
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
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Re: Keeping drilled holes aligned

Post by toglhot » Mon Jan 13, 2020 2:10 am

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

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NP317
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Re: Keeping drilled holes aligned

Post by NP317 » Mon Jan 13, 2020 2:31 am

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
4-Spotting Rivet Holes sml.jpg

Harold_V
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Re: Keeping drilled holes aligned

Post by Harold_V » Mon Jan 13, 2020 2:55 am

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
Wise people talk because they have something to say. Fools talk because they have to say something.

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SteveM
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Re: Keeping drilled holes aligned

Post by SteveM » Mon Jan 13, 2020 7:54 am

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

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GlennW
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Re: Keeping drilled holes aligned

Post by GlennW » Mon Jan 13, 2020 10:04 am

SteveM wrote:
Mon Jan 13, 2020 7:54 am
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.
Glenn

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whateg0
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Re: Keeping drilled holes aligned

Post by whateg0 » Mon Jan 13, 2020 10:07 am

Harold_V wrote:
Mon Jan 13, 2020 2:55 am
... 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
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Re: Keeping drilled holes aligned

Post by John Hasler » Mon Jan 13, 2020 10:57 am

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.

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NP317
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Re: Keeping drilled holes aligned

Post by NP317 » Mon Jan 13, 2020 11:58 am

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
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Re: Keeping drilled holes aligned

Post by Mr Ron » Mon Jan 13, 2020 2:06 pm

If I use a carbide spot drill, will it stay on location, or will it "skate" on a slippery brass surface?
Mr.Ron from South Mississippi

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