Minimug, Second Attempt

For my next print, I thought that I’d re-do the minimug, see if it printed better this time.
Reprap, fun for kids of all ages

As you can see from the photos, the bottom started out fairly badly again, with some random strings not sitting on any supported surface. However, once a decent base was provided, the middle layers printed beautifully, absolutely perfect.

Completed Minimug
I think that one of the problems I’m having is that my strand thickness isn’t quite wide enough, or not as wide as SF thinks it is. Thus, when doing the top and bottom layers, the filaments don’t always sit on top of each other, and drop off into space.

One thing that I don’t like about this design is that it prints sideways. I don’t think that’s optimal for an object of this shape. I’ll try and find another minimug that prints vertically. I suspect that it should turn out fairly well.

I can see that my main target for the next few prints will be to try and establish a better base. If I can get the base off to a good start, then the print should be nearly perfect. I think I’ll also bump the strand thickness up from 0.6 to 0.7mm, see if that helps. I’ll also bump up the hot end temperature by 5 degrees, to 235, to help the layers stick a bit better.

Second Print

Last night, I tried doing another print. This time, I went for a 20x20mm calibration cube from SpaceXula’s Thingiverse page.

This was also my first print with the Pyrex base. As you can see in the photos, it’s got a lovely floral motif on it. Luckily, this motif’s on the bottom of the plate, so there’s no interference with the print.

The main problem was starting the print off. I had Z-level issues again, and it took a little while for the filament to start coming out of the hot-end and start sticking to the bed. On the first couple of attempts, the tip was a little bit too low, and it picked up the Kapton tape, so it’s looking like a bit of a mess, already. Fortunately, I was able to get a good start on about the third attempt.

Once the print started well, the rest of the print went perfectly.

This print was vastly more successful than the previous one. The size was less than 0.5mm out from 20mm. and the Z-layers were perfect. The only problems are the slight lean, the cause of which I’m not sure of. While it was on the bed, I didn’t check to see which axis it was, so I’m not sure whether it’s X or Y.

The top was also not quite completely filled in.

Overall, though, it was a fantastic print. Much better than I thought I’d be able to get at this stage.

Final Assembly, and First Print

With the extruder completed, the only job remaining is to hook up the extruder motor and the hot end to the electronics. The new wire-stripper made that a much easier job.

 
Connecting up the hot-end

 Molex connector for easy removal
One the extruder and hot end was complete, I removed the hot end, so that I could do some extrusion calibration. Whilst some default values for Wade’s extruder are known, Greg hasn’t provided any starting values for his extruder. I started out by doing some 50mm extrusions, and calibrating using Prusa’s calculator. Once that was done, I reconnected up the hot end, and put everything together. The printer was complete!

  Finally complete

I started off by doing a few extrusion tests. They went well to start with, with the hot-end warming up, and spitting out a line of filament. I then tried to set the Z-value of the tip. Then the printer started acting strange. The Z-motors were going crazy, not spinning enough. Spinning up, then down. I couldn’t figure it out. I went to the IRC channel, but no-one was interested in helping today.

Not sure what else to do, I started fiddling with the Z-connector on the board. Sure enough, with some fiddling, the Z-motors would either work perfectly, or not at all. I took the connector off, to have a look, and discovered that one of the wires had broken inside its sheath. The intermittent connection of the wire was causing the erratic behaviour. I cut the last couple of centimetres of the cable, re-stripped and re-connected them.

The Z-nuts also kept falling out of the bottom of the Z-carriages whenever the printer was supposed to descend. I think that the problem is that the bushings are a bit too stiff, and the Z-carriages aren’t sliding smoothly along the track. To solve this problem, I glued the nuts in place, to make it easier for the carriages to come for the ride. Travelling upward’s isn’t as smooth as I would like, either. I think I’ll put a little bit of lithium grease on the Z-rods, to smooth out the travel there.

Once those issues were fixed, I tried doing a print, starting off with the standard Reprap minimug. However, I ran into more issues right away.

