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Author Topic: Drilling PVC  (Read 110692 times)

Posts: 442

« on: December 28, 2011, 07:20:51 PM »

I got a microfox for Christmas and am really eager to try out Fox hunting with my 7th grade students (I am a teacher).  This weekend I tried making the tape measure yagi but didn't like the way the tape measure elements are distorted when clamped to the 1/2 inch T's.  I noticed that the curvature of a 1 inch tape measure really lies nicely over a 3/4 inch piece of PVC.  So why keep it simple!  I determined that if I could drill a 13/16 inch hole in a short piece of 3/4 inch PVC and use that in place of the 1/2 T's and 1/2 crosses and then run a piece of 1/2 inch PVC through the holes as the boom, the tape measure elements lie really nicely on the 3/4 inch PVC without distorting.  And the 1/2 inch boom doesn't interfere with the lie at all.  Great idea, so I thinks!

My problem is drilling the holes in the PVC.  I have a small drill press and V block so I can hold the pipe still and get it centered really well.  However, when I advance the drill bit through the PVC, it chatters and eventually catches and splinters the PVC.  I have tried both a spade bit and a twist drill with the same results.  I think the problem is that once the point exits through the first wall, there is nothing to guide the bit until it reaches the opposite wall.  Hence the chatter and splitting.

So after all of that, my question is - how is the best way to drill this hole through the PVC without splitting it?  Any tricks to the trade?


Posts: 18079

« Reply #1 on: December 28, 2011, 08:44:07 PM »

I was just out drilling PVC pipe for a direction-finding antenna, and I've never had any
problems.  But I use a high-speed twist drill rather than a spade drill.  After the drill
passes through the first side of the pipe I stop, plumb the drill, and start into the far
side slowly (just as I do when starting the first side.)  I've never had problems with
this - except that I never get the hole quite straight.  In some cases it is actually
better to drill a separate hole from each side, but you can't always get a bolt to
fit though it properly.

But on re-reading your description, I see the difference - I rarely drill anything
larger than 1/8" in the PVC pipe or fittings.  For a 13/16" hole I'd drill a pilot hole
about 1/8", then go in from each side with a larger bit.  A twist drill at fairly low
speed should work, but first I'd experiment with one of the new-fangled step
bits and see if that does the job.  (It might not, since the step drill is designed
for drilling flat plates.)  If you drill too fast then the plastic will melt rather than
being cut, and will stick to the drill when it cools.

However, this really shouldn't matter - I wouldn't bother using such an approach
for a tape-measure yagi.  I've built at least 6 or 8 of them over the years I suppose.
While the first one followed the original WB2HOL dimensions, since then I've adapted
other yagi designs to use tape measure elements with better results.  The original
was designed for a sharp rear null, but I never use that when I'm hunting, so I
choose yagis for good gain and half-power beamwidth.  However, if you are using
an unmodified HT without an external Offset attenuator, the null might be the only
way you can take bearings on stronger signals.

I have seen folks using 3/4" PVC pipe for the whole frame, then put the elements
THROUGH the Ts and crosses and insert small pieces of 3/4" PVC pipe to hold them
into place.  (This may require filing out part of the fitting, depending on the thickness
of the tape.)  My approach, however is simply to secure the elements to the outside
of the croses and Ts with fiberglass strapping tape:  cheap, simple, and light-weight
compared to using hose clamps.  For the driven element I use a wrap of tape plus a
sheet metal screw through the tape and into the PVC fitting on each side as it lacks
the structural integrity of the continuous element.  You can't really drill the tapes,
so I punch a hole in the tape with a small nail. mark the location on the PVC, and
pre-drill a hole slightly undersized for the screw.  (I used to use the screw for the
connection to the element, but that isn't very reliable over time.)

The tape also appears to overcome one of the primary causes of failure for tape
measure yagis - stress either at the screws or the hose clamps where they are
attached to the boom.  The tape has enough "give" to it that it helps to keep
the stress from focusing at a sharp edge.

Actually I usually the 3/4" or 5/8" tapes from a dollar store - each is long enough
to build a 2m yagi with some extra reinforcing in the center of each element.  This
is lighter and more convenient than the heavier 1" tape, and the reinforcing helps it
to snap back into shape faster.

Meanwhile, here is another method of attaching the tapes that might work for you:
« Last Edit: December 29, 2011, 08:38:40 AM by WB6BYU » Logged

Posts: 14790

« Reply #2 on: December 29, 2011, 08:19:13 AM »

Start with a very small sized bit to drill a pilot hole. Drill all the way through both sides. Then use that pilot hole to drill from each side, outside in. Keep increasing the size of the bit a little at a time until the hole is the proper size.

Bob  AA4PB
Garrisonville, VA

Posts: 445


« Reply #3 on: December 29, 2011, 03:17:26 PM »

When drilling PVC, I've found that running the bit at a higher speed and plunging into the material at a slow pace works best.  However, as others pointed out, you should step through the drill bit sizes to obtain the desired hole. You could also purchase a stepping drill bit, I've seen automotive shops using this style of drill bit when drilling rear handles on pick ups and SUVs, when installing rear cameras in the plastic door handle assembly.  The drill bit always seems to leave a nice clean hole.


Posts: 18079

« Reply #4 on: December 29, 2011, 04:15:45 PM »

In fact, a small hole saw might work better than a standard bit.

But you need to take small pieces, so moving the drill in slowly, without getting the
material too hot.

Posts: 5510

« Reply #5 on: December 30, 2011, 11:38:12 AM »

My problem is drilling the holes in the PVC.  I have a small drill press and V block so I can hold the pipe still and get it centered really well.  However, when I advance the drill bit through the PVC, it chatters and eventually catches and splinters the PVC.  I have tried both a spade bit and a twist drill with the same results.  I think the problem is that once the point exits through the first wall, there is nothing to guide the bit until it reaches the opposite wall.  Hence the chatter and splitting.

So after all of that, my question is - how is the best way to drill this hole through the PVC without splitting it?  Any tricks to the trade?

To prevent fracturing plastic... a step drill bit or a hole saw is the answer.

A pilot hole (with a much smaller drill bit) is necessary with either.

Hole saw is probably superior method, if you went with a step drill into the side of a small diameter pipe, you would need one of the "thick material" step drill bits.

« Last Edit: December 30, 2011, 11:40:10 AM by N3QE » Logged

Posts: 1897

« Reply #6 on: January 01, 2012, 09:43:44 AM »

Another approach that may help is to *just* break the sharp edges on the two cutting flutes w/ a small india stone sharpening slip. This works particularly well for drilling polycarbonate, and may help w/ PVC too. Start w/ a good, SHARP, high speed steel twist drill (no brand-X import junk) and just barely break the two edges at the end of the flutes; this will keep the drill from trying to dig into the plastic -- though it will not work well in metal once this is gone.

Also drilling a tiny (say 1/16 -1/8" depending on the size of the final hole) starter hole first will keep the bit from wandering at the start of the hole, The other side should be easier as the bit is supported (a little anyway) by the initial initial/top hole and the second surface is concave not convex.

Posts: 6

« Reply #7 on: January 02, 2012, 12:30:44 PM »

How about keeping it simple?

Put something (wooden dowel) inside the PVC pipe that will allow the drill to go though what will act like a solid.  Of course, you will need to first center drill it for a true start, then step up the sizes until you reach the desired diameter.

If you have a a stop on the drill press that you can work against, allowing the drill bit to advance in small amounts, you will be able to drill a nice smooth hole through the pipe.

When you are finished, pop out the remaining bits of wood & then deburr the hole.

Good luck with your project & hope your students appreciate your efforts.

73 de Jim - KE8G

Posts: 1208


« Reply #8 on: January 04, 2012, 01:33:49 PM »

Sounds like your bit is dull or spinning too fast .... drop the RPM some.

