Taz 6 Dually - Second extruder making contact with print volume

We have recently installed the Dually on our Taz 6 however we are having difficulties when printing using only extruder 1 as we intend to do some of the time. Both extruders were calibrated to the same height from the print bed and the first layer or so goes down fine but eventually extruder 2 starts to meet with the print volume causing it to ‘scratch’ it and in a recent print had sufficient enough force for the motor to skip resulting in vertical steps in the print. The problem seems to get worse as the print height increases suggesting it could be the z axis calibration but a test cube, with extruder 2 well out of the way, comes out perfect. I have tried adjusting the z offset mid print in the hope I can salvage it but this obviously isn’t a permanent solution. Can anyone offer any suggestions as to what I might be doing wrong or how we can reduce this? (I am a fairly new Taz user). Otherwise I feel I have no option other than to remove the dually until I need to print dual material or temporarily adjust the height of extruder 2 to prevent these collisions. I have attached a photo mid print showing the problem (extruder 2 is on the right). Thanks in advance.

You answered your own question. T1 is too low if it is coming in contact with the T0 extrusion. Are you using a feeler, paper or business card to calibrate the extruders? Make sure to move the toolhead to ensure you’re measuring the nozzle height in the same spot on the bed for both extruders.

It sounds like the additional load on the Z axis may be getting the driver chip hot and triggering a thermal safety thus dropping an occasional step. Making the impacting get worse the higher you go up in height.

Thanks for the replies. I have adjusted the z height of both nozzles using feeler gauges but to be honest I think the problem is inevitable as the nozzle runs so close to the last layer that even the tiniest jolt results in it touching the print volume resulting in the scratches or worse delicate sections of a print being knocked over (especially since the second nozzle is cold). It’s not helped that their seems to be a lot of play in the dually, it easily moves up and down by as much as 1-2mm when gently pushed. The only solution I can forsee if to manually adjust the second extruder nozzle up 2-3mm to prevent it from making contact and re aligning it when it is required or switch back to the single extruder.

On a seemingly separate note, since switching to the dually, the auto level process occasionally misses or comes very close to missing the leveling discs in the corner of the print bed. The only way I have been able to correct this is to adjust the limit switch positions and/or adjust the steps/mm settings in the firmware but obviously the latter has the potential to produce inaccurate prints. Am I missing something? I’m struggling to have anything positive to say about the dually so far!

2-3mm seems a bit extreme to me… should be able to get it much closer. The vertical play in T1 (as you mentioned) is probably affecting the accuracy of the feeler gauge. Hard to tell if its raising inadvertengly.

Try the attached thumbscrew cap for the adjustment screw. Raising the extruder, fitting in the allen wrench, re-homing Z wasn’t working for me… much easier to give the thumbscrew a turn and printing a test line to compare the initial extrusion width worked best for me. Print the singlecolor version first then the dual color when you sort out T1. The thumbcap should fit pretty tight and with the hex key in the middle… Pipe wrench/pliers came in handy to squeeze the part onto the screw.

Hope that helps.
M5 - Thumb screw.Color2.v8.stl (78 KB)
M5 - Thumb screw.Color1.v8.stl (207 KB)
M5 Thumbcap.SingleColor.v8.stl (285 KB)

So I managed to sort out the auto leveling issue, not sure how! However the second nozzle is still making contact with the print volume even after careful adjustment, slow printing and travel speeds and a 1mm ‘hop’ in an attempt to move out of the way while the print tools are in transition. I’m printing using only one extruder at the moment (rigid plastic) but obviously I’m going to get the same problem when adding in the NinjaFlex.

I really don’t know what else I can try and am going back to the single extruder and temporarily giving up on the Dually. Very disappointed to say the least, hopefully Lulzbot can help me but any other suggestions are more than welcome. I have attached an image of the latest print with a clear line across the volume correlating with the point at which the second nozzle is making contact with the print volume. You may also notice considerable warping which again is disappointing for such a simple print with Lulzbots recommended settings for PLA. I didn’t expect this with a printer of this cost am I expecting too much?

Its too bad about your conclusion on the dually. The obvious answer is to continue to raise the T1 head until the T0 extrusion is cleared. Dialing it in by quarter turns of the adjustment hex until it clears the layers of a small test object is tedious, but absolutely possible.

Not sure of your process, but how are you checking that the nozzle is just touching the feeler? The feeler is great for initial determination of a start point, but looking at the printed extrusion a better method. I guess you could try measuring the extrusion (or a few perimeters) from each nozzle and compare the results. This would give you quantitative numbers. Unless you have the flexydually that has a .6 and .5 nozzle if I remember correctly.

I’ve had good success with the dual head extruders. My only drawback is the print speed… since the second print head is so far away from the rails, the quality is really poor when printing fast… at least over time the quality has decreased. Slowing down the print speed helps.

This is exactly why I’m terribly upset with my LulzBot TAZ 6 and dual v2 especially for its price.

But checj out the dual v3 they just released 2 hours ago. If you still have time hurry return the terrible v2 (30 days).

Btw I’m keen on selling my dual v2, anyone interested please pm me.

I’m having these exact same issues with the V3 I’ve had for about a week now. I’m also going back to the single extruder. This thread was very inciteful towards the problems I’m having.

Don’t have a dual head extruder but my single printhead was making contact with the printed material. Made several changes but the one that may help you out is disabling Combing in the Cura settings. This forces a retraction while traveling over printed material. Good luck.