It's been a while since I posted. The main problem with reprap seems to be that one can either do things or write about it...
Except for a month away on vacation, I have been very busy doing.
I decided to construct a Mendel out of my printed parts. This I did, using a hardware kit from http://www.mendel-parts.com/, in about a week.
I designed a supported hot-end using a standard PTFE/Brass nozzle, and spaced the extruder so that it gave maximum clearance.
I moved my electronics over from XCBot and got it printing in PLA. At this point I discovered that having temperatures too low is a common cause of nozzle failures...
Then I went on vacation for a month.
When I got back, I set about purchasing Mendel her own electronics, and I also bought an Adrian's style hot-end from Mendelparts.com. After much deliberation, I decided on another RAMPS controller. The main reason is I wanted to have a heated bed.
I bought a complete kit as I may want to sell Mendel on after I design my own replacement.
After getting everything tidy, I started printing in ABS.
While trying to print a case to put my RAMPS electronics into, I learned a few things about designing for FDM printers. Large objects with double layer thick walls tend to have the upper wall come off the bottom of the print. Perhaps a heated chamber will allow me to design thin-walled boxes in the future.
In any case I have had good success designing and printing various things....
As mentioned early on my journey, I found a way to make a stainless steel isolator and a resistor heater block and a nozzle, using not much more than a drill-press. At the time, I had no way of testing my isolator, but since, I've printed most of a Mendel using it and am happy. It works great.
I started printing my mendel using a PTFE isolator, but was experiencing leaks, and went back to the all metal design.
A recent image of my current iteration:
You can see that I have a slightly longer MIG tip as nozzle, cut off with a tubing cutter so that the hole shrinks. The M6 thread on that is fully tightened (using flats files on by hand) into my aluminium resistor block. The block has 2 large holes and a shallow one for the thermistor.. one of the holes is M6 threaded right through the block.
I have surrounded the block with PTFE plate 1mm thick, and wrapped it with kapton. Kapton tape only would likely be enough, but the layer of PTFE makes it harder to get burned. I have secured the (etched one side) PTFE to the block with permatex high temperature gasket maker. This holds the resistor in and adds more insulation. I also secure the thermistor with gasket maker, and a layer of kapton holding it in. From drilling to heat, less than an hour has passed for using this as the gasket maker doesn't mind 220 degrees C before curing.
Inserted into the top of my aluminum block is the stainless steel threaded isolator. It is secured with a check-nut (not shown).
It is an M6 threaded rod drilled out as per the above blog article. I used a drill press and a hand drill to re-work this bit of threaded rod.
One special tool I had was a tapered reamer to open the bottom of the 3.2mm hole into a taper.. nophead seems to think this is important, and after playing with a standard brass nozzle, I am inclined to agree. Force to push the feed-stock through this hot-end is much less than through my bought brass one, with the same exit hole.
You can see I also ground down part of the isolator to reduce heat path up the isolator.. this was done with a dremel with stone on it. I mounted the dremel on a hinged board so that it was able to come close to, but not touch a bit of 3mm rod mounted in a vice. I then inserted the isolator, turned on the dremel and rotated it by hand until the dremel was removing no more material... This makes for a thin spot relative to the inner hole, and eliminates the risk of grinding through.
Threaded onto the isolator is a bit of copper plate I had around, drilled and tapped M6. This is to help transfer heat out of the isolator, into the salvaged heatsink. You can see the heatsink compound on that interface.
The Heatsink is from an old power supply, the roughened black anodized texture on it makes it very powerful. It is also drilled and M6 tapped. Notice it is not touching the extruder chasis, more heat isolation at work.
Mounted is my 40mm fan, (later changed for a 30mm salvaged fan mounted in an rp printed duct.
I can say that this arrangement allows virtually no heat to enter my extruder chasis. The little fan and great heatsink pulls all the heat out of my isolator before it can make it's way into the structure above.
