# After v1.15 → v1.20 upgrade, Apply Tension always fails — bottom-belt deviation ~40mm **URL:** \ **Category:** Troubleshooting\ **Created:** [May 3, 2026, 2:39am UTC](https://forums.maslowcnc.com/t/after-v1-15-v1-20-upgrade-apply-tension-always-fails-bottom-belt-deviation-40mm/25745 "2026-05-03T02:39:43Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![ian\_ab](https://avatars.discourse-cdn.com/v4/letter/i/a587f6/32.png) [@ian\_ab](https://forums.maslowcnc.com/u/ian_ab)\ **Post date:** [May 4, 2026, 7:37am UTC](https://forums.maslowcnc.com/t/after-v1-15-v1-20-upgrade-apply-tension-always-fails-bottom-belt-deviation-40mm/25745/21 "2026-05-04T07:37:39Z")
Suggest you have a look at the firmware updates. Some of these are well worth running with. If you are happy cutting, then enjoy. ---
**Author:** ![Nov27th2025](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/nov27th2025/32/29771_2.png) [@Nov27th2025](https://forums.maslowcnc.com/u/Nov27th2025)\ **Post date:** [May 7, 2026, 12:19am UTC](https://forums.maslowcnc.com/t/after-v1-15-v1-20-upgrade-apply-tension-always-fails-bottom-belt-deviation-40mm/25745/22 "2026-05-07T00:19:31Z")
Yes; I’m looking forward to attempting to upgrade again. ---
**Author:** ![AndyDarragh](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/andydarragh/32/29074_2.png) [@AndyDarragh](https://forums.maslowcnc.com/u/AndyDarragh)\ **Post date:** [June 16, 2026, 10:07pm UTC](https://forums.maslowcnc.com/t/after-v1-15-v1-20-upgrade-apply-tension-always-fails-bottom-belt-deviation-40mm/25745/23 "2026-06-16T22:07:25Z")
I think my errors are similar to these and I was also relatively stable using firmware V1.15. Now I have been getting center deviation errors with Firmware v1.21 and horizontal setup [Maslow Failure to Take Slack after Cut.log](https://forums.maslowcnc.com/uploads/short-url/2cbPr2bakDq0nRz8UhZkm4RYbue.log) (15.8 KB) . Find anchors runs fine and I get fitness between 1.28 and 1.75 . Cutting goes fine. I drive the sled about 3 feet left of center to change out the workpiece. The last time I set this as the park location but did not park it. I released tension. I changed the workpiece. I tried to Apply Tension and it went into Extended state with a center deviation error (see attached). So it seems that I have to run Find Anchors every time I want to cut something. I see bad connection as well as center deviation errors in the log. Any obvious solutions? I used a fresh yaml file and have reloaded the firmware and index several times. I am running tension force at 900. Do I HAVE to use Park instead of releasing tension? Regards, Andy ---
**Author:** ![bar](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/bar/32/10_2.png) [@bar](https://forums.maslowcnc.com/u/bar)\ **Post date:** [June 17, 2026, 12:19am UTC](https://forums.maslowcnc.com/t/after-v1-15-v1-20-upgrade-apply-tension-always-fails-bottom-belt-deviation-40mm/25745/24 "2026-06-17T00:19:44Z")
1.22 is going to have a pretty major rewrite of how all of that works which might fix this issue. Do you see the same behavior on this version: > [@Interstitial Firmware Releases](https://forums.maslowcnc.com/t/interstitial-firmware-releases/20215/918): > > Latest Test versions 2026/06/09 [index.html.gz](https://forums.maslowcnc.com/uploads/short-url/wqK3C41xHEeb4LIfl21GkLi6ot4.gz) (146.4 KB) [firmware.bin](https://forums.maslowcnc.com/uploads/short-url/yNHqRDBdCqlaKHikwK1glCFSJi6.bin) (1.9 MB) Updates since V1.21; Sanity check startup Z with non-reset warning for high Zm Retry LM solver with perturbed anchors FluidNC Config Items: show active Config/Filename instead of hardcoded maslow feat: OTA “Check for Updates” with configurable release stream Render live Find Anchors path trace from calibration waypoints Update startup Z/Z-home handling, persist Z-stop home across restart Find Anchors: switch canv… ---
**Author:** ![ian\_ab](https://avatars.discourse-cdn.com/v4/letter/i/a587f6/32.png) [@ian\_ab](https://forums.maslowcnc.com/u/ian_ab)\ **Post date:** [June 17, 2026, 1:42am UTC](https://forums.maslowcnc.com/t/after-v1-15-v1-20-upgrade-apply-tension-always-fails-bottom-belt-deviation-40mm/25745/25 "2026-06-17T01:42:19Z")
> [@AndyDarragh](#): > > Do I HAVE to use Park instead of releasing tension? All park does is move to the designated location. I have found Releasing Tension near a corner sometimes causes the Maslow to move as the belts release, and then Apply Tension doesn’t work (I’m guessing because the Maslow has moved too far) and the tensioned belts are outside the limits. I have been setting park to the centre, releasing two belts, moving the Maslow out of the way physically, replacing work, moving it back and reconnecting belts then Apply Tension. This seems to work every time. You should not have to run Find Anchors unless your frame has changed, but if it loses its position, you need to do the Retract, Extend dance ---
**Author:** ![AndyDarragh](https://yyz1.discourse-cdn.com/flex031/user_avatar/forums.maslowcnc.com/andydarragh/32/29074_2.png) [@AndyDarragh](https://forums.maslowcnc.com/u/AndyDarragh)\ **Post date:** [June 17, 2026, 7:22am UTC](https://forums.maslowcnc.com/t/after-v1-15-v1-20-upgrade-apply-tension-always-fails-bottom-belt-deviation-40mm/25745/26 "2026-06-17T07:22:05Z")
This interstitial firmware release helped a lot. After I ran “Find Anchors”, I was able to release and apply tension consistently and quickly, even if I drove the machine away from the middle. I had to abort my cut because the bit slipped loose, but when I restarted, it came back in Ready to Cut state. The only thing it didn’t do correctly was to remember it’s position after I parked it and shut down - it came back in an unknown state. Thanks, Andy [Previous page](https://forums.maslowcnc.com/t/after-v1-15-v1-20-upgrade-apply-tension-always-fails-bottom-belt-deviation-40mm/25745.md?page=1)