Find exact center and drill concentric holes in metal rods

Picture of Find exact center and drill concentric holes in metal rods

Finding and marking the exact center of a small metal rod or dowel is more difficult than finding the center of a larger circle. I recently wanted to mark the center of a 1" long x 3/8" diameter brass rod, then drill a 1/8" concentric hole the entire length. Yes, just a brass rod with a hole down the center. A professional machinist with a metal working lathe might have no problem with this, but for the average garage shop guy (me) it was no easy task. I learned a few tricks and made a jig that made the job easier and the results better. 

With apologies to my friends in metric countries (everybody except U.S.), my example is in Imperial units. Everything applies to S.I. components and drill bits.

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Step 1: Find the center of the rod - Method # 1

Picture of Find the center of the rod - Method # 1

Method # 1 (not necessarily the best).

The classic method of finding the center of a round object is to use a center finder head attached to a standard metal rule, such as used in a combination square. You hold the round item in the V-notch and scribe a fine line. That line is a diameter of the circle. Rotate the piece, and scribe another line. Where the two lines intersect is the center. Easy and accurate for large circles (say over 1" diameter), not so easy for a 3/8" rod. Forget about using a pencil; use a sharp knife point, like an Exacto knife. Even with a sharp knife, the line can be a bit off center.



Step 2: Find the center of the rod - Method # 2

Picture of Find the center of the rod - Method # 2

Method #2 

Use a Forstner or brad point drill bit the same size as the rod. The point at the center will be reliably dead center. Place the rod and drill bit on a hard flat surface, and with the point of the bit scribe a couple of lines on the rod end. Where the lines intersect will be the center. 

Step 5 and 6 is great.
But how do you keep the rod fixed so it won't turn with the bit ?…
Thanks for posting !!…
Bill WW (author)  vincent75201 year ago
Yes, keeping the rod fixed is sometimes a problem.

As with all we do, at times we must be creative. It is best for the rod to fit tightly into the hole. I have at times wrapped electrical tape around the rod to create a tight fit. Also. use oil on the drill bit and drill slowly.

Also once you've made a centre mark with the drill you can remove the rod and secure it with a clamp.
Aaah ! So you ask us to make an effort too !…
Nobody can blame you for that.
Thank you for posting.
Have a great week.
cepterbi1 year ago
that's some smart thinking with the last one.....I wouldn't come up with something so simple yet effective. Happy to have learned this as it will certainly come in handy in the future. Tnx
Bill WW (author)  cepterbi1 year ago
Thanks for the comment.
For small work pieces, and a small drill bit, as in the photo, it is still a bit tricky.
Bill WW (author) 1 year ago
Thanks for the comment.
For small work pieces, and a small drill bit, as in the photo, it is still a bit tricky.
isacco1 year ago
I like this instructable very much. It is useful, clear and well illustrated. It will be of great help for my workshop.
Bill WW (author)  isacco1 year ago
Thank you Isacco.
fagnelli1 year ago
For small jobs, you can use the "pretend machinist" method:
1. Chuck the bit upside down.
2. Lower it into the drill press vice and secure it.
3. Unchuck the bit. Now you have the bit secured in the vice and pointing up.
4. Chuck the rod you need to drill, start the rotation and lower it on the stationary bit.
jexter1 year ago
Great Instructable. When I saw the first image I thought the idea was to:
1) Clamp the block of wood to the drill base
2) Drill hole the size of the rod
3) Put rod in hole (don't move wood block)
4) Switch drill bit to the size you want in the rod
5) drill hole through rod

Might work I guess, as long as there isn't any play in your drill press. I like your idea better!
Bill WW (author)  jexter1 year ago
Thanks for the comment, jexter.

Yes, I tried your idea also. In theory, and in practice most of the time, your idea should work perfectly. For some drill presses there is not too much room for switching drill bits, and having a top quality drill press would help too. You know, a nice big solid machine.
r-philp1 year ago
I have had some luck drilling holes in the exact center of circular stock by placing the stock in the chuck, clamping the drill bit in a vise. After lining up the bit on the center point, I turn on the drill press, and bring the work down onto the bit. By rotating the stock and keeping the bit stationary, the drill "wants" to seek continue through the center, and doesn't drift off center, even with deep holes.
Bill WW (author)  r-philp1 year ago
Thanks for the comment.
Never thought about chucking the part in the drill press chuck, great idea! Also, th drill press chuck will likely be larger and will accept larger dia stock.
Balord1 year ago
Hey Bill! If you ever have need of this again (for this particular size and shape, you can get what I learned to call "Pop-rivet" drill bits of various sizes (according to pop rivet size) with 1/8" being one, that are pretty much self centering. The will drill a hole in auto body steel without center punching and ALSO without any wobble-away with a hand drill. Coupled with your block jig you should be able to drill your jig, place the brass rod in, put the pop rivet bit in the drill press. The point is mechined in such a way as to bite into the surface at the first contact and with a drill press you should be able to bypass the punch & dimple step all together. Only other thing I might suggest would be clamps that would be less likely to move...and actually of your press has a fence on it you could get by with one C-clamp to hold it against the fence.
Another cool way is chuck the rod in a pillar drill, lower it down into a clamp then unchuck it. Whatever you drill then will be not only right in the middle, but straight too.
good idea!
Link your idea up with Bill's block. Once the rod's in the hole, clamp the block to the table and you've created an instant production set-up with no measuring what-so-ever... i LIKE it.
bfk1 year ago
Very nice. You taught me quite a lot. The additional advantage of your drilled block is, you can keep it in place, insert and drill multiple rods without having to find their centers.
Tip: Don't tap the scriber with a mallet too hard (if at all). Scribers are made of very hard, but brittle steel, and you don't want it to shatter.
action pig1 year ago
I have struggled with this before! Very clever, nice 'ible!
rimar20001 year ago
Your methods are very interesting, Bill. I like that of the steps 5 and 6, they are very clever. Excellent instructable!
Now drill a hole lengthwise through a 1' by 3/32" brass rod.
Bill WW (author)  AJMansfield1 year ago
I think this is how they make seamless tubing, but with a mandrel, not a drill.

I don't plan on doing that any time soon.
Bill WW (author) 1 year ago
Thanks for the ideas and comments.

I "inherited" a wood lathe last year when my next door neighbor passed away. Will start to learn this new tool soon.

Spent a lot of my working career doing Civil and Mechanical Engineering in NC, TX, GA, AL, MS, as well as Midwest and Northwest states.. But not Colorado. Now have been retired 10 years.
jbrauer1 year ago
I like the idea of using the scribe as a wiggler.

I already have a couple of lathes, but if I was doing a bunch of these I would try this:
1) drill a scrap aluminum block the same size as metal rod, just go half way
2) use the point at the bottom of the drill hole to center your small drill bit, and drill through with the smaller bit
3) put the rod in the hole, flip the block over, and drill through the small drill bit exit hole into the brass rod
Phil B1 year ago
Thanks, Bill. I think I have tried these at one time or another. It is good to see them in one place.