Extruder design limiting speed? You bet.

I was having issues going much over 50mm/s with a .5mm orifice hot end, I knew the printer is capable of doing much much more. With direct drive I had issues going much over 30mm/s...

When I mention those speeds I mean the speed at which I printed my walls, infill speed was somewhere 10-25% higher.

My findings and conditions are.

Initial build.
- 1.75mm Filament
- 2mm bowden setup
- ~1m long bowden tube.
- Direct drive with 1.75mm optimised gear.
- .5mm orafice

Result = Top speed 30mm/s outer shell 40mm/s infill.

First iteration.
- 1.75mm Filament
- 2mm bowden tube
- 1.75:1 gear ratio lashless gears
- 1.75mm optimised gear
- .5mm orafice

Result = Top speed 50mm/s outer shell 55mm/s infill.

Second iteration (Took 6 revisions to get right)
- 1.75mm Filament
- 2mm bowden tube
- ~60mm bowen tube length.
- 2:1 ratio belt drive
- 1.75mm optimised gear (No hobbled bolt here)
- .5mm Orafice

Result = 100mm/s outer shell 120mm/s infill....

Funny thing is that I haven't tested over 100mm/s and 120mm/s speeds yet. I have to say the belt drive acts as a direct drive as far as lash is concerned,

I Just found it astounding how much more speed you can get out of these printers with a properly tuned extruder design. I have made the tolerances very fine with this design and should be able to print with ninjaflex as well as almost any sort of springy type of filament. I have also designed this extruder to be able to go to 2.5:1 ratio with no modifications except the pulley. I may go to 2.5:1 if I need more torque. As it stands my end effector is fairly heavy as well as having solid aluminum arms vs carbon fiber arms. I will be doing further revisions to the moving parts of the printer to get higher acuracy at these speeds. Although the 100mm/s speeds are still producing reasonable quality, I think I need to increase the precision of the drive system. My arms are sitting at 335mm long made of solid alu, relatively thats allot of weight to swing around at over 100mm/s.

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Maybe you can help me, I finished building a delta type printer, I have a nema 17 stepper with an ezstruder setup for 1.75 mm with ~2 1/2 ft bowden tubing, using an E3dV6 hotend, initially everything seemed to work, I actually printed a couple of small parts that came out very good, now I can't seem to extrude anything, it's driving me crazy, I don't know if it's the hotend or the extruder setup I'm using.

Any help would save me many headaches.

Thanks,
JMF

Heat up the hotend and try to push filament directly into the hotend with your hand.

If it does not go easily then you need to disassemble and clean up the hotend.

If it does go easily then try to push it into hotend also through the bowden. If it is going hard then there is some problem with bowden (probably some garbage is in it or it is bend somewhere.

If you can push the filament through bowden to hotend easily with your hand then there is a problem with the stepper (driver), or driving gear.

Thanks Hercek, I'll check out your suggestions ....

Extruder pressure is important, however I suspect you have some sort of clog. I assume your using PLA? If the hot end has an all metal heat break, yoou may want to check the heat break for imperfections.

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Thanks Jaguarking11, I'm beginning to think it's just my extruder setup in general, I have it working ok at very slow speeds, but cannot print at any decent speeds, the filament can't keep up then the print gets all stringy due to lack of filament.

Starting to get bummed....

here is my extruder doing its job. Check it out.

[www.youtube.com]

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Nice video and extruder you are designing, how long is your current bowden tube ?

My bowden tube is around 600mm, roughly 2 feet long.

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Nice. Btw, I do not believe "no lash" is important for a bowden extruder. You get lash of about 8 mm in the bowden, so few tens of mm in the extruder itself does not matter.

Quote
hercek
Nice. Btw, I do not believe "no lash" is important for a bowden extruder. You get lash of about 8 mm in the bowden, so few tens of mm in the extruder itself does not matter.

I am not sure where your getting 8mm of lash from. Can you enlighten me? I used to run 4.5mm - 5mm retraction with 1m worth of bowden tube. If what you say is correct, then I should be able to get about 1/4 turn of my pulley when the machine is cold and the plastic is firmly jammed in the hot end. I do not seem to be able to do that currently.

One more point to have is that the more lash you have on the extruder itself the more you will have with the bowden, I have a feeling this is not exactly linear......

Please let me know where you got the source for this kind of lash. I would love to see the data, I am not in any way trying to be satirical about this. I hope I do not come off that way. I simply would like to see the data.

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@jmf: I'm bummed too. I've been wrestling with this stuff since October. I finally got myself running at 60+ mm/sec but I'm going in circles trying to calibrate this thing, especially since I can't seem to get the auto-bed-leveling to work using G29 or G30 in either RichCattel or Johan firmwares.
I'm also running 3mm filament, which wasn't my choice and does not seem to be a good choice for a Kossel Mini either, the Bowden tube torques the effector too much.
My Bowden tube is a snug-fit (3mm) thick PTFE tube cut as short as I could get away with, about 18 inches. I did this to minimize feed friction. I also decreased my hob size (Mk 8), built a tighter filament hob-clamp, and put cooling fan on my extruder driver heat-sink. I was STILL having problems trying to inch my way forward past 10 mm/sec. When I jumped to 60, surprisingly it didn't fail in a steaming mess like I would have guessed.

