Wednesday, November 2, 2011

J-Head Nozzle Review and Testing Update

The J-Head Mk III-B has been reviewed here:  http://captain-slow.dk/2011/10/30/j-head-nozzle/

While this review is very positive, there is clearly room for improvement.

Over the past weekend, others have also indicated that PLA takes an exceptional amount of force to extrude.  After some experimentation, it appeared that the melt zone should be increased.  Therefore, I have machined a small batch of test nozzles that have a small 3.5mm diameter "heat-chamber" machined into them.  These nozzles are shipping out for testing today.  If this change proves to be an improvement, it will be implemented shortly after the results are known.

4 comments:

  1. The comment system appears to be buggy.

    I have found that a smaller melt zone is the key to a good PLA hotend. If the melt zone is large you end up with lots of hysteresis as well as more filament expansion which cause more friction. My newest hotends only have a melt zone of about 10mm and have allowed me to lower the temperature from 215c to 170c

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  2. Hello,

    Sorry about the comment problems as the spam filter had improperly tagged your comments. (I will look into that.)

    The current design is such that the plastic filament only contacts the hot metal, of the brass nozzle, at the very tip of the nozzle. This is due to the PTFE sleeve going all the way to the very tip of the nozzle.

    The test design stops the sleeve about 9mm from the tip or approximately the width of the heater block section. So, the filament will be able to be in contact with the hot metal for about 9mm. Another test nozzle has been created with the sleeve terminating about 15mm from the tip in order to compare the results.

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  3. I just ordered a few J-Head nozzles to test and hack about with (Older versions), keep up the good work, I'm really enjoying the progress with this design.

    Does having a core of alu that far up as a Heatsink work efficiently? Is it only really cooling the PTFE tube? I would imagine you really need the PTFE tube to be cooler as low as possible to help with filament transport and I would be tempted to also cool the PEEK at the same time. I clamp a ring of aluminium lower down the barrel (near the hot-end) using a standard Aluminium M12 smooth bar holder ($1) drilled out to 16mm as a heat-sink, it's very effective for me.

    I would really like to see hot-ends have a print speed rating, I have used some designs recently that struggle to get past 80mm/sec. Maybe a force required rating is also useful, I have yet to see a fast all Stainless steel design...

    Cheers,

    Rich.

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  4. Hello,

    The Mk III heatsink works very well, even though it is pretty high up. Unfortunately, has to be high up because of the length of the threaded section of the nozzle. The PTFE tube passes through the heatsink and due to the design, of the heatsink, it will help to cool the PEEK as well. Internally, the heatsink is slightly under 4mm away from the brass.

    Ideally, and as you mention, the heatsink should be lower. (If the heatsink was lower, a shorter hot-end would also be possible.) That being said, I am working on an experimental design that incorporates elements of the Mk III and MK IV. In addition, the threaded section of the nozzle will be shorter and, if it works out, there will be a heat chamber section.

    Having proven speed ratings, for each hot-end design, would be a great idea!

    Regards,

    Brian

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