Holes in square tubing

Apologies for not knowing any of the right terminology; this is not my area of expertise by a long shot. Also, apologies if this is in the wrong place.

I have drilled a bunch of 1mm diameter holes in the face of a square aluminum tube. The material is listed as 6061-T6, and is 1/4" thick (the tube itself is 2.5" square and 8' long, if that is relevant).

Naturally, by virtue of drilling the holes, the material is now raised slightly around each hole. I need the surface to again be flat. I think I could deal with having to countersink each hole a bit, if that would be sufficiently easier than any other solution, though I'm not really finding appropriate bits in that size.

Are there any other solutions available that I could do myself with limited equipment? If not, I am not entirely certain what sort of shop to approach to ask them to perform this work, and exactly what would be the easiest thing to ask them to do. Am I looking to have the entire face cut? Can you let me know appropriate terminology and help me look in the right direction?

Thanks!

Sounds like you have a slight burr around each hole. Is there a reason why won't a flat file remove the burrs and smooth the surface adequately? Aluminum is soft. You might need a couple of iterations of file, re-clear the holes with drill, re-file. Doing this in production would be another story.

scotchbrite pad, sandpaper, file, countersink, etc.

All depends on your surface finish requirements following.

Easy way, if you don't want to buy something, take a surplus tap and or drill bit or any other cutting tool and grind a point on the front, just spinning it between your fingers while holding it up against a grinding wheel, then grind half of it away (making a D, if you look at the end of the tool).

can you take some quality pictures showing the condition you have to improve on? What are you using now for drill bits to get it done and the equipment you are using?

MSC Industrial Supply Co.


Boom. Done.

How many holes per piece? How many pieces? Are the holes through or blind? What is limited equipment, just a drill press? Plan on doing it by hand, with a powered hand tool, with a machine tool? Or are you planning on something for future production where the operation can be done in one step? Inquiring minds want to know. What is the finish reqirement? If this is DIY a simple Foredom or even a Dremel with a pointed bit like this Busch Carbide Burs, 9deg Hart, Fig. 414AU or this Product Details - dremel.com would work for a one off in aluminium. They may bounce around some if you aren't careful but they'll get it done.

JR

In a perfectly drilled hole, there should be no dig out on front, and just a small burr on the rear of the hole. I assume that the problem you are trying to correct is the dig out on the front of the hole, not the burr on the back of the hole.

It is not unusual to experience dig out when drilling small holes in soft materials. The proper adjustments to technique to avoid this are as follows:

(1) Change the geometry of the cutter. Due to the complexity of this solution I will not discuss it further.

(2) Increase the drill speed. In your situation the drill should probably be operating at about 8,000 to 10,000 RPM. You can buy mini drill presses that spin this fast. Once you have a working system, you can experiment with lower or higher speeds and compare results, but I would start at 8000 RPM.

(3) Feed at the max rate. The drill needs to be fed into the work as fast as it can go without bending.

(4) Lubricate. The lubricant can make a large difference. You can try kerosene, but you might have better results with lanolin. Make sure it is absolutely pure lanolin with nothing added.

jlrii said:

How many holes per piece? How many pieces? Are the holes through or blind? What is limited equipment, just a drill press? Plan on doing it by hand, with a powered hand tool, with a machine tool? Or are you planning on something for future production where the operation can be done in one step? Inquiring minds want to know. What is the finish reqirement? If this is DIY a simple Foredom or even a Dremel with a pointed bit like this Busch Carbide Burs, 9deg Hart, Fig. 414AU or this Product Details - dremel.com would work for a one off in aluminium. They may bounce around some if you aren't careful but they'll get it done.

JR

Click to expand...

There is only the one piece, but there are 500 holes (yes, I'm a nutcase). They are through holes. I do have a drill press, but I had to do these with a powered hand drill because of the size of the bit/holes (the drill press is old and cranky and far better suited to non-precise tasks). This is just DIY. I'd love to make more of these at some point, but not looking to ramp up to anything more than DIY.

jscpm said:

In a perfectly drilled hole, there should be no dig out on front, and just a small burr on the rear of the hole. I assume that the problem you are trying to correct is the dig out on the front of the hole, not the burr on the back of the hole.

