Nothing fits together while trying to assemble first mk3s

Hello!

I'm trying to assemble a mk3s bear kit from fysect with 2.1 ABS printed parts from ebay.

Nothing seems to fit as described in the manuals / tutorials, my experience does not match what I've read from others. A lot of reworking of the printed parts seems to be necessary. I can't tell wether this is normal and wether I should be able to work with the components I have since I have nothing to compare them to. Not sure what info I need to supply so someone can judge what might be wrong, so I'm just attaching some random photos. If I should describe, measure or take photos of anything else, please let me know.

It just seems that I need to use tools too much that aren't very prominently featured in the manuals and tutorials. Like small chisels and hammers and acetone and router bits and more - and some of those are mentioned in comments or hints sections, but not that much. Also it's sort of weird when in some places the manual tells me to "temporarily secure a part with tape so it does not fall out during the next steps" and that sounds reasonable, except my experience is like: "Fall out!? It took me 3 chemicals and 5 tools to get that locknut in there and now it's in there forever or until someone throws that y-belt-holder into a volcano!". It seems like a lot more work and harder than it should be and - more importantly - I'm beginning to doubt that I'll have a working printer at the end if I continue like this.





Thanks!

The printed part are from some random person, no way to know of they are in tolerance or not

Most common issue I've seen is people using the wrong type of belts

Cheap belts from china will not work. Although they have he same tooth profile, the overall belt thickness is to large.
You need Gates GT2 belts not some random cheap belt.

But it sounds like you got a rubbish set to plastics from someone who didn't have a clue what they where doing.

Edited 1 time(s). Last edit at 12/01/2020 04:16PM by Dust.

The seller of the printed parts was very helpful, sent me a bunch of advice; even offered to edit some meshes and send me altered versions of some parts that are easier to use. They seem very confident in the quality of the delivered print parts due to having already assembled a fair amount of i3 printers. That's part of the reasons why I'm doubting my abilities to assemble that thing and haven't ordered a second set somewhere else yet. I have no baseline for how hard this should be. If there's a way to confirm what's wrong (before I order more stuff) by examining those part or the fysetc parts or my technique, that would make future decisions much easier.

I already bought a random second belt and tried it. That belt had the same dimensions and was slightly harder. I measured both the belts and compared them to random data sheets / specs I found online, they seemed OK. They are both ~0.62mm (measured with very light pressure) at the narrow part between the teeth and ~1.43 with the teeth. The softer one can be compressed to ~0.45mm between the teeth with moderate force or to 1.27 including teeth. Distance between the STL file vertices of the parts (@teeth) are 0.65mm (y holder) and 0.75mm (x carriage). A 0.4mm SS316L wire was already too thick to fit all the way down in the printed part (before I started chiselling). Not sure if that kind of difference between model and printed parts is to be expected / OK.

I tried to measure the thickness of the thinnest surface I could find on the print parts (the sides of the rambo doors I think). Total size seems fine, but plastic appears to be on average ~7% thicker than the models vertice distance in many places, gaps between plastic are narrower as seen in the photo above. Don't know if that can be translated into print tolerance / extrusion multiplier offset somehow. Since I'm going to need it to calibrate the printer at some point anyways, I ordered a slightly better tool for measuring thickness which should arrive later this week, maybe that will help.

As for my "technique" - here's the latest episode of "WTF am I even doing!?" in case anyone's bored enough to read it: I tried to insert 2 LM8UU into the x-end idler. At first, I followed the assembly manual and tried "a small screwdriver". I quickly realized that "a small screwdriver" was not enough, so I squeezed "a rather big screwdriver" into the gap instead, almost stabbing myself a couple of times during the process. Also briefly crammed a coin into the gap, catapulted the print part through the room with a small chisel and used some oil and acetone on random objects in my vicinity. That was enough to get the bearings stuck barely 1mm in and create some stress lines on the surface of the plastic but not much more. So then I browsed more Internets and found a video of someone using a scary metal hammer to beat the bearings into submission. I did use a soft hammer instead, still managed to get one of the bearings in. The bearing looked a tiny bit battered and sad, or maybe that was just my imagination. I looked into the hole from the other side and noticed that the bearing shaved off some plastic. Didn't want to break the bearing, so I asked a Random Internet Chat Room Person for advice and they told me to put an AA battery between the hammer and the bearing since the battery should be sturdy enough for reasonable force but take visible damage before the more sturdy bearing would. This advice worked very well: I carefully administered visible damage to the battery while the bearing did not budge the tiniest bit. Came to the conclusion, that I should probably get that bearing unstuck again and maybe chisel away at the printed part first. The comment section of the assembly manual said to use an aa battery, here, too, inserted from the other side. That battery did not fit in there at first, but I managed to get it in with the screwdriver and hammer. Then I realized, that now I have a bearing AND a battery stuck inside the print part and that a second battery would not fit because the plastic is already under pressure in the middle and won't budge enough to get a second battery behind the rim. So then I stacked hex nuts on the battery and hit them with the hammer until everything fell out. Bearing looks slightly used but still OK probably. I wondered for a while, if I was too careful and should have just confidently hammered in those 2 bearings. Then I took a closer look at the smooth rod & corresponding holes and realized, that there's no way those would fit either. Measured the smooth rods, they seem fine (8.00). Measured the total length of the printed part - seemed fine too. Measured the diameter of the holes, they seem fine'ish on one axis (getting up to 8.43mm, measured with moderate pressure) but I think they might be oval (only up to 7.94mm on other axis). Not sure, hard to measure. Didn't find a drill that looked right for those holes, gave up for the day.

Sorry if I'm overly verbose yet still inaccurate, I have no idea what information I should supply.