There are several possible methods to fix upper to sole. Here are the main:
In the past the upper was fixed to the insole-leather with “littleway” hooks and then the sole was pasted to neoprene or similar materials. Nowday this system is unusual and the shoe is directly pasted during lasting process using thermal adhesive, without “littleway” hooks.
It’s the most simple method to sew upper and sole. Upper edges are turned outwards, outside the last and sew externally. The upper is pasted to the middlesole leather and then stitched to the outsole.
3)Goodyear welt construction
The upper and the insole-leather (in this case it’s a middlesole-leather with a particular channeling.) are sewing with a flat seam to the welt by a special machine with a curved needle. Between middlesole-leather and tangent line to welt there’s a cork filling. The mid-sole is then sewing to the welt. In this construction both welt and sole are not pre-finished, but the excess on the edges will be trimed and finished later. To avoid sewing breaking, a grooving covers the second seam (it’s a channeling 1mm wide and 2-6mm deep from the sole edge) or a fastened insole rib ( an high precision machine channels under the sole, then the sole is seamed, an adhesive is applied and the relieved edge by the channel is closed and leveled). In Goodyear construction with border welt, instead of sewing welt, the outsole is only sticked on the welt.
A chain stitch seams the outsole, the upper and the insole leather .Sometimes could be used also “littleway” hooks (which are not visible on the insole-leather) and an overcast stitch instead of chain stitch, which increases shoes flexibility and resistance.
5)Blake Rapid construction
Once the shoe is on the last, the first sole (middlesole-leather) is applied and it is stitched by blake sewing machine to the insole-leather and to the calf leather upper.
A first adhesive is smeared on middlesole-leather and lasted shoe.
The shoe is pressed by the sole cementing machine , then before blake sewing the last is slipped.
The blake sewing sews the insole-leather and the middlesole-leather and it is visible inside the shoe. The shoe is re-lasted and a second adhesive is spreaded on middlesole-leather and sole. A rubber or leather sole is applied, then the shoe is pressed again by the sole cementing machine and the sole is roughed round. The rapid sewing machine sews the second sole or treadsole-leather to the middlesole-leather.
If the shoe has a welt, the rapid sewing machine inserts and sews it. The rapid seam is clearly visible on the welt and the bottom of the sole. If the shoe hasn’t a welt, it is visible only on the bottom of the sole.
The structure of the welt with the middlesole-leather guarantees the shoes will fit the foot perfectly and an excellent air permeability.
The double stitched Blake-Rapid shoes has got the advantage to guarantees the best possible imperviousness to water and durability of the bottom and also the possibility to be easily resoled.