Considering a new extruder design

I have not had anything to do with reprap before but am considering making a new extruder(I imagine someone has made something similar before??)

I will probably start next weekend but I have only got some strimmer line I found in the garden shed to make tests with.

Can anyone in the UK post me some free sample plastics to test my design with??

I will post back an extruder in exchange(should take a couple of weekends to finish my design).

I hope to be able to reduce most stuff by a third.

Hello Mung,

Welcome to the Forum and RepRap.

People on this forum would probably send you some sample plastic, but you need to give us a bit more info about what you are planning, what you are going to connect the extruder to and what electronics you have already?

So do you have a CNC mill?

Where in the UK are you?

What's your background and what's the plan with the new extruder design?

And take a look at Thorp's thread in this section to see a nice Machined Extruder build in-progress.

Cheers,

Rich.

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[richrap.blogspot.com]

Hi richrap

Thanks for feedback

I will answer your questions but really it's too early to give definite answers to most of them:

1) Don't know, but all options may be available
2) Maybe
3) The deep south
4) I don't really have any background I suppose you could say I am a hacker or an idiot(depending upon success)?
5) The plan is to reduce everything by at least 33% (weight, cost, size).


I don't have a plan yet as I don't know what materials I have available or what the extruder requirements are.

I will hopefully start work next weekend so will go to the hardware store to get some stock parts this weekend and then do some tests. I will probably do some research in the evenings next week but I may try to avoid too much as I don't like to be too influenced by previous ideas(I imagine my design will be similar to most others due to there being only one optimal design).

I doubt my guestimates are worth much at the moment but I am guessing a budget of £2.50, weight of 50grams and size should fit within a 50mm cube.

Of course this excludes time costs which could be huge if I valued my time.

I doubt the design (if it works) will be something everyone can build at home.

Basically low cost is my main concern as I refuse to spend more than a few pounds on a hobby.

############################################################################################################


I had a look at the Thorp build as suggested, sorry to say it looks awful to me, far too well built and over engineered.

I guess I will have a look in maplin and the hardware store and get some metric fasteners, plywood, copper and brass, and whatever is cheapest transistors and resistors, anything that looks cheap and useful for a lashup.

1) a) Has anyone used strimmer line before in an extruder???
b) As far as I could find it is most likely polyamide 66 are there possible adhesion problems with polyamide?

2) I saw in the Thorp thread mention of 125N force to extrude the filament is that a serious figure(surely not) what is the lowest force I could use(I hoped less than 20N)?????

I have 2mm and 3mm strimmer line, I guess the best size will be 2mm, I may see if there is anything smaller at the hardware store.

I imagine strimmer line should be okay for testing if the extruder heats and extrudes even if it is not good enough for printing.

If I get anything working with the strimmer line next weekend I will post pictures here and maybe put an ad' for PLA and ABS filament in the wanted forum and here.

Hi Mung,

I'm sure you could build something for £2.50, but I doubt it would work as an extruder. Or was the decimal point in the wrong place?

A good extruder needs a hot-end and very importantly an insulator (usually done with PTFE or PEEK) you need a small thermal point the filament (plastic) can turn from solid to liquid. Then you need a stepper motor with a torque of 4.4 Kg-cm (43.15N-cm) force to drive it. - My point is that you need to budget of more like £25 for a working Extruder.

My previous home-made extruder was made with low-cost parts (many off ebay) and the WADE printed part (body) could be easily made in wood with basic tools. The gears could come from a piece of old equipment if you like. It's been very reliable - RichRap Hand-made Extruder and Hot-end

Then you need a way to drive the motor, heat the hot-end and control the temperature. That's just the extruder, if you want to build an object then you need a Cartasian bot of some description to position the extruder.

If you check this forum you wil see many people have lots of problems with their extruder, they leak, break, stop, strip, and many underpower them.

Good luck, and let us know how you get on.

Rich.

