RepRap: Builders

Another 3D Capture Technique

noreply@blogger.com (AKA47) — Fri, 20 Nov 2009 07:12:00 +0000

A quick heads up for another webcam based 3D Capture Technique that claims rapid capture.

http://mi.eng.cam.ac.uk/~qp202/

Ponoko Darwin Progress

noreply@blogger.com (Russ Nelson) — Sun, 15 Nov 2009 01:29:00 +0000

I started building my Ponoko Darwin about a year ago. Got everything put together in about two months. Needed to upgrade the PC connected to the reprap, took on a job working for a start-up, and had no free time whatsoever. I still need to have a reprap, so I got started working on it again. Found several problems:
1) I have a Reprap Mother Board v 1.0, which isn't documented. Had to buzz out the pins.
2) I'd failed to solder the motherboard's stepper connectors; just diagonal pins.
3) In spite of what the website says, the Reprap's opto end sensors are inverting. When empty, they emit +5v. When interrupted, they emit 0.45v. Had to invert the sense. Perhaps the Sanguino test firmware should say "ran into endstop" when that happens?
The tests are running now. The X and Y operate fairly smoothly. Z is a bodge. WAY too much friction, even though I used a dry teflon libricant. Fails to move even when I have the stepper driver cranked all the way up. Will only move if I help it along. I suspect the problem is in the ball chain's mating with the gears. Advice cheerfully accepted for alternatives.

One More Machine

noreply@blogger.com (Wade) — Mon, 09 Nov 2009 19:46:00 +0000

Mo stopped by today to pick up the set of Darwin parts I printed out for his team of engineering physics students at UBC. They've got some interesting plans for their Darwin, but I'll let them explain what they're up to.

Instead of a case of beer, Mo, Jacob and Bing paid for this set with a box of MXL pulleys suitable for Mendels and Darwins that Bing imported from China, plus a hardcover copy of Cory Doctorow's novel Little Brother. I've been a fan of Cory's novels ever since I read Printcrime, which I was introduced to by the RepRap forums, and his latest novel features an interesting take on 3d printers. Sooner or later I'm going to have to send Cory a set of parts!

So, next up, Mendels!

Wade

Rapman 3.0 commissioned

noreply@blogger.com (Forrest Higgs) — Mon, 09 Nov 2009 05:22:00 +0000

We printed the traditional minimug after a morning tuning the system. This was my first try at printing the minimug. I was running the extruder 5 degrees too hot for the batch of ABS that I was using and the y-axis drive shaft was loose. You can see how the top melted from the extruder running too hot.

Here you see the taping of the first successful minimug print with a tripod-mounted Flip.

The completed minimug on its print raft.

The completed minimug peeled off of the printing platform

A closeup of the completed minimug. There are a few print hairs on the inside which were easily removed.

Thanks are due to the many fellow Rapman builders at the BitsFromBytes Forums and especially to Bogdan Kecman who has been an constant source of useful advice on getting past the little problems one encounters in getting the excellent Rapman Reprap printer going successfully.

Okay, I think I'm getting the hang of Skeinforge.

There was a little displacement for the first 10 layers because of a loose y-axis belt. I paused the print and tightened the belt. After that the print went smooth as silk.

Forty percent fill, 50 mm 15 toothed involute profile gear. Printed at 16 mm/sec in about 45 minutes.

Another Child Darwin

noreply@blogger.com (Wade) — Thu, 29 Oct 2009 20:46:00 +0000

In the hopes of increasing my printing speed, and to confirm that it is actually possible to make a RepRap with RepRapped parts, I've printed out and assembled a child Darwin. It's mechanically complete, and the axis all run quite nicely - at least 3000 mm/min so far on the X and Y. I have yet to get a firmware that will run the stepper based pinchwheel extruder, so no minimug yet, but I thought I'd post my results so far. I'd love to hear from anyone who has a stepper driven extruder running with any of the Arduino/Sanguino/Extruder controller firmwares. Also, a big thank you to Barry, who soldered up and donated the stepper drivers and opto endstops!

Also, while I've been assembling the 2nd Darwin, I continued printing out parts, and am now just a few parts away from completing a third set of printed Darwin parts. They're going to some students from UBC, more about that later. Interestingly, the parts fit on the bed when you dump them out of a bucket onto the bed, but unfortunately, the Darwin isn't able to utilize the entire bed space for printing. :)

Here's the parent machine:

A little worn down, but still printing!

Wade

Lazy Susans and filament

noreply@blogger.com (Forrest Higgs) — Wed, 28 Oct 2009 14:53:00 +0000

Three millimeter filament generally comes packed in two formats, first as ...

coils as seen with the four 5 lb lots of PLA at the seen on top of a standard shipping spool of ABS seen carrying 20 lbs and capable of carrying 40 lbs which is the second format.

