Problems with PVA and dual extrusion

[ivanhandler]

I have dual extrusion set up and mechanically it works. My problem is with PVA. For some reason, it gets blocked in the hot end and won't retract during a tool change. I was running at 200C, I upped it to 220 since that is what it took to be able to manually pull it back. It also appears to not extrude enough to be ready after a change, but this is at the 2nd or 3rd layer. I upgraded my extruders to Bondtech since I was getting way too much filament grinding and extruder clogs due to the retraction heavy prints I have been making. Any insight would be greatly appreciated.

[pouncingiguana]

Is your PVA properly dried out? I've had issues with it when it's absorbed too much moisture. Drying it out in an over (or a filament dryer if you happen to have one) can solve this issue. Not to say that it couldn't be something else, but that's what fixed my problems with it. Also assuming you're running it through an HE280 and not another hot end.

[ivanhandler]

Thanks, I'll try that. I have had it out for a while, it's pretty dry here, but that's a fairly subjective judgement on my part.

[ivanhandler]

I baked the PVA to eliminate moisture and still am having troubles. So I just put in a white PLA to see if I could get that to work and it didn't. Here is what I don't understand.

I get the first layer down. Everything works just fine. The model PLA retracts to just above the Y-connector and the support PLA gets pushed down into the HE280, a layer is put down on the priming tower and then the support layer is printed. So far so good. But when it comes to the tool change, the model PLA hardly moves at all and you can see it slowly creeping down the bowden tube when it is in the priming tower. The tool change retraction is set to 3 mm. There must be some mechanical issue I am not seeing. Any ideas? Thanks again to all of you who have suggestions.

[pouncingiguana]

Take a close look at your second extruder. Make sure it is gripping the material well and doesn't have bits of it stuck in the gear teeth. If that still looks fine, try heating up the hot end and doing a few tool changes... does it have the same problem?

[ivanhandler]

Thanks! These are good ideas, I will have some time tomorrow to try them out.

[RegB]

I am trying to do this on an Artemis, well not quite this I am trying to do it with ABS, so different material and somewhat different hot ends.

Anyway, I noticed mention of tool change retraction of 3 mm and that seems extraordinarily SHORT (to me).

I'm thinking that each material needs to get fully out of the way of the other material - and that means retracting all the way back to the fork of the Y junction.

Maybe 3 CENTimeters ?
That looks closer, just eyeballing it.

[RegB]

Re previous post.
I just checked the CURA 3.5.1 default settings;
Nozzle switch retraction distance; 16 mm
Nozzle switch retraction speed: 20 mm/sec

That is with ABS, but I don't think the material type matters, only the dimensions of the filament paths in the Y
FWIW, etc.