 
Extrusion Test

The extruder was frequently locking up. It would only turn for a few seconds before it would stop. Having a look at it, I found out what the problem was. With Wade’s design, the extruder turns so that it has the effect of loosing up the nut on the far side of the extruder. This is compensated for by using two nuts. Greg’s has the opposite problem. Because it turns in the opposite direction to Wade’s design, it tightens up the nuts. It keeps on doing this until the extruder binds up from the force of the nut.

I got around this problem by taking off the standard nuts, and replacing it with a Nylock nut that a lot less prone to movement. Hopefully, this will fix the problem. I then tried to print the minimug again. To increase the chance of success, I decided to add in a raft in the Sfact settings. The print started off badly, with the tip dragging through the kapton tape on the heatbed, due to being too low in some places, but then went to the centre of the print bed, and started printing at just the right height.

The raft went down perfectly, with sharp lines, and stacking nicely. However, after that, things starting going downhill. It started to print some of the minimug off the raft. It kept printing, but it was messy, as strands were just loosely dropped on top of each other.

At least the raft looks good

After a while the extruder stopped extruding properly, it was hardly outputting any filament at all. At this point I stopped the print, as it was failing badly. I then had a look at the extruder, to try and nail down this problem. It puzzled me for a little while until I realised that the small gear was turning freely on the motor shaft. I tightend up the grub screw. Hopefully, it’ll work for a while. I intend to file some flats on the motors, but unfortunately, our machinist at work has broken his hand, making it hard for me to use his help.

My main problem is that the heatbed just isn’t flat, and when it’s not flat, then you can’t get the tip close enough to the bed. I also don’t like trying to set the Z-stop when the tip is so close to the bed. It takes quite a few tries to get it so that it’s ‘just right’. I’m tempted to inverse the Z-stop, set it as an upper limit, then use the software to set the lower limit of travel. That would probably work particularly well with using Nophead’s idea of the magnetic calibrator.

 Minimug. Theoretically, anyway.

I was going to take the heatbed off, and just print on the upper steel bed, but my wife Cathy suggested that I could use one of her glass trivets. Given that it’s designed to be used as a trivet, it should be made of Pyrex. In any case, she wasn’t stressed if I broke it, as she doesn’t like it.

So after a lot of work, and a lot of problems encountered, I finally got the printer to print – something. Hopefully, I’m over the hump for the physical issues, and I can just tackle calibration for now. I think for tonight’s print, I put the minimug on the back-burner, and do a calibration cube, see how that turns out.

New Wire Strippers

Building the printer over the last few weeks, I’ve had to strip a lot of wires. It’s been a real pain to use the crimper / stripper that I’ve had for the last few years. It strips wires, but it’s slow and finicky.

When I was in Countyco last week, looking for a 1mm allen key, I saw these wire strippers for $20. I didn’t think much of it at the time, but after stripping a few more wires over the weekend, I thought that it might worthwhile.

I picked this up this afternoon and stripped a few wires for the hot-end as soon as I got home. Wow. Dead easy and does a perfect job in seconds.

If you don’t have one of these yet, and you’re doing a reprap build, run out and buy one, now. You won’t be disappointed.

Greg’s Hinged Accessible Extruder

Since my Arcol hot-end doesn’t attach to the default Wade’s extruder, I had to go searching around for a new extruder. One of the Australian forum-goers suggested contacting Greg Frost, to print me up a new part. I contacted Greg last week, to get him to print me out a new base for the Wade’s Extruder. However, he quickly upsold me one of his Hinged Accessible Extruders. It arrived in the post today, to my great joy.

Greg’s Parts

The most noticeable thing is the difference in quality between Greg’s parts and Nophead’s. Nophead is justifably famous for the quality of his parts, so having a look at Greg’s gave me a better idea of what is achievable by us mere mortals.

Unlike Nophead’s parts, Greg’s parts came ‘raw’, so they needed a bit of work with a knife and drill to tidy up before the build. This gave me a good chance to have a look over the parts and the design. Greg’s design is very interesting, with some definite improvements over Wade’s. As seen by the name, the improvements are aimed towards accesibility. This is very noticeable with regards to the filament access, but it extends to all other aspects of the design.