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[richrap.blogspot.com]

I had a look at parts in the hardware store at the weekend and think £25 may be nearer the cost than £2.50, the UK seems to have extreme inflation over the last 3 years. Maplin seems like a dead loss as far as prices go but window shopping gave me a few ideas as to what is available.

I made one purchase for the extruder barrel as I thought I could make some experiments, before working out exactly what is needed.

I had a search in the evening to try and find cheaper suppliers for some of the stuff I saw in Maplin and the hardware store, looks like CPC may be the preferred supplier as it has a better selection and seems much cheaper than RS components.

Did a little research on polymers and seems 1.25mm may be an optimum diameter and is also available as strimmer line from ebay at around £6(£2.50 is postage so bulk buy could be a lot cheaper) for 155 meters. I imagine ployamide should not be much different for extrusion than ABS

I did a little experimental machining and extrusion tests on Sunday and there seems like a lot of work involved in making an extrusion barrel, over 4 hours in front of a lathe with many different trials and mistakes resulted in 11 barrels 5 failures, 5 very expensive broken drill bits. Tooling costs could be very high maybe due to my poor machining skill with very small drill bits(I guess maybe possible to get 10 nozzles per bit with practice but deep drilling is not a good idea)

I did some very basic test extrusions of 2mm strimmer line pushing it through with fingers and it seemed quite easy with 0.35mm and 0.5mm nozzles at 235C' .

Now I have more idea of what materials are available I will need to do some more research.

My initial thoughts are that it may be doable but price could be the major problem.

I have now made an outline specification:

Building of a polymer melter and extruder, including electrical heating element, extrusion nozzle, thermal insulator and barrier such that mounting points are below 60 degrees celcius when extrusion nozzle is at 300 degrees. Drive mechanism to force solid polymer rod of upto 2mm diameter into extruder heater element with force of 50 newtons or that required to extrude at a rate of 50mm per second. Optional axis positioning drive

My revised guestimates are: budget £10(£16), weight 75g(180g), size within a 40mm cube(60mm).

My guess at manufacturing time would be 2-3 hours of actual machining time, and 1-2hours assembly, for a single extruder though batch production would cut machining time a lot as setup is a large proportion.


I imagine development time will be 50-60 hours of actual manual work spread over a couple of months of weekends (the time in between the manual work hopefully allows the ideas to develop)

I was considering making up a quantity of barrels for testing purposes to get some empirical data on optimal extruder configuration.

Has anyone done this before?

Data such as

Barrel length, barrel material, barrel geometry (external diameter, internal diameter), temperature at cold end, temperature at hot end, heater type, temperature, thermal sensor type, extrusion media type, extrusion media diameter, nozzle diameter, flow rate, hot zone distance from nozzle, hot zone length, extruded filament diameter, weight of extruded media in time. media hardness after extrusion, hardness before extrusion. extrusion force. etc.....

I am hoping to get a first lashup done and tested next weekend if I get parts from cpc delivered, maybe one or two revisions each weekend after that. Hopefully I may actually get something that works before I get bored with the idea.

imo, take a look at wade's extruder and it can be given to a machinist to be realised from dur~ aluminium.
could use the .stl files even with distances drawn all over as a nice 3d technical drawing.
or the main block can even be done "in garrage" from a 4-5-6 mm sheet and a ~30mm square bar.

the dificulty resides in the gears, a cutter in modulo 1,0 or 1,25 might be needed depending on the distance between centers, so might wanna check what kind of involute gear cutters the machinist has before designing - usually they dont have a full modulo range, at least not here.

Hi Mung,

Quote
Mung
Has anyone done this before?

Data such as

Barrel length, barrel material, barrel geometry (external diameter, internal diameter), temperature at cold end, temperature at hot end, heater type, temperature, thermal sensor type, extrusion media type, extrusion media diameter, nozzle diameter, flow rate, hot zone distance from nozzle, hot zone length, extruded filament diameter, weight of extruded media in time. media hardness after extrusion, hardness before extrusion. extrusion force. etc.....

