Author Topic: The Living 3D Printing Thread  (Read 132783 times)

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Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #500 on: Sun, 13 October 2013, 10:54:19 »
straight cut gears are more durable. more surface area per unit diameter

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Offline Leslieann

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Re: The Living 3D Printing Thread
« Reply #501 on: Sun, 13 October 2013, 19:35:51 »
straight cut gears are more durable. more surface area per unit diameter
Actually, angular cut gears have more surface area and tend to run more smooth as they are always engaged, leaving them less prone to shock damage and giving them a smoother operation. In general, they tend to be considered stronger overall. The two main selling points on straight cut gears are that they're easier to produce, and they don't produce side loads. Another benefit is that when shaped properly, straight cut will have lower friction, however, this tends to equate to more noise, particularly as speed increases. Friction and ease of production is why race cars use them, while street cars use angular whenever possible for noise reasons.


As for the whine, straight cut are more prone to it however there is methods you can use to reduce it, such as dissimilar materials for each gear (I do this on herringbone), oil bath, tooth profile, pitch, speed and load. Given equal circumstances, straight cut will make more noise than angular. Speed is why most extruders are silent even with straight cut, the rotation speed is simply too low for much noise during normal printing, retraction and loading filament can still cause whine. Herringbone can also produce whine when run in reverse, or when misaligned. On my old nozzle, too much retraction caused my head to jam, so being able to hear the retraction was valuable at the time as I could tell when it was doing it too often and switch to another slicer, but was quiet the rest of the time. I kind of got used to it.



Personally, I just find them interesting,  I love mechanical stuff, and herringbone gears aren't something I've had any experience with so I wanted to try them, but I'll have to see how the latest ones turn out as they do have a dark side.  When misaligned, particularly in reverse, herringbones generate a massive side load. This side load can be enough to destroy small bearing races and extruders, I've destroyed two of each so far due to poorly printed gears. I had no idea the amount of side load they could produce.  The last gears and extruder I allowed for some float of the gears so they could keep themselves aligned properly and that seemed to solve it. I have better gears now.
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Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #502 on: Sun, 13 October 2013, 22:24:02 »
woah, owned! hmmm.. let me think about this one a bit. i always thought that straight lines packed the most teeth into a cylinder.. (and by straight i mean an arc of 0deg, not like parallel to the cylinder straight, there could be some angle theta for which each ray is offset by theta, and an optimal theta for each cylindrical shape)

but my spatial reasoning is frankly ****. is there a really simple way for me to grock why arc cuts give you more surface area?

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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #503 on: Mon, 14 October 2013, 05:09:41 »
Based on this web http://www.roymech.co.uk/Useful_Tables/Drive/Gear_Efficiency.html
Efficiency of spur and helical gear is the same. But the site considers only gear losses. Axial force needs to be compensated for when helical gears are used. That compensation probably results in some loses.

I'll stay with straight cut gears. I like the fact I can put a gear on without moving gear axe away first.

Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #504 on: Mon, 14 October 2013, 06:09:44 »
cptbadass's 3am musings agree with leslieann but couldn't remember why. something to stare at later.

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Offline Leslieann

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Re: The Living 3D Printing Thread
« Reply #505 on: Mon, 14 October 2013, 16:53:21 »
but my spatial reasoning is frankly ****. is there a really simple way for me to grock why arc cuts give you more surface area?
Very over-simplified answer...
The straightest distance between two points is a straight line, and a straight cut gear, is a straight line.



I'll stay with straight cut gears. I like the fact I can put a gear on without moving gear axe away first.
I'll probably go to them at some point, it would certainly make assembly easier.
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Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #506 on: Tue, 15 October 2013, 11:35:27 »
but my spatial reasoning is frankly ****. is there a really simple way for me to grock why arc cuts give you more surface area?
Very over-simplified answer...
The straightest distance between two points is a straight line, and a straight cut gear, is a straight line.



I'll stay with straight cut gears. I like the fact I can put a gear on without moving gear axe away first.
I'll probably go to them at some point, it would certainly make assembly easier.
yep, that was my immediate thought, but it's a packing problem, and straight lines are easier to pack, no?


