lead screw question

Hey there guys
i had a question about the z axis really in general.
So i had calibrated the z axis to the best of my ability. I notice when i click auto home it obviously lowers the z axis till it hits the switch. then when i print something it does the same thing EXCEPT it will go all the way down then back up then down again. I believe this is calculating the steps to height ratio right?
Please correct me if I am wrong. because once it goes to 0 then moves up to a number of known steps with the motor, then back down again it can probably calculate the distance it has moved with the number of steps? yes?

the reason I ask this is because I want to upgrade it with a lead screw. The company I bought the printer from says my threaded rod "is fine" even though i have sent them multiple videos which you can clearly see wobble AND you can see the carriage on the z move which is affecting my prints. when it prints on the Y axis the lines are beautiful and straight but when it makes lines on x they are terrible to say the least.
Here is an example of what I am talking about
Please note this is not my print i am just saying this is what it looks like
[blog.lincomatic.com]

the lines are minimized when i print at .1 resolution but are more prone for delamination because i do not have a hot box yet.

to my conclusion. my main question is besides printing z axis STL's and inserting new lead screw do I have to modify the firmware at all?
I am guessing no if my logic above is correct? I just wanted to affirm or deny my analysis of what I think the printer is doing.

Thanks guys

Edited 1 time(s). Last edit at 01/19/2016 06:55AM by bizit524.

Interesting guess, but no

There is no feed back, it can move as many steps as it wants, it only thinks It knows where it is because of the endstops and the predefined steps/mm

In general It homes at speed, then to get as much accuracy as it can it goes up a little then re homes much slower to check its home position.

When you change your lead screw you will have to update the Z steps/mm

eg in marlin its a line like #define DEFAULT_AXIS_STEPS_PER_UNIT {80,80,4000,500} // default steps per unit for Ultimaker
Where these are the steps/mm for X,Y Z and E axis

Depending on the printer design the print issue could be a belt not being tightened enough and not a rod wobble

@frans - yes this could be I tried to tighten it as far as possible but the stock end carriages are pretty poor. I have found on thingiverse much better end carriages with a belt tensioner
I will be printing these soon

@dust - i do not know the step- mm. I have seen through youtube videos that you can edit the firmware with audrino SDK. However the question on that i had was not answered by any videos I saw. Is there a way to extract the current config from the arduino ? All of them were showing that just download the appropriate configuration.h from a website then upload again.

I will have to look up the new rods I will be ordering soon for it.

If i remember correctly M502 will load factory defaults and return the steps /unit values in the console, among other information.

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