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Drilling round booms for a VHF or UHF yagi.
The use and drilling of round boom material is not beyond the average ham’s work shop. Since the cheaper brand of home handyman tools have become common in the stores, the ability to own or borrow the needed tools has become an affordable reality.
Why I prefer round booms over square?
1. I am a traditionalist, a yagi should have a round boom. :-)
2. There are telescoping sizes available in round that are not found in the square sections. This is important if you wish to lengthen, join or strengthen a boom as the neat mechanical fit of telescoping sizes provides both strength and relatively low weights
3. A round boom provides a lower profile for side winds and in the long run lessens the load on the rotator and tower.
Most of the tools needed to produce a drilled boom for your next yagi are modest and can be found in either your or a close friends workshop, the only exception to this is the slide and clamp to keep the boom aligned. But we will get to that in a minute, so let’s start with a little list of basic hand tools you will want to have around.
You will notice that a hacksaw is NOT on the list of tools, it is probably the most dangerous tool to have around for cutting ali tube as it can wander horribly and spoil an otherwise great looking boom.
Decide on a design well before you start to assemble your material, be sure the chosen design is able to be scaled or adjusted to meet your available material or that you have the same material used in the original design. Many builders have come unstuck by thinking they can fudge an existing design to a new material size.
I am not here to push or recommend a particular design, this part is all up to you.
On to the jig, in many ways this is the heart of how this all comes together. It consist of three parts, one being a length of rectangular hollow section (RHS) tube [70x45mm in my case] you can buy from your local metal supplier. The next two parts require you to do a bit of cutting and bolting to assemble the components into the finished items.
Rather than me trying to describe a blow by blow of how they were built I am sure that each person will have their own take of how best to get to the finished product. I am only trying to show that is can be done in a home workshop with a minimum of tools. Indeed my jig here is loosely modelled on a friends setup in VK6, who has built many more yagi’s than I over the years. His jigs were hand crafted works of art where as mine are from the “mechano set” school of assembly.
The basis of the jig can the thought of as a bed like used in a lathe, in that every thing on the jig moves relative to this bed, which provides a consistent reference for the drilled holes in the boom material. By having the sliding clamp and the drill locator point as items attached to the bed, the angle of each hole should be the same each time you lower the drill press head.
As the cliché goes, a picture is worth a thousand words so here are some photo’s of my boom drilling jig, firstly here is an overview of the jig setup out the front of the shed, your driveway could just as easily be used for this.
Here is my boom drilling setup, when assembled there is not much to it, one drill press, one length of RHS tube and two custom made clamps
Sack truck's are a cheap and plentiful around here hence they get used for all sorts of jobs :-) There is a length of 32 mm ali tube on the jig ready to go.
This is where the action happens, the boom is centrally located in a V block which is secured in place on the RHS tube.
Once it's location is checked, each hole drilled will be centred on the boom
Another view of the business end of the jig, yes it is simple and not complicated BUT it gives reproducable results.
Look down the bed of the jig, the two pieces of angle iron make a nice V for the boom to sit in ensuring the drill bit's path is always through the middle and not off to one side.
Here is the other end of the jig, the top section clamps the boom so it can not rotate but allows the boom to be slid along as you drill each new element hole.
Once the clamp nears the drill press when drilling element holes, you will need to lower the drill into the last drilled hole and lock the chuck in the lowered position. Most drill presses that I have seen have a collar around the depth handle to allow the up/down movement to be locked in one location, in this case down. Once this is done you undo the nuts on the clamp jig and slide it back to the furthest point away from the drill. The you can let the drill come up and start on the next series of holes.
Another view of the clamp that slides along the bed, it was built using bolts where possible as I did not have a welder. A friend tacked the two pieces of angle iron in place for me.
This is the "dril end" jig, there is no magic to the jigs, a trip to my local metal supplier and a few hours with the hacksaw produced the bits needed from the scap bins
This is the "sliding" jig, it's sole purpose is to stop the boom material rotating inbetween holes being driled, once again, no magic just gave the elbow a work out with the hacksaw.
Both jigs sitting side by side on the RHS section used for the bed.