delta complex objects

how does everyone print complex objects like the one blow on their delta printers? The problem is that the bowden tube needs more force to push plastic so the temperature need to be higher to compensate for this. The higher temperature doesnot give the plastic enough time to cool even with a 50 mm fan blowing at full force. And if i lower the temperature the filament gets stripped because the force needed to extrude gets too high..

Such models are a breeze to print on my mendelmax with a all metal hotend.. but on the 3dr with a bowden and a j-head the quality is either crap with droopy loops and strings or the model fails mid print...

any ideas or suggestions ..

thingiverse

Can you post a picture of one of the prints? I recently did a twisted vase on .3mm settings with an all metal hotend, and it came out good; however, I assume that the cellular vase is more complicated because of the many spaces/gaps that the Nozzle would travel in. I am planning on printing that vase in the near future.

I assume that you have already done all of your calibrations: tower and extruder.

@ wildcard

some prints




this is the problematic print ...

A big problem on deltas is the bowden.
When you gear down the extruder to get enough power, you cannot retract fast enough to stop drips and strings.

A few things have found that helps...
Good filament.
Some filament goes from liquid to rubbery goop, and then transitions from goop to boiling very quickly. Leaving a very small temp range you can actually print with. Others just require a lot of heat and others are prone to stringing. The one plastic I found that always seems to work well is Ultimachine. It transitions to liquid at lower temp, and has a wide temp range.

More cooling/less speed
Add a fan off to the side if you have to. The faster you go, the more air you need. Don't be afraid to use an auxiliary fan.

A hobb and extruder.
3:1 gear reduction is about right, more than that and you cannot retract fast enough, less than that, and you don't have enough power. Unfortunately, that ratio is not easy to get in an efficient package, printed gears stink and metal gears are all 5:1. Even if you solve that, 1.75mm hobbs lack traction, especially those meant for 3mm. The best 1.75mm hobb is the one coming on the Griffin Pro, however it only works on 8mm shafts at the moment and won't be available until Oct. If you have an extruder with a 5mm shaft, the best hobb out there is the Ultibots 1.75mm hobb.

Edited 1 time(s). Last edit at 08/09/2014 07:09PM by sheepdog43.

I cut my extruder stepper to 1/8th microstepping (which of course halves the steps/mm), but it definitely improved the torque.

@sheepdog

thanks for the tips.
i am using a gregs's extruder modified to using a mk8 hobbed gear. It has a lot of grip but it stil strips the filament at lower tempersatures. I even tried a spur gear with the same effect .I think the j-head needs a lot more force to push, so i have to use higher temperatures to keep the filament from stippping.

I will try adding more fans . The problem with a auxillary fan on the side is that it cools the part so fast that on a cold bed it just pops up after the fist 20 layers. I am now trying a 50mm centrifugal fan with a spout on it.

any link to the ultibots hobb

Also in your experience is a metal gear motor better than the usual gregs extruder. I also see people using direct drive but i dont know how they get enough torque to go extrude.

Another option i can try is to use a small belt to get a 3:1 ratio..



@grat

I am ready using 1/8 microstepping...

got much improvement with a ducted fan.





the one on the right is without a duct.

Quote
ekaggrat
@grat

I am ready using 1/8 microstepping...

Ah well, was worth a suggestion.

I suspect part of your problem is that there's a lot of jumping about on this model, so jerk and acceleration will play more of a part than they do in the other items you've printed.

My first effort to print it ended in a lot of filament going in the wrong directions.

Quote
ekaggrat
@sheepdog

thanks for the tips.

You're welcome.

J-heads are actually only rated for about 100mm/s for larger diameters, as are most heads, and less for smaller diameters, which is part of the problem.


Pop-off?
Try a different method of securing it. 3M or Scotch brand painters tape should hold it, I had trouble getting it to release usually. Put down the tape, rub it with rubbing alcohol (more alcohol, more stick!), then lower your head a touch, and raise the heat. It will stick so well, you have to sand off the blue tape remnants.

I've used Mk7 hobbs, but not an Mk8 (I have about half a dozen hobbs).
With a .35mm J-head and near boiling Ultimaker filament, the worst hobb I own peaks at 150mm/s (delta speeds, not cartesian) and several, including the Mk7, that average about 220mm/s. The Ultibots pulley peaked around 340mm/s, with this setup, I blew out standard 125psi pneumatic fittings regularly. The Griffin hobb managed well beyond 400mm/s, the slicer was at 600, but it wasn't quite hitting that speed. Unfortunately, after just 5 minutes the head backflowed out the top, damaged both 145psi pneumatic fittings and tore the bowden tube in half. A few days later, the J-head had a crack up the side, too. I must say though, it was a spectacular 5 minutes!

Ultibots Hobb

Metal geared stepper motors are far less hassle, but they stink at retraction. If you have a .4mm or .5mm nozzle, yolu may get away with just direct driving the extruder without any reduction. This results in fantastic retraction, rarely if ever strips filament, but is more likely to not have enough pushing power.

Personally, I use 400 step 1/32nd native steppers. Works great, however standard Arduino can't keep up, I had to go to ARM.

Edited 2 time(s). Last edit at 08/10/2014 02:08AM by sheepdog43.

@sheepdog43

Thanks again for the tips and the link. I will soon convert to a heated bed as i don't like the cold one. In my part of the world the blue tape is too expensive so mostly i have to do with carbon fiber vinyl on a acrylic bed.

The unibots hobb looks good in the pics i will order one and see. When the griffin's hobb is available please put me down for a few.
Also one more question what is the retraction speed and acceleration do you use ?

i use the following settings

#define DEFAULT_MAX_FEEDRATE {380, 380, 380, 29}
#define DEFAULT_MAX_ACCELERATION {2000,2000,2000,10000}

#define DEFAULT_ACCELERATION 380
#define DEFAULT_RETRACT_ACCELERATION 380

You're most welcome.

I really like that Ultibots hobb, it really is the best thing out right now for 1.75mm, I'm sure you will like it. You can crank it down without distorting the filament as much. I'm not saying it will never skip, but it's better than the others I've used by quite a bit. As for ours, we expect to have our store up and running sometime in October and our hobb should be similarly priced to others and ship about the same time. If I remember, I will send you a PM. You will need to either use our extruder (stl's will be available) or design your own as our hobb will not fit in most extruders.

On retraction, I recommend you use as high a speed and acceleration as you can, without the motor skipping. Unfortunately, each controller, motor and even firmware can handle different speeds, so even if I gave you a common number it may or may not work, it's just trial and error.

Here is where I would start: Warning, all of these could cause motor skipping.
#define DEFAULT_MAX_FEEDRATE {800, 800, 800, 800}
#define DEFAULT_MAX_ACCELERATION {3000,3000,3000,3000}

#define DEFAULT_ACCELERATION 800
#define DEFAULT_RETRACT_ACCELERATION 800

Remember, those are just a guess, I tend to run fast and hard, abusing the heck out of my printers. My numbers would be worthless as chances are, you aren't using parts that are even remotely similar. My printers are rolling test beds for the Griffin Pro, so I'm kind of lucky in that I get to play with things not even on the market yet and deal with manufacturers others haven't. It's been fun, tiring exhausting, and quite expensive. I could lie and say I'm doing destructive testing, but honestly, I just like pushing my printers. It's part of the fun for me.