But the key to getting from 10 to 60 mm/sec? I changed the retraction from 1.5 to .5 mm. If I release the hob on the extruder motor from the filament and push in in and out, I get about 1-2 mm play.
I would guess that you need at least that much + some amount to actually suck the molten tip back into the nozzle. At .5mm, I'm probably not doing any retracting at all. It doesn't seem to be hurting my parts much; I do get some strings I don't want. If the retraction is too much, it pulls molten PLA above the hot-zone in the heat-break, where it can't remelt and you end up with jammed hotend. Personally I don't see how this ever DOESN'T happen. One thought is that it is that at high speeds the actual melt-zone is further toward the nozzle and you can afford to retract further because when the filament slows down, the heater catches up and the molten threshold moves closer to the top end of the hot end and remelts anything that might have tried to stick to the walls.

In order to lower the sideways torque which I'm sure is causing all kinds of geometry errors, I put back the original tubing: FEP, about 2.5 ft, sloppy internal fit, maybe 4 mm? With that in place I can measure about 5 mm of play, MUCH worse. It means a lot more back and forth with my extruder motor and I'm now getting jams again, although I've been messing with everything including the version of software so who knows..

Edited 1 time(s). Last edit at 01/12/2015 11:22PM by shadowphile.

Quote
jaguarking11

Quote
hercek
Nice. Btw, I do not believe "no lash" is important for a bowden extruder. You get lash of about 8 mm in the bowden, so few tens of mm in the extruder itself does not matter.

I am not sure where your getting 8mm of lash from. Can you enlighten me? I used to run 4.5mm - 5mm retraction with 1m worth of bowden tube.

The retraction size you need to get no stringing is your lash in the bowden. And quick couplings. I'm considering lash in quick couplings to be part of bowden lash in the text before and here. You maybe one of the lucky ones who have it at 4.5 mm only and it works fine. How big it must be depends on the particular filament used, the bowden, and quick couplings. So it will be somewhat different for each printer. I actually run a printer at 10mm retraction to get no stringing. I know at least one person who uses the same 10mm and that is also the person who told me that 10mm or somewhat smaller retraction is common with Φ1.75 mm filament, about 70cm bowden and quick couplings. That is the reason I mentioned the number 8. It was not supposed to be precise. We need to retract so that filament in the hotend does not push on the molten pool of plastics. So the minimum retraction size needed to get almost no stringing is the lash in bowden and lash in the extruder. Even sloppy extruders will have only few tens of mm lash. So if one needs about 8 mm retraction then most of it is in the bowden.

It is not like your lash in the extruder gets somehow magnified in the bowden. It is more simple: lash in the extruder gets added to the lash in the bowden. That means the point holds even for you. If you need only 4.5 mm retraction then the tiny part of it which happens in the extruder itself is negligible compared to the whole number of 4.5 mm. Hence some small play in the extruder does not really matter for bowden systems. It would be a bit more important in systems without bowden where retraction sizes are about 1-2 mm.

I can understand you adding the coupling lash to the overall fit. My couplings have almost no lash. They are the 10mm thread couplings made of brass and have a blue spring. I used to use much more expensive couplings that required me to torque the tube into them to reduce lash, and even then it was too much of a pain. Goes to show, you don't always get what you paid for. My couplings were less than 50c a pop. The other ones were I belive around 3usd a piece.

I am using 1.75mm filament on my system. I have successfully printed with a 1.55mm hot end on it so I see no reason to go 3mm, not only that but local supply of 3mm filament is much lower than 1.75mm stuff. The bowden tube I have is teflon 2mm tube. The length of the tube is now 600mm or so. My retraction is around 3mm and I am experimenting in dropping it. The other part of the lash I have noticed is that the tube does expand under very high force, and also the filament I use (ABS) is somewhat springy. Another part of my lash problem is that I have a teflon lined hot end, once I upgrade this thing to a solid stainless heat break I should be much better off.

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Quote
shadowphile
@jmf: I'm bummed too. I've been wrestling with this stuff since October. I finally got myself running at 60+ mm/sec but I'm going in circles trying to calibrate this thing, especially since I can't seem to get the auto-bed-leveling to work using G29 or G30 in either RichCattel or Johan firmwares.
I'm also running 3mm filament, which wasn't my choice and does not seem to be a good choice for a Kossel Mini either, the Bowden tube torques the effector too much.
My Bowden tube is a snug-fit (3mm) thick PTFE tube cut as short as I could get away with, about 18 inches. I did this to minimize feed friction. I also decreased my hob size (Mk 8), built a tighter filament hob-clamp, and put cooling fan on my extruder driver heat-sink. I was STILL having problems trying to inch my way forward past 10 mm/sec. When I jumped to 60, surprisingly it didn't fail in a steaming mess like I would have guessed.

