Drive Gear Slipping /Irregular extrusion

[Haas]

Hey All,
New problem here with my Makerbot Replicator 2
I've been racking my brain trying to solve this and haven't really found a solution in previous threads. Makerbot support also has not bothered to respond to my ticket in over a week.

I'm having a regular irregularity in the extrusion. This is apparent as soon as the first layer of a raft is laid down. as you can imagine, nothing can be printed this way.
I have checked the stepper drive gear and cleaned it till it shines like new, yet half of the gear slips against the filament when the slightest amount of resistance is applied. I can stop it by pinching the filament with my fingers, but only for a portion of the rotation of the motor, then it picks back up. I've tried running the loading script with the extruder block exposed, and confirmed the gear is continuing to turn at a constant rate, but its not pushing the filament through constantly.
Above is an image illustrating the problem.

The thicker parts are when it's extruding just fine, and the thinner areas are when the gear is not pushing. It seems to be pretty much 50/50 in a regular wave.
This Makerbot has the updated spring-loaded tension arm, not the plunger. It is providing plenty of pressure against the filament and gear. The gear is clean and free of any plastic, dirt, or oil, and as far as I can tell the teeth do not appear worn.

Has anyone seen this? Solved this? Do I just need to replace the gear? If so, is there a better one than the Makerbot one?
Thanks in advance!
-Haas

[Dan Newman]

On 29/01/2014, 9:24 AM, Haas wrote:
>
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> <https://lh4.googleusercontent.com/-W1rF0zirHkY/Uuk3i3pf-uI/AAAAAAAAARM/Wh2UafgGIk8/s1600/WP_20140124_001.jpg>

Have you tightened the set screw which affixes the pinch gear to the motor
shaft? If it gets loose, then slippage like you describe can and will
occur.

Dan

[Jetguy]

Are you sure the gear is not slipping on the shaft?

[3.1] Tighten the drive gear

If there is no clicking, it's possible that your plunger still isn't tight enough. It may also mean that the filament drive gear in your extruder is slipping on the motor shaft. Disassemble your extruder, as shown on page 52 of the Replicator 2 User Manual. Use your 2mm hex wrench to tighten the set screw holding the drive gear to the motor shaft.

 

 

On the drive system, plenty of pressure is not necessarily true. I take that with a grain of salt. I use monster springs on all my extruders and never have a problem.

[Haas Weston Colby]

Yes, I actually tightened it down to the flat side of the shaft long ago so this is not possible.

I have the Mk8 so there is not plunger, and I've even stretched the spring to provide extra pressure. 

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नमस्ते 

[Jetguy]

Sorry I meant roller or whatever.

Point being, you assumed spring pressure was OK, in my experieince, no it's generally not optimal and I would consider something stronger.

नमस्ते 

[Haas Weston Colby]

While it was running a loading operation I marked the place on the gear when the slippage started and stopped with sharpie, and indeed, it is happening in exactly the same area on every rotation, and it's one entire half of the gear.

So I decided to get out a macro lens and see what's going on….

The Good Side:

The Bad Side:

It's barely visible with the naked eye, but there does seem to be a bit of a groove worn into the gear, and I suppose it does look a little worse on the bad side. Could this be enough to cause total slippage?

I've printed A LOT of glow-in-the-dark PLA on this machine and had more than a few jams. As we had discovered in a previous thread, the GITD filament is pretty abrasive. So, I'll venture to conclude that over the course of several jams, while the stepper kept spinning it rubbed against the filament and wore this valley into the teeth. 

Plausible I suppose, but I hate to blame yet another failed printer part on GITD.

I won't be sure until I replace the gear.

[Jetguy]

The stainless material of the gear is what has made this design so successful. Many other companies use a soft steel locking hub and then cut the teeth using a tap.

It's easy to spot these, the teeth have a slight angle. The downside is the teeth are very weak. They can easily wear or be damaged. Brass ones could be even worse.

So I have and still beleive to this day, the MakerBot drive gear is superior.

 

So I doubt even the abrasive GITD is a direct cause. What is a heck of a lot more plausible is inserting a hardened hex key at some point to clear a jam and that easily explains why half the wheel is damaged and the other half isn't. So a tip would be, watch inserting hardened keys to clear jams!!

I'm not saying that is the cause here, just pointing out what I know.