I have not talked about resistor size in this post as it is dependent on power supply voltage. I'm using 19.5V laptop power supplies, so I am using a 10 ohm resistor. Larger power resistors are always good, but due to the fact that we are heatsinking and temperature controlling them... maximum temperature rating is far more important. Like nophead, I'm using vitreous wirewound resistors. I get mine from RS components here.
Simply drill the resistor hole out to be slightly larger than your resistor you wish to use, wrap the resistor in aluminum foil until it is a tight fit in the hole. Secure the resistor from sliding with goop, or kapton and the job is done.
To recap, I'm able to extrude through a .5mm copper hole, with a skeinforge feed speed of 60mm/s with this setup. It cools off and heats up with no problems, doesn't jam or leak. The most advanced and expensive tool used was a drill press. (needed for the isolator and nozzle, not so much for the resistor block).
If one only had a hand drill and a tap, the resulting block could be mounted on an 'old school' threaded nozzle and isolator..
The cost of the SS threaded rod as a couple of euros. The cost of the aluminum was negligeable (I used scrap), the cost of the MIG tip was less than 3 euros. I could make another one of these and be printing through it in a few hours. In fact I will for my mendel. I'll let you know about any problems I encounter mating it to a Wade's extruder on the ABS mendel carriage.
I came up with an idea to turn a 0.8mm hole in a .6 MIG electrode into a smaller hole...
take one of these:
Actually I used something like this, but same principal:
Stick an M6 thread into a bit of plate to use as a handle on the tip.. and slowly work you way down till it parts.
It ends up looking like the opposite number to this:
Last step is to drill out the length of the body to 3.5mm. laying your 'handle' on the drill press table gets you straight, but then you need to hold the tip from spinning (vice-grips). Then drill as close to the end as you dare.
The resulting nozzle hole is pretty much the same as my 0.5mm purchased nozzle, and it looks like the reduction is .1 to .2 mm deep.
The nozzle works very will in my new extruder with all metal isolator.
I figured that shining a light on a matte-black surface would be more efficient than hooking up wires to my moving Y build platform.
After getting some black construction paper to 100 deg C in less than a minute... I was worried about having too much heat with my 150W radiant heater bulb. Not the case as it turns out.
I bought some matt black high-temperature paint, cut a 2mm aluminum plate to my table size (30x24), wiped it with acetone and sprayed it matte-black.
A couple hours later I rested it on a thermocouple, on my MDF build platform, and turned the light on it at a distance of about 30cm, normal to the surface.
The temperature under the plate topped out in about 8 minutes, at 77 deg C. I put a piece of glass on it, and when it took another 10 minutes to get back to 80 deg, I canceled the operation, realizing that the top surface of the glass would be cooler than the plate anyways.
Next was a layer of Kapton on top. The temperature quite quickly came up to 80 to 90 deg. C. The tape obviously absorbs IR.
I decided to print a Wade's large gear, as I had printed one the night before on acrylic, mostly successfully, but with a bit of warp.
I positioned the light at a 45 deg. angle, aimed into the extruder's hot-end. Temperatures were still about 90ish in front of the extruder, as measured by my IR non-contact thermometer. (I checked with the heat-light off for a sec to be sure it wasn't effected.)
I couldn't get my ABS natural to stick to it, I even wiped it with acetone... Someone on IRC was talking about 'drymount' adhesive spray, which I had laying nearby.. so gave it a try in desperation. (Amazing what you'll do when you have an audience on IRC watching a webcam feed ;-)
Drymount worked great for getting the print to stick.
And the 80 - 90 deg C surface temperature, plus whatever the natural ABS makes internally from the light, works for keeping the print straight.... where it's warm...
But the backside was cooler.. by quite a bit... and showed quite bad shrinking... even worse than my whole gear was exhibiting on acrylic for some reason.. I aborted the print when I saw the back lifting.
It's clear to me that to do this, would need 2 150 watt lights, front and back... resistive heat is starting to look pretty good to me.
I never did buy the bottoming tap.. I figured that since I was only tapping PTFE, and I had aluminum threads right above... I'd just make myself a tap out of Stainless M6 threaded rod...
