Using a Bowden cable on the reprap prusa cold end


This post is to document something that I thought was fairly standard , but after talking to a few people I discovered it isn’t. Some people (I’m looking at you jkeegan) even thought it wasn’t possible. I have been using thin hdpe tubing for some time to enable my extruder to unspool filament by itself.

The benefit of the tubing is that it removes the effect that pulling has on the carriage positioning. The cable has a small washer between it and the extruder, and butts against a 3mm hole I drilled in the handle of my extension cord reel. That arrangement allows all of the pulling force of the extruder to be focused on spinning the reel as opposed to lifting the z axis off of the bed.

I used this setup most of the time I was working with the cupcake, and just set it up again for my gen 6 prusa.

Downsides: it does probably require more torque. You also need to be smart about using as little hdpe tubing as possible, as it seems like the friction scales non linearly. You also want the line to be as straight as possible between the spool and the extruder. My setup in the video is about as long as you want it to be. I could easily see using 10cm of tubing and simply setting the spool on the top of my prusa. That ought to have very little drag compared to the current rig. PTFE tubing might be worth looking into as well

I may end up building a bracket to allow mounting the reel on top. That seems like it would be a pretty manageable setup.

Just because I know someone will end up asking where I got that reel from: home depot is the answer, but you can also find it at amazon here

The hdpe tubing I believe is used for cold water lines such as ice makers. I picked it up at home depot as well.

completely unsorted reflections on building a clonedel


1) Last weekend I completed drilling out my clondel kit and started bolting things together. Here’s a list of things I realized.

2) Having precisely cut threaded rods is nice, but not necessary provided they are longer than spec.

3) Drilling out the metrix createspace clonedel kit is difficult verging on impossible to do exactly. The vertex pieces that require precision don’t have flat, 90 degree sides. Also, some of my pieces varied +- 3mm in thickness. That is a big problem when the piece is 15mm thick, and it’s off in the – direction. I had to do a fair bit of eyeballing on those undersized pieces or else the drill bit would have just ripped through one side. This kit is a lot better than nothing, but the first thing to print is definitely replacement pieces. I also think I have one of their earlier versions judging by the way my z motor brackets look, so potentially they have improved since the first few batches.

4) I scavenged some 8mm rod from two desktop printers. That gave me enough for the z and the y axis. To get the long rods needed for the x axis I think I will probably need 2 more printers to destroy. I’ve been toying with looking into the rods from ikea filing cabinets to see if they are even vaguely straight or consistent. I doubt it.

5) Looking at the printers made me wonder if dc motors could be used with opto-encoders for this project as a replacement for the steppers. I’m not sure what would be the best way to do it, but I’m considering making a “stepper driver board” out of an arduino to see if I can get it to behave as a drop in replacement.

6) It appears like the thin and thick sheet are unnecessary for a prusa. Well that’s nice.

7) I’m looking into using my xylotex 3 axis kit as the stepper interface for this prusa. I think that just means I need to put the mosfets, end stop pins, and thermistor circuits on a shield for my mega and I ought to be good to go.

Nema 17 on the left, Nema 23 (with 260 oz/in of torque) on the right
8) I’ve got 3 nema 23 260 oz/in steppers that would be delightfully overkill for this. I’m wondering if it is worth the trouble of building new brackets for everything. I know that torque does not necessarily equal speed, but I would like to see how fast those would print. I would try the extruder (possibly) and the x and y with those monsters. The z axis doesn’t need that kind of speed.

9) I ended up buying some 8mm linear ball bearings from ebay. 12 for $15 isn’t too bad considering they will last a lot longer than the pla.

10) Using the testing setup of repg from Ben Jackson I have been able to connect to a mega 1280 and a 328. I can’t do much else before it crashes, but at least its a start. Repsnapper seems to work flawlessly with the 1280, untested on the 328.

A Makerbot disaster struck!