With Wade’s design, there’s a lot of bolts which are underneath other bolts, which basically means that you have to disassemble large amounts of the extruder to work on other parts. This is noticable with the X-carriage mount. To get to it, you have to remove the motor. To remove the motor, you have to remove the hobbed bolt and large gear. And that’s the first mount. Greg’s design fixes nearly all of these problems, particularly with the innovation of the angled motor mount.

Once all the parts were clean, and the kids were in bed I got to work, assembling the extruder. Greg hasn’t released any instructions on how to assemble his extruder, it has to be done by inference from the photos on Thingiverse. If you’ve assembled a Wade’s previously, then it’s pretty easy, but if Greg wants to make his extruder more popular, then it will be assembled by some people who haven’t assembled an extruder before, and they’ll need some instructions.

One very annoying thing with the build was that the M3x10 screws that are used to hold the motor to the frame in Wade’s no longer work. Unfortuately, I was out of 20mm screws, so I had to take three 20mm screws out of my Nophead’s Z-couplings, replace them with 25mm screws, and then use the 20mm to hold the motor on. Even worse, these didn’t work! With one washer in place, the screws bottomed out on the motor, leaving the motor loosely fitted to the frame. I had to add in a second washer in to make it fit correctly. This is definitely an area that could be improved with the extruder.

A major problem was with the hobbed bolt. The hobbing on the bolt I have is very narrow, only about 3mm wide, but it lines up perfectly on Wade’s Extruder. However, on Greg’s it was quite a way out. To make it fit, I had to put 3 washers between the big gear and the extruder, to push the hobbing across. Even then, it’s ever-so-slightly out of alignment, about 1/2 mm. Hopefully, this won’t cause any issues.

Once all together, the bolt was pretty stiff, and turned slowly. Hopefully, the stepper motor will have enough torque, and this won’t end up being a problem.

The next problem I had was that I didn’t have enough short 4mm bolts to hold both the extruder to the X-carriage, and the hot-end to the extruder. Luckily, with the new extruder, I had a couple of very long 4mm bolts extra, since the Hinged Extruder doesn’t need the four spring-loaded bolts (just one) that Wade’s does. A short bit of hack-saw work later, and I had a couple of extra bolts handy. One downside: These bolts don’t have a screw or allen-key attachment, so they were slow to attach. I had to slowly tighten the bolt with a pair of pliers.

 

Once the Arcol was attached, I then realised that I’d need to remove it again, so that I could calibrate the E steps / mm for the extruder. Argh.

After it was all together, I decided to call it a night. All I need to do now is connect up the hot end to the electronics, then I’m good to print. I should be able to get my first print done tomorrow night! Minimug, of course.

Software Update

I’m still in ‘waiting mode’ at the moment, so in preparation for eventual printing. To help get everything ready, I thought I’d update the software. It’s only a month old, but a month is a long time in Reprap, particularly with the software.

I went and downloaded the newest version of Pronterface. It doesn’t seem to be much different from the old version, but will undoubtedly have some improvements.

I’d also heard about the fork of Skeinforge, called Sfact. It doesn’t seem to be covered in a lot of the reprap documentation, but it was definitely worthwhile finding. It’s a simplified version of Skeinforge, with a lot of the unused options removed. It’s even got a simple configuration page, where the most common options are set. It definitely makes life a lot easier for a newbie like myself.

I also went and downloaded the lasted version of Sprinter. I went through and put in the correct configuration settings, ready to go.

That’s one more thing out of the way.

Heated Bed Build

Since I can’t do anything with the extruder / hot end at the moment, I thought that I’d set up the heated bed today. I was originally going to wait to do this step until after I had done a few test prints, but I thought I’d save myself some effort later, and do it now.

As with the hot-end, the biggest hassle is getting the thermistor set up. I hope these last a long time, since they’re such a pain.

