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Extruder Gear Pops Out - what other options are there?

Posted by bryancostanich 
Extruder Gear Pops Out - what other options are there?
December 05, 2013 07:47PM
Hey all! i built a reprappro mono mendel, but the extruder gear keeps popping out when i'm running it. i've tried tightening the bolts to keep pressure on the filament in there too, still no good. i actually think it's kind of a crappy design.

is there a list some place of other options for the extruder feeding setup? i found lots of designs for the hot end, but not the feeder part.

Re: Extruder Gear Pops Out - what other options are there?
December 06, 2013 01:57AM
What extruder does this kit use? I took a quick look and it doesn't look like it uses the classic Wade extruder.

Perhaps you could print yourself a completely new and different extruder, if you could get a different type to fit
Re: Extruder Gear Pops Out - what other options are there?
December 06, 2013 02:55AM

Sounds very odd that the gear pops out. The design means that the filament should hold the gear in as it slots into the 'V' of he hobbed bolt. With filament in I cant pull the large gear out. Could you post a pic of you extruder and one of the gear ?

Re: Extruder Gear Pops Out - what other options are there?
January 06, 2014 05:11PM
Here are a couple shots of the gear. I wonder if the teeth bits on the metal piece are just not big/sharp enough?

note that there are extra washers in there as spacers, to force the gear further down, because it seemed like it was in the wrong place (works about the same either way - which is to say, it doesn't work worth shit).

Re: Extruder Gear Pops Out - what other options are there?
January 06, 2014 06:18PM

I have that extruder, and I physically can't pull that gear out when filament is loaded.
I don't think those washers are helping.. I think they are moving the filament to the side of the hobbing causing the gear to pop up ?

I notice my gear does ride up a bit and seat itself on the filament when my printer is running.

I'm using 1.75mm filament, don't know if it makes a difference if you are using 3.0 ?

my money is on those washers. I wonder if they lock the hobbed bolt against the bearing ? i.e. they prevent the bearing doing it's job ?

I put mine together as here -> extruder

You might want to try without the additional washers, it's not designed to have them.
Re: Extruder Gear Pops Out - what other options are there?
January 06, 2014 07:23PM
That's how i had it in the beginning. same effect. actually, it was even worse. adding the washers was the only way i could get it to work even remotely reliably. worked on natural colored 1.75 PLA. today i put some black through it and it didn't work at all.

and no, the washers don't lock the hobbed bolt against the bearing. the washers only touch the inside portion of the bearing. it spins freely.
Re: Extruder Gear Pops Out - what other options are there?
January 06, 2014 08:24PM
That's odd.
Does it line up with the idler properly.
I genuinely cannot lift mine out when there is filament in it, so I'm wondering if there's a mistake somewhere.
The bolt that runs through the middle of yours looks longer than it should be ? but don't see how that would hurt.
It's done up right so that you can't pull filament backwards through it I presume ?

I'm wondering what is wrong, something is, the design is fine, there must be hundreds of them out there as its the original extruder I believe ?
Re: Extruder Gear Pops Out - what other options are there?
January 06, 2014 08:29PM
just reading your post again, it didn't work at all??

It's not lined up against the idler bearing or pushing against it then ?

Actually, thinking about it, when mine turned up there was a large lump of extrusion where the face of the idler bearing should be against the hobbed bolt.
I could put it together, but I took it apart again and cleaned it all out.

Was there large lumps of plastic to clear out of the print?

Might be worth taking it apart and checking. If you can pull filament backwards through it, then it's def wrong. Can you ?
Re: Extruder Gear Pops Out - what other options are there?
January 07, 2014 07:28PM
The problem is that the gear w/hobbed bolt slowly works its way up, so that at some point, the hobbed bits are not in contact with the filament. i tightened the bolts on the side and that had no effect. i think i have my printer limping along right now, i'm going to try and print out a new extruder piece. i think it could have just been a poorly printed piece.

we'll see. truthfully, i don't think this particular extruder is a great design. i like the hot end, and i like this one conceptually, but i think the way the gear and the hobbed bit go together is shitty.
Re: Extruder Gear Pops Out - what other options are there?
January 07, 2014 09:46PM
just check this one thing for me !

take it completely apart... and where the bearing is, that the hobbed bolt should be pushed against, check that the part of the bearing that faces the hobbed bolt isn't covered with a bit of plastic, or that there is no plastic around that bit of it of it. I mean the side that the hobbed bolt pushes on to.

am I making any sense ? I don't mean the bearing, behind the hobbed bolt. I mean the other one, the one that the filament is trapped against.

There's a hollow bit inside the extruder, where the bearing sits in, not the bearing that is affixed to the hobbed bolt and large gear. The other bearing. the bearing that is sitting inside the large lump of plastic that the hobbed bolt pushes against and traps the filament against.

that bearing was obscured by a bit of plastic in the channel inside the extruder when I got mine. I had to file out a bit of plastic so that the hobbed bolt could push onto that bearing. Thing is, it went together with the bit of plastic there, I thought it was ok, (well actually I spotted it, didn't know if it should be like that, couldn't find anything that said it shouldn't, so left it, but I had exactly the same symptom as you till I removed it)

With the hobbed bolt pushed onto that bearing, and the bit of filament between the 2 of them, there is no way you can pull it out, the filament actually stops it coming out.

can you see the reason for my consternation.. I think your hobbed bolt isn't pushed up against the side of the other metal bearing. (not the one behind the hobbed bolt, the other one!).