I am hoping to get a first lashup done and tested next weekend if I get parts from cpc delivered, maybe one or two revisions each weekend after that. Hopefully I may actually get something that works before I get bored with the idea.

Yes, RepRap is 6+ years old now, so many people have done this and continue to do so for new designs and sizes etc.

See this design from Adrian, as a good and robust starting point - Adrian's well supported nozzle

And again from Adrian see this new (minature) concept design - Tiny little thing

More Ideas here - Extruder_Nozzle_Variations

Nophead's Plumbstruder is a fine piece of engineering, and extremly reliable - Plumbing and reprap, great!
If you have the time, read all of Nophead's blog, it will answer so many things you don't even think you need to know yet.

Good luck with the testing, and I hope you get something working -
Short melt-zone and good heating block, then use some brass (or a modified brass screw) to make something for testing, or buy one ready-built if you think you will get bored of it, this is a project worth getting deep into...

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[richrap.blogspot.com]

richrap Wrote:
-------------------------------------------------------
> Yes, RepRap is 6+ years old now, so many people
> have done this and continue to do so for new
> designs and sizes etc.


Can you tell me where the test procedure schemas and test methods are?
Where can I access the results database?

I am hoping to make up a test rig this weekend and do some tests to find the optimum barrel configuration, so I would rather not duplicate work that has already been done!
How do I submit my test data to the database?

I already have 11 different barrels for testing(2 of which I have experimented with already).

Unfortunately I have not got anything that was ordered from cpc so did not get a prototype lash up, I wasted most of my time trying unsuccessfully to compile rtai kernel and emc2 to run on an ipaq.

I started working on a test rig for the extruder as I could not find any Reprap extruder testing procedures.

I made three experimental lash ups based on some scrap parts I found and I think I have a design for the first prototype roughed out in my head now, I did not do any test extrusions or hot work but think the geometry of the extruder and gearing should be fine.

I wasted a lot of time trying to get a thermocouple working from scrap wire I found in the shed.

I now need to wait for the cpc items to arrive and source some more materials (25x15mm U channel with 3mm wall in brass or alloy)

Materials:

I guess cost price for materials in production quantitys to be about £9, with a retail price around £40.

1 x small D.C. motor
1 x small stepper motor
short piece of 25x15mm metal U channel
short piece of 20mm brass bar
small piece of 6mm plywood (would be a plastic part in production)
small piece of 1mm or thinner steel sheet
small piece of copper pipe or sheet
thin alloy sheet or foil
1 x m4 25mm set
4 x m4 nuts
4 x m3 screws and nuts.
2 x threaded brass spacers
6 red fibre washers
2 x bearings
3 wood screws
fire cement
heat resistant silicon
a few washers for packing
epoxy adhesive

Electronics
I have not looked at electronics but guess:

1x high gain darlington
2x uln2003 darlington arrays
dsub socket
2 10ohm resistors 3w
8 10k resistors
4 diodes
thermocouple wire
10k variable resistor
1 small piece of proto board
solder
connector block

Tools:

lathe (3jaw + 4jaw chucks, milling attachment, tailstock chuck, toolsteel)
small drills
tap and die set
small files
soldering iron
pliers
tin snips
screw drivers

I may try and upload some photos of experimental configurations later.

picture of experimental parts (hopefully?)

picture removed due to bad scaling, I reposted it below

Edited 1 time(s). Last edit at 02/01/2011 02:44PM by mung.

Thought I should give a few notes on the attached photo above.

The photo shows 4 experimental extruders I made last weekend starting from left to right chronologically with the partially complete final experimental extruder in pieces at the bottom.

Only the first two have been run hot and did not work well at all, the third and fourth were really just made to workout different configurations of geometry.

There are also about 16 extruder barrels in the photo they are made from brass wood screws(mostly 30mm slightly shortened) and threaded with M6 and M4 threads.

The green filament is the polyamide strimmer line, the thin line has been extruded through a 0.35mm nozzle and the thick line is the unextruded 2mm strimmer line.

There are a few bits and pieces of thin steel sheet from a dismantled transformer and some other small brass parts.

