HBP Testing and New Filament

First the good news. I finally did some testing with my prototype glass heated build plate and was able to successfully get to a usable temperature for ABS. I first tried to test it by laying it on a piece of G10 which my current build platform is made from and hooking it up to a suitable ATX power supply. After 15 to 20 minutes, I wasn't able to crack 90°C. My first thought was that this was an issue with the heating conductor since we kind of missed the mark a little on the conductor trace and ended up with too high resistance. But while cleaning up from the test, I quickly realized another possible issue when I felt how warm the G10 had gotten.

For the next test I decided to put the plate on a sandwich of cardboard and foil tape. This worked much better and I was able to reach a decent temperature fairly quickly. I also took some shots of the plate with the IR camera at work during the test to try to get an idea of the heat distribution. I don't think that worked out like I had hoped. I'm fairly sure the camera was seeing through the glass to the heating element and cardboard below. But even though the pictures might not be an accurate representation of the heat on the surface, measurement with a thermocouple showed the top surface to be right where I needed it. And if my calculations are correct this is only using about 6.6 amps from a cold start, and somewhat less once it's warmed up. This is just on a 130x150mm plate, so a larger plate will require proportionally higher current.

Unfortunately, I'm not sure our idea for the thermistor will work out. I didn't know how the arduino was measuring resistance until I did a little research, and with my limited experience in electrical engineering (nearly none), it didn't occur to me that the amount of resistance we were getting out of the thermistor trace on the plate would be difficult to work with. The arduino with RAMPS is doing a voltage comparison by creating a divider on a 5V circuit with a 4.7k resistor on one side and the thermistor on the other. The typical thermistor is 100k and has a really huge swing in resistance which works great with the 10 bit resolution of the analog inputs. But my thermistor only vaies from 230 to 290 Ohms over the temperature range I'm interested in which isn't enough. I could swap out the 4.7k resistor for something close to the value of the thermistor, but I'd rather not mess with the board, and I'm not sure what affect the increased current (~50mW by my calculations) would have on the arduino board. So I think I'll just tape a 100k unit to the top of the board for now.

I ordered some new filament from Ultimachine. So far I had only used some samples of black, green, and silver PLA from Ultimachine (it's not chocolate, but you can get a few Octopuses/i/odes out of it) and a pound of natural PLA from MakerGear. All of those had worked really well and I had no qualms about ordering more variety of plastic from Ultimachine. I got a pound each of the orange, blue, and silver PLA, and a pound of natural ABS in anticipation of having a usable HBP. I managed to print the small gears and pins of the screwless cube gears thing in natural PLA before I ran out. I thought I'd give the orange a try for the big gears. I took a caliper to the filament and got measurements all over the place, from 2.8 to 3.1mm. I also noticed that the texture of the plastic was significantly different from any other PLA I had tried. It seems much softer. This did not bode well, but I decided to give it a try anyway. It did not work. I did manage to get one successful 20mm calibration cube, but had issues with everything else. At first I though there was a problem with the extruder because the filament was stalling. I tried cranking up the heat thinking maybe it just wasn't melting as quick as the other stuff but that didn't help. I took apart the cold end to see if the hobbed bolt had gotten gummed up by chewing into the plastic, but it really wasn't bad. I tried really cranking in the idler bearing on the filament, and it helped a little, but not enough to get a decent print. My final conclusion is that the filament is just too big in spots to fit into the hot end smoothly. I changed over to the silver and it worked fine. I hope that I can trade in the orange, because it's not going to work for my machine.

I clearly need to blog more often so I don't feel like I'm writing a novella every time I decide to post. Next up, dealing with mechanical issues and some ideas for vertical X-axis design.

Glass Heated Build Platform

I finally got the prototype made. It came out really well and even though I have no idea how well it will work yet, visually I think it's great. I have some video of the writing process, but it took almost 30 minutes, so I need to do a bit of editing before I post it. Here are two shots of it right after writing the conductors and before baking:

Just after writing heater element

Both heater and thermistor elements

The first picture shows just the essential part, the heating element. It's about 2.2 Ohms overall so at 12 Volts that should use 5.5 Amps and dissipate 65 Watts. I think that will be enough for the 4"X5" piece of glass. The extra lines you see in the picture are actually just scratches in the X-Y stage.

The next picture shows the completed pattern which includes a very long thin looping conductor which ideally will work as a thermistor using the natural TCR (temperature coefficient of resistance) of the conductor. The higher the resistance, the better range I should get as a function of temperature, hence the need for long and thin. The resistance of the thermistor came out in the neighborhood of 230 Ohms. Once I can fire up and control the heater, I'll have to generate a lookup table to use in my firmware for bed temperature control.

