High power hot-end for fast printing - dual resistor & easier thermistor

This is the first of a few new hot-end designs I have been testing, I mounted it to my new ‘Bling’ machine for some speed and temperature testing, it’s performing well, here is how I made it - 

I decided to try a new shape for the heater block, normally you want a low profile block with a short hot-zone, but I specifically wanted to try a triangular shaped block for a number of reasons / goals - 

• I wanted to mount 2 x Resistor heating elements in the block so a wide base made this easy.
• I wanted to try a longer heating zone to see how fast I could extrude.
• Triangle gives smaller mass at the top, hopefully to reduce oozing due to the longer heating-zone.
• I wanted to be able to easily wrap the block in PTFE sheet, a triangle gives a easy to wrap shape and is insulated at the top with two thickness of PTFE.
• For the future I want to be able to extrude fast @ 300 degrees C with less than a 4 degrees C temperature drop while printing solid layers.

Next I REALLY wanted to switch away from using the tiny dipped thermistors the size of pixi-dust with ultra thin connecting wires, they are such a pain to use and don’t really have many plus points apart from the low thermal mass/quick response. I now only use a ‘normal’ Axial style. I can fully recommend doing this, it’s 1000 x easier to build and much less fragile, I also think I get much better temperature reading stability, response time is fine.

HONEYWELL S&C / FENWALL  135-104LAG-J01 Link Here - 

Thermistor Type:NTC; Resistance:100kohm; Thermistor Tolerance:± 10%; Beta Value (K):3974K; Operating Temperature Range:-60°C to +300°C;

You can buy them from Farnell -  only £0.25p

I have used 2 x 10ohm Vitreous enamel resistors in parallel; this gives approximately a 5ohm load where you would normally use a single 6.8ohm resistor.

The resistors are either side of the nozzle, giving nice constant heating.

The axial thermistor is slightly above the resistors and is just touching the side of the nozzle barrel, this placement gives me a quite constant 3 degrees C lower reading than the inside of the nozzle throughout the temperature range, which is fine.

Wrap the thermistor body and legs in Kapton to insulate.

Use Aluminum foil or tape around the Resistor body, it should be a good tight fit in the block. 

All in place and secured with Fire cement.

The part make-up looks like this. (Ignore the PTFE washers; I didn’t use these in the end).

I also wrapped the heating block in a strip of 0.5mm PTFE sheet.

Still using PEEK in this design, I expect to remove this part in the next version.

All wired up using high temperature heat-shrink and silicon coated wires.

And assembled.

I added a small heatsink, but I doubt this is really required.

The PEEK block is only luke-warm to the touch even after 4+ hours of printing – Note I am using a small 40mm directional fan aimed at the PTFE.

I will do some more tests to see if I can switch off this fan and still keep a cool cold-end.

My Fan-duct for Greg's Linear bearing X Carriage is on Thingiverse here.

It’s printed just over 2Kg of material so far at ~160mm/Sec and it’s performing well; I’m really happy with it. All of the multicoloured Faberdashery printing in my previous blog update was done with this setup along with some ABS parts and build sheets.

I have not yet found an upper speed limit as I need to do more testing, but it manages to print PLA at 180mm/sec with only a 2 degrees C drop in temperature when doing whole build-plates of full infill layers.

I will be testing ABS more extensively with it over the next week and seeing how fast I can get it working with different materials.

My main observation now is that you do need to run this style of hot-end at a minimum of 80mm/sec, and I need a 1.5mm extruder reverse to make sure oozing is not a problem. At speeds lower than 60mm/sec it’s better to use a smaller heating zone/block.

Next time I will still use a triangular block but make it slightly smaller overall and a little shorter.

Thanks for looking, I would be really interested in any comments or opinions on high-speed printing and hot-ends designed for speed and also high (290+ temperature) - you'll see why in a future post....

Rich.

1st Prusa Child & issues with ABS printing

I have been printing with the Bath Prusa Mendel for 2 weeks now. It’s been a good learning process along with discovering more things about Skeinforge, high speed printing, hot-ends, and using ABS.

I now feel comfortable about the tool-chain and using the Prusa Mendel along with some of its limits, so I can now try a few more adventurous things in the coming weeks.

Below are some of things I have printed so far, and the issues I had along the way.

PLA works well, I have used 4 different types from 3 different suppliers, and they all have a slightly different extruding temperature and flow differently.

