# Sometimes tool changing fails **URL:** \ **Category:** U1 Toolchanger\ **Created:** [March 15, 2026, 7:58pm UTC](https://forum.snapmaker.com/t/sometimes-tool-changing-fails/41486 "2026-03-15T19:58:54Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![hunter86\_bg](https://avatars.discourse-cdn.com/v4/letter/h/f08c70/32.png) [@hunter86\_bg](https://forum.snapmaker.com/u/hunter86_bg)\ **Post date:** [March 15, 2026, 7:58pm UTC](https://forum.snapmaker.com/t/sometimes-tool-changing-fails/41486/1 "2026-03-15T19:58:54Z")
I’ve assembled my U1 an hour ago and it’s already printing the built-in dragon. I have noticed that sometimes on tool change (both retrieval and parking), the head (both #2 and #4) doesn’t attach/disconnect properly which leads to errors. One occasion was when the head was not properly aligned with the pin (but 50+ swaps were fine). On another, the head was not properly detached. What kind of calibration I should do to fix the issues (I already did the Homing Calibration)? Best Regards ---
**Author:** ![hunter86\_bg](https://avatars.discourse-cdn.com/v4/letter/h/f08c70/32.png) [@hunter86\_bg](https://forum.snapmaker.com/u/hunter86_bg)\ **Post date:** [March 15, 2026, 7:59pm UTC](https://forum.snapmaker.com/t/sometimes-tool-changing-fails/41486/2 "2026-03-15T19:59:48Z")
![IMG_20260315_212857_527](https://us1.discourse-cdn.com/flex022/uploads/snapmaker/original/3X/a/3/a3e377c4259bdc248a0033c569fb2fa79fccdf74.jpeg) ---
**Author:** ![Simon76](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.snapmaker.com/simon76/32/32089_2.png) [@Simon76](https://forum.snapmaker.com/u/Simon76)\ **Post date:** [March 15, 2026, 8:48pm UTC](https://forum.snapmaker.com/t/sometimes-tool-changing-fails/41486/3 "2026-03-15T20:48:53Z")
Maybe you need to calibrate the pick/park positions [https://wiki.snapmaker.com/en/snapmaker\_u1/troubleshooting/u1\_how\_to\_adjust\_the\_pick\_and\_park\_coordinates](https://wiki.snapmaker.com/en/snapmaker_u1/troubleshooting/u1_how_to_adjust_the_pick_and_park_coordinates) Did you do the belt tensioning step described in the startup manual? If not, this might also help ---
**Author:** ![hunter86\_bg](https://avatars.discourse-cdn.com/v4/letter/h/f08c70/32.png) [@hunter86\_bg](https://forum.snapmaker.com/u/hunter86_bg)\ **Post date:** [March 15, 2026, 9:02pm UTC](https://forum.snapmaker.com/t/sometimes-tool-changing-fails/41486/4 "2026-03-15T21:02:56Z")
I did. I just checked again the print and I noticed a layer shift (both print and tower), so I’m going to do the belt tensioning again. ![IMG_20260315_222628_447](https://us1.discourse-cdn.com/flex022/uploads/snapmaker/original/3X/0/0/0096d510cba3e546ff8be6517709b9011dfb4d09.jpeg) ---
**Author:** ![Cylonmode](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.snapmaker.com/cylonmode/32/30291_2.png) [@Cylonmode](https://forum.snapmaker.com/u/Cylonmode)\ **Post date:** [March 16, 2026, 10:24am UTC](https://forum.snapmaker.com/t/sometimes-tool-changing-fails/41486/5 "2026-03-16T10:24:23Z")
Open a ticket with support, they respond quickly and are helpful. Till they respond, I’d say do the belt tensioning step again, at least 3 times and go slow not fast. Could be a coordinates issue or something else… Does it home properly? Do you have the issue with printing only or homing as well? ---
**Author:** ![hunter86\_bg](https://avatars.discourse-cdn.com/v4/letter/h/f08c70/32.png) [@hunter86\_bg](https://forum.snapmaker.com/u/hunter86_bg)\ **Post date:** [March 16, 2026, 11:19am UTC](https://forum.snapmaker.com/t/sometimes-tool-changing-fails/41486/6 "2026-03-16T11:19:51Z")
I did manual bed leveling, new mesh + 3-phase belt tightening (loose the screws, 2 loops, tighten gently, 2 loops, repeat another 2 times) and the results are crazy good and 0 tool parking errors. ![IMG_20260316_125713_145](https://us1.discourse-cdn.com/flex022/uploads/snapmaker/original/3X/2/7/27ac94bfa931faebed95b45d8b878f680695ac6b.jpeg) ![IMG_20260316_125658_765](https://us1.discourse-cdn.com/flex022/uploads/snapmaker/original/3X/d/a/da6d2fe273064d8350272481b961241c57247bcf.jpeg) ![IMG_20260316_125652_732](https://us1.discourse-cdn.com/flex022/uploads/snapmaker/original/3X/3/9/39320486e7482596300cefad5b688e67338e240a.jpeg)