RepRap: Builders

I successfully extruded some ABS plastic today, but it was "crunchy"-- it was very brittle and actually crumbles in your hand.

Does anyone have ideas about what could be happening? Is this an indicator of too high or too low temperature?

The narrator puts the finishing touches on Tommelise 2.0 to do plastics milling... read more

Labels: milling, reprap, repstrap, sheet HDPE, sheet polyproplyene, Tommelise 2.0

In which your narrator solves the problem of making a microcontroller operate in I2C Slave mode via a hardware rather than a software fix... read more

In which the narrator discovers the dangers of trying to do too many things at once with 8-bit Pic microcontrollers... read more

Bottoms up!

I've had my Darwin close to finished for over a month now, but various software problems have kept me from being able to print until now. I was never able to get the Java host software to work reliably, and due to a slightly off center extruder screw, I decided to try and incorporate Zach's magnetic encoder board. That worked beautifully, but code space limitations meant I had to run the Gcode variant of the firmware (thanks again to Zach!), which required installing and understanding an entire new tool chain, which again took a fair amount of time. It's all good now though!

I had a good laugh on my first minimug attempt though. With great apprehension, I watched the mug take shape, but after the raft was built, the mug looked decidedly triangular, not circular. I almost stopped the print, thinking some joker had switched out the files on the Wiki, when I realized that the minimug.stl file needs to be rotated 90deg about the x axis, otherwise it prints on it's side. Printing a mug on its side definitely does not fit the "no overhangs greater than 45 deg" rule, but it sorta worked anyway. Check it out:


Both mugs are a bit lumpy yet, as my Darwin is a bit loose in most directions - all of my cast bearing inserts are 1 to 2 mm too large, making all the tolerances very loose. Soon I'll print out some new bearing inserts and drill them as close to 8mm as I can, that should sharpen things up a bit.

Finally, a fuzzy cell phone shot - I'm now cranking out RepRap Power Rings, I figure they'll make nice playa gifts next week at Black Rock Desert, a little harbinger of what's to come. :)

It's been a couple of weeks since that last update. I have made a good deal of progress on the build. Things went very well for the most part. I also did as much work as I could on the X and Y axis assemblies. They are almost complete and I will be getting more parts this week.

Here's a picture of the main bot so far:




Things haven't been tightened because I don't have the slide bearings yet and 4 of the side diagonals are missing. I just had to see what it was going to look like.

What went wrong:

1. I broke 2 more of the plastic parts even though I have been extremely careful when tightening bolts.
2. I have not been able to locate a US vendor for slide bearings with the exact specifications as the Skiffy ones from the UK.
3. The side diagonals were short on 2 sides of the main assembly. All of the rods are specified at a length of 600mm and I found that 610mm long rods worked for me for 4 of the rods that make up the 2 side diagonal assemblies. I'd be curious to know if anyone else encounters this. I measured all of the dimensions between rods and I come out with a different diagonal spacing for 2 of the four sides.
4. I've seen the thread on the mechanical forum about splicing the Z belt. It looks like any of the suggestions will work but I'm curious to know what Ian had intended. Hopefully he will add his input to the thread or maybe a procedure on the Bits from Bytes web site. I'm guessing that it's probably the same as for the original Darwin as described by Adrian.

Recommendations:

I wasn't happy with trying to adjust the corner brackets that clamp onto the 8mm smooth rods so I used 2 70mm smooth rods and inserted them in parallel with the rod being clamped onto. Here's a picture:



I then took up the slack on the M3 nuts so that the plastic bracket pieces were parallel. Not too tight because you won't be able to remove the 70mm rods. When all of the nuts are snug, remove the 70mm rods and tighten the nuts about another 1/2 to 1 1/2 turns. Once again, not too tight or the bracket parts may crack.

I hope this explanation makes sense.

Wherein your narrator decides, perhaps foolishly, to rewrite Tommelise 2.0's firmware in Mikroelektronika Basic... read more

I have been trying various options with my 'rolling nut' filament feed design with much learning and many questions arising. More detail here.

I have also had an idea for making teeny weeny nozzle holes. Rather than drilling them in metal nuts etc (and the latest aluminium one from Bitsfrombytes.com is rather nice) how about this :


I purchased some brass tube - 2mm OD, 1.4mm bore - from B&Q. I snipped off a short section, inserted the leg of a resistor and squashed the end with my wirecutters. Pull out the resistor leg leaving an almost perfect 0.5mm hole. Its not clear in the photo but the hole passes through the nearest part. The result is almost round with a small slot. I will experiment further.