There are a few shorter and longer screws also that may be tested.

The four assembled experimental extruder barrels and heaters all use 2 x 10 Ohm resistors as heaters and don't use any temperature sensors(thermocouple may be used in first prototype) .

I really think that 1.25mm filament may be the best choice for the final extruder but I will try and get everything working with 2mm first.

I will hopefully complete an extrusion test rig this coming weekend so I can assemble the various extruder barrels to find which is the most efficient configuration.

Currently most of the barrels are bored to 1.5mm along the length of the screw with 0.35mm nozzle of 2mm, ready to be modified for different configurations.

I will drill out the barrels larger for different lengths and different nozzle diameters to see what effect that has on extrusion pressure, speed, and melted plastic quality.

I get the feeling the testing may be canned after a few tests as I only need to make a few tests to make sure my calculations and assumptions agree with reality.

There is also a possibility I may not get anything done this weekend as I may have help available to try and get a mill installed and working.

Edited 1 time(s). Last edit at 02/03/2011 05:46PM by mung.

Not much progress this weekend.

The test rig was canned as too much work was required to get a decent repeatable system and I found the results I needed from just two extrusion tests (may post a photo of the test rig as far as i got in case others want ideas if they are looking into testing).

I assembled and heat tested what is probably the final experimental lash up and everything looks quite promising for a multifilament lightweight and cheap extruder, of course only time and test will tell if it will work and be reliable.

I got the worrying thought that all the work may be pointless if ABS and PLA extrusion is totally different from polyamide which I have been using?

I think Polyamide could be quite toxic as the smoke (seemed about as much as the average smokers exhale given off of the nozzle) from my hot tests left me feeling a little ill and I worry cancer may occur a few years from now?

I actually could not find any mention of PA66 being a carcinogen but did find this note :

"Processing fumes may cause irritation to the eyes, skin and respiratory tract, and in cases of severe overexposure, nausea and headache"

No help with mill so my quest of many years has still not been realised.


IS THERE ANYONE THAT WANTS TO BUY A HOT END AND EXTRUDER TO TEST FOR A FEW HOURS OF EXTRUSION AND GIVE ME SOME FEEDBACK?

I DOUBT I WILL BE GETTING ANYTHING TO TEST THE EXTRUDER IN ACTUALLY 3D PRINTING FOR QUITE SOME TIME?

SO UNLESS SOMEONE WANTS TO BUY A TEST HEAD I WILL BE PUTTING THE PROJECT ON THE BACK BURNER FOR AT LEAST 6 MONTHS.

I WILL PROBABLY MAKE A FIRST PROTOTYPE THEN WORK ON MY OTHER IDEAS.

I AM STILL WAITING FOR PARTS FOR A PROTOTYPE BUILD, AND NEED TO ORDER SOME CHANNEL WHEN I CAN AFFORD IT.

It has been mentioned elsewhere on the forum that if you burn nylon you get hydrogen cyanide. I don't no if that is carcinogenic but it does stop you breathing!

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[www.hydraraptor.blogspot.com]

nophead Wrote:
-------------------------------------------------------
> It has been mentioned elsewhere on the forum that
> if you burn nylon you get hydrogen cyanide. I
> don't no if that is carcinogenic but it does stop
> you breathing!

Yeah I heard that also, but all plastics will give off some hydrogen cyanide when burnt.
I think I read somewhere that gram for gram ABS will produce more hydrogen cyanide than nylon will when burnt, something to do with the butyl bonds causing better nitrogen cleavage (I don't even understand how nitrogen cleavage works, but that's what I heard).

I imagine that having a better cleavage would effect your breathing though.

I cannot work out how to delete some of my earlier posts to tidy up the thread, anyone have any help on this?

... why delete old posts?

It's a sort of archive of thoughts, brainstorming and ideas that can be usefull for someone with related questions, searching through the forum.

When deleting, many following posts will loose their references and will be useless too - so deleting is the last thing i'll do ... i'ts only aimed for deplaced posts or removing spam or such ...

***Edit - anyhow, i've deleted three of the posts you meant, as they didn't have any meaning or references - but this isn't a usual action ...

---

Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Have not really done anything this weekend, but later on this week I may make a Youtube video of the development so far.

I am not going to go any further than the experimental stage for the foreseeable future as I will have to buy £25 of channel (minimum order is enough for 35 extruder heads) to make the prototype. Hopefully when I get other stuff finished I will get back to the extruder.


The final experimental lash up seems to work, but will see if it runs fine on video after being run a few times.

As promised I have made a very short video, I may make another but probably not for a few months as this project is now canned.


Below is what I posted on youtube.

Final extruder experimental testing.

This is just a very quick video of the experimental lash up to test nozzle geometry and polymer extrusion work as simulated in PMARC with inviscid skin friction and overlay of heat equation within the flow dynamics.

The design was made to use the cheapest motor available (off the shelf the motor can be bought for £0.50).

Unfortunatly I did not switch in the current limiter so the heat was on continuous maximum so nasty poison smoke was being emitted and hence the very short video before I removed the power.

Heat up time is around 40 seconds at 3.8amps or 60 at 3amps, if cut down to 1.4amps the nozzle should run around 240degrees celcius.

Testing the heat shield 40 minutes nozzle at 300C the cold end ran at about 30degrees.

Thought I should add that the heat is from room temperature (I touch the nozzle before I connect the power to see its cool) and the thermometer is rather inaccurate as its hard to get good contact with the nozzle(I slip off at one point). Unfortunately its rather hard trying to make sure the thermometer is still in frame and watching the current switch on the power supply and trying to connect the motor to the power when the nozzle gets to extrusion temperature.

The motor was running for probably 4 seconds and extruded about 30mm of the 2mm Polyamide strimmer line through a 0.3mm nozzle, it can just about be seen forming a large glob of glassy plastic, as the nozzle was over heated and not extruding vertically it did not form good filament threads.

Edited 1 time(s). Last edit at 02/09/2011 05:30PM by mung.

Just thought I would finish up with all the development so far before I get on with other work.

The attached photo should show the quad extruder nozzle that I started rigging to make tests with, its unfinished and will be so for at least a couple of months now.

Hopefully I may get round to adding a photo of the extruder test rig even though it was never really properly completed.

I'm sure there are some other notes I should add about the final experimental extruder but I cannot think what at present.

I will probably make a web page documenting the extruder in a few months when I get back to it.

So far I guess most of my guestimates were fairly accurate, project has probably taken 40 hours of actual manual work and the final experimental extruder was as good as a complete usable extruder.

Edited 1 time(s). Last edit at 02/10/2011 09:52AM by mung.

I've worked on my own homemade nozzle myself, and it's not "as good as a usable extruder" unless it's actually a usable extruder.

My rig "worked" fine, but problems cropped up once it was attached to the machine. There's a big difference between pushing hot plastic and actually using the hot plastic to build a nice part. I'll probably get it working eventually, but at some point you just want to print.

I'm sure you'll get it working too. Good luck and have fun!

Just thought I would also post a link to my new project in case anyone is interested in hobby cnc machines.

cnc mill

When I have finished the cnc mill refit I will probably get back to working on the extruder.

I hopefully will make one more post on this forum at the weekend as I said before to finish up documenting all the development I made on the extruder and the test rig, but after that will probably not be here for a few months, and be on cnczone instead.

Buback Wrote:
-------------------------------------------------------
> My rig "worked" fine, but problems cropped up once
> it was attached to the machine. There's a big
> difference between pushing hot plastic and
> actually using the hot plastic to build a nice
> part.

Thanks for the reply Buback,

I probably should not ask this as I am on another project now, but as I am here and will check back here when I pick this project up again I will ask now for future reference.......

What problems cropped up?
What would you say the main differences are between testing and actually running the extruder to print?
What are the differences in back pressure between extruding into free air and onto a print layer?
Do you know if anyone has done tests into interlayer adhesion (or is it cohesion?) and temperature and pressure of extruded plastic?

