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PP Academy – Live : Making a 3.1 extrusion screw

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This topic contains 8 replies, has 3 voices, and was last updated by  Anonymous 1 month ago.

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Anonymous

PP Academy – Live : Making a 3.1 extrusion screw

15/07/2019 at 15:08

More a community experiment and also a case study but there will be a live broadcast (not sure yet how) the 25th of July providing you the insights of making the perfect extrusion screw for v3. The session is harder than the v4 screw (larger diameter = less shatter); we’re still waiting for details from PP Eindhoven.

Requirements

1. normal metal lathe which can deal with a 70 cm stock, 30 mm diameter, target pitch=22mm, please level her out and clean all the gearing and lead screws as well calibrate your tailstock. You also need an adjustable 4 jaw chuck in the 300 Euro range. The price is around 1000 – 2000 Euro for such lathe. Ideally you have a good inverter which enables you to add limit switches. Consider using the inverter brake function without resistor bank rather bad for your motor.
2. all the tools show below in the picture; notice the massive live center, get a new one; it makes a big difference.
3. stock : 30 mm diameter, chromoly or mild steel (hardening)
4. balls, it’s dangerous and easy to make mistakes
5. time, the entire process last 9-12 hours but we record and document the more essential parts
see you in a bit; if you miss the session, it’s going into the wiki but it’s better to be around live. this post will be updated with links and details the next days.

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18/07/2019 at 18:15
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here a short bla bla video ; time-laps video still in progress but more or less; a full day work for the screw. the results of the extruded beams seems excellent. i am still waiting for the results of a larger one, running at 2.2KW at 1:30

19/07/2019 at 08:55
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Here a short version of the timelaps; makes little sense to make a longer version 😉 I will head over to the documentation.

starter
19/07/2019 at 18:12
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Good work. Results look good.

 

You should look at using a travelling steady on the lathe. It will allow a much larger depth of cut and reduce your machining time considerably. Not too hard to make if you don’t have one, especially as you do not need to make it adjustable – just tailor it for this job.

Also I notice that you are reversing the lathe to return to the start of the cut. If you use a thread dial you can leave the lathe running, disengage from the lead screw and manually return to the start while the machine is running, it is much faster. Again, you can easily make a thread dial if you don’t have one.

 

/DM

 

starter
19/07/2019 at 18:14
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BTW. I’m never really a fan of grinding on a lathe – the abrasive gets into everything and has a tendency to cause wear & damage.

19/07/2019 at 18:26
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yeah, no worry, it’s cast iron from the 60’s; I had a look with the magnification glass, all ok 🙂 I should do nonetheless a scraping job but for this I will have to take lessons in Switzerland first. I’ve made a follow rest (see first pictures) but it was more in the way than really useful and since the screw just works, I preferred to have this task easy and risk-less for students as well. I’ve gone way deeper but it creates more shutter at the end and you have to get out on time which could trigger a little heart attack. But yeah you right; it can go faster but trust me; you want this rather slow, it gives you also enough time to think about the next cut 🙂 The thread dial is also problematic on my one, it would just slip in another channel and I’d have re-adjust the tool post; besides, it would also wear out the lead-screw  more fast; rather annoying to use.
Still, looks like we make extrusion screws our primary business; a nice thing to do, even with 70. I am still looking at options to cut them via NC or at least modded lathes where the cutter sits in on follow rest.

warrior
19/07/2019 at 22:25
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Is there a tolerance on the screw OD to the tube? Also the profile and roughness of the root?

This Old Tony has kittens in his videos….and half a million views….just a suggestion.

starter
20/07/2019 at 06:45
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Ahh yes, I can see the rest now. Ideally they need a force from both the back and from above to stop the bar from trying to climb upwards as the bar flexes. I can actually imagine the chatter from the photos, can be scary stuff.

 

Yes I agree, always good to take the route of less risk for students. Screw cutting can be complex and easy to mess up.

 

Great work.

20/07/2019 at 11:24
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@s2019; yeah, there are lot of numbers. Unfortunately with the materials and tooling I have here, I am already happy it’s tight as possibly; I leave around 0.1 mm clearance and more; that’s also the maximum I can manage whilst straightening out barrel and screw. Regarding the cats in videos, possibly I put them in the next videos. I thought I get away with the fly jumping along the screw in this very video. The next screws I do will have flange, ready to be mounted on a DIY thrust bearing plate which goes also connects directly to the motor. I just managed to have my first and own extruder and will see what are the next steps over summer break.

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