3.8.1 Loud bang on 7th bed level position (Solved)
My MK3S (kit build) had worked perfectly for over a year with all previous firmwares, but when I upgraded to 3.8.1 I got a loud bang on the 7th bed level check point before each print. Upon investigation, I discovered that the nozzle could not reach the full -Y position indicated on the flex sheet. The front Y axis bearing was hitting the bearing rod support in the front left corner of the machine. Basically the bearing support, a 3d printed part supplied in the kit, was too long to allow full -Y motion of the nozzle. And trust me, the kit was assembled exactly as designed. The rod support was 0.375" (9.5mm) long in the Y direction as installed. I removed the part, sanded it down on both sides until it was 0.323" (8.2mm) long, and the problem went away. Is this a known problem? Has anyone else experienced this?
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RE: 3.8.1 Loud bang on 7th bed level position (Solved)
Any chance you bought a clone and not an Original Prusa? The bearing holders on the MK3/S bed (Y) are not 3d printed, they are u-bolts.
Maybe post a picture of the part you're talking about?
RE: 3.8.1 Loud bang on 7th bed level position (Solved)
Vintage I think he means the printed y axis rod holders, not the bearing U bolts. The bearing are supposed to bump into those as thats the front bed end stop with the motor mount being the back endstop iirc.
RE: 3.8.1 Loud bang on 7th bed level position (Solved)
They shouldn't hit that under normal operation unless there's a crash or homing fail. My bed *never* hits the front when doing MBL.
So at that point I'd suspect either an issue registering the home at the rear of the travel or something else is making the bed travel too far forward...
RE: 3.8.1 Loud bang on 7th bed level position (Solved)
I think he means the printed y axis rod holders, not the bearing U bolts.
neo... right your are: it was the bearing itself hitting the 3d printed rod holder during bed leveling (7 out of 9). To restate: it only started after I loaded 3.8.1. I certainly believe I bought a real MK3S, and have the receipt to prove it. As I was investigating this, I put the printer on its side, ran the bed all the way forward, and could see that the nozzle was 1/2 to 1 mm forward of the Y Axis limit line on the smooth bed sheet, properly installed. Anyway, this problem is fixed for me, but I wanted to put in the forum in case anyone else encounters the problem. Thanks for the responses...Jack
...there are only 10 kinds of people in this world--those who know binary and those who don't...
RE: 3.8.1 Loud bang on 7th bed level position (Solved)
Its been awhile since I built a mk3s but is it possible that you have the belt tension parts in the middle of the bed adjusted such that the bed sits further forward with respect to its usual position ? Id check mine but a) its a MK3 (non s) and b) I'm currently printing a long print 🙂
RE: 3.8.1 Loud bang on 7th bed level position (Solved)
possible that you have the belt tension parts in the middle of the bed adjusted such that the bed sits further forward with respect to its usual position ?
Neo...finally got back to this, but no, I checked, and the belt tension parts appear to be installed correctly. These parts never come close to hitting anything over the full Y axis travel. During the bed level sequence, the bed first travels towards the back to find the +Y stop position. This position is defined by the back bearing body hitting the back plastic rod support. I measured the nozzle to be at a Y position of -10 mm relative to the Y=0 marking on the bed support (sheet removed). If I then moved the bed all the way forward, the nozzle only got up to 208 mm or so, if memory serves me. The front bearing body was hitting the front plastic rod support, preventing full travel of the nozzle to 210 mm. I never realized this, because I never printed anything there. I'm thinking that previous firmwares didn't go there either during the bed leveling. As I said above, I shaved off 2.3 mm of the forward rod support, and now everything works fine. The nozzle can now travel to Y = 210 mm, with no room to spare. Bed leveling is nominal. Incidentally, I also verified the bearing bodies were properly installed on the bed support plate.
So this is going to remain a mystery for me. No other reports of this problem, so I guess it's me and my Prusa, but it's a mystery as to what's wrong with my build. Thanks for your help and suggestions...Jack
...there are only 10 kinds of people in this world--those who know binary and those who don't...