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Olsson block bore non-concentric?

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I bought an Olsson block from PrintedSolid, who seem to resell from gr5.

I noticed that the hole was a bit off-center from the threaded boss on the top side but I didn't think much of it at first.

I'm still having some print problems and remembered that plastic flow can have shear problems with protruding edges in the flow.

The bore is not as bad as the first image in this product description, but it was noticeably off: http://gr5.org/store/index.php/olsson-block-no-tools.html

Anyone here seen that offset in their Olsson block and still got great results?

Edited by Guest

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Yeah that's from me which means it came from 3dsolex.

It's an optical illusion. I recently sliced something in Cura which had a threaded rod through it - large threads. The amazing thing I noticed is as you go through the layers EVERY layer is a perfect circle but the circle spirals around with the threading. So any cross section looks like a circle that is offset (not aligned).

If the threading stopped lower down you would see that it is indeed perfectly centered. I just now took out a handful of blocks and found the worst 2 looking ones (and the "thin" looking side was in 2 different directions. Then I screwed on the steel coupler. Still looked bad because only the flat part of the olsson block is clearly visible. Then I inserted the teflon isolator. PERFECT. Within half the thickness of paper easily. I could see no error even with reading glasses and looking from both ends.

So it's an illusion created by the fact that any cross section of a thread looks like a circle "off-center".

So please explain about your printing problems - maybe post a photo?

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You still aren't very clear.  But I'm thinking you are talking about the horizontal bands.  What is happening is some layers are getting too much plastic and some not enough.  That can either be caused by Z error (Z axis doesn't move consistent amounts so you end up with too much or too little plastic on a layer) or inconsistent extrusion (e.g. temperature is fluctuating, or repeated tangles of filament or inconsistent filament hardness (slips sometimes, grips sometimes, etc).

Usually it's the Z.  This would have been visible in old prints however before you modified the olsson block.  So first check temperature - while printing go into tune menu and see if the temperature is oscillating.  If for example you usually print at 220C and it overshoots to 240C the first time - no big deal but if then it undershoots to 210C and oscillates (forever!) between 210C and 230C then you can get this banding.  So watch the temp.  Normally it shouldn't move by more than 2C.  I mean if the fan goes from 0% to 100% the temp may dip down by 3C but it should recover within a minute and then stop oscillating.

If it's oscillating then you probably installed a higher value heater.  You can reduce the 3 PID values by the increase in wattage so 25W to 35W reduce the P and I and D values by the ratio of 25/35 or 30% less.  Or you can run PID autotune but just reducing them all by 30% may give you even better results than the autotune which is tricky.

But really your problem looks more like a Z issue.  Maybe clean the Z rods.  Maybe remove the plastic cover and get at the bearings and loosen them and move the bed up and down and then retighten.  Push the bed up and down a few times with power off checking for resistance.  Many people have taken their beds apart and cleaned out the bearings with WD40.  You want the rods and bearings dry and clean.  No oils.  No dust.  No water.  Many people have spent the $5 or so for a replacement Z nut.  Hmm.  I should stock those.  There's quite a bit of play in the Z axis for some Z nuts, and then for other's there is zero play.  I don't know why.  You can feel the play when you lift the bed up and down slightly.  There are other topics on this forum where people had great success by simply taking apart the Z bearings/mounts and puttnig it back together.

I know it sucks having to debug issues on a print when you have other things to do but the sooner you fix this the sooner your printer will be printing perfect again. Hey what state do you live in? If Massachusetts you should come by my house and I'll help you for free.

Edited by Guest

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Well, it's hard to be clear on why but I just don't consider the part to be "pretty good". The banding is nowhere near what I consider should be up to the standard of a well tuned UM2.

I suppose it could be the Z stuff. The rods look perfect, the lead screw looks over lubed but if it's lead screw, I would expect to see more periodicity to it.

I am certain my PTFE bushing is mushed out so that's coming in the next day or two, try that and play with the Z and see what else I can check.

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I replaced the PTFE bushing with the TFT from your store. It turned out there was hidden damage in the bore that likely made it not guide the filament well into the heater block.

The replacement bowden tube & thicker clips were probably a help too, the original one had seen better days.

https://www.flickr.com/photos/34962649@N00/27036614514/in/dateposted-public/

The one on the right is before bushing replacement, middle was directly after, left most one is after a couple build parameter tweaks.

Edited by gr5
fixed url

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