PSA: Purge mechanism not skelestruder compatible

Hi @vintagepc64

I am super sorry for the excessive delay. I took a look at the model and made some changes. The purge mechanism will fit but needs 3 mods. A remix has been posted on Thingiverse here. If you print and test fit it would be great if you could let us know how it works 🙂

Great, I think I should have some time to try it out this weekend!

The initial fit looks good, it clears the PINDA and fan shroud now, and does not interfere with the Z motor mount anymore. 

I don't think I'll have a lot of time to actually work with it this weekend, but we shall see. Hopefully I'll at least be able to do some test purges.

I played around a bit and I think we can shorten the action trigger arm slightly, though not by much unless the mechanism screws sit flush, Currently my purge position is X~=246. No rush on that; it can be dialed in later. 

Alas my printer resets after doing a purge or moving away from the mechanism. I've made a different post about that as it's a more general issue I don't think is specific to the skelestruder.

I think we are in business; the reset issue has been worked around and it is producing nice little pellets. Next step for me is to review/revise my post-processing script to produce appropriate toolchange gcode that respects the filament ramming/cooling/whathaveyou settings. But I probably won't get to that this weekend.

OK, so it sorta works. I don't think it's quite positioned right. I moved the mechanism up a bit as it is slightly too low (1mm) but this wasn't enough, it looks like. My blobs are kind of hourglass shaped around the washer. They don't jam, but I also don't think it's right. 

Alas, there's no more room to move the mechanism up - I already had to cut off part of the shield as it interferes with the fan shroud, and the linkage is just shy of the PINDA right now. (PINDA is already basically as far up as it can go, my live Z is ~-0.300)

Image attached, showing both what a blob-in-progress looks like and how the nozzle normally rests without a blob. 

I think it might work if the height of the washer could be raised a little bit so it surrounds the nozzle more; not sure how practical this is though. 

Any thoughts as to what I can do?

Any thoughts?

@vintagepc64

Sorry I missed this. Please make sure to tag us (@BigBrain3D) that way we get an email alert.

Let me review this and get back to you.

No worries. Appreciate you taking the time to look into it. 

Hi @vintagepc64,

The nozzle position looks good in relation to the washer and the tack.

As an aside, the connecting arm is upside down which can affect clearance. I know you said 'it barely misses' but barely is fine.

Attached you will find an 'experimental' low height cage. I've tested about 250 blobs on it. I did use Aluminum tape to bridge the gap between the cage and washer and that helps keep strings from getting stuck.

It looks like you may be experiencing a problem with the blob cooling too fast. The blob must form completely under the washer. If there is any premature cooling the blob will form as a column instead of a hershey's kiss. There was another thread about this and a possible solution too, which required putting the M107 immediately after the blob was fan cooled. Please read through it and see if the videos look like the same issue you are having. If not, please reply with a video, it's worth 10K words ? 

https://www.bigbrain3d.com/community/general-discussion/issues-ejecting-blobs/

@vintagepc64

On second glance It's difficult to see if the nozzle is far enough forward. A video would really help.

I've managed to get your purge mechanism working with my Skelestruder!

I didn't want to lost the tensioner on my bear X axis, and I found that no matter what I tried that it would either be too low or too high.

• I made an alternative bracket that mounts directly to a modified bear X end and has slots to be adjustable. I also had to add 0.1mm to the diameter of the hole that the arm swivels in. Could be from a little overextrusion.
• Action arm and spring arm printed in PC, rest in PET
• X axis kept missing steps with 4 springs, look off the outermost one and now works well
• Purge position 247.3 - it is a little too far right but works
• I also use jltx's Z axis, and this works perfectly
• My tack wobbles a little, if it becomes an issue I'll have to print a new catcher as reseating doesn't help.

https://www.thingiverse.com/thing:4141935

I was also tempted to flip the bracket and incorporate into an x-end (maybe Taurus). This would make the springs and mechanism exposed to allow for easy maintenance and spring tension tuning without having to remove the bracket. But that' for another day.

I'll report back after some more testing.

Yes, the upside down connecting arm was deliberate so I would have rounded edges facing up rather than a square edge. Might be my imagination but I get the idea it's slightly shorter this way.

You may be on to something - These are from my postprocessor while I was testing it; the ramming sequence ejects a small amount of filament which, despite the fan being off, is probably cooling enough to interfere with the subsequent blob formation. I'll have to address that.

@vintagepc64

My suggestion is to make and eject a blob before the tool change. Just start creating a blob with the difference of 40mm minus the amount ejected during the tip shaping.

@revajo

This is fantastic work! Thank you for contributing ? we liked the Thing on Thingiverse too!