Practical Darwin 1.0 Extruder materials - HDPE

The wiki instruction page: [www.reprap.org]

Says: "The extruder needs a supply of 3 mm diameter polymorph filament as input."

Like others here, I have the HDPE from the RepRap foundation store.

Using the Extruder Exerciser, where should I start? Here is one Forum reference:
[forums.reprap.org] (Dan Putman)


Practical HDPE questions
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1. Heater temperature? I'm setting 170c
2. Motor speed. My motor seems to start pushing around 75 setting.
3. Nozzle tip hole? ".55MM measured diameter of the extruded filament is ~1.0MM"
4. Can you describe your parameters and what rate of extrusion. So to extrude 30cm using a .55mm tip, fastest motor speed that works, etc.


Other questions:

1. Are my screws not tight enough or too tight?
2. How long does it take to get the heater hot?
3. Any other parameters to adjust in the RepRap host software?


Thanks.

Edited 2 time(s). Last edit at 12/31/2007 11:16AM by RoundSparrow.

Yes the official project only uses PCL (Polymorph, CAPA) and PLA but neither are available in filament form yet.

I have been using HDPE for a few months now. I got started with facts and figures from Forrest Higgs' blog [3dreplicators.com] and have gained a lot of experience since by experimenting. I am using a fairly standard RepRap extruder but nothing else so I can't help you with the software but I can give you my figures :-

1. I can extrude above 160C but I tend to get jams if I run below 180C. To guarantee a weld when extruding a new layer onto a layer that has cooled back down to room temperature you need to extrude HDPE at 240C. If you are making small objects, in the region of 20mm cube you can get away with 200C as the object is visited often enough for it to keep it hot. Larger objects need 240C and smaller objects need a fan or a pause between layers.

2. I run my extruder to get 4mm of 1mm filament per second and that is about 75% PWM. [hydraraptor.blogspot.com]

3.4. Yes I also have 0.5mm hole which gives 1mm filament but I run the axes at 16mm/s which stretches it to 0.5mm. [hydraraptor.blogspot.com]

Recently I have slowed down the axes to 4mm/s when doing the outline but I throttled back the extruder so the filament is still 0.5mm, i.e. stretched the same amount. [hydraraptor.blogspot.com]

1. If I don't tighten them fully I get jams. I don't think they can be too tight. I suppose the symptom would be the motor stalling. The problem is than my 3mm filament is about 3.1mm and oval in places. I made the extruder 3.2mm bore but I wish I had made it 3.3mm.

2. It takes about 2 minutes for my machine to warm up [hydraraptor.blogspot.com] YMMV depending on heater resistance, drive circuit and thermal insulation.

3. Sorry, can't help you there.

Edited 1 time(s). Last edit at 12/31/2007 12:34PM by nophead.

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[www.hydraraptor.blogspot.com]

Quote
nophead
3.4. Yes I also have 0.5mm hole which gives 1mm filament but I run the axes at 16mm/s which stretches it to 0.5mm. [hydraraptor.blogspot.com]

Recently I have slowed down the axes to 4mm/s when doing the outline but I throttled back the extruder so the filament is still 0.5mm, i.e. stretched the same amount.

Not to get too off topic, but I, like many here I'm sure, have been following your testing as you post it on your blog. It sounds like that's a ton of stretchage after coming out of the extruder - the cross section of the stretched filament is decreased by a factor of 4 vs. when it comes out of the extruder. You may have already done this (I don't remember), but have you tried extruding at much slower rates so the filament is stretched little or not at all after leaving the barrel? I'm just wondering if the filament might have some kind of "memory" of its initial extruded diameter, which could be contributing to the objects' deformation along with the well-known shrinking phenomenon.

I just got my extruder running reliably.

1. I *think* I'm running HDPE at 180C but my thermistors keep dying.
2. I can get a reasonable amount of extrusion at a setting of 50. Full speed is possible but seems to strain the extruder.
3. I'm getting a 1.2mm extrusion using a .55mm tip
4. At a extruder motor setting of 50, I was getting about 2mm/s. At full speed, about 7mm/s.

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1. I agree. I don't think there's such a thing as too tight. I'm leaning towards getting rid of the bits of tubing and just clamping it down. One thing I'd like to do is come up with a way to open the extruder without fiddling around with four screws. Maybe four guide pins and a quick-release clamp.
2. Seems to take ages. I think I need to re-do my heater and come up with a practical insulator. Something that stays in place, can be easily removed for servicing and doesn't catch fire. (Very important, that last bit)
3. About the only thing I play with are the two thermistor settings.

My limited experience so far indicates that HDPE is really pushing the extruder design to its limits. I'm thinking that I really need a longer barrel with more interconnect between metal and PTFE, plus a more solid connection between PTFE and clamp.

