I have a similar problem, but using an aluminum drive wheel. In addition to the teeth filling up with plastic, the teeth eventually get deformed because I am using aluminum. With freshly cut teeth, I can get up to 20 pounds of pull. After they start slipping, the pull goes down. I plan to try steel teeth next to fix the deforming problem, but have not gotten around to trying it yet. Not sure ifby damonb - Reprappers
Putting my own two cents in- I agree with nophead about fragile solutions. Using plastic parts in areas meant to melt plastic is just asking for trouble. That goes for the use of kapton tape as an insulator as well PTFE as a thermal barrier. Part of the problem I see with reprap in general is that it seems to me there is very little engineering going on. There is a lot of hacking, but almost nby damonb - General
I think the OKC/Geeks OK attempt has pretty much fizzled. The forum at GeeksOK never had much activity and I think it was too hard to try to get eveyone together at the same time to have a monthly meeting. I managed to make one meeting and by the time my schedule allowed me to make another, there were no more meetings scheduled.by damonb - Oklahoma City RepRap User Group
A great resource for etching PCB's at home is I have used toner transfer to make boards with components having a pin spacing as small as .4mm pitch. Photoresist is my preferred method now. If you plan to only etch just for this project, then you probably will not save that much in money or time versus just buying. However if you are a serious electronics hobbyist, then I think it is worth wby damonb - Controllers
Are there any thermal fuses that operate in the 500F temperature range. I would really like to have a failsafe that kills the power to my heater if something goes wrong with the temperature control. The closest I have found are replacement thermal fuses for coffee pots that open around 400F.by damonb - Plastic Extruder Working Group
Thanks Wade. I sort of figured the nozzle would have to be electrically isolated, but was not 100% certain. For now I will just attach on the main body of the barrel and insulate with kapton, like I have been doing. Reif, thermocouples are very easy to use and you can make them smaller than any thermistor. The wires on mine are about 5 thousands of an inch. I built a small capacitive dischargeby damonb - General
Did a quick test with my current test barrel. I cut 2 1/16 inch slots about 1/32 inch deep into a piece of 1/8 inch brass. The length was roughly 3/16 of an inch. I probably should have made it 1/8 of an inch. Unfortunately the the 1/8 inner diameter barrel is a few thousands larger than the rod, so the fit was not a press fit. So there is not complete thermal contact between the rod and barrel.by damonb - Plastic Extruder Working Group
While still struggling to get my heater barrel work reliably, I was thinking about the thermal conductivity of ABS. Doing a simulation in ansys with a 450F heat source surrounding a piece of 1/8 inch ABS made me realize that it can take up to 10 seconds for the center of the ABS to be become molten. This could also be something that could limit the ultimate extrusion speed of a reprap, because tby damonb - Plastic Extruder Working Group
At the risk of hijacking the original thread.. Do you by any chance have any pictures of your setup? I have seen very few people investigating using the extruder with existing cnc machines. I am curious how you have your extruder attached to the mill head. My plan is to attach it to the side facing right where there is a single slot. That would maximize my travel area. It would also provide theby damonb - General
I am in a similar situation. I have a taig mill and just building an extruder. My mill also uses Mach 3. My plan is to use my mill and control software as is. I will use skeinforge to generate the g code. I have a 4 th axis on my mill and will use the stepper from it to drive the extruder. I will either use an off the shelf temperature controller or build a dedicated one to maintain the barrel teby damonb - General
I finally have gotten a successful extrusion on my extruder. The one mentioned in the earlier posts did have problems with plugging up as was suggested might happen by freds. My first variation was to switch to a lower section of brass and an upper section of .148 diameter .01 wall stainless steel tubing. Still had the plugging problem. I knew from my previous attempts that that all brass ledby damonb - Plastic Extruder Working Group
Shortening up the heat zone is something I can try. I also noticed, in my rush to see the whole thing working for the first time, that I forgot to put any insulation around the windings.by damonb - Plastic Extruder Working Group
After about a years delay from my previous attempt, I finally got around to making another extruder. This time based on a worm drive. The worm drive and gear are from sd-spi.com and give an 18:1 gear ratio. This gives 3600 steps per turn. My stepper is rated at 53in-oz holding torque. So the with 18:1 I get roughly 950 in-oz holding torque. Not sure what dynamic torque would be, but it is way moby damonb - Plastic Extruder Working Group
Just let me know where the meeting place is and I will try to be there.by damonb - Oklahoma City RepRap User Group
I am not sure of the force my extruder requires, but look at the charts at it looks like my setup is just under the threshold to start extruding going by the rating on my stepper. Though that is holding torque. I suspect that turning torque is less than that. I was just sitting here taking apart an old cordless screwdriver I have to see if that could be adapted to be driven by my stepper mby damonb - Mechanics
I finished getting the heater barrel mounted. A picture is attached. As some had suspected, the stepper I had did not produce quite enough to torque to extrude on its own. Actually I was sort of surprised it did not work because the radius where the the filament contacts the drive wheel is about .4 inches. This means I should have seen about 8 pounds of down force. It did not take a lot of handby damonb - Mechanics