While several solutions have been confected to deal with coiled filament, I wanted to use ABS directly off the spool. Having lived and worked in Guangdong in China for several years I became happily acquainted with the lazy susan tables which enabled hungry Cantonese dinner parties to load their rice bowls at dim sum restaurants with a minimum of fuss.

The ball bearing race mechanisms for such tables are readily available in larger US hardware stores for about $10.

I also bought a pair of precut plywood rounds at the same store. Once I locked the race down, I lubricated with a light oil spray.

What you wind up with is a mounting table for quite a heavy spool of ABS which uncoils with about an ounce of force.

I suspect that one could knock together a much smaller spool for coiled filament and use the lazy susan arrangement for those as well. Given that most extruders exert kilograms of force to push filament into the extruder barrel this arrangement shouldn't cause feed problems. I'll keep you posted on how it works out.

Colour Printing - the next step

noreply@blogger.com (Tony) — Wed, 28 Oct 2009 13:18:00 +0000

To follow on from the basic twin extruder test in the last blog, here we have the results of my first test using support material

The machine is loaded with two colours of ABS, mainly for convenience at this stage, Black for the object and Yellow for the support material.

The file chosen is a bearing cap, printed from the bearing axis up, this has a semi-circular void that runs front to rear of the part. Actually this file prints very well without support material but it is a small part suitable for testing the head change.

Small it may be, but it still contains a fair number of layers and therefore lots of head swapping!

The first test was done with a hand edited file, I added several new lines of G_Code to manage an orderly change over from one head to the other. On more complex parts, it would not be practical, the new codes need to be added by Skienforge.

Skienforge already deals with support material by issuing a temperature change to flag the start and end, I need several other codes inserting at this point. To do this I have made a simple modification to Skienforge to pick out the support material, then insert my new codes as required.

The image shows the first complete part made by running the file from Skienforge.
Finish on the part is crude as the G_Code has been generated with 0.4mm layer thickness, this ensures a relatively quick build and gives a manageable file size.

The print is far from perfect, but I have to say I am encouraged by the results.

Cutting Spur Gears with Meccano

noreply@blogger.com (AKA47) — Tue, 20 Oct 2009 15:07:00 +0000

An item of interest I found when worrying the web about gears.

Meccano Gear Cutting Machine

It is a machine made from meccano that can cut more meccano compatible gears using a Threading Tap. It uses an existing Meccano spur gear as a template for the one to be cut.

A novel way to make gears without a lathe.

Interestingly enough it should be only a small set of modifications to make the machine able to cut worm gears by hand also without the need for a lathe.

I don't have any Meccano but thought this would be useful enough to cover here for those who might.

Just about done

noreply@blogger.com (Forrest Higgs) — Mon, 19 Oct 2009 03:24:00 +0000

I finally sorted out the last parts of the extruder on my Rapman and should be able to start printing after I get acquainted with the operations manual.

I need to put that spool of ABS on some sort of bearing loaded rack so that the ABS will feed into the printer smoothly.

Colour Printing

noreply@blogger.com (Tony) — Sun, 18 Oct 2009 16:55:00 +0000

First attempt at two colour printing, not the most astonishing object but you can see the potential.
The print has been done on a BfB V3 machine fitted with twin extruders. The two single colour objects were printed together from one file, the two colour object by swapping heads through the build, changes triggered by G_Code.
You can see the potential for running support material along with the main print, swapping seamlessly back and fourth between the two.

The wall is single filament thickness so alignment has to be reasonably good between the heads. The object is far from perfect as its only the third print of a new machine fitted out with the twin head.
More to follow on this.

Open-Source to the rescue!

noreply@blogger.com (Renoir) — Tue, 13 Oct 2009 20:36:00 +0000

To build anything in a RepRap, you need to have a 3-D design, save it as a STL or triangle mesh file, and load it into the RepRap host software (or skeinforge).

To create these designs, RepRappers use different programs - Either an adapted 3-d modelling programs, originally used for animation (like Blender and Art of Illusion), or freeware versions of CAD software (like CoCreate). These solutions work, and work well, but each program has seperate advantages. I've been looking out for a 'better fit' - a CAD-style program, that supports building meshes and solids.

Make magazine today furnished me with a link to FreeCAD.

It's pretty slick - either I'm quite lucky, or it works quite well. Within a few minutes I was able to load it up, get started, create a small cube model, export it to an STL file and import it successfully into the RepRap Host software (not always an easy thing!).

OK, lets give it a real test...