After writing the conductors, the plate was fired for 3 hours at 850°C. Then I was able to solder wires to the conductor pads. I'd like to think of a better interconnect for the next version, but for the prototype, this will be fine.

Now I need to make myself a decent power supply out of one of the old ATX PC supplies I have lying around.

Unfortunately, this past week has not been all good for me on the 3D printing front. I was having a little trouble with backlash, mainly on the X-axis, and in the process of tightening the belt managed to pull off both of the bushing holders on the motor end, and two of the bushing holders from the X-carriage.

Bushing holder separation on X-axis

This is apparently a problem for more than a few people. I believe the belt went slack over time due to the motor mount being designed with a bit too little plastic. Eventually the belt tension pulled the pulley in enough to cause slack. I guess I got a little ham-handed trying to take up the slack and you can see some of the results. The cable tie I had on there was not enough to prevent the detachment of the bushings. Maybe it's me, but I think the desire to reduce the amount of plastic in the printer parts has gone a bit too far. I'm also at a loss to understand why the channel in the X-motor end and X-idler end faces away from the source of tension. I have a hard time believing there isn't a good reason for this orientation, but I'm damned if I can figure it out. I'm really impressed by the work I see on vertically oriented X-axis parts by Emmanuel and the Russians and I would like to do something similar once I get up and running again.

My goal with building the printer was to make parts for other projects, but I'm getting totally sucked in to the idea of improving the design.

The Best Laid Plans...

So much for the plan. Life events have made it a bit of a challenge to coordinate my schedule with that of the production team at work. So other than finding a time that I can actually make the test version of the glass HBP, I'm all ready to go. Here's a piece of the pattern that I'll be using for the first attempt (click to see it full size):

The lines represent the path that the Micropen will travel to lay down the conductor. The red path will be the heating element made with an overlapping 20mil line for a final line width of about 2mm. The blue trace will be a thermistor which will not overlap and be only 10mils wide and 550 inches long. I'll have to come up with a custom thermister table once I can test it out. I'm hopeful I'll actually be able to do this tomorrow or the next day.

Sadly, I haven't had much time for printing things lately. I managed to make half of the corners and the pins for a screwless cube gear, but the center is proving difficult for me to print in PLA as it's so small at the bottom that it's not cooling off quickly enough. I'm going to try printing it along with something else to see if that helps since I don't yet have a cooling fan on my x-carriage.

Plan for Glass Heated Build Platform

Example heater and thermistor on glass

I've read many success stories of using glass on top of a heated build platform, and some struggles as well. Seems that if you can get the plastic to stick throughout the print, removal after cool down is easy. So I've decided to use glass as the top surface, but rather than go the traditional route and just lay it on top of the heater, I'm opting to actually create the heater on the glass surface. I've mentioned previously that the company I work for makes resistors (including heaters and thermistors) on all sorts of substrate materials and shapes including glass vessels. The electrical elements are made by Micropenning the conductive ink onto the surface then baking.  So making a heater and thermistor on a flat square of glass should be easy.

The point of doing it this way for me is to ensure that the glass is very evenly heated since I won't have to worry about even contact with the surface beneath, and possibly to reduce the power requirements for the platform. Oh, and just because I can. I plan to create a test piece this coming week to check the uniformity of the heat distribution on the glass with my heater pattern, as well as to confirm my math on the electrical properties of the heating circuit. I'm not an electrical engineer, and I'm trying not to bother the experts at work too much (though they may say otherwise). I have a couple of nice pieces of scrap borosilicate glass to use from one of our previous projects. I may try standard tempered glass later if it proves out and I decide to make a few more.

RevK's 11&39 Wade's Gears

I tweaked my skeinforge settings a little more and printed out these fantastic gears by RevK. They really do print out very easily and they came out way better than I expected at this point. I think they'll go great on the Greg's Hinged Accessible Extruder I plan on printing once I can do ABS on my new HBP.

Just some stuff I printed

It's been over a month since my last post, and even though I've printed a bunch of things I still don't understand Skeinforge very well. I managed to combine settings from a few posts on forums to get fairly reliable prints with PLA. Here's a few of the things I've made:

More octopodes

Shuriken refrigerator magnet

Octopodes or octopi, I like them both. But the thicker legs on the former are the way to go if you are printing with PLA.

My boys had to flight test the shuriken, hence the lack of pointy bits as you can see in the picture.

30mm and 20mm companion cube

The companion cubes were something I was dying to print since I say them on Thingiverse. The one on the right is my first attempt at the normal 20mm size. I believe I used a 0.25mm layer height, and it just didn't get enough of the detail that I was hoping for. Once I got more comfortable playing with settings in Skeinforge, I redid it scaled to 30mm with a 0.2mm layer height. Much better. I'll do it again when I get some nice gray ABS.