On the printing front, things progressed quite quickly. I decided to start with Repsnapper skein, as it seemed a quick solution to learning what goes on in a CNC print. I then realised that I had no idea what controls what, even in the simplified UI of Repsnapper... I read through the documents on the wiki and started making changes, then looking at the g-code to see what changed... I soon progressed to running the extruder a few cm above the build platform, and seeing if I thought the extrusion was coming out slower than the axes movement. I then started to try to print, and after 3 or 4 bad starts, I got this.
I found that a lot of my problem is not lowering the extruder low enough to get a good stick on the surface.
I quite quickly got 'dialed in' with Repsnapper, but wanted more control, and top/bottom filled layers, so Skeinforge was the order of the day.
By the Way, I made some notes about how I got up and running for my first print in Repsnapper on the Wiki here: Initial_printer_Setup_Notes
I picked through the program, and with the help of people on IRC, managed to get printing quickly enough.
Considering this is just 2 days of printing, and maybe 20 test blocks, I'm pretty happy with my progress.
I decided to try to print something 'real'. I've always been fascinated by the possibility to print gears in reprap, so I figured my first non-test object should be a Wade's large gear.
As you can see it turned out usable, but a bit warped. I have realized that a heated bed is a necessity when printing with ABS.
As of this afternoon, I have made 3 things. All usable parts of an extruder, or a Mendel.
I'm pretty happy with what I've managed to achieve in 3 days of printing. I can only credit all the work done by other people, writing down enough information that I could pick up enough information to make wise choices, and get 'up on the curve' quickly.
This evening, with the help of Prusajr and Bill20r3 on IRC, I tuned my Skeinforge settings even more. I have more parts to show for my efforts, each noticeably better than the last.
I must say that I'm a believer that open source hardware really works. If someone had told me 4 months I could design and build my own 3D printer, and have it producing acceptable, usable objects before the end of the summer... I'd have thought they were crazy.
In the next day or two, I will outline my experiments using an IR heatlamp to heat my build platform from above.
Against all advice, I decided to roll my own here too... I don't mind failure as a way to learning, and I feel that I've read enough over the past months to have a decent chance of getting this to work.
I decided to use salvaged nylon gears out of an old printer. They fit the old Nema 14 stepper I had (perhaps they were connected in the printer) and gave me using two stages, a reasonable gear ratio.
Pictured below is a first draft of the design, I ended up using a full 60x60x4 mm angle, and attaching the motor mount/front bulkhead with small (4-40) csunk screws.
Pictured also is my all metal isolation, as per nophead's no comprimise extruder. I used a MIG welding tip cut short (which I believe caused me problems, more later), in the bottom of my aluminum heater block. Two resistors giving me about 15 watts, and a thermistor. The heat-sink is out of an old power supply.
This design also came to me. I am not a fan of supporting the heater through M6 thread in PTFE, as it is soft and many people have reported stripping the threads while learning to use their printer. I also ordered a brass barrel with .5 mm hole in it in case I couldn't work out the bugs in my all metal design.
Here is design one hooked up temporarily for testing. The motor and gears have a LOT of torque. As I discovered, it will take a large bite (1/4 of the diameter) out of the filament when it jams without even noticing...
A closer view of the Hot-end. I left space between the heat-sink and aluminum chasis to minimize the transfer of heat. I'm using high temp gasket sealant to glue the etched PTFE 1mm plate onto the block. I'm holding it with SS locking wire as a strap. I was still waiting for kapton tape to arrive in the post. I've stuck a bit of PTFE in there to keep the thermistor wires off the strap.
It worked very well.. during 2 or 3 hours of testing, the top of the Stainless isolator and chasis never got above 30 degrees C. It was cold to the touch if I ran the fan... at 5V. 12V was overkill.