Let's load up some data from a complex file: a human head.
To really test it, I created a large sphere, stuck it on top, and did a 'union' (Join).
This is not nice: most complex geometries cause all sorts of bent and broken and backwards triangles. Lucky there is an analysis tool to point all this out:

From FreeCAD

Pressing some of the 'repair' buttons sorted all this out.

From FreeCAD

This exported easily to an STL file: and then loaded straight into the host software.

From FreeCAD

It started to slice and print to gcode : it got to 55 layers through before I got bored and turned it off.

FreeCAD is currently alpha software so far, but certainly one to watch!

Sorry for the off topic post

noreply@blogger.com (Brian Korsedal) — Sun, 11 Oct 2009 23:27:00 +0000

Hi,

I'm building a reprap, but I'm way over the alloted schedule I made for myself (big surprise, when is anything done on time... :( ). So I've had to make a choice between continuing to work on my reprap or to do other things that I scheduled for this time.

I put my reprap on hold for now. I'm working on a designed based on a robotic arm and using FPGA's. If you want to know anything about it or would like to continue working on something similar, I'll email you what I got.

I'm taking a trip around the globe. I'm riding my bike from San Diego to San Francisco for three weeks in November. Then spending December with my family in Michigan and South Carolina. Then I'll spend six months circumnavigating the globe. The current travel plan is Hawaii, New Zealand, Australia, Japan, Philippines, Indonesia, China, Malaysia, India, Russia, most of the countries in Europe, Iceland, Greenland, Canada, then home. If you live along my route and wouldn't mind letting me sleep on your floor or couch for a day or two, drop me a line. :)

You can also follow my progress on:

http://thebikepacker.wordpress.com/

Again, sorry for the spam, but technically I am a reprap builder and this is a blog for builders.

Cheers!

-Brian

One step forwards

noreply@blogger.com (Renoir) — Sat, 10 Oct 2009 19:49:00 +0000

G'day all.

I've been quiet recently - I had packed everything away into the garage as we were planning to move. Plans change, we're now not moving so I unpacked the RepRap and fired it up.

From ResistorHeater

First problem : blocked nozzle, due to a broken thermistor - overheated - and set the ABS solid.
Cleared down and drilled it out.

I replaced the thermistor with a spare 100k makerbot one - my last spare.

Interestingly enough, I soldered in a 100k thermistor from Maplins into a spare circuit, connected it up, and the temp read about 20C at room temp, and 34C while holding it - pretty good without any change in configuration. It might be a suitable replacement for the 'official' ones.

Replacement thermistor in, I warmed up the heater and 'let rip'

From ResistorHeater

It works! Extrusion is pretty slow (232mm/minute) and wide (nearly 1mm diameter through a 0.8mm nozzle) but it comes out reliably and pretty consistently. Temp was about 225C and power (screw thread/servo) at 180/255.

Now I have something working, I can refine the nozzle size ( I should be able to get some 0.6mm B&Q nozzles) and the original BfB 0.4mm nozzle, plus I have some small drills.

I now need to get my settings and speeds right in the host software - my current version is months old, maybe I should update. I've been thinking about upgrading to version 3 electronics, too, but with the excellent Mendel design out with a much smaller footprint, I quite fancy that. It might be time to build a Mendel using my Darwin....
:-)

Working with Cotronics 907

noreply@blogger.com (Forrest Higgs) — Thu, 08 Oct 2009 05:59:00 +0000

I let the first application of Cotronics 907 on the Rapman extruder barrel air dry overnight. The material was quite hard. The next morning I used some fine grit sandpaper to smooth it down so that the mounting flange could slide over it. It took some time to smooth it out sufficiently, but you can see that it dressed dowquite nicely.

I was also able to dress the PEEK thermal break so that it fit into the extruder barrel socket firmly without jamming.

Unfortunately, I read the oven curing instructions incorrectly and encountered a problem that the Cotronics people were very open about with this product. If you don't cure it properly and heat it too hot and too fast, it tends to form blisters which separate the ceramic slip from what you are putting it on. Thus my careful sanding and dressing of the flange joint was for naught. It is worth noting that once I saw the bubbles I was able to remove the 907 with the wire wheel on my bench grinder relatively easily while it was still warm.

From there I applied a second coat, this time with the flange in place so that I wouldn't have to do any sanding. Doing it that way I was able to put the basic underlayer for the nichrome heating coil, the flange fillet joint and the flange pad all on at one go.

After four hours of air drying, two hours curing in my fan oven at 90 C, another hour of post curing at 120 C and a final post curing hour at 200 C, I was able to secure the nichrome heating coil as per BitsFromBytes instructions on yet again.

