Tapered Screw press

[Matt Trevatt]

I looked very hard but ther wasnt a thread for dumb newbies!

I own a small oil factory in Indonesia and I am trying to get a tapered srew for a screw press made up. Not unlike a screw thread for a hand mincer.
I have a an orignal I am trying to get workshops here to copy but most guys wont even try. 1 shop did and managed to make a pretty good thread but it wasnt tapered. How hard is this> I know a little about lathes and thought it would be pretty straight forward. If you can make a untapered thread wouldnt it just be a matter of moving the tailstock off center?

I am hoping that I can get some info I can take into the workshop and show the guy how to setup his lathe.
Jack of all trades master of none ;-)
Matt

[Kiwi]

This is what you need.

[Matt Trevatt]

Ok that makes a heap of sense. So the universal joint is some sort of CV joint from a car?

[Andre' B]

Such things can be done on a CNC lathe or even a mill with a 4th axis.

Or any manual lathe with a taper cutting atachment.
Or the cheapest way to do it with just a basic lathe is to set the tailstock over and do the turning/threading between centers.

Edit:
Got a picture of the part?

I can not believe the thread needs to be all that perfect so if all else fails a few hours with a sharp file should get it done.

[Matt Trevatt]

Hoping there will b a pic here when i post!

[HuFlungDung]

That is quite a large profile to cut on a manual lathe. It would be considerably easier on a cnc lathe where you could profile the thread in steps with a relatively small radius round nose tool. Even on a cnc lathe, it would be difficult to get the surface speed high enough during the cut in order to get a good finish, however, I suppose you could polish it afterwards.

My opinion would be to mill the thread on a cnc mill with 4th axis.

The screws that I have seen for small oilseed presses have to have an excellent surface finish or else they won't feed without constantly plugging up. Since the gashes inside the barrel are all that actually grip the seed as it flows through, there must be a large difference between the quality of finish of the screw versus the finish of the barrel.

[Matt Trevatt]

Ok well I know that I can get a untapered screw cut that should work. I have noticed with other oil presses that they can be untapered but they are typically much longer probably double the length of the 1 I have. I assume the extra barrel friction from the length allows you to increase the preasure.
Does this sound right?

Originally Posted by HuFlungDung That is quite a large profile to cut on a manual lathe. It would be considerably easier on a cnc lathe where you could profile the thread in steps with a relatively small radius round nose tool. Even on a cnc lathe, it would be difficult to get the surface speed high enough during the cut in order to get a good finish, however, I suppose you could polish it afterwards. My opinion would be to mill the thread on a cnc mill with 4th axis. The screws that I have seen for small oilseed presses have to have an excellent surface finish or else they won't feed without constantly plugging up. Since the gashes inside the barrel are all that actually grip the seed as it flows through, there must be a large difference between the quality of finish of the screw versus the finish of the barrel.

[HuFlungDung]

Does your press form an extruded meal slug? I've only seen the Komet (German) press thus far, and that is what they do. Their screws are not very long, maybe 8 inches, but are hard chromed and given an excellent finish. I've never tried to make a screw for this particular press, but I've heard of several attempts by others to make the screws, but apparently the Germans have some technical knowledge on chroming and finishing that escapes the imitators

Their presses are reportedly sometimes hard to 'prime' to get the meal to flow through if the screw is anything less than perfectly finished.

AFAIK, the head space restriction at the end of the barrel creates the pressure. Various gashes are present in the barrel and on the head to provide traction on the meal cake. The oil flow is essentially backwards through the meal through drip holes in the barrel.