Problems with first few layers, and top layer

I reacently been getting some quite good prints on my mendel90 with a variety of layer heights and two nozzle sizes (0.5mm and 0.35mm), however with all of the prints I've experienced a problem with the first few layers, as they all seem to to slightly too large. The prints all have a first layer about 1 mm larger than the rest of the print, quickly tapering (after the 3rd layer) to the correct size. On the most part this is merely a cosmetic annoyance. However, on attempts to print gear bearings, it means that they wont turn, as the inner gears are, at their base, wider than they should be.

I've tried re-calibrating bed height/ leveling the bed, without any success, and tired a few different parts all with the same problem. I've lowered the first layer line width to 100% again little improvement. Any help would be greatly appreciated. Pics are attached. (as you can see the bottoms are all slightly curved out, straightening after the 3rd layer)

I've also had some problems with the top layer of my prints, as it seems that my printer just suddenly stops finishing filling in the top layer completely seconds before the print should finish. Any ideas on how to solve this?

The shrinking first few layers is a sign the bed is too hot.

Not sure why it stops too soon. What does your end.gcode look like and what host and firmware are you using?

Edited 1 time(s). Last edit at 04/04/2014 06:46PM by nophead.

---

[www.hydraraptor.blogspot.com]

Are you using the fan after the first layer? That will also help with the first few layers shrinking.

---

[www.hydraraptor.blogspot.com]

I had the same experience as you with parts having the first three layers wider than the subsequent layers. They also tapered as you describe. My Z-height was off. The way I proved this was measure the height of an object - I was doing a Wade's small gear that was 15mm high. It measured less than 15mm. So I reset the Z-height (decrease the height) by the difference between the 15mm and the wrong part height. After reprinting the part it was a perfect 15mm tall (+/- 0.02mm depending how firm I squeeze the caliper) and the bottom layers are not flared out. The sides go straight up from the bottom.



Flared bottom part is on the left.

Hope this might help you.

Would the problem with the Z height work the same if my part is too tall? I have the exact problem, but opposite direction. My first few layers are thinner than the rest of my print so it tapers outward as the the print moves up, just every so slightly. I measured my print and it's 0.23mm taller than what is designed. Or is it more of a heat bed issue? I've tried with a warm and cold bed and it seems to not make a difference.

Not sure if I should of made a new post or not, but my problem is related.

Thanks.

---

Printer: Makerfarm Prusa I3 6"
Nozzle: 0.5mm Jhead
Filament: 3mm
3D CAD: Creo Elements/Direct Modeling Express
Slicer: Cura
Printer Interface: Pronterface