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Offline Leslieann

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Re: The Living 3D Printing Thread
« Reply #507 on: Thu, 17 October 2013, 04:37:58 »
I believe it has more to do with the tooth profile necessary for straight cut to engage smoothly. You don't actually use the entire face.
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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #508 on: Thu, 17 October 2013, 11:36:23 »
Well, at least based on what is in openscad MCAD library, there is no real difference between spur gears and helical gears. The profile is the same, it is just "twisted" in case of helical gears. Both kinds of gears engage only at a line. The difference is that for helical gears the line is not straight. I can see only 2 significant differences:
* helical gears generate axial force,
* helical gear engage at different phases of tooth touch point at the same time.

The second point actually can make a difference since involute gears transfer force without tooth sliding (rubbing each other) only at one point of the tooth engagement phase. That is when the teeth touch point is at the pitch circle. I would assume that at this point the power transition is the most optimal. Elsewhere the rubbing should waste some of the useful power. Although the moments (levers) of tooth engagement are the same in all the phases, the friction is changing. This can possibly introduce some variations in the power transition and therefore vibration and the "whine" of the spur gears.

The good think for helical gears is that same part of it is always at that optimal point (at the pitch circle).

Disclaimer: I'm not a mechanical engineer, I'm just "brainstorming" why involute helical gears may have something good to them.

But our geared extruders should be good enough with spur gears.


Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #509 on: Thu, 17 October 2013, 22:31:32 »
fantastic animation; thanks. i'm starting to see the intricacies. you really really have to model things as time variant in R^3, as the force vectors involved cannot be contained in any simple intuitive subspace. INTERESTING!

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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #510 on: Mon, 21 October 2013, 14:13:48 »
I did first test with 24V power source.
It allowed to increase maximum motor speed by about 60%.
Stepper driver pots did not need a change.
BANG_MAX/PID_MAX was reduced to 120 (still about two times the power so hotend heats up much quicker).
PID parameters need to be auto-tuned again.

Offline vvp

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Re: The Living 3D Printing Thread
« Reply #511 on: Sat, 09 November 2013, 10:07:01 »
OK, I like 24V 3dPrinter power source.

I made one by modifying regular PC power source so that it has floating ground and connected it to series with unmodified PC power source.

Anyway, I saw same schema of a PC power source and it looks like it should be easy to modify -12V rail so that it can handle high currents. Looks like only replacing two diodes, capacitor, stronger current leads and maybe using 3.3V coil in the final filter (if the original one has too small wire diameter, this would disable 3.3V output, but who cares). A floating ground modification would be needed too but that is trivial. After the change we could use -12V +12V rails for a 24V power source. It looks simple. Did anybody try it? Any experience?

Offline Leslieann

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Re: The Living 3D Printing Thread
« Reply #512 on: Fri, 15 November 2013, 17:59:07 »
You could probably get a 24v psu for cheap and smaller in size.
I need to look at what the Ramps board requires for higher voltage, it seems like a better way to go. However, if I do, I'll be buying a PSU, as what you're doing is a bit beyond my ability.


I strongly suspect my heated bed is the source of many of my problems.
Ramps is rated for 5amps max draw and the bed is rated for 10 amps, others get away with 16amps to power everything, my printer found 18amps to be underpowered, and actually destroyed a mosfet and a cheap Chinese 20amp PSU (all 3 had active cooling).



I have a question for you VVP
In a printer chat, someone claimed that the 3watt resister we use for hot ends actually draws closer to 40watts due to some "trick". When I asked how this worked, I got no response. Any ideas or is he just full of it like I suspect? And if he is correct, then what is the 40watt cartridge heaters actually pulling?
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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #513 on: Sat, 16 November 2013, 08:55:03 »
Actually, I found one more power source scheme and that cannot have -12V rail strengthened easily as I proposed. So the idea is not that universal. I do not know which kind is more common. My guess would that the one which can have -12V strengthened. Anyway, it looks like one needs to check how his/hers particular PC power source is connected at the secondary side.

In general, off-the-shelf 24V power sources are easily available as 24V switching power sources for LED lights. They seem to top at about 350W which should be enough. I only consider adjusting PC power source since me (and probably almost everybody else) has some spare one from older PCs.

I use two small (SFX format) PC power supplies in series to get 24V. One of them is floating ground of course.

