Using toroids can be difficult when you do not know that science behind the device. There are many intricate parts to consider when building and using toroid coils. When using toroidal coils in frequency-critical circuits (like VFOs), they can potentially cause drift problems. Drift is calculated through looking at the changes in ambient temperature. Excessive drift will cause variations in a core's permeability. Ultimately, this leads to frequency shifts because the MU causes the coil inductance to vary.
As a means to combat change, it is important to choose toroids made from proper materials. Number .6 powdered iron is amongst the most stable cores for use in VFOs. The coils are coated three times in polystyrene Q Dope, which helps to keep the wires in place after being wound (increasing frequency stability).
After doping is settled, it is time to affix the toroid. It is important that their leads do not support the final device. This is especially the case when mounting toroid coils vertically. This lessens vibrations that can cause breaks in a small-gauge wire. Using quick setting epoxy on the bottom edge of toroids helps to hold it firmly in place on the mount.
For more information regarding toroid doping and affixing, please reach out to professionals in the toroid core winding industry.