Just as I was getting to the end of the White PLA I had a hot-end failure jam, the nozzle was flexing down and catching on objects, on closer inspection the PTFE had split around the top and the PLA was jamming in the barrel.

I replaced the split PTFE and also the Hobbed bolt as I was getting slipping and inconsistent feed

 No change in spring tension or cleaning of the teeth seemed to fix it.

The White PLA from Adrian was used up printing upgrades, spares and experimenting with speed.

First upgrade was the Prusa Z Rod Constraint by ScribbleJ shown above.

And a few of my own 8mm T-slot mounting blocks as I needed some for my other machine.

I then switched to Gold PLA and started to print a full set of upgraded Prusa parts.

This included the new Prusa Z Axis using LM8UU Linear bearings.

And Greg frost’s LM8UU X Axis and Y Holders for Linear bearings.

So after the first week I had managed to get it working well and print these.

I decided on Andrew dent’s MV6 frame and foot vertex pieces as I like the look of them and they are a little fatter than the official Prusa ones.

I was getting confident at this point and even did my first print using multiply in Skeinforge to get me 9 x M8 bar mounts printed in one go.

I printed a few fun things to keep my princess happy –

This is one of the exceptional Heart bracelets by MakeALot

And a 1.8 X scaled version of the Princess Heart Crown by syvwlch

So a few days later I had the first child set of Prusa Mendel parts I decided to name ‘Mendel-Bling’ for building up my next machine. 

At the weekend I decided to experiment with ABS. It’s the material I first started with on my original repstrap back last September and I was expecting it to be easier than PLA… it was not, but maybe that was my unfortunate choice of colour.

Sunglasses on, it really is that PINK.

As it was looking quite hard to get this ABS extruding I decided that my first ABS print should be another extruder, that was a good choice as shortly after printing this the PLA extruder melted.

It’s good that I had an ABS X carriage or that would have melted also.

Extruder replaced. Still using PLA gears for good wear resistance.

When printing with the Pink ABS it needs 263 degrees C to extrude, I’m running it at 270 because of the following issue. - At 80mm/sec and 30% infill the Hot-end power is on 95% of the time and that quickly goes to 100% when doing solid infill layers while the temperature also drops 8-10 degrees, that’s right on the limit of the power I can get into the material with this particular hot-end, any faster and the extruder will jam and grind through the filament as the temperature drops too much.

Take a look at this short video of a Pink print below, the hot ABS comes out looking slightly Purple and as it cools turns back to Pink, it’s really cool watching it print especially doing solid infill, this is my first coloured ABS so I don’t know if they all do that?

With Natural ABS I still see a temperature drop at 80mm/sec but not as much while the extruding at a lower (230) temperature.

So really I should slow down the ABS speed to be safe and then build a better hot-end that can deliver more power quickly into the filament so I can speed things up again.

I don’t see this temperature problem with PLA, but I have only gone upto 100mm/sec at the moment, I’ll wait until I have my Linear Bearing Prusa (Mendel-Bling) before going any faster.

I have a puzzle to build up tonight, the Heart Gears by emmett

Thanks for reading,

Rich.

Skeinforge Version 41

I have been using Skeinforge for just over 1 week now and I'm starting to get a grip on this most fantastic program.
After initial machine setup and printing with Reprap Java Host I always wanted to move over to Skeinforge, but it has a bewildering array of settings and control, quite daunting when you first start.
- But well worth the effort - 

This image shows my best possible print quality I managed from Java Host to generate Gcode (on the left) and one of my very first Skeinforge prints with initial 'good' settings, and it's still getting better and better all the time I learn more about Skeinforge.


Some excelent information and advice from long-term Skeinforge users for the new Version 40/41 can be found on the Reprap forum here - http://forums.reprap.org/read.php?154,75635
And also on the Mendel-parts forum here - http://www.mendel-parts.com/new_forum/phpBB3/viewtopic.php?f=37&t=256

Many thanks to everyone as I would have wasted a lot of time if not for this head-start.

The Skeinforge manual and settings descriptions are also found here - http://fabmetheus.crsndoo.com/wiki/index.php/Skeinforge

My setup is not typical of a Mendel or other Reprap, so your exact settings will be different, but the following information, notes and advice may help you get going if you are new to Skeinforge and are not sure where to start.

One of the first problems I had was the fact I didn't know how well my machine would print so it was quite hard to judge when I actually had it calibrated to a good standard.

Other than looking at other people's prints on thingiverse it's hard to say how good your machine should be?