If it was.. you wouldn't be able to physically remove the big gear with the hobbed bolt on it.

It's not loose in that hole.. it's trapped there by the piece of filament.. IF the hobbed bolt is pushed up against the other bearing.

(I still don't trust your washers though)

I'm not being insistent, My judgement gets coloured by my day job, I do technical support charge controllers for wind turbines as part of my day job, I spent half an hour on the phone to someone last week who was swearing blind that he hadn't broken it.. and I was trying to work out what the failure was.

Half an hour later, he actually said.... "I haven't done any of that,.. all I did was common the negative of the dump load across to the negative of the turbine and then take that to the battery", and when I said "Why did you do that?, it doesn't say to do that in the manual", he said "it doesn't say not to do that". When replied "It doesn't say not to get a hammer, smash it into tiny pieces and flush it down the toilet either!", I'm sure he thought about going to get a hammer.
Re: Extruder Gear Pops Out - what other options are there?
January 09, 2014 05:11PM
Hi Bryan

Sorry for the delay replying. We have been inundated with emails recently, and are a couple of days behind.

I've read through the thread, and it's still not quite clear to me what is going wrong. A couple of points:
- your hobbed insert looks fine. The teeth look fine
- the extra washers will force the hobbed too far into the extruder body, and the teeth will miss the filament path.

How many 623 bearings do you have in the whole extruder? There should be three.
1. One is installed, as you have done, on the hex head bolt between the large gear and the hobbed insert, with the chamfered end of the hobbed insert pressed against it. Preferably without the washers.
2. The second is in the back of the extruder drive, and is held in place by the motor. This supports the end of the hex bolt, so it doesn't get pushed back by the filament.
3. The third is the idler, which pushes the filament against the teeth of the hobbed insert. It goes in the slot in the extruder, held in place by a 12mm M3 cap screw.

I suggest you take the extruder apart, and assemble it like this, so you can check it's working correctly:
Assemble the large gear, put the second bearing in the extruder block, and put the large gear in the block. If you look in the slot for the idler, you should see the teeth. If you feed some filament into the filament feed hole, you should see it feed into the teeth of the hobbed bolt. If there is some plastic in the way, trim it, but don't be too aggressive - it's there to support the filament.
Once you're happy that the hobbed insert is in the correct place, remove the filament, and put the idler bearing in. The two top bolts flex the extruder block, to apply more pressure to the filament, pushing it harder into the teeth. You can test this by hand, before putting the motor on.

If you want to post/send some more pictures (of the block would be useful), if the above does not work, it will be easier to diagnose the problems, and send you new bits, if you need them.

Please let me know if that helps.

RepRapPro tech support
Re: Extruder Gear Pops Out - what other options are there?
January 24, 2014 07:36PM
@DaveS: I checked, there's nothing in there. it's clean.
@Droftarts: it's assembled correctly. see the images below.

Here's the deal, I pop the gear in, load a piece of filament, it catches and feeds just fine. moderate grip. but as i turn it, i can actually pull the hobbed gear assembly out of the top. this is what's happening when it runs. it works for just a bit, then the damn thing works its way out the top.

also, i pulled the washers out, and it's still the same issue. i've mentioned that before.

Re: Extruder Gear Pops Out - what other options are there?
January 24, 2014 07:52PM
Hi Bryan. It certainly looks correctly assembled. One point; the longer screw, is it normally tensioned to the same extent as the screw nearest the camera in the second picture? If it isn't, this could be why the filament escapes the teeth, and eventually the gear pops out, due to side pressure from the idler bearing. You can mount the extruder in a couple of different positions so that the screw isn't used for mounting, and can be tensioned correctly; see: [www.reprappro.com]

Are the gears particularly tight on each other? This might cause a lot of lift on the large gear, and I suppose cause it to hook up the filament. What filament are you using? Is it particularly soft?

There is a bit of wiggle room between the gears. If you put the large gear in, put filament through, then slacken the motor bolts. Rotate the large gear (which will turn the small gear) so the motor shifts to the place of least resistance, then do up the motor bolts.

I hope that helps.

RepRapPro tech support
Re: Extruder Gear Pops Out - what other options are there?
January 24, 2014 07:55PM
Both screws are tensioned. If i don't, then the hobbled bolt grip is _extremely_ loose.

Gears aren't particularly tight on each other.

I've tried a ton of different 1.75 filament, all with more or less then same results. some i could get to work for a bit, others won't work for shit.

I'm not sure I understand the last instructions. What's the point of that?
Re: Extruder Gear Pops Out - what other options are there?
January 24, 2014 08:04PM
The last instruction is just if the gears are tight, and the small gear is forcing the big gear up.

If you would like, I'll order a replacement extruder drive kit sent to you, under warranty. This will be all the parts, apart from the motor, which would seem to be working fine.

RepRapPro tech support.
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