1 Topic by BFresh

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Topic: Keep getting blocked hot ends

I keep getting blocked hot ends (see photo). I am using Lawsy's Mk5 print head as the solidoodle jigsaw disintegrated. Also, I use my SD3 most days, often all day.

I am having the problem with both standard SD hot ends and also the J-head.

I want to stress I'm definitely not letting the hot end sit for too long when it is hot either.

I have replaced the hot end a number of times and sooner or later the problem comes back. Fortunately I have gotten pretty good at cleaing and rebuilding hot ends.

I have checked all my settings including flow rate, feed rate, and have calibrated the crap out of my printer. I noticed that the nozzle diameter was set to 0.5 in slicer so I set it 0.35 thinking that was causing the problem, however it is back.

Molten filament was coming back up the nozzle and causing a blockage in the peak body, so I reassembled the hot end with no gaps like this. See photos of the bits I removed from the hot end.

The problem will appear, then go through a period of me cleaning the hot end with wire and it getting blocked again very quickly several times, then I'll put a new hot end on or fix something else. And it will be fine for a while, but it keeps coming back.

I am tearing my hair out.

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2 Reply by techbuilder2175

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Re: Keep getting blocked hot ends

It appears that the hobbed drive gear is not aligned properly.

Have you tried running guitar wire through and visually see if it goes through straight?

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3 Reply by IanJohnson

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Re: Keep getting blocked hot ends

Here is a post I had not gotten around to publishing, but it deals with exactly the same problem -

http://solidoodletips.wordpress.com/201 … ed-j-head/

The key is to make certain that no gap can form between the barrel and the teflon tube inside the PEEK.  At the top of the J-Head is a small piece of PTFE tube inside of a hollow set screw that holds the telfon liner inside.  When the J-Head is disassembled, take out that bit of tube and unscrew the set screw.  Use the back of a 1/4" drill bit to push the teflon liner down a little bit into the area where the barrel will be.   When you screw the barrel in, it will push the teflon liner back up.  Then put the set screw back in to the top and tighten it down so it holds the teflon liner tight against the barrel.  Then put that little PTFE tube back inside the set screw.

PTFE doesn't have to get very hot before it starts to soften.  I wonder if getting too hot lets it compress a little and gradually open up a gap.  Screwing the barrel in as tight as possible won't close that gap, but pushing the liner down from above with the set screw will.

Solidoodle's Makergear style PEEK uses a pin through the side to hold the liner in place so you can't adjust its position.  However since the heater block is separate from the barrel, you can screw the barrel in as far as it will go to close the gap so long as no plastic is left in there.  With that one, it is hard to know if the gap is really closed, or if it is just really hard to screw the barrel any further, and it is easy to snap it if you force it too hard.

4 Reply by BFresh

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Re: Keep getting blocked hot ends

Ian Johnson, I was getting that problem a while ago and figured that out. There is definitely no gap in my J-head or standard SD hot end. I am still getting the problem though

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5 Reply by BFresh

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Re: Keep getting blocked hot ends

techbuilder2175 wrote:

It appears that the hobbed drive gear is not aligned properly.

Have you tried running guitar wire through and visually see if it goes through straight?

Tried that, still failing.

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6 Reply by solijohn

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Re: Keep getting blocked hot ends

BFresh wrote:
techbuilder2175 wrote:

It appears that the hobbed drive gear is not aligned properly.

Have you tried running guitar wire through and visually see if it goes through straight?

Tried that, still failing.

But does it go straight?
And is your thumb screw calibrated properly?
Is your gear munching filament?

This could the cause of your issue.

Former Solidoodle employee, no longer associated with the company.

7 Reply by BFresh

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Re: Keep getting blocked hot ends

solidoodlesupport wrote:
BFresh wrote:
techbuilder2175 wrote:

It appears that the hobbed drive gear is not aligned properly.

Have you tried running guitar wire through and visually see if it goes through straight?

Tried that, still failing.