On that I put a slip coat of 907 and after it had air dried was able to put a coat 907 to secure the leads for the heater as per BitsFromBytes instructions. I was also able to place the thermistor in its socket as you can see from the following picture.

Using the "helping hands" electronics jig, I was able to secure the thermistor leads and the extruder assembly. This was very handy because it let me monitor the assembly for shorts in both the heater coil and the thermistor while I was applying the 907 ceramic adhesive.

I will be letting it air dry till morning after which I will do the 8 hour curing and post-curing in the fan oven. Hopefully, I didn't overdo the ceramic application and the curing will be successful.

Getting away from fire cement...

noreply@blogger.com (Forrest Higgs) — Wed, 07 Oct 2009 06:38:00 +0000

I'm currently finishing building a Rapman variation on Darwin. The construction has gone remarkably smoothly until recently when I began to build up the extruder's heater barrel. I had the whole thing finished with the nichrome and thermistor properly embedded in fire cement which encased the aluminum barrel.

When I tried to insert the PEEK thermal break, however, things went wrong. The PEEK cylinder jammed in the extruder barrel's sleeve and in trying to get it back out again I managed to apply a bit of torque to the barrel. This shattered the fire cement.

I was able to recover both the thermistor and the nichrome heater wire, largely because the fire cement, even oven cured, has the consistency and tensile strength of dry silt mud. I cleaned the barrel with a small screwdriver and electrical pliers with zero trouble. You can see the results here.

I had used ceramic coatings before with nichrome and called Danny at Cotronics in Brooklyn. He recommended their 907 formulation which is, if I've read the data sheet correctly, a mica-based ceramic adhesive formulation with considerable compressive and tensile strength. Better still, I was able to order it through a retailer, McMaster-Carr, here in California in Long Beach. I was able to get it ordered, shipped and delivered overnight using a local courier service for about $5.

You apply 907 with a brush. The adhesive in liquid form is a bit like very wet clay mud getting an even coat on the aluminum barrel was quite difficult. Once dried, however, it developed a very hard, glassy surface as you can see here.

Right now I am trying to decide whether I should sand it down before or after I heat cure it. If I'd been smart I would have painted it on after I installed the heater barrel flange, then having to slide the flange over the ceramic adhesive wouldn't have been an issue.

It adheres very tightly to the aluminum.

PLA vs ABS - warping

noreply@blogger.com (Wade) — Mon, 28 Sep 2009 00:13:00 +0000

Warping was a major issue for me when I was building larger objects out of ABS plastic. The lack of warping with PLA is quite striking; I thought I'd post a comparison photo here for the rest of you to enjoy. The x carriage on the left was made with ABS, and the x carriage on the right is PLA, as well as the idler bracket in front. That ABS x carriage isn't the best part I made out of ABS, but it isn't the worst either; most of my larger parts exhibited worse warping than that.

Scaleable encoders

noreply@blogger.com (Brian Korsedal) — Sun, 20 Sep 2009 19:46:00 +0000

I've heard a lot of people talk about high resolution optical encoders being quite expensive. I've decided to use cheap optical sensors from optical mice to make optical encoders for little optical elves who live in optical cities making optical cookies with their little optical ... whoa ... shrooms are kicking in ... Anyway, Avago Technologies makes some pretty good ones. They optically measure the mouse sliding over a surface and convert this to a 16-bit delta X and 16-bit delta Y. The $2 encoders get 1600 dpi and the more expensive ~$6 encoders get 5000 dpi (claimed on the data sheet, not experimentally verified).

They perform multiple useful things.

First, they constantly measure the change in X and Y. This can be used to make a linear optical sensor or a rotary optical sensor (you measure the tangent). I think the rotary sensor might need a look up table to translate from delta Tangent to delta Angle, but this can be determined in the future. The linear sensor can measure travel in two dimensions. If it was possible to mount it under the table of the maker bot, it could record the XY motion at the same time.

Secondly, most can capture a 32x32 image. Some update this image over 1000 frames per second. This can be used to read a printed strip to update the absolute angle. In my design I have a strip of binary hamming encoded numbers that my sensor will periodically read to update the angle.

Third, the resolution scales linearly with the distance of travel. I use this to record angle. If I need a more accurate angle measurement, I increase the diameter of the strip it reads. I'm planning on printing my strips on CD labels (not how it looks in the picture). I'm using a half circle strip. The CD labels are about 118 mm in diameter. Therefore my strip is 118mm * PI / 2 (half circle) / 25.4 (mm to inches). About 7.29 inches long. My optical mouse sensor has a claimed resolution of 5000 dpi. Therefor my sensor has a theoretical resolution of 36468 ticks. I'm a bit skeptical of manufactures claims, but I should be able to get between 14 and 16 bits of resolution.

Fourth, as the machines scale up I want to maintain the same level of accuracy at the tip of the machine as the smaller machines have. This means that I will need much higher accuracy of the encoders. I accomplish this by making the encoder bigger.

Fifth, it might be possible to operate some of these devices as a camera to image objects far away. Some have a laser built into the device. These emit coherent light. Great thing about coherent light is that if your optics are focused to infinity then everything looks in focus. It doesn't depend on the distance. It might be possible to mount one of these next to the print head and use it to image the surface we are printing on or the object we are printing. This is a bit of a stretch, but it might work.

Sixth, one could be mounted on the print head to calibrate it's motion. A calibration algorithm would move the head down till the sensor is just above the surface of the table and then move the head in the XY plane. Using data from the sensor the motion of the print head can be characterized and corrected.

reprap/makerbot gcode visualzation from skeinforge

noreply@blogger.com (Peter) — Sun, 20 Sep 2009 17:30:00 +0000

hi all,

i thought i'd post some preliminary screenshots and videos of a visualization tool that i started writing yesterday. the tool is for visualizing the toolpath of the reprap/makerbot extruder, and it's inspired by the visualization tool that Zaggy hinted he was creating in his Thingiverse post for the printed extruder ( http://wiki.makerbot.com/makerbot-127 ). my tool is also in a very early stage, so the visualization is still very simple, but it's still kind of pretty to look at. it's written in 'processing', a language i just learned yesterday, which is java-based and multiplatform. i think replicator-g is also java-based, so there may be the potential to incorporate some more interesting visualization tools (such as this) directly into replicator-g somewhere down the line, if that's something folks are interested in. it also might be useful in the near-term for demonstrations, if you're giving a presentation for a reprap/makerbot and would like some video or pretty pictures of the toolpath of the object that it's creating.

thanks for reading :)

BAMbot (bamboo robot)

noreply@blogger.com (Brian Korsedal) — Sun, 20 Sep 2009 01:03:00 +0000

The whole goal behind this version of a repstrap is to radically reduce cost and lay a framework for scaling the RepRap up to larger sizes. There are some major differences between my design and the RepRap. Here is a short list of them:

Arm based as compared to Cartesian robot.
FPGA based electronics
Does not natively support G code
DC gear motors and sensors as compared to stepper motors

Some of these changes seem quite drastic and might cause some flame wars to erupt, but here is my reasoning for these changes.

First I choose to base my design off of a robotic arm as compared to a cartesian robot. The robotic arm design is not as stable as a cartesian robot and it is far more difficult to control. However, the upside is that an arm can print out things bigger than itself. I would like to increase the scale of my design by about 50% per generation. I'm also a big believer of monolithic design, printing out very complex parts that combine multiple functions. That's the beauty of a 3D printer. Also, the weight/cost is better as I scale the design up.

Second is the choice of FPGA based electronics instead of the ATMega based design we currently have. When I design something I tailor the design electronics to the type of computing that will occur. You can think of two different classes of calculations. Those that would occur in your frontal lobes and those that occur in your brain stem. The frontal lobes would control things like user interface, converting G code to optimized paths and anything with a lot of if/then branching statements. The brain stem interfaces with the hardware, controls timing of signals, pwm and adaptive filtering. Brain stem functions belong on an FPGA. Frontal lobe functions belong on a microprocessor.

We already have a very powerful microprocessor in my system. It's a PC, Mac or Linux box that the device is connected to. I'm going to move these functions into the 'print driver'. The print driver will output something I call t-code. It's similar to a .wav file. It will record the desired angle of the joints at a certain sampling rate. The rate is built into the file. The PC will write this code into a ram buffer on board my repstrap. The FPGA reads these points out, upsample/interpolates them to a higher rate and uses adaptive filtering to make the joints of the robot match what is recorded in the t-code.

In the future I hope that this will allow more intelligence in the code which converts from model to g-code. It will allow this block of code to optimize the acceleration and motion profiles offline. It will also allow much more number crunching to optimize the paths. Perhaps some of this will be added into the modeling tools allowing you to specify tolerances on the surfaces. Some surfaces don't need to be exact and this can be used to increase the print speed or reduce the materials. Some need to be very precise and this would allow the tools to adjust the print head accordingly.

As the above paragraph comments on, I don't natively support g-code. I hate g-code. It does not contain any acceleration/velocity data. This makes writing a good motion controller very difficult. Especially writing a motion controller which acts in real time. This is better to evaluate the motion offline in unreal time and record it to file. My design takes in T-code. A simple file with sample points with specified time. I'm sure someone will write something that evaluates G-code and converts it to t-code specific to this machine (all t-code is device specific by nature).

