IR probe inconsistent trigger height
-
Hey, guys! I'm having an issue with my IR probe running on a Duet 2 WiFi with RRF3.1.1.
I've followed these calibration steps, but whenever the bed is heated, I get very inconsistent readings between G30 S-1 commands (they vary by as much as 0.5-0.7mm), the more inconsistent the closer I am to the bed center. With a cold bed, the readings only dffer by ~0.02mm at most.
The bed is this one, so the printing surface is a flexible PEI coated textured sheet. I've already performed PID tuning on it.
Any advice? Is the probe incompatible with the print surface? Could the electrical heating signal interfere with the probe in any way?
-
@tetele Sounds like the bed is warping when it heats up. The bed mounts needs to be able to allow the bed to expand.
-
Just to make sure I understand, you're saying the actual bed is warping, not just the flexible steel sheet, right?
If so, how can I allow it to expand? The printer is a BLV MGN Cube and the bed is mounted to the supports using M4 screws and springs (it's a CR-10 bed, basically). Is there any other hardware or tweaking that I should add to the equation?
-
One way is enlarge the holes where mounting screws go through the bed. From looking at a photo of the heater portion, you don't have much space around the holes before it get to the heating trace.
On my corexy printer, I use 310mmX425mm 1/4" MIC6 aluminum as my bed base, with a heater and insulation attached to the bottom. 300mmX400mm PEI sheet attached to the surface. I also use the three point mounting for the bed.
-
@tetele I had the exact issue with my BLV cube kit. I could actually park the nozzle above the bed and see it moving up and down as current was applied to the heater. I decided it was garbage and am moving to an aluminum bed, also with a kinematic mount. Eventually I may even finish it.
https://forum.duet3d.com/topic/17691/my-blv-mgn-cube-build-upgrade-saga-ongoing?_=1602450999312 -
@Stephen6309 said in IR probe inconsistent trigger height:
One way is enlarge the holes where mounting screws go through the bed. From looking at a photo of the heater portion, you don't have much space around the holes before it get to the heating trace.
@Stephen6309 I've opened up the holes on both the bed and the bed mounts (from 4.5mm to 5mm in diameter), although having the chamfered screw holes probably has more influence than my enlarged holes. Still the exact same behavior. https://imgur.com/a/Vo0Wjv1
@whopping-pochard said in IR probe inconsistent trigger height:
@tetele I had the exact issue with my BLV cube kit. I could actually park the nozzle above the bed and see it moving up and down as current was applied to the heater. I decided it was garbage and am moving to an aluminum bed, also with a kinematic mount.
Yeah, I noticed that movement as well after posting here. However, I will try a glass surface on top of the bed first, before moving on to your more expensive solution.
Thanks, guys! At least I can rest assured the IR probe is working fine.
-
@tetele said in IR probe inconsistent trigger height:
I've already performed PID tuning on it.
Just to make sure, did you save it after tuning with M500 and add M501 to the end of config.g to load at startup?
-
@Phaedrux Yup
-
@tetele You might enlarge the hole in the bed mounts on the 2020, to allow the screws to pivot.
-
@Stephen6309 I did that as well, but it didn't seem to do much. Do you mean to more than the 5mm I've already drilled them to?
I'm just about to install and try some glass plates I just bought to see if that makes any difference.
-
@tetele Going to more than 5mm won't help. What the bed heater is made of, isn't thick enough to prevent warping. Make sure you use black glass or black paper underneath clear glass, otherwise the IR won't see it.
-
On first impression, switching to a glass surface made everything better, almost perfect. It created some adhesion problems, but those are easier to fix.
Thanks for your advice, guys!
