Tag Archives: calibration

Calibration

Even though the first print turned out very good, I knew that there was a lot of improvements to be made, so I did some calibration.

The guide I used for calibration mostly came from the 3D Nation guide. The primary steps I followed were:

  • Extruder rate
  • Extruder PID
  • Temperature Tower
  • Retraction Test

The extruder rate calibration was pretty easy, removing the Bowden tube from the extruder and measuring the feed on 100m samples. I ended up having to adjust mine by about 0.5%. Commands use were:

M92 E400 - Set rate of extruder to 400.
M500 - Write this setting to the EEPROM

Next up was the Extruder PID calibration. Fortunately, the Marlin firmware makes this ridiculously easy with the following command:

M303 E0 C8 S210

and then taking a note of the outputs. For my printer:

Original PID Settings:

Kp: 26.27 Ki: 2.49 Kd: 69.41

Final PID Settings:

Kp: 22.37 Ki: 1.81 Kd: 69.18

Which are then set using the command: 

M301 P22.37 I1.81 D69.18

The temperature tower was the next test, which was pretty easy, given that you only have to load up some gcode and hit ‘print’

As you can see from the image, the filament I have works best at between 195 and 200 degrees, which is pretty typical. You can also see that the printer seized up at bit on the 185 and 190 degree layers. This was just a bit of binding on the z-axis leadscrew. Putting some lithium grease on the leadscrew solved that problem.

The next test was retraction. This one gave me quite a few issues. Overall, the print turned out great, but I just could not cure the slight stringing issue between the two towers, no matter what my settings. I’ve just accepted that this cheap filament is just a bit too stringy to be fixed. The stringing is extremely minor, and very easy to clean up after the fact.

Here’s a comparison of the same piece – after (left) and before (right) calibration. As you can see, big differences. The new print is essentially perfect. Not really sure how to improve this much further.

and another print of a puzzle box, which also turned out great.

More Ooze Fighting

Unfortunately, I didn’t have much luck getting help for my ooze problem in the Reprap forums. The only respondent suggested that the best way to fight it is to replace the hot-end, with a J-head nozzle.

While I do have a J-head spare, I’m not quite willing to give up on the Budasnozzle yet. I thought I’d sit down with the ‘daily branch’ version of SFact (which has more retraction-related settings), and battle my way through the various settings, see what the effects are.

Here’s my output from my tests:

Retraction settings:

v1 – Use Fixed Retraction
Retraction speed – 13.3mm / s
Retraction distance – 1mm
Restart Extra Distance – 0.1mm
Result – Corner bulge worse than SF default

v2
Retraction speed – 13.3mm / s
Retraction distance – 2mm
Restart Extra Distance – 0.2mm
Result – Even worse.

v3
Retraction speed – 13.3mm / s
Retraction distance – 0.1mm
Restart Extra Distance – 0.2mm
Result – Really terrible – filament everywhere. Did I save the second one correctly before skeining?

v4 – retry v2 again, slow down filament speed to 30mm/s just to get a better idea of what’s happening.
Retraction speed – 13.3mm / s
Retraction distance – 2mm
Restart Extra Distance – 0.2mm
Result – The same as V2. Notice that the Z-axis bars are moving around a bit. Probably need to tighten up X-axis bars again. Maybe print some Z-stabilisers.

v5 – Change settings again
Retraction distance – 3mm
Restart Extra Distance – 1mm
Result – Okay, it looks like the ‘restart extra distance’ is causing a lot of the blobbing. It’s the extra filament that gets fed into the extruder before starting the next section. Take this back to 0, I think.

v6 – Restart Extra distance at zero.
Retraction distance – 3mm
Restart Extra Distance – 0mm
Result – Much better. Internal blobs lowest of all prints. External still higher than default settings. Can you set a negative Restart extra distance?

v7 – Restart Extra distance at -1.5.
Retraction distance – 3mm
Restart Extra Distance – -1.5mm
Result –  Very good. Improved internal blobs even further. Corner blob improved but still larger than defaults

Here’s some of the results from the tests;

While I wasn’t successful in removing the ooze, I’d still call tonight a success. I’ve learnt a lot about SFact’s retraction settings, and feel like I have more control over the machine, in general.

Calibration Time

While my Prusa is printing fairly well, there’s still a lot of room for improvement. My calibration methodology so far has involved just fixing the glaring problems, rather than going through a systematic calibration process and optimising the printer’s performance at every step.

The top two tasks on my ‘to do’ list are calibration related, so it makes sense to tackle them all in one go. Seeing the success that Julian has had with his calibrations has inspired me to sit down and go through the calibration profile described in the wiki.

First off: Thin-walled cube. This one is used to test the layer thickness. As per the calibration procedure, I started off with 0.4mm, working my way down in 0.01mm increments – all at 30mm/s speed. 🙂

As you can see from the photos, they all turned out great, with no issues at all of the extruder tip plowing into the previously deposited layer. SFact is obviously doing a really good job in controlling the extrusion for all these different heights. As the layer thickness decreases, the fineness of the layers becomes extremely apparent.

The one on the left is 0.4mm layer thickness, and the one on the right is 0.31mm.

Stage two was looking at infill.

The first one I ran, I only had the infill solidity at 0.35. It turned out fine, perfectly flat. The second one I turned up the infill solidity to where it was meant to be: 1.0. In this one, there was a noticeable convexity to the top of the print. It was only minor, but quite noticeable.

However, I couldn’t find the setting in SFact that ‘s meant to fix the issue – ‘Infill width over thickness’. This must be one of the settings that been taken out with the move from Skeinforge to SFact. Maybe the best way to adjust this these days is by changing the ‘Filament Packing Density’ – I’ll have to check. Since there wasn’t anything more I could do here, I moved onto a third test – Oozing.

Oozing has been the biggest issue with my printer since I started printing. There’s two main issues that I have. The first is at the ‘uplift corner’. I always get a bulge at the corner where the printer stops to lift up the layer. The lifting up process causes the print to pause for a second. The ‘dribble’ from the nozzle at that point always creates a slight bulge.

The second issue is a more typical ooze issue – ‘fly aways’ at the start and end of exposed ‘towers’. This can be seen very clearly in some of my earlier prints – seen here. These problems aren’t too bad. The results can be cleaned up with a knife fairly easily, but better not to have the problem in the first place.

Unfortunately, I wasn’t able to make any real headway today into this problem. SFact has two main ooze-related settings – ‘Oozerate’ and ‘Filament Retraction Speed’. I fiddled with these settings, as can be seen the above photo, but without any real improvement.

As an additional step, I went and downloaded the ‘daily branch’ version of SFact. This has a lot more ooze and retraction-related settings. I tried a couple of test prints, but again, had no significant success.

I’ll keep trying with some additional settings, but I think I’ll have to go to the forums’ and ask for some help there, get the expert’s opinion.

 

 

Speed Trap

As I commented in Julian’s blog, it’s interesting to see the difference in quality that he gets between the different speeds. I haven’t noticed too much of a difference myself, but I put that more down to my lack of calibration than anything else.

I thought that I’d replicate his three-speed experiment to compare and contrast the results. I used the ‘single-wall calibration cube’ as my test object.

The four speeds were: 30, 45, 60 and 90 mm/s. They’re all looking fairly good up until the 90mm/s one. The main problem there was that the filament was going down so fast that it didn’t give the layer below a chance to cool down before starting the next layer. If I’d had some active cooling, or a larger object, I think it’d have looked great.

I didn’t notice until I’d finished doing these cubes, but my X-Axis belt was slightly loose. I think I could have got them looking even better!

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.

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.