reprap.me J-head back pressure

I'm nearing the end -I think- of a tantillus build but am experiencing problems with extruding, my nozzle (http://www.ebay.co.uk/itm/281188467531?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2648) presents a huge ammount of back pressure, compared to my ancient MK5 reprap store nozzle where I could fairly easily manually push filament through, I need to use both hands and ensure the filament does not flex and even then it feeds at a painfully slow rate.
Needless to say, the extruder cannot handle this ammount of force and just chews up the filament with the drive gear.
I have tried adding a coating of olive oil to the filament as it feeds into the extruder, but this makes no difference.
Is there anything I can do to the nozzle to reduce this pressure or do I just have a bum nozzle?
I didn't properly research the J-head- I would have ordered it from hotends.com if I had known there was such a thing as a 'genuine' J-head.
I should mention I am using 1.75mm filament which I understand can cause problems with clone J-heads.
If I am doomed, does anyone know if the J-head lite is compatible with the tantillus or must I shell out $60 and wait for shipping from hotends.com
thanks
-francis

Even genuine J-head does have high back pressure. The problem with RepRap.me's j-head is the conversion to 1.75 which has never worked and the J-head wiki entry says it did not work correctly. You could try increasing the extrusion temperature and/or make sure you are using the correct thermistor table in Marlin. If it using the wrong table you may not be anywhere near the correct temperature. You could also drill out the nozzle hole to be sure it does not have dirt or burrs in it.

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Thanks for the reply Sublime,
I'm using repetier instead of marlin but I have confirmed the temperature with a thermometer. I've run the nozzle as high as 260C which I understand is actually beyond the safe 245C for PTFE. When I pull the filament out of the nozzle, it has a plug at the end with a diameter of 4-5mm and a length of around 7mm, is this normal? Looking at a section of the J-head it seems to me that pressure from the molten filament could push against the 3mm-1.75mm liner, pushing it up away from the nozzle tip and creating a reservoir above the heated zone, just speculation but that would explain the plug and the back pressure.
I'll give the drilling a go in the morning, toothpick and toothpaste right? but other than that bum nozzle?
hotends.com are currently out of stock of J-heads, is there any other hot end which I might look at if I can't sort this issue? I don't want it to seem like I am reluctant to tinker with this nozzle but this build has taken quite a while longer than I thought it would have and I am anxious to get printing : )

The plug as you describe it is a result of the 1.75mm conversion and is the reason why you can not convert a 3mm hotend into a 1.75mm one. RepRap.me sells a lot of products that are not what the name implies. Like the stepsticks they sell are not stepsticks because they do not use the correct chip on them. RepRap.me does not care as long as they make the sale. I personally would not buy anything from them.

In the past I have used a really small drill bit to drill out the hole. I have never heard of using a tooth pick and toothpaste. If the nozzle is made even close to a J-head from hotends.com then the hole will be at least 0.5mm long so it will take a real drill bit.

Hotends.com posts new hotends every friday night. You can also email him. Or try one of the suppliers he recommends on the j-heads blog. The only other hotend I can endorse would be a makergear hotend. They are a little too long for Tantillus but work well. The E3d one looks to work well but I do not think it will fit in a Tantillus because of the cooling fins.

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The toothpick and toothpaste trick is for polishing the inside of the barrel a couple of other posts mention that a rough barrel can cause a lot of friction, I thought that was what you meant by drilling. I had been eyeing up the E3d, I will email them about the dimensions and post what I find.

Ok I went ahead and ordered the E3d nozzle, just because I liked the idea of being able to print in teflon/delrin one day. as it ships the nozzle does not fit onto the tantilus carriage but a quick job with a hacksaw and a little dremel grinding bit quickly sorted that. The nozzle is about 10mm longer than the J-head from reprap.me which may be something to bear in mind if you plan to use your tantilus to print more tantilii. I also had to alter the fan mount which was easy enough, I just split off the clips with a knife and used some very fine copper wire to secure the fan to the heatsinks. so far I have just been running the extruder to calibrate the feed and so far it works. I will post again when I have the machine calibrated and printing though I can't imagine there will be a discernable difference between this and the J-head.

This is where I removed material with a hacksaw to allow the heatsink to clear the linear bearings on the bottom of the carriage. Because the heatsink is aluminium, this is a very easy job, the whole thing could have been done using the dremel and you could create a more tailored fit, it just didn't occur to me to use a dremel until I realised I would have to remove material to clear the bolt.

This is where I removed some material using an small end mill in a dremel to allow space for the bolt which holds the lasercut retention clip in place. If you don't have a dremel (what's wrong with you) you could use a file, even a wood file would be up to the job. If you are really stuck for tools, you could use a sharp knife to shave off the material though I can't imagine that would be a pleasant task.

And here is the whole assembly together before being slipped onto the XY carriage.
Something to be aware of is that the heatsink partially blocks one of the holes which carry the wires, you can see I have had to run my thermistor wires around the carriage instead of through, this is because I had already crimped the pin terminals onto the ends. you can see I was able to feed the fan wires through as they were not yet crimped, something to bear in mind if you try this yourself.

I hope that is helpful to someone : )

Edited 4 time(s). Last edit at 02/10/2014 04:46PM by blabberjack.

Any thoughts as to whether the case fans on the Tantillus would be enough to eliminate the hot-end mounted fan? Perhapse bumping up the size of the case fans?

I'd be happy to give it a go once everything is set up but to be honest, the fan isn't in the way at all so you don't lose any build area. I routed the wires through a cable tidy with the rest of the bundle and wired them right in to the +12v plug so that, when the power supply is on, the hot end fan is on. I'm sure with PLA at 200C-ish you'd be fine even without the fan but it ships free with the hotend and causes no problems so I don't really know why you would forgo it.

For the sake of simplicity if nothing else but also to have as little mass on the head as possible.