Wednesday, January 28, 2009
Monday, January 26, 2009
Worm Gear Filament Feed Test Bed
Here's the Worm Gear Filament Feed test bed. Constructed from laser cut acrylic.
The bracket on the right is a spare and the one on the left shows the test bed with gears, axles, O ring springs and an M3 machine screw to test the operation.
The O rings are used in place of springs and are common 16mm ID by 2.5mm. They provide the worm gears with more grip than springs and are both readily available and cheaper. They ideally need to be fitted to pulley wheels or at least collars that keep the axles square to the brackets.
This is something to be sorted that wasn't apparent until I assembled it all. I guess this is why prototyping and testing is useful.
Thursday, January 22, 2009
Introductions and Thermal measurements
I decided that I'd put together a RepStrap in my own unique way: I want to use largely reprap components, but I want to tie it all together with some electronics that I already have around, most notably, I intend to use an embedded 486 processor card running Linux as my RepRap controller, with an attached FPGA expansion card to do all my I/O. I already have both of these cards and no other practical use for them, so it just makes sense to me.
To that end, I started looking over the RepRap electronics, and immediately noticed one improvement that would be necessary if we are to continue with swappable toolheads: Toolhead controllers. There is quite a nexus of control and measurement right on the toolhead. It doesn't make sense to me to be mixing analog, PWM, quadrature, etc., all on a thick cable and sending them back to a controller. It makes far more sense to put a secondary controller right on the toolhead and then ship the information back using RS-485.
So in an effort to revamp the toolhead electronics, I've been going step by step through the parts of the toolhead, trying to do things better, faster, cheaper. I'll take a moment here to say that I don't think the work that has been done on RepRap is bad. I think it's excellent. I think that a move away from the token-ring style network of controllers was absolutely necessary, and the gen2 electronics are great. But I think it is important to move back towards a modular approach for the toolhead since the toolhead is going to become modular.
My first point is the thermal sensing system. Thermocouples are the route we need to go for higher temperatures, I think most people agree on that. However, I disagree with the implementation of the thermocouple reader. It's expensive, and noise prone (think long analog line near PWM signals, here). I have an alternative which I've discussed in the forums, and here it is! The MAX6675 thermocouple reader board.
The parts cost is minimal, (Digikey part numbers shown for ease of use, single unit prices shown on all but the MAX6675, which is priced from Maxim's online store) $0.86 for connectors (A98333-ND + 708-1028-ND), $7.18 ($3.88 @ 1000 units) for the MAX6675, and $0.54 for the filter capacitor (399-3526-ND)
I've tested this board on an ATmega162, and the temperature readings are accurate. The interface is quite simple, just a left-justified two-byte SPI frame, with a 12-bit temperature code, in 0.25C increments, and a flag for detecting open thermocouples
In one shot, the temperature sensing will be cheaper, smaller and more reliable.
By popular demand, here is the schematic!
Monday, January 19, 2009
Dodecahedron Test Print
Now that I have my Pinch Wheel Extruder working really well, I'm starting to really print a bunch of stuff in earnest. This is a print of the Dodecahedron designed by Nophead.
I printed off 4 of these, each time modifying the settings in Skeinforge to attempt to get a better print. I think that by the end, I got a pretty nice result. I still need to tweak the settings for better results though.
Sunday, January 18, 2009
More Power Resistor Heater Experiment's
Experiment with four Five Watt Resistors
Saturday, January 17, 2009
In which your narrator mills an equivalent to an expensive commercial anti-backlash nut on Tommelise 2.0... do you want to see more?
Help Wanted getting SD to work with the GCode Interpreter
Now I have been working on getting the Sanguino to talk to the SD card. Zach has gotten the backend for the SD card done and it works great..
My next step and where I am stuck at getting the Gcode interpreter to read a Gcode file line by line from the SD card and weeding out what is not used.
The Gcode software already weeds out what is not used when you send it from the computer, so that is there. I just do not have enough experiance with strings to get the software to read line by line.
So I am asking for help in what could be the future. I am able to test and help with the code.
You can contact me at bwattendorf at gmail.com
Thanks to all and I hope we all will be able to print without a computer soon
Labels: help wanted
I kow I'm posting too much but.... Heres my collection of others "extruder rules of thumb".
I've just read nophead's beaut new heater/hot zone here: http://hydraraptor.blogspot.com/2009/01/fanless.html
and then there's geo's thermal modeling here:
and then larry's hot zone working here too:
So what do we learn from all this?
1) thermal gradient zone from hot to cold MUST be critically short, to avoid jams.