Most hotends use 3W wire wound resistor of 6.8Ω, axial leads, 13mm length, 5.6mm diameter. We mostly power it with 12V which gives us power of 12/6.8 ≅ 21W. Much more than the nominal 3W, but it does not really matter. The point is that resistor power rating is limited above all by how quickly it can get rid of heat. That is the reason the higher power resistors are bigger in size. Since our hotend resistors are surrounded by thermally conductive paste and inserted in a metal block they can get rid of heat much better than when they are simply soldered to a PCB. On a PCB it would have maximum 3W, in our hotend it can withstand 21W easily.
I actually power this 6.8Ω resistor with 24V which leads to maximum power of 24/6.8 ≅ 85W. And I did not have any problem with it yet. But notice this is the peak power. I use PID and limit the duty cycle to at most 120/255. That means that my maximum average power is about 86/255*120 = 40W. Which is just the power the guy mentioned. By the trick, he probably meant two things preventing baking our 3W resistors to ashes):
1) good heat transfer from resistor to hotend
2) limiting PID duty cycle if more than 12V power source is used.

Some people go from hotend resistor to heaters. This way they make sure that they really do not go over nominal values. I do not think it is needed. Wire wound resistor should be enough and they are cheap. Just make sure that heat is transferred well from the resistor to the hotend. Although I'm thinking about replacing the hotend resistor with a 15Ω one to limit peak currents and a chance they will induce something to thermistor wires. But I'm not in a hurry. The high currents I have there now do not seem to do any harm. So the replacement is just a quest for unnecessary perfection :) I'm not considering going for a heater.

The 40W cartridge heaters, if specified for 12V, should pull 40/12 ≅ 3.3A. They should have resistance about 3.8Ω. I do not think is it that great idea to use them, since they are more expensive. They will heat up your hotend sooner. I already achieved that by moving to 24 V, which gives me also higher speed on steppers (but I care only about extruder stepper speed).
Other advantage, I can think of, is that they are run on nominal values so they stay in warranty. I never heard of hotend resistor failure yet and it did not happen to me, so I think cartridge heaters are just vanity ... at least till I do not find some data confirming their usefulness :D Any wire wound resistor which just fits nicely in your hotend should be fine. If you care much find surge wire wound resistor (these can withstand short current peaks better) and look for the ones which are rated for the biggest temperature.

Edit: spelling.
« Last Edit: Sat, 16 November 2013, 15:25:58 by vvp »

Offline Leslieann

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Re: The Living 3D Printing Thread
« Reply #514 on: Mon, 18 November 2013, 00:03:23 »
Thanks.
My understanding is people like the cartridge because it's easier to wire up and you can use a set screw to hold it in place against a mating surface without fear of destroying it. Also, it's been sold as producing more heat (higher wattage), but that appears to be fake.

Hmm, based on the math you provided, that means my heated bed is drawing just a bit more than the 10 amps claimed. The hot end wattage also means people using a 5amp power supply to power a Ramps board, Arduino, fans and hot end are actually very underpowered. That's one thing I dislike about open source, for all the good information, there is also lots of bad.
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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #515 on: Mon, 18 November 2013, 05:16:42 »
I have RAMPS 1.3. It's wiki page claims 11A for heatbed (which is about right) and 5A for steppers and hotend (which is too small). Most motors (driven by the most common (green) pololus) can take about 1.3A without thermal shutdowns. So the minimum rating for motors and hotend should be 4*1.3 + 12/6.8 ≅ 7A. The fuse is somewhat low for this too (its holding current is 5A and tripping is 10A). If you are very unlucky you may have problems with fuse ... but you probably will not, the fuses are slow (like about 15s trip time at 25A).

Things change when you use e.g. 24V power supply instead of the common 12V. Steppers and hotend can handle it with a software change only (limiting hotend resistor duty cycle). But our 12V heatbed will not work reliably with 24V power supply. That would lead to about 22A of current and that is more than the fuse would safely allow without tripping (its tripping current is just at 22A), the MOSFET can handle it but would probably need a heat sink and the PCB traces and your wires would probably need strengthening too.

Offline Leslieann

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Re: The Living 3D Printing Thread
« Reply #516 on: Mon, 18 November 2013, 20:41:20 »
I have RAMPS 1.3. It's wiki page claims 11A for heatbed (which is about right) and 5A for steppers and hotend (which is too small). Most motors (driven by the most common (green) pololus) can take about 1.3A without thermal shutdowns. So the minimum rating for motors and hotend should be 4*1.3 + 12/6.8 ≅ 7A.

That's about what I was thinking.
I'm going to step mine up to an 8 amp brick, that way I can also run a fan and lights.
Not sure what to do about the bed, I know the circuits are separate for the bed (Ramps 1.4), maybe it's possible to use a 24volt bed and leave the rest on 12volts. I don't really want a huge power supply attached, but I may do that but make it easily removed.
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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #517 on: Tue, 19 November 2013, 05:46:26 »
... maybe it's possible to use a 24volt bed and leave the rest on 12volts.
Yes, it is. Though, you need a bed which will not pull more than 11A at 24V if you increase the voltage. If you have 12V only PCB heatbed then you need to switch it. I have seen a dual voltage (12V/24V) PCB heatbed. I think (not sure) it is still pulling about 10A at 24V option. If so then you would get a heatbed which heats up considerably faster. I personally do not care. When I heat it up I cover it with a piece of cloth and it is quick enough for me.

Offline damorgue

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Re: The Living 3D Printing Thread
« Reply #518 on: Sun, 01 December 2013, 15:15:40 »
How is the quality nowadays on all you guys' machines? Any updates, are you all up and running?

Offline Leslieann

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Re: The Living 3D Printing Thread
« Reply #519 on: Mon, 02 December 2013, 00:04:12 »
Mine's fine, I just need to invest in better power. Most of my funds have been diverted to other things lately.
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Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #520 on: Mon, 02 December 2013, 01:21:48 »
i'm running and producing at about as high a rate as a rep2x is capable of. basically i print until i break something, i fix it, then when it comes back up again, i print until it breaks again and so on. basically, there are a lot of disposable parts in the replicator. it's a very clever design, and the disposable parts are remarkably good at light duty cycles. but i tend to push tooling limits, and _when_ the parts fail. they fail in very bizarre ways. i've had galling on "steel" rods with bronze bushings (chinese steel :|), huge amounts of warpage in the z-stage, and my current y-axis accuracy is well, pretty low. the only remaining original ABS parts in the machines are on their last legs and showing visible wear in the .5 to 1mm range in bizarre directions (vibration, i think). at this point i feel like i know the design well enough that i have a pretty good idea of what needs to be improved and what can stay consumable, but implementing major changes takes time

shrug

as far as machine capability, my biggest issue right now is just printing very small parts. temperature and movement control is just not advanced enough to get the kind of tolerances you need to print small parts --- the machine tolerances start running into the part size and then you end up with a whole bunch of failed builds.

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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #521 on: Mon, 02 December 2013, 10:57:51 »
The Rostock here works fine. The print quality improved with every change to the original design:
1) Ball joints instead of the original universal joints. MP-Jet joints were used instead of Traxxas (no need to connect diagonal rods with springs). This helped the most.
2) Geared extruder, no problem with skipped steps, but it is still slow (the maximum print speed is about 5 cm/s), the hobbed bolt grinds the filament at higher speeds. This should be improved more.
3) Idlers were replaced. The original ones were based on 608 bearings. The new ones are from two MF148 (8x14x4 bearing with flange). Half turn of the belt was added (so that the belt touches the idler with the smooth side).

I also found I cannot print reliably thin and tall objects (e.g. 1 cm diameter, 20 cm height tube). After about 15 cm the printed object is bending and the surface is not perfect. At least that is what I think is happening. The material is ABS.

Offline damorgue

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Re: The Living 3D Printing Thread
« Reply #522 on: Mon, 02 December 2013, 12:13:30 »
Feel free to test this for me  :thumb:

Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #523 on: Mon, 02 December 2013, 17:38:26 »
you put that in the dropbox earlier right? i think i have it and have looked at it. i should have printed it before the extruder gearbox went out last week. i tried to revive it with replacement springs, but something else is wonky in the filament drivetrain. with MBI's design, you basically replace everything around a failed part when the part fails, and life is good, so i have new parts coming, but i think that one was too small (or was it?...) to print with my current limitations. basically, right now if i don't keep the filament moving very quickly, the drivetrain gets stuck. it's almost like the issue that the hot ends have with PLA (they're just too damned hot), but it's purely mechanical. the ABS is fine, and to clear the blockage you just push it on through and try your print again.

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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #524 on: Tue, 03 December 2013, 11:14:06 »
It looks like a tough part to print using FDM. It will require a lot of support. Also that thin pillar few mm in diameter and long about 14mm would be a ***** to print. Especially when the printer does not have a fan and uses a bowden. It probably can be done with a lot of support and a different support material which can be dissolved away. Bowdenless printer would be better to get more precise material deposition especially on the small parts where blobs cannot be hidden inside the part.
I would try SLS or SL for this.

Offline damorgue

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Re: The Living 3D Printing Thread
« Reply #525 on: Tue, 03 December 2013, 12:08:30 »
It is my intention to use SLA or SLS in the end, that is the reason for the thin pillar actually since they take advantage of anchors. I just wanted to test a few things with a cheaper method first, but I just figured out a way to accomplish the same test with a different model.

Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #526 on: Tue, 03 December 2013, 14:19:36 »
aren't you trying to test the material? obviously an extrusion print isn't going to look anything like an SLS print from a material properties standpoint..

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Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #527 on: Tue, 03 December 2013, 14:20:05 »
like those buttons i printed for you. you're going to get a lot less elasticity out of the sls version of those...

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Offline damorgue

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Re: The Living 3D Printing Thread
« Reply #528 on: Tue, 03 December 2013, 14:29:40 »
like those buttons i printed for you. you're going to get a lot less elasticity out of the sls version of those...

I have already printed those in other methods and they are fine :)

I am trying out a few solutions for the structure mostly. My intentions was to get rough estimates with FDM first though.

Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #529 on: Tue, 03 December 2013, 15:05:10 »
good, but i wouldn't even bother printing in our materials to prep for sls. i mean just between two factories and runs of abs filament at the same print duty i can get two completely different bulk materials. heck, as you know, just between two colors from the same factory same run date, there can be a huge amount of difference, and that's just for abs.

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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #530 on: Wed, 04 December 2013, 13:45:19 »
If you do not need all the free space inside the part then just design it solid (filled in) for an FDM test run. Sparse infill can be used so it is not a big deal whether the part has a big volume or not. As it is now, I would tell it is unprintable with a standard Rostock. Especially that thin pillar.

Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #531 on: Wed, 04 December 2013, 14:49:55 »
shrug. i can print it with HIPs supposed. basically i'd print a solid HIPs block with your part in it.

hah!

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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #532 on: Wed, 04 December 2013, 17:20:31 »
Yes, that would work :)
It would be probably enough to surround the pillar with HIPs. I guess, it would not turn out very well anyway but at least it would be there. The rest could use also the standard support. It would be pain to remove it but it should be doable. But when using HIPs for the pillar then it can be used for all support.

Makerbot2 does not use bowden extruder so it should not have such a big problem with small parts which do not have enough internal volume to hide blobs in.

Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #533 on: Wed, 04 December 2013, 18:21:03 »
the problem with long tall skinny parts, and really really small parts is collision. if a head collides with a printed bit of extrusion, bad stuff happens depending on how much support that part has w/rt stiction to the build plate (which is ultimately where all the forces into the part go while it's being printed).

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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #534 on: Thu, 05 December 2013, 03:19:14 »
Leslieann:
I just noticed that the 11A fuse for heatbed on my RAMPS 1.3 is rated for only 16V (the 5A fuse for steppers and hotend is rated 30V). Your RAMPS 1.4 is probably the same so if you would want to switch heatbed to a 24V version then you should change the fuse too.

Offline Leslieann

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Re: The Living 3D Printing Thread
« Reply #535 on: Thu, 05 December 2013, 16:04:08 »
the problem with long tall skinny parts, and really really small parts is collision. if a head collides with a printed bit of extrusion, bad stuff happens depending on how much support that part has w/rt stiction to the build plate (which is ultimately where all the forces into the part go while it's being printed).
On tall thin stuff, I usually still a pad off to the side with a thin upright (1x or 2x nozzle diameter), this lends support and can be broken away relatively clean after printing compared to putting a pad and support on the thin wall.

Leslieann:
I just noticed that the 11A fuse for heatbed on my RAMPS 1.3 is rated for only 16V (the 5A fuse for steppers and hotend is rated 30V). Your RAMPS 1.4 is probably the same so if you would want to switch heatbed to a 24V version then you should change the fuse too.
Yeah, I have been reading up on it a bit more and saw that.
I need to get the new printers operational before I start messing with that, anyhow.
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Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #536 on: Thu, 05 December 2013, 16:19:57 »
with your bowden tubes.. have you guys tried using sacrificial walls and towers as a wiper mechanism?

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Offline Leslieann

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Re: The Living 3D Printing Thread
« Reply #537 on: Thu, 05 December 2013, 17:43:07 »
with your bowden tubes.. have you guys tried using sacrificial walls and towers as a wiper mechanism?
I have my retraction down pretty well, to where I don't have a need really.

The thing with bowdens is you either need a lot of retraction or take out slop where you can. I run 10or13mm of retraction (I don't remember where it's set at the moment), and I place clips to take up slack in the pneumatic fittings, which can add more than 3mm of slop.

One issue I have seen though, is retraction needs to be fast, and anything much over 3:1 gear reduction and I can't retract fast enough. I have a prototype extruder I plan on trying that is 2:1 reduction to see if it gets better. I had an pg35l extruder motor but the 20:1 reduction was entirely too slow and I wasn't happy with it, or how hot it got. My 3:1 works well (it's from a 3mm extruder system), but 2:1 might be better for 1.75 systems.
« Last Edit: Thu, 05 December 2013, 17:46:32 by Leslieann »
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Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #538 on: Thu, 05 December 2013, 18:39:31 »
you don't have issues with creep out of the hot end at all with the bowdens? naturally we have gravity bringing a bit of extra melt down out of the nozzle and need to wipe every once in a while.

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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #539 on: Fri, 06 December 2013, 02:56:48 »
you don't have issues with creep out of the hot end at all with the bowdens? naturally we have gravity bringing a bit of extra melt down out of the nozzle and need to wipe every once in a while.
It may be needed with dual extruder when one head is heated and does not print anything for a longer time. I did not try to use it but I think the wipe column is almost useless for single extruder rostock. Moreover it can be harmfull since it adds retracts which (if frequent) deforms filament and results in wrong extrusion amounts. The other point is that non-printing moves are quick and head is not pressurized during them. Hardly anything gets out of the nozzle because of gravity in such a short time (typically below 0.5s). The bigger problem is retract and retract reverse times. Depending how quick your extruder stepper is, these can take about 0.2s. But the important difference is that the nozzle pressure is rising/falling during these times. The filament is pushed to the hotend with forces around 20N (for speeds about 2.5 cm/s, 185C PLA). This value is about 2e5 times higher than the gravitational force for a bit of melted plastics in the nozzle. OK, 2e5 is the maximum at the time of retract start and retract reverse end only but still it is a huge number.

The consequence is that tiny blobs of material are deposited at the retract and retract reverse locations. Slicer can handle this easily if there is enough internal volume to hide them in. For very tiny parts there is not enough internal volume and it causes visible/measurable seem on e.g. thin walls. Thin pillars not only do not have the internal volume but also bent which is much worse problem actually. And if they are alone there is also problem with their cooling.

That is the reason I'm trying to get not only stronger extruder but also a very quick one. This also made me to go to 24V for the motors. It increased the usable extruder speed by about 60%. I actually expected speedup by 100% but it was not true. I do not know why I achieved only 60%   :confused:

Anyway, I believe the problem with tiny blobs during retract and retract reverse are mostly fixable with better slicers. The slicer should have some model to estimate how flow will change with the falling/raising pressure and move the head along the planned extrusion path acordingly. If the bowden friction is predictable enough (I hope it is) and the fluid dynamics in the hotend is predictable enough (I think it is) then this should be doable.

Edit: spelling.
« Last Edit: Fri, 06 December 2013, 03:01:33 by vvp »

Offline mkawa

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Re: The Living 3D Printing Thread
« Reply #540 on: Fri, 06 December 2013, 03:01:15 »
it's too hard to estimate flow changes. depends on material, actual hot end temperature etc. etc. etc.

that's the thing with steppers for extrusion. life would be much easier with simple dc motors..

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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #541 on: Fri, 06 December 2013, 03:11:40 »
I think it is hard to predict friction forces, maybe even impossible to predict them well enough for the prediction to be useful. But there is a chance the friction forces are small enough that errors here would not matter that much.
I think the situation in the nozzle itself should be predictable enough.  Reynolds number will be small. Heating and viscosity change related to it complicate it but my guess is this is doable.

Probably the most easy way would be to measure flow speed experimentally and just put the measured table in the slicer code. That is if we find the flow speed is repeatable enough for the same filament feeding speed changes.

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Re: The Living 3D Printing Thread
« Reply #542 on: Fri, 06 December 2013, 03:30:42 »
friction isn't the issue. filament pressure depends on density of your particular filament formulation and diameter of filament and a whole bunch of other things. for a given filament spool of high quality you should be able to experimentally determine these values, but it's a per-spool thing. the stepper error makes it even more complicated.

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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #543 on: Fri, 06 December 2013, 04:52:27 »
You are probably right, if the filament does not get deformed in extruder to create waves in the bowden then the friction should not matter. And if it gets deformed the problem is in the extruder.

And the tables would depend on the filament. Maybe the dependence can be reduced to few parameters which would need to be calibrated for a given filament. But that means a lot of experimental measurements. Maybe trying a more theoretical approach (after experimentally verifying it works for one filament) is not that bad idea.

Regardless of all that, I'm not going to devote my time to this project. Thin structures are not that important to me :)

Offline Leslieann

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Re: The Living 3D Printing Thread
« Reply #544 on: Fri, 06 December 2013, 22:39:31 »
The consequence is that tiny blobs of material are deposited at the retract and retract reverse locations. Slicer can handle this easily if there is enough internal volume to hide them in. For very tiny parts there is not enough internal volume and it causes visible/measurable seem on e.g. thin walls. Thin pillars not only do not have the internal volume but also bent which is much worse problem actually. And if they are alone there is also problem with their cooling.

That is the reason I'm trying to get not only stronger extruder but also a very quick one. This also made me to go to 24V for the motors. It increased the usable extruder speed by about 60%. I actually expected speedup by 100% but it was not true. I do not know why I achieved only 60%   :confused:

Anyway, I believe the problem with tiny blobs during retract and retract reverse are mostly fixable with better slicers. The slicer should have some model to estimate how flow will change with the falling/raising pressure and move the head along the planned extrusion path acordingly. If the bowden friction is predictable enough (I hope it is) and the fluid dynamics in the hotend is predictable enough (I think it is) then this should be doable.

Better slicers help with blobs, but also faster retract speeds. I never had the problem until I went with a geared extruder. They were REALLY bad on my PG35L with 50:1 gear reduction. That's the reason for the 2:1 extruder I haven't gotten around to testing. People look at extruder power, but never speed, and in my experience, speed is just as important. 

As for your not understanding 24v motors not delivering double the power... Like every motor, they are optimized for a specific voltage and rpm. Any deviance can raise or lower rpm and power, but not at the same efficiency. I'm a bit surprised it's 60%, but not surprised you didn't get double.

Now you have me curious...
I was interested in 24volts for my bed mostly, but now, I'm wondering if maybe 24v on the motor side would allow me to go back to a direct drive extruder. The EZ Struder is a fantastic extruder, it juts lacks the power for any nozzle below .5mm.
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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #545 on: Sat, 07 December 2013, 08:00:40 »
Now you have me curious...
I was interested in 24volts for my bed mostly, but now, I'm wondering if maybe 24v on the motor side would allow me to go back to a direct drive extruder. The EZ Struder is a fantastic extruder, it juts lacks the power for any nozzle below .5mm.
Probably not. Depends on the speed you need for normal extrusion when printing. My guess is that your typical printing speed is 100 mm/s. With layer height of 0.3 mm and extrusion width of 0.6mm we get filament feed rate of (100*0.3*0.6) / (π*(1.75/2)) ≅ 7.5 mm/s. Typical filament driving pulleys have diameter 9 mm, and lets assume 200 steps per revolution, then we get stepping speed of 7.5/(π*9)*200 ≅ 53 steps per second. That is a too small number for driving voltage requirements. I have here a voltage/torque characteristics of a stepper (not a NEMA17). There is only about 3% difference between torques at 12V and 24V driving voltage up to the speed of about 70 steps per second.

Higher driving voltage does not help at low speeds because the motor torque depends on the magnetic field strength. Magnetic field depends on the coil current. And the coil current is limited/set by the stepper driver. This is for the static torque (zero stepping speed).

For raising stepping speed there is complication. Motor coils have inductance which limits the speed you can raise current in a coil for given driving voltage. The higher driving voltage the quicker you can raise the current. With higher stepping speed you may not be able to raise the current to the stepper driver limit quickly enough. Before you are able to raise the current it may even happen you actually already need to lover it because the next step is due. That means lower effective current with higher stepping speeds and hence also the lower torque.

Summary: Higher driving voltage allows you to achieve higher stepping speeds at the same output torque. If the driving voltage is higher than stepperMaxCurrent*stepperCoilResistance, then it does not increase the stepper static (holding) torque at all.

If you want to get a better idea about it, read the wiki page about RL circuit.
« Last Edit: Sat, 07 December 2013, 08:04:32 by vvp »

Offline Leslieann

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Re: The Living 3D Printing Thread
« Reply #546 on: Mon, 09 December 2013, 16:27:13 »
It's not the low speed that's an issue, it's the high speed for retract that's the issue.

Interestingly, my Minebea (a division of Panasonic) steppers are actually much faster than the Kysan stepper, by almost double. If I push the Kysans extrusion speeds above 2200mm (per minute) the stepper goes wonky, meanwhile the Minebea can go up to about 4800mm per second. The Kysan however has about 1/3rd more torque. I'll have to see if it can spin the direct drive better and save the Minbea for the geared extruder.
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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #547 on: Tue, 10 December 2013, 05:31:13 »
Higher voltage will give you significantly higher speeds for retract and retract reverse.
Higher voltage will increase your low speed (i.e. extrusion speed) torque only by an insignificant amount.

If your extruder skips steps while extruding filament (during normal printing speed without retracts) then higher voltage probably will not help. If your extruders skips steps during retract or retract reverse then higher voltage will probably help.

What exactly happens (what is considered high speed and what is considered low speed) depends on the resistance and inductance of the motor you are using. Quick and dirty estimate to get an idea. Whoever is expert on stepper motors feel free to fix errors and improve it.
For example one of my motors has resistance R = 2Ω and inductance L = 3.2mH. From this I get time constant of τ = L/R = 0.0032/2 = 1.6ms. Maximum current (without pololu current limiting) at U = 12V is 12V/2Ω = 6A. That is more than 3 times the maximum current the motor and the pololu can handle. So lets approximate the exponential (over which the current is rising) with a linear function I = k*t; where k = U/R/τ = U/L. The motor max current is about 1.5A. If we do not want to distort the square signal into a motor coil much (we want the low frequency idea) then the current raise time up to 1.5A should not be (lets say) more than 1/10 of the signal width. So for the signal width we get 10*t = 10*(I/k) = 10*(1.5/k) = 10*(1.5*L/U) = 10*1.5*0.0032/12 = 4ms. That is about 250 steps per second. Based on the previous post that means that I should expect only below 10% raise in torque for printing speeds below 100 mm/s (the signal distortion for this speed should be below 10%).
Btw. this also nicely explains why I got increase of only 60% in retract speed when I increased the voltage to 24V. There is probably still enough torque required during retracts that the linear approximation of the coil current rise does need to rise to maximum significantly before the coil current needs to be switched off again.

I wrote this ugly post mostly to brainstorm about it myself (the only 60% increase was bugging me). It is just a "on a napkin" computation which was done in a text editor instead. I posted it. Maybe somebody will fix the bugs in it :-)

Offline Leslieann

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Re: The Living 3D Printing Thread
« Reply #548 on: Tue, 10 December 2013, 19:41:37 »
When I say skipping steps, is it acts as though it's getting too many signals at once and doesn't know what to do.

By the way, I got the new printer built, I have to make one adjustment, an endstop screw is off 5mm, but still operates.
Current print area is 17in diameter x 18in high, which is more than enough for a TKL keyboard, a cheap ($20), minor change and I can easily do a full size.
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Offline vvp

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Re: The Living 3D Printing Thread
« Reply #549 on: Wed, 11 December 2013, 05:06:49 »
Cool. I'm thinking about building a wider (and shorter) delta printer. And stiffer. But I'm not in a hurry. Maybe in a year or so :)