Hot end jamming fix

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Hot end jamming fix

Postby ohcolinho » Sat Jul 13, 2013 8:17 pm

Hello all, longtime lurker first time poster here :P

So far I've been loving the Rostock Max, its a well designed kit and great features. However, since the beginning I've been having extruder woes, not limited to the hot end jamming, retraction inconsistency, and requiring more force than what seems normal (compared to other 1.75mm hot ends i've had) to extrude through the hot end.
After finally disassembling the hot end to unclog a hotend jam, I think I've figured out the reason for the jamming!

Looking at the Hot end 3D CAD models, the total length of the small 4mm OD PTFE tubing should be 45.59mm long in order to ensure that the filament is fed directly into the hot end nozzle
Measuring the ptfe tube that was in the hot end that I received, I found it to be 40mm long. Thus there was a 1.5mm gap creating volume for the ABS to squeeze into and sit around, rather than directly extruding the nozzle.

Here is a diagram showing the gap, as well as what the proper length of the PTFE tubing.
Image

Heres the picture of the length of the PTFE tubing I got with my extruder
Image

Lesson learned: don't assume the hot end was assembled perfectly, take it apart and inspect the PTFE tube length and make sure there aren't any gaps!

Another problem I found was that the PTFE tubing was that a bit of it was crimped down on the end facing the nozzle, thus creating a corresponding dent in the PEEK piece.
Image

Corresponding indentation in PEEK
Image

I suspect that this may have enabled the ABS to initiate its creep into the gap, and the eventual pressure of the filament shoved more molten ABS into the gap further widening it.

I Hope this helps for others with hot end issues!

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Re: Hot end jamming fix

Postby 626Pilot » Sat Jul 13, 2013 8:46 pm

Nice find.

When I install Windows, it comes with Internet Explorer. Some people like IE, but to me, its only purpose is to download Chrome or Firefox. I look at the stock hotend the same way: use it to print some calibration pieces, then use it to print mounting hardware for another hotend like the Budaschnozzle. Mine has jammed so many times printing PLA. I've used one fan, even TWO fans blowing directly across the PEEK section - it still jams. With ABS, I have much better luck, but the damn thing STILL jams once or twice a day, probably because the method of using two nested PTFE tubes to keep the filament straight has too much to go wrong with it. Eventually I have to unscrew the nozzle and clean everything out. What a mess.

In my honest opinion, SeeMeCNC should just ditch this hotend. The guy at http://hotends.com is selling a better J-head hotend for about 55 bucks, vs. the $40 the SeeMe hotend is listed for. It has less internal friction, and the PEEK is milled so that the thing will actually cool well enough for PLA with a single fan. It's a proven design that has already gone through a bunch of iterations. On top of that, the EZStruder is designed to mount directly to this type of hotend. Sure, they're trying to sell to more than just Rostock owners, but I've begun to wonder if SeeMeCNC is considering dumping the old hotend in favor of making their own J-heads. I doubt it would cost much more to produce, if anything, because it's designed to require the least machining possible. It's not like they don't have the know-how.

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Re: Hot end jamming fix

Postby Michi86 » Mon Jul 15, 2013 3:46 am

Got the same problem :D
i fixed it (because i have no PTFE tube at home) by miss out the rubber from the bowden tube holder (is this the correct name?), so that the bowden tube holder pushes in the too short piece of PTFE tube into the nozzle ;)

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Re: Hot end jamming fix

Postby ohcolinho » Mon Jul 15, 2013 3:08 pm

Update: The cool people at SeeMeCNC is shipping me a new PEEK adapter to replace the damaged one! I'm impressed by their service :)

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Re: Hot end jamming fix

Postby JohnStack » Mon Jul 15, 2013 3:23 pm

I tried taking off the Peek on the stock hot end, it was _really_ jammed I guess.

SeeMeCNC is working on a new hot end so there's that.

Tricklaser too!

I have used the HotEnds.com version. Peek Fan MANDATORY. Don't run it without, no matter what temp.

I have not had time to install the eBay version here: http://www.ebay.com/itm/new-1pcs-RepRap ... 19dc6515ef

And a while back, I ordered what all the long timers run: the E3D from http://e3d-online.com
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Re: Hot end jamming fix

Postby RichW » Mon Jul 15, 2013 7:41 pm

I think the teflon liner acts like heat shrink when it's heated too much. One of my problems has been with the inner liner shrinking in diameter. The first one I replaced, had to have the hot end drilled out to 2 mm. It was hardened as well as shrunk, I never thought to check the length. It would seem that ABS is just too much for the SMCNC hot end.
I expect to change to an all-metal hot end soon, either a custom piece or the E3D looks good to me.
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Re: Hot end jamming fix

Postby PartDaddy » Wed Jul 17, 2013 4:01 pm

Starting with a stock SeeMeCNC Hot End and resistors for the heating elements (not cartridges). . .


First: Oly & I designed this hot end for ABS and PLA. It can not handle high temperatures (ie. over 250C). You begin to take a change melting the PEEK.



Second: review ohcolinho's post. I'll be reviewing hot end assemblies in production. The 2mm ID x 4mm OD teflon tube should be cut square and seat into the nozzle. However, it should not compress much, if any, when the nozzle is tightened. On the top end, it will touch the push-to-connect fitting. It should not be short.



Third: What we found is that a cooling fan is needed on the RAMBo board. The direct drive EZStruder requires more power to push the filament. What many people think is a "plug" is nothing more than the stepper driver overheating. The chip has thermal protection and shuts off in an over-temp situation. It shuts off for only a fraction of a second, then turns back on. What you notice is a "skip" in the extruder. Plugs do happen, however, many problems we're seeing involve an overheated stepper driver chip. A fan, like our little 25mm fan, pointed at the driver chip solve the problem.

My notes on plugs: PLA is more sensitive to plugging rather than ABS. This is why we always recommend starting with ABS. The speed, layer, temp, retract, etc. all effect printing. With the SeeMeCNC hot end, too much heat can cause problems when printing with PLA because heat creaps up the hot end. A fan, say 40mm in size pointed at the top half of the hot end solves a lot of problems. I've been printing with a 0.35" dia nozzle, 50mm/s, our translucent orange PLA, bed 60C, nozzle 175C with a 40mm fan blowing on it. John has been printing about the same, but with our little 25mm fan inside the fan shroud available on our seemecnc github.

We've spent many hours testing a new nozzle design which gives even better results when printing with PLA. It will be available soon. It is backward compatible with all hot ends shipped with the Rostock MAX.
~PartDaddy

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Re: Hot end jamming fix

Postby JohnStack » Thu Jul 18, 2013 1:03 am

Hey PartDaddy, What are the official tube lengths inside the nozzle?

Recommended fan size to be that small or something larger to cool the entire board?

[edited]
Last edited by JohnStack on Thu Jul 18, 2013 12:59 pm, edited 2 times in total.
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Re: Hot end jamming fix

Postby RichW » Thu Jul 18, 2013 12:08 pm

Thanks to Part Daddy for the skinny on the EZstruder and Rambo situation. I have been having pretty good results with the EZstruder on small jobs, but the printing of a new magnetic effector plate has been giving me trouble. As long as a large area is being printed, with a steady flow of ABS thru the hot end, everything is Jake. When the small details are all that's left, the flow stops. I will try it again with a 30mm fan on the Rambo.
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Re: Hot end jamming fix

Postby 626Pilot » Thu Jul 18, 2013 1:29 pm

I'm glad to hear SeeMe is working on a new hot end. Will be interesting to see what it looks like.

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