Mounting it will not be simple, I have considered flairing the top end and simply dropping it into a bigger (2mm) hole, or using silver solder (melts well above 250 C).

Copper would be better as it is more malleable, but B&Q didn't have any small enough. I will check to see what capillary tubing I can get from my local laboratory supplier.

STOP PRESS : I just had another thought - we used to get tiny carburettor jets, made by a company called AMAL - for use in gas engine conversions (Calor gas, not gasoline gas). These are weeny nozzles - I just dug out some and the hole is 0.35mm in a brass body with a 1BA thread. The 1BA male thread just about works with an M6 nut. From what what I remember they were cheap AND available from our local Calor gas depot. Why re-invent the wheel?

I've written a bit more about my feed roller concepts on my blog,
here. The rollers are an alternative way to guide filament along the feed screw with lower friction than the standard RR extruder.

The shift to a more powerful firmware compiler for Tommelise 2.0 comes a bit sooner than the narrator expected... read more

Hello, everyone:

Last week, I posted some pictures of my extruder head made to run on a CNC machine.:



I've decided to begin my own blog for the project so that i dont clutter this one, and because my direction is a bit off the typical RepStrap path ( more in the blog).

I dont get a lot of time on the project, but I think i've finally convinced myself that even though it will take some extra time to blog my results, i'll get more than enough help from the folks here to make it worth it :)

Enjoy, if you are interested, here

The gantry supporting the z-axis on Tommelise 2.0 is finished... read more

Hi all, I have blogged my progress on my filament feeder developments here : http://fusedfilaments.blogspot.com/

Haydon 36000 and 26000 steppers are tested in situ on the new z-axis... read more



Tommelise 2.0 z-axis stepper test from Forrest Higgs on Vimeo.

In which the narrator measures the lifting power of the Haydon 26000 linear stepper... read more

The narrator takes off a few hours and knocks a z-axis positioning table together for Tommelise 2.0... read more

Progress so far on the build of a Toby Borland original design PlyRap. Build details and instructions are nearing completion and can be found on the RepRap Wiki here. This is a very close replica of the one Toby built for the Science Museum, Kensington London.

The (additive) RepRap doesn't have the rigidity requirements that subtractive CNC machines do. This makes various positioning systems possible. Several have been mentioned (Matt's hexapod 1, 2, Viktor's tripod and Dylan's 4 axis design to name a few).

There is a very simple plotter design based on hanging a pen by two threads. The threads are rolled up or down through pulleys. I won't explain more, just look at these video's:

Another nice spritesmod project project page.

More video's of hektor, here.

The reason this system works (no upward rigidity) is because the write head is pretty light.

A big advantage is that you can work on a large canvas, or, tatada daaa, a LARGE BUILD AREA! Because this approach is not limited to two axes, you could also put a write head on three strings. I know it wouldn't have the precision you'd like, but often the tolerances for larger scale objects are also bigger. I can imagine that someone could pretty easily make a 3 string version of hektor with instead of spray paint a PUR spraycan (Polyurethane)

It would not compete with RepRap's resolution, but it will be manufacturing on larger scale. I can imagine a nice playful version to investigate this method:
You have a three axis system and put the pulleys on three poles, on a beach. There, you connect, besides the threads, a hose to the write head that transfers sand that is colloid. This makes it possible to make 3D sand-sculptures. Nice?

I was also thinking of automated construction sites (being reminded of a patent to print buildings). If you make it VERY big the poles would need to be able to handle a lot of force. This positioning system wouldn't work in that case.

More pro's:

• The entire device would be pretty mobile. As with hektor (video 2), there would be a case that controls the machine. Apart from that, three motor/pulley assemblies and a write head. (less chance of TSA molesting your precious child :S )
• easy to construct
• could be controlled with the Arduino, RepRap stepper drivers and steppers. The most radical changes are in software and the frame. Victor has dealt with the 3D positioning based on non-orthogonal axes and will probably have pointers.
  

More con's:

• Low resolution, which isn't necessarily very low: it also depends on how fast you go, room conditions (even becomes sensitive to wind) or perhaps a movement model that deals with inertia of the write head.
• Probably more I didn't think of yet...
  

I know this isn't a drop-in replacement for the RepRap Darwin (it is not intended as such!), but it certainly has its interesting characteristics. Let me know what you think!

