accurate drilling at an angle?

I need to drill some fairly accurate holes at an angle through some aluminum square tubing (or whatever you call tubing that's square instead of round).

I guess the main problem is that my cheap drill press has some play in it so that the bit doesn't necessarily follow the intended path straight down. So when I put the metal at an angle, the bit is going to move towards the deeper side as it drills into the metal.

... should I use something to press on the spinning chuck shaft so that it drills closer to correct?

... if I were to drill straight down through the aluminum with a smaller diameter bit, when the aluminum is angled will the larger drill bit end up going through the center of that hole? (Yes, this is easy enough to test)

... is there some trick I don't know about?

Thank you.

Reply to
John Doe
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You may be able to get close enough using a drill guide. No matter what, guide hole or not, you're going to have a problem with the drill generating side force and deflecting away from the hole. Someone smarter than me will answer, and I'll learn something.

In the mean time, I would do this with a square-face (NOT ball-end) end mill in a nice rigid machine like a mill/drill or a real milling machine

-- not a cruddy old drill press.

Reply to
Tim Wescott

You can first come in with an endmill to make a flat.

Then come in with a centering drill and drill an accurately located hole. It will not deflect because it is on the flat.

Reply to
Polymer Man

"Polymer Man" wrote: (clip)Then come in with a centering drill and drill an accurately located hole. It will not deflect because it is on the flat. ^^^^^^^^^^^^^^^ Yeah, but OP said he had to drill THROUGH the tubing. Your method will get the drill started okay, but what happens when it gets to the other tubing wall from the inside?

I guess he could lay out the "exit point" very accurately and come in from the other direction using your method.

Reply to
Leo Lichtman

Since you need accurate hole location, and all you have is a drill press, then you need to make a drill fixture. Depending on the number of holes you could make it out of aluminum. If you need to do lots of holes then aluminum could still be used but you would need to buy a couple drill bushings. They are pretty cheap, and harder, lots harder, than your drill. I don't know what tools you have or how handy you are but here's a couple suggestions. Make a box, by bolting 1/2" plate together, that slips over the tube with little clearance. Drill and tap a hole for a screw to hold your part in the fixture box, so that it can't shift while drilling. Set this box up at the angle you want. Grind a flat where the drill will enter, drill first with a center drill, then an undersize drill, then ream or drill with the final size drill. Turn over the fixture and repeat. Then you can drill through from the outside for each hole. This all requires careful layout. If you need the drill bushings then order them and the reamer for them at the same time. To support your fixture you could make an angled support out of MDF. This would cradle the fixture at the correct angle, is very repeatable, and would allow turning over the fixture fast. You can put a dowell into the MDF to locate the fixture the same each time. If you have only a couple parts to do then the whole thing could be made of wood. If only 1 part then clamp some MDF to the part, grind a flat so the drill starts easily, drill undersize, then the final size. The MDF is dense enough and hard enough to act as a drill bushing for a hole or two into aluminum. Good luck! ERS

Reply to
Eric R Snow

Hey John D.,

Best to create a "flat" with an end-mill in the drill chuck for the drill to at least get started in, and better if you can make the end-mill go right through the first side. Even a ground off to flat ended drill bit will work in a pinch. It will be fairly straight. If you can't do that, then lay the material flat and get a dimple drilled at least to help. Bit of practice won't hurt. You don't say how steep this "angle" is, or whether the tube is straight and is it open ended, or how many of these holes you need to make. If it is open and straight, you could get a piece of wood (at least for a test) that is a fairly snug fit inside the tube, and drill VERY easily through that, and when the drill bit touches the "far side", just go in little pecks to lessen the deflection. Or even the "flat ended" drill bit trick again, in lieu of an end-mill. The larger the drill bit, the less deflection you should have, so don't use a "small" bit first. If you've got more than a couple of holes to do, use hardwood.

If you want to get elaborate, drill straight through a piece of steel, say 1" stuff, then hacksaw the steel off through the hole so that you have created a drill guide of the desired angle to clamp to the outside of the aluminum to help guide the drill bit through, then through the wood inside. One other thing that the wood inside does, if it is tight enough, is help eliminate the burr inside too.

Take care.

Brian Lawson, Bothwell, Ontario.

Reply to
Brian Lawson

If you only have a few holes to drill, you can use a small drill and start a hole perpendicular to the tube. Don't drill it very deep. Now use a countersink on the hole. Now try a small drill at the angle you want. Followed by the full sized drill. Don't drill through the other side.

Repeat the above for the other side.

I am assuming that you don't have a end mill and that you do have a countersink.

This will not be super accurate, but better than trying to just drill at an angle.


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