- thermally insulating material in gradient zone above heater (typically PTFE, sometimes stainless).
- reduced cross-section of material directly above hot zone reduces heat transfer by effectively using "air" as more of the insulating material. ( eg, remove threads and some metal in stainless components)
- use heat sinks at the top of the gradient, to distribute wasted heat that gets through the zone, and effectively drop temperature more suddenly. either large perpendicular ones, or circular turned ones work. Should be of thermally conductive material, contrary to the first point above.
- other points?
2) hot zone should be short, to avoid slumping and dripping, and keep heat focused and un-wasted.
- complexity of custom-made heater elements is daunting ( either nichrome, or other engineered solution)
- minimise the thermal mass of the hot zone ( make it small), including hte nozzle.
- insulate the key areas ( the hot area, and the tip), either with fibre-glass, high-temp silicon blanket, or with PTFE ( typically just over the tip), to improve efficiency, reduce convection, and stabilise the temp ( keep the tip as host as the rest).
- connecting to non-hot-zone areas via the "thermal gradient" area is non-trivial.
3) nozzle constriction zone (ie section of small hole) should be as short as practical to reduce the internal pressure, and hence load/wear on the motor and parts.
- carefully engineer this part for minimised thermal mass, or buy it from those that can.
- should be removable, as it is known to jam, or need swapping.
- modified acorn-nut, or custom-lathed brass parts are both the norm, and both work well.
Anything else I should have included?
P.S. Has anyone done a water-cooled thermal-gradient zone? It seems like it's the best way to do this. I think I have to try. :-)
Friday, January 16, 2009
ceramic resistors as a low-tech heater element
Take 1or 2 x 10W ceramic resistors, strap them to the barrel with wire, twist wire tight twice, and hey-presto, an instant heater element. No nichrome or waiting for glue to set, no special engineered parts/blocks ( except the usual tip and shaft ), no bolts, or washers, and voila!
Initially, with just one 5.6ohm resistor in air, I got 280dec C (measured on the outside surface of the unit with a thermocouple) with my powersupply, and without any insulation around it. That told me I had a go-er... so .....
Now with two resistors in parallel, and the increased thermal losses from the brass and increased surface areas, my "heater" reaches 200degC+ without insulation, and with a breeze blowing :-)
I expect it'll extrude just fine when I get the other parts of my extruder built, and insulate it, and if-necessary give it a bit more juice than the ~10.5V I have across it now, but YMMV.
I used a bit of JBweld-like stuff to fill the air-gaps as air is a poor thermal transfer agent. Actually I used Loctite gasket sealant, but it's irrelevent as it's not structural, just for improved thermal transfer. you could just as easily use CPU grease in this case, if you like.
Downside: longer "hotzone" shaft, resulting in theoretically more potential for ooze of hot material.
anyway, here tis: In these pics, it's running, and at-temp!
Thursday, January 15, 2009
Since I already mentioned this in a forum reply to Wade; I though I would blog on it here so people could comment directly.
My suggestion would be to add a inexpensive presure sensor to the Z mount to allow the following functionality:
- Measure upwards pressure from a calibration touch down or abort if it had run into the bed. It could also be used for a calibration cycle where you touch down on the four corners of the bed or the maximum build area to check for alignment or height of Z (which in IMHO is the measurement that can be the most variable measurement).
- Measuring contact force for a stencil cutting blade or drawing pen to get more uses out of the bot. As a stencil cutter it could cut logos, labels, paper or PCB exposure or silk screen masks.
Since it is variable resistance it could interface to one of the analog ports for the Sanguino in place of the second extruder which no one has really done yet. Though I am reading between the lines and thinking that the extruders are going to be slave boards now.
Though if you still wanted to have a directly connected second extruder you could do away with the separate Z-enable pin (tie it to X & Y enable for a generic stepper motor/movement enable pin) and then devote that pin to Z contact pressure.
You know that’s a problem with this forum, everyone has ideas that you have to chip in with before you do a show and tell of something new LOL!
And then there were two
Cutting the stepper gear for the linear stepper ensemble was routine, almost boring... Do you want to read more?
More pinch-feeder options?
It runs at 5rpm when run at the specified 12volts, but I had the guy at 'RS' run it off his variable power supply , and even at 6volts (and no PWM), it was impossible to even slow down with my bare hands, let alone stall it. It also continues to run as low as 2volts, so it's gotta be WAY below the RPM needed, and no PWM reqired to control its speed, is a bonus.