--
Erik de Bruijn
My RepRap Blog

Labels: 3D positioning

The circuitry for handling the control of the z-axis (vertical) went onto the controller board without a hitch... read more

I started my mechanical build of a RepStrap this weekend using the laser cut parts kit that I purchased from Bits From Bytes. Here are some of my sub assemblies.




What went right:

1. Parts are very well made. Well done Ian!
2. Drawings were easy to follow and no major assembly problems so far.
3. I have all of the sub assemblies built as far as I can go with the parts that I have.

What went wrong:

1. Some of the M3 and M8 clearance holes in the laser cut parts were very tight. I opened the holes up a tad using a small fine round file.
2. The areas meant to captivate M3 nuts are very tight for nuts measuring 5.4mm in width. I didn't want to force them and possible crack the part so I ended up taking a fine flat file and opening up the cavities ever so slightly.
3. I ordered some of the wrong hardware, M8 bolts not threaded the full length for example.
4. Having trouble locating a few parts such as the sleeve bearings.
5. I had already cut the plain rod lengths from the old Darwin specification and the new lengths are different. Need to order more stock and and re-cut the rods to the new lengths.

Recommendations:

1. Don't throw away anything from the sheet of laser cut parts. I lost one of the smaller parts.
2. Print out the PDF of the parts sheet available on the Bits From Bytes web site and check all of your parts.


2. Take a fine flat file and remove any small bumps on the edges of the laser cut parts.
3. Before assembling any laser cut parts, run the proper bolt through any clearance holes to make sure they fit before trying to assemble them.
4. When you get to the extruder construction don't forget that there are 2 videos that are absolutely essential. One of them locks up and I seem to remember a post on one of the forums about the lock up but I can't seem to find it.

Next:

I already have the electronics built and tested as well as the Java host application up and running using source code in Eclipse. I have built the firmware from source and that's what I'm running in the PICs. I don't have an Arduino yet.



I will have my rods cut this week and order more parts so I should be able to get a lot done next weekend. This is the most fun I've had in a long time.

Labels: Laser RepRap RepStrap

The xy positioning table is responding correctly to print data from the EEPROM print buffer... read more

Hello, everyone:



I've been following RepRap for a while. Like Brendan and NopHead, I am a cnc hobbiest, and last year converted my 3-axis mill to cnc. I started following reprap with the idea of adding an extruder head to my mill. I'm basically following the "EmcRepStrap" path.



I've made enough progress on my extruder, though, that I thought I'd share my experiences with the group in case someone else finds them useful.



Starting with the RepRap extruder, I wanted to make a few modifications/goal adjustments:

1. I'd like to run reliably at high temperatures
   
2. I'd like to use an off the shelf heater
   
3. I would like to be able to "grow" into high accuracy and higher feedrate

Last week I finally finished and tested my first lashup-- it fed about 3ft of filament quite nicely so i've started configuring my EMC machine so i can start making some profiles. I'm very excited.

A couple of extra pics. The first shows the extruder block and barrel. After experimentation i found that a shorter heater would be ideal-- a 3" barrel was just too long.

This one shows the v-groove rings and skate bearings. This concept worked very well. Though you have to have a lathe, the rings are easy to make, and eliminate springs and such. ( It does take a bit to get the adjusting right though )

Some key features:




Extruder Drive

• Heat is a 1/4" diameter, 2" long cartridge heater
• Feed is via a threaded rod, like the normal reprap extruder
• I used skate bearings with custom v-groove rings added to minimize friction while feeding
• The bearings are mounted on eccentric drilled posts to allow adjustment to pinch the filament the correct amount.
• Temperature measurements are via K-type tcouple in a ring around the tip
• Normal acorn-nut nozzles for now
• Extruder barrell is three parts-- brass heated section ( inside the alum. block), aluminum connector with heat sinks, and stainless steel exit. This design seems to keep the filament from melting at entry
• An aluminum block transfers heat from the cartridge to the barell
• For the lashup, the hot part of the extruder is attached to a piece of cement backer board from Lowes
  

Electronics:

• Gearmotor with AS 5040-based encoder for closed loop control


• PIC 18F4331 with two PID loops, one for heat control, one for motor position control.


• Gains are set via serial interface


• MOC 3031 Triac controls the heater. duty cycle is based on cycle control. The triac is a zero-crossing one so i dont have as much noise.


• The PIC also has step/direction inputs and safety interlocks.

My plan is to treat the extruder as a rotary axis in EMC, and to control the extruder with a python-based HAL module and pyVCP Axis plugin, what i'm working on now.

