Future thoughts: z will be light "as feather" with counterweights like in building elevators. What you think?

Yes it will work, but do you need it?
Are you using a spindle/threaded rod to position Z, or a pulley system?
The counterweight really only makes sense if you are going to use a pulley system, otherwise you will very likely not need it.
Threads that are not exceptionally steep are mostly selflocking, which means that they will not move without a motor turning it in either direction when under load.
Typically the gearing you get when using threaded rod is high enough to move even very high masses.
1 KG is hardly any load for a M8 or even TR8 thread with a NEMA 17 driving it.

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My mistake, maybe numbers in picture will misguide someone ( as i misguided mr. Srek already, sorry ).

So, those weights above (1kg and 0.9kg) are just random example, that only explains, that the counterweight will be slightly lighter than printbed weight.

I do not know the final weight of the "z printbed assembly", as i did not designed it yet.
I done some mass pre-measurements for alumininium printbed plate (~ 2200gr 400x400x5mm) and glass plate (~1200gr), so those 2 are ~ 3400gr in total.
Heavy, already...hm?

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Srek

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zsrevda
P.S. Future thoughts: z will be light "as feather" with counterweights like in building elevators.

You are aware that this will not help if you are not working against gravity? There is no free lunch in physics

Please explain Your 2 sentences. What is working againsr gravity and free lunch in physic? I understand literally translation,
but i do not understand this in my question.
I must mention that i am not joking with you ,and i respect your knowledge, just English is not my native language (very obviously).
Regards.

What weight the setup is able to move depends on the torque the motor is capable of. If the whole setup has the mass of several kg you will need more then a NEMA 17 and standard stepper drivers.

As for the free lunch, the counterweight does not realy make it that much easier if you are planning for any kind of speed. The setup counters the force of gravity, but it does not change anything regarding the mass that needs to be accelerated.

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I thought that z axis is not a "speedy" one in core xy setup and in 3d printer setup in general.
Total mass of several kilograms is reduced to (for eg.) 100 grams, in "counterweight" setup i proposed above,
so tiny nema17 will handle only that 100 grams + printed model weight.
The rigid structure with counterweight will handle all the rest.
Am i getting something wrong?

Yes, you are not accounting for the mass you need to accelerate.
The counterweight is only compensating the pull of gravity, it doesn't change anything regarding the mass you have to accelerate.
Think back of physics in school. To move something you need a force. The formula is f (force) = m (mass) x a (acceleration)
With counterweights the force applied by gravity (a= 9.81m/s²) is accounted for and cancled out, so you only have to apply the force neccesary to accelerate the mass as if it were in free fall.
Different to classic setups where gravity will help you stop, in a counterweight setup the breaking acceleration has to be done using the motor as well.
Edit: Maybe an analogy will help.
If you need to move a car 1 meter the question is do you have to move it verticaly or horizontaly. If you have to move it horizontaly the wheels make it possible for you to push a 1t vehicle alone. If you want to push it verticaly (up) that doesn't work. Using a counterweight of equal weight as the car however does make it possible for you. You are then in the same scenario as if the car were horizontaly, only that instead of overcoming the friction of the wheels you have to work against the friction in the pulleys.
The one thing you have to do in both scenarios is to apply the force neccesary to start the car moving and to stop it again. This is what you are missing, the counterweight changes the Z setup into something that is equivalent to a X or Y setup, but you STILL have to get the thing moving.

To be honest, you don't seem to have any experience in mechanical engineering. Maybe you should try to start with a proven design and not an own construction, otherwise you might run into a level of problems and frustration that kills the project.
My first printer was a badly designed kit (wooden classical Mendel) that just didn't work. Like you i was forced to take the parts that i got and make something that works from it. With the help from a friend, who had a lot of practical engineering know how, we build a machine that still runs, but suffers from several problems that severly limit the speed and print quality. On the up side, i learned so much from that project and many others that the printer i am currently engineering is shaping up very nicely. The prototype delivers comparable print quality to any other machine i know and is fast, silent, easy to build and inexpensive. It took me 5 years to learn what i needed for that though.

Edited 2 time(s). Last edit at 01/10/2016 04:27PM by Srek.

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Thx mr. Srek, for fast and long answer. Yes i am aware of my little knowledge in physic and how it works in mechanic, but what the heck, i am here to learn,
and have no problem with asking. I want to learn and take advantage of your 5 year experience, and any other member here, who is willing to help as you done .
I just hope to learn things faster from your help guys.

As long as my 3d printer is on PC only, there is no harm. (it can even look like an elevator at this stage )

Here is a concept picture of my design before i joined this forum and before recent printhead modification ( this topic ),and any counterweight mod,
and some construction plates missing, and there is no z axis construction, and no electronics, and.... but this is only the begining.

Regards.

So that is what I meant to you before, when I said you had "accounted for weight, but not for mass".

A rock in space has negligible weight (due to lack of gravity), your counterbalanced Z platform has negligible weight (due to the counterweight), but both items still have mass, if you strapped a rocket to the rock it would still take energy to get that rock moving, just as it will still take energy to get your counterbalanced Z platform moving.

That said, you don't need to consider this for a Z axis that is only moving vertically, if you use a leadscrew then a NEMA17 motor will be more than capable of lifting 3.5Kg. This is very different to the X and Y axis discussed in your other thread, Z axis moves slowly (no rapid changes of direction), so can easily cope with a much larger mass than X or Y.

This is a good online calculator for leadscrew torque here http://www.daycounter.com/Calculators/Lead-Screw-Force-Torque-Calculator.phtml

I would agree with Srek's advice though, unless you are an experienced mechanical and electrical engineer it makes a lot of sense to copy (or adapt) a known working design for your first printer. Designing a printer from scratch is a minefield for the inexperienced.

Zsrevda - you're obviously keen and very adept at design and drawing - they are amazing. But I second what others say about the learning curve, I have 2 printers, an i3 which I bought ready assembled but in need of some major work, this enabled me to learn to fault find and get a feel for how 3d printers behave, something which actual hands on experience gives you over any type of theoretical planning. They are such complex and beautiful machines especially when running you need to see, feel and observe the effects of your changes on printing objects. My second printer is a delta, so more complex in its operation, I think I would have been less comfortable starting off with this machine, I am glad I learned from the i3 which is conceptually simple and cheap and readily available.

I am planning next on building a corexy from a kit and then heavily modifying it . After that I would take on a self designed and self built printer.

The issues you have highlighted so far are essentially solutions to problems that do not exist, i.e. the threaded rods/leadscrews move the z carriage without any problem generally with no counterweight needed, and the x and y benefit immensely from being lightweight where it does not compromise mechanical stiffness etc.. . I wouldn't have known this without actually learning it from operating a printer. Also try to keep any design to as simple as possible, there are hundreds of things that can and do go wrong on a 3d printer all the time and every little bit of extra complexity adds more potential failure modes to the system.

We're all different and maybe you can jump straight in at the deep end, but it is a curve and you're on the steep part. I do not wish to stifle your creativity as you could come up with a brilliant idea that helps us all, but its a case of knowing what the problems are before designing solutions to them, unless you have all the time (and money) in the world to spend.

I'd focus some of your energy into hands on messing around with parts and electronics then go back to the CAD with this knowledge.

I wish you luck and will be happy to see how it progresses/to help if I can.

Edited 1 time(s). Last edit at 01/11/2016 07:52AM by DjDemonD.

What exactly are you trying to achieve?

Do you want to replace the leadscrews of the Z axis with a belt because of the Z-axis wobble some people get?
I myself also want to use belts for my Z-axis, but I am thinking about using a pulley system for my belt Z-axis.
You not only increase the resolution, but also only have to use a fraction of torque with pulleys.
They add mechanical complexity, but if your goal is a belt driven Z, pulleys and properly tight polymer bushings or preloaded linear bearings (for the friction to help the motor hold the Z-carriage) might be your best bet.