Size limits to fdm print jobs?

[PaulS]

but wait threes more... Have we ever seen @csorrows and John together? kind of like batman or superman right?.and of course the dead give away is when John\Chris said his FT5 is factory stock. As we all know, no 2 ft5's are the same and nobody builds the ft5 stock.. I have to say you went to a lot of trouble to create this forum just so we could fix your printer for ya... Not to mentions doing the sisyphus thing with the eternal manual updates, wouldn't it have been easier just to do it right the first time? forget a new topic, we might need a new category here LOL
Disclaimer, if anyone is taking this serious, you are in the wrong forum!
for the record. my FT5 was and always will be my 1st luv. that said can't complain about my tornado, for what it is, awesome toy but still a distant shadow to frank N printer...

[PaulS]

all BS aside, I think it would be cool to get a Q and A session with John some time. Words from the master himself kind of thing...Maybe @csorrows can talk to his alter ego...

[PaulS]

before the "mediator" of this forum (whatever his name is ) pings us for off topic, so maybe doing large format on the vertical is less desirable maybe expand build plate and go out instead of up? last few large prints were very slow primarily because of all the support material having to be printed. free standing supports about 1 foot appear to get a little sloppy IIMHO. anyone else seen this kind of thing? suggestions?

[Ron]

I would second that thought.
The vertical direction is less "stiff" because the support rods and lead screws would be getting progressively more compliant as their lengths are extended.
And in the middle of their travel they would be most compliant.
The frame vibrations induced from X and Y motions could easily couple with the Z rods and produce oscillations.
Think of a stork standing on one very long leg during an earthquake.
Horizontal on the other hand (particularly the Y axis) could be extended quite a lot with little or no ill effect.
The ball slide rails and their supporting 2020 rails and plates are quite rigid and of course there are two of them in the Y axis.
But extending X would be OK too.
It would essentially eliminate the concern for having two very long Y axis slides aligned perfectly parallel.

The concern with support material is a valid one.
For very large vertical prints the mass of support material could easily exceed the mass of the piece being printed.

Heating the bed would become the next problem to consider.
If you went double in size using an aluminum tooling plate with two mains-powered heaters, it should work nicely.
Even a combined 1200 watts would only represent 10 amps at US-standard mains voltage of course.
And with mains powered heaters PSU loading would be of no concern regardless of size.

[PaulS]

OUTSTANDING! thanks @Ron my thoughts exactly, always good to know there is another mad scientist in the world LOL so to expand X above, maybe use linear rails instead of rods and some sort of gantry for support from above? cant have x sagging in the middle of the bed so... hoping for 2 or maybe even 4 feet on x and at least 4 feet on y max 2 feet on z but guess will rarely break 1 ft mark . wish we could have multiple print axis' then we could have print beds in 2 or 3 sides eliminating vast majority of support needed. kind of like a fence for a table saw... ugh no way i could program a 6 axis machine at this point anyway lol moving on

[PaulS]

dint you also mention something about swapping in pieces on the print bed so you can print less support material? now that is genius! think i might actually be able to make that work. Will take a few tries but if i can pick what layer supports start printing on then that could be doable. it would have to be a per support tower setting so will have to dig into s3d for that unless someone here knows already? where is John/ @csorrows when you actually need him?

[Dave]

@PaulS - Have you looked into IDEX - "Independent Dual Extrusion"?

It's a catch-all for everything from independent carriages taking turns for multi-material, taking turns for variable layer height, to dual or quad simultaneous prints of the same object, to cooperative printing of different sections of the same object/model. Really cool stuff.

[PaulS]

WOW @Dave i had not seen that but certainly along my lines of thinking here. Most of that multi head tech is well beyond my my technical limits at the moment but i am certainly going to take some chassis design tips from this. exactly what i was talking about here but on an even larger scale then i imagined... Going to b 1 hell of a birthday present but believe it or not i expect to be well under $1000 for the entire project! dual PH is a given just not sure i can get them working in tandem like that on my duet fi. will have to pint that forum for sure!

[Ron]

maybe use linear rails instead of rods and some sort of gantry for support from above?

Oh, I may have made a faux pas.
I thought you were talking about an FT-5 which has the linear ball slides and 2020 slide supports (which makes them very rigid).
Were you talking about another type of printer that uses slide rods?
If so, you might consider changing it over to a slide/support system in the manner that the FT-5 uses.
You could for example use the same type of slide rails (longer of course), or go to a larger capacity slide rail (wider carriage), and/or use 2040 or 2060 stock with the longer axis being vertical.
That would be extremely rigid and would be rather unlikely to sag even if doubled in length (or more).

If I were to do such an expansion to my FT-5 in one axis only I would expand the Y axis for a simple reason- inertia.
The moving mass of the X carriage would not be changed, and merely lengthening the Y rails would have very little effect other than the belts being a bit "stretchier".
So performance-wise it might need to be slowed down a little bit, but probably not much, if at all.
Also, the Y slides are very well supported and are already very rigid.

The double heater bed plate thing would apply to almost any style of printer though.
Just be sure to use a material for the bed plate that is rigid and which also has low thermal expansion, or at least which will not warp like a potato chip when heated.
In the case of an FT-5-"like" setup the Z moves very slowly so the increased mass of the plate should not be all that much of an issue.
Mine is at least 3X the "stock" mass at the moment and I am having no problems with it.

Just my $0.000000000002 worth.....

[PaulS]

yup this would be a scratch built machine similar to ft5 frame is the question maybe cr10 style would be better for large print expanding x and y more and z less...

[Dave]

maybe cr10 style would be better for large print expanding x and y more and z less...

For huge prints, scaling up a printer with a Y-axis moving bed just seems like you're asking for problems.... lots of problems...

[PaulS]

as compared to z, more or less is the question... looking to go somewhere around 4 ft by 4ft by 2 ft is my current guess what axis is best short for this volume?

[Dave]

That's a tough one actually...

If the bed was 4x4', you could print a coffee table really easily, and the top would be nice and flat (printed upside down). But a stool would have to be printed sideways... you'd have a whole spool of plastic just in the supports!

Structurally, you'd need something pretty beefy for a 4' X-axis span... or some active compensation for the beam sag?

Or you could just build a Delta.
https://www.3ders.org/articles/20140729-5-meter-tall-giant-magna-delta-3d-printer-unveiled-by-japanese-creators.html

[Ron]

Even with a Delta at that scale you'd face issues with frame expansion and bed warpage.
So grid leveling would be a must I'd expect.

[PaulS]

any idea how to get around lead screws on Z axis? not fond of built in errors in movement accuracy...maybe counter balance bed so it can be belt driven on vertical?

[Ron]

Actually, there are already belt-driven Z-axis versions of delta printers.
So that isn't such an odd idea at all.
But lead screws are probably more accurate and powerful in the end than belts could be unless you were using some of the precision steel band drives (read that as- $$$$$$$).

If you go with 2mm pitch (single start) lead screws rather than 8mm pitch (4 start), you are already in the 0.625 micrometer per step territory (at 1/16 micro-stepping) with a lot of force available.
Add zero backlash nuts and I would think that it would be more than accurate and repeatable enough.

[Dave]

Plus you can change the ratio with a simple pulley change to gain some resolution. I have 40T pulleys on the leadscrews on my FT-5 Z-axis, for a 2:1 ratio instead of the 1:1 of the factory build. (This uses 200mm belts).

[Ron]

I have been thinking about doing something similar actually.
Perhaps when I eventually build a mini FT-5 from the left overs I'll do that.
I was thinking along the lines of the standard 20 tooth motor pulley and 32 or 36 tooth pulleys on the lead screws.
The Z motion doesn't need speed, but it might help a single motor cope with the moving mass.
At the same time I will install zero backlash nuts on the lead screws.
Just something else on my endless "to do" list.

I run a light smear of THK grease on the lead screws now, by the way.
It definitely helps them to run smoother and quieter.

[PaulS]

the lead screw issue i am referring to is the minimum 1 step of the motor = x distance depending on gear ration. problem is,this does not exactly line up with layer height so every so often 1 layer will be too high or low depending on pitch of thread. this is well documented and far better explained on youtube LOL not sure if gear ratio would help this as you still have same problem with single step. i went to .9 motors for this reason but think belt systems are immune to this problem right?

[Ron]

Actually, belts would be no better than lead screws in this regard, and perhaps worse due to backlash between the belt teeth and the pulleys.
A step change is a step change.

With FT's 8mm pitch lead screws (8mm of vertical travel per revolution) and 1/16 micro-stepping using the A4988 drivers, the basic motion is 0.0025 mm per micro-step.
However, micro-stepping is not an exact position driver despite the common wisdom.
It relies upon balancing magnetic fields to achieve some compromise position based upon the residual torque and drag.

So for full steps between the motor's magnetic pole positions (where the rotor and stator poles are aligned) on a standard 50 pole stepper (200 full steps per resolution), the resolution is 0.04 mm per full step.
If you do a 2:1 pulley reduction as you have done, it becomes 0.02 mm/step.
And if you then go to 0.9 degree motors (100 poles, or 400 full steps per revolution) it becomes 0.01 mm/step.

If you are running 0.25mm layer heights and the standard setup, there would be a 0.01mm "error" every 6 full steps.
However this is non-cumulative, so....... ?

Finally, if you went to a 2mm pitch lead screw (2mm per complete revolution) and your motor and pulley reduction you would reduce that to (wait for it.....) 0.0025 mm/step (full steps that is).
Which is coincidentally 100 full steps for a 0.25mm layer.
Now you are talking accuracy.

Oddly, I am not sure why the 8mm pitch lead screws were used to start with on the Z axis.
Tradition perhaps?
2mm (single start) makes so much more sense in this application.
The Z motion is just not that fast, nor does it particularly need to be all that fast, I'd think.