Oh, and it's all metal gears too. Only thing I don't like is the price... but RS is always stupidly expensive, so I'd consider soucing this from a cheaper supplier, or direct from the manufacturer. ( who is "Igarashi Motoren", Model IG33)
*waves to zac*
Non nobis Domine
In which Tommelise 2.0 successfully mills it's second gear... do you want to hear more?
Monday, January 12, 2009
pinch-wheel feeder - commercial variant
This post is in response to Zac's post from today, on http://blog.reprap.org
Strangely, I was thinking about ( and even started work on sourcing parts ) for a pinch-wheel feeder too.
I've just seen Zac's post on the main blog, and his is so much simpler then mine, but I thought I'd share some pictures of what I was hoping to achieve as a comparison.
Below is a commercial pinch-wheel feeder, or as they refer to it a "wire drive motor", that is designed to feed steel wire inside a MIG welder I own. My plans were to either source another one of these and modify it, or to build one from scratch if sourcing isn't possible.
Hopefully the pictures are thought-inspiring if nothing else.....
For comparison to Zacs, the differences to zac's unit are:
1) rollers are same size as each other ( don't know if this is a benefit or not)
2) neither roller uses "soft grip" ( eg rubber) nor "toothed traction", it's simply a very large "pinching force" ( since the filament is being melted anyway it's not a big concern if its distorted, so long as it still passes through the extruder head.
3) the tension is infinitely variable by turning the tall black knob at the top to squeeze the top roller down more through a stiff spring that is integral to the knob.
4) the two rollers have a V groove in them to keep the wire/filament aligned.
5) The motor that comes with this unit ( the large silve cylinder at top-left ) is way too large and fast for the purpose, so I was going to down-size to something slower, and it apears zac's found a good candidate.
6) opening the unit, is simply a case of loosening the tension, and swinging the knob out of the way. the free-wheel can then tilt up out of the way too. this is demonstrated in the second picture.
For scale/size comparion, the "grey square" section of this unit is 100mm ( 4inches) tall, and 90mm wide. Oh, and the wire normally feeds from left to right in this pic, but there's no reason it has to, as the unit has reverse ( to assist unclogging).
Saturday, January 10, 2009
Feeding ABS with Worm Gears and Threaded Rod
Here's a method (inspired by all the other folk experimenting with alternative filament feeds) of feeding filament using Worm Gears and 3mm Studding.
Next job is to design the holder to mount it all to a RepRap extruder and a feed motor assembly.
The pitch of the M3 is 0.5mm per turn giving a feed rate of 0.5mm per turn of the drive shaft.
The tooth pattern cut into the gears is aprox 1mm deep so 0.33 of the diameter of a nominal 3mm plastic filament.
Whilst it all feels to grip pretty well I will need to actually make an assembly and do some measurements to see how well it works really.
I cut the worm gears myself on a mini lathe and they were surprisingly easy to do. The details can be found on my blog.
The technique should be adaptable for use with a Pillar Drill used as a lathe or Vic's Afghan Lathe.
This was done some time ago but seeing other folk using terminal strips for connections reminded me that I needed to blog it.
For the PlyRap I purchased a Sanguino to control the machinery. A quick look at how many connections I needed to make (and perhaps remake) as I experimented meant that the on board 0.1" solder pads would be quickly used up or put beyond re-use.
The solution above was to find some 0.1" pitch screw terminals (and as I am using a re-purposed ATX PSU, a floppy drive power connector) and bring out the connections to these. I mounted the connectors onto strip board made the neccesary connections for the power connector and soldered the Sanguino to the board using 0.1" pitch SIL header pins.
Press fit hubs for Acrylic Components
Not entirely related to what we are doing, but a useful technique that I am sure will find use somewhere.
Just recently there was a need to make some custom laser cut snail cams for an automata project. I wanted to use the press fit brass hubs available from Commotion but there is a problem press fitting parts into acrylic, in that it invariably cracks or shatters.
A solution is to take the grub screws out of the hubs and then heat the hubs in a domestic oven to about 220 or 230 degrees C.
The hubs can then be press fitted into the acrylic parts initially by hand then finished using a vice to make good the alignment.
The technique worked so well that I went on to laser cut some drive sprockets for wire chain and fit hubs to them the same way.
The picture above shows the hubs fitted, the snail cams are two layers of 3mm Laser Cut Acrylic laminated together with Dichloromethane.
There is a picture of the Automata I was building on my Blog.
Friday, January 09, 2009
First Print – Version 3.0.0 Laser cut machine!
The version 2 machine I have been testing ground to a halt a couple of weeks ago. Cause of the failure was worn out brushes on one of the two motors used to drive the extruder. Not too drastic a failure considering that I have used the same two motors on my extruder for months.
