I was looking for a pair of korts to match the pair of props i have... but couldnt find the right diameter... so i decided to make my own Kort nozzles.
You can make them ready tapered, but its finding a tapered 'plug' to wrap the ply round... plus its a to cut the ply in a cone to follow the taper...
You will notice i have a lathe... and i cant think of another way of shaping the Kort unless its held back to the plug and spun in a drill.
Find a 'plug' that is the inside diameter of the kort you need. This can be a bottle, can or in my case, was a specialy made plug from some pine glued together and turned to the right diameter.
Wrap some trace or any paper around the plug to stop the first layer of ply from sticking to the plug.
Cut some strips of 1/32" ply to slightly over the width of the kort you need and chamfer (sand) the ends as shown in pic 001
Wrap the first piece of ply around your plug and glue (I use CA for speed) the chamfer to the inside of the wrapped ply, ensuring that the ply will wrap all the way round the plug without running off 'true' to the layer below it. see pic 002... and glue the rest of the ply around itself.
After the glue has dried, make sure that the plug will move within the ply as it needs to be removed later!.. see pic 003... and then return the plug to the inside of the ply so it maintains its shape.
Sand down the joint so there is another chamfered edge to the ply that has just been wrapped.. see pic 005.. and then add the next piece of ply (ready chamfered) over the previous piece. Keep checking that the ply is true as each layer is wrapped around itself.
As each piece of ply is glued and added, roll accross the building board to keep the ply tight against the layer under it. pic 006 Add as many layers as is needed to get the correct thickness of the kort.
I sanded the edges roughly square and then threw the kort in the lathe to true up the edges.
A true kort (Marlin 19a profile) has the shape of an aerofoil inside it to speed up the water as it passes through the kort. This means the outer face of the kort is tapered, in this case 9 degrees... I set the lathe to this and cut the 9 degrees. pic 007
I then trued up the inside diameter of the kort and cut a 1 degree internal taper to start the 'trailing edge' of the aerofoil shape. see pic 008
Once the inside and outside (at the trailing edge) was sanded, i turned the kort round and started to cut the leading edge by cutting a 15 degree internal taper to meet up with the 1 degree trailing edge taper i just cut. pic 009.. followed by a 45 degree taper to meet up with the outer edge see pic 010.
Then using scraps of sandpaper, finish the leading edge of the aerofoil shape and sand the whole kort smooth. see pic 011.
I now have two very very strong kort nozzles that just need sealing and painting (its a shame to paint those patterns!) and the prop tips cutting down to fit the internal diameter of the kort.
Toesup Here is another way to make kort nozzles from plastic pipe or fittings. I just go to the local DIY box store and look at pipe, connectors and anything that looks like it might work. I was also able to stop at a plumbing store and when I asked for their advise they gave me a small box of cut offs to play with. You can use a straight shaft all the way through to keep alignment of the pivot point and then cut it out of the center of the nozzle when finished. I now use a couple of vee blocks clamped to a board and use these to align the pivot points. Use a straight shaft to align the blocks first. Jerryj98501