Hi all,

My Mendel is running smoothly now. But I'm having some difficulty getting the first layer to stick. I've looked around the blog and other sources and I've got a couple ideas of what it might be. I thought I'd post anyway and bounce my ideas off the collective head.

So my best guess is the temperature isn't high enough. When I heat up the hot tip, I bring it up to about 230-240 and everything runs smoothly. Then I start to print and the first half of the first layer sticks well, but then it starts rolling up and getting caught on everything. when I pause the print, because repsnapper wont update the temp reading while printing, I noticed that the temp has dropped considerably (often to just below 200). the PLA is always coming out fine but it just stops sticking.

My second guess is that my nozzle is to far from the bed. ( I admit I am posting without extensive testing on this one). I have tried a couple different heights. The way I have it set now, the bead is laid down directly onto the bed (no sagging) but it remains undeformed. I have tried it in the past with the nozzle much closer to the bed and the bead is flattened, however, this was causing too much pressure in the nozzle and the extruder stepper was skipping.

Is the bead supposed to be flattened ?

I will try different heights between the two discussed above and hopefully that will work.

As for the temperature, I have a hunch that it is the power kill switch i installed that is limiting the amperage and causing the temp to drop when all the motors are moving ( as opposed to just the hot tip heating up) i have another one rated too much higher values which I hope to install in the very near future.

Any ideas are always appreciated.

May the shwartz be with you.

J.Armstrong

I'm guessing that you're printing on blue masking tape at ambient temperature.

You do want the filament to be pressed to the bed so that it ends up flattened. I like to extrude the first layer at the layer thickness height on heated glass. But, I found that this is hard to do reliably on blue tape. For blue tape, it works better to lower to about half the layer thickness. On Skeinforrge, you can change the feed rate and the flow rate for the first layer. It helps to slow it down to between 1/2 to 3/5 of the speed of the rest of the layer and then lower the flow rate by the same amount. I don't remember this option is present in repsnapper if that's what you're using to generate g-codes.

I adjust the bed height by turning on the tip heater to extruding temperature and waiting for things to expand for a few minutes. Then I put a piece of paper (post-it pad works well) under the tip and home the z. The paper is about 0.1 mm so I nudge the z by +0.1 mm. If you can pull the paper with some light resistance, then you're height is good. If it's too tight, then I raise the z opto endstop. If it's too loose, then I lower the z opto endstop. Then home and nudge the z again and repeat.

You can measure the temperature with repsnapper while printing. If you enable updates, it will do it.

The word from Nophead and others is not to put any safety limits on the power to the extruder heater. The best way to keep your tip safe is to set your resistance if you're using nichrome wire such that the temperature stays below 300C under full voltage. The 6.8 ohm resistor in Nophead's hot end design was chosen for that purpose.

Cheers!

Edited 1 time(s). Last edit at 03/26/2011 05:36AM by brnrd.

I see you are using repsnapper. Check your gcode after you generate the model. In the initial extrude temp set code, for whatever reason repsnapper defaults it to M104 S73.0. Just edit that line to your desired temp (I run 225 degrees so mine becomes M104 S225.0) and you should be ok.

There is also a suggestion not to update temp during printing as it can cause communication issues.

Since PLA flows at 180C I use 200C for the fist layer. PLA holds heat very well and thus I think your issue is too high a temp. Try 200C and see how you do. I als agree that the first layer should be a bit less than your layer height.

-Jay

There are four critical factors: HEIGHT, SPEED, TEMPERATURE and SURFACE.

HEIGHT: Above the bed. This is the most critical aspect. As little as 0.1 mm can make a big difference.
SPEED: Low and slow as opposed to high and fast. With Skeinforge you can set different settings for the first layer. Make it much slower e.g. half as fast.
TEMPERATURE: ABS and bed are both important. With Skeinforge you can extrude the first layer at a higher temperature (maybe as much as 10°C higher) which makes it stick better. And the last factor is the temperature of the bed. With a cold bed you will have problems. You can warm it up with a hair dryer but the best solution is to install a heated bed. This will fix your sticking problem and also allow you to print very large objects without warping.
SURFACE: For ABS kapton tape seems to work well for most people. For PLA glass or blue painters tape.

For PLA your temperature is too high. I print PLA at 210°C very successfully.

If your temperature drops 40°C while printing the first layer then CHECK the GCODE!

Quote
Obi wan kenobi
Luke, use the source!

There is probably a command telling to to use a different temperature.
There is a setting in the software to tell the slicer program what temperature to use regardless of whether you are using the RepRap Host, RepSnapper or Skeinforge to generate the GCODE.

---

Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

What about temp settings to ABS?

Also any documentation on how to use repsnapper?

Thanks reprappers

Yes please.

It seems odd to me that people freely recommend extrusion temperatures, but very few other parameters. Sometimes I see feed and flow recommendations. I've been told a couple times now how critical the first layer height is, but I haven't yet seen anybody recommend (or point to documentation) for what that height should actually be. For speed, we have here a recommendation for half speed for the first layer. Half of what? Then we have a recommendation to use a heated bed, but nothing about what temperature to target. I hope I don't sound like I'm complaining about the advice given. I just want more of it.

Yes please refer to sources or photographs if we want this project to move on.

I have been following Reprap since 2007 (junior year of college) and this(2011) is my first year building it, and after 4 years there is not enough doc. for a newbe like me to follow along yet I have to dig through and directly email folks.

Lets go community! Lets scale it up a notch! Reprap has great potential!

See Adjust the Z=0 in the wiki for first layer height.

See ABS in the wiki for ABS extrusion temperatures.

Half of NORMAL SPEED (i.e. the SPEED you run at when it is NOT the first layer)!

Heated Bed temperatures in the wiki and on nophead's blog.

BTW, I recommend to everyone that can read English that they read nophead's blog from start to finish. He has done a lot of experimenting and documents his results very clearly and thoroughly.

---

Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Thanks Bob for the directions

Wow. Apparently I'm no good at finding information in the wiki. Thanks.

My response assumes that you are using an acrylic print bed, covered with Kapton tape. I have observed that cold aluminum covered Kapton has trouble sticking because the plastic cools too quickly.

Always, ALWAYS clean the surface with isopropyl alcohol. Use the 70% or higher, which has little water content. If you don't you will see spots where moisture and oils from your fingerprints will cause the plastic to float.

I also recommend that you characterize your print bed height. You can do this by fixing a permanent marker to the x-axis, and running it over painter's blue tape. Voids will indicate low spots, and thick lines will indicate high spots. Hopefully, you will see areas where there is relative uniformity. Try and keep your prints within those areas, at least until you have time to level things out. By the way, it is not at all uncommon to have a poorly leveled bed. What is common is to be in denial about it :^)

If your firmware supports acceleration, print speed on the first layer is not a big issue, as long as you begin printing very close to the surface. This is due to the fact that the head moves slowly at the begining and end of the moves, so the filament has time to pin itself down.

One thing about print bed leveling. I was advised to put springs under the bed with screws holding it down. This allows you to adjust the bed from 4 sides and thus have it perfectly level.

see the huxley photo here: [www.techzonecom.com]

The spring screws prevent the head from exerting too much force on the surface if you bottom out during a move, or say, during the first layer(s) print. As far as leveling the bed, the spring loaded screws only serve to level those four points. If you are not using a machined piece of aluminum, or quality glass for your bed, chances are that it bows, sags, or both, to some degree. Printing with a raft can make up for this, assuming that the high and low spots are not very significant, but then again, even the raft has to stick before you can use it.

Leveling the four points is a good start though.