Slow feed speed, slower RPM on bit and best of all, use a SHARP UNIBIT .... no problems up to 1" with the UNIBIT I have. If needed, you can put a little cutting oil on it but I have never had PVC chatter.

Gene W5DQ

Gene W5DQ
Ridgecrest, CA - DM15dp

Posts: 270

« Reply #9 on: January 05, 2012, 04:06:27 AM »

I've been making PVC 2m/220/440 Quads/Quagis/Yagis for years. Using 1/2-1.25" PVC.
The biggest issue I had was keeping all the holes aligned properly to insure all elements/spreaders stay true and aligned in the booms. Using V block doesn't work, as soon as you reposition the boom you will be off a few degrees on the next drilling and the elements look crooked.  Shocked

My easy solution was to get square tube metal stock that has an ID just a little larger than the PVC OD. I drilled and tapped two bolts into the steel tube to trap/hold the PVC boom within. Then properly measure the the hole placement and drill through the metal tube and PVC boom (makes a great repetitive boom drill-jig for multiple boom making). The metal tube insures the holes remain 90degrees from one another as you just slide the tube across the drill press plate.  Grin I run my press at ~700PRM, never have an issue.

If you want more rigid boom you can stuff a wooden dowel inside the PVC, just make sure you lock the dowel into place before drilling (glue or machine screw).

You will need a drill press - makes it much more easy and repeatable.  Cheesy



Posts: 442

« Reply #10 on: January 05, 2012, 01:26:29 PM »

Thanks for all of the advice.  I am going to try the unibit - I've wanted one of those for a while but now I have a great excuse to pony up for one.  Drilling schedule 40 PVC us goint to require a fairly deep cutting section.

In the meantime, I think I'll go the route suggested by WB6BYU and the web link provided.  That looks like a very clean and lightweight installation.  I can see where cutting the larger PVC into 1/3 circumference pieces may be a challenge but I think I can do that fairly easily on my table saw.

Thanks for the feedback Kuby.  Yes keeping holes aligned in a pipe can be a challenge.  I have found that if I just place the piece of pipe along a piece of wood or iron and just use the edge to draw a line, I can drill the holes on the line and keep things lined up pretty well.  Of course if you are going to be doing an assembly line type operation, the drilling jig is the way to go.

I'll post some pictures when I finish with the antenna in the next few days.

Thanks again to everyone.


Posts: 270

« Reply #11 on: December 23, 2012, 08:05:54 AM »

My type of Jig for even a one time use works great.....

I made 10el Quagi that was ~20' long. I clamped a 10' steel 2"L stock onto the drill plate as a drill plate extension and used two ~12" square tube jigs to insure all my holes remained perfectly aligned. I just slide the jigs along the plate extension and drilled away. Since I had to piece 3-boom sections of PVC for this antenna I had to make sure all were true and the quad holes were perfectly 90degrees .... This method made the antenna look like a pro job.

This Square steel tube as a jig insures Quads/Quagi holes are a perfect 90 degrees and in-line....

True, I made a 3/4el 2m Quad jig for repeats, but I use this type of jig on all round stock to insure all holes remain aligned!     


Posts: 48

« Reply #12 on: January 05, 2013, 07:48:44 AM »

Kuby, N6JSX,

       Have any pictures of your jig set ups to drill PVC?  I'm not a machinist, but your jig sounds fairly simple and easy. It also sounds like something I could use for antenna projects. I just can't visualize it


Posts: 833

« Reply #13 on: January 10, 2013, 04:35:01 AM »

From memory, you want an angle rather less than the standard 116 or so degrees. But I would drill a small hole - say 1/4 inch - and use a taper reamer to gently ream the hole to the size you want.

Posts: 1703

« Reply #14 on: January 23, 2013, 03:25:29 PM »

Never use a spade bit.

My favorite is a step drill, one of the 10 sizes in one like Unibit.
I have one for smaller sizes and one for larger.  Never have
troubles with them.  the other that works well is standard
twist drills like commonly used for metal. Those work well
for sizes from 1/16th through 1/2 inch.  For larger either
the step drill or hole saws.


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