I'm also thinking that, for practical purposes, I may need to use polymorph whenever possible (e.g. corner brackets), saving HDPE for applications where it's absolutely necessary (the extruder body). The problem now is finding a supply of polymorph filament.

Interesting point Kyle. I am only stretching it back to the diameter it was when it passed through the hole so rather than let it expand outwards I am persuading it to expand the same amount length ways instead. It requires very little force to stretch it when it is molten.

My open box tests use 1mm walls extruded at 4mm/s without stretching. They warp similar amounts so I think the warping is completely explained by the ~2% mold shrinkage quoted for HDPE.

I will make a solid test object with 1mm filament so that I can make a direct comparison and report back.

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[www.hydraraptor.blogspot.com]

Steve,
Yes I agree: full speed strains the motor because it is a 6V job run at 12V, completely under engineered IMHO. Should be easy to upgrade to a 12V motor.

I have some stiff springs rather than the tubing but they are fully compressed so I need some stiffer ones. I don't like the tubing idea because it has memory.

Completely agree on the quick release idea. Although I don't often have to open it, it's a pain when I do. I used wingnuts but they are fiddly. Next time I have to open it I will put two on the back and two on the front to make them easier to spin.

My heater doesn't have any insulation so it's a mystery why yours is slower. Mine is 8.6R but I have about 2V more so it should be about the same as 6R on RepRap electronics. The acorn nut adds a bit of surface area and so does the thread so perhaps a lot more heat is lost.

I have also thought about turning a ring into the PTFE and putting a ridge in the clamp, but after it slipped once I tightened it and it has held since. Mind you my clamp is made from Delrin and has the right size hole so it may work a bit better than the cast version.

I have never had a problem with the thread slipping, I can't think why that would be unless the tap used was the wrong size.

Until I get some PCL (PolyMorph) filament I don't really know whether HDPE pushes the extruder or whether it is on the edge anyway. Certainly it looks like PLA pushes it more than HDPE.

I don't think HDPE is needed to make the extruder body, it doesn't get hot. I think it is just the motor mounts that are a problem with PCL.

Considering it takes hours to make anything significant the MTBF of the machine needs to be at least hundreds of hours or it will become very frustrating. I think mine is currently in the 10's of hours region. I should really get my software to keep a log of running time.

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[www.hydraraptor.blogspot.com]

Based on Nophead's last comment: I can work on code (proposed Java patch) to make it a standard feature of RepRap Host to log whenever the heater is active. That would seem to be good basic information and it isn't like it really consumes that much disk space to record a csv file or something that shows heater on time.

Edited 1 time(s). Last edit at 12/31/2007 09:23PM by RoundSparrow.

The amount of extruded filament would also be useful.

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[www.hydraraptor.blogspot.com]

nophead Wrote:
> I have never had a problem with the thread
> slipping, I can't think why that would be unless
> the tap used was the wrong size.

I spoke too soon, it just happened :- [hydraraptor.blogspot.com]

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[www.hydraraptor.blogspot.com]

The hose clamp seems to work well but I had to re-tighten it once the barrel heated up.

I was playing with AOI yesterday and added a ridge to the quick-connect extruder. Interesting thing: There's no orientation of that part that has no overhangs > 45 degrees. It'd have to be modded to make it RepRap-able without support material.

Ok, so conclusion is that nophead is the authority on practicals of HDPE. I wasn't even trying for anything as high as 200c so I need to start at maybe 215c and my clogging problems should hopefully go away.

However, it is looking to me that JBWeld isn't holding up to 240c on a regular basis (nophead is having what I consider major damage after ~13 hours of runtime).

I guess: I'm looking for practical building tips on a Darwin Extruder 1.0+ that can deal with HDPE... ?

How accurate is your HDPE filament?

One thing that surprised me about the RepRap design is that there are no clearances and tolerances anywhere. 3mm filament is expected to go through a 3mm hole. My 3mm filament measures about 3.1 so I made my extruder bore 3.2mm. I will make the next one 3.3 I think, as some of my filament is a bit oval.

Once the temperature is high enough I find the main cause of jams is not enough force on the springs. Enormous force is required to make the screw cut into the HDPE. I remember Vik saying he sharpened the thread for PLA.

I also spray the polymer guide with PTFE spray to make it more slippery.

The JBWeld held up for a lot more than 13 hours as I leave it on and tend to forget it like my soldering iron! At least 100 hours I would say and although it became fragile it was still working fine until I touched it.

I get the impression that my bare wire heater insulated with JBWeld is more efficient than the ones made with insulated nichrome.

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[www.hydraraptor.blogspot.com]

SOFTWARE Configuration... in the RepRap host software. Go to File/Preferences/Extruder0

1. Set "Extruder0_MaterialType(name)" to "HDPE"
2. Set Extruder0_ExtrusionTemp(C)" to "215"