How do I drill holes straight across a length of pipe?

[sixdogs]

I need to drill some holes across a length of 8 ft tubing so I can make a harrow-type thing to smooth dirt. The holes need to be in a line so the tines are all equally in contact with the ground. How do I mark those holes on the pipe so they are in a line on the pipe and don't drift one way or the other?

Do I just hold a string across one end and then the other or is there a better way? The string way could still drift at an angle? I'm going to use a vise in a drill press so the holes will be straight going through the pipe but I'm not sure how to line up the starting line holes.

Any advice appreciated.

 

[bcp]

Clamp a piece of angle iron to the pipe, with the pipe in the "V." The angle iron should be smaller than the pipe, so the edge is your marking line. It can be a little smaller or larger than the diagram shows.



Bruce

 

[/pine]

you could make a jig out of a pine 2x2...mark and drill the holes in the 2x2...then using some large hose clamps or even zip ties to clamp the 2x2 to the pipe...the "pilot" holes in the 2x2 should keep the bit straight going through the tubing...

before drilling the tubing make some control marks to make sure the jig does not travel any...

 

[Egon]

Metal scribe. Center punch.

 

[Sodo]

Make your line on the pipe with a pen. Angle iron as bcp mentioned works great as long as the angle size is 1/2 the pipe diameter or less. Clamp the angle to the pipe in case either the pipe or the angle are not perfectly straight. Then eyeball the length of it (from one end) to be sure it's straight & not spiral. If it's a little bent that's OK because each hole is still on the center.

Mark your points. Then with an angle grinder, put a little level 'ding' on the pipe that is a flatter surface. Since you ground your 'points' off, mark them again then center-punch, and drill on that new 'level' surface. If you want the dings to disappear, make them smaller than your intended hole size.

This will make the straightest harrow in your entire county. But anyway, it's easier to drill on a pipe if you grind a little flat spot first.

 

[k0ua]

I need to drill some holes across a length of 8 ft tubing so I can make a harrow-type thing to smooth dirt. The holes need to be in a line so the tines are all equally in contact with the ground. How do I mark those holes on the pipe so they are in a line on the pipe and don't drift one way or the other?

Do I just hold a string across one end and then the other or is there a better way? The string way could still drift at an angle? I'm going to use a vise in a drill press so the holes will be straight going through the pipe but I'm not sure how to line up the starting line holes.

Any advice appreciated.

Perhaps this could help you make the straight line on the pipe. Another way would be to find the center of the pipe on both sides, and drill the holes and put a nail thru the holes. Do this on both ends, then stretch your chalk line between the nails and snap it. If you don't have the angle iron to make the mark with. Now that you have a straight line on the pipe, build a wooden V block out of a couple of 2x4's with the ends chamfored off at 45 degrees and then screwed/glued together to form the V with your table saw Or if you have a V bit for a router you could route out a V block on a single piece of wood.. I would make one at least 2 foot long to cradle your pipe on your drill press table. You could make a facsimile of a V block on a 2 x 4 by gluing/screwing strips of 1x1 wood spaced correctly apart so the pipe was just barely above the surface of the base piece of wood. You would need to carefully measure with your intended pipe so that it is perfectly cradled on your strips and tangent on all sides.. Now clamp this onto your drill press tabletop perfectly centered. Insert pipe and rotate until marked line is Top Dead Center under the drill bit. This should drill straight centered holes in your pipe... There, free advice, worth every penny that you paid for it. Who knows, it might even work!

Mark Lines, Center & Opposite Points on Round Objects - Pipes, Pipe Caps, Rods, etc - YouTube

 

[J_J]

What could be any easier than what bcp suggested.

Once the pipe is clamped, just drill along one of the edges for a perfect line of holes.

Use small pilot bit for the first set of holes, then remove the angle and drill to the correct size hole. .

 

[k0ua]

Make your line on the pipe with a pen. Angle iron as bcp mentioned works great as long as the angle size is 1/2 the pipe diameter or less. Clamp the angle to the pipe in case either the pipe or the angle are not perfectly straight. Then eyeball the length of it (from one end) to be sure it's straight & not spiral. If it's a little bent that's OK because each hole is still on the center.

Mark your points. Then with an angle grinder, put a little level 'ding' on the pipe that is a flatter space. Since you ground your 'points' off, mark them again then center-punch, and drill on that level surface. If you want the dings to disappear, make them smaller than your intended hole size.

This will make the straightest harrow in your entire county. But anyway, it's easier to drill on a pipe if you grind a little flat spot first.

Hey, thanks for the tip on grinding a flat spot on the pipe to get the center punch and drill bit started, I hadn't thought of that.

 

[jmc]

Could be wrong but I think part of the problem Sixdogs is anticipating was, once you have a straight line down the pipe, how do you get that line at "top dead center" and the drill bit centered on the line.

One technique I've heard about and used on non-precision centering would not require a line in the first place. And it does require a drill press or mill. Place a small scale, like a 6 inch scale, flat on top of the pipe, and perpendicular to the pipe. Lower the drill bit (motor off) until it touches the scale and if the drill bit is off center, the scale will tilt to one side. Keep trying until when you sandwich the scale between the drill and the pipe, it stays horizontal. And yeah, don't grind a flat on the apparent TDC first. It only works on a curved surface.

Note: if you have a conventional drill bit (118 degree included angle, chisel point), orient the chisel edge to be parallel with the length of the pipe. (So the chisel edge does not span TDC). A more modern drill, like a 135 degree split point, will always make contact at its center, no matter what it's rotational position.

 

[jaotguy]

OK to get perfect holes "aligned" ...

drill the angle iron first with a small drill bit . . . . . . .

then clamp the angle iron to the pipe ....

drill thru the alignment holes ... ( drill can't wander ) don't worry about drilling at a bit of an angle at this point ...

remove angle iron ...

drill larger holes as needed ...