It is not unusual to experience dig out when drilling small holes in soft materials. The proper adjustments to technique to avoid this are as follows:

Click to expand...

Some of the holes just have a bit of burr at the front. I don't care about the back (inside the tube), where there surely is burr. However, a number of the holes look more like a mound at the front, around the hole. I assume this is what you are referring to as dig out. I know that better technique would improve this for the future (and cost a lot more), but I'm asking about solving the current problem now that the piece looks like this. Any advice would be appreciated.

magneticanomaly said:

Sounds like you have a slight burr around each hole. Is there a reason why won't a flat file remove the burrs and smooth the surface adequately? Aluminum is soft. You might need a couple of iterations of file, re-clear the holes with drill, re-file. Doing this in production would be another story.

Click to expand...

Some of the holes are more than just burr (there is a raised "mound" all around). Also, for the ones that are just burr, I'm not sure really what is the most effective technique to file this without inadvertently marking the surrounding surface.

There are, in woodworking tooling, countersinks with adjustable collars to control depth. One of those would let you make you cut a clean, uniform chamfer on each hole at very little expense.

jds10011 said:

Some of the holes just have a bit of burr at the front. I don't care about the back (inside the tube), where there surely is burr. However, a number of the holes look more like a mound at the front, around the hole. I assume this is what you are referring to as dig out. I know that better technique would improve this for the future (and cost a lot more), but I'm asking about solving the current problem now that the piece looks like this. Any advice would be appreciated.

Click to expand...

If you want to repair holes with digout already made, I would recommend re-forging the holes. Methods involving grinding or cutting will usually leave a non-hole-like shape.

To re-forge the holes, the idea is to push the metal back into the hole. Make a small needle-like tool out of aluminum or maybe even a hard plastic. The tool has to have a flattened face to ride smoothly on the work. Use it to carefully push the dig out back into the hole. Use a magnifying glass. Once you have the top of the hole perfectly flat re-punch the hole using either a 1mm ball bearing or a 1mm pin punch. You will probably have to resurface the top of the bar with scotch brite or other mildly abrasive pad to rub out the burnish marks left by your push tool.

jds10011 said:

Some of the holes are more than just burr (there is a raised "mound" all around). Also, for the ones that are just burr, I'm not sure really what is the most effective technique to file this without inadvertently marking the surrounding surface.

Click to expand...

One more approach:

With 500 holes to do, I think I would just use a 1/8" diameter single flute countersink like this:

Item number 2846A121 at McMaster-Carr. (Direct link posting not feasible for their site)

Put it in a hand-held drill motor and have at it. These countersinks have zero tendency to chatter and will make quick work of each hole. Turn it at a slow speed with moderate pressure. Might use a drop of WD-40 for a cutting fluid, but probably unneeded. 3 or 4 revs and that hole is done. Even using a countersink there may still be a very slight raised area around each hole. So, you may still end up using a piece of 400 grit Si-Carbide paper on a backing block to get rid of every last trace of raised edge and also brightening the entire bar surface, if that is acceptable.

Speaking of slow speed, I would not worry about turning your drill bit at very high speed. More to be gained by being certain your bit is sharp and of decent quality. I have drilled a lot of holes much less than .060" diameter at only 2000 RPM. Works fine. Look at any chart for drill size vs RPM and they all say crazy high speeds for small drills based strictly on SFPM. It could be that higher RPM results in faster penetration under ideal circumstances. (At six diameters depth, your greater concern is pecking often enough to prevent snapping the drill. I like to use a sensitive feed chuck in this circumstance.) But plenty of small holes are successfully drilled in aluminum way under "chart" RPMs. (I know that opinions among reasonable people vary on this subject--just stating mine)

Denis

Take a belt sander and give it a fast once over.

what is the problem with a piece of sandpaper? the finish or is it anodized? you can use a larger drill (preferably 135°) to deburr by hand, but 500 holes?

A small electric DA sander with a fine pad works for me on similar things, will only remove the burr and next to nothing off the material, cheap, fast and easy.

piloted aircraft countersink in a cage. buy one used from ebay
Bill D.

9 Piece Countersink Cage & Cutter Kit | Brown Aviation & Aircraft Tools