I’m not sure what’s been going on with my makerbot, but I don’t like the way it has been progressing! All week long I have been having trouble with my extruder board. I’ve been talking with Matt at Makerbot and he has been super helpful, but we haven’t figured it out yet. It will give me the dreaded “toolhead 0 : not found” error, and once finally connected it will “get tired” mid print and stop heating.

Well… today it stopped heating the extruder tip while printing, then it snagged on the print, bent the brass tube, and the hot end snapped off of the mount with a little flourish!

broken makerbot hot end

I’m going to try to find the drawings for the plastic mount piece that broke. Thankfully that ought to be easy enough to make by hand. After that I have to say I’m at a loss as for what I can do to prevent this from happening again. This is why they call it DIY. I just wish sometimes it was more “doing”, and less “yourself”.

$10 DIY Makerbot filament spool

I can’t believe it took this long, but I finally had a bad filament tangle last week, and a few aborted prints because my old setup wasn’t working. I really needed to get my filament spooled so that it would nicely dispense, and not jam, tangle, or unspool.

I really love the way the official makerbot kit looks, and I bet it really works smoothly. I just don’t have $90 sitting around. I’ve already spent that on ABS, relays, arduinos, and prusa parts!

I went down to the old Home Depot and picked up a cheap ($8) extension cord spool and a few feet of nylon water tubing. My extruder hasn’t had any trouble with its grip, so this creation has the extruder just pull the filament off the spool. I drilled out the handle and carefully spooled the ABS on the spool. THAT took a while, but it’s way better than having to constantly babysit the machine.


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Makerbot extruder fixed!

It all came down to this…

When I assembled the extruder (makerbot mk4) the allen wrench that came with the kit never felt right. Regardless I tightened the set screws on the gear until the allen wrench felt like it was about to strip it, and then I went on my merry way. After watching my extruder not work for the last few weeks I finally:
1) rebuilt my hot end
2) put longer leads on the thermistor and nichrome so I could move the extruder board out of the way
3) put a light on my table next to the maker bot, and
4) noticed that the motor shaft was spinning but the gear was not!

So I disassembled the extruder, found the RIGHT sized allen wrench (1.5mm maybe?) tightened everything down, and I was on my way! It’s frustrating that it took so long to figure it out, but I’m so glad that I finally did. I spent the morning printing out an accessible wade’s extruder and playing around in skeinforge.

I wasn’t able to print out the small gear on the wades extruder no matter what I tried. It always ended up getting eaten by blob monsters. I eventually figured out how to use the multiply feature in skeinforge and printed out 9 of them. With no raft to boot! The no raft thing was only cool because I figured out how to do it, but in the end three or four of them broke free and were garbage.

That last pic is what I was really surprised with. I have never printed without a raft before, and I was really happy with how flat and smooth the surface was. One more thing pushing me towards building that heated bed!

assembling a metrix createspace molded wades extruder

I recently bought a molded reprap prusa mendel kit from Metrix create space. They are a hacker space in Seattle, Wa. The molded kits cost anywhere from a third to half of what a set of printed parts cost because they take far less time to produce. One downside of the printing method is that parts will end up sloppier and require some more post processing.

Here is what the base looked like as it arrived.

Here is the other three parts, unprocessed.

The next picture is where you can start to see the disadvantages of this method. There is a lot of plastic on the bearing holder (purple) that needs to be cut away, and you can see the way that the miniscus on the big gear has made the entire gear cupped. I want to clearly state: none of those are deal breakers. This is a great deal, and even the RP parts require a fair bit of processing. I was surprised when these parts came in, but after thinking about it I don’t think I should be. They appear to be functional, and that’s all that really matters to me. As long as they last long enough to print their replacements, I’ll be happy!

Hit the jump for how to build it!

Makerbot down! We have a makerbot down!

I’ve only had the makerbot for a month now, but it’s refusing to print. Sigh. I know it’s a diy kit, but this little puppy only had three whistles printed on it before it rolled over, ready to die. Here is my thought process as I go about trying to fix it.