If you have any other pointers to designing an extruder I would be grateful for your help and all advice will be considered when I get back to this project in a few months.


Regards

Mung

well it really depends on what your putting the extruder on.

I was making a glass hot end for the extruder, but my heating block (aluminum) kept falling off the glass tube. the aluminum has a much higher CoE than the glass, so the compression fitting would loosen up once it got hot, and the pressure of the filament would just push it off.

it worked great when pushing it through by hand, but it didn't actually work at all once on the machine because of the above problems.

and no, i don't know of any resources other than the forums, the reprap wiki, and the blogs. you just have to read them all (that's what i did)

extrusion nozzle tester pictures.

I should add some notes about it but as I never really got round to ironing out all the problems maybe it's better not to.

You should be able to see how it works from the pictures, if not you can ask and I hopefully will explain all at some point in the future.

My guess is that a decent test rig should take about 10 to 20 hours work to make (this one took about 2 hours to hack together).

The one thing missing is a mechanism to pull the extrusion layer test tape through at a given speed (I did it by hand on the two tests I did).

I must say the whole thing was a total failure as far as repeatable tests go, but it sort of gave me some results that vaguely agreed with my calculations.






?
?

Edited 6 time(s). Last edit at 02/14/2011 12:48PM by mung.

Buback Wrote:
-------------------------------------------------------
> well it really depends on what your putting the
> extruder on.
>
> I was making a glass hot end for the extruder, but
> my heating block (aluminum) kept falling off the
> glass tube. the aluminum has a much higher CoE
> than the glass, so the compression fitting would
> loosen up once it got hot, and the pressure of the
> filament would just push it off.
>
> it worked great when pushing it through by hand,
> but it didn't actually work at all once on the
> machine because of the above problems.
>
> and no, i don't know of any resources other than
> the forums, the reprap wiki, and the blogs. you
> just have to read them all (that's what i did)

I imagine it should not really matter what the extruder is put on other than the problem of maximum acceleration rate and the temperature the extruder is exposed to.

All extruders are going to be moved in three dimensions (unless the work piece is moved), all robots will have similar characteristics at the point the extruder is mounted regardless of the intermediate kinematics?

I cannot see how what the extruder is put on will effect its function.

I assume CofE is Expansion not entropy or elasticity though this could be a matter of uncertainty?.

I doubt there could be any problems with compression fittings or loose joints on my extruder as all joints are made with threaded screw fittings, and expansion should not be much of a problem as all parts are made of the same material.

The motor has run through about 3cc of polyamide in tests so far, I have not had any stalls of the motor or stripping of the in feed filament, of course I have not run the extruder with a solid base to extrude onto, and this could cause considerable extra back pressure.

The only problem I could see with blockage would be due to poor quality and contaminated extrusion media?.

Of course with any complex engineering system there can be unseen or compounded factors that may lead to uncalculated and erratic problems in function and of course only long term testing will show what may happen after long term wear and stress?

If I have half an hour free at some point I will try and make a video showing extrusion onto a surface to see what effect that has.


As far as I can see the final experimental extruder as made works fully as an extruder(the video shows it running quite well), but my idea was to design an extruder that uses readily available off the shelf stock parts, the experimental extruder uses parts from my junk box that I could not buy from a supplier.


I am not sure if this is a rant?:::

When you say "just read all blogs and wikis and forums" I think that is not really useful or feasible. If the Reprap team wanted to really spur development they should provide some real scientific and engineering data for 'would be' developers to work from and make calculations.
Most of the blogs may be entertaining reading, but from the sample I have seen none have much in the way of hard facts based on experiment or calculations.

Would be nice if the wiki had tables of all the physical properties of the plastics being used especially data such as melting temperature, hardness, heat conductivity, and density, and graphs of viscosity at different temperatures.

Also data for other standard building materials would be a useful addition to the wiki things like coefficient of expansion, coefficient of friction, hardness, density, heat conduction, etc.... of glass/brass/steel/aluminium.

This would make life easier for developers trying to workout if it's better to make a nozzle from brass with less friction on the filament and better heat conduction but a thicker wall as it is weaker than steel which can have a thinner wall but lower conduction and higher friction.

Also an outline in the wiki of the development method used in engineering, would help those without any engineering background who want to try reprap development as a new hobby.

If the wiki could provide this sort of information it would help people actually develop something new and improved rather than just copying some one elses designs.

Anyway enough ranting, I know if you want something done, best way to get it done is do it yourself, and unfortunately I am not going to do any of what I have just suggested.


I may have some time to do a little more to the extruder tests as I will be waiting on new ballscrews for my other project at some point (unless the servo electronics take considerably more time than I imagine).

Still I doubt I will be making a prototype for a while as the stock required has fairly large minimum orders and I have other projects that may add to the order for materials (I have sometimes left orders 6 months till I can make minimum size to get free delivery)



Anyways as always thanks for the the response Buback I do like it when people respond as it acknowledges my existence and makes me feel maybe I may have some effect on this universe even if it makes very little difference. Please don't take my response the wrong way, I know everyone is lazy (or at least I know I am so assume everyone else must be). Unlike using glass I think that my design is really only minor changes and better machining tolerances than the standard types of pinch wheel extruder so I cannot see why there should be any unseen problems with it.
I feel my extruder works well and cannot see why there should be any problems with the prototype when it is built. If the worst case happens then I will simply need to get a more expensive motor.

I am sure you could get your glass extruder working but I get the feeling it could become very complicated compared with metal nozzled extruders.

mung Wrote:
-------------------------------------------------------
> When you say "just read all blogs and wikis and
> forums" I think that is not really useful or
> feasible. If the Reprap team wanted to really spur
> development they should provide some real
> scientific and engineering data for 'would be'
> developers to work from and make calculations.
> Most of the blogs may be entertaining reading, but
> from the sample I have seen none have much in the
> way of hard facts based on experiment or
> calculations.
>
> Would be nice if the wiki had tables of all the
> physical properties of the plastics being used
> especially data such as melting temperature,
> hardness, heat conductivity, and density, and
> graphs of viscosity at different temperatures.
>
> Also data for other standard building materials
> would be a useful addition to the wiki things like
> coefficient of expansion, coefficient of friction,
> hardness, density, heat conduction, etc.... of
> glass/brass/steel/aluminium.
>
> This would make life easier for developers trying
> to workout if it's better to make a nozzle from
> brass with less friction on the filament and
> better heat conduction but a thicker wall as it is
> weaker than steel which can have a thinner wall
> but lower conduction and higher friction.

There are actually a few issues with providing some of this information.

The info that is out on the net isn't always 100% accurate, or would have to contain variances based on the blend of material. For instance, ABS is a blend of 3 different polymers within a certain ratio. These ratios are not fixed, and so in cases where the ratio of one polymer is slightly higher than the others, you get different properties in the material. An ABS blend that has more Butadiene than another blend will exhibit more rubber-like characteristics. PLA also comes in different blends as well, each with different physical properties.

The manufacturers don't always tend to provide all the information for some of these plastics either. I've searched for a bit and not found a CTE value for PLA. I'm sure it's documented somewhere, but where?

As for testing these sorts of properties ourselves... We can easily do some basic tests, but certain tests need specifically calibrated equipment, which leads to who will pay for all of this? Most corporates only want the info for themselves. Most universities don't do much testing of material properties unless they have a specific need to test a material, and they'll usually only test that material, possibly with one or two others as a comparison.

Also, remember that the Reprap team is us, people spread around the world. While Adrian Bowyer of the University of Bath is (in many ways) the 'figurehead', he doesn't (usually) specifically push the project in any particular direction.

Note: I definitely agree that getting more info on the wiki helps everyone. I've helped out a bit where I can. If I had access to all the necessary info, I'd be happy to help.