But does it go straight?
And is your thumb screw calibrated properly?
Is your gear munching filament?

This could the cause of your issue.

Looking down from the top, the curve of the hob gear is centralised to the hole of the hot end.

I didn't know you had to calibrate the thumb screw, how do you that?

What do you mean by munching filament? The hobbed gear does leave teeth marks on the filament.

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8 Reply by IanJohnson

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Re: Keep getting blocked hot ends

I have had problems caused by the washer below the spring getting snagged on the thread of the bolt.  I had the spring tightened down a little too much, and since the edge of the washer was caught on a thread the idler arm couldn't push back on the spring when it needed to.  That is a long shot in your case, but if you have the spring on the idler arm pushed down too tight, it can make it difficult for the extruder to feed the filament consistently.

However that is a problem at the extruder gear, and not something that would cause the filament to buckle trying to get in to the hot end.  My only suggestions at this point are to try a larger nozzle like .5 or get try a completely different kind of hot end like the E3D.

Have you tried different filaments?  If you keep having the same trouble between the J-Head and Solidoodle hot ends, maybe the common factor is the filament.

9 Reply by solijohn

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Re: Keep getting blocked hot ends

BFresh wrote:
solidoodlesupport wrote:
BFresh wrote:

Tried that, still failing.

But does it go straight?
And is your thumb screw calibrated properly?
Is your gear munching filament?

This could the cause of your issue.

Looking down from the top, the curve of the hob gear is centralised to the hole of the hot end.

I didn't know you had to calibrate the thumb screw, how do you that?

What do you mean by munching filament? The hobbed gear does leave teeth marks on the filament.

Yeah, it shouldn't leave teeth marks. It's most likely too tight. If the drive gear it ripping little chunks of filament, you are going to have issues down the road.

Former Solidoodle employee, no longer associated with the company.

10 Reply by BFresh

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Re: Keep getting blocked hot ends

I have tried putting a small piece of tubing below the hobbed gear and it doesn't curl out like it did before, it just stops going into the hot end.

I tried it with the thumb screw looser and it still did it. I tried tightening the thumbscrew and put a fresh bit of filament in and it then the hobbed gear just ground against the filament.

When I put in filament without cleaning the hot end, it works for a little bit but then stops again. And it will extrude filament fine when not printing (i.e. not over the bed).

Just to reiterate, it is a inconsistently occuring problem that I get with bot types of hot end, and I have only had this problem since using Lawsy's mk5 print head. That's not to say that it's definitely a problem with the print head, as it has been working well with lawsy's print head

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11 Reply by BFresh

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Re: Keep getting blocked hot ends

After trying several times to clean the J-head, it kept printing ok for a while then seemed to keep getting blocked. I put on what I thought was a blocked SD hot end (same problem of filament twisting out and not printing) and it seems to be printing fine now.

I'm still not sure wtf happened.

I also installed an M5 rod, flexible couler, and slop nut, and bot printers are printing better than ever!

Cleaned everything in the J-head, and even put the correct sized drill bit through the PTFE sleeve inside the j-head to make sure it was clear. Maybe I'll buy another J-head but use the new new ptfe sleeve and peek body and the old j-head and vice-versa.

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12 Reply by 2n2r5

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Re: Keep getting blocked hot ends

BFresh wrote:

After trying several times to clean the J-head, it kept printing ok for a while then seemed to keep getting blocked. I put on what I thought was a blocked SD hot end (same problem of filament twisting out and not printing) and it seems to be printing fine now.

I'm still not sure wtf happened.

I also installed an M5 rod, flexible couler, and slop nut, and bot printers are printing better than ever!

Cleaned everything in the J-head, and even put the correct sized drill bit through the PTFE sleeve inside the j-head to make sure it was clear. Maybe I'll buy another J-head but use the new new ptfe sleeve and peek body and the old j-head and vice-versa.

Don't forget to post result pictures for the slopnut! I love seeing people that profit from my work.

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