Compression screw

Precious Plastic Machine Development
#1

Hi everybody, I know that normally in order to create compression, people tries to change core/flight rate along screw length, but Another option could be to work on the pitch rather than reducing the flights depth (increasing the core diameter)…
Here an idea using a wood auger as a base…
– to weld a lever to the tip of the auger
– hold in a vice the tail,
– heat up the auger tip by a gas torch
– acting on the lever, twist the hot part in order to shorten the pitch at the tip of the auger

…make sense…?

#2

It might work, but keeping the auger bit straight while bending it would be extremely difficult. The smallest bending would cause friction inside of the barrel tube

#3

you can also just cut it normally if you’re ok being 10 hours at the lathe.
after turning the profile (3 sections, on by one, also to change the pitch for the last), you straighten her out again, then you cut the final diameter, not before. this works only with a diameter of a final min. of 25 mm, if you have a powerful motor (3kw), i’d rather suggest making the screw 30 mm, less bending but that’s not a big deal.

#4

You can grind it on a lathe with a toolpost grinder, or even turn it carefully with light cuts at speed. But if you have a cylindrical grinder that’s even better.

The tube option might work too, but I think the twisting might reduce the outer diameter, it would be interesting to see by how much.

#5

Ciao Andyn, thanks also to you!
I agree, it’s a critical point.
You cannot do it on a lathe, but rather a cylindrical grinding machine.
In my area are pretty easy to find, but not sure this is true everywhere and that’s why I suggested the option of doing the operation using a tube as a guide.
You do not like it?
S

#6

I think Olivier is right about the problem of keeping it straight enough. One way round this is to use a larger diameter auger than needed and then grind the perimeter back to cylindrical in a lathe.

#7

Thanks for the reply Olivier!
You are right about straightness.
And thanks for bringing this up!
ok, the process could be done inside a tube that keeps it straight… 🙂
sounds better…?