The failure took out the FET controlling the motor so the whole print head has had to come off the machine for repair.
I have been working with Bits from Bytes to develop Version 3 of the Laser cut design so this failure seemed a good time to make the switch over to the new machine. Ian at BfB has done a tremendous job with the update, particular credit should go to his new design extruder and improved drive systems. I will leave it to Ian to fill in the details over the next few weeks. Bear with him though, his priority at the moment is to get production going.
In addition to the mechanical changes, I have worked with Ian to produce a set of electronics based on the PIC32/SD card solution. Ian has taken the PIC designs and produced two new boards for the machine, one for the main controller incorporating the stepper drivers and SD card, the other, is a small board for controlling the extruder with serial coms connecting the two.
Initial results are promising, very close, if not as good as the prints from CNC Mill solutions. The stiffness of V3 is far better and you can see this in the print, V2 was good but the extruder head was able to move a little causing a slight ripple in the printed filament(see the magnified image in my blog “PLAy time”) Contrast this with the latest result from V3, we now have a very clean print at double the speed!
The Print is in ABSTemperature 240DegC (measured at the nozzle)
0.5 Dia Nozzle
Printed direct onto MDF with no raft (Not easy but possible!)
Thursday, January 08, 2009
A design for sealing the leaks
I had my first real printing experience with my McWire based RepStrap yesterday. I am printing ABS with the BitsFromBytes Lasercut Extruder. The first layer worked out pretty well, I think:However I was forced to stop printing at this point. The extruder drived stalled due to the enormous amount of leaked ABS:
I am sorry, I had to use the flash on my camera. You can see the huge mushroom of ABS leaking out of the space between the PTFE insulator and the halfnut on the big washer. This is not the first time this happens, and I have to disassemble the entire thing, remove the pressure bearing on the filament to be able to pull the hole mushroom-insulator-and-heater-barrel thing. Which gets annoying after doing it five times. As you might also see, I tried sealing the leak using PTFE tape and a hose clamp, which did not work.
Since I spend some of my christmas holiday hunting down replacement parts for the heater section and I have someone who can machine parts for me on a lathe and a milling machine, I thought up this part, which might be able to seal the leak properly:
Now unfortunately the lathing-and-milling-person has called in sick today, so I cannot try it out this week.
What do you think about the design? I hope the drawing is not too bad. The dotted lines should be threads.
Could it seal the leak? Should I be using aluminum and not stainless steel? I only have a very small piece of brass thread protruding out of the big washer (the black line on bottom of the picture), so I would not like to thread the PTFE directly into it. I think it would not hold and would get very hot.
Anyways: I have a first real printing result! This is so great :) Thanks everyone who helped me so far :)
Wednesday, January 07, 2009
Making a thrust collar in Art of Illusion
In which your narrator walks you through the differences between preparing a design for printing as opposed to preparing one for milling in Art of Illusion... do you want to see more?
Monday, January 05, 2009
Even the pictures used to advertise the product look familiar too.
Sunday, January 04, 2009
First Extrusion with New Extruder Design.
I've just extruded my first filament, using a new extruder design (short heated zone, composed of stainless steel, aluminum, and brass.) I've only built the heated parts of the extruder -- and fed the welding rod by hand. Nevertheless, I was able to extrude both ABS and HDPE. Details (and photos) are available in my latest blog entry. More photos are available in my picassa public gallery. But here is one photo of my first extrusion from the new heater-barrel assembly:
Friday, January 02, 2009
New Ponoko Builder
Hi. Just thought I would introduce myself. Been wanting to build a Reprap for a while, but didn't want to put my effort into a repstrap with too much custom engineering. Hate doing things only for myself; must share, always! To that end, I've been working with Vik on improving the Ponoko build instructions. We're testing a system for creating a BOM (Bill Of Materials) by marking up the instructions. This should help in two ways: first, in creating the list, but second in ensuring that every part used is mentioned in the instructions. So far, I'm pleased with it. The real test will be integrating it with Zach's excellent parts lister, and in seeing if other builders are willing to use it.
So far my build is going well. Trying to stick to as much standard stuff as possible. Only real differences are that I'm using NEMA 17 motors (but they're supported in the Ponoko version), and I'm using a BBB Arduino clone because I already had one. Electrically compatible; not pin compatible. Am building my own motherboard for it. If I was starting from scratch, I would use Zach's Sanguino motherboard.
I'd post photos, but they'd look just like Vik's Ponoko build instructions. Remaining work: wiring harness and software.