The photoset is here:

http://www.flickr.com/photos/bluedirt/sets/72157594427254054/

Forrest has pointed out already that the gap between the last roller and the filament entry point is a bit long, which is true-- I'll fix that but for now if it works dont mess with it , right?

I've noticed a few good things and a few bad things about this design so far:

• [GOOD]The v-groove bearings work very nice-- there is very little friction wasted in feeding the filament
• [GOOD] The heater is very reliable and the PID control results in rock-solid temperature, even when feeding etc. Since its a "line current" heater it heats up very quickly.
• [GOOD] the design can operate to very high temps
• [GOOD] the barrel can be easily replaced with other materials/lengths without messing with the heater
• [BAD] for some reason with this design the t/c temp and the nozzle temp seem to be quite different, though perhaps my DMM probe is just wrong.
• [BAD] its pretty ugly
• [BAD] it requires more parts for which you need a lathe to make
• [BAD] adjusting the feed rollers takes some patience-- harder to adjust than spring loaded.

I make progress very slowly cause of my day job and family, so you probably wont be seeing prolific posts. However, i'm happy to answer questions or certainly welcome your ideas!

Dave

Labels: repstrap bluedirt

This weekend, while I waited for some ABS to arrive (with all of the warping issues I've heard about, I'm going to avoid HDPE for now), I decided to build a filament holder for my RepRap.

The goal was to seamlessly provide material for the extruder without introducing twists or kinks in the supply line.

Vik Oliver wrote about a nice setup last year, one that dangles the spool above the machine from a support structure, protects the material from humidity, and prevents kinking with a swivel. Here is a picture of his suggested structure, borrowed from that page:


Several people have had success with this design, and some elegantly use a basket with a hole in the bottom instead of the strap, but I thought I would try something a little different. I didn't want flimsy support beams jetting out of the top of my RepRap because they would get in my way when reaching around the machine to fix it, and could be aesthetically displeasing. Because my RepRap is supported in mid air with my laundry hamper frame, as opposed to on a table, I had some space underneath to play with, so I decided to adapt the design to hold the filament under the robot.

One important point about designing this for under rather than over the RepRap, is that a basket is not well-suited for the job.


The three support chains get in the way of any filament coming out of the top of the basket, and any coming out of the bottom would probably kink because of the tight turns involved.

I decided that my holder would have to be hung from its center, so that the spool can unwind around the sides. This is like taking the original design and turning it inside out.

I went to my local hardware store and came back with:

• 2 carabiners
• three key rings (in my case, two 2cm diameter and one 3.5cm diameter, but other sizes will work)
• Three 12cm x 12cm L brackets (larger will work, smaller won't work well unless a larger can is used below)
  
• a swivel used for fishing with a 15lb capacity.

I also had laying around

• 6 small bolts (in my case, M5x15's)
• 6 washers
• 6 nuts
• A double twist-ties that came wrapped around my filament coil.
• A 8.5cm diameter (larger will work, smaller may not) tin can (yummy... canned pineapple... )
• A pulley (this could probably be replaced with a loose cable tie or another key ring)
  

Bolting the L brackets at 120 degree increments around the tin can, and tying everything up to the swivel with the twist ties and key rings, I made the following device:



Two carabiners clip onto the bottom-most diagonal of my RepRap, on either side of the crossing bottom-diagonal, to keep the contraption centered.




Lastly, a pully attached to one of the legs of the stand ensures that the filament is pulled from the side of the spool, rather than persuaded off of the top.


The whole thing spins effortlessly, and the stiffness of the filament keeps any stray rotation from getting out of hand. With a short, 10 minutes of extruding, I could see the holder slowly rotate as more material was needed. Several rotations were observed without any problems. Success!

It is very satisfying to have something (anything) go from concept to functional physical reality in one day. I suspect this satisfaction may become more commonplace once I have a rapid prototyping machine in my apartment. :)

In retrospect, this design does not exhibit a feature that the original had, namely the moisture barrier. I can think of a couple ways to retrofit it with a bag, but I think I'm just going to hope it is not necessary. I have heard that some filaments absorb moisture quite readily, but does ABS? What has been your experience?

Until next time.

~Andy :)

Labels: basket, filament, holder, swivel

In which your severely dsylexic narrator gets most of the geometric reversals sorted out of the PC-side software and Tommelise-side firmware... read more

Tommelise 2.0 is now using data from the EEPROM buffer to drive the xy positioning table... read more

Tommelise 2.0 can toggle back and forth between buffer mode and print mode... read more