I decided to find something bigger on Thingiverse. I really like the way MakeALot's Bracelet V came out. Even though it's a very periodic, mathematical design, it still has a somewhat organic look.

Bracelet V

Invader Number 3

I also decided to try some earrings, and I'm not up to the caliber of what Schorhr can do, so I got the space invader things, scaled down invader number 3, printed it and drilled a hole in the hand (tentacle?) for the hardware. Big hit at the sci-fi get together my family went to.

New Z-axis Coupling

So enough of the toys already. I really wanted to make something useful. One of the problems that showed up early was that my Delrin z-axis couplers were apparently not as straight as I had hoped they would be. So I ended up with a bit of a wave in the vertical plane on all my prints. First I tried to fix it using the plastic tubing and threaded coupler method, but I couldn't get the coupler to hang on to the tubing. So then I tried nophead's Z coupling that still uses the tubing, but clamps the joint very nicely. It worked beautifully. My subsequent prints (including the 30mm companion cube) have been very straight.

Filament Spool and Mount 

The next useful thing I wanted to do was to make something to hold the filament. Until now I've just been sort of draping around one of the Z motors. Problem is, I have to then baby-sit the printer to make sure the filament doesn't get caught up on anything.

Redesigned Part of Spool Mount 

I really liked the design of randyy's filament spool but I needed to find a way to mount it to my printer since the spool mount was designed for a Makerbot printer. As usual, I was not the first person to want to do this, and reprapperMC had already figured out a solution I was happy with. Unfortunately, I didn't have enough threaded rod on the end of the Z motor mounts to fit this particular spool mount. So I took my first real foray into OpenSCAD and redesigned the necessary part to be thinner at the bottom, and to clear the smooth Z rod clamp. I also wanted to be able to easily swap out the spool in order to change colors or materials. So I made a block for the top of the mount rod that could recieve the hub that was originally designed to fit the laser-cut wood on the Makerbot machines. Took me a couple of tries to print right due to small size and ambient heat wave, but it works very well.

Block to Receive Spool Hub 

Original Spool Hub and New Block

My RepRap is now a self improving machine. My next big step is to make a heated bed. Fortunately, I work for a company that specializes in adding resistors and circuits to pretty much any type of object, so creating a heater and thermistor on a piece of glass will be a walk in the park. The mechanical part of adding it to the machine will be much more difficult for me.

Test Cube and Other Stuff

I merrily played with the manual controls in RepSnapper and calibrated as well as I could with my primitive ruler in terms of making sure the three movement axes roughly followed my commands. I think my timing was good relative to the releases of Skeinforge as others who are much more experienced than I already figured out how to adjust the firmware to handle SF40's new volumetric extruder control. So I followed the empirical method in one of the forums for figuring out how many steps it took on the extruder motor to feed one mm of filament into the extruder and plugged that into the firmware. That gave me some confidence that the extruder was working properly too.

I have to say I was somewhat concerned that the PEEK insulator on the MakerGear hot end I was using would get hot enough to melt or at least warp the extruder plastic or X carriage. I brought a nice calibrated thermometer home from work and was really pleased to find that the temperature of the PEEK seemed to be staying below 80°C without any kind of active cooling. I can't say enough about how happy I am with this hot end setup.

As much as I would have liked to jump right in and print a replacement gear for the really warped large one my extruder, I still needed to calibrate, and I'd probably need a heated bed so I could print with ABS. I don't think the PLA would hold in that situation.

First print

So I looked for a tried and true standard on thingiverse and found the 40mm test cube. I found some settings to use as a starting point in Skeinforge (I haven't the faintest idea where any more) and ran the thing through. I really didn't understand what most of the parameters meant, but I got greedy and decided to shoot for a 0.2mm layer height. Out popped the G code which I then fed to RepSnapper. I noticed that the object appeared to be centered at 0,0 on the preview grid, but since the starting point was also 0,0 I figured the printer would just end up being forced to adjust and the cube would print with a 20mm shift away from the origin. I think I forgot to carry the 1 or something ;) I ended up with the lovely thing you see to the right.

It tried to print each layer shifted 40mm in the positive Y direction. Not surprising I suppose. But it certainly seemed to be trying to do the right thing. So I cleaned up the mess and prepared for another go. Realizing that 40mm is pretty big, and not wanting to use that much plastic at this point, I ran the stl file through Skeinforge again but used the scale function to make it half as big. I also did a little searching and found out you can use the multiply function in Skeinforge to move the origin of the object, which I did. The next print almost worked, but the nozzle seemed to be dragging through the plastic and just making a mess. I stopped it after the second layer.

I was having a hard time figuring out how to deal with the ooze right before a print and I figured that was what was tripping me up. So using the same code, I tried again and just did my best to keep the nozzle clean before the actual print started. And the results were........ fantastic!

Printing my first thing!

First successful print - 20mm cube

 It was the best looking roughly 20mm cube of black plastic I had ever seen. Maybe my judgement was a little clouded by finally getting something approximating what I asked for after all that work Googling, and assembing, and testing, and Googling some more. (Just noticed Googling is not in the Blogger dictionary, or is it Chrome, hmmm).

Flushed with this success, I tried to do it again. No joy. Decided to pack it up for the day and try again tomorrow. The next day wasn't any better. I just couldn't get the PLA to stick. You may have noticed in the pictures, I was using Kapton tape on the bed. I thought maybe I had too much residual plastic on the nozzle and took the whole extruder off so I could clean it up properly. A coworker suggested I polish the nozzle so I did. Tried again and it still didn't work. I was getting really frustrated at this point.

I turned to the reprap channel on IRC for the first time and was advised that PLA doesn't stick so great to room temperature Kapton and that preheating it with a hair drier might do the trick. About the same time, I had a revelation that I hadn't cleaned the bed at all since applying the tape. So I used some alcohol to clean it up. I used the hair drier for good luck even though I don't think that had anything to do with my issue but sure enough, my next print stuck fine.

Misshapen baby octopus

Real progress

I really thought I had it licked at this point, and being bored with cubes already decided to go hunting for something more interesting on Thingiverse. That's when I discovered the Bucket O' Octopi. I was still being stingy with the plastic and left my scale settings at 50%. The result was less than overwhelming, even though it was recognizable. The double legs are because I bumped the print bed after the first layer.

Time to start learning what all those numbers mean in Skeinforge. But before doing that I decided to just take a stab at some parameters and try again. On the next G code export, I noticed some numbers fly by in the terminal window. I could have sworn it said the layer height was set to 0.1mm. Sure enough that is what it said. I double checked my layer height setting in SF and it said 0.2mm. Then it dawned on me that for some strange reason, scale affects the layer height, but not the width. While this is pretty clearly a mistake in the code, once aware of it, you can easily work around it. Rather than try for the half size octopus again, I decided to go for the adult size. And it worked! Well, mostly.

Somewhere near the top of the head, something happened. I couldn't see it very well not having a ring light and all. It looked to me like it might have been stretching the filament a little too much on the infill, and on a layer near the top it broke. The end of the strand pointed up and caused the subsequent layers to get a little messy in that area as the nozzle dragged through it. But again, I was very pleased anyway as it seemed like I was making real progress.

One other thing I realized after all this is that the first successful test cube I printed actually had a layer height of 0.1mm. I didn't think that was even possible.

As I was saying, now it's time to learn what all those Skeinforge parameters are for. But first, a beer.

Hardware Done, Time for Firmware and Software

So all this blogging about the hardware might lead you to think I was really patient about waiting until it was all finalized before loading up the brains with some code to make it actually move. Well, I may have left out a little bit. I loaded Tonokip's firmware once I had all three movement related axes ready and made sure they were moving using Repsnapper for manual control. I was floored that they not only moved, but in the proper directions. A big thanks to all the RepRappers who took the time to document various pieces of the puzzle.

While getting the extruder all put together, I did some more research on firmware and software on the RepRap site, various blogs, and by lurking on IRC for a while as well.  This is probably one of the hardest parts of the whole process. A thread in the forums had just spawned a new page on the wiki that was intended to list computer OS/printer electronics/firmware/host software combinations that were known to be working. I just rechecked and it appears this never really got off the ground. I'll add to it once I feel my combination is worthy. The best options for you depend on many things. The wiki has a decent rundown of the various tool chains that might work for you.

I was looking for firmware that worked easily with my RAMPS setup. Initially I looked at the Teacup firmware but found it too confusing for my first attempt. I found the Tonokip firmware much easier to understand and configure for my setup. I later changed to Klimentkip and will probably move further up the evolutionary ladder to sprinter in the near future. All I needed to do was copy the RAMPS config file, check the pins and end stop settings (I used mechanical end-stops), and uncomment the include statement for the correct thermistor table.

For host software I decided to use Repsnapper just for control and sending the G-code to my printer. From my research, I gathered that Skeinforge offered the most advanced options for G-code generation and also a proportionally steep learning curve. I decided not to try printing with Repsnapper directly fearing that I would just be disappointed with the results anyway. Probably an unfounded decision as I've since seen some pretty good results from other RepRappers. Skeinforge is really a bear to learn, but I'm making progress.

Nothing left to do but print stuff.