TG All metal Hot End - Call for help

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Liquid
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Re: TG All metal Hot End - Call for help

Postby Liquid » Sun Jun 02, 2013 7:29 am

Thank you for your input cohbra.

I believe I understand exactly what was expressed.

My question is, will laminar flow come into play in an area the is .35mm in diameter. If so, am I understanding correctly, that what you are saying is the length of that .35mm diameter orfice should be 2.5-3 times the width, which would put it at a rough number of .35mm in width x 1.05mm in length?

With a transition from 2mm to .35mm being at say 20 degrees? vs 59 degress that most bits have?

If the reservoir is too small (or nonexistent), then you might notice pulses in the extruded material


Thats funny, with series 1 stock setup, I can see the very very minute vibrations/pulses the stepper creates, in the prints, almost like its printing a record in the smallest detail. In fact that can be seen in some of my pics of the vase prints. Although I cant attribute it to a small reservoir, as I just have never investigated that.

https://drive.google.com/folderview?id= ... mJ2akIyZ3M

I would also recommend reducing the mass as much as possible in the elements that are heated which will reduce the amount of time required to raise or lower the temperature. However, I'm suspecting that a well tuned PID will be much more critical if the mass is considerably reduced.


I think Ive got a pretty decent mass in that area. From what Im thinking, it isnt too big to heat up and keep heated, and it isnt too small of a mass which will fluctuate all that much. Im betting that it will soak and remain soaked at a consistent level, but only time will tell on that.

I was going to attempt to bring some math in that area, but I dont want to create something that is so locked in, it isnt easily reproducible on a larger scale, for a broad range of different types of printers, using the average hobbyist's tools. Im going to rely on the good ole method of just tinkering to find some middle ground. Although a little math wil probably come into play after I test something.... just because.

Obviously I have to research a bit, but I will definitely take the input into consideration when actually building and testing.

Cohbra11
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Re: TG All metal Hot End - Call for help

Postby Cohbra11 » Sun Jun 02, 2013 9:24 am

TheTechGuru wrote:My question is, will laminar flow come into play in an area the is .35mm in diameter. If so, am I understanding correctly, that what you are saying is the length of that .35mm diameter orfice should be 2.5-3 times the width, which would put it at a rough number of .35mm in width x 1.05mm in length?

With a transition from 2mm to .35mm being at say 20 degrees? vs 59 degress that most bits have?


It's hard to say exactly how much it will come into play, while the rules still apply, the dynamics often change when you vary the input parameters such as flow rate, viscosity, etc., especially when smaller scales are involved. I've been in engineering for a number of years, and I have really come to appreciate all of the theory and equations we learn in school, but sometimes the best results come from some plain old trial and error testing while ignoring the theory.

As far as the transition goes, I would say 20 degrees would be much better than 59. Unfortunately, that is a lot more difficult to achieve on such a small internal diameter because they just don't make a drill bit (that I know of) with a 20 degree tip and it is still too small for an off the shelf boring bar. There are some tapered drill bit/reamers out there (http://www.mcmaster.com/#combined-reame ... ls/=n0orok), but it doesn't look like they make them quite as small as you'd need. A little more in-depth research online, and you might be able to find something from one of the tooling manufacturers. You could experiment with grinding your own bits as well, but it would be very difficult on such a small bit. Your best bet, I think, will be to grind the tip of a boring bar to the desired angle, then carefully & slowly run it in to finish the taper, after it has already been pre-drilled. A sinker EDM would be a great way to form this cavity in the nozzle, but it would obviously be quite expensive to go that route.

An unfortunate side effect of the shallower angle though is that it will add to the length of the nozzle requiring more distance to transition between two given diameters. So once again, you'll have to balance the tradeoffs between the two.

Liquid
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Re: TG All metal Hot End - Call for help

Postby Liquid » Sun Jun 02, 2013 9:42 am

I was thinking of griding a bit at 20, not sure how that will translate with a twist drill, but we shall see. In the meantime I will look into others means, just in case. Its harder with reamers, as you usually need a through hole for something like that.

