Drilling straight through aluminum square tube

I've worked with wood most of my life, but I'm not as experienced with metals... I recently found that I have to do a project for work that involves drilling multiple holes through both sides of 3/4"x 3/4" and

1/16 thick square aluminum tube to make antennas. Imagine a TV antenna basically... There needs to be multiple matched holes along each tube, and into those holes, 1/4" solid round will be inserted through both sides. In other words, the holes on both sides of the tubing have to be aligned pretty darn well, otherwise a slight misalignment will translate to the 1/4" round being way off center by the time it gets to the end... Which is about 1-2 feet long. There will be a tad bit of wiggle room since the round will be attached by threads on the end, and a nuts on both sides of the square tube, but not a whole lot.

I had no idea this would be so difficult. I went and got a Sears 9" bench drill press and proceeded by clamping the tube into a press vise. I figured once I had it lined up and centered, I could just slide the tube down for each hole... Wrong. There seems to be no rhyme or reason to how it turns out in the end. If both holes end up being centered on both sides, it seems to be luck more then anything. There seemed to be a lot of slop in the spindle on the drill, so I took that back and tried a Ryobi... Worse. The run-out on it was so bad, I could see it with the naked eye on just a 1/8" bit. When I rotated the bit 180 degrees and made an indentation, there was almost 1/32 of an inch space between the two. Ridiculous. I can't believe there isn't even a decent small bench press available nowadays, but that's a different story.

I've tried using short bits, center punching first, not center punching, 1/16" pilot holes, a countersink for a starting point... Nothing works. I've actually had better luck just drilling with a hand drill, but that only works for the top hole... There's no chance at getting the alignment right with bottom hole by had. I tried one of those portable drill press stands, but it just wasn't precise enough. Is there some kind of a portable drill guide I could use with a bushing or something?

I'm kind of lost at this point... Am I really trying to do something that can't be done without a mill? That's hard to believe. The actual physical aspects of the holes is good... Nice and clean. It's just the alignment I seem to have a problem with. I had no idea something that seemed so simple would give me such grief. I have a lot more respect for you metal heads now. Any ideas are welcome.



Reply to
Loading thread data ...

Dave: Since you are working with such a thin wall on your tubing, I would suggest trying a 1/4 inch end mill. You can chuck it up in your drill press since it is hardened, it may slip if it hangs, but if you get a center cutting one, it may resolve your problem. I would suggest a 4 flute end mill. If you can resolve the slop in the drill spindle, that would help. I drill a lot of 2 inch square tubing for trailer hitches. We use an annular cutter in a drill/mill. also, be sure you are not drilling thru the side where the seam is. It is hardened and thicker and will caouse drifting of your drill.

Reply to

Sounds like you need to make a small fixture with a hardened drill bushing to guide things. A drill bushing for a 1/4" bit will be about

3/8" to 1/2" in diameter by 1/4" to 1" long, commonly with a flange on one end. In your case, use a longer one to get the guidance for the far wall. These are replaceable when worn, run about $4 from
formatting link
(page 2423)

The fixture can be made of wood (hardwood) or metal (alum> I've worked with wood most of my life, but I'm not as experienced with

Reply to

Can you purchase a bushing block to stabilize the drill bit prior to it hitting the tube?

How many holes are we talking about for the whole project? 100, a million, etc.

Joe - V#8013 - '86 VN750 - joe @ yunx .com Northern, NJ Ride a Motorcycle? Ask me about "The Ride"

formatting link
Born once - Die twice. Born twice - Die only once. Your choice...

Have unwanted music CDs or DVDs of any type? I can use them for our charity. eMail me privately for details. Donation receipts available.

Reply to

Why not get ahold of the traffic department where you live, and ask them about buying a length of the pole they use to mount road signs? Look around your neighborhood and you'll notice most of the traffic signs are mounted on a piece of square tube that has holes every inch on all four sides. It may be worth it to you to make some adjustments in your project, materials, etc., to not have to drill all those holes. Ronnie

Reply to

I'll bet that in addition to the drill chuck being junk, the table is not square with the spindle. If you did this in a bridgeport, it would work fine, so it should in a good drill press. THink about finding a good quality used drill press. An old delta, rockwell or some other, with a real chuck and a sqare table.

I really like ht esears drill presses, but I alway replace the chuck , usually with a taiwanese albrecht cl> I've worked with wood most of my life, but I'm not as experienced with

Reply to

It's tough to get better than about +/- 0.015" accuracy when locating holes with a center punch and drill press. The slop in the quill bearings, chuck, table, and the starting point of the drill all add up pretty quick, as you found out.

If you need better accuracy than that, you'll have to build a jig and spot-drill each hole before going in with the bigger bit. Of find a cheap milling machine -- almost anything will have better rigidity and accuracy than what you're using now.

