Alignment Issue

[BigBoy1]

I have a tube, 6" long and 1.5" in OD. I need to drill 3 holes, each 120 degs. from the previous one. These holes are through the wall of the tube. 0.25" from the end of the tube. There is no problem drilling the set of holes on the first end of the tube as is mounted in my vertical rotary table (RT) and then drilled in the correct locations.

However, the problem occurs when I need to drill another set of 3 holes in the opposite end of the tube. These holes are to be in the same angular position as the first set of holes. How would I align the tube in the RT so that when the hole was drilled it would be in correct alignment with the matching hole on the other end of the tube? Once I get the first one lined-up, the rest will be easy. Getting the first one aligned is the problem. Appreciate any assistance or ideas. Thanks.

[Tony]

how close does it need to be? how about good old fashioned layout lines.
run one down the side of the tube and use that as your location.

[Arbo]

Mount the tube in your lathe and scribe a line lengthwise down the tube using a cutting tool laid on its side just touching the work and moving the carriage from one end to the other. Using a small prick punh will then get you within a few thousandths alignment from one end to the other.

[Carld]

I use Starrett key seat guides like these. http://toolmonger.com/2008/08/21/dea...eat-clamps-34/ You can use them on almost any scale to scribe a straight line on a shaft. I have not bought from that company, I just did a google to get a photo.

[tdkkart]

Lay the tube in the V of a piece of angle iron, line up the edge of the angle iron with one hole or it's mark, then use the edge to scribe a line along the tube.

[duckman]

After drilling the first holes clamp a VEE block on to the tube in the middle, indicate flat, turn pipe around and indicate flat again with out moving the VEE block, you can't get much closer than that.

[LKeithR]

After drilling the first holes clamp a VEE block on to the tube in the middle, indicate flat, turn pipe around and indicate flat again with out moving the VEE block, you can't get much closer than that.

This idea gets the prize. Simple and more accurate than anything else. We use the same principal when we're bending tubes and have to align multiple bends in a single piece...

[RussZHC]

Put a tight fitting pin or if threaded, a threaded pin, into each hole at one end, flip and use the pin as a "stop" against the side of a jaw (of course it is a bit more complicated mathematically, i.e. knowing the center of the pin, and would be fiddly the first time, still...)

[DATo]

Put the tube in a mill vise and put one hole centered at each end at the proper spacing from the edge. Now set the thing up in the rotary table and locate the outboard hole with a drill blank or piece of straight stock of the same diameter in the drill chuck. Rotate and put in the other two holes ... then, take the part out, flip it, and repeat on the other side

[Lew Hartswick]

Put the tube in a mill vise and put one hole centered at each end at the proper spacing from the edge. Now set the thing up in the rotary table and locate the outboard hole with a drill blank or piece of straight stock of the same diameter in the drill chuck. Rotate and put in the other two holes ... then, take the part out, flip it, and repeat on the other side

+1 Or as they say "ditto" . :-)
...lew...

[baldysm]

Take a piece of hex stock and bore a hole in it so that the tube just slides in. Super Glue the tube in the hex block.

Put the assembly in the mill vise. Drill your holes. Rotate the hex, drill more holes, and rotate again.

Acetone will dissolve the Super Glue.

You could use set screws instead of Super Glue, but the glue won't mar the part at all.

I don't see how the V block idea solves the 120 degree issue. The hex block will get all the holes in alignment and 120 degrees apart.

[BigBoy1]

Problem Solved!!

I used Duckman's excellent suggestion of using the VEE block but I modified it slightly. After I had the holes drilled at one end, I clamped the VEE block to the tube but I put the flat bottom of the VEE block, perpendicular to the table. I then used an angle plate and squared the flat surface of the VEE block to the vertical side of the angle plate and clamped the VEE block tight to the tube. I removed the tube and VEE block and mounted the other end of the tube into the rotary table and again squared the bottom of the VEE block to the angle plate. Once square, the tube was clamped into the rotary table and the other set of holes drilled. Worked like a champ!

Thanks to all for the suggestions.

[Black_Moons]

Clamp a level onto the pipe.

[Harvey Melvin Richards]

When I need to drill aligned holes in pipes, I use a Reglus Angle Indicator. I think the V-block method could be more accurate when done right, but the Reglus would be close and much faster.