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Meltdown

Total disaster. I updated the SFact with some new settings that I had high hopes for, that I thought would take the print quality to the next level.

I turned on the hot end. After a few minutes I saw that some filament was leaking out of the hot end. Strange. Then I saw this:

The PEEK block has melted into the nozzle. PEEK's meant to have a melting point well over 265 degrees C.

The only cause for this that I can think of is that the thermistor wasn't quite attached to the heater-block correctly. This would then have generated an incorrect temperature reading, causing the electronics to over-drive the hot-end past the melting point of the PEEK.

Unfortunately, the printer's going to be out of action until I can get some parts in to rebuild the Arcol hot-end. While I'm at it, I should make a list of 'critical spares' and consumables that I should have on hand for the printer.

Reprap Shot Glass, Second Attempt

After getting the thermistor working again, I tried printing out the rep-rap shot glass, with the new skeinforge settings. It turned out excellently.

Much, much better than the first attempt. There's still a few problems that need sorting out. In the picture below, you can see some 'sagging' that occured on the right-hand side.

The 'solid' infill isn't coming in as completely solid. Still needs some work here.

The base, however, looks nearly perfect. You can clearly see the join between the two pieces of kapton tape.

A huge improvement. I'm really happy with the printer now. I suspect that I could start to print out parts for the reprap. While they wouldn't look the best, they'd have sufficient accuracy and strength to do the job.

Bases, and Filament Retraction

Since my last printings have worked fairly well, I thought that I'd try and get the base working perfectly as my next goal. So, for today's prints, I thought I'd do some experiments with the printbed and base. I tried to use the Pyrex base both with and without the Kapton tape, and at different temperatures for both the filament and heatbed.

Using the Pyrex base without Kapton was a total failure. The filament did not stick at all, under any conditions. With the Kapton on, I tried using the heatbed at temperatures from 110 to 130, and the extrusion from 220 to 235 degrees Celsius.

I also experimented a bit with the height of the tip above the base, varying it from about 0.1 to 0.4mm. I had a few troubles with this step, as the printer wouldn't always pick up the activation of the microswitch, and keep driving the tip into the base. Having a closer look, it seemed like the switch was occasionally getting caught up on the Z-mount, without actually activating.

I tried for a little while moving the microswitch to the top of the printer, but there's something wrong with the Sprinter firmware. Once the microswitch was in place, with the appropriate firmware settings, the Z-axis would only travel upwards, not downwards at all. After a few attempts at this, I gave up, and returned the microswitch to the bottom. This time, however, I moved it to the right-hand-side of the machine, where it seems to get a cleaner activation, and doesn't get caught on the Z-mounts, like it was doing on the left.

The best results obtained was when I used the Kapton tape, had the tip 0.4mm from the bed (measured with feeler gauge), and had the tip at 230 degrees. For the base, I start out with it set on 130 degrees (so that the surface was measuring 120 +), then turn it down to 110 degrees as soon as the print started.There's not many pictures to show here, as the prints would generally fail almost instantly, or I'd stop them after the first couple of layers.

Once I had the base settings fairly well sorted, I thought then that I'd print a different minimug. This one is slightly larger, and prints vertically, instead of horizontally. I thought that with the new base, and the vertical printing it'd turn out better than the previous minimug.

Not the case, unfortunately, as you can see from the above photos. Watching it closely, it looked like the retraction wasn't working properly. It'd retract the filament when doing a move, then take a fair while (at least 2-3cm of travel before the filament would start coming out again.The base, however, turned out quite nicely.

To fix this problem, I would have to go into SFact, and change the retraction distance. Since I didn't know what would work, I set the value to zero, so I could work upwards from there. Since I was also fiddling with the SF settings, I thought that I'd speed up the printer to the default speed. I'd been operating with it on 1/3rd speed, so I thought that I'd fix that up, see how it went. I thought I'd also try out a different object, the thin-walled calibration object.

 

 

The first couple of tests of this object turned out dreadful, until I adjusted the retraction down to zero. The settings improved things, but I there's still room for more improvement. I went back into SFact and make some more changes to the settings. This time, I slowed down the speed for the first layer, and bumped up the filament extrusion ratio.

Just when I was ready to try out my new extrusion and retraction settings, I had a problem with the thermistor. The electronics was no longer reading a value from it. I've either blown a thermistor (which seems unlikely), or I've got a bad connection. Most likely the latter, but I thought I'd leave that for another day.

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.