J-Head not working.

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Lez0
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J-Head not working.

Post by Lez0 » April 9th, 2018, 7:53 am

Hi
I have a Folger FT5 and have made a new head for it using a J-head hot end. I also replaced the extruder with a metal one.
I would love to replace the existing print head with something better.
Everything seems to be OK except the nozzle only works for about 2 minutes then seems to get blocked.
I have cleared it a few times and there is only plastic in the nozzle tip.
The plastic I pulled out look OK to me but I am no expert.
Has anybody had a similar problem with these hot-ends, I have tried 2 from different companies and get the same result.


Thanks

Lez
Attachments
2018-04-09 12.38.28.jpg
The plastic I pulled out.
2018-04-09 13.42.34.jpg
Custom head I made

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jonnybischof
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Re: J-Head not working.

Post by jonnybischof » April 12th, 2018, 2:35 am

It could be that your filament is heated too far "up" into the hotend, which makes it jam. The rings tha show up about 20mm (guessed) from the nozzle in your pictures show that the filament was soft at the point where the PTFE tube ends and the metal channel begins. As far as I know, that shouldn't be the case.
Maybe the fan which cools the fins is not on, or not strong enough? (Must be 100% on at all times, even while heating up).

What is your retraction distance setting? With all-metal hotends you usually have to go to a lower setting (like 2-3 mm) rather than the Ultimaker (Cura) standard of 4-5 mm. Makes a big difference since the melted filament doesn't get pulled up into the cold zone as much.

You might also try just lowering the printing temperature by a few degrees. Anything that helps keeping the "cold zone" as cool as possible.
Best regards,
Jonny

Lez0
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Re: J-Head not working.

Post by Lez0 » April 18th, 2018, 3:29 am

Hi
Thanks for the reply.
Your guess is very good it's 18mm!
It seems the filament is melting in the PTFE, I don't think this should happen.
I got threaded parts with PTFE and without, with a 2mm hole. I tried both but got the same results.
The nozzle came with a 30mm fan with a shroud, as per most of them. I tried that and I also made a new one with a 40mm fan and bigger shroud, both with the fan at 100%
I even tried without a fan. In all cases it made no difference.
The test I used on all of them was to extrude 100mm of filament at at time. The first it would OK, and it always stopped about half way throught the second 100mm.
I did try and print with it to start with, but it kept getting blocked after a minute or 2.
I tried a slightly lower temperature but that made no difference.
I had the retraction set as standard 6.5mm in Cura, I have never changed this.
It does seem that the heat is going too far up as you say. I think it may be a design fault, I don't know.
One thing I came across yesterday was heat paste, I am not using any when I assemble this nozzle, do you think I need it?

I am learning all the time about the "art" of 3D printing. I think I may be out of my depth with this one.

regards
Lez0

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jonnybischof
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Re: J-Head not working.

Post by jonnybischof » April 18th, 2018, 11:21 am

I don't know the specifics of the J-head. Check the instructions about what to do with that paste...

I suppose the retraction distance is much too high. When you retract, you pull up the hot plastic into the "cold" part of the hotend, which is not desirable. Maybe just try 2-3 mm setting. It won't hurt, worst case is you get surface blobs in your print.
Best regards,
Jonny

Lez0
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Re: J-Head not working.

Post by Lez0 » April 20th, 2018, 11:53 am

I was only extruding the plastic to try it and it got blocked, not running a program, so there should be not retraction should there?
I have replaced the original MK8 extruder with a new one and it prints a lot better.
I think I'll stick with this for a while until I get more time to work on this. I have a lot of prints waiting to be done.

Thanks

Lez0

Lez0
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Re: J-Head not working.

Post by Lez0 » May 21st, 2018, 8:50 am

Hi all
I had a bit of time so I had another look at this. I got another J head and tried it.
I set it up so the head was fixed to the frame so it would be easy to change things. I was only going to extrude filament not do any printing.
I used ABS with the hot end set to 230°C, I could push the filament by hand and it came through OK.
I tried extruding it using the motor. It wouldn't work and the motor made the usual soft clicking sound of stalling.
I could pull the filament out back through the top, strange, nothing holding it.
Stripped it done and found no problems, put it back on the printer.
Tried again and same thing, I could push the filament by hand and it would come out, if I used the motor it stalled.
So it seems the problem is not so much the nozzle getting clogged but the filament being difficult to feed through, or it could be the new motor isn't powerful enough, or I need to increase to power to the motor.
I have to put in some TMC 2130's onto the main PCB, so I'll look at it then.
I'll keep you informed.

Lez0

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