But the key to getting from 10 to 60 mm/sec? I changed the retraction from 1.5 to .5 mm. If I release the hob on the extruder motor from the filament and push in in and out, I get about 1-2 mm play.
I would guess that you need at least that much + some amount to actually suck the molten tip back into the nozzle. At .5mm, I'm probably not doing any retracting at all. It doesn't seem to be hurting my parts much; I do get some strings I don't want. If the retraction is too much, it pulls molten PLA above the hot-zone in the heat-break, where it can't remelt and you end up with jammed hotend. Personally I don't see how this ever DOESN'T happen. One thought is that it is that at high speeds the actual melt-zone is further toward the nozzle and you can afford to retract further because when the filament slows down, the heater catches up and the molten threshold moves closer to the top end of the hot end and remelts anything that might have tried to stick to the walls.

In order to lower the sideways torque which I'm sure is causing all kinds of geometry errors, I put back the original tubing: FEP, about 2.5 ft, sloppy internal fit, maybe 4 mm? With that in place I can measure about 5 mm of play, MUCH worse. It means a lot more back and forth with my extruder motor and I'm now getting jams again, although I've been messing with everything including the version of software so who knows..

I've been fighting the same things that you appear to be, extruder and calibration of the printer itself, oh well, I'll keep plugging away, thanks for the tip on retraction...

It seems to me a quick method to measure the exact amount of retraction is to release the filament from the extruder hob so that it will push in and out manually.
Make sure the hot end is hot and primed and ready to extrude, then shut it off and let it solidify.
Push it in manually until it stops (all movement is now lash). Mark the point where the filament enters the extruder feed mechanism (or similar), then pull out snugly and measure how far the mark has moved. That would be your retraction size.
However, at this point you will stop the oozing but you will not retract anything left hanging past the nozzle. For that it sems like you would need to add a little more retraction to make a suction. (won't be much)

This probably also matters how much clearance there is between the heatbreak ID and the filament OD. I noticed that my e3d v6 3mm bowden model hotend is not tight on my filament, actually looser than a similar knock-off model. It would allow more room for the molten plastic to move up around the solid part of the filament, requiring an adjustment to your retraction.

Sound good?

I really like the looks of this extruder design even though I'm pretty happy with mine(stock geared Kossel Mini extruder) I'm never satisfied. I'm currently seeing 60mm/second retracts, have you checked yours to find your extruders limit? I usually run about 4.7mm of retract, anymore and I start seeing the width of seams increase on say a vase being printed without vase mode enabled increase.

While printing speed is not really a priority on my list as I prefer highest quality I've found that a high retract speed can help reduce and in my case pretty much prevent stringing with most filaments as long as the proper hot end temps are used. I'm always looking to improve my printers performance though and have been wondering if a stepper larger then a nema 17 on the extruder would allow something like your extruder to work as well as 5:1 geared setup torque wise while offering improved retract speeds.

Right now I'm torn between trying different gear ratios and stepper sizes with moving to 0.9 degree stepper motors all around. I know most people agree they offer no advantage over 1.8 degree steppers but I would like to see for myself as I'm in pursuit of the highest quality prints.

Honestly I have not tested the retraction speed. I run about 3.5mm on mine and am fairly happy. My goal is to reach the highest speed possible with aceptable prints. At this point my limiting factor is effector and arm weight. I am working on replacing the whole setup soon enough.

I am also ordering parts to run a batch of 10 extruders to test the market. Unfortunetly its going to take me a while to gather all the parts. I plan on selling these with the motor for about 60USD shipped. If that is aceptable to you guys then stay tuned and I will have the first batch of 10 going shortly.

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Quote
ChrisT88
I'm currently seeing 60mm/second retracts, have you checked yours to find your extruders limit? I usually run about 4.7mm of retract, anymore and I start seeing the width of seams increase on say a vase being printed without vase mode enabled increase.

5:1 gear down is too much. You should try to find something smaller. I use 2:1 and retract speed of 200 mm/s and 10 mm retract. Works fine. It is good if you can get retract time below 0.1s.

Quote
hercek

Quote
ChrisT88
I'm currently seeing 60mm/second retracts, have you checked yours to find your extruders limit? I usually run about 4.7mm of retract, anymore and I start seeing the width of seams increase on say a vase being printed without vase mode enabled increase.

5:1 gear down is too much. You should try to find something smaller. I use 2:1 and retract speed of 200 mm/s and 10 mm retract. Works fine. It is good if you can get retract time below 0.1s.

This is exactly my feeling. I think 2:1 or 2.5:1 is fairly ideal. At least this is my feeling. Large gear reduction increases latency quite a bit. Some people are going nema 23 with direct drive, others are using printed gears.. I prefer a properly belted extruder, at least right now. I am very happy with my setup.

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Belt is better than gears because belt is quieter. It is also more expensive.

Ok, I setup a preorder info page here. -> [forums.reprap.org]

I hope to have the first batch done by the end of feb. I am placing the orders for the various parts as I type this.

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