 

And, if GITD was to blame, this goes back to what I said about the spring. If the spring is strong enough to NEVER,EVER, let the filament slip, then there cannot be wear as you have shown on half the gear. Unless you are running flexible filament, it's nearly impossible to get too strong of a spring that distorts the filament so much it won't feed into the thermal barrier opening. You will break something long before that happens with normal ABS and PLA.

नमस्ते 

[Haas Weston Colby]

Thanks Jetguy,

I'm pretty sure I've never done that, but frankly I've been inside the guts of this thing so many times, I'm not eliminating the possibility.

Im ordering a couple new gears from MB and see if we're good. I'll also get a new spring from them.

What are you using for a spring in yours?  I did feel that the stock spring was becoming-not-so-strong, so I stretched it by a few MM between two pliers and it did seem to help for a while until now, but from a physics standpoint, I realize this may not really be a big difference.... It still feels pretty darn tight, but if there's something stronger I can source, I'll use that.

[Jabu]

What are the odds of the stepper motor shaft being bent? 

[Jetguy]

Low but anything is technically possible. They are normally pretty hard shaft, but is not so hard they are brittle and thus they "could" be bent in shipping somehow.

Normal forces and normal usage shouldn't bend it. What I'm saying is, this didn't happen in the extruder, this happened before the motor was ever in a bot when the pallet of motors was dropped 10 feet and this motor was on the corner of the pallet kind of situation. If it was bent, it took a serious force to cause it.

On Thursday, January 30, 2014 4:47:06 AM UTC-5, Jabu wrote:

[Chris Fastie]

I am having a very similar issue with a Replicator 1 with 160 hours on it. I got it with 10 hours on it, and it printed well until about hour 140. At that time, periodic underextrusion started and is now common. The underextrusion is most conspicuous on top surfaces, but occurs throughout builds. It seems to be most common when the printing pattern is the mode with alternating 90° to produce a surface (does this have a name?). The photos below are all Sainsmart PLA, 0.15 mm layers, MakerWare and standard firmware (7.5), default profile parameters, 70mm/sec extrusion, with variation in temperature (205° to 225°C), 

Above: The center piece has not-quite-cyclical underextrusion. The piece on the right was printed afterwards, and has a good surface, so the problem is intermittent.   

Above: Close up of the center piece above. Maybe the underextrusion is cyclic, but is just worse during some cycles?  

Above: There is mostly too little PLA here, but it's worse at more or less regular intervals.

Above: Even when the surface is good, the periodic pattern is conspicuous.

I have experimented with some settings in profiles ("feedDiameter":,"feedstockMultiplier":,  "gridSpacingMultiplier":, with no improvement. So I think this is a hardware problem.

Is this symptom diagnostic of a particular malfunction? (I am going to watch the drive gear in action now. What will I observe?)

Chris

[Jetguy]

On a rep-1 are you using the stock plunger?

At 160 hours it's surely worn.

That is most likely your problem and again the basic test is to simply run the load filament routine and while it's extruding grab the filament going into the extruder and try to stop it. the motor MUST skip steps (click. If it doesn't skip, the filament is slipping, the plunger is worn and not pressing against the filament hard enough. That is "the test".

[Chris Fastie]

Yes, I assume this Rep 1 has the factory standard extruder hardware. That's all you get from it, 150 hours?

While running Load, I can stop the movement of filament just by holding the filament, and there is no noise at all. In fact, when I am not holding the filament, the extrusion from the nozzle stops completely every several seconds, then continues.  That certainly explains the cyclic underextrusion. 

Is a worn plunger likely to cause cyclic variation?

The shelves look pretty bare at the MakerBot store. Is it worth replacing the Delrin plunger, or is it silly not to do an extruder upgrade? Is there a single source for the upgrade?

[Jetguy]

Silly not to do an upgrade. http://www.thingiverse.com/thing:35810

Print in ABS, get yourself a 623 bearing(here, get 5 for $7 http://www.amazon.com/Amico-Double-Sealed-Groove-Bearings/dp/B008DSKCI6/ref=sr_1_2?ie=UTF8&qid=1391111220&sr=8-2&keywords=623+bearing

 

Yes, 150 hours is all you get. They sold replacement plungers and the support docs talk about replacing or adjusting them.

But the truth is, once you go bearing spring based roller system, you'll never go back.

 

Look, if you can't print it, PM me, I printed a ton of these. Heck just cover the cost of the bearings and mailing $10 and I'll send you a matched pair.

