Sunday, April 18, 2010

 

inexpensive, simple, acrylic makerbot-inspired 3d printer with heated table and build chamber



Hi folks,

I thought I'd take a second to post some pictures from a design that my father and I have been working on for a while. Our goal, after making a 3d printer with a much larger bed size, was to make a smaller table-top one that I could keep with me in my apartment. Being a grad student (poor) who doesn't like the smell of heated plastic, but who also wants fantastic prints, we set out to design something inexpensive with a contained chamber, with a print size at least the size of a makerbot. In the end, my dad did a fantastic job designing and building the machine, and I think it has some neat features with respect to their simplicity and inexpensiveness that future designs might consider or adapt.

Overall, the design probably cost around $200-$300, all said and done (minus the 5lb spool of ABS plastic). We built 2 sets of makerbot electronics for about ~$225 (so, around $100 for one set), probably spent around $100 on extruder parts like the motor, barrels, and things (these have become pretty expensive as of late from makerbot... I think our first extruder using bits from the RRRF was probably only $20 or so :) ), and finally there's probably about $50 of acrylic for the sides and z-axis. We had some $5 steppers hanging around for the X and Y axes, where the slides were taken from matched sets of old inkjet printers, and the Z-axis stepper is from an old plotter.

Probably the neatest aspect of the design is the Z-axis. It's a "cigar box" design, and is almost entirely made out of acrylic. The essence of the design is that a large rectangular piece of acrylic moves up and down along the Z, sandwiched between several other pieces of acrylic. A single threaded rod is used as a lead screw (compared to four threaded rods with the Makerbot design), and the MK4 extruder mounts to the Z using a right-angle bracket. The advantages of this design compared to the traditional makerbot design are that it's likely far less expensive to produce and requires far less parts (no timing pulleys, belts, and one quarter of the lead screws and nuts), and as such is probably much easier to align, too. If you laser-cut the parts, you could probably have a simple design that would cut out on a single sheet, and end up with a complete Z-axis that you could bolt together fairly easily, as well. The disadvantages are that the design needs to be able twice as tall as your maximum build height, but that's not too bad at all if you only have 6-7 inches of Z travel -- infact, its probably about the same height as a makerbot right now).

Other bits of interest include the build chamber and the magnetic heated build platform. The build chamber currently isn't actively heated, but from the heated table and a fan on the variable voltage regulator, it gets up to around 40°C while building. The nichrome wire for the heater barrel is 8 ohms rather than 6 ohms, to give a bit larger heat zone, and we run it a bit higher than 12v. The table has four 2 ohm (25 watt, I think -- from memory) power resistors, and it's fed with about 18v, and heats up to 100°C in a couple of minutes (it's very fast).

I've included bunches of pictures below. As always we're happy to hear comments or questions.

The build was the 'tin-tin' rocket from thingiverse, which I figured would be a particularly challenging raftless build given that the only contact points between the table and the model are three ~2mm points. (I paused and added a little tape to the build at one point, and held it in place near the very top scared that it would fall off, but I really shouldn't have done this because it was doing fine and now the top is a bit funny... :) ).


(click on the thumbnails for larger pictures)















































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thanks for reading! :)

peter
[peter's website]

Thursday, April 15, 2010

 

Hydra's First Print!

So after working ~30 hours on this project over the last 3 days we finally printed a part on the Hydra platform! Some details on the print:

Printing speed: 40 IPM
Stepper driver movement method: Half-stepping
Resulting resolution: 0.00125"
Printing medium: ABS plastic
Nozzle temperature: 240C
Print bed material: plexiglass
Firmware: Hydra-MMM v1.4 (to be released to the public soon)
Host Software: Hydra-MMM v1.3 GUI
Gcode generation software: Skeinforge
Total time for print: 9 minutes

And without further ado, here is a picture of the test print in progress

A YouTube video of the print is here: http://www.youtube.com/watch?v=V-_Qu8GxbtI

We were actually able to extrude the top layer of the dodecahedron just fine which was surprising from past experience. I think our extruder speed is a bit on the slow side so we are actually stretching the filament a bit as the machine moves from point A to point B. This stretching effect puts it in tension and allowed to to span the void across the top of the object without drooping down into the interior of the part. I suspect that voids up to ~1 inch would be possible to span at the moment with further gains possible using active cooling or from further tweaking of the print speeds. You can also see from the video that we have a heated platform setup, but it was not used for this print as we are still waiting for our 1" wide roll of Kapton tape to arrive.

First impressions of the part were very impressive. The machine has incredible accuracy and rigidity compared to my first repstrap I built using a belt drive mechanism with a threaded rod frame. We still need to figure out how to get Skeinforge to vary the start point of each layer. For this print, each layer started in the exact same spot so we have a relatively prominent seam on the side of the part. I know the setting exists, but Skeinforge is a little cryptic and every time we think we found it, we export the gcode and the problem still persists. We got it to vary the start point on the base layers, but the walls all started at the same location. We will keep investigating, but if anyone knows a solution feel free to shout out in the comments! Even with this problem, the surface accuracy was astounding, but should probably be expected with a machine as accurate as Hydra. I can't wait to add some microstepping drivers and see if we can improve the already impressive 1.25 mil accuracy that we have with half-stepping.