Thermistor

After the thermistor was set up, I stripped some wires. One set went from the electronics to the PCB. The second went from the second ramps supply to the electronics. I took the time to silver all the bare wires, to stop them from fraying. Then I soldered the wires to the PCB. You can see my seriously inferior soldering below:

Power to the PCB

I don’t really need to insulate the PCB from my print-bed, as it’s made of steel. However, I don’t want to waste excess heat and electricity by having the heat escape out the bottom. To that end, I cut two items. The first was a square of cardboard, to act as the main insulator. The second was a piece of Sisalation. This is that paper-ish material that’s used by builders as wall and roof cladding. It’s only $2 a square metre, and I had some laying around, to give it some additional insulation without going to a second piece of cardboard.

All layers together

Once all the pieces were ready, I thought that I’d test the bed before screwing everything together. I wired it up, turned on Pronterface, then set the print bed temperature to 110 degrees. Right away the temperature started climbing on the bed. Sucess!

Testing Setup

To check the temperature, I used both the thermistor and my IR gun. The thermistor generally showed a temperature about 10 degrees below that shown by the IR gun. At first I thought that I had the wrong thermistor in the firmware, but a quick check showed that it was ok. I then realised that the thermistor was cooling down too quickly in the open air.

Test in progress – working

With the test successful, I screwed the base down to the printer, then covered the PCB with a layer of Kapton, to enable easier removal of the printed pieces.

Mounted PCB

Once the PCB was fully mounted, I fired it up again. This time, with the thermistor between the bed and the cardboard, it was more insulated against heat loss, so it showed exactly the same temperature as the IR gun. The electronics did a good job of keeping the bed at temperature.

Final Test – Bed up to temperature!

A problem with the heated bed is that it’s not completely flat; it’s got a noticeable bow to it, particularly when mounted on top of the cardboard. Most seem to solve this problem by having another surface on top. Many are using Pyrex glass sheets, so I think I’ll order one of those, and attach it to the top of the PCB.

Axes Alive!

I finished wiring up the axes yesterday, so I thought I’d plug everything in and give it a test run. Just about everything worked first go!

All the endstops worked, and all the axes travelled, with the sole exception of the Y-axis, which travelled in the wrong direction. After flipping the connector around that axes was working correctly, too.

I noticed that the axes were running into their stops at the non-endstop end. I figured that the maximum travel distances were incorrect. So I measured them up accurately, then went into the firmware and made the following changes:

const int X_MAX_LENGTH = 170;
const int Y_MAX_LENGTH = 170;
const int Z_MAX_LENGTH = 88;

after which the printer then would correctly stop at these limits. I recorded a short video of the printer homing:

Once this test was done, I wired in the extruder and gave it a test, which was successful as well. I didn’t bother measuring the steps / mm for this extruder, since I’ll be changing it next week for a Greg’s Hinged Accessible Extruder.

There’s not much else I can do on the printing front until I can get the extruder and hot end sorted out, so I’ll have a look at the heated bed, try and get it set up as well.

Strong Stepper Motors

 

In various classes they teach you that there’s no real difference between motors and generators, it just depends on which way the current is flowing. This short video really shows that principle, as well as the strength of these little stepper motors.

I was trying to level out the X-carriage yesterday when I noticed this effect. These motors are completely mechanically separated from each other. They’re just connected electrically, through the connector block you can see in the middle of the video. Turning one of the Z-rods turns the other, with a surprisingly high degree of efficiency.

Electronica

Now that the hardware’s finished, it’s time to wire up the electronics. One annoying thing about my stepper motors is that they only have short wiring, which doesn’t allow them to reach all the way to the electronics from every location. I’ll have to extend a few wires, which will be annoying.

Z-motors connected together

First motor connected up
I tried putting the electronics in various locations, but it turned out that the bottom-left corner had the best combination of tidiness and short cable runs.

On a lean

I zip-tied the electronics to the frame, to stop them from wandering. Unfortunately, it’s on a bit of a lean.  Once the printer’s up and running, I’ll print up a tidier box to put the electronics in.

The endstops were then screwed on, and attached to the electronics as well. I just need to extend the wires for the extruder and the z-motor, hook them up, and then I’ll be all finished!