Symptoms: The extruder would no longer extrude. RepG registers 220 and the hot end seems to settle nicely there. The motor turns on but nothing comes out. I have a mk4 extruder and was in the process of printing a wade’s extruder when the symptoms started (do you think it got jealous?) If I grabbed the filament with pliers then I could push plastic out the tip, but it also squeezed out between the pfte insulator and the brass barrel.

My Diagnosis: After adjusting and re-adjusting the difficult pressure wheel on the mk4 I settled on the idea that the tip must be partially blocked or not hot enough. I took it apart and broke the brass barrel in two. Then I made a new barrel out of a bolt and bought a new barrel (two path approach!)


Here you can see that the nichrome wire has burned/melted the kapton tape. Is that normal?

Results:
None good. The stock barrel behaved exactly the same. It would flow, but weakly and only with considerable pushing on my end. The new hot end I made fared about as poorly. I tried to re-use the nichrome wire from the original hot end build, but at some point it had burned off its coating and this was very problematic.

Next steps:
1 – rebuild stock barrel/ptfe combo
2 – test resistance of nichrome on new barrel
3 – buy and build wades extruder
4 – use both extruders on mk4 setup to see if it is the hot end, then swap in the wades extruder to see if it is the motor.

Drilling out a bolt – the hard way

After breaking my makerbot extruder head I decided I wanted to try my hand at making one from scratch. It’s a brass m6 tube with a nozzle screwed onto one end. How hard can it be!

It turns out it’s really hard, but I ended up having luck with a technique called the “afghan lathe”

Before I get too far into it I need to explain that most bolts are made of hardened steel. To de-hardened them all you need to do is to get them red hot with a blowtorch and let them cool slowly. Here is a pic of me doing just that to two m6 bolts.


After your bolt has cooled, it should look something like this.

Start out with a drill press, a vice, some c clamps and a drill bit. Put the drill bit lightly into the drill chuck backwards. Lower the drill press until you can grip the drill bit in the vice (which should be sitting on the drill press table) Clamp the bit in the vice, and the vice to the table VERY securely. Release the chuck on the drill press. Now you are going to take the bolt that you de-tempered and put it in the chuck. I left the head poking out. That will make it easier to get a good straight grip on it. Tighten everything down and grab some machining oil.
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Announcing a new habit – Makerbot!

Due to a long and strange twisting string of circumstances I recently ended up with a makerbot kit at work. I have a build video and a lot of info, but here is the first of two quick posts about my trials and tribulations with this little guy. This is more a question to the world, as I am having a terrible time finding answers for it.

I built the bot and printed a whistle within a few hours. Everything seemed copacetic. A few weeks went by (in which I got to go to nyc resistor and meet Bre) and I came back to the bot to print something. It was just not working right. It would extrude for a little bit and then stop, and I could force it to restart and then it would stop again. I’m not sure if the extruder was bad, or the tip was blocked, or the software was just messing up. I took apart the hot end to check for blockages, but I didn’t heat it up fully before disassembly.


Well, this happened. I had two wrenches, one on the shaft and one on the extruder tip. I was trying to unscrew the tip after drilling the plastic partially out of the barrel. And then the brass tore in two. I eventually hit it with a very hot hot air gun (not a hair dryer) and got the plastic to melt out and then I was able to unscrew it easily. So the moral of the story is to always clean out the tube before attempting to unscrew a hot end.

Then I ordered parts from makerbot, assembled the parts when they came in, and still had the same problem! My bot will print out the beginning of a raft if it is warmed up enough, but then it stops extruding and just wiggles around for a long time, not printing anything.

In possibly related news, both versions of the extruder have seeped plastic from above the fender washer. See a picture below. You can see a plastic piece that looks a bit like a leaf coming out of the left side of the washer. In my mind this means that my motor is pushing the filament according to plan and the tip must be blocked.

I just can’t see any reason why my brand new tip would be blocked when I could see light through it!

Well, I’ll put the answer here when I find it. I have a wade’s extruder and a new hot end on its way. Possibly those will fix it. Possibly not. I will also have an upcoming post on making a new hot end, and the Makerbot Cupcake making of video.