I choose DC gear motors because they are much cheaper and offer a better power to weight ratio. My whole design is based around choosing components that offer the best power or strength to weight ratio. Also, by designing using servos I'm paving the way for printable motors. I'm sure that the initial motors that we design will not be on par with the performance we can buy off the shelf. However, using a servo loop and adaptive filtering we should be able to work with a wider range of motion systems. From air muscles to flat voice coils. Hopefully we can handle anything that moves and control it.

Currently I have a first draft of the mechanical system for my design. I'm working on a better version which will use motors with 2x torque, larger encoders and shorter arms. I have a angle sensor put together but not tested. I'll hopefully be getting the FPGA board in next week or the week after. Then I need to order the extruder head. I'm going to use the Bowden extruder because I need as low weight as possible.

What you see here is about $70 worth of components. The motors are about $5 each and the bamboo came from ponoko.com for about $40. Each joint has a 15x28x7 mm bearing (about $1 each). Then some assorted screws and wires. Add to this the price of the electronics motherboard (using a $100 FPGA board right now, but a custom solution could be under $30) and the sensors (could be as low as $3 each for finished boards). I think this design could be copied for under $200 in quantities of 1 and under $100 in quantities numbering in the 100's.

... if it works ...

-to be continued

Printing with 2mm filament

noreply@blogger.com (Frank Davies) — Fri, 11 Sep 2009 19:15:00 +0000

I recently obtained a few feet of 2mm white ABS filament and decided to try printing with it.

I use a pinchwheel consisting of a small brass spur gear. A ball bearing is on a lever and presses the filament against the pinch wheel due to the force of a rubber band (with multiplication from the lever). There is not much holding a 3mm filament from sliding sideways and out from between the spur gear and the bearing, but 3mm filament is stiff enough that it is not a big problem. When I tried the 2mm filament, I had to modify the level a bit to allow it to come close enough to the spur gear to press the 2mm filament against it. I also printed out a better filament guide to prevent the 2mm filament from moving sideways.

Once I had done these modifications, and had tweaked the skeinforge settings (halved the feedrate and decreased the expected extrusion width slightly), I was able to print well with the 2mm filament. Here is a paperclip (http://www.thingiverse.com/thing:655) by "unfold". While I was extruding, I heard a slight popping noise (frying?) which I do not hear with the 'natural' colored 3mm ABS filament (from Village Plastics). I suspect that I may be running the tip a bit hot for this material.

Interestingly, I got good results with a 2mm filament in a 3mm+ hole, which holds 3mm filament fairly snuggly. When I pulled out the 2mm filament from the extruder, it looked like this:I described the heater end of my extruder here recently (builder's blog of August 29, 2009). It looks to me like the 2mm filament is just pressing up against the dished end of the acorn nut and not spreading out much. I am probably deluding myself, but it looks like this is a hint at a simpler extruder.

Frank Davies

Polylactic Acid

noreply@blogger.com (Wade) — Mon, 31 Aug 2009 07:23:00 +0000

It sounds nasty, but polylactic acid (PLA) is some pretty cool stuff. Up to this point I've been printing objects with ABS, but I've had recurring issues with warping, especially on larger objects (100mm or so). I've also started running my Reprap in my apartment again, until I can find a a new workshop out West; the smell of melting ABS hasn't been so popular with the other apartment dwellers. :)

I experimented with turkey bags and CPU fans to try and create a heated, sealed build envelope for ABS, but in the end it seemed more trouble than it was worth. Seeing Nophead, Vik and Adrian's results with PLA, I thought I'd give that a shot.

I'm glad I did! PLA is slightly more brittle than ABS once it's extruded, but that is more than made up for by it's almost complete lack of warping, the ease of part removal, and the lack of any bad smells. It gives off a faint odor of cotton candy when it's printing, which makes me think of Fraggles and Doozers, but so far I haven't started eating any of it.

Here's a shot of Adrian's pinch wheel extruder, printed out in tasty PLA. Even better, this stuff is more or less biodegradable, so if I don't end up building a pinch wheel extruder or recycling it, I can at least mulch it (slowly) in the garden. :)

Extruder Heater update

noreply@blogger.com (Frank Davies) — Sat, 29 Aug 2009 14:59:00 +0000

Several months ago I posted an extruder tip design that used a transistor in a TO-220 package (http://builders.reprap.org/2009/04/inspired-by-nopheads-observation-about.html). It worked, but not for long, probably since I was running the transistor at a temperature(>230C) much higher than its rated maximum of 150C. After I had gone through a few transistors I switched to using a 10 ohm load resistor in a TO-220 package. The first resistor mechanically broke during an overnight print run. It looked like the resistor had hit the printed object. I replaced the resistor, and the second one had been working continuously ever since. I have printed more than 5 pounds of ABS with it so far. I must credit Nophead with the idea of having the barrel temperature drop over as short a distance as possible.