My 15 watts could keep up, but it felt under-powered. It took a couple minutes to heat up without the fan, and with the fan going perhaps 3-4 minutes. I recorded the duty cycle on my digital scope, and the heater was on for 60% of the time when not extruding, gradually increasing to 85% as I increased extrusion speed.
I intend to set up a grinder to carefully thin down the SS barrel above the resistor block, thus preventing some of the heat from escaping up to my heat-sink.
My MIG tip has a 0.8mm hole in it so I was pushing quit a bit of plastic out. I increased the speed until I found a limit, where I couldn't melt the plastic fast enough for it's speed. The extruded filament speed still felt slow at this limit.
The heater was still only on for just over 80% of the time when this limit was reached. Stripping of the filament drive started happening regularly as I ran the un-melted feed-stock into the heater end.
I believe I have discovered that one can have too short a melt zone.
One thing about having easy backup options, is you perhaps don't spend as much time working on a problem as you might otherwise...
I had set out to cut another MIG tip longer, and try to decrease the hole size to .5mm or less. During my attempts to melt the end of the nozzle with my TIG welder (so I could re-drill), I oxidized the top badly and decided to give that idea up as a bad job. I will perhaps re-visit stretching the tip by rolling it, which should shrink the center hole in the narrow neck, and I can then cut it off at the narrow point.
In the mean time I built a more conventional PTFE isolated hot-end with the purchased brass nozzle, based on the above design... as pictured below.
I also built another hot-end, this time with the same resister that nophead uses in his.. I run it at 12V and get 20 watts of heat in my little block.. it heats up very quickly indeed.
Over the course of an hour of testing, I felt the isolator was keeping the heat away from my chassis very well. while the outside of the PTFE gets quite warm to the touch, the chassis is only slightly warm. I still have the fan mounted, and if I ran it, would keep all heat out of the top-end completely.
I had hoped that the exposed aluminum holding the nozzle into the PTFE would help cool it down and prevent melt above the nozzle, but that is not the case.. twice I got jams after having it 200 degrees for 7 or 8 minutes... extruding slowly or not.
When I took it apart, I saw that I had a plug above the nozzle, jamming it. Tomorrow I will do a better job of making the nozzle meet exactly with the PTFE inside. I'll be shopping for an M6 bottoming tap.
I also spent some time figuring out how to live broadcast using ustream. I hope to use this facility to get help tuning up my system when I start Printing, hopefully tomorrow or the next day. I have recorded a little silent walk-around of my extruder on my ustream feed: http://www.ustream.tv/channel/xcbot-feed
After taking 3 weeks off, I finally got XCBot operational. (as a "thing" that moves surfaces around in 3 dimensions anyways)
Here is a photo of my temporary electronics mounting. My plan is to use XCBot to either mill, or etch-resist a pcboard to mount my stepper controllers and FETs on. For now I'm running from a breadboard. Everything is securely mounted, as I don't want something to pull loose and let the magic smoke out of something expensive.
I supply a USB cable for data, 12V from a switching external disk PS for running my fan (and possibly a heater), and 20V from a large laptop PS to drive the steppers (and possibly a heater). They all attach to the electronics on the top.
Here is a close-up showing my 20V power switch. It is there so that I can kill drive to the motors when things go wrong. I've also included a fuse in case a short should occure.
A view from the other side, showing my cooling fan. the little stepper motor on the RH side is destined to be my extruder motor. You can see how I've attached things. An acrylic plate inside the t-slot, drilled for a tywrap.
I've run most of the wires inside empty slots. A bit of stiff, plasticized, card stock holds it in.
Other stuff, including the opto limit switches, and trigger sheet-metal, I've attached with this wonderful double-sided tape. It has great holding strength
After securing everything, I re-flashed the Arduino Mega with Tonokip's firmware, and fired up repsnapper (my host software). Things went very well. I had to reverse the opto directions in the configuration file, and also the motor directions for Y and Z axes.
I'm still exploring the limits to my axes speed capacity, and learning how to use repsnapper, but to commemorate the moment Youtube videos of XCBot in action are HERE, and HERE.
