Budaschnozzle issues and thermal compound?

Hi fellow printer hackers,
My first printer, a MM 1.5, is now assembled, mechanically calibrated, but has yet to print anything. It's using RAMPS, Marlin, and a Gadgets3d Budaschnozzle 1.2 hotend (EPCOS 100k thermistor, #1 in Marlin).

Looking at some recent threads about jammed extruders/hotends, dripping PLA, etc, I see where they are coming from, and I have a question.

My first printing attempt was at 185C, and the filament jammed in the hotend's PTFE tubing, above the heated zone itself. After some research, I saw that ultimachine was printing their PLA at a much lower temp, 168C. Since I had the same filament, I dropped the temp down to 166, and the consistency was the same, but the hotend still jammed the same way. That it jammed at 166C was a puzzle, and I took a picture of the disassembled budaschnozzle that shows how the PLA was kinked above the heatzone. It appears there is just too much heat, even at 166C.

Other posts mentioned using thermal cement or compound on other parts, like the heating resistor, and that got me wondering about the budaschnozzle hotend. While a snug fit, it is definitely not a 100% thermal connection. Does the thermistor require compound in the heater block?

Interesting. I'm glad I saw this. That hot end is the same one I have (I think) from G3d? Do you have a cooling fan blowing on it? I haven't extruded with mine yet but my first impression was that the heatsink looked pretty cheesy. I actually cut 'veins' in mine with a hacksaw in order to allow more cooling air to circulate. I wonder what other people will say about this. Good luck.
joe

We're you running a fan to cools the thermal break on the Hotend?
IMO you can't reliably print PLA with a buddaschnozzle or for that matter pretty much any Hotend I've used without one,

No cooling fan is installed. In my last paragraph i was referring to the fit of the thermistor in the heating block, and that while it is reporting a sufficient temp, the actual temp is obviously much higher. I will try adding compound in the thermistor's hole to see if the temps change.

I see a lot of people printing without fans, so the need is not universal. However, I will try that after adding the compound.

Poly: I have an original Buda, I print PLA without a fan or issues.


I had the pla kink/jam twice; once my hot end had shut off and i was forcing extrusion, the second time was before I had accurately calibrated my E steps per mm.

Today I had a chance to do some testing. I reassembled just the nozzle, heating block and threaded tube to check temperature and manual extrusion. My idea about using thermal compound wasn't tried, as I confirmed that the thermistor is getting a good reading just sitting in the block. I checked temperatures at 100, 160 and 185C against an IR thermometer, and the reported temps by firmware were right on. So excessive heat wasn't the issue.

Once up to temp, I pushed filament through by hand (3mm, actually 2.85mm). Initially, it was extruding OK, but what happens is that the melted plastic seeps backwards between the heated threaded core and the incoming filament, making a toroidal bubble on top of the threaded core. Once formed, this cools and adheres to the incoming filament, and that's when it jams. I cleared it several times, and ran other 3mm PLA through, and the jam is entirely repeatable.

The issue is that the threaded core has a 3.5mm ID. The difference between it and the incoming filament is 0.65mm, but that is significant enough to let PLA back-flow like this. If that gap was smaller, even at just the top, it would act more as a seal and prevent the PLA from flowing backwards. I understand why it's oversized, and it's to accomodate various filament diameters, but the particular combination I have just doesn't work. I suppose the bottom edge of the PTFE tube is supposed to act as this gate, but the PTFE tube I have has an even worse ID, at over 4mm, so plastic flows right up that, jamming the extruder when normally assembled.

Not sure what to do next besides try a different hotend.

foshon Wrote:
-------------------------------------------------------
> Poly: I have an original Buda, I print PLA without
> a fan or issues.

Yeah some people seem to, I've never managed it, mines a 1.2 I think.

I agree with 'Polygon' that a fan aimed at the top of the hot end is sensible. Anyway, you have a point BrentB about the bore size of the hot end threaded rod - it IS too big in my opinion. I make my own hot ends and my original one was just a 3mm bore and PLA worked perfectly with it. I also made one with a 3.5mm bore and PLA acts just like you described- completely useless!

The pdf source for the 1.2 shows a diameter of the threaded extension at 3.175. G3D has been very naughty, lol.


Buda threaded extension pdf

The hole seems too big, however repeating what other people have said, you might be able to get away with it by adding a small cooling fan (only a tiny one is needed)

G3D is obviously using a 1/8th drill then, instead of a metric one. Still, 1/8th should be OK I would have thought - sounds like someone put the wrong drill in the lathe if its 3.5mm!

