thinking of digging into 3D printing, can i just add a head to my CNC router?

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10 Nov 2021 14:05 #225988 by travis036
Given this extruder head: www.ebay.com/itm/154647079845 (haven't bought yet)

Titan extruder step value/pulse parameter
Leji motherboard:
16 subdivision: 382.166
32 subdivision: 764.331
64 subdivision: 1528.663
128 subdivision: 3057.325
Chitu motherboard:
16 subdivision: 0.002617
32 subdivision: 0.001308
64 subdivision: 0.000654
128 subdivision: 0.000327
Other open source motherboards:
16 segmentation: 382.166


it looks like 16x microstepping gets a value of 382.166, whatever that is.it isn't number of steps, as the decimal is not devisable by 16... and if that is the distance in mm the filiment moves per step, it seems excessive, but i don't know that muc about filiment use...
if i use this extruder, how do i get the STEP_SCALE for my ini file (installing the extruder on joint_3, A)? mathmaticly i can't make sense of the numbers...
the Gcode i posted looks like it is advancing axis A in a linear movement, as the reported filiment used is near the same as the A movement.
in my INI for the 3D printer config, i have "MIN_LIMIT = -1e99" for no minimum, and "MAX_LIMIT = 1e99" for no maximum, and also set for immediate, or no homing.
My plan is to just get a 4th stepper driver matching my current ones, but with the current limit set much lower for the NEMA17 stepper.
any thoughts? should i use a different stepper-drive extruder?

~Travis

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10 Nov 2021 16:32 #226007 by tommylight
Yea i have the same geared extruder part without the hotend, it works but it slips easily as it have very dense and very shallow teeth. Despite that i can push over 30mm3 of filament through it. But if it slips, it will continue to slip so a quick brass toothbrush stroke fixes it.
I like it as it is very lite, i slapped a 36mm pancake round motor with a DIY Vulcan/V6 hotend with 60W heater, total weight 148 Gr!
And yes, those are steps per millimeter required in the ini file.
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10 Nov 2021 16:46 #226011 by travis036
Hmm, good info, i will keep in mind the slippage issue and solution. i wonder if a stiffer wheel tension spring would reduce slippage? something to try i guess.

And yes, those are steps per millimeter required in the ini file.

ok, will LinuxCNC accept a value of 382.166? i don't seem to remember if it will take a decimal value for STEP_SCALE.

~Travis

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10 Nov 2021 18:22 #226018 by tommylight
Springs will not help, i have it fully un-tightened. Weak motor with 0.9 degree steps so very limited power.
Tightening the spring in my case stalls the motor.
With a normal Nema 17 it will have to much torque so the built in spring is more than enough.
And yes, ini file takes decimals.
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14 Nov 2021 09:50 #226444 by travis036
Haven't tried running the configs yet, but my LinuxCNC 3D printer configs are on my github here: github.com/travis-farmer/linuxcnc/tree/m...y_LinuxCNC_3dprinter
in the folder "ard_3dp_PID" is a rework of various examples i found online. there are two files, "ard_3dp_PID.ino" the arduino sketch (compiles, but untested until i get my extruder). and "ard_3dp_pid", a Python script to handle the HAL connections (also untested).
i have ordered an extruder, the one i told about. I have also ordered, and received yesterday, a 1KG roll of black PETG. interesting that the filament was ordered, and came from California (to Maine), and the extruder was ordered the same day, from New Jersey. it won't arrive until monday... figure that one out... ;)
so anyway, i posted the configs untested as i have to fix the heater in my CNC shed before i can spend much time testing (a little cold in the mornings, here in Maine). so if i have any obvious errors, it would be so nice to be able to fix them in the warmth, rather than trying to debug in the cold. ;) also, as i iron out the errors, if anybody else can use the file examples, feel free. :)
changes i plan on the arduino script: i want to add a LCD screen at some point (easy to do) for feedback so i can match the info from the arduino PID with what LinuxCNC is reporting to my pyvcp panel.
also, how do i make LinuxCNC wait until the At Temp pins (head-attemp, bed-attemp) are true, before continuing? i have a pyvcp spin-box to set the bed temperature, and one for the head temp as well, though the M104 can set it as well.