Im pretty sure, I can make a jig to grind them consistently with a grinding wheel.

Cohbra11
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Re: TG All metal Hot End - Call for help

Postby Cohbra11 » Sun Jun 02, 2013 10:59 am

About the laminar flow, I pulled up the formula to calculate Re (the Reynold's number) which gives you an idea whether flow will be turbulent or not.

It looks like it is not an issue according to the Reynold's number due to the small diameter, and the high viscosity of liquid PLA. I still can't help but think that due to the precision required, the length of the straight section will still play into the nozzle's ability to provide a clean flow of extrusion.
PLA Re.PNG
Extremely small Reynold's number indicates that laminar flow is basically certain.
PLA Re.PNG (5.61 KiB) Viewed 2992 times

I would suggest making the first nozzle extra long, printing out a test part, then shorten the nozzle by X amount, reprint the same part, then repeat the process until you run out of nozzle to trim off. The results should give you an idea if it even matters, and which length is best if it does matter.

jbrisbin
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Re: TG All metal Hot End - Call for help

Postby jbrisbin » Sun Jun 02, 2013 12:05 pm

A suggestion on the mundane side:
If you build a nozzle, then create a cleaning tool that matches the interior profile of the nozzle and include it with the nozzle.

For existing nozzles that could be as simple as drill bit of the correct dimension with a collar at the appropriate point to limit the depth.

To avoid scoring the barrel tube, a custom tool with a shoulder at the right point and sharp edges only at the tip might work better and would be extensible to exotic designs that don't have a common drill bit profile.

Like the modern, rat-free, leak-proof ship*, the uncloggable nozzle may still be a few revision cycles away.

* Six inches of only slightly used neutral filament to the first to identify the reference. Please include SASE with your submission. ;)

Liquid
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Re: TG All metal Hot End - Call for help

Postby Liquid » Sun Jun 02, 2013 12:57 pm

That would actually be pretty easy if the drill profile works at the standard 59 degrees for the nozzle. There are collars that fit on small rods to check depths, held on to the rod using a set screw.

The same can be done with a 2mm drill bit. Attach the collar after a nozzle is done being turned, set the depth, and ship it out with the hot end.

If custom collars are created, it could have and inside diameter of just under 6mm also, in order to align itself with the center of the inside of the nozzle. Making it easier to "twist to clean"

It would add to the cost time and material wise, so it might be better off as a cheap addon/option.

Liquid
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Re: TG All metal Hot End - Call for help

Postby Liquid » Sun Jun 02, 2013 1:05 pm

I would suggest making the first nozzle extra long, printing out a test part, then shorten the nozzle by X amount, reprint the same part, then repeat the process until you run out of nozzle to trim off.


Oh Im def going to be cutting more than a few up, checking for as much as I can. Thanks for the info too.

AndrewRutter
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Re: TG All metal Hot End - Call for help

Postby AndrewRutter » Sun Jun 02, 2013 1:29 pm

TheTechGuru wrote:Ok, after a little more thought...

Im convinced the MBI mk7 barrel ID is missing the reverse taper (Draft Angle) where the barrel meets the nozzle firstly.


ding ding ding!

Yep, it doesn't actually need to be a taper, but you need to have an expansion relief zone where the ID increases. A simple step out is just fine, but it needs to be there. Its what stops the PLA from jamming. It also removes the need for a polished barrel (which really is navel gazing, its not going to save you from the underlying problem).
The Mk7 screws into an aluminium mounting block with attached heatsink, rather than using a long aluminium jacket. But either way you want to cool the top of the thermal break (the stainless) as much as possible.
I suspect that the other hotends are simply much less efficient in terms of force required to extrude. The Prusa hotend is using 3mm filament and a beefy geared drive. I've tested a few of the other drive mechanisms out there and most seem to be exerting huge pressures on the filament and and hence can then force the filament through any old bit of hot tubing.
I've been able to build drive mechanisms that used NEMA11 motors with the MG hotend. They were not sutible as the motor ran so hot the drive wheel eventually started softening the PLA, but they were generating enough force

The laminar flow stuff is very interesting. Given that you are not trying to create free extrusion, I'm curious to know if it will make any difference. Although it might reduce back pressure and hence reduce extrusion force.