Reply to
Tim Killian

... the holes on both sides of the tubing have to be

... works for the top hole... There's no chance at

I must be missing something here. As I understand it, you need to have holes on opposite sides of the tube aligned. It seems obvious that you would just start at the top and continue through the other side. That it seems so obvious is why I think that I must be missing something. What is it?

The other part is how the series of holes down the length of the tube are aligned. There are 2 parts: how far apart they are and how closely they are to a straight line. You need to quantify both of these. E.g., they have to be 1" apart +- 1/32 and they need to be within a 1/32 of a line. A 1/32 was just an example, but your being a woodworker and not having much metalworking experience, 1/32 would be a realistic goal. If it needs to be much better than that, you'll probably need some help.

If 1/32 is good enough, a simple jig should get you there. Let us know and I'll go into it more.


BTW - you're in luck using aluminum - it works more like wood than it does steel.

Reply to
Bob Engelhardt

On 29 Jan 2005 10:02:00 -0800, the inscrutable "Ronnie" spake:

Has anyone here EVER successfully purchased anything from "the city" or "the county"? All I've ever heard was "We're not set up to do that." Of course, I haven't tried the "bribing the lone workman with cold beverages ploy" yet, either.

======================================================== TANSTAAFL: There ain't no such thing as a free lunch.

formatting link
Gourmet Web Applications ==========================

Reply to
Larry Jaques

snipped-for-privacy@aol.com wrote in news:1106983013.521991.220000 @z14g2000cwz.googlegroups.com:

If you're pretty good at wood working, this should be a pretty easy fix. Build a jig out of wood. Use a good quality hardwood board to make a base to which you will attach a fence. Next drill a 1/4" hole so that the center is precisely 3/8" from the fence, drill another that is spaced the same distance that you want the holes spaced on the tube., this hole will be used for a dowel pin that will determine the linear spacing of the holes. I would drill the holes first, then locate the fence by inserting a 1/4 inch pin in the holes then placing a 1/4" piece of flat stock between the pins and the fence. Instead of just using 3/8", I would measure the tubing and divide by two and locate the center of the hole at that dimension. Now clamp the jig to the table of the drill press. Locate the inside hole in line with the spindle of the drill press. The easiest way to do this is to insert the pin in the hole and then chuck on it with the drill chuck. Allow the jig to float to the center of the drill chuck. After you drill your first hole you are going to put a pin in the second hole and put the previously drilled hole over it to give you the linear spacing. Now drill the hole in the tube as follows: Locate the first hole by measuring, clamp the tube to the base and the fence. You should be able to use "Quick Clamps". Get a combination drill and countersink otherwise known as a center drill. Start the hole by drilling with this bit so that the countersink is just slightly larger than 1/4". Change bits to the 1/4" drill and drill through one side only. Now unclamp the tube and insert the pin in the hole located under the spindle. Flip the tube over putting the previously drilled hole over the pin. Repeat, drilling with the center drill and drill. If the mis-alignment is no good either adjust the jig or if being exactly in the center of the tube isn't very important, flip the tube and rotate it end for end. For the second and subsequent holes insert the second pin and use it to locate for precise spacing between holes. You need to minimize the drill runout if you can. If you can't, try using a small trepanning tool, or a two flute end mill instead of the drills.

Hope you can understand what I'm trying to describe. Good luck,


Reply to
Dan Murphy

Purchase? No. But a lot of the time the workmen will give you small stuff for free. Ask in the yard, not the front office.

--RC "Sometimes history doesn't repeat itself. It just yells 'can't you remember anything I've told you?' and lets fly with a club. -- John W. Cambell Jr.

Reply to

Purchased, no... But I've got friends there and I've acquired some decomissioned stuff for the price of a question...

Regards, Joe Agro, Jr.

formatting link

My eBay:

formatting link

Reply to

Those are all good suggestions guys, thanks. As to the idea of the table being off square, that was the first thing I checked. So it wasn't that. But I did end up building a jig as suggested, and it helps a lot. But as a side note... I noticed Harbor Freight had it's little press on sale for a ridiculous 39.95 this week. I had absolutely no expectations, since I tried two presses that were more, with poor results. But I figured for $39.95, what did I have to lose. If it didn't work, I was going to give it to a friend... Well, guess what... Not only is it better quality then the two over $100 presses I tried, but it seems to drill straight. Go figure. Maybe I just had bad luck with the others.

Thanks for the help,


Reply to


Since you work with wood, do you happen to have one of those self-centering dowling jigs? Like this:

formatting link
Mine's a lot older and uses cast clamping jaws instead of extrusions, but I use it periodically for putting in centered cross-holes where a drill press would be hard to use. If you've got one, give it a whirl. Try those piloted sheetmetal bits, too("Bullet bits"). Spacing your holes might be a problem, but not unsolvable.


Reply to

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.