I think the step genie is just a programmable logic device. I thought about using a CPLD to generate the step signals, but I wanted to get the extruder built and not get sidetracked on logic programming. In a future version of the board I may go the CPLD route and then the board should be able to handle bipolar or unipolar.by damonb - Mechanics
Phil, The drive is direct drive. I will know soon enough if force and resolution are good enough. I think the force will be enough, but not sure about the resolution. I will know soon enough. What other details did you need to know about the drive board? I think I included everything in the intial description. The step genie chip(the DIP) has half stepping mode and is a unipolar driver. The FTDby damonb - Mechanics
Attached is a quick picture of my filament drive for the extruder I am working on. The center wheel is attached to the stepper, which is hidden. The upper wheel is the idler pulley. The arm is a pressure arm. The screw at the top, which is a little hard to see, adjusts the pressure on the filament. The circuit board is the stepper controller. It uses an FTDI 245R, step genie controller(stickerby damonb - Mechanics
Attached is what I was thinking about for at least two color capability. This is an extension of a single head design I am currently working on. With an appropriate clutching mechanism, when the stepper is turned one direction one filament is extruded and the other direction causes the other filament to be extruded. The extruder assemblies could be made pretty flat, so you could stack severalby damonb - General
I have to take back what I said about the wire welder not working. It works now. The yellow and green jumper wires you see in the picture in the previous post were total junk. After I rewired them I am able to pretty much blow apart the 34 gauge thermocouple wire with 4800uf and 32 volts. 20V is giving me some pretty good welds but I am still have some trouble with the wire sticking to the elecby damonb - Plastic Extruder Working Group
Just an update on the silicone/graphite test. The results were not successful. If there was any conductivity it was very intermittent. After doing a little more research, it looks like carbon black is the material I should be using. I should be able to find this in an artists supply. The particle size should be in the 100nm range which is what carbon black is in. The graphite powder used for lby damonb - Plastic Extruder Working Group
The tungsten electrodes are used in a TIG welder. They are 1/8 inch diameter. I got mine free. I found them under my house of all places and several years ago. Being a packrat comes in handy sometimes. :-) Who knows how they got there. You should be able to find them at any welders supply. When I do get around to trying again on the welder I will go with some heavier gauge wire. All I had to wby damonb - Plastic Extruder Working Group
I wish I could say that the SCR's helped, but it did not. I was hoping I could get an effect like a dental welder or a hotspot, but it is just not working that way for me. I may go back and look at it at some point in the future, but I have other parts of the project work on. At this point, the best way for me is to strike an arc between the wires and weld them together that way.by damonb - Plastic Extruder Working Group
I am using the SCR's because they are easier for me to use than MOSFETs. I am hoping part of the inconsistent welding I am seeing is due to the arcing I get when I touch the capacitor to the electrode. That represents wasted energy that should be going into welding the thermocouples together.by damonb - Plastic Extruder Working Group
nophead, I agree that measuring the force applied to the barrel is not representative of the pressure at the tip of the barrel. However getting an idea of the forces involved pushing the filament through the barrel could provide useful information. Especially related to slipping of the pinchroller and how much force is required for a given temperature and extrusion rate. Having the force sensoby damonb - Plastic Extruder Working Group
The plan would be to place the force sensor between the heater barrel and the support. I am not trying to directly measure the pressure of the melted plastic. Just the downward force applied by the filament drive. You are right that I need a hole or at least a U shaped sensor because of the body of the barrel. It may be possible to cut a hole in the flexiforce sensor, but at $16 a sensor I amby damonb - Plastic Extruder Working Group
My welding of the thermocouples has been very hit and miss. In the simplest form I used some tungsten electrodes connected to about 1200uf electrolytic and charged to anywhere from 16V to 30V. Sometimes I blow the wires apart, sometimes they stick to the electrodes and sometimes they weld to each other. At this point I have made a small jig to hold the electrodes and I can put the wires betweenby damonb - Plastic Extruder Working Group
While researching thermocouples, I saw some references to welding the thermocouple directly to the surface to get a more direct measure of temperature. While this would be a neat way to do it, I do not understand how this would work. I would think that the signal would be shorted out. Does anyone have any information on how this works electrically?by damonb - Plastic Extruder Working Group
I would like to add some kind of pressure sensor to the heater barrel so I can measure the downward force applied by the pinch roller driver. One pressure sensor I have seen mentioned is called the Flexiforce force sensor. It looks like they just use some kind of pressure/resistance sensitive ink. However it looks be a proprietary formulation. I was wondering if anyone had any suggestions on soby damonb - Plastic Extruder Working Group