Tag: RepRap

PLA Burning

Polylactic acid (PLA) is a material often used as a material for filament for RepRap technology. Sometimes determining type of plastic you have is not easy and comparing how different plastic filaments burn can be of big help. This video show how PLA is burning.

Polylactic acid (PLA) je vrsta plastike koja se pravi iz obnovivih izvora i vrlo je korišćena u reprap 3d printerima. Kako je nekada teško odrediti tip plastike samo gledanjem test gorenja plastike može da bude od velike pomoći. Za poređenje, ovako izgleda kada gori PLA.

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I’m half trough with modifications on my rapman’s hot end so I decided to share some of the experience with the rest of you.

First – why?

Shorter the transition zone from the solid filament to the molten plastic the better. Better means

  • Higher precision (you can better control the flow)
  • Less stringing (less ooze + better control)
  • Smoother run / consistent flow

Now, the “smoother run” is the major problem you have to solve as it quickly go from “running not-smooth” to “not running at all”. What actually happens if the transition zone is too long is that between liquid top at the one side of the transition zone and hard part on the other side your filament is “soft”. By being soft when you push it in the heat barrel the filament compresses in length but increases in diameter pushing against the wall of the tube it is traveling trough. The “smoothness of the flow” depends solely on

  • How smooth / slippery the tube walls are
  • How much pressure the filament is putting on the wall itself

The first issue we usually solve by using the slipperiest material that can withstand temperatures up to 260C – PTFE (a.k.a TEFLON ). The tube must be properly machined so that inside walls are smooth. Drilling it with a standard drill reduces the slipperiness a great deal so try to get your tube properly machined from day 1. Big problem with PTFE is that at temperatures we run (up to 250C) it gets “soft” and cannot fully hold shape (this really depends on the actual mixture but the harder PTFE you have the less slippery it is) so some reinforcement is required. The smart people in BFB solved this by encasing the PTFE tube inside a PEEK tube, another material that can withstand temperatures we work on but without loosing structural integrity. This combination has proven to work very good and now I see other hot end manufacturers started to use it too. This is actually where we come to our first problem with BFB hot end. The PTFE tube does not look as it is made from quality machined PTFE but looks more like a “next best thing” – extruded silicone tube. It can also withstand high temperatures and is also slippery, only it is not as slippery as PTFE. Replacing this tube by properly machined hard PTFE tube is the first step in improving your hot end. At the moment when I write this post, the only supplier of machined PTFE tube replacements that I know of is László KREKÁCS. His website/blog/webshop are not working yet so just send him email ( order[AT]arcol.hu ) and check details directly, he is very nice person to talk to I can recommend him without hesitations. You can also find a local cnc shop and make your PTFE tube replacement machined locally, and you might want to check with the BFB if they start to sell upgrades to the existing hot end (or new improved version of one) but attm bfb only offer stock hot end.

Very important to the slipperiness problem is that you have no “gaps” in the flow of filament. This is often assumed to be so, but in reality the PTFE/silicone tube touches very hot (250+C) aluminium and it can deform in the joining point because of the heat. If a gap is formed between aluminum and tube the filament will expand into that gap and the force needed to extrude it would become more then 100 times greater then if there was no gap. There are also some other deformations in this point that can have nasty effects, breaking the seal can lead to all sort of nasty problems, like the last one Forrest had.

Hot end after PTFE tube failure

Hot end after PTFE tube failure

PTFE tube failure

PTFE tube failure

Since going “more slippery” then PTFE is hard, the next thing to do is to shorten the transition zone as much as we can. The only thing to do it (other than using other filament) is to

  • prevent heating of the filament except on the very end where we want it to melt
  • dispose of the heat propagated trough filament itself

The first point sounds simple – we don’t heat it anyway, well, it is not that simple, all our PTFE, PEEK etc are linked to the very hot aluminium heated barrel and they are pressed to it strongly so there is a lot of heat transfered from the aluminium nozzle to the PTFE and PEEK tubes. This tubes are also heated by the filament itself (second point) so in order to solve both problems BFB shortened the PEEK tube and continued PTFE reinforcement with aluminium tube. This tube now serves as a heat sink to cool the PTFE tube and by that to also get rid of the heat propagated up the hot end from hot barrel trough PEEK/PTFE tubes and trough filament itself.