Yes, I find 1/8inch drill bit (3.175mm) works fine with PLA from 175 up to 194 C for me. I made my own extruder after extensive reading and it worked from the first time I tried it. My solid PTFE insulator is 1.5 inch long. I only had one jamb when I left my hot end heated for 30 minutes without extruding at all. My new rule is 15 min max at full temp without extruding (20 min still ok but close).

The bore should be slightly larger than the filament because the plastic filament swells as it is heated, and if it were to exactly match the filament as it went in, it would jamb as soon as it started heating. At 3mm filament, a tenth of a mm or two is fine as the plastic will cool as it sleeves up the outside of the filament shaft and make a plug the same size as the bore making like a piston. This works well as long as the bore is constant diameter all the way down and the difference in filament diameter and bore diameter is not too large. A filament which is too far undersize will cause problems like you say also.

I agree 3.5mm is a little too big. Filament diameter tolerance from Natureworks thru Ultimachine is 2.9mm +/- 0.1mm so yours at 2.85 is a good average value. When I first saw your picture, I was wondering if you were using 1.75mm in a 3mm hot end, but the 3.5mm dim explains why it is doing that.
I used thermal conductive paste from power resistor to heater block, but beware grounding leads with paste as it may flow a little when first heated.

Edited 1 time(s). Last edit at 03/15/2013 12:40AM by rrr7.

Excellent information, guys. The other defective part is the otfe tube. Where the filament is folded in my picture, the ID of the ptfe is 4.0mm. This morning I received the ptfe tube I ordered from lulzbot, and its ID is 3.0mm. I think that will act as the "piston bore"/seal as mentioned.

I'll try it out this weekend.

Then you are a lucky one or you have material which like to melting too fast with budaschnozzle (don't care that problem starting at low temperature, PLA softening point is very low and it become soft at 70C every 10C up it is more and more soft) I never saw anyone who is able to printing with PLA and without fan (fan for hotend cooling) but in thingiverse is a lot of different versions of holders for cooler mine 40mm cooler I got from local shop but as I see G3D buda come with fan cooler already - which clearly means they attach it to solve PLA issues. The correctly fan placement is to point an air into copper heatsink (the gold round part).

Edited 1 time(s). Last edit at 03/15/2013 09:26AM by tommy_rapper.

Actually I just added a fan for my printer too and I run PLA but the fan is for the printed part near the nozzle, not the thermal isolator. I did not need the fan to print PLA, and have printed many parts successfully without it. I thought about adding some cooling air to the isolator, but have not as yet.
Especially in small parts or features, the heat builds up and the part fails in a gooey mess after a couple dozen layers. This does not happen with larger parts as the successive passes take time and the surface has time to cool and solidify. The fan allows smaller parts and features to be printed with better quality and also aids in getting better bridging. Software cooling methods for the print can use wait states or orbits in Skeinforge and others, I am just not that patient and wanted more control for bridging.
A cooling fan on the thermal isolator may or may not prevent jambs, I would probably not trust it to sit idle and hot for more than 20 minutes without extruding something anyway in my experience. But the fan on the isolator should do no harm unless it cools the nozzle end too much.

As long as the extruder body and x carriage are NOT made of PLA, then I guess the fan could be optional if you are printing PLA which of course, is a lower temp plastic. A fan would be a must have for PLA to cool the smaller parts I would have thought- problem is, my hotend is un-insulated as yet so a fan directed at the part for cooling also cools my hot end. Does anyone have issues with a fan and a "naked" hot-end?

Success!

Today I revisited the problems I've had with Gadgets3D's buda hotend. I reassembled everything, trimmed the Lulzbot PTFE tube to fit snugly, fired it up, and it didn't jam once. That confirms the theory that the ptfe tubing, when properly fit, acts as a thermal AND melted-plastic barrier, a seal of sorts.

I printed about ten 20mm calibration cubes today, letting the hotend heat, print, and cool each time. The hotend never jammed, and the PLA extruded nicely. No fan was used, and the temp was 185C.

Thanks for all the comments, they helped figure out what goes on in a hotend.

CNCJOE, if your PTFE tubing is not 3mm ID, I'd just order a PTFE tube from Lulzbot and be done with it.

Lesson learned: I should have ordered it from Lulzbot to begin with!

Thanks for the advice bud. Happy printing!