Which machine would be the best for this worm?

[Palafox]

Right now, on a random basis, some clients ask us for feeding worms. We make them in a traditional lathe and we finish the machining process by hand. To make one "feeding worm" we take three or four days. We want to reduce and improve our delivery times.

Which CNC machine would be the best for this product? My first thought was a VMC with a fourth programmable axis. These worms, at most, measure 1 meter, so it would have to be a big machine in the X-axis. The price will rise. My second thought was a CNC lathe with a programmable chuck with/or equipped with "live tools". The price will be lower than a 4axis VMC.

What do you think about this? Do you think of another type of machine than can be more suitable for this product?

These worms are made of plastic.

Best regards.

[Geof]

Working in plastic you should be able to cut these on a CNC lathe using the G32 threading program. You would need a travelling steady and it would have to be done in many small cuts.

[Palafox]

I forgot to say, that some "feeding worms" have the same pitch from the beginning to the end. Other "feeding worms" have different pitches according to customers request. This feature is asked when the customer wants a rapid product entrance but at the end of the worm he wants a slower product delivery or viceversa.

Also, sometimes the bottom of the "thread" (body) can be in a conical shape like in the small "feeding worm" in Picture 1. The thread has the same diameter but at the bottom it has a bigger diamater and it gets smaller. Also, the same "fedding worm", has a smaller thread at the beggining but at the end, the thread is much bigger. This feature is the more complex. Worms showed in the second and third picture have the same diameter and the same thread all over its geometry so I think it can be done with a G32 program.

Thank you very much for your support.

[Geof]

I believe you can change pitch in the G32 cycle. There is something about that in my Haas manual.

[Palafox]

Excellent. So if your Haas manual has it, then the path to follow is a CNC lathe.

[Geof]

Here is the page describing G32 in the pictures below.

[HuFlungDung]

I think I'd be tempted to do it with the 4th axis on a VMC rather than a lathe. I'd use a 4th axis wrap function in OneCNC to layout the geometry in a simple 2d format. Knowing the helix angle of the thread, one can layout a full scale triangle in software CAD to create a toolpath along the hypotenuse. If the curve is fancier, you just adjust the 'hypotenuse' to take in the additional features. It would be challenging CAD work perhaps, but not too obscure to figure out.

The only other thing you might want or need would be a multi-angle adjustable head for the VMC, for the purpose of making it easier to get a tapered bottom in instances where the taper is constant, otherwise you could form the bottom in multiple passes with a ball nose endmill.

Another advantage of the VMC as I see it, is building a 'trough' to steady the part would be quite simple. It can be as simple as a groove in a piece of flat bar, or it could be an 'angle iron' positioned so as to resist the cutting forces.

You could mill a simple screw in plastic in just minutes on the mill, after you make the initial setup and learn how it is done.

The chip control is excellent on the mill compared to the lathe, and the cutting speed can be readily optimised by the spindle speed rather than being limited by the Z axis speed of a lathe.

[wizard]

When I first saw the pictures I thought you were dealing with screws used in plastics molding and extrusion machines then it was noted that they are plastic. I can't say I've ever done this sort of thing but obviously it is done very often to support the plastics industry. This in better grades of steel.

So while I can't offer a solution form a personal standpoint I can suggest trying to make contact with somebody in the plastics industry that makes screws and augurs for the extrusion and injection molding industries. I've seen these, in this industry, from a foot or two in length up to about 15 feet and diameters up to about 8 inches. This leads me to believe that they are either done on a CNC lathe or a machine specifically adapted for such use. To be honest some of the screws I work with look like they have the profile ground into them as the taper at the driven end has a radius to it.

Dave

[JimPAC]

I would shop around for a decent old lathe that is adaptable to a 2D tracer

Years ago I had a job from International Harvester to turn the same thing just bigger for grain augers, I made 22,000 0f these and there were 8 different sizes!!

I would compare cost anyway!

Jim

[Palafox]

Ouch!!! Ignorance punch!!!

What is a 2D tracer? How does it works?

(I made a search in Google and I didnt find anything about it. I just found a GE 2D tracer in ebay offered by a person that does not know how it works and he sells it as/is)

[RICHARD ZASTROW]

Palafox, The "Big Boys" machine extruder feed screws on thread milling machines and thread "whirling" machines. These are usually variable pitch, variable root dia. and sometimes variable OD's. Often there is a different root/flight radius on either side of the flight (thread). I machined some on a manual horizontal milling machine (before N/C CNC) with a low lead dividing head by following a template with a dial indicator. A real PITA!!!!

[Geof]

Originally Posted by Palafox Ouch!!! Ignorance punch!!! What is a 2D tracer? How does it works? (I made a search in Google and I didnt find anything about it. I just found a GE 2D tracer in ebay offered by a person that does not know how it works and he sells it as/is)

I think this is a lathe where the cross slide has a probe that rides against a template along the back of the machine. The template has a profile that matches the shaft that is being turned. On the machines I have seen the cross slide was driven hydraulically and the probe controls the hydraulic piston position through a valve.

I don't see how it is applicable to making big variable diameter variable pitch screws.

I agree these could be done on a customized milling machine or lathe. However, why don't you scale one of your screws down to about one tenth size, take this to a CNC lathe supplier and see if they can figure out how to program it using G32. The way I understand G32 it is possible to program different sections of a screw with different pitches but I can't figure out from the manual description whether you can vary the pitch continuously over a certain length. However, if the machine had Macro ability it should be possible to combine this with G32 and do almost anything.