Drilling Through Pipe

I'm working on my second iteration of a quadrafilar helix antenna used for our Field Day satellite operations. One thing that has been particularly tricky has been to drill through 1.5" PVC with holes that are truly perpendicular to a line marked on the pipe. And with a string of 4 holes, each 90 degrees from each other, it has been a challenge.

Any good ideas on pulling this off? I have a decent drill-press, but so far this task hasn't been to the precision required to get the antenna just right. It is going to be even more critical on the 430MHz version of the beast.

--NCR

One thing you can try is two pieces of all thread. Drill the first hole put the all thread thru. Turn 90deg. You should now be able to measure or see plane now. Drill second one. Same thing. now you have points of reference. Other way is to make a jig that does it for you. Two blocks perhaps clamped/screwed together. Turn the jig block. 90. turn back... -90. can you see what I am getting at?

Wrap a piece of kite string around the pvc. Cut it so the string fits completely around the pipe without any extra. Lay the string out and measure it. Divide the measurement by 4. If it's 10 inches long, each segment would be 2.5 inches. Starting at one end of the string, use a magic marker to make a mark at 2.5, 5.0, 7.5, and put one more mark at the end of the string. Wrap the string around the pvc again, and mark the pvc where the marks on the string are. Use your drill press to drill a small hole in the pipe at each mark. Then drill the desired sized hole at one mark, and making sure the bit contacts the hole 180 degrees opposite, continue the drilling. If done carefully, they should be exactly 90 degrees apart. I hope that makes sense.

It aint fancy, but it works for me.

Both good ideas, that I will try on Thursday. Taking a couple night off to play hockey, new season and I'm anxious to get out there and get hurt.

Take a set of V-blocks which will snugly clamp the smallest pipe diameter, lock them together and drill a couple of pilot holes through both sides of the assembly, centered exactly in the apex of the Vee. (Works best with a piece of pipe in place and no more than 0.050" gap either side...preferably zero.)

Now drill an indexing hole at 90 degrees to the others. This will be at the "split" between the blocks.

Place your pipe in the blocks, clamp together securely then drill. When done you rotate the pipe 90 degrees to line up the indexing hole with the drilled hole then make your next set of holes.

For each larger size of pipe, make some metal shims which fit on either side of the pipe between the blocks and allow you to clamp the pipe tightly. Drill an indexing hole exactly in the center and line the hole up with each previously drilled "half hole" in the two V-blocks. Find the 90-degree center as before.