@claustro I think the image of the calibration pattern is rotated 90°. Assuming that is correct then the Y calibration is the line on the left and the X calibration is the line on the bottom.
It looks like there is pretty much no resonant frequency in the range 0Hz to 90Hz for Y and the X resonant frequency is about 4/5 of the way along the line at just over 70Hz.
Important question: was input shaping disabled when you ran the test?
@CNCModeller Sorry I have been busy elsewhere and didn't see your questions.
I know you've bought bearings now but, for reference, here are some considerations for flanged bearings:
I, like @rqthree, have found a 0.1mm bite to be about perfect. More than that and it increases drag. Less than that and it both reduces thrust and also makes the tolerances much tighter, e.g. something like a 0.02mm error is a much bigger proportion of a 0.05mm bite than of 0.1mm.
There is nothing particularly special about 9.1mm. It's what I was targeting when I made my videos because it was about 0.1mm smaller than the diameter of the unground flange and I wanted to take off as little material as possible. Realistically, I could have gone for 9.15mm. My primary considerations for diameter are:
Drag on the filament is minimal as long as the bite is small enough. @rqthree initially designed a counter-torque mechanism into his extruder but later found it was not needed. The back-torque provided by the melted filament in the nozzle is sufficient. I benefited from this knowledge and have never even implemented a counter-torque. You do see a bit of backlash and it varies a bit by filament type. You may find retraction distances benefit from a bit of re-tuning. But I have not found it affects the print. Obviously consistent filament diameter becomes an important factor, but any decent filament these days has fine tolerances. It also helps if you minimise the path length through the hotend heatsink as this decreases the springiness of the filament section between the extruder and the nozzle.
Speed: there are a couple of guys on the CroXY Discord server who are exploring using VDE for high-speed. The simplicity and weight considerations are just too tempting. At high enough speeds VDE does under-extrude. There can also be issues with having to run the motor hotter which is problematic with the filament running through the shaft. More flanged bearings definitely help under-extrusion but they add drag and increase the likelihood of multiple grooves making a mess of each other. A mix of larger and smaller bearings mounted asymmetrically is also helpful. Firmware can help a bit as well, Marlin now has nonlinear extrusion and I think someone (@oliof maybe) said that RRF has has this feature for ages. Possibly Klipper does as well, I don't know. The guys at CroXY are, I think, experimenting with drilling a larger hole in the motor shaft and lining it with PTFE tubing. Mounting the motor on the hotend heatsink and sharing cooling air with the heatsink is also something to explore.
One idea I may go back to one day is a two bearing VDE. This required the filament path to be constrained by the walls of the hole leading up to the bearings, so adds friction, but it would allow for much larger bearings without any risk of interference.
@rqthree's observations about using PLA for a printed carrier match my experience. I have not experimented widely here but in my best round of testing I did swap from PETG to PLA when I noticed there was a difference.
@oliof said in Hollow shaft extruder:
@rqthree "being done is a decision" that must be made. Kudos!
Yeah, rq3's comments struck a chord with me too.
Some updates from me...
I have experimented further with the LDO motor. For everything other than ridiculously fast printing it's great. The primary limitations I have found are that continuous current much above about 600mA will eventually cause it to get too hot for PLA and at any current E jerk needs to remain quite low (e.g. max 7mm/s) for the VDE which has quite a high steps/mm ratio. On the other hand it has great acceleration and speed, I can get 1000mm/s/s even with the high step/mm count of VDE and top speed is about 60mm/s (with no load) and over 10mm/s driving filament into the hot end.
One day I might figure out how to get TMC CoolStep to help with the current. And I have dreams of implementing a jerk-less version of Linear Advance in Marlin which would pretty much remove the jerk limit as an issue.
In other news, I have uploaded a video about the bearing grinder jig.
And, further news, with a PLA printed carrier the 3 back-to-back bearing pairs version of the extruder seems to work pretty well. I have used a bite of 0.07mm for this version. @o_lampe it works a lot better than with your printed carriers which leaves me wondering whether something like material flexibility might be an issue. I am also coming to the conclusion that it's best to grind the bearings first and then measure them and print a carrier to match their edge diameter. That's a lot easier than grinding an edge down to the exact diameter.
@rqthree I vote we call this push pull version VDE337.
@o_lampe said in Hollow shaft extruder:
Is that the retraction speed or can you actually extrude at 50mm/s? What are actual PLA print speeds with 0.4mm nozzle and say 0.3mm layer?
That's retraction speed. I think the motor can move at that speed while printing without stalling (but will have to confirm for sure). However with compression of the helical thread actual extrusion speed will be a whole lot lower. I specced the motor for extruding about 16mm/s which would give about 320mm/s linear printing speed with 0.4mm x 0.3mm lines. However with nozzle back-pressure I don't expect to get 16mm/s.
I have finally had a chance to play about with all the new toys.
The 3 x double bearing idea doesn't work very well in my tests so far. I have found that with a 0.1mm bite depth the torque applied on the filament is too large. Reducing the bite depth to 0.07mm helps but the grip is a lot worse than the best I have seen with other configurations. This is using the SLA printed carriers. One test left to do for a definite change-only-one-variable test would be to print a carrier myself in PLA. But my guess is that won't improve matters and so it's not high on my priority list.
The SLA carrier with three single bearings with 9.1mm edges works fairly well in printing but I have not had time to test it extensively.
The LDO motors work nicely, but running them at their rated current of 1A RMS they get way too hot. I have found that 700mA RMS is acceptable if room temperature is low enough - they get about 30°C hotter than ambient. At 700mA I can drive the filament at 50mm/s and accelerate at 1500mm/s^2 without a motor stall. Jerk speed is 7mm/s (this is relevant for linear advance in Marlin and, I think, for the equivalent in RRF).
Total extruder mass is 53g. It is a drop-in replacement for my 39mm Nema 17 style motor because the mounting hole spacing is the same as the diagonal distance between Nema 17 holes. I just had to print a smaller holding clamp.
@rqthree Rip and I have collaborated extensively on VDE. By which I mean I have second guessed pretty much everything he has done, tried it myself and generally found that he was right after all!
@o_lampe Looks really good. The filament should be constrained as soon as possible after leaving the extruder. Can you get some PTFE tube in there?
I vaguely think someone asked me to grind some bearings for them some time back, but can't remember who. If it was anyone here, can you remind me?
@o_lampe Using the threaded collar to feed the cutting edge was entirely something I stumbled across. But it works well.
Oliof says the motors are schedule for delivery this week.
@breed Speed didn't seem to be an issue even at top speed. But there is more driving of the bearings than cutting of the edge going on. If I move the bearings so they are more off-centre from the mandrel shaft then the motion of the cutting disk over the flanges should have a greater radial component over the flanges and, therefore, result in more cutting.
I've just posted a brief video featuring a bearing grinder I am working on. [Edit: credit to user DeadLock on the 3D Printing Discord server whose ideas I have borrowed.]
@o_lampe That is a very reasonable concern and a good point.
@o_lampe Deadlock is working on it. His initial design has too much friction.
I reckon we need lots of ways of getting these bearings as different people will be happy with different solutions. e.g. pretty much anyone can already use my method but most regard it as too fiddly. Some will be happy to use a home-printed jig. Others will just want to buy the part and not be too worried about cost.
@o_lampe The rods are mounted at an angle so the center of the rods will be closer to each other than the bearings.
PS I have sent a message to Funssor.
@tombrazier I'm posting here my drawing of a sharpened MF85ZZ so I can point potential manufacturers to it...
VDE-100_Bearing.pdf
@breed Ah I was looking at https://www.funssor3dp.com/ and found nothing. Didn't think to check the Aliexpress store. I wonder whether the two are related at all.
David did post videos on YouTube of a functioning extruder so it definitely works to some degree. One thing I would want to test is whether it retracts and de-retracts without accurately. Another would be whether it grinds up the filament considering how many "teeth" will be contacting the filament. If making one myself I think I would try to arrange for all the threads to fall into just one or (probably) two grooves.
I agree with @o_lampe and @Herve_Smith that these are rather expensive although I note that they are a lot cheaper than buying a metal lathe so maybe that's was in the seller's mind when setting the price. There have been 3 sales so far - I wonder who is planning to make these extruders other than @breed.
I am now beginning to wonder whether we might be able to persuade them to list sharpened flanged bearings. (Maybe for not so great a markup!)
@breed Well that's very interesting. And also confusing: who is this marketed at? It claims to be for a "Funssor rolling screw extruder" but Funssor don't appear to sell those. The image is taken from https://www.thingiverse.com/thing:5447706, which is a re-upload of David Leitner's screw extruder. I wonder how long it's been available on Ali.
@lee-iii-will One thing to watch out for with a large gap between the pusher and puller sets of wheels is when thread compression happens. The larger the distance along the filament between wheels the greater the alignment challenge when the thread pitch changes. On the other hand, with greater misalignment there will also be more force against the side of the groove and potentially more thrust. I think whether it works or not can only really be established by testing.
Hardened steel wheels are interesting. I have assumed (without actually testing it) that sharpened bearing flanges will be chewed up by glass or carbon filled filament. I would hope hardened steel might be able to handle these filaments.
Hi guys, I have been on holiday for a few week, hence the radio silence.
Nice work from several of you.
@zero-K how does your extruder do?
@breed Your pressure bearings that aren't canted will probably be fine with many filaments. Quite some time back I tried a VDE-100 with only plain bearings (i.e. no edge) and it had very little grip. I think that was with PLA. I conclude that filament slides over plain bearings very easily. Something like TPU might be a different matter, though.
@o_lampe I got the carriers, thanks. Now I have my work cut out for me grinding bearings! On the plus side, one of the users on the 3D Printing discord server is working on a Dremel attachment to help with this.