Piezo20 probe and piezo kit now available
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Ok, so I'm probing. So far the only real issue I've hit is I can't probe if the hotend is heating or even hot. No biggie, I calibrated the Z offset for the probe, and I'm good to go.
To mount it, as I noted earlier I use the 713maker hotend mount for my v6. This made it extremely simple.
First, I put a locking right on the collet for the bowden (I have a stub of a bowden to my Y adapter for filament switching). I had to chop the lock ring down to be really small - no bigger than the collet itself. Around the collet / bowden I put a 3.2mm tall nylon washer (12.7mm OD, 8.2mm ID) I got at the hardware store for 23 cents. It's just taller than the collet when locked, and just barely fits around it. Above that I put the piezo with a hole drilled in it (I also filed down the solder some), with the coated side facing up. On top of the coated side I put a bigger nylon washer. 1.6mm thick, 25.2mm OD, 18.5mm ID - also from the hardware store for 50 cents. I cut a small bit out of it to allow the wires to pass out. Then I simply put the locking ring from my hotend mount on top as usual.
Pictures are here if they help - total additional cost for mounting was 73 cents. http://imgur.com/a/tYFXb
Edit to say I did hit some early issues beyond those noted above for inverting the probe. Turned out I had a bearing that failed fairly catastrophically and was causing enough vibration I couldn't calibrate the piezo for all the noise. Replacing that and tightening the belts up took care of things from there.
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This is great feedback kraegar. Do you think the piezo disc is heating up with the hot end? At around 50-60 deg C they are meant to stop working.
Micro-locking ring is a good idea too.
(Not Piezo related but… I've got one of those y splitters on order I'll have to pick your brains about how to set it up on RRF)
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I'll put a temp sensor near the piezo to check the temp. It's odd - it looks like electrical interference, except just turning the heater off doesn't help. It doesn't work reliably again until the temperature drops < 40c.
I was considering re-trying the tuning of the piezo with the heater on, to see if I could get it to filter out the noise. Not sure if I want to bother.
I'll make a separate post on the Y adapter.
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I am still occasionally seeing it register the tap at my Y tower a tad late - I can see the effector "tip" a bit. It's only at the Y tower, and I'm not sure what's causing it. I can't adjust the sensitivity without affecting the other probe points negatively, so I suspect it's something about either the bed there, or that tower / belt. Adjusting belt tension didn't help it. This is the tower that had a bad bearing, and I'd hoped that would fix it. It seemed to improve, but is not 100% resolved.
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I was getting v poor probing at one point but only on the left side of the bed. I wondered if it was the bowden tube or one of the screws being looser than the others, turned out to be a loose electrical connection.
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If I probe at 850mm/min (with jerk & acceleration reduced, though) I don't get the tipping at that point. below 500mm/min, it starts doing it at more points, all on that side. I suspect maybe effector tilt isn't giving me as clean of a tap on that side. (I have plans to have an aluminum effector milled custom, but haven't had time to properly design it)
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Ok, first, don't tap that fast. Results got progressively worse.
Second, I found my issue, I think. I like repeatability as proof, so I'll do a lot of rounds of checks and see how consistent it is. When I'd tightened down the piezo probe down with the 3 screws on my hotend, I got one lower then the other two, so my hotend was sitting at just a slight angle. This was causing poor results on one part of the bed. I straightened it up and now (4 rounds done) I'm getting good probe points all around the bed. I'll report back if that turns out not to be the fix.
Edit: Just finished a height map. I should try slowing down the probing speed now that things are better. This was at 600mm/min. http://imgur.com/kk1uaGH
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Could you post your repeatability figures if you captured them?
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I didn't… And then I tweaked too far trying to improve more, and heard the ceramic crack on the piezo. Sensitivity definitely went down. I'll drill another today and swap it out.
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I'm probing at 300 mm/min.
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Perhaps my "simple mount" isn't good enough?
I drilled a new disc, it's still very sensitive going by the LED. But when I try to dial in R1 there's no room between "triggers on any printer move" and "doesn't trigger on tap".
The top nylon washer I'm using is 3.5mm in diameter, and that's all of the piezo it's touching - is that too far in, and preventing it from bending enough perhaps?
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Do you mean it's 3.5mm difference between ID and OD?
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Yes.
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I think you may be running into the same problem DjDemonD had in the beginning. Looking at your effector it doesn't like you're controlling lateral movement of the hot end. DjDemonD had to add sliders to allow vertical movement of the hot end while preventing lateral movement causing triggering.
Idris
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The Slot for the hotend does actually by design have the hotend groovemount on an E3D "drop down" a bit into the mount. If anything it might be a little too snug of a fit. That's what I was hoping would make this ideal.
How tight do you push down on the piezo? Just do it's held flush against the hotend, or do you flex the piezo some (in a "resting" state)
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It can be preloaded a small amount, as long as further upward pressure will bend it more, we're only talking 0.1mm more. Its the rate of bend that generates the signal rather than the absolute amount.
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Ok, back in business.
I think my piezo was grounding the brass plate against my hotend mount. Maybe. I trimmed a spot in it around each screw, to be sure it wouldn't make contact. I also went back to the piezo I got the best luck out of… don't think I actually damaged it. I'm using a P1 probe type with a low trigger value. Seems to be working at the moment, anyway.
I think drilling these without damage is going to be the challenging part, at least at first.
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My repeatability testing is now underway. If you have suggestions on the methodology or ways to display the data, let me know and I'll adjust: https://docs.google.com/spreadsheets/d/1EwNdSNXZR_OhwChLFrTYqFDFcKjB-4z6OwGkocKgW7E/edit#gid=0
Currently I'm just moving to Z5 and doing a G30 s-1 50 times. I have the min, max, average, and stddev at the bottom.
Edit to note I'm powering off and doing a full delta calibration between each set.
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Thats good data. When I had a piezo in a machine running marlin I did the M48 repeatability test a few times and came up with similar results.
Recv: Mean: -2.492500 Min: -2.510 Max: -2.475 Range: 0.035
Recv: Standard Deviation: 0.009014Not quite as good, but the hastily rigged carriage this machine uses is quite wobbly itself.
I've mainly been using my delta autocalibration deviation as the metric, which is, I accept, flawed as there are many other factors feeding into this.
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My delta calibration leaves a bit to be desired still. Just working on the probe for now.
Calibrated 6 factors using 16 points, deviation before 0.055 after 0.054
I still have some work to do in solving an oddity I've talked to dc42 off and on about, to get that down. Having more accurate probing (and using the nozzle) should hopefully help that.