Doing some measurements without filament in the chamber stock bfb hot end measures under 40C on both PEEK and aluminium tubes while tip is heated to 240C, but with the filament inside, the aluminium tube reaches up to 70C leading to conclusion that filament in that region is way over 90C so if you are using PLA the filament is already starting to “swell” at the top of hot end and your transition zone is way longer then it should be (the transition zone should never be higher then end of PEEK tube). Adding a fan to blow at the hot end improves cooling of the aluminium tube so helps a lot, but using fan provided by bfb I was only able to drop this temperature by another 10C. Now, this is all while we had “stationary” piece of filament in the hot end, when you start extruding, you are bringing cold new filament in and the heat propagation is slowed down by the speed new filament comes in. This is why, with default / stock bfb hot end when extruder drive rpm is over 30RPM you are able to print properly as with the fan cooling the aluminium tube and the “fresh/cold” filament coming fast you keep the transition zone short. Problem start to exponentially increase as you slow down the exuruder RPM so at 10RPM it is almost impossible to push filament as it is soft all trough the hot end and with 5rpm you can even see filament swelling outside the hot end which completely blocks it (as it gets stuck at entrance to the hot end). Since I need low RPM extrusion to print high precision objects (0.15mm layer height) printing more then 20 minutes is almost impossible with low melting point filaments like PLA. This is why I started to modify one of my hot ends (have bunch of them, different nozzle sizes …).

HotEnd my mods

HotEnd my mods

Let’s start from the tip – first mod I made to my nozzle is to get a blank from bfb and drill with 0.25mm drill. This does not at all sounds as simple as it sounds. I spoke with 5 different cnc shops and with over 20 lathe owners and every single one of them told me that “they cannot help me as drilling 1mm of aluminium with 0.25mm drill is incredibly hard”. I finally did it myself by hands! Moving up, you can see the big “bulk” on my hot end, this is an insulation ring made out of silicone and some baking paper, it allows even poorly powered heater to retain heat at the tip. Above it you can see some copper wire, this wire actually goes around the whole nozzle connecting the steel triangle with aluminium heat barren with 3 hexagonal rods. This wire is then connected to the earthing wire that earths the nozzle preventing buildup of large amounts of static electricity by plastic flowing trough aluminium nozzle. This reduced incidents with electronics to only a firmware problems (no more resets from static electricity). The latest modification is the added heat sink to the aluminium tube. The tube itself has a very low surface so it is not very effective heat sink. As I have some left over thermal adhesive that I purchased to glue heat sinks to my allegro stepper drivers (think pololu) I bended the aluminium heat sink around 10mm steal pipe to form it properly and then I glued it to the aluminum tube. I’d add a same thing to the peek but unfortunately the thermal glue I have don’t adhere to PEEK :(. There is one modification in this region that is not visible on the picture and that is thermal grease I applied between PTFE tube and the aluminium/peek tubes to increase thermal transfer from PTFE tube to get the heat faster out. The next modification I’m thinking about is to make the aluminium tube longer by 1cm and to shorten the PEEK tube by 1cm. On the picture you see original MDF insulation plate and then original plexy insulation plate. I future I want both of these to be cut in aluminium because the original idea of the MDF ring imo is that bfb guys wanted to prevent heat to move up and damage the acrylic mount plate and acrylic x-carriage. Since I already replaced original acrylic mount plate and acrylic x-carriage with aluminium parts having this insulation is actually contra productive as the huge chunks of aluminium (mount plate + x-carriage) are actually a huge heat sinks and puny heater could not keep them hot even if it was heating only them, so changing these insulation pads to aluminium (and coating them with thin film of thermal paste) will additionally improve heat disipation from the top of the hot end further improving the flow by further reducing the transition zone.

Now, as I work with limited tools that I have at my disposal there is a guy who invested a lot of  time (and money) into designing a new hot end from scratch. I noticed he already incorporated many of the things I mentioned in this article and after talking with him I found out that some more improvements (not related to heat but to the flow, should increase quality a lot) that are not that obvious are implemented. I’m going to visit him in few weeks to get some of the prototypes (and of course a final 3.0) and test them myself. But before I gave his new hot end a try, I will continue to improve on the one I already have.

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Gospoda koja redovno obilaze blog primetiše da me nema već neko vreme pa rekoh da razjasnim neke nedoumice :). Prvo, za sve one koji su pitali, ne, nisam opet zapalio iz zemlje i trenutno ni žena ni ja ne razmišljamo o tome, čak naprotiv, jedan od osnovnih razloga što nisam bio dostupan par meseci je što smo draga mi žena i ja iznajmili neki prostor u zemunu gde ću ja moći da imam radionicu za dalji rad na usavršavanju reprap tehnologije e žena moći nesmetano da radi na svojim kreacijama. Dodatno će tamo biti i “show room” kako za dugmence tako i za reprap/rapman.

Jedna od novina koju nisam podelio sa svima je to da sam na poziv dr Adrian-a (čoveka koji je započeo ceo reprap projekat), pristao da postanem deo reprap core team-a (jezgro reprap tima koje rukovodi putem kojim se reprap projekat kreće). Trenutno radim na nekim unapređenjima za MENDEL i radim na potpuno novom konceptu masine koja je u stanju da otštampa model većeg kvaliteta nego što trenutno to reprap i njegova deca mogu. Više o tome kada bude rezultata za pokazivanje :).

Na kratke staze, što se da videti iz prethodnog posta, radim na vrućoj podlozi za štampu za rapman i za mendel. Problemi u izradi su “standardni” –  za svaku glupost se čeka po 2-5 nedelja da stignu iz farnela, digikey-a i ostalih dobavljača pošto naravno niko nema ništa egzotično poput 2r2 otpornika na lageru !!!!!!!!! sramota … sve što mogu da kažem je da se zahvalim firmi TECHNODIS iz beograda koja je uvezla za mene 99% tih “čudnih” komponenti koje nijedna firma kod nas ne drži na lageru (da mi je jasno šta je tako čudno u 50W 2r2 otporniku da nijedna firma u Srbiji ne misli da je imati 10tak komada na lageru pametno, ili zašto termalni lepak koji se koristi da zalepite cooler za čip mora da se čeka 5 nedelja ?!?!?!?).

I kada smo već kod neinformisanih firmi, ako ste primetili, skoro je u Blic-u, neki “genije” od novinara napisao punu stranu gluposti o makerbot projektu gde je naveo Bri Petisa (super lika koji je dosta uradio za reprap community) kao pokretača celog projekta, što je čista laž pošto je Bri samo jedan od vlasnika firme Makerbot koja prodaje reprap klon u kitu. Dakle daleko od toga da su oni bilo šta započeli a posebno da je makerbot “otac” reprap tehnologije (za one koje mrzi da čitaju, Darwin je prvi reprap i njegova deca su razni klonovi poput makerbot-a, rapman-a, shapercube-a i ekipe. Darwin je v1.0 reprap-a, sada je aktuelan Mendel koji je 2.0 i koji već ima svoje klonove)

I za kraj, jedna lepa vest. Pored mog rapman-a, mendel-a, minimendel-a i nekih repstrapova, Srbija je dobila jos jednog rapman-a i to v3.1. Printer je kupio Mašinski fakultet u Kragujevcu za svoj rapid prototyping tim. Printer je sklopljen pre neki dan (na sklapanju je radio Milan Radović, student iz Kragujevca kome je rapman osnova za diplomski rad na temu rapid prototyping tehnologija) i već je uspešno otštampao nekoliko objekata.

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Vruca platforma za stampanje

Malo sam usporio sa postovanjem, i ovde i na MySQL delu, uglavnom zbog obaveza na poslu i kod kuce, ali i zato sto sam se bacio na neke malo vece zahvate sa reprapom … Radi se punom parom na v2.5 i na v3.0 reprapovima, no o tome neki drugi put, ne ocekujem da ce neko ozbiljnije poboljsanje same konstrukcije biti tu pre sredine 2011. Dakle, na cemu se trenutno radi … kao sto sam spominjao vise puta, “warping” je veliki problem sa 3d stampanjem, posebno u kucnoj varijanti. Veci objekti su “nemoguci za stampu” ako se koristi ABS ili PP/PE zato sto su warping sile toliko velike da objekat pokida sam sebe. Posle nekoliko meseci utrosenih na isprobavanje razlicitih tehnika koje smanjuju warping efekte (razne tehnike sa otvorima u objektu koji prekidaju warping sile i zadrzavaju ih u limitima koje materijal moze da podnese), ugradjen stres u sam objekat je i dalje suvise velik da bi objekat bio dovoljno cvrst da se koristi kao finalni proizvod (kao “rapid prototype primerak za gledanje” moze ali..). Jedini nacin da se zadrzi kvalitet objekta je da se spreci gomilanje tog stresa i jedan of efektnih nacina da se ovo izvede je uz pomoc vruce platforme na kojoj se stampa i koja grejuci objekat odozdo dozvoljava objektu ravnomerno hladjenje i samim tim ne dozvoljava ugradjivanje prevelikog stresa u sam objekat. Kako su za razlicite delove objekta potrebne razlicite temperature same platforme, i kako bi maticna ploca rapmana bila u stanju da kontrolise temperaturu platforme napravio sam mali, zgodan kontroler koji regulise temperaturu ploce.

HotBed Controler v1.0 Schematic

HotBed Controler v1.0 Schematic

Kontroler je moguce setovati putem 2 tastera (target temp+ i target temp-), pritiskom na oba tastera trenutni target temp se cuva u eepromu odakle se cita pri inicijalizaciji, i preko i2c protokola posto se kontroler ponasao kao slave I2C uredjaj. Moze se procitati / upisati nova odredisna vrednost za temperaturu i moguce je procitati trenutnu temperaturu ploce. Firmware je realizovan u CSC PICC C-u na pic16F819. Pic je odabran kao “najmanji pic iz fioke sa dovoljno pinova da tera lcd, 2 tastera, i2c i analog read”. Source je dostupan ovde.

Sama platforma je realizovana sa 5mm debelom 276x260mm aluminijumskom plocom koju je obezbedio jedan mladi repraper iz Kragujevca (hvala jos jednom) na koju su pricvrsceni 50W 2R2 otpornici. 8 otpornika je vezano 2 po dva u paralelu pa zajedno u seriju tako da je ukupni otpor grejaca oko 4R4. Grejac (otpornici) se napajaju sa 40VAC 10A izvora koji je kontrolisan preko MOC3043 + 25A 600V triakom na kontroleru. Sama kontrola se zasniva na prostom “if (target > current) {heaterON();} else {heaterOFF();}” posto sama inercija grejaca kao i ne preterano potrebna preciznost (+-2 stepena je vise nego zadovoljavajuce) ne zahtevaju neki ozbiljniji PID kontroler, mada obzirom da je pic iskorsten tek negde oko 70% bilo mi moguce implementirati i neki malo bolji PID.

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Netfabb Engine for Rapman Basic

Stigao je dugo ocekivani software za procesiranje 3d objekata u G-Code. Pravi ga Netfabb, firma koja pravi i netfabb studio (jedan od najboljih alata za popravku i manipulaciju STL fajlovima) koja ima 30+ godina iskustva u rapid prototyping svetu.

Za sada je od dva najavljena proizvoda, Netfabb Engine for Rapman Basic i Netfabb Engine for Rapman Professional (prvi kosta 100-200E, drugi nesto oko 1000E) izasao samo Netfabb Engine for Rapman Basic i to beta verzija. Testiranje te beta verzije je pokazalo neverovatan pomak u kvalitetu stampe na reprap uredjajima. Netfabb direktno podrzava samo rapman verziju reprap printera ali kako je g-code genericki vrlo verovatno ce isti trcati i na Mendelu bez vecih problema.