Liquid
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Re: TG All metal Hot End - Call for help

Postby Liquid » Mon Jun 03, 2013 3:07 am

ding ding ding!


sweet lol. Dont know why I didn't register the heatsink, it was staring me right in the face the whole time. eee.

I've tested a few of the other drive mechanisms out there and most seem to be exerting huge pressures on the filament and and hence can then force the filament through any old bit of hot tubing.


Ahhh, I see. Im guessing its better to design something for a setup like the Series 1, as whatever works for a setup that doesnt need a huge amount of force to extrude, will surely work well for the brute force monsters. Not so well the other way around.

Does anyone know if most of those machines use a 6mm installation thread and mounting plate for the hotend?

On another note.

So Im making some changes. I just contacted nophead and he gave me a few pointers. You hit the nail on the head Andrew, I appreciate to guidance on that. It was interesting, because to get to that conclusion I had to cram other peoples information and experiences. Learned a few things along the way.

Im still going to make my original design, knowing it will have a few limitations, to use as a baseline, a version with a draft angle where the nozzle meets the barrel, and a few others I have in the shadows.

Ive got some ceramic inserts on the way also for additional testing, and talking with a local company about a sealed air washer to act as a possible insulator, to make things interesting....

eeee.... Im a little further into this, than I had originally imagined. What had originally turned into a $600 test, looks like it may being $1500 to secure the tooling and materials. Thats still VERY cheap though, and I think it will turn out to be very interesting. Ive personally never attempted creating/testing anything without spending at LEAST $5000 before, so Im pretty thrilled so far.

Just to address anyone who feels I may be over thinking this, just realize that Im not shooting for average printing temps here, or trying to just do enough to keep up with the "norm". Ive got very specific ideas on what I want the performance to be. Once I stumble on to something that fits those ideas, I will refine everything to its simplest form, refine materials, machining etc. I didnt get paid to make something work, I got paid to make something that works, and refine it for production. So just bare with me. Any input or help is appreciated.

Liquid
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Joined: Sat Feb 16, 2013 12:46 pm

Re: TG All metal Hot End - Call for help

Postby Liquid » Wed Jun 05, 2013 2:41 am

Made some first cuts on the lathe yesterday afternoon. I must say Im pretty happy with the performance of the lathe. I know I said I wouldnt be modding it.... but I did. Might as well tweak the lathe while waiting for everything to arrive.

Completely disassembled it, lapped all the "ways" of the saddle, cross slide, compound slide, gibbs etc. Removed the head (area behind and holding the chuck) packed it with grease as it was bone dry. Uninstalled the motor and properly aligned it with the gear drives, tensioned the main belt. Installed a Quick Change tool post.

Disassembled the chuck, chamfered most of the edges where the clamping blocks ride. Packed the internals with grease. Aligned the tail stock. Packed all the axis bolts with grease. Packed the apron gears with grease, chamfered the half nut edges.

It so super smooth now, and Im just so excited to gt into this. I still want to create shield around the saddle to keep chips from falling on the ways, and direct them to a more central location. Compressed air isnt good for cleaning these type of machines as it can lodge chips where they dont need to be, and using a brush to clean it all the time can get time consuming. So a shield(s) will help with that.

Im stil waiting on the hss drill bits and micro bit holder, but Im nearly there. Ive also tweaked the hotend a bit, in a few different versions, and hopefully will be testing soon.

Does anyone know where the best place to get any of the following in 1.75mm size? Nylon, Polycarbonate, any other high temp material?

Anyone have a preference on what they want to see me test first? I plan on doing some quick tests before I send any beta anything out.


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