Because of this success, I would like to present the details of the extruder tip design and some instructions on how to make it

Heatsink: This holds down the temperature at the end of the extruder barrel. I have used a 6.3mm (1/4”) thick aluminum L bracket with a total surface area of about 15100 square mm (23 square inches). Since heat flow from the barrel is important, the barrel screws into a threaded hole to so that the thread-to-thread contact can conduct heat. I have also made a second experimental extruder with an aluminum heatsink of about half the area. I think that as long as the heatsink is not too hot to touch after several hours of operation, then it would be good enough. This heatsink also plays a structural role, since it is part of the force path involved in pushing the filament into the barrel. In my extruder, I have the pinch wheel motor attached directly to the aluminum L bracket (which means that the motor also heats the bracket).
10-32 nut: This is in the heat flow path between the barrel and the heatsink, so do not use a lockwasher. I suggest brass as a material, though I have also used an aluminum nut made by cutting up a threaded aluminum standoff from my junk box.
Extruder barrel: This is a tube made by putting a 10-32 thread on a 4.76mm (3/16") OD, 0.71mm (0.028") thickness stainless steel tube (K&S Engineering stock No. 7113 Stainless Tube 3/16 x 0.028 (4.76mm x 0.71mm) UPC code 14121 17113). In order to put on thread successfully, put a 3.17 mm (1/8") diameter rod in the tube. Putting the thread on the tube with a 10-32 tap is tricky, but putting a rod inside the tube to hold it straight helps. The tubing gets so thin that you can see ridges on the inside of the tube pushed up by the teeth of the die.
10 ohm resistor in TO-220 package. Stackpole P/N TR35T110 5% B , Digikey P/N TR35T110J-ND. Other manufacturers could be used. If you use something different, I suggest picking as large a wattage as possible, based on the idea that larger wattages would have a better thermal connection between the actual resistive element and the heatsink tab, and probably be more reliable. The mounting hole must be drilled and tapped for 10-32 thread. Given how little material is removed by the drill bit, it might be possible to tap it without drilling first, but I have not tried this. The material is copper, and not thick, so be careful to keep the tap straight as it goes in.
Thermistor holder: I have done this two ways. The original heater has a small bracket made from copper sheet. More recently I have used a crimp lug with a #10 hole and suitable for 22-18 AWG wire. I take off the plastic insulator and pry open the crimp barrel slightly along the seam. I open the gap enough that the thermistor can be slid in and is held by the spring of the metal.
Thermistor: Allied Electronics P/N 254-0019. Use your favorite.
10-32 acorn nut, with 0.5 mm hole drilled in the end (done with a PCB carbide drill).

Heating time: This extruder heats and cools very quicky. It usually can go from room temp to 225C in just under 3 minutes.

Filament jamming: Others in the reprap community have noted that filament can jam in an extruder barrel if it is allowed to soften back up the filament and form a plug pressed against the inside of the extruder barrel. I have noticed this to some extent with my extruder under experimental conditions, but under normal operating conditions it is not a problem. By normal operating conditions, I mean starting the extrusion process right after the thermistor shows that the tip is up to temperature. It takes a few seconds for the filament to start coming out, but this is on the edge of the print raft so that it does not matter. I use skeinforge, and it does not turn off filament extrusion long enough to allow the filament to jam. I also set the file that skeinforge appends after the print to turn off the heater. This allows good startup the next time.

Frank Davies

FiveD endstops

noreply@blogger.com (1m93) — Thu, 27 Aug 2009 21:51:00 +0000

Aaaaargh, finally found why the max stops didn't work, where they were dearly needed!
Escaped from Java Host to replicatorG and Eriks' 3D-to-5D script. Though building here sends all axis way beond the Max!
Anyhow, this is the code adjustment made in cartesian_dda.pde (code taken from svn #3252):

bool cartesian_dda::can_step(byte min_pin, byte max_pin, long current, long target, byte dir)
{
bool canStep = true; // 2009.08.27 JvO
//stop us if we're on target
if (target == current)
canStep = false;
#if ENDSTOPS_MIN_ENABLED == 1
//stop us if we're home and still going
if(min_pin >= 0)
{
if (read_switch(min_pin) && !dir)
canStep = false;
}
#endif
#if ENDSTOPS_MAX_ENABLED == 1
//stop us if we're at max and still going
if(max_pin >= 0)
{
if (read_switch(max_pin) && dir)
canStep = false;
}
#endif
// All OK - we can step
return canStep;
}

Next puzzle is why the stepper-extruder doesn't wait for the temperature. Hm, expected to find such a thing in e_can_step.