[DHeadrick]

If you need to upgrade both feed mechanisms for your replicator 1, look at:

3-in-1 extruder upgrade

Your other options are fairly limited unless you want to make your own.  The free upgrade from Makerbot for a spring loaded feeder is only for a Replicator 2 (which means it would fit your right side extruder only).

[Jetguy]

Also, if you have a Replicator 1 and haven't done the regulator mod, you are really running risk of total destruction of your bot.

That's another $5 mod that could save you serious$$$

[Jetguy]

Seriously Replicator 1 owners, you need to pay attention to this https://groups.google.com/d/msg/makerbot/boGwLWit2R0/VcUB1q8zTAoJ

Or his thread https://groups.google.com/d/msg/makerbot/Jrwqqxfiw8Y/geFQ7xUweTYJ

Or this thread https://groups.google.com/d/msg/makerbot/nd2b0YbK2hU/osQxD_dTRJ0J

or https://groups.google.com/d/msg/makerbot/5n4HwWyazlE/h2aXgH57JKcJ

"My 3rd MakerBot blew today. As I was removing a print there was a small static discharge on the build platform. I then placed my hand on the side of the Replicator near the SD card (as I always do when I navigate using the controls). There was another small zap. This time the screen flickered. The system seemed like it was off, then it would click on, then instantly off again in a loop. Like it knew there was a short somewhere (computers do this when they detect a short). I turned it off asap. When I turned it on, POP! Smoke. The voltage regulator literally exploded. A big chunk was missing (right / top corner)."

If you own a Replicator 1 and are running stock, you are on borrowed time and the extruder is the least of your problems.

[billyd]

Jetguy I am here with my hat in my hand. My extrusion problems were not the stepper motor as you suspected. After spending more time I have come to realize the fault lies in makerware slicer. Since buying simplify 3d the gaps in the walls I was getting (see 3 in 1 extruder thread) have gone away.

I believe recent versions of makerware have a defective slicer output which produces underextrusions randomly. I have printed the same exact models using simplify3d, and using very similar settings. The makerware output leaves small gaps in the walls, and the simplify3d does not.

I noticed this problem appearing in the last couple of months, and after replacing just about every part involved with extruding, the problem persisted. Once I switched the simplify3d slicer, and understood enough of the software to use it properly!!!, the problem disappeared. But when sliced with Makerware, the gaps return.

I have no idea what the OP's issue is, it is presenting itself differently than mine. Also I am using the 3 in 1 extruder.

On Wednesday, January 29, 2014 12:24:24 PM UTC-5, Haas wrote:

[billyd]

Sorry jetguy meant to say as you suspected it wasn't (regarding the stepper motor). I can't figure out how to edit posts.

[Jetguy]

It's cool and thanks for the feedback.

The problem of weak extrusion has so many causes, and each bot has unique problems.

It's funny that in this thread we have covered them all, I think???

[Chris Fastie]

You guys nailed it again. I swapped the Delrin plunger from the left extruder (which has hardly been used) to the right, and the underextrusion went away completely. So I have another 140 hours to figure out what to do next.

The right plunger had a single, tidy, shallow groove in it. I guess I could have rotated it 90°, a strategy which could provide 420 more hours of single nozzle printing!

I still don't quite understand the cyclic nature of the underextrusion. It must mean that the drive gear is not perfectly centered or perfectly round, and the cycle represents one rotation of the gear. 

Thanks for the help.

[Ryan Carlyle]

A gear fastened to a motor with a single set-screw will never be perfectly coaxial with the shaft. The set screw pushes the gear to one side. The looser the tolerances between the gear bore and the shaft diameter, the more accentric the gear will spin.

[Bryon Miller]

Print an extruder upgrade and get the parts from an ace hardware, that won't wear out unless you print in pla, then it will warp eventually, but you have a rep 1 so print it in ABS.

[Drew in Sunny Florida]

I have noticed that the infill is not always touching the edge wall outlines in prints since the last MakerWare update.  Again I thought I was just imagining this but now I am thinking it is a real slicer issue.  Did they make some kind of change that would cause sloppier intersections of the extruded plastic ???  I have noticed that where the infill meets an outline the infill does not squish upwards as it used to.  This may be the issue they were looking to fix.  

So far not a real problem for me just something I noticed.  

On Thursday, January 30, 2014 6:10:26 PM UTC-5, billyd wrote: