Dr D-Flo's big build

DrDFlo

All great points! Couple responses:

leadscrews on XY gantries are not my liking. They're OK for Z-axis, since gravity takes care of backlash there and Z is slow anyways.

You can't use belts at this size, so that leaves rack and pinion or ball screws. Both of which I would gladly upgrade to, but $$

@o_lampe said in Dr D-Flo's big build:

Since the extruder is a bit underdimensioned for the 5mm nozzle (20mm/s, really?) it is OK to use slow leadscrews too. But two bads doesn't equal good

Not sure what is meant by this. For non-vase mode prints, like the generative design desk or even the roof panels, higher travel speeds between print moves would greatly speed up the print times and there would be less oozing to clean up. So faster print speeds with less lead screw whip is definitely my most pressing issue.

@o_lampe said in Dr D-Flo's big build:

Steel panels for the enclosure will not help to keep the chamber at steady temps. These forced air enclosure heaters will make a lot of draft, which isn't good for ABS.

Printing ABS was more exploratory, and I admit there are quite a few improvements that could be made. Most large format 3D printers do not use any sort of chamber heat. I visited Oak Ridge National labs the other day and they print ABS nonstop on their BAAM, but their secret is that they use chopped carbon fiber composite and also formulate their own ABS with additional additives to prevent it from warping. I am sure they also have their print speeds carefully tuned.

@o_lampe said in Dr D-Flo's big build:

You're mixing steel panels and aluminum extrusions like there is no thermal expansion issue.

This is not an issue. Panels have through holes that are larger than the bolts. Also, there is a rubber washer between them. Perhaps more of a concern is the steel lead screw in each of the actuators. I am looking at a high-helix aluminum lead screw from Igus, which would solve this but this a costly component and the thread is proprietary.

@o_lampe said in Dr D-Flo's big build:

The crossbeam of the X-axis is fixed on both ends. You had to do that, because of the donut-bearings you're using. (forgot the english term for these, sorry)

These are angular contact bearings, which take on the axial load when tightening the lead screw.

@o_lampe said in Dr D-Flo's big build:

I could rant on and on, sorry if I sound harsh. My english skills are lacking.
Just my 2 cent anyways

I have immensely enjoyed building this project and interacting with the community. The printer works well with PLA and PETG (not yet shown on video), but now I am in the phase of determining what upgrades are worth the performance increase while not having to rebuild the entire machine.

Phaedrux

@DrDFlo said in Dr D-Flo's big build:

You can't use belts at this size,

Modix does.

https://www.modix3d.com/big-meter/

JoergS5

@DrDFlo said in Dr D-Flo's big build:

can't use belts at this size, so that leaves rack and pinion or ball screws.

Compliments, you have a great printer and you have a new subsrciber on YT.

There is a solution which may interest you, called ServoBelt:
https://www.cnczone.com/forums/linear-and-rotary-motion/59570-forum.html
For other use cases, there is also a version of it for rotary axes called ServoBelt Rotary. Both are patented *), but the inventor created the thread to help noncommercial users.
The solution uses belts with the advantage that stretching of the belts is limited by the construction.

*) reviewing the thread on CNCzone, I see the patent may be abandoned or expired, but I am no patent expert...

o_lampe

Thanks for your reply.

@DrDFlo said in Dr D-Flo's big build:

So faster print speeds with less lead screw whip is definitely my most pressing issue.

I agree with that. A belt drive might have it's own demons, but who cares about ringing while doing fast travel moves? I think Duet toolboards come with acceleration-sensor to dial out ringing anyway.
HTD3M belts is what I'm using on my CNC and they were strong enough to rip my gantry apart when one of the Y-motor failed.

One more thing about ABS printing: the pellet conveyor blows lots of cold air into the chamber while filling up the funnel. That air should be guided outside of the chamber or it will cause turbulences and a sharp temp-drop right above the extruder.

@DrDFlo said in Dr D-Flo's big build:

These are angular contact bearings, which take on the axial load when tightening the lead screw.

No, I meant the GE12 spherical bearings. They allow some DOF should the Z-axis sag, but not in the right direction. A Maxwell or Kelvin mount system would be better also for thermal expansion. Here's my approach for a 3-point Maxwell mount. Does also work for 4-point Z-axis.

droftarts

@JoergS5 said

There is a solution which may interest you, called ServoBelt

When I eventually get back to my CNC build, this is what I was going to do (though not buy the commercial solution), using 3mm HTD belt, which meshes with itself nicely. My hope is that it reduces the ‘springiness’ of the belts enough to cut aluminium.

Ian

T3P3Tony

@DrDFlo said in Dr D-Flo's big build:

You can't use belts at this size

Ivan's print head is significantly lighter than yours but belts appear to be working for him on a similar size printer:
https://youtu.be/TKE7-Q5jBjE?t=479
Be interesting to do an examination of where the cross over point is for belts vs screws in terms of as weight / acceleration / top speed trade offs

If anyone has a link for some research on that I would be interested!

P.s. nice find with the servo-belt @JoergS5

DrDFlo

@T3P3Tony

@T3P3Tony said in Dr D-Flo's big build:

Ivan's print head is significantly lighter than yours but belts appear to be working for him on a similar size printer:

@Phaedrux said in Dr D-Flo's big build:

Modix does.

Perhaps, I wrote a standard FFF belt configuration off to quickly, but with pellets, my print head weighs > 30 lbs (13.6 kg), which is likely 10x heavier than Modix or Ivan's. For a belt to work, I will have to use a thicker belt and tensioning will be a concern because those c-beams are likely to buckle.

@JoergS5 said in Dr D-Flo's big build:

There is a solution which may interest you, called ServoBelt:
https://www.cnczone.com/forums/linear-and-rotary-motion/59570-forum.html

A pinon belt system, such as the one you linked is definitely interesting. I need to think about it more, but it may be possible to implement with with only a small modification to my carriages, if I can run the belt on the back of each actuator. I see that Bell-Everman NEMA 23 actuator supports 50 lbs. Cool!

Phaedrux

@DrDFlo said in Dr D-Flo's big build:

my print head weighs > 30 lbs (13.6 kg), which is likely 10x heavier than Modix

This may be the case. The Modix head is quite heavy as it is but probably not 30lbs.

At the meter scale everything becomes harder!

o_lampe

@DrDFlo said in Dr D-Flo's big build:

I will have to use a thicker belt and tensioning will be a concern because those c-beams are likely to buckle.

The cross section of the C-beam isn't very stiff. I'm surprised you use V-rollers for such weight? The rollers can pry open the V-shaped extrusion. Especially, when the unused V-slots aren't closed. (I hope, I made myself clear)

How much airflow does the vibrator on the extruder generate? Another source of turbulence and temp-drop, messing up ABS prints?
Extending the exhaust of the turbine is an easy fix, I guess.

DrDFlo

@o_lampe

@o_lampe said in Dr D-Flo's big build:

The cross section of the C-beam isn't very stiff. I'm surprised you use V-rollers for such weight? The rollers can pry open the V-shaped extrusion. Especially, when the unused V-slots aren't closed. (I hope, I made myself clear)

Do you have an example of the plastic v-wheels changing the geometry of c-beam or similar 20x20 extrusion? I have not seen this before, but I would be curious to see how heavy the payload was.

I could move to a more rigid C-beam: https://makerstore.cc/product/us-lr-chv-s/

However, I have been quite happy with the V-wheel system. Not only is it cheaper, but it also allows me to introduce some play on the print head by loosening the eccentric spacer so that if the pellet head runs into a Z-seam or another protruding artifact that it will move up slightly and keep printing.

@o_lampe said in Dr D-Flo's big build:

How much airflow does the vibrator on the extruder generate? Another source of turbulence and temp-drop, messing up ABS prints?
Extending the exhaust of the turbine is an easy fix, I guess.

I have the exhaust plumbed so that it exhaust away from the print. It generates 1 CFM but is only on for 3 seconds.

oliof

@DrDFlo said in Dr D-Flo's big build:

Do you have an example of the plastic v-wheels changing the geometry of c-beam or similar 20x20 extrusion? I have not seen this before, but I would be curious to see how heavy the payload was.

I've seen completely messed up 2020 x gantries from ender style i3 clones where overzealous tightening of the eccentric nut deformed the v slot channel. I will see if I can recover photo evidence.

o_lampe

@oliof
That's what I meant. The more weight you have to move around, the more you preload the wheels.
@DrDFlo I'm glad you didn't follow that usual route.

I also had chinese V-slot extrusions, where the angle of the V didn't match the roller contour.

sotpurk

@DrDFlo @o_lampe
"I am upgrading to a 12 mm high-helix lead screw for faster travels at lower RPMs, but I am limited here by the c-beam aluminum extrusion profile"

Why not go with a rack and pinion setup?
I am coincidentally making a very similar printer with the same extruder.
The differences are as follows:

Integrated servos instead of steppers for X and Y (Stepperonline iSV-T motors)
Using chains and custom sprockets for Z.
Modded the MDPH2 with a RTD pt1000 as a failsafe for the terrible grounded thermocouple on the extruder (Probably going to replace that too )
the X and Y motors use a 1:5 Planetary gearbox and connect to 1.5 module pinions that travel on racks. There's no backlash, it's smooth and it's really fast.
It's bigger.

DrDFlo

@sotpurk Woah this is an epic build! Sorry for the late reply, but is there any update on your build?

sotpurk

@DrDFlo I got a bit occupied with another project so it still roughly looks the same, but I've changed the Y and X printed mounts to CNC ones and doing the same for Z.
It's producing decent prints now apart from the entire frame oscillating at heights (which is expected since I'm going to support it externally later on)

Because the gantry is rather heavy, It's a lot of wasted energy to level/mesh the bed so I came up with remapping an actuator that has an end-stop at one end as Z when probing. That way only the actuator moves instead of the entire gantry moving in Z; but the 6HC doesn't allow the motors to remain energized when changing assignments so I'm waiting for a 6xd board to be delivered where I can do this externally. (there's no reseller in my country so importing takes too much time) (https://forum.duet3d.com/topic/31694/keep-motors-energised-when-changing-assignment?_=1680794473398)

Also installing a vacuum loop from the extruder for feeding pellets (the momentary exposure to moisture in the air isn't a big deal since the primary storage is isolated and it's only fed when being printed so no long-term exposure.)

Swapping the current worm gears as well, I was under the impression that worm gears can't be back-driven but seems like that's only the case when certain conditions are met. So have ordered new gearboxes with higher ratios (will use the old ones on another build) but man, imports.

Ideally, the extruder doesn't need to move beyond 120mm/s to achieve its maximum output but I've tested the machine to reliably move at 800mm/s which was scary fast.

Here's my most recent print:

sotpurk

@DrDFlo Hey, could you possibly also share your config file and the speeds at which you print? It would help a ton
I'm having trouble with the extruder since the motor is heating up a lot even while extruding PLA at relatively low speeds so a reference config would help a lot.
Thanks