kris

Awesome, thanks

Printed this in 1/87, ABS white. Cheers Kris

Both PLA and ABS have a comparable Youngs modulus. The filament will behave as a spring; compressed when printing and elongated when retracted. That change in length is proportional to its initial length. In addition it is forced into a curved shape. If the feeder is placed in the middle above the build plate the extruder will only travel about 10cm in each direction. There still needs to be some curvature to account for the change of distance between the feeder and the extruder when it travels. But the distance can at least be cut in half. I have three UM2s; two only operate with ABS and one purely with PLA. Under certain extreme conditions they all can suffer from underextrusion. I am not a fan of putting the filament behind the printer as intended. This makes material change cumbersome. Instead I place material next to the printer in a low friction spool holder.

Hi to all of you feeder experts. I have been thinking of maybe putting my feeder directly above the printer. Pretty much in the center and not very far away from the extruder. Has this been tried? I fail to see the point in putting it at the rear, making the ptfe tube very long. The shorter the distance the less prone to buckling and friction. And by reducing the length there will be less total elongation of the filament and maybe a more immediate response to retraction and hence less grinding. Just a thought so far...

any news on this?

Didn't change anything :( It still retracts the 5mm with cura 15.02 RC2

Awesome...many thanks!

Hi I tried the new pause/ change material option on the UM2 in an attempt to print a two colored model. Pausing with the current plug in and changing material went fine. But trouble is that after changing material the UM2 will retract the new material about 5mm and continue printing with nothing, until the material reaches the nozzle again. Does anyone have any experience with this? Cheers Kris

Did the feeder grind into the filament? This would prevent it from moving the material to the extruder. I have no idea what your model looks like, but I am guessing there is a lot of retraction involved. Have you tried printing slower? I print PLA only on a dedicated UM2, anything above 50mm/s and 0.1mm layer thickness is critical. If tolerances are not critical I raise the temperature to 240C which will make the PLA flow much easier. ABS is a different story

Always use brim. For ABS I increase the platform temperature to 110, for PLA to 90. Enclosing the build volume also helps.

Hi Shnick, I use two UM2's, one purely for PLA and one for ABS. Both PLA and ABS from Innofil. For PLA: Going any higher then 50mm/s and 0.1mm layer thickness will always cause underextrusion for me as well. I usually stick below these values. If the dimensions are not critical I even raise the temperature to 240°C. ABS is a totally different story: 75mm/s and 0.25mm layer thickness are no problem at all, I even lower the temperature from 260°C to 240°C usually without any signs of underextrusion for >20h prints. Seems to me that at least the Innofil PLA is a lot harder to extrude. I'll change to colorfabb hoping it will get better. Cheers, Kris

I always print ABS @ 230C, with the bed @ 110C and enclosed build volume. Almost no warping and very uniform shrinkage.

Have you tried cleaning the nozzle? It might appear to be OK, but maybe it isn't. I would try that first. Maybe using the atomic method?

Yeah, I basically have the same problem. I need my printer operational so I can only incorporate small changes. Baby steps... After reading on the forum about what parts usually break down first, I have even ordered spar parts in advance. I.e. a spare nozzle, a new temp. sensor and PTFE bushings. Since then nothing has happened, it just prints & prints. I guess it is scared now ;-) I guess the extruder is a good basic design, but there is room for improvement.

I hope that is not a problem, at least I designed everything so that the rear fan does not extend over the rear of the extruder. Here is the mold (ABS). No idea if this will ever work...but I guess it is worth a try.

I have no idea what the temperature back there is, but I guess it is pretty high due to the proximity of the nozzle. I am printing the mould for the silicon casting as we speak.

I would like to hear your opinion on the following idea: My UM2 is not very noisy at all, but maybe I can make it even quieter? All I can hear is basically the rear fan. It does vibrate quite significantly, causing structure borne noise. The fan is rigidly connected to the aluminium structure. And I noticed if I unscrew it and hold it in my hands there is no noise at all. Silicon acoustic decouples can be purchased for larger fans, but I couldn't find any for the tiny rear fan. So I figure casting my own in silicon. The mold can be 3D printed. Here is the virgin coupler: It is a bit shorter then the thickness of the fan, so it holds the fan in place with some tension.

Yes, any settings would have to be changed to account for the new temperature gradients. About the washer: I have tried that as well. 1. I used ceramics. I figured it would withstand the temperature and it also has low thermal conductivity. ZrO2 seemed like a feasibly option. The problem is, ZrO2 is a better thermal insulator compared to e.g. steel, but it is 10 times more conductive then PTFE. The analysis seems to indicate that this in fact eases heat transfer to the PTFE bushing. In addition it is unknown what the material does when it gets in touch with PLA/ ABS. It might increase friction. If you decrease thickness, you need to cool it. Otherwise it will saturate quickly. 2. I then optimized a steel heat break which later was incorporated into the nozzle.

I think you are correct. Trouble is, the nozzle needs the heat, the PTFE bushing doesn't. Thus heat needs to be drawn away from the bushing. I do not believe that the problem can be solved by using a different material, they all have their drawbacks (e.g. added friction, thermal expansion etc). Instead it should be possible the improve the current design, hopefully to the point were is functions reliably and parts do not have to be exchanged frequently. After countless iterations, here are the things that work the best according to the analysis : 1. One added heat sink close to 1310-Z2P-A 2. Heat breake integrated in nozzle 3. Added ventilation holes to 1310-Z2P-A The results are shown down below. There still is a heat accumulation at the bottom of the bushing. But it is smaller and the overall temperature is lower.

Had exactly the same issues. I only print ABS now, I never mix materials any more. Will maybe buy a second UM2 for PLA.

I totally agree. The design needs to be updated. Having to change the Teflon bushing on an arbitrary basis is not satisfying.

The extruder design needs to be improved in order to reduce the heat flow to the PTFE part. At the moment the component is subjected to too much heat. I am pretty sure there is potential as I have posted in my heat analysis of the setup.

Aroth, did you clean the nozzle? Even if the PTFE bushing looks bad, you might simply have a clogged nozzle.

Difficult to do anything against shrinkage since it is a material property that more or less behaves linear with temperature. One thing you can do however, is to make sure that whatever you print cools uniformly. Hence heated build platform & heated build volume. For that I use a greenhouse to make sure the part I print stays uniformly at a higher temperature until it is completed.

The PTFE bushing does not look good to me. I would suspect it is not up for the task anymore. Have you considered replacing it? The new ones are glass fiber reinforced and have a much better endurance. In order to get one I think you need to get in touch with customer support.