x-carriage movement

Hi All,

I'm seeing some strange artifacts in my prints, and my current theory is that it's the x-carriage rotating backwards and forwards in the Y axis as the filament applies pressure in various directions as it unrolls from the spool... (if that makes sense!)

Have a look at the attached image, you'll see the wobble in the lowest 50-ish layers. It's consistent across most of my prints. We're looking down the X-axis at the model, so something is moving in the Y axis in a regular and predictable way. My y-axis belts are tight, z threaded rods are straight (or pretty damn close), and I'm thinking that as the filament unwinds from the spool at the start of the print the forwards/backwards pressure it applies on the x-carriage changes as it settles down into a "static" kind of position...


I've got a Prusa i3 box frame, built pretty much stock from the github files. With the extruder hanging off the side of the two x axis smooth rods, there's a little bit of flex in the whole x-end, smooth rods, x-carriage assembly and I can move the whole thing by hand a degree or two. It doesn't take much pressure on the incoming filament to make it visibly move.

So, questions are:
- Any other theories on what would be causing a consistent error like this?
- Any ideas/parts that would be good to brace the x-carriage a bit firmer than it currently is?
- Or any other good ideas

Cheers,

Is it consistently at the same height?

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Ralph.Hilton
Is it consistently at the same height?

Pretty much, the shape varies a little but it's always in that bottom 10mm or so. Once it gets passed that things generally print pretty well.

Definitely faced the problem few months ago. Looked similar - about 10-12 layers in one place, then shifts a bit to side and continues to print fine.
Not quite sure, but as I remember tightening the y-belt (with EXTREME force) solved it.
Good luck!

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Tolstiy
Definitely faced the problem few months ago. Looked similar - about 10-12 layers in one place, then shifts a bit to side and continues to print fine.
Not quite sure, but as I remember tightening the y-belt (with EXTREME force) solved it.
Good luck!

I'm pretty sure my y belt is tight enough (hums like a guitar string when plucked, and if I force it any more it just pings out of the belt clamps!), but I'll double check tonight. I can't think of a reason the y axis would change it's behaviour after the lower layers of the model, which is why I'm looking suspiciously at the x-axis side of things... The Z layer thickness looks right, and if the Y is behaving as it should then that only leaves X

Another thing to check is how the filament is coming of the spool if there is drag it will cause it to pull the extruder

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My guess now is the Z rod(s) are deformed. I would try turning them upside down and see if that makes a change. Can you make a video of the printer in operation and show the top and bottom of the Z axis aswell as the X and Y idlers?

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chris33
Another thing to check is how the filament is coming of the spool if there is drag it will cause it to pull the extruder

The filament is all on rolls and wound onto holder like this. They run on 608 bearings and rotate very freely. I actually tension them up a little to stop then running too freely and unrolling too much filament. I'm using 3mm PLA which is pretty inflexible stuff. I often find it's in a completely different position at the end of the print than the start, which is why I'm looking at that as the culprit.

I might try some filament guides to get the filament going into the extruder in a more predictable manner. I'd still like to stiffen up the x-carriage, as the fact that I can move it by hand does worry me.