As previously mentioned, yesterday I completed extending my 4m pole into a 7.5m mast. 🙂 This is all in the hope that I'll have it ready for the VHF/UHF field day next week-end. But with rain today I may not have time to finalise and test the guying system, but we'll see.
Anyway, on with the details of the setup.
The mast is now made of two sections:
– The original 4m 40mm OD aluminium tube; and
– The new 4m 44mm OD aluminium tube.
Both have a wall of 1.6mm and were sourced from Alucom here in Canberra (Fyshwick).
I also went to Bunnings and grabbed a 1m length of PVC with an OD of about 40mm and a wall of about 2mm. I've cut two 50mm lengths of this, and then cut a slit down length ways. These are then stretched over the top of one another and then over the 40mm aluminium tube. This alone is tight enough that you can actually have the 40mm tube standing inside the 44mm tube. However, once I add some beams etc I need more strength, so the PVC tubing has been pop riveted in two places to the aluminium tube.
This means there's now a nice sleeve around the 40mm tube starting 500mm from the bottom and which is about 4mm thick. This fits very nicely to act as a stopper for the 44mm base length, and further will act perfectly on the other side to rest the guy plate against (it's other key purpose). For the guy plate resting point it may not be the best as far as wear and tear long term, however I think for the amount of use it will get it should last many years. If it was going to be for a permanent setup at my QTH (rather than the field use it's intended for) I would want this to be metal.
Finally, mid way between the two overlapping sections of the tubing I have drilled a hole to accomodate a high tensile bolt. This serves three purposes:
1. Stops the sections coming apart when I'm trying to raise the mast;
2. makes the sections turn together when I rotate the mast (which for the moment, is via the strong arm method); and
3. As an extra bit of strength and security should the sleeve fail for any reason.
Anyway, so there you have it. Photos below should provide the detail of the above.
Next I'm making the guy ring. Long term I'll cut this from some steel plate, but for now as a trial of the whole thing I'm making it out of 6 ply plywood. Oh, plus I also need to make a baseplate as I don't think I'll be able to lift the mast up _with_ the beams and into the umbrella stand.
1. Wide angle of mast free standing in umbrella stand;
2. Detail showing both sleeve and bolt;
3. Detail of sleeve;
4 and 5. Detail of bolt;
6 and 7. Detail of sleeve with 44mm section of tube slid down a bit.