Apply Heat Transfer Vinyl to Tricky Objects

I know, I squandered that career in modelling I was destined for... I like playing with different materials on the vinyl cutter and I've used HTV or Heat Transfer Vinyl a little bit, but usually limited to flat smooth fabric items. At home I've used the domestic iron to apply designs to bags and tee shirts and at the Ffiws makerspace where I work sometimes we have a larger flat plate heat press. However I wanted to experiment with HTV on more awkward surfaces, i.e this baseball cap. I'd seen crafters in the US using smaller irons specifically designed for HTV but I couldn't find them in the UK or running at 240V rather than 110V.  However, another area that uses these irons are aero modellers building lightweight planes which have a heat shrunk covering applied to wings made from balsa ribs and spars. I ordered one to have a play with for less than £20.   

There are commercial hat presses for sale or heat presses with replaceable elements in different shapes for different objects and these obviously apply heat and pressure uniformly and make HTV hats trivial to create. However for small batches the iron works well. After cutting the HTV on the vinyl cutter and weeding (removing the parts of the vinyl that aren't part of the design) I stuck the HTV and the heatproof backing onto the cap in the correct position. Note that if you want to have a go at this you want to find a 5 panel baseball cap rather than a 6 panel baseball cap as a 6 panel has a seam vertically down the front of the cap. The curvature of the hat makes it almost impossible to stick the HTV backing down too, more because of the thickness of the backing rather than the stickiness. You also want to curve the HTV/Backing to conform to the hat rather than making the hat panel flat as that would then crinkle when the hat returns to it's normal state. I used extra kapton tape (heat resistant tape) to hold the HTV panel in place, but neither the tape or the backing adheres that well, it's only when you tack the first part of the design with the iron you can feel assured it won't move.  

My original plan was to stuff the hat with an old towel to try and keep the hat firmly in shape, however I realised that it was easier to cover one hand with 3 layers of the towel and push into the back of the design with one hand and then hit it with the mini iron using the other hand. I set the iron to roughly 160C and applied the iron to each section of the design for around 15 seconds. I made a slight error on the first attempt as I hadn't noticed a bit of kapton was stuck under and lifting an edge of the design, so I opted to cut the black HTV ring around the yellow design and add that as a second layer to cover the slight error! One thing I noticed is that due to the curvature of the cap the HTV backing kind of self releases when the HTV is stuck which is very useful and means you automatically peal the backing whilst it's still hot. I'm pretty pleased with the results and the iron is great and will be useful for this as well as other model making activities.