Printing test-part

noreply@blogger.com (Patrick) — Thu, 27 Aug 2009 12:12:00 +0000

Inspired by a paper from Kruth et al. (2005, Benchmarking of different SLS/SLM processes as rapid manufacturing techniques) I also designed a benchmark model for the RepRap. It looks quite random but by printing it you can check whether your RepRap prints geometrically correct. I included the following features:

-vertical holes for M3, M4, M8 screws
-vertical hexagons suitable for M3, M4 M8 nuts
-horizontal teardrops M3, M4 M8 and hexagons for suitable nuts
-sharp edges with angles of 15, 30 and 45 deg
-thin walls 0.5mm, 1,0mm, 1.5mm and 2mm horizontally and vertically
-stair effect at sloped walls with angles of 15, 30, 45, 60 and 80 deg
-round corners, radius 4mm to 16mm
-gear teeth with 2mm wide teeth
-in addition to this, you can also check perpendicularity and parallelism of your printed objects, which were the general intentions of designing a benchmark.

You can download both the STL and the AoI file from SourceForge

/mendel/mechanics/test-parts

Printing it took about two hours, so why not watching a fancy movie while your RepRap prints its benchmark.

The very first version included a complete horizontal hexagon for M8 nuts, but apparently this made the object to big in height, so I just cut it off, leaving just a small offset ;)

The gear teeth were not built as expected but as a round corner with a bubbled rim. I am also missing the 0.5mm thin walls. The 1.5mm walls consist of only two parallel strings and are not solid, there is a small gap between them in both directions.

Identifying backlash

noreply@blogger.com (mccoyn) — Tue, 25 Aug 2009 02:13:00 +0000

I was printing parts when I noticed that the diagonal lines on the foundation were not evenly spaced and the infill overlapped badly. Since the lines are diagonal, I wasn't able to figure out whether the backlash was in the x-axis or the y-axis. Watching the machine carefully didn't provide any clues.

I decided to write a custom gcode file to reveal where the backlash was.

G21 ;metric is good!G90 ;absolute positioning
T8; select new extruder
G28; go home
M104 S220.0 ;set temperature
G4 P307 ;delay
M107 ;cooler off
G4 P100 ;delay
G1 F5.0; feed for start of next move
G1 Z0.4 ;z move
T8; select new extruder
G1 F1500.0; feed for start of next move
M108 S1400.0 ;extruder speed in RPM
M101 ;extruder on, forward
G4 P400 ;delay
G4 P200 ;delay
G1 X100 Y0 F2000
G1 X100 Y5 F2000
G1 X5 Y5 F2000
G1 X10 Y10 F2000
;
G1 X10 Y30 F2000
G1 X30 Y30 F2000
G1 X30 Y28 F2000
G1 X12 Y28 F2000
G1 X12 Y10 F2000
G1 X14 Y10 F2000
;
G1 X14 Y26 F2000
G1 X30 Y26 F2000
G1 X30 Y24 F2000
G1 X16 Y24 F2000
G1 X16 Y10 F2000
G1 X18 Y10 F2000
;
G1 X18 Y22 F2000
G1 X30 Y22 F2000
G1 X30 Y20 F2000
G1 X20 Y20 F2000
G1 X20 Y10 F2000
G1 X22 Y10 F2000
;
G1 X22 Y18 F2000
G1 X30 Y18 F2000
G1 X30 Y16 F2000
G1 X24 Y16 F2000
G1 X24 Y10 F2000
G1 X26 Y10 F2000
;
G1 X26 Y14 F2000
G1 X30 Y14 F2000
G1 X30 Y12 F2000
G1 X28 Y12 F2000
G1 X28 Y10 F2000
G1 X30 Y10 F2000
;
M103 ;extruder off
M104 S0.0 ;set temperature
G1 F5.0; feed for start of next move
G1 Z1 ;z move
G1 F2000; feed for start of next move
G1 X0 Y0 F2000

The long lines on the resulting print should be evenly spaced. If there is any backlash, it will alternate between a small gap and a large gap. The magnitude of the backlash is half the difference between the large gap and the small gap.

Looking at the image, I see that the horizontal lines are not evenly spaced. Using my digital calipers I measured the y-axis backlash to be 0.6 mm. I went ahead and measured the x-axis backlash as well to be 0.2 mm.