As far as the software and firmware, this was the first real test of the Hydra-MMM firmware and it's handling of the stepper-driven extruder. Up until this point, most of the testing centered around X, Y, and Z moves. For prototyping, the extruder stepper motor is added and needs to be controlled by the firmware. The Hydra v1.4 firmware has the ability to independently move the extruder motor, which is useful at the start of a layer when you want to get the filament flowing before moving and at the end of the layer when you want to pull the filament back and stop the ooze. Before starting each layer we moved the extruder stepper forward a few steps to get the filament to start coming out of the nozzle before beginning the XY moves of that layer. This helped ensure that we didn't have any gaps in the part where the plastic wasn't being deposited. Currently, the extruder motor speed is defined by a variable E_STEPS_PER_INCH, which was first found theoretically and then slightly tweaked to match the real work results. We simply varied the number until 1" of movement resulted in 1" of filament being printed. This number could be decreased to stretch the filament (smaller filament) or increased if you wanted a thicker extrusion. Changing the feedrate of the XY moves will change the speed of the extruder motor to match this velocity, but the relation between these two remains constant. Later versions of the firmware may allow for variable speeds of the extruder motor, but at the moment the results are good enough that I am not sure this is required.

We will hopefully be getting the heated bed up and going tomorrow so we may have some better prints to show off, but in closing, we also printed a traditional test object on the machine before shutting it down for the night. Cheers!


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Thursday, April 08, 2010

 

Starting a new online store for Reprap electronics rep-up.com



I am posting about a online store my son and I are starting called rep-up.com Our goal is to sell Reprap and Makerbot electronics and parts. In order to try and fund this startup we have started a kickstarter project which you can get to at www.rep-up.com for now. Any body looking to bid this is for the US only because of shipping.

Our goal is to focus on boards and kits right now.

 

Mini-Mendel is built and working!

I built another child machine, this time a Mini-Mendel:


For some more details and pictures, see my blog post here.

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Monday, April 05, 2010

 

Hydra Takes Its First Steps!

So I have been way behind on the blog posts over the past week, but we just hit a pretty major milestone with the Hydra multi-headed manufacturing machine project. The mechanical construction for the cartesian positioning system was finished at the end of last week and all of the major parts we were waiting on had also arrived by the weekend. Many many hours were spent over the weekend to get all the motors, couplers, electronics, and software working as desired. I'll go into more detail below, but for the impatient ones, here are some pictures of our progress

Close-up of the Bosch Colt router mounted on our Z-axis assembly. The router fits very snuggly in it's custom mount and appears to have some very impressive runout figures. You can also see that a second support was added to the Z-axis to help prevent it from wobbling. The additional of 2 more sleeve bearings definitely made the assembly more rigid.

Overview of the whole machine with all the motors mounted and electronics wired up. Taking a piece of advice from Tony Stark, we decided to run before we could walk and attempted some simple milling. A small piece of low-density wood was mounted to the table and cut using a general purpose dremel cutter. The Gcode was written by hand and tested using the Hydra-MMM host software file previewer before being sent to the machine. The cutting path was very simple, but it proved that the machine worked and that the spindle was more than capable of cutting these low strength materials. We then moved on to bigger fish...

Attempting some PCB milling using PCB-Gcode and some Eagle board layouts. A piece of cheap double sided copper clad from radio shack was mounted on the table and the Drewtronics 45 degree bit was used for the cutting.


If you want to see a video of Hydra doing PCB milling, I posted our first attempt on YouTube so you can see how this thing performs: http://www.youtube.com/watch?v=1v6gg4_JAmI


The final result of the PCB milling. The PCB drill bits from Drill Bit City have not arrived yet so no holes were drilled, but the accuracy of the traces was very promising! By the way, in case anyone was wondering, the board is a PIC stepper motor driver that I designed similar to the ones I posted about a week ago.

So now to the details...

There were a couple big setbacks that kept the project from doing any cutting earlier in the weekend. The first, and most dangerous was the fact that the couplers we had made to connect the motors to the ACME screws were slipping. The set screws we had used weren't holding well enough and the screws were simply tearing up the surface of the ACME screw shafts. To fix this we made the couplers have double set screws (one on each side) and also filed a D-face into the ACME screw shafts so that one of the set screws could grip that instead of the round surface. This seemed to solve the problem, however, we have also added some loctite to our shopping list as I have a feeling the vibrations from the motors are the culprits here.

The second hurdle was figuring out how to mount different materials to the work table. The intention had always been to use some type of clamp set with a wide array of tapped 1/4-20 holes, but we hadn't really thought much about how long this would take. We ended up drilling and tapping 49 holes (7x7 with 2" spacing) in the 0.25" thick aluminum table. This was no small task and took a pretty long time especially for the tapping. The end result looks very professional and has more than enough strength to hold the parts we intend to machine.

Finally, there were some minor issues with the electronics as well that will need to be addressed before further testing is performed. The stepper motors we are using have a 2.5 Ohm resistance per phase. If they are being run in a unipolar configuration, this means there is only 1.25 Ohm resistance from the coil end to the center tap. We are running the motors from a 5V supply which means we are pushing about 4 Amps per motor. The motors are only rated for 3 Amps so extended operation at these conditions may very well damage the motors. However, the larger concern is the fact that we have 5 motors that are each drawing 4 Amps. That is 20 Amps just for the motors! This is causing some serious heat issues within the electronics. The plan is to add some TO220 power resistors to decrease the current draw to around 2 Amps and add some heatsinks to boot. This will have to work for the time being as I am still having trouble getting my a3982 motor drivers working. I actually got one to work for about 30 seconds, but then I started to increase the current and am pretty sure I ended up blowing the chip again. No idea how I am doing this as I am using the exact values the reprap stepper driver v2.3 circuit is using and I have checked them against the a3982 datasheet and it shouldn't be possible to exceed 2 Amps current output. Not sure how it's happening, but the chips keep dying so I may have to look at some other alternatives. The Pololu a4983 stepper drivers with microstepping seem very nice at inexpensive as well. If I can't get my own circuit working, I will likely end up buying a few of those.

It's been a long day, so that is all for now, but we are hoping to have the extruder working by the middle of the week so keep an eye out for some more updates!

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