# 3DTouch triggers way too close

Today I finished building and adjusting a Prusa-Clone printer. The brain is a 32-bit board with Smoothieware on in. To run the auto bed leveling routine I installed a 3DTouch (BLTouch clone, sorry low on cash). After many headaches, I got everything working fine and I'm happy with the result. Except for one thing...

When the 3DTouch is probing, it is triggered when the nozzle is about 1 mm from the bed. If I set the probe higher, the nozzle crashes onto the bed. If I set the probe lower, the probe would be on the same level of the nozzle, not so good for print time.

Anyone with similar experience or how to sole it?

• So guessing from your story, you are running Marlin? Have you changed the Z-offset on the printer itself? Jan 15, 2018 at 14:00
• No, actually I'm not. I'm running on a Smoothieware powered board (no flag found about that). The question is not about the software, which I know how to manipulate with the offsets, but regarding the hardware, the 3DTouch (also no flag) Jan 16, 2018 at 14:41
• I installed a 3D touch yesterday on my Anet A8 and i had 0 problems setting it up. Are you sure you wired it correctly? And also set it up correctly in the firmware? How are you sure its not firmware related? Jan 17, 2018 at 7:36
• The probe works ok and it does what it's supposed to do, it justs triggers way too late. The pin has to be introduced quite a bit before it triggers. Jan 20, 2018 at 13:03
• Probably something wrong with the probe itself then. Cause i have a clone aswell and it touches very lightly. Jan 22, 2018 at 7:40

That it triggers when the nozzle is about 1 mm from the build plate is how it is supposed to work. The installation manual describes how to setup the sensor.

The mount needs to be adjustable so that the distance between the bottom of the sensor (not the pin) needs to be 8.3mm above the tip of the nozzle.

When taking the above distance into account, the probe should be hitting the build plate first when it is extended. When the probe triggers, it triggers at a certain distance from the nozzle. It is this distance that you need to add as an offset so that the printer knows where the actual Z=0 is. To determine the offset, you home the printer, make sure the Z-offset is zero (with command M851 Z0), then lower the head until a piece of paper gives a little drag when pulled under the nozzle. From the display you can read the offset, e.g. -1.4. With command M851 Z-1.4 you set the offset between level and trigger point. Use M500 to store the new settings.

• This is good advice. I'll add that I have found that I get better results if I do a M851 Z0 to clear the previous offset before I start the homing process. Otherwise, you have to do some math. But I have found that the math never results in an accurate offset. Starting from M851 Z0 always does. I even bought a feeler gauge because I thought variability in paper thickness might be throwing me off. Oh yeah, make sure you add in the thickness of your paper/gauge. Teaching Tech has a great video. youtube.com/watch?v=BV11-VOQjMc Apr 16, 2022 at 13:58
• This is the best Z offset calibration video in my opinion because they do everything in pronterface making it printer/firmware universal. youtu.be/y_1Kg45APko?t=66 Apr 16, 2022 at 14:01
• @BrunoBronosky Only purists take the paper thickness into account, you generally shouldn't or have a need to do that.
– 0scar
Apr 16, 2022 at 14:10
• Oscar, in most slicers if you have a layer height of 0.2, the first layer height is 0.3. Paper is about 0.2 also. So, if you don't account for the paper, you are getting a first layer of 0.5 (or 166%) which is pretty excessive. If you are not extruding above 100% to compensate for that, you are likely to have adhesion problems. Apr 17, 2022 at 13:20
• @BrunoBronosky Paper thickness is closer to 0.05-0.1 mm, so that is pretty neglectable, if you use 0.2 mm thick paper or a thick feeler gauge I can imagine you might want to compensate, but standard copy paper is not that thick. If you are a purist, compensate, if not don't. I think about 99.5 % of the people with printers don't compensate for the paper thickness. In all my years I've never done this, besides, I never use a 0.3 mm first layer, even not with PETG and never have adhesion problems. You also forget that default extrusion for the first layer is always out of the box more than 100%.
– 0scar
Apr 17, 2022 at 15:31