Prvu novinu koju nam uvodi Netfabb Engine for Rapman Basic je kalibracija. Pre nego bilo sta krenete da stampate, neophodno je kalibrisati software za materijal koji zelite da koristite. Za pocetak, Netfabb Engine for Rapman Basic podrzava samo ABS i PLA materijal i nudi vam slot za svaki od njih u nekoliko boja. Procedura kalibracije je vrlo jednostavna, zahteva da otstampate izgenerisani fajl i izmerite debljinu zida na 14 objekata. Bice vam potreban dobar subler (po mogustvu digitalni) posto je potrebno izmeriti vrednost sa tacnoscu od 0.01mm

Druga novina (ocekivana od ovakve firme) je interface, najzad je tu jedna aplikacija za procesiranje STL-ova koja se ne startuje iz konzole. Na zalost aplikacija za sada radi samo na windozi (ja sam je testirao na win7 64bit ultimate) ali su mi Alex i Charly rekli da se uveliko radi na testiranju linux verzije tako da se ocekuje da ce i basic i professional verzije raditi i na linuxu. Inteface je vrlo intuitivan i jako brz… radi cak i pod virtualbox-om. Za razliku od profesionalne verzije basic verzija nema dongle i koristi licence key i online aktivaciju te se vezuje za samo jedan racunar. Professional verzija ima dongle koji moze da se deli kroz mrezu tako da mozete imati instaliranu aplikaciju na mnogo racunara, samo je limit da samo jedna u jednom trenutku moze da radi.

Sledeca drasticna razlika u odnosu na sve ostale programe za procesiranje 3d objekata je raft (raft je podloga koja se otstampa na povrsinu za stampanje koja obezbedjuje idealno ravnu podlogu za stampanje objekta i dobar spoj izmedju objekta i povrsine za stampanje). Raft koji pravi netfabb je toliko drasticno razlicit od svega do sada vidjenog da treba da prodje jos vremena da vidimo koje su mu sve prednosti. Za pocetak – stampa se brze, cvrci je, lakse se uklanja, a deluje da znacajno smanjuje warping objekata. Za pocetak odlicno, videcemo kako ce se pokazati u buducnosti.

Brzina je nesto gde svaki processing alat ima veliki problem. Obrada velikog broja podataka je nesto sto prosto “ne moze brze”, pa, izlgeda moze. Netfabb Engine for Rapman Basic je od Skeinforge-a (do sada najbrzeg processing alata) brzi bar 10 puta!!! a na istoj masini je od originalnog reprap host-a brzi preko 20 puta. Da li zato sto je netfabb engine pisan u paskalu i kompajliran u nativni kod (skeinforge je python, reprap host je java) ili zato sto su ludi Nemci napisali to mnogo dobro, ili zato sto jos uvek ne podrzava sve stvari i nema sve mogucnosti koje imaju skeinforge i reprap host – videcemo, za sada je mnogo brzi, kada izadje finalna verzija sa svim opcijama uporedicemo ih ponovo.

I za kraj, test objekat je ruka – otstampana u PLA materijalu, ruka je visoka ~12cm

neociscena – direktno u stampacu:



Štampanje u vazduhu

Rešen da poteram mašinu malo preko nekih definisanih granica napravio sam objekat koji testira koliko je RapMan sposoban da štampa “u vazduhu” tj. koji negativan ugao može da podnese. Standardan limit ovde je 60 stepeni, tj ako je “overhang” veći od 60 stepeni (ugao prema horizontali manji od 60stepeni) mašina neće moći da odštampa isti ako ne koristi support.

Napravljena su tri testa. 2 sam štampao ja i jedan je štampao jedan moj kolega (Tony, čovek koji inače piše firmware za RapMan) pošto on ima ABS u boji (ja imam samo beli).

Svi testovi su napravljeni sa osnovnim setovanjem koje je ovakvo:

CARVE/Layer Thickness: 0.35
CLIP/clip over ..: 1.0
FILL/Grid Extra Overlap (ratio): 0.4
FILL/Infill Solidity (ratio): 0.1
INSET/Infill Perimeter Overlap (ratio): 0.4
INSET/Calculate Overlap from Perimeter and Infill: True
INSET/Remove Extrusion Overlap: True

Prvi test, ja štampao koristeći beli abs na temperaturi od 243 stepena:

Objekat neočišćen:

Objekat očišćen::

Objekat je izuzetno čvrst po celoj visini, “overhang” delovi ne pokazuju znake slabosti.

Drugo štampanje je napravio Tony Koristen je identičan gcode fajl samo je razlika što je korišten crni ABS. Crni ABS inače zahteva malo veću temperaturu štampe nego beli ABS (zbog pigmenta) tako da je ovo približno testu belog ABS-a na 240-242 stepena.

Objekat neočišćen:

Kao što se da primetiti, ovaj print je skoro idealan. Dakle odabirom prave temperature možemo zaobići standardni limit od 60 stepeni. Objekat je vrlo čvrst i ne pokazuje znake slabosti. Ovo uopšte nisam očekivao.

Treći print je test šta se dešava ako štampamo hladnije nego što je idealna temperatura. Ovde je temperatura spuštena na 237 stepeni, dakle 6 stepeni manje nego za prvi print, štampano opet belim ABS-om.

Objekat neočišćen:

Objekat delimično očišćen:

Kao što se sa slike da primetiti objekat je u priličnom haosu, teško ga je očistiti, kvalitet objekta je “neupotrebljiv”, objekat ima dobru čvrstinu na ravnom delu ali na overhang delu nema čvrstinu i može se slomiti na tom delu upotrebom malo jače sile.

Da zaključimo, 60 stepeni limit za overhang bez korišćenja support materijala može da se prebaci ako lepo pogodimo i usaglasimo temperaturu sa materijalom koji koristimo. Uz dobar tuning moguća je štampa overhang-a od čak 30 stepeni.

Objekat, ako želite sami da probate da otštampate možete naći na thingieverse sajtu.

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RapMan Pro

RapMan Pro

RapMan Pro

BitsFromBytes je izbacio i PRO verziju svog repstrap kita RapMan Pro koji je prikazan pre neki dan na nekom sajmu u Engleskoj. RapMan Pro jos uvek nije u prodaji posto BitstFromBytes trenutno radi na dual extruder modelu koji ce biti u stanju da stampa sa dva razlicita materijala (po zelji korisnika moze da bude i isti materijal samo razlicita boja ali je osnovna ideja da drugi extruder pusta PVA ili slican support materijal koji se lako extruduje a moze lako i da se ukloni – PVA se na primer rastvara u vodi) tako da ce biti moguce stampati mnogo komplikovanije oblike.


Bits From Bytes je napravio wikimedia stranu za RapMan dostupnu ovde. Pored foruma i bloga, wiki bi trebalo da postane odličan repozitorijum znanja vezano za RapMan samogradnju, konfiguraciju kao i vezano za samu štampu.



Imam malo neke plastike za RapMan-a koju nisam mogao da dokucim sta je … prosao kroz neke testove sa neta i dosao do toga da je CA ali .. ispostavilo se da je ABS. Test sa paljenjem parceta je doveo do finalnog zakljucka, hvala drugu Mike-u na testiranju, on je palio svoj ABS a ja moju nepoznatu plastiku pa smo poredili :)

elem, ovako gori ABS:

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PP je mnogo nezgodan za rad. Vrlo je elastican i samim tim podlozan “warp” problemu. Sa njim mora da se radi sporo i mora da se obrati paznja na detalje… Neke osnovne premise u radu sa PP:

  • PP nije lepljiv – tj, ne lepi se za svaki materijal te morate naci adekvatnu podlogu za stampanje. Lepi se ok na PP i na HDPE. Ja koristim kuhinjsku plasticnu dasku za seckanje (napravljena od PP – 80% njih su od PP-a a onih 20% od HDPE tako da svaka radi posao) sa odlicnim rezultatima
  • Mora sa stampati sporo da bi se izbegao warp .. dakle 6-8mm/sec
  • Kako stampate sporo, obratite paznju da ne istiskate previse materijala, RPM od 12-18 za motor extrudera je ok
  • Temperatura je isto bitan faktor:
    • Raft: 215
    • First Layer Outline: 208
    • First Layer Within: 230
    • Shape Next Layers: 230
    • Support Layers: 208
    • Supported Layers: 230

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