~Travis

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15 Nov 2021 21:36 #226603 by travis036
Well, my extruder arrived, but i think the stepper that came with it was defective. it was locked solid, and would not turn. i fortunately had a few spares from an old GRBL kit that puffed the magic blue smoke one day (the steppers are all fine). so i learned a bit about how it is put together, when i carefully took apart the extruder to change out the stepper. it is a bigger NEMA17, but it should still work fine. i didn't have any of the Leadshine stepper drivers as spares. the 3 i have are in use on my CNC. but i do have a crappy HY-DIV268N-5A that should work fine for the little NEMA17. i set the amps for 0.6A, and 1/16 micro-stepping. but i head the printing on the label could be wrong on these, so who knows what it is really set for.
i will get a better driver when i can afford one. this one should be able to at least make some moves, once i get the settings figured out.

now... if only i had a 3D printer so i could make some mount fixtures to mount my extruder on my machine... ;)

~Travis

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18 Nov 2021 20:42 #226916 by travis036
pondering on how best to establish exact extruder-tip to bed height...
now, i have a Z tool offset probe thing. you know, the electronic switch that you use on a CNC router to check the tool length.
currently, my machine is setup with Z-axis zero at the top of the stroke, with the home at the lower limit (will change to the upper limit at some point). and Z motion lower than home is in the negative numbers. ideally, i want to be able to make sure my extruder head is able to get as close as possible to the bed surface, without damaging the nozzle tip. so here are my thoughts: if i probe down to the tool-setter probe thing, and rather than retract, i let it stop there. that is my first known measurement. i set Z work-zero here. then i very slowly move the extruder down toward the bed surface, and use a known metric sample, like a metric feeler-gauge, i move the tip very slowly until the gauge just drags. so them i have a known height of the tool-setter, once i figure in the thickness of the feeler-gauge.
with these measurements, i could:
1) check the repeatability of my home switch.
2) know the exact probed height of my tool-setter.
3) check the repeatability of my tool-setter.
4) check the flatness of my work-surface using the tool-setter.
once the tool-setter accuracy is established, i should use it to set Z-axis zero so it is just barely touching the bed-surface, and have the position move up from zero in positive numbers, rather than down from zero toward the table. that way, at any given time, i can KNOW exactly how high off the table the tip of the nozzle is. so if i set it to Z5mm, i should be able to check the measurement from the table to nozzle tip and read 5mm.

what i am getting at, is if the first pass is 0.2mm off the bed, i need it to be accurate, and precisely located. or am i over thinking it? (usually the case)

I have, along with my Titan extruder, a 1kg roll of PETG (it was cheap, and can be done without a heatbed). so when i can get things in test mode, at least i have material to try and extrude.
as the tool-setter will likely be mounted in a fixed location at some point, i could in theory use it as the Z-axis home in 3D print mode. just home X and Y first to position Z over the tool-setter, then home down with Z. if the repeatability of the tool-setter is good, it should be pretty accurate.
i also have a 3D probe tool (electrical), so when setting the work-zero for Z, in case things change, i could make a fixture to hold the 3D probe in the same spot every time it is mounted, and figure out the XYZ offset from the nozzle tip, and be able to zero perfectly every time... though maybe this isn't needed for 3D printing, as much as it is for CNC routing... again, over thinking things...

the filament roll will be mounted either right over the extruder, or behind the gantry with PTFE tube to guide it to the extruder. haven't decided yet...

now, what are filament dryers for? i know what the name implies, but really, why does filament need to be kept dry, and does my PETG need this? i have not yet removed it from the vacuum sealed bag yet.

~Travis

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19 Nov 2021 21:47 #227024 by travis036
i may abandon the 3D printer adaptation idea...
I like the challenge of making my machine able to do something new, but it seems rather more involved than i was thinking it was. making sure my filament stays dry, seems more of a PITA than i am after right now. i honestly thought i could just put an extruder head on, and design something up, print it out, and away i go.
but keeping it dry is more than i want to deal with right now. perhaps it is just frustration, i really don't know, and right now, i don't care anymore...

~Travis

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19 Nov 2021 22:31 #227030 by tommylight
Keeping filament dry it ... overhyped.
Never dried them, ever, they are open and so days it is very humid, in a shop with 2 missing windows.
Also drying it is a simple as heating the bed to 50C and leaving the roll on the bed 15 minutes per side.
PLA does not care much
PETG does care a bit
HIPS does not care much, i have yet to test with very high humidity
ABS i do not know, i have an open roll for over 2 months, not used yet, we'll see how that ends up.
Last two have much more issues with warping...
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20 Nov 2021 21:55 #227126 by cakeslob
Not looking to start something here, and I do not know if this is a contentious issue within 3dprinting , but once I started in the injection molding industry, it was very clear cut that drying plastic is actually very important to guarantee the best results. Before that I never used to dry and my prints were fine, but once I started , it was a lot less trouble and better results. I dont know what the 3dprinting community says about drying, they march to the beat of their own drum, even if its not industry standard or best practice. But there are very few plastics that dont need drying , I dont think any are used in 3d printing at the moment(thermoplastic polyolefin doesnt need drying, maybe polypropylene) .
You dont need to dry, but its a lot easier if you do, it at least minimizes fudge ups in your print.
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