Delta jamming at high speeds with large nozzle

(Note: printer specs at the end)
Hi, I have been printing PLA ok with my large-format delta for a while. It has an E3D 3mm extruder and up to now have always used a .4mm nozzle and 'play it safe' speeds of 30 mm/sec.
However, I had a high-volume part about 6" by 6" that would take way too long with my usual setup.
With some tweaking I was able to print at 70 mm/sec with a .6mm nozzle, although my print time is still huge.
Quality looked good but around 8 hours in it jammed up. I kept reducing the retraction length but it still kept failing; in fact much sooner than before. I also played with the temperatures but it is hard to test something that wants to fail 8 hours into a job.
Any ideas? I've had decent luck with Shaxxon 3mm PLA as far jamming issues. (MG Chemical brand was horrible, always jammed immediately)


Secondary issues and rants:
I'm really sick of the whole PLA-jamming issue; seems like a problem screaming for a resolution. All-metal hot-ends are great but we need a material or coating that will end this nightmare for everybody.

On a separate front, I decided to try ABS because that is usually jam-free. I have avoided though because of the warping.
My bed will get to 100 C ok (glass bed). I hung a pair of garbage bags over the machine to get the chamber temperature up.
It printed the whole thing but warping was terrible! This is a hollow 4 sided box about 5" x 6" with 10mm thick walls.
I don't know how so many people print fine with ABS; seems like the chamber has to be hot enough to bake a cake!

Specs:
Frame is 20x20 uprights, 20x40 bottom horizontals, all-metal vertex parts.
Height is about 1 meter. Platform has heavy-duty rods with 80mm spacing. Extrusion-riding v-wheels with bearings for the stage mounts.
0.9 degree steppers running from Duet, DC42 firmware.
3mm filament with a geared-down workhorse extruder, tremendous grip (although top-speed is not great).
Mechanical z-probe with optical switch.
350mm glass bed with 300mm 500 silicone heater. With an infrared thermometer the center temperature is spot-on at 100 deg C.
Usually use Slicer for my models.

Edited 1 time(s). Last edit at 09/01/2016 02:06PM by shadowphile.

I am not sure that all-metal hot ends are best for printing PLA. My Ormerod printer hot end uses a PTFE liner, and the only time it jammed was when I was testing stupidly high amounts of pressure advance. My all-metal E3D has jammed numerous times, usually when I try to unload filament, very rarely during printing. I use 7mm retraction, but the Bowden tube is 650mm long so the actual retraction at the hot end is much less.

It's worth checking that your hot end fan is keeping the heatsink cool enough, preferably no more than 40C.

Edited 1 time(s). Last edit at 09/01/2016 05:30PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Well I've recently read comments blaming jamming on weak extruders more than on hot end throats. I presume you are using an E3D V6 genuine hot end? Unless you are printing high temperature filaments why not try a PTFE lined throat for PLA? Is it heat creep up into the throat? Seems like a long print really tests the ability of the fan and shroud in preventing the heatsink from warming up. Maybe try a 40mm to 30mm fan shroud and use a high powered fan?

For ABS, I find printbite is basically a material with magical properties, but you have to use a lot of heat, I print my first layers with ABS at 255 C and bed at 120 C, then drop to 240 C/116 C for the rest of the print. And I wouldn't attempt to print an object that size unless I was fully enclosed and could guarantee at least 45-50 C evenly throughout the chamber (small low RPM fan blowing air diagonally downwards usually works).

These days if its large and needs to be strong its PETG all the way, I have only had one jam with an e3d clone v5 hotend (now on its way to being melted down and made into something useful), almost no warping and whilst I never seem to be able to get a nice surface finish, it oozes worse than pla and bridging is useless, the parts are unbelievably strong.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Hmm, have you tried increasing the temp a little bit?
Will increase stringing, but might get you over the 8 hours hump.

And stringing is easy to remove, if you have a heat gun. Quick blast and it is gone.

Lykle

Quote
Shadowphile
On a separate front, I decided to try ABS because that is usually jam-free. I have avoided though because of the warping.
My bed will get to 100 C ok (glass bed). I hung a pair of garbage bags over the machine to get the chamber temperature up.
It printed the whole thing but warping was terrible! This is a hollow 4 sided box about 5" x 6" with 10mm thick walls.
I don't know how so many people print fine with ABS; seems like the chamber has to be hot enough to bake a cake!

In my experience even small drafts with ABS can cause problems.
Recently I needed to print 2 of the same large prototypes for someone, these were about 13 inches across by about 12" tall. I ended up having to print 4 of them at 11 1/2 hour each - .2mm layers at 55mm/sec - .72mm nozzle - .82mm extrusion width.
I had problems with the first two because midway through a small bit of filament would get stuck to the bottom of the cooling shroud and drag through the still soft print. On the first one I thought it was a fluke... well it wasn't.
I also had the door on my printer propped open about 0.4 inch with a magnet because I wanted to keep the temp below 55C so as to not overheat the part. There was significant warpage.

So I figured out what the problem was with the stuck on filament bits - I raised the cooling shroud slightly (I ground the bottom of it with a Dremmel), and in the process this increased the airflow slightly as well (more cooling air to the top of the part). With this setup I printed two more models, with the door closed. The chamber was then at 58C. Everything was perfect - no warp at all - prints stayed perfectly stuck on the bed. The bed is glass with hairspray. Here is a video of one starting Youtube

On a side note - you might want to measure your filament. I had two rolls early on that were out of round - enough so that they would cause jams.