First Step - Measuring E-steps/mm for the new Dimension changes in V40/41

I'm using a Bowden extruder setup that has some extra issues ascociated with controling filament hysterisis but the following is required for any extruder in any configuration.

My extruder being belt driven is also different from a Wades or Adrian's geared version, but in principle operates in the same manner, but with different gear ratio etc.

I setup my Extruder on a stepper motor test jig I had made to test Pololu modules, it's just providing a simple button to full-step the stepper motor.

I'm using 1.75mm Feedstock and now Dimension requires you to set 1mm of INPUT feedstock. 

Before the firmware required 1mm of Extruder Feedstock, this is an important change and makes a big difference for making nozzle size changes easy and generally everything else easier.

I marked the filament with tape on the extruder output and then counted how many full-steps (button presses) were needed to extrude 10mm of feedstock.

I did this again in the reverse direction to make sure of my count. Take as accurate measurement as you can for this.

10mm of driven feedstock = 348 full steps

I am really running my Extruder at 4 x microstepping, so 348 x 4 = 1536

And in the Firmware you need to provide a value for 1mm of feedstock so that would be 1536/10 = 153.6

So I used 153, recompile and download.

Then you need to accuratly measure your feedstock, I measured with a digital micrometer 10 random section of the coil and the average was 1.792mm

These settings need to be entered into the 'Dimension' tab in Skeinforge.

Many of the sections in Skeinforge do not need messing with, the ones you will need to play around with are 'speed' 'raft' and 'fill'

After setting your input filament perameters Feed and Flow under 'speed' are the most infulentual settings to play with along with 'infill width over thickness (ratio) in 'fill'


The next bit of advice is to make your machine Go Slow for initial test and calibration of flow/feed, I wasted quite a lot of time trying to run my machine too fast before I had these settings correct, you can easily speed it back up afterwards.
So set the 'speed' for the machine to 20 or 30mm / sec

Set your flow/fill speed -

Set the extruder speed Feed and Flow the same value, I started at 16mm/sec and went up and down from there.

This picture shows the effect of Flow/Fill on my machine (0.25 layer height) 160 layer 40mm tall 10mm cube.

I decided to turn off 'Limit' as I have acceleration in my Firmware, but you may want to enable it to help protect your machine from over-speeding especially on the Z axis.

If you are not using a heated bed (or even if you are) you may want to make the first layer go slower than the rest to help it stick to the bed.
Raft can do this, although you don;t actually need to make a raft just use it for slowing down the first build layer outline and initial fill.
See the Above links to Reprap forum and Mendel-parts for more on this and all the other sections.


Then tune your solid fill rate - 
Some of the guides talk about setting 'infill width over thickness (ratio)' to 1.7 from the standard default of 1.5. I found that my solid layers had too little plastic at 1.7 and 1.5 so my setting is 1.4, this gives me a perfectly filled solid layer without any 'spare' plastic, if your nozzle is pushing about plastic on subsequent layers of a solid fill (object base) then raise this number. if it's too sparce and you have tiny gaps between filament make this number smaller.

This solid base was with it set to 1.5, I settled on 1.4 in the end.

These are the different tool-paths for 1.0, 1.5 and 1.7 infill width over thickness (ratio) settings

Correct Filament Reversal length -

* Very important with a Bowden extruder *

I did get lucky with my first guess at required Filament reversal length, but the above image show the effect of not having enough reversal (lots of strings)

On the left is a 1mm reversal, middle is 2mm and printing on the right is a 3mm filament reversal. I may be able to get away with 2.5, but for now I'll stick to 3mm.

It's easy to fool yourself into thinking you have ok settings using a standard test cube, I have found that this model (below) is an excelent peice for machine calibration and it's quick to print so you can try out settings quickly.

It's a hollow pyramid by (3dprinterbot) found on Thingiverse -.http://www.thingiverse.com/thing:8757

This was still early on in the Skeinforge tweaking, but even so a great improvement over Java host.

No Strings !

Java host generated on the left, and Skeinforge V41 on the right. (With strings, but in the right places)

This was my most recent print, with super-refined settings. 

This proved to be a good test of filament spanning, you can see the solid layers at the top, under this is hollow, and then a solid base at the print bed.

I stopped the print as I have hit a problem with Gcode generation on Hollow objects. 

I'm going to need some help on sorting that.

Anyone like to guess on what this object is? 

When I get it all printed out you can see if you were correct.

If you are new to Skeinforge, I hope that some of this may help you or at least show you that it's worth learning how to use it.

Thanks for reading.

Rich.