The G0KSC Element Insulators
COMMERCIALLY MADE INSULATORS NOW AVAILABLE IN OUR SHOP
Amendment 21/7/2010 I have established that insulators should be as small as possible, extending either side of the boom by an absolute minimum. A commercial offering by Stauff (www.stauff.com) provide an excellent alternative to home making and these clamps are just 30mm wide.
Please Read This section - If your antenna(s) is 6m or above and your insulators are more than 30mm wide and or electrically connected to the boom, any antenna you build with them my need correction. If you are stuck or unsure and want to explore this option, do let me know via Email.
Probably the most important part of your Yagi antenna are the insulators you will be using and sadly, there are not too many good quality insulators commercially available (without buying the whole antenna system!). To this end, I decided to design an insulator that would be relatively easy to make and provide excellent performance at the same time.
The main consideration for me when looking for the material to use was to find something which would be easily available to most Hams in most places in the World. Step in Plexiglass and Perspex. Used in anything from signs to tables, both brands of acrylic are available to buy widely and at reasonable prices. This is in addition to offering excellent insulation properties and being relatively lightweight too.
I buy mine from Ebay in A4 or A3 sizes and purchase 15mm thick sheets of clear Plexiglass. Buying sheets sizes much greater than A3 becomes a little expensive and as a result, a little less economic.
Insulator Sizing
For 50 and 70 Mhz I cut my insulators to 30mm wide by 100mm long. This 100mm can be reduced for 220 or 144 Mhz and increased in both width and depth for 28 Mhz and lower bands. I have not experimented with these insulators on bands other than 50 and 70 Mhz but will report on my findings (ideal sizes) once I have. However, logic suggested there should be no degridation in performance on the other bands and the associated strength should allow for the supporting of elements down to and below 28 Mhz.
Tutorial - Making the Insulators 
I have a table saw and table router which does make things a little easier. However, the same job can be carried out with hand-held devices too. If you really do get stuck, let me know. For a fee and can supply some of my own.
The insulators are cut from the 15mm thick Plexiglass/Perspex and are 100mm long by 30mm wide. First, I cut a 100mm wide strip from top to bottom of the A4 sized plexiglass and routed a 1 inch grove in the centre from one end to the other (assuming your boom is 1 inch square, if using metric sizing, adjust accordingly)which should be between 1 and 2mm deep. When you have done this, you can test your work by placing the Plexiglass onto the square boom length and if you have completed the task correctly, the piece should not move side to side.
Now cut the 100mm length into 30mm strips, you will have around 9 pieces from a strip this size so you have a few spares in most cases. As we did with the 100mm strip, we now need to route a grove in these 30mm wide strips from the elements to sit within. These need not be ½ inch. I made this around 4 to 5 mm wide In order that the elements sit above the insulator just touching it on each side of the grove. 4 to 5 mm give enough to keep the elements in place with minimum insulator effect on the elements themselves. Check out the photos of the insulators to ensure yours look like these!
For most of the insulators you are done but we need to do a little more work with the driven element insulator which we will cover now.
Driven Element Insulator
The dipole section will have a nylon 8mm (60 to 100mm total length) rod inserted into each piece of the dipole and just 10mm of nylon showing between the 2 aluminium lengths. These again are available on Ebay along with Plexiglass rods which are also acceptable to use albeit a little more brittle.
The driven element is the only 
element where the stainless steel bolt will NOT go through the element itself. Instead we need to countersink the drilled M6 hole in the insulator with a hole big enough to fit the head of our bolt into.
This should be 5mm deep into the insulator in order that the bolt sits well below the dipole centre. Next we need to align the dipole upon the insulator and measure along each side 5mm from the nylon joint on the dipole and drill through both the element and the insulator (see pic). This time, we need to countersink the holes as we did above but this time, the countersink will be from the bottom of the insulator. Insert stainless bolts (50mm M6) from the bottom up into the elements, place a washer upon these with a nut and tighten them. The protruding portions of the bolt will be used to bolt our coax to.
You should be now done and ready to install your remaining insulators and coax! If you have any problems or suggestions, do let me know justin '@' g0ksc.co.uk
73 Justin G0KSC