2 screws that appear to have no purpose with one of them loose
My assembly of the MK4 went smoothly and has been printing well for over 6 months. However, recently I've had problems (not dealing with those here!) and decided to check all the screws for tightness. All OK except for 2 - one each on the X axis assemblies.
Step 3 Assembling the X-end-motor (part I): At this point you fit an M3 x 25mm screw and leave the head level with the top of the body:
"Screw the M3x25 screw into the plastic part. Do not tighten the screw completely. Keep the screw head aligned with the top surface of the part." followed by:
"From the "bottom" side of the part, insert and tighten the M3x16 screw.There is no thread in the plastic part, no nut. The screw cuts a thread into the plastic when tightened."
No problem with this step except that there is no further mention of the first screw! Leaving it loose?
I've had a chat on-line-live without a resolution e.g. I don't think the operator knew the answer.
So, my question here is: What are these 2 screws for? The M3 x 25mm (which is left loose) and the thread forming M3 x 16mm . . . I just don't like screws that are loose and are not there for adjustments
Thanks - Dave H.
RE:
Hi Dave,
the M3 x 25 screw is part of the X axis Belt tensioning system 
in a later step, you insert another screw into the other end of the assembly to act as a pushrod, once the motor is installed and the belt is installed, with the Motor screws loose, you can tighten the M3x25 screw which pushes on the M3X10 pushrod, and that causes the motor to be moved, tightening the belt. once adjusted, you need to re tighten the motor screws.
the m3X18 screw is one of four screws which act as endstops for the X axis smooth rods inside the X axis End pieces. 
These have two functions
Stop the adjustment of the X axis Belt squeezing the X axis ends together by butting against the ends of the smooth rods
Reduce the likelihood of the X AXIS ends splitting along the inter layer bonds, when the smooth rods are inserted.
these screws do not need to be tight, the self cut threads will act as locknuts and the pressure of the smooth rods will ensure that they do not unscrew in use
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: 2 screws that appear to have no purpose with one of them loose
Thanks for the answer, Joan . . . This has made me feel a little foolish! As, I'm actually needing advice on a totally different screw - d'oh! No wonder the Live-Chat guy wasn't able to help.
The screw I should be asking about is the second one in: Step 6 Assembling the X-end-idler (part II) - Which has the text: "Insert and tighten the second M3x16 screw from the "top" side of the part" - Which, of course, answers my question: should it be tightened? I'm now seeing that they just are end stops for the X axis rails so not really that important!
Anyway - thanks again for your reply - it has led to the right answer I was after.
Dave H.
RE: 2 screws that appear to have no purpose with one of them loose
success then! 🙂
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK