V4 Hot End tech details?

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papilio
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V4 Hot End tech details?

Post by papilio » Mon Apr 02, 2018 1:39 am

I very much like the form factor of the V4 hot end and am quite eager to attempt incorporating one into the design of my current project, a large delta build. Realizing that it's not designed for this, I'd appreciate hearing from MakerGear users regarding the following (or anything else!).

I'd like to point out first that this printer will have direct drive extrusion, so I don't anticipate having to use retraction settings above 1mm as is typically the case with deltas having Bowden tubes. I understand that retractions of greater than 1mm can be problematic with the V4.

My primary concern is cooling -- am I correct in assuming that the stock M2 or M3 clamping/mounting plate serves as a heatsink in the standard configuration? While I'm able to machine the appropriate bracket out of aluminum, the weight limitations of a delta effector assembly rule out anything very massive. Fan-cooling is of course an option although the small heat break on the V4 would likely limit a fan's effectiveness.

I'm also wondering about the high-temp capabilities of a PTFE-lined hot end. While I see in other posts that the V4 is rated to 300C, the current understanding seems to be that non all-metal hot ends are limited to perhaps 245C max as this is claimed to be the temperature at which PTFE begins to break down (including the release of noxious fumes).

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ednisley
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Re: V4 Hot End tech details?

Post by ednisley » Mon Apr 02, 2018 2:26 pm

papilio wrote:direct drive extrusion ... the weight limitations of a delta
You probably need a reduction gear drive, because a bare motor won't have enough torque to ram filament into the hot end at any reasonable pace.

If the delta drive motors in your printer can sling a carrier loaded with a stepper + gearbox + a part cooling fan(?) at speed, then an aluminum mount won't make the least bit of difference.
the temperature at which PTFE begins to break down
Assuming Wikipedia has the straight dope, parakeets keel over near PTFE heated above 300 C, so the 250 C I've been using for PETG seems fine:

https://en.wikipedia.org/wiki/Polymer_fume_fever

In any event, the volume of heated PTFE seems minimal.

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papilio
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Re: V4 Hot End tech details?

Post by papilio » Mon Apr 02, 2018 8:10 pm

Hi Ed, thanks so much for the reply and feedback. Very helpful information.

I'll be using a Zesty Nimble remote drive extruder with which I've been very pleased, this has a 30:1 gear reduction. I'm doing my best to keep the effector assembly as light as possible of course, and as I do so enjoy watching a delta machine print I'm trying to keep the hot end neighborhood as minimalist and unobstructed as I can. Below is a CAD rendering, seen from the rear.

Assembly of the printer is nearly complete except for the actual hot end. At this point the tiny aluminum bracket seen is the way I'm envisioning mounting the V4, along with the 30mm blower fan I'll be using if required. Might the bracket appear too insubstantial in mass for it to be able to do its part in dispersing heat? Just trying to get some feel for how much heat is likely to be present at and above the heat break.

Happy to hear that the situation regarding the use of a teflon liner is not nearly such a limiting factor as so much online discussion seems to believe -- almost makes one wonder whether the "need" for all-metal hot ends is truly genuine in a lot of cases. You do raise another possible concern, regarding the force required to drive the filament through the hot end/nozzle, do I understand that the friction here with the V4 is greater than is typically encountered with more conventional hot ends for some reason?

Thanks again for your assistance!


Image
Last edited by papilio on Wed Apr 04, 2018 12:30 am, edited 1 time in total.

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insta
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Re: V4 Hot End tech details?

Post by insta » Tue Apr 03, 2018 5:48 pm

30:1 is ridiculous overkill for the v4. You can feed the filament through with tweezers -- you just can't do it SUPER fast. It has a relatively small melt-zone. Ed's good about doing all the volumetric math though.
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papilio
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Re: V4 Hot End tech details?

Post by papilio » Tue Apr 03, 2018 6:23 pm

Thanks insta! Of course, 30:1 is way overkill as far as providing torque -- I believe that's just the best compromise the designers of the Zesty Nimble were able to arrive at with their remote drive cable. In any case, thus far it's worked beautifully for me.

And thank you for the feedback on the V4's behavior, I've just ordered one so we'll see how things work out!

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Re: V4 Hot End tech details?

Post by Gwhite » Tue Apr 03, 2018 6:33 pm

One thing you may not be aware of is that the V4 hot end has a necked down section between the hot-end body and the clamping section. I assume this is to minimize heat loss to the mounting clamp:
V4 Hot End.jpg
V4 Hot End.jpg (11.49 KiB) Viewed 507 times
Unless the mount for the hot end gets too hot for other components attached to it, I wouldn't think a fan would be necessary. The last thing you want to do is to cool the hot end...

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papilio
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Re: V4 Hot End tech details?

Post by papilio » Tue Apr 03, 2018 6:41 pm

Thank you Gwhite, yes I have been aware of that in the design -- and why it's such a bad idea to try to switch nozzles in situ! :o

It's my hope that this nice little heat break performs well and keeps the top cool. I'd certainly prefer to run the thing without a hot end fan, but if it does prove necessary there will be a flap to keep the breeze off of the heater block.
Last edited by papilio on Wed Apr 04, 2018 12:39 am, edited 1 time in total.

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ednisley
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Re: V4 Hot End tech details?

Post by ednisley » Tue Apr 03, 2018 7:21 pm

papilio wrote:Zesty Nimble remote drive extruder
Hadn't seen a Nimble before; the worm gear should provide enough torque!

The tradeoff will be extrusion speed and that may be the real problem

If I understand their numbers correctly, there's a 1/30 speed reduction between the motor and the filament drive gear. The Makergear planetary gearbox reduces the motor speed by 1/5.5 (-ish), so if the drive gears are about the same diameter, the motor must run five (-ish) times faster to feed filament into the Nimble at the same pace.

Looked at from the other direction, the M2's default 480 (-ish) step/mm becomes 14.4 k step/mm for a Nimble, so extruding filament at 10 mm/s requires 144 k step/s.

Marlin firmware can't generate more than 40 k step/s from an Arduino, so it can't run a Nimble extruder faster than 3.6 mm/s.

In any event, NEMA 17 stepper motor torque falls off a cliff above 1000 (-ish) full step/s, which 16 microstep mode turns into 16 k step/s. Fancier firmware on a faster controller will just whack into the motor's top speed limit; you're not going to get an order of magnitude more speed for 144 k step/s from the motor.
too unsubstantial in mass
The only way to know is to try it, because one careful measurement outweighs a zillion expert opinions. Being a brutalist kind of guy, I'd skip the fancy cylinders-on-ribs-with-fillets and go for a triangular-ish flat plate, but your design definitely wins on stylin'.

Extrude for a while, measure the clamp temperature, then decide.

I'd machine a teeny pocket in the clamp for a thermocouple bead, because I can't think of any other way to get an accurate temperature from the thing.
the "need" for all-metal hot ends is truly genuine
I won't even stick a toe in those waters ... [grin]

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papilio
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Re: V4 Hot End tech details?

Post by papilio » Tue Apr 03, 2018 7:44 pm

Thanks again Ed! I'm quite impressed with the replies and level of understanding on the forum.

My limited experience running the Nimble has been very positive -- IIRC some of the beta testing had been done by Simon of Precision Piezo (running Duet on his delta), the primary bottleneck in the extruder's performance appeared to have been the retract speed which in his experience was limited to about 30mm/s but thus far has proven workable. Michael Hackney was an early beta tester and has good things to say on his blog. I'm looking forward to a delta with its Achilles heel having been removed. In any case I'm no speed demon, I'm fine taking as long as needed to get nice-looking prints.

I'll be using the Duet control board myself so no problem keeping up with the math.

And thanks much for the tip on thermistor installation!

You're surely correct, only direct experience will decide things for sure, so the V4 was ordered this morning. The responses which I've gotten here helped greatly to clear up a few questions and to encourage me to go ahead with the scheme.
Yeah, I know ... I tend to indulge my love of industrial design when I build these things. :D
I won't even stick a toe in those waters ... [grin]
Hehe, sounds as if we may be of similar mind on this.

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Re: V4 Hot End tech details?

Post by sthone » Tue Apr 03, 2018 8:42 pm

I